HomeMy WebLinkAboutDosewallips River LazyCPowerlines Resiliency Plan_Revised_111424
Tami Pokorny
Natural Resources Program Coordinator
Jefferson County Public Health
615 Sheridan Street
Port Townsend, WA 98368
Ph: 360.379.4498
1900 N. Northlake Way, Suite 211
Seattle, WA 98103
DOSEWALLIPS RIVER RESILIENCY PLAN
POWERLINES/LAZY C REACH
November 2024 Update
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TABLE OF CONTENTS
1. INTRODUCTION .................................................................................................................................................. 1
1.1 2024 Revisions ......................................................................................................................................... 1
1.2 Project Location ....................................................................................................................................... 1
1.3 Study Area ................................................................................................................................................ 2
1.4 Floodplain Development .......................................................................................................................... 1
2. REACH CONDITIONS ........................................................................................................................................... 4
2.1 Geology .................................................................................................................................................... 4
2.2 Channel and Floodplain Morphology ....................................................................................................... 6
2.2.1 Upstream Lazy C Sub-reach (RM 2.4-3.0) ................................................................................... 6
2.2.2 Downstream Lazy C Sub-reach (RM 2.0-2.4) .............................................................................. 8
2.2.3 Powerlines Reach (RM 1.0-2.0) ................................................................................................... 9
2.3 Hydrology and Hydraulics ...................................................................................................................... 11
2.3.1 Hydrology .................................................................................................................................. 11
2.3.2 Hydraulic Modeling ................................................................................................................... 11
2.4 Sediment Transport Dynamics ............................................................................................................... 15
2.4.1 Lazy C Reach .............................................................................................................................. 15
2.4.2 Powerlines Reach ...................................................................................................................... 15
2.5 Channel Migration History ..................................................................................................................... 20
2.5.1 Lazy C Sub-Reaches ................................................................................................................... 20
2.5.2 Powerlines Reach ...................................................................................................................... 20
2.6 Channel Migration Zone Delineation ..................................................................................................... 21
2.6.1 Lazy C Sub-reaches .................................................................................................................... 22
2.6.2 Powerlines Reach ...................................................................................................................... 23
2.7 Large Wood ............................................................................................................................................ 23
2.7.1 Lazy C Sub-reaches .................................................................................................................... 23
2.7.2 Powerlines Reach ...................................................................................................................... 26
2.8 Riparian and Wetland Communities ...................................................................................................... 27
2.8.1 Lazy C Sub-reaches .................................................................................................................... 27
2.8.2 Powerlines Reach ...................................................................................................................... 28
2.9 Aquatic Habitat Conditions, Salmonid Use, and Periodicity .................................................................. 30
2.9.1 Aquatic Habitat Conditions ....................................................................................................... 30
2.9.2 Habitat Use ............................................................................................................................... 32
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2.9.3 Hood Canal Summer Chum ESU (Oncorhynchus keta) ............................................................. 33
2.9.4 Puget Sound Chinook (Oncorhynchus tshawytscha) ................................................................ 34
2.9.5 Coho (Oncorhynchus kisutch).................................................................................................... 34
2.9.6 Pink / Humpback (Oncorhynchus gorbuscha) ........................................................................... 35
2.9.7 Steelhead and Rainbow Trout (Oncorhynchus mykiss) ............................................................. 35
2.10 Summary of Impairments ...................................................................................................................... 36
2.10.1 Upstream Lazy C sub-reach ....................................................................................................... 36
2.10.2 Downstream Lazy C sub-reach .................................................................................................. 37
2.10.3 Powerlines Reach ...................................................................................................................... 37
2.11 The Warming Climate ............................................................................................................................ 38
3. PROJECT GOALS AND OBJECTIVES ................................................................................................................... 41
3.1 Resiliency Plan Assessment Goals .......................................................................................................... 41
3.2 Resiliency Plan Assessment Objectives .................................................................................................. 41
3.3 Resiliency Corridor ................................................................................................................................. 42
3.3.1 Reference Conditions ................................................................................................................ 42
3.3.2 Ecological Resiliency ................................................................................................................. 44
4. RESILIENCY OPPORTUNITIES ............................................................................................................................ 47
4.1 Longer-Term Opportunities ................................................................................................................... 47
4.2 Education, Outreach and Engagement .................................................................................................. 48
4.3 Development of Programs and Options for Landowners ...................................................................... 48
4.4 Conservation Easements, Acquisition and Relocation Actions .............................................................. 50
4.4.1 Upstream and Downstream Lazy C Reach ................................................................................ 50
4.5 Short-Term Opportunities ...................................................................................................................... 52
4.5.1 River and Riparian Restoration ................................................................................................. 52
4.5.2 Bank Alcoves ............................................................................................................................. 53
4.5.3 Engineered Log Jams and Large Wood Placement ................................................................... 53
5. PRIORITIZATION AND SEQUENCING ................................................................................................................ 55
5.1 Prioritization Framework ....................................................................................................................... 55
5.2 Action Sequencing ................................................................................................................................. 57
6. CONCEPTUAL RESTORATION DESIGN .............................................................................................................. 58
6.1 Short Term Actions in Lazy C Reach ....................................................................................................... 58
6.1.1 Upstream Lazy C sub-reach ....................................................................................................... 58
6.1.2 Downstream Lazy C sub-reach .................................................................................................. 59
6.1.3 Design and Construction Considerations in Lazy C Reach ........................................................ 61
6.1.4 Conceptual Construction Cost for Lazy C .................................................................................. 62
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6.2 Short Term Actions in Powerlines Reach ............................................................................................... 62
6.2.1 Dosewallips Active Channel Restoration Actions ..................................................................... 63
6.2.2 Side Channel Restoration Actions ............................................................................................. 64
6.2.3 Floodplain Restoration Actions ................................................................................................. 64
6.2.4 Design and Construction Considerations in Powerlines ........................................................... 65
6.2.5 Conceptual Construction Cost for Powerlines .......................................................................... 66
6.3 Future Full Valley Restoration Concept ................................................................................................. 66
6.4 Stakeholder Engagement and Selection of Preferred Design Concepts ................................................ 67
6.4.1 Stakeholder Engagement .......................................................................................................... 67
6.4.2 Selection of the Preserved Design Concepts ............................................................................ 68
7. REFERENCES ..................................................................................................................................................... 69
LIST OF TABLES
Table 1. Estimated Discharge Values ....................................................................................................................... 11
Table 2. The frequency of stable log jams throughout the project area compared to reference conditions. ........ 24
Table 3. Periodicity of selected salmon in the Dosewallips River ............................................................................ 33
Table 4. The magnitude of future peak flows 2070-2099 projected as result of warming climate. ....................... 39
Table 5. Scoring and Prioritization of Restoration Opportunities by Reach. ........................................................... 56
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LIST OF FIGURES
Figure 1. Project vicinity map. .................................................................................................................................... 2
Figure 2. Project area map. ........................................................................................................................................ 3
Figure 3. Land ownership and parcel boundaries within the project area. ............................................................... 2
Figure 4. Examples of residential development along the river within the Lazy C floodplain. ................................. 3
Figure 5. Geologic map of the project reach ............................................................................................................. 4
Figure 6. Example of glaciolacustrine and glacial outwash deposits on hillslopes along the right bank .................. 5
Figure 7. Relative elevation model (REM) map of study area. .................................................................................. 6
Figure 8. Example of typical plane-bed channel morphology found throughout the Upstream Lazy C reach ......... 7
Figure 9. An alcove (wide spot in river channel) along left bank at RM 2.9. ............................................................. 7
Figure 10. Left overflow channel in the Downstream Lazy C sub-reach at RM 2.2. .................................................. 8
Figure 11. Braided channel morphology within the Powerlines Reach. .................................................................... 9
Figure 12. Map of the four side channels (SC) in the Powerlines sub-reach. .......................................................... 10
Figure 13. Photo of side channel 1 (SC 1 in Figure 12, RM 2.12) which was inundated during the field visit. ........ 10
Figure 14. Existing condition hydraulic modeling results for the 1-year (2,100 cfs), 10-year (11,420 cfs), and 100-
year (17,120 cfs) flood recurrence events. .............................................................................................................. 12
Figure 15. Comparison between estimates of the existing condition 100-year floodplain..................................... 14
Figure 16. Estimates of the stable particle size under the existing 1-year and 10-year flow levels. ....................... 15
Figure 17. History of channel migration within the project area between 1939-2019. .......................................... 17
Figure 18. Continued sediment deposition in the Powerlines reach ....................................................................... 18
Figure 19. Predicted evolution of channel and floodplain morphology within the project area ............................ 19
Figure 20. Active bank erosion along the left bank within the Downstream Lazy C sub-reach. ............................. 20
Figure 21. Channel migration zone (CMZ) delineation for the project area. ........................................................... 22
Figure 22. Stable large wood jams and large wood pieces within the project area. ............................................... 24
Figure 23. Cedar snag with cut marks in the Upstream Lazy C sub-reach. .............................................................. 25
Figure 24. Examples of stable log jams within the Downstream Lazy C sub-reach. ................................................ 25
Figure 25. Examples of stable log jams within the Powerlines Reach. .................................................................... 26
Figure 26. Examples of stable log jams within the side channels of the Powerlines Reach. ................................... 27
Figure 27. Riparian condition along Upstream Lazy C sub-reach. Photo looking upstream, 10/9/20. ................... 28
Figure 28. Canopy height map of the project area. ................................................................................................. 29
Figure 29. Typical riparian conditions in the Powerlines Reach. ............................................................................. 29
Figure 30. Typical habitat conditions within the project area. ................................................................................ 31
Figure 31. Estimated depths for the 1-year (2,480 cfs), 10-year (13,480 cfs) and 100-year (21,060 cfs) recurrence
peak flows predicted by 2070-2099......................................................................................................................... 40
Figure 32. Example of a reach of the Dosewallips River at RM 10 with anabranching channel morphology. ........ 43
Figure 33. Resiliency Corridor for the Lazy C and Powerlines Reaches. .................................................................. 45
Figure 34. Private and public parcels relative to risk from erosion and channel migration. Public ownership
largely lies within the High Hazard area. ................................................................................................................. 51
Figure 35 Low-Profile and Deflector Log Jam Concept in Upstream Lazy C sub-reach ........................................... 59
Figure 36 Apex and Associated Jams along existing Side Channel at RM 2.3 .......................................................... 60
Figure 37 Large Deflector Jams along Left Bank near RM 2.0 ................................................................................. 61
Figure 38 Apex Jam Array within Active Channel .................................................................................................... 63
Figure 39. Proposed Side Channel Enhancements in SC-1 ...................................................................................... 64
Figure 40. Potential example of future conditions in a riverine floodplain with a functional large wood cycle
recruiting large conifers as stable hard points. ....................................................................................................... 65
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ATTACHMENTS
A. Mapbooks - Relative Elevation Model, Channel Migration Zone, and Hydraulic Model Results
B. Conceptual Designs
LIST OF APPENDICES
Appendix A Data Sources
Appendix B Aquatic Habitat Assessment
Appendix C Data Gaps Summary Memo
Appendix D Hydraulic Model Development
Appendix E Summary of Impairments
Appendix F Conceptual Construction Cost Estimates
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ACRONYMS
BPA Bonneville Power Administration
CMZ Channel Migration Zone
DEM Digital Elevation Model
DNR Department of Natural Resources
ELJ Engineered Log Jam
ESA Endangered Species Act
FEMA Federal Emergency Management Agency
LIDAR Light Detection and Ranging
LWD Large Woody Debris
NSD Natural Systems Design
NWI National Wetland Inventory
REM Relative Elevation Model
RM River Mile
SMS Surface Modeling System
USGS United States Geological Survey
USFS United States Forest Service
WDFW Washington Department of Fish and Wildlife
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1. INTRODUCTION
Jefferson County (County) has contracted with Natural Systems Design Inc. (NSD) to assess potential restoration
actions for the protection and restoration of watershed- and site-scale geomorphic, hydrologic, and hydraulic
processes contributing to the resiliency of the lower Dosewallips River on the eastern side of the Olympic
Peninsula. The lower Dosewallips River supports Puget Sound Chinook (Oncorhynchus tshawytscha) and Hood
Canal summer-run chum (Oncorhynchus keta), both listed under the Endangered Species Act as federally
threatened species. A Resiliency Plan is intended to provide an assessment of physical and biologic conditions
and begin to describe actions that can help preserve and restore important ecological habitat, as well as assist
landowners exposed to flood and erosion hazards.
One key goal of the Resiliency Plan is to provide educational outreach to local residents and stakeholders
regarding the many facets of river valleys such as flood and erosion hazards, regulatory delineations (e.g., Flood
Insurance Rate Maps), historic changes, physical processes, ecology and salmon habitat. The plan is a “living
document” that can evolve into the future with new information and is being led by Jefferson County with the
intent to continue to coordinate communications.
This Resiliency Plan characterizes historic conditions, anthropogenic disturbances, and their link to the current
conditions within the lower river. The findings presented herein provide baseline information, a summary of
impaired processes, and recommendations for actions and approaches that can guide community members and
resource managers in developing a strategic approach to holistically protecting and improving conditions in the
lower Dosewallips River. This Resiliency Plan is only the first step in identifying restoration opportunities within
the framework of stakeholder concerns related to existing homes and infrastructure present in the Lazy C I
development within the river’s floodplain, channel forming processes, aquatic habitat protection and
restoration, and resiliency to climate change
1.1 2024 Revisions
Jefferson County presented the first iteration of this Resiliency Plan to the Dosewallips River Collaborative and
community stakeholders in June 2021. Since that time, the community has provided feedback to Jefferson
County that the inclusion of a potential future ‘full valley restoration’ concept and related information regarding
programs to support potential future voluntary buyouts and relocation of at risk structures from the floodplain
is inconsistent with local community priorities. Jefferson County has requested that references to the potential
future voluntary relocation of homes as part of a resiliency planning process be removed to create this updated
version of the Resiliency Plan. No other components of the plan have changed.
1.2 Project Location
The Dosewallips River flows eastward from the central Olympic Mountains through steep forestlands into Hood
Canal just north of Brinnon, Washington (Figure 1). The basin’s headwaters are situated within Olympic National
Park and Olympic National Forest and the remainder of the basin is owned by the State of Washington
Department of Natural Resources and State Parks, private timber companies, and private citizens. The tidelands
are owned by State Parks and private landowners and several areas are also leased for commercial shellfish
production. The river has a watershed area of 116 square miles (mi2) and a relief of 7,770 feet spanning from the
peaks of the Olympic Crest to Hood Canal. The watershed receives an average annual precipitation of 77.6
inches which falls as both rain and snow during the fall and winter months (October-February). The watershed’s
high relief and precipitation produce a high sediment load (Labbe, 2005). Most of the basin is forested, with 63%
of the area covered by tree canopy (streamstats.usgs.gov). Within the Dosewallips watershed, there are reaches
with high quality habitat interspersed with reaches that have been heavily impacted by human use. Supporting
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factors for salmon habitat in the watershed include that much of the land is publicly owned with Olympic
National Park and Olympic National Forest owning 93% of the watershed, with much of that in protected status
(Shared Strategy 2007).
Figure 1. Project vicinity map. The Dosewallips watershed is located on the east side of the Olympic
Mountains and drains into Hood Canal in the Puget Sound. The Duckabush watershed immediately south of
the Dosewallips is also delineated since it has a longer-term hydrologic record.
1.3 Study Area
The study area is located between river miles (RM) 1.0-3.3 (as measured from Hood Canal using the 2018 lidar
digital elevation model [DEM]) along the mainstem of the Dosewallips River directly downstream from the Rocky
Brook confluence and canyon (Figure 2). Termed the ‘Lazy C’ and ‘Powerlines’ reach in previous assessments
(e.g., Labbe 2005), the reach contains the Lazy C development as well as other private parcels at the upstream
end from RM 3.3 to RM 2.0 and a Bonneville Power Administration (BPA) powerline corridor which crosses the
river between RM 1.1 and 1.2 at the downstream end of the study area. The Lazy C development consists of two
subdivisions, Lazy C I, in the valley bottom, and Lazy C III on the hillslope north of the valley. While there was
originally a Lazy C II development in the 1960’s, the concept for a Lazy C II development was abandoned in the
1980s due to channel migration and frequent flooding and the properties were gradually acquired and protected
by Jefferson County.
The study area encompasses the entirety of the alluvial valley bottom and surrounding hillslopes and has been
divided into two reaches for the purposes of this study based on geomorphic characteristics (such as
morphology and channel migration history) and current development- the Lazy C Reach (RM 2.0-3.3) and the
Powerlines Reach (RM 1.0-2.0). The Lazy C Reach consists of two sub-reaches, upstream (RM 2.4-3.3) and
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downstream (RM 2.0-2.4), which were further distinguished because the downstream portion of the reach acts
as a transitional area in geomorphic characteristics such as morphology and patterns of channel migration.
The reaches and sub-reaches of the project area have the following characteristics:
1. The Upstream Lazy C sub-reach is located between RM 3.3 to 2.4 and includes the straight portion of
channel and adjacent floodplain.
2. The Downstream Lazy C sub-reach is located between RM 2.4 and 2.0 and includes a 90-degree bend
along the right side of the valley and the portion of channel that runs adjacent to Appaloosa Drive within
the Lazy C I development (Figure 2).
3. The Powerlines reach is located between RM 1.0-2.0 and includes the meandering segment of channel
and surrounding undeveloped floodplain.
Figure 2. Project area map. The project area includes the Lazy C and Powerlines sub-reaches and encompasses
the entirety of the alluvial valley bottom.
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1.4 Floodplain Development
Development of the river’s floodplain in the area now known as the ‘Lazy C’ began prior to 1939 with a road
visible towards the upstream end of the reach and the downstream floodplain cleared of trees in the 1939 aerial
image, although no houses had yet been constructed. The existing housing development first appears in the
1968 aerial photo which shows five homes had been constructed along with the Appaloosa Drive loop and
Mustang, Morgan, Pinto and Palomino Lanes. The extent of development accelerated between 1968 and 1994,
filling in with houses that have persisted into the current developed condition. The current valley bottom sub-
division is named Lazy C I and consists of 118 parcels and 1.3 miles of roads which are primarily concentrated in
the downstream end of the floodplain between RM 2.0-2.6 (Downstream Lazy C sub-reach, Figure 3). The
upstream end of the floodplain (Mossy Lane, Figure 3) is generally forested with houses and larger lots
interspersed between the forest and along the left bank of the straight section of the Upstream Lazy C sub-reach
between RM 2.4-3.0 (Figure 4). This area is not within the formal Lazy C I sub-division but is functionally within
what we are terming the ‘Lazy C floodplain.’ The right bank hillslope along the Upstream Lazy C reach is
undeveloped and is categorized as vacant land by Jefferson County and owned by Washington State Parks. The
left bank hillslope is bisected by Dosewallips Road which separates the floodplain properties from the Lazy C III
sub-division on the hillslope.
In addition to the existing private residences, there were also historical development activities in formerly
private parcels in the floodplain downstream of the current Lazy C I sub-division. These parcels were connected
to the Lazy C I sub-division by Palomino Lane which extended along the north side of the valley about 0.4 mile
downstream (east) of its current terminus at RM 2.0. An additional sub-division was envisioned for this area by
the landowners and colloquially termed the Lazy C II. However, channel migration processes between 1980-
1994 washed out roughly 1,100 feet of the road and the plan was abandoned. The area is now part of County-
owned lands within the Powerlines reach that were purchased from willing sellers and protected by Deeds of
Right to Washington State to support salmon habitat.
The floodplain of the Powerlines reach is undeveloped except for the BPA powerline corridor that bisects the
valley between RM 1.1 and 1.2 at the downstream end of the study area. While the powerlines themselves are
not in the floodplain, BPA vegetation management in the corridor under the powerlines results in periodic
control of the vegetation in the floodplain under the lines to maintain a limited vegetation height.
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Figure 3. Land ownership and parcel boundaries within the project area.
The original Lazy C development was envisioned to include three sub-divisions in the NW ¼ of Section 34
Township 26 North, Range 2 West, Willamette Meridian (indicated by the bold black line). Lazy C I and the area
informally referred to as Lazy C II are south of Dosewallips Road. Lazy C I includes the Appaloosa Drive loop
upstream of RM 2.0 including the larger parcels along Mossy Lane (NE ¼ of Section 33). The proposed Lazy C II
sub-division was located east of Lazy C I within the upstream portion of the Powerlines Reach and no longer
exists due to channel migration. Lazy C III is located on hillslope north of Dosewallips Road. The project area also
includes parcels along Mossy Lane that are within the Lazy C reach but not within the Lazy C I sub-division.
Parcel data was downloaded from the Jefferson County GIS portal in May 2020.
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Figure 4. Examples of residential development along the river within the Lazy C floodplain.
Photo A is of a house near RM 2.6 (refer to Figure 3) along the river’s left bank. Photo B shows houses at RM
2.4 situated on lower elevation floodplain that is inundated during a 10-year recurrence peak flow (Figure 14).
Photos C and D show development on the floodplain next to the actively eroding left bank between RM 2.1-
2.0, an area also subjected to flooding during a 10-year recurrence peak flow. Photos taken on 10/9/20. Flow
is left to right.
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2. REACH CONDITIONS
The following chapter describes the existing geomorphic and habitat conditions present throughout the project
area and forms the basis of the resiliency corridor and restoration plan described later in this report. The data
sources used in the study are listed in Appendix A, a summary of the aquatic habitat conditions is presented in
Appendix B, and a data gaps summary memo is presented in Appendix C. Methods used in the development of
the hydraulic model are presented in Appendix D. Maps with results of the study including the relative elevation
model, channel migration zone, and hydraulic model outputs are also included in mapbooks presented as
Attachment A.
2.1 Geology
The geologic and glacial history greatly influence the conditions found at the study site today. The Dosewallips
watershed lies on the eastern slope of the Olympic Mountains which are composed of an “accretionary wedge”
of uplifted and folded oceanic crust that have formed (and are continuing to be formed) by subduction of the
Juan de Fuca plate under the North American plate. The upper portion of the watershed is composed of slightly
metamorphosed and highly erodible marine sedimentary lithologies deposited during the uplift processes.
Because of their highly erodible nature, these marine sedimentary materials provide the Dosewallips River with
a high sediment load (Labbe, 2005). The middle and lower portions of the watershed are composed of less
erodible Crescent formation basalts (Figure 5).
Figure 5. Geologic map of the project reach (Polenz et al., 2014; Washington Department of Natural
Resources, 2021)
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Alpine glaciers likely extended from the Olympic crest downstream to at least the Rocky Brook confluence just
upstream of the project area (Polenz, 2021; Hellwig, 2010). While these glaciers may not have directly
influenced the geology and topography of the study site, the site was likely influenced heavily by continental
glaciation during the last glacial maxima. The Cordilleran ice sheet extended into Puget Sound around 15,000
years ago, covering the region in a thick layer of ice that spanned between the Olympic and Cascade Mountain
ranges. During this period of glaciation, the ice sheet likely extended into the project site, covering the site in
roughly 300-600 feet of ice, and carving the U-shaped valley seen today. The ice sheet likely dammed the river,
forming a glacial lake in the valley upstream. Deposits from these processes are seen in the geologic record
today, with the hillslopes surrounding the site overlain with glacial outwash and glacial lacustrine deposits –
both of which are highly erodible which makes them susceptible to mass-wasting processes such as landsliding
(Figure 5 and Figure 6). These deposits are overlying Crescent formation basalt, which extrudes beyond the
deposits in several areas of the project reach – most notably on the right bank near RM 2.2 across from the Lazy
C I and at the downstream end of the Powerlines reach where they form a bedrock constriction at RM 1.0. The
valley bottom is filled with Holocene alluvium (river derived sediment) that has been deposited since the retreat
of the Cordilleran ice sheet.
Figure 6. Example of glaciolacustrine and glacial outwash deposits on hillslopes along the right bank across
from the Lazy C community at RM 2.4. The image highlights how these deposits are prone to mass-wasting
(landsliding). Photo taken on 10/9/20 of the right bank near RM 2.0. Flow is right to left.
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2.2 Channel and Floodplain Morphology
2.2.1 Upstream Lazy C Sub-reach (RM 2.4-3.0)
The river through the Upstream Lazy C sub-reach exhibits a straight, plane-bed channel morphology with few
pools and coarse bed substrate (Figure 7 and Figure 8). The channel is confined between the Lazy C I sub-division
and the southern valley wall and shows little evidence of recent channel migration (See detailed discussion
below) with minimal inset floodplain formation. There is a bedrock alcove along the left bank near RM 2.9 at the
upstream end of the reach where a deep pool has formed next to the resistant material (Figure 9). The adjacent
land underlying the residential development contains evidence of historical interaction with fluvial processes
with several meander scars and relict channels present beneath the forest and roads (Figure 7). NSD observed
and documented the floodplain stratigraphic sequence (coarser cobbles and gravels beneath finer silts and
sands) along the left bank in this reach during the field survey. Coupled together, these observations (relict
channel features and floodplain stratigraphy) indicate the Lazy C was likely once a frequently engaged floodplain
surface that was well connected to the main channel of the river. However, the historical floodplain is now
roughly 5-10 feet above the low flow channel which suggests that the channel has become incised and
disconnected from its floodplain through the Lazy C reach.
Figure 7. Relative elevation model (REM) map of study area. The REM was developed using a lidar DEM
collected on 10/6/17 and 7/22/18.
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Figure 8. Example of typical plane-bed channel morphology found throughout the Upstream Lazy C reach (RM
2.4-3.0). The photo was taken near RM 2.8 on 10/9/20 looking downstream.
Figure 9. An alcove (wide spot in river channel) along left bank at RM 2.9. The alcove is formed by a bedrock
outcropping along the left bank and across the river from a tributary confluence (Figure 7). A deep pool has
formed directly adjacent to the bedrock and the pool and slow water associated with the alcove is providing
complex holding habitat for salmonid species. The site is a point where major floods inundate historic
channels that flow through the Lazy C reach floodplain. The photo was taken on 10/9/20 looking towards the
left bank. Flow is from left to right.
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2.2.2 Downstream Lazy C Sub-reach (RM 2.0-2.4)
The Downstream Lazy C sub-reach contains a greater diversity of channel morphologies than the Upstream Lazy
C sub-reach (Figure 7). The channel splits around a forested island between RM 2.2-2.4 where the river bends 90
degrees towards the north as it is constrained by a high left bank comprised of glaciolacustrine deposits and an
outcropping of Crescent formation basalt. At the time of the field survey, roughly 80% of the flow went through
the left channel. The right channel exhibited a meandering pool-riffle morphology whereas the left channel was
a straight, high-energy riffle. The channel flows northward after the 90-degree bend where it is adjacent to
Appaloosa Road within the Lazy C I development.
There is another flow split near RM 2.2 where a left bank overflow channel has formed within parcels purchased
by Jefferson County to replant and provide habitat restoration opportunities that support salmon recovery. The
left overflow channel contains low complexity and retains older bank armoring along the left bank (Figure 10).
There is another 90-degree bend at the downstream end of the reach where the river is actively eroding the left
bank downslope from Dosewallips River Road and migrating towards the Lazy C I development. The floodplain is
better connected than the Upstream Lazy C sub-reach and is roughly 2-5 feet above the low flow channel. There
is also a left bank floodplain overflow path near RM 2.4 where the left bank floodplain is 2 feet above the low
flow channel (discussed in further detail below). The downstream end of the relict channels noted within the
Upstream Lazy C sub-reach description are also contained within the floodplain in this reach.
Figure 10. Left overflow channel in the Downstream Lazy C sub-reach at RM 2.2. This was the active channel of
the river in 1995 through 2015. During this time, the river migrated into the left bank which led to placement
by Jefferson County Public Works of riprap in 2006 to protect Appaloosa Drive. This channel has little habitat
complexity. The photo was taken on 10/9/20 near looking downstream.
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2.2.3 Powerlines Reach (RM 1.0-2.0)
The Powerlines reach exhibits a complex, multi-threaded channel morphology and well-connected floodplain
(Figure 7). The channel has expressed a full meander sequence and spans the entirety of the valley bottom from
hillslope to hillslope. The main channel exhibits a primarily meandering pool-riffle channel morphology with
deep pools at the outside of meander bends separated by steeper riffles.
There are, however, two areas of the reach that exhibit braided channel morphology, one between RM 1.8-1.9
and the other at the downstream end between RM 1.1-1.2 (Figure 11). These segments contain broad, poorly
sorted gravel bars intersected by a series of unstable braid channels. These areas provide poor quality spawning
habitat due to the unstable nature and frequent bed mobilization of the braided morphology. The downstream
braided segment also exhibits a degree of over-widening, likely due to the lack of mature vegetation underneath
the BPA powerline corridor. A bedrock constriction defines the downstream end of the sub-reach.
Figure 11. Braided channel morphology within the Powerlines Reach. The photo was taken near RM 1.8 on
10/9/20 looking downstream.
There are four side channels within the reach, three of which were connected to the main channel during the
field visit (Figure 12). Side channel one (SC-1) enters the river across from the Lazy C I development near RM 2.2
and contains a complex pool-riffle morphology (Figure 7 and Figure 13). Side channel two (SC-2) begins near the
outside of a meander bend near RM 1.8 and contains a mixture of pool-riffle and plane-bed morphology. SC-2
exhibits signs of channel modifications activities such as straightening and wood removal. Side channel three
(SC-3) begins near RM 1.7 and is wider than the other three side channels, likely because it is the most recent to
have formed, is surrounded by immature riparian vegetation, and experiences higher energy flood flows due to
its short channel length. All three side channels were connected during the October 2020 field visit. Side channel
four (SC-4) begins near the outside of a meander bend near RM 1.45 and was not connected during the field
visit. The side channels are surrounded by diverse floodplain landforms that have formed in the lee of migrating
meanders. The floodplain ranges from 1-7 feet above the low flow channel throughout the Powerlines Reach.
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Figure 12. Map of the four side channels (SC) in the Powerlines sub-reach. The side channels were mapped
during the 2020 field visit and confirmed using the REM map.
Figure 13. Photo of side channel 1 (SC 1 in Figure 12, RM 2.12) which was inundated during the field visit. Due
to the small tree sizes, there is little functional wood in the side channel. This side channel is a potential
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avulsion pathway. The photo was taken on 10/9/20 looking downstream. Hydrology and
Hydraulics
2.3.1 Hydrology
Estimates of peak flood flows with recurrence intervals of 1 year, 10 years, and 100 years in the Dosewallips
River were made for the project area based on the historical discharge record available from the active USGS
gage on the Duckabush River (USGS gage #120454000), the inactive USGS gage that was on the Dosewallips
River upstream of the project site (USGS gage #12053000), and a comparison of the drainage areas upstream of
the gages and at the project site. More details regarding the methods for peak flow development are included in
Appendix D: Hydraulic Modeling. The discharge values used for hydraulic modeling and contingent analyses are
shown in Table 1. The 1-, 10- and 100-year recurrence peak flows are also referred to as the 1-, 10- and 100-year
floods.
Table 1. Estimated Discharge Values
RECURRENCE INTERVAL DISCHARGE ESTIMATE (CFS)
1-year (100% probability in any given year) 2,100
10-year (10% probability in any given year) 11,420
100-year (1% probability in any given year) 17,120
2.3.2 Hydraulic Modeling
A hydraulic model of the Dosewallips River was developed using Hydronia’s RiverFlow-2D Plus GPU and Aquaveo
SMS v13.0 computer software. RiverFlow-2D is a two-dimensional finite volume computer model that provides
depth averaged hydraulic parameters at centroids within a triangular mesh model domain. Flood flows with
recurrence intervals of 1 year, 10 years, and 100 years (100%, 10% and 1%, respectively, probabilities of
occurrence in any given year) were modeled and the results were validated against regional knowledge and
experience contributed by landowners in the area. A more detailed description of the development of the
hydraulic model is available in Appendix D: Hydraulic Modeling.
Lazy C Reach Results
The hydraulic modeling results largely support the geomorphic analysis of the region. The 1-year flood, which
can be understood as the bankfull flood, is fully contained within the channel banks in the Lazy C sub-reaches,
with no connected floodplain habitat and no flooding within the residential development (Figure 14).
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Figure 14. Existing condition hydraulic modeling results for the 1-year (2,100 cfs), 10-year (11,420 cfs), and
100-year (17,120 cfs) flood recurrence events.
Within the Lazy C reach, water overtops the banks between the 1-year and the 10-year flood. At around 3,900
cfs, water flows north from RM 2.4 along a relict floodplain channel and begins to flood the Lazy C I
development, traveling through private parcels to Appaloosa Drive. By approximately 5,300 cfs, it is estimated
that floodwaters cross Appaloosa Drive and inundate parcels on the other side of the road. At the same flow an
additional relict channel near RM 2.45 begins to inundate from the mainstem, flooding additional parcels along
the left bank. By 6,600 cfs the southwest portion of Appaloosa Drive is entirely inundated. At about 8,600 cfs, a
long relict floodplain channel that runs from RM 2.9 straight through the Mossy Lane and Lazy C I developments
and reconnects to the mainstem at RM 2.0 begins to inundate as well, flooding the full length of Appaloosa
Place and Pinto Lane, and spreading into adjacent parcels.
By the 10-year flood, Appaloosa Place, Pinto Lane, and the southwest portion of Appaloosa Drive are inundated
– flooding portions of the residential development with 0.5-2.5 ft of water. Between the 10-year and the 100-
year flood, more of the Lacy C development is flooded. At 14,000 cfs, water flows into a relict floodplain channel
that leaves the mainstem at RM 2.7 and inundates the full length of Morgan Lane. By the 100-year flood,
floodwaters inundate much of the Lazy C I development, including many along Pinto Lane., Morgan Lane, and all
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the parcels on the outer perimeter of Appaloosa Drive. Inundation depths are still in the range of 0.5-2.5 ft
typically, with some pools up to 4 feet deep forming in places.
Flow velocities range between approximately 3-8 ft/s in the channel during the 1-year flow with the lower
velocities found in the Downstream Lazy C sub-reach and within the side channel near RM 2.3. Velocities
increase with increasing discharge, ranging from 5-13 ft/s within the main channel at the 10-year flow and 5-16
ft/s at the 100-year flow. The highest velocities are found within the straight channel section between RM 3.0-
2.4 because of the lack of channel complexity and large wood. Flow velocities are much slower within the
floodplain overflow pathways, ranging from 1-6 ft/s with the higher velocities found along roads within the Lazy
C I sub-division.
Powerlines Reach Results
In the Powerlines reach, the 1-year flood overtops the banks and inundates portions of the floodplain with many
floodplain channels and three established side channels being inundated at this flow. All the side channels in the
Powerlines reach are flowing with water 2-3 feet deep during the 1-year flood, indicating that they must
inundate at lower flows with more frequency than the 1-year flood – a finding that was confirmed for SC-1, SC-2,
and SC-3 which were inundated during the field survey. Lower flows were not modeled, and gage records are
unavailable and thus the exact threshold for inundation of these side channels cannot be pinpointed from this
analysis. A backwater is formed at the bedrock constriction at the downstream end of the project area,
extending approximately 900 ft upstream during the 1-year flow.
The 10-year flood overtops gravel bars and inundates a wider swath of floodplain. Most notably the left bank
floodplain between RM 1.2 and RM 1.0, just upstream of the bedrock constriction, is fully inundated at this
discharge level. This is in part due to the increased backwater effect from the canyon, which at the 10-year flood
raises WSE for approximately 1,500 ft upstream of the constriction. By the 100-year flood, the full valley is
inundated and the backwater influence from the constriction is even more pronounced, extending upstream
approximately 2,100 ft.
Flow velocities are generally lower in the Powerlines reach than the Lazy C reach due to the less confined
channel and better-connected floodplain. Velocities in the Powerline reach range between 3-6 ft/s in the main-
channel and 1-6 ft/s in the side channels during the 1-year flow, with the slowest velocities found within SC-2
and at the downstream bedrock constriction. Velocities increase during the 10-year flow to between 3-10 ft/s in
the main channel and 3-8 ft/s in the side channels with slower, shallower water spreading out across the
floodplain. Because of the significant backwater that is created during the 100-year flow, velocities decrease
despite the increase in discharge, with broad areas of slow 1-3 ft/s water spreading out across the valley
between RM 1.0-1.4 and within the floodplain near SC-2. Main channel velocities are greatest at the outside of
the meander bends near RM 2.1 and 1.6.
The floodplain is well-connected throughout the Powerlines reach due to the low relative elevation, high density
of side-channels and floodplain channels, and backwatering associated with the bedrock constriction at the
downstream end of the reach. The high degree of floodplain connectivity is beneficial to aquatic species because
it provides access to high quality and complex floodplain habitat, encourages the maintenance and formation of
those habitat types through channel migration and avulsion processes, and generally improves ecological
processes within the project reach such as nutrient cycling, riparian forest development, surface
water/groundwater exchange amongst many others. The existing hydraulic conditions will increase the short-
term effectiveness of restoration actions (described below) because raising water surface elevations is not
necessarily needed as part of the restoration strategy due to the well-connected floodplain.
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Comparison to FEMA floodplain mapping
The hydraulic modeling results for the 100-year flow closely match the FEMA Flood Insurance Rate Map (FIRM)
designated 100-year floodplain (Zone AE) presented in the 2019 Jefferson County flood insurance study (FEMA
2019; Figure 15). FEMA defines the AE Zone as “high risk” with a 1% chance of flooding any given year and a 26%
change over a 30-year mortgage. Homes within an AE Zone typically require flood insurance
(www.amica.com/en/products/flood-insurance/what-is-an-ae-flood-zone.html).
The overall inundation patterns between the two model results are similar with the entirety of the Powerlines
Reach and most of the Lazy C floodplain predicted to be flooded during the 100-year flow. The primary
difference between the results of both studies is that the overflow channels along the left bank of the Lazy C I
floodplain between RM 2.0-2.5 are captured by the 2-dimensional model presented in this study and not the 1-
dimensioanl model used to delineate the FEMA floodplain. Because the model used in this study utilizes more
recent topography and can predict complex 2-dimensional hydraulic patterns, we feel that it is a more accurate
predictor of inundation under the 100-year flow but is not a regulatory delineation. All floodplain regulations are
associated with the FEMA FIRM (FEMA 2019).
Figure 15. Comparison between estimates of the existing condition 100-year floodplain from this study and
the FEMA designated floodplain. Estimates of hydraulic conditions for this study were made using a 2-
dimensional hydraulic model relying upon 2018 lidar topography. The FEMA floodplain was designated using a
1-dimensional hydraulic model (HEC-RAS) updated using 2015 topography (FEMA 2019).
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2.4 Sediment Transport Dynamics
2.4.1 Lazy C Reach
The Lazy C reach has a high sediment transport capacity and is acting as transport reach for sediment mobilized
from both upstream and local sources (Figure 16). The confined channel morphology and low levels of
floodplain connectivity act to concentrate flow during floods, increasing the amount of force capable for moving
sediment. Because of this, the applied grain stress (force responsible for transporting sediment) exceeds the
threshold for motion for gravels under the 1-year flow level and for the entirety of both the upper and lower
Lazy C reaches under the 10-year flow level - meaning that gravel deposition is limited, and most gravels
mobilized into the reach are transported downstream during floods. This is exhibited in the coarse bed
substrate, plane-bed morphology, and lack of gravel bars found throughout the Lazy reach. Two exceptions to
this trend are the right bank split channel near RM 2.4 and the left bank overflow channel across from
Appaloosa Dr. near RM 2.2 – both of which show evidence of broad deposits of gravel.
The low rates of channel migration within the Lazy C reach, as well as the low levels of available spawning
habitat, are directly related to the high transport capacity and limited ability for gravel deposition. Sediment
deposition encourages bank erosion, channel migration, and floodplain formation, which in turn forms and
sustains complex aquatic habitat, including deposition of gravels suitable for salmonid spawning.
Figure 16. Estimates of the stable particle size under the existing 1-year and 10-year flow levels. The stable
particle size was estimated using the predicted shear stress distributions and the Shield’s equation and is a
measure of the sediment transport capacity at the project site. The estimates predict which particle size will
remain stable under the noted flow level – with all smaller grain sizes predicted to be transported.
Powerlines Reach
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The Powerlines reach has a lower sediment transport capacity than the Lazy C reaches and is acting as a
depositional reach for sediment mobilized from upstream and local sources (Figure 16). The well-connected
floodplain, wide active channel corridor, and meandering pool-riffle morphology cause flows to spread out
across the valley during floods, limiting the amount of available force within the channel capable of mobilizing
sediment. Furthermore, the backwater created by the downstream geologic constriction further reduces the
sediment transport capacity. This creates broad areas of the reach in which the applied shear stress is below the
threshold for transporting gravels during the 1-year and 10-year flow levels – causing sediment to deposit
throughout many areas of the reach. This is especially exhibited in the upstream braid bars between RM 1.8-1.9
and the downstream braid bars under the powerline corridor between RM 1.1-1.2, the latter of which is directly
related to the backwater effect of the geologic constriction. The extensive sediment deposition throughout the
reach is responsible for the high channel migration rates and subsequent development of the well-connected
floodplain and side channels, as well as the high frequency of bed mobilization, which can negatively affect
salmonid spawning habitat.
The depositional nature of the Powerlines reach and low capacity for coarse sediment to be transported through
the downstream geologic constriction will cause sediment to be continuously deposited within the reach, a
process that has implications on river processes upstream within the Lazy C reach. Sedimentation in the
Powerlines reach is driven by the backwater depositional zone created by the geologic constriction at RM 1.0
(Figure 15 and Figure 16). Through time, sediment has continued to fill the valley throughout the Powerlines
reach, encouraging the active channel migration (Figure 17) that has formed a new floodplain surface across the
valley following episodes of historical channel incision. Sedimentation propagates upstream with time. Since
channel migration results from sedimentation within the river, channel migration also propagates upstream -
towards the Lazy C reach. This process is exhibited by the up-valley meander migration that has occurred since
~1950 as the river progressed up-stream (Figure 17). As deposition in the Powerlines reach continues over time
it will propagate upstream towards the Lazy C Reach, raising the channel bed and water elevations along with
triggering more channel migration (Figure 18).
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Figure 17. History of channel migration within the project area between 1939-2019. The primary low flow
channel was digitized from historical aerial images and overlain on the 2019 NAIP image. The historical aerial
imagery used for this analysis was downloaded from the USGS Earth Explorer.
Sedimentation in the river not only triggers channel migration but can result in channel widening, particularly
with deposition of mid-channel gravel bars. The river has widened the active channel corridor from ~180 feet to
~360 feet between 1980-2017 in the Downstream Lazy C sub-reach. Because most sediment is retained within
the reach instead of being transported downstream, the upstream propagation of the aggraded material will
cause continued upstream migration of meander bends (with associated bank erosion) and eventually transition
the Lazy C reach from a stable plane-bed transport reach into an active pool-riffle/meandering reach with a
lower slope like the Powerlines reach (Figure 19).
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Figure 18. Continued sediment deposition in the Powerlines reach is encouraged by the downstream bedrock
constriction and is encouraging the channel to migrate upstream.
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Figure 19. Predicted evolution of channel and floodplain morphology within the project area assuming no
flood protection actions are taken.
If channel aggradation continues to propagate upstream into the Lazy C reach it will increase the extent and
frequency of flood inundation resulting from a reduction in flood conveyance. This will increase flood hazards to
the Lazy C development community. If there was no development in the area the process would have a positive
effect on aquatic habitat formation. Given the increased hazard exposure over time and the potential for
habitat recovery, finding solutions such as acquisition or relocation of at-risk properties is advised. Otherwise,
flood defenses may be necessary that will adversely impact habitat recovery. If homes and associated septic
fields are subjected to flood damage, it will adversely impact residents and the river’s ecological health. This
expected change in flooding extent and frequency will also be compounded by the predicted increase in the
frequency and magnitude of peak flows under climate change scenarios (described in detail below).
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2.5 Channel Migration History
2.5.1 Lazy C Sub-Reaches
The channel between RM 2.4-3.3 has remained in the same location against the southern valley wall since at
least 1939 which is the earliest data of available historical imagery (Figure 17). There was a steady outward
migration of the channel between 1939-1980 in the Downstream Lazy C sub-reach between RM 2.2-2.4,
however the channel was arrested by the valley wall and has now formed the flow split and forested island
discussed above. The channel through the Downstream Lazy C sub-reach between RM 2.0-2.2 has continued to
migrate up-valley towards the Lazy C development since 1939, although the migration was arrested between
RM 2.1-2.2 with the placement of riprap along the left bank. Active erosion continues in the downstream end of
the reach near RM 2.0 where recent migration rates of 18 feet/year were estimated between 2015-2017 (Figure
20).
Figure 20. Active bank erosion along the left bank within the Downstream Lazy C sub-reach.
The erosion is due to continued up-valley migration of the channel and is eroding into an un-vegetated
portion of the Lazy C residential development floodplain. The photograph was taken looking towards left
bank of the river and the intersection of Appaloosa Dr. and Palomino Lane at RM 2.0 on 10/9/20. Flow is left
to right.
2.5.2 Powerlines Reach
The Powerlines reach has experienced a much greater degree of channel migration since 1939 than the Lazy C
reaches with the current meander planform extending across the entirety of the valley. The current meander
belt formed between 1939-1951 when a previous meander in the middle of the reach cut off. Since 1951 the
channel has continued to progress outward towards the valley walls and up-valley towards the Lazy C housing
development.
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As is common with the progression of a river meander belt, scroll-bar floodplain features have formed in the lee
of each meander as point-bars formed during erosional processes have become vegetated (See locations of
scroll-bars in Figure 12). Furthermore, the abandoned paths of the main channel have formed into side channels
with each of the four side channels being in a former main-channel location. Thus, the active channel migration
processes within the Powerlines reach are responsible for the high diversity of channel and floodplain habitats
currently present. Additionally, the evaluation of historical channel migration patterns reveals the widening of
the active channel corridor around the BPA powerline corridor, especially compared to other narrower sections
of the reach.
2.6 Channel Migration Zone Delineation
The Channel Migration Zone (CMZ) expresses areas at risk of being influenced by erosional processes both in the
short term (next 10 years) and long term (next 100 years) and can be used as an educational and planning tool
to aid landowners and project stakeholders. NSD delineated the CMZ to inform the project stakeholders and
residents about current erosion risks and the trajectory of future erosion within the study area. NSD completed
this delineation (Figure 21) using methods adapted from Washington State guidelines (Rapp and Abbe 2003),
modified to included additional geomorphic considerations. The CMZ presented is entirely educational and has
not been formally adopted by Jefferson County, who is responsible for any regulatory constraints within CMZs.
The CMZ was developed using historical aerial imagery and existing lidar topography and is differentiated into
the following categories:
Low flow channel: The low flow channel digitized from 2017 aerial imagery. Areas adjacent to the
low flow channel are at high risk to short term erosion.
Active channel: The active channel corridor (unvegetated gravel bars) digitized from 2017 aerial
imagery. Areas adjacent to the active channel are at high risk to short term erosion.
Historical Migration Zone (HMZ): Areas that contained the low flow channel and active channel
corridor during the period of historical record from 1939-present. Because areas within the HMZ
have experienced recent erosion, they are at high risk of future erosional processes.
Geomorphic Migration Zone (GMZ): Areas within the valley bottom that include topographic
evidence of recent (past several thousand years) occupation such as relict channel features and
floodplain landforms. The GMZ encompasses areas that have likely experienced river erosion during
the time before the earliest available aerial image. Areas within the GMZ are at risk for future
erosional processes, however the time in which the erosion will occur varies depending on the
distance from the current river or avulsion pathway.
Erosion Hazard Area (EHA): Areas with a high likelihood of near-term erosion risk, such as those at
the outside of actively migrating meander bends or within active floodplain overflow pathways.
EHAs were also delineated along the toe of the hillslope as this area is susceptible to near-term
erosion when adjacent to the main channel.
Avulsion Hazard Area (AHA): Areas within low-lying, well-connected floodplain that are prone to
sudden channel shifts. Natural processes such as meander cut-offs can cause the entire river to
rapidly abandon its existing flow path in favor of a shorter one. Other processes such as landslide
dams can also cause a river to shift into an AHA by blocking an existing channel location and forcing
the river to occupy location. The risk of erosion within an AHA is high, even if the area is far from an
existing channel location, because of the sudden nature of river avulsions.
Alluvial Fan Hazards (AFH): Alluvial fans are broad, fan shaped areas of sediment that are deposited
within a valley at tributary confluences because of a sudden change in channel slope (and thus
sediment transport capacity). Alluvial fans often contain several “distributary” channels and can
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experience rapid shifts in channel locations as sediment deposited within one channel causes the
active channel to occupy another distributary channel.
Geotechnical Erosion Hazard (GHA) Setbacks: Geotechnical Erosion Hazard Setbacks were
delineated along hillslopes that are prone to slope instabilities such as landslides, slumps, and toe
erosion from the river. The setbacks were extended to the top of the slope to indicate that mass-
wasting processes pose a risk to the entire hillslope.
Figure 21. Channel migration zone (CMZ) delineation for the project area.
2.6.1 Lazy C Sub-reaches
The CMZ delineation demonstrates that the Lazy C and Mossy Lane residential developments are at risk of
future erosion, especially in areas adjacent to the current channel between RM 2.0-2.4, within the flood
overflow path near RM 2.4, and within the relict floodplain channels which could act as avulsion pathways
during a sudden shift in channel location.
The entire Lazy C and Mossy Lane housing developments were delineated within the GMZ due to the erodible
underlying material and location within the valley bottom. The downstream portion of the downstream Lazy C
sub-reach along Appaloosa Drive is at especially high risk of future erosion due to the active, recent, and up-
valley migration of the river. As discussed in Sections 2.3 and 2.4, the up-valley migration is expected to continue
due to continued aggradation of sediment in the Powerlines reach. Additionally, the area within the flood
overflow pathway near RM 2.4 was delineated within an AHA because of the potential for the river to cut off the
90-degree bend and occupy a new channel through the floodplain. Both areas could experience erosional
hazards in the near term due to the proximity of the current channel and frequent inundation of the flood
overflow pathway. The relict floodplain channels that cut across the housing development were also delineated
as AHAs because of the potential for a landslide from the unstable southern hillslope to dam the river and cause
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a sudden channel shift. While there is no evidence that landslides of that magnitude have recently occurred
along that hillslope, it is possible that one could form due to the erodible nature of the underlying lithology or as
the result of an earthquake. As such, the entire hillslope was delineated to be within the geotechnical erosion
hazard setback area. The remainder of the Lazy C I and Mossy Lane developments (and valley bottom in
general) are within the GMZ and thus are also at risk of future erosion.
2.6.2 Powerlines Reach
While there is no residential development within the Powerlines reach currently, NSD delineated a CMZ for the
reach to inform project stakeholders about the risk of habitat loss due to erosional processes. The greatest
erosion risk within the Powerlines reach is the potential for an avulsion to occur within one of the four side
channels due to a meander cut-off. While avulsions are natural processes that allow for the creation of a
diversity of aquatic habitats, the lack of stable large wood and mature riparian vegetation within the reach due
to historical logging and stream clearing activities increases the risk of avulsion above what would be expected
under historical conditions.
Without the resistance from stable large wood and mature riparian vegetation, the river can cut-off and avulse
more frequently and before the riparian forest has had time to mature (roughly 100-150 years). When avulsions
happen before the forest has time to mature, it can create shorter, wider channels without structure and habitat
complexity. SC-1 is at the greatest short-term avulsion risk of the four side channels because the meander that it
spans has the greatest sinuosity and longest channel length. This side channel contains high quality and complex
habitat, and spawning activity was noted within the channel during the field survey (Appendix B). The remainder
of the Powerlines reach is within either the HMZ (due to the active channel migration processes that have
occurred during the period of record) or the GMZ and is also at risk of erosion, although the risk of habitat loss is
less than if an avulsion occurred in one of the side channels.
2.7 Large Wood
2.7.1 Lazy C Sub-reaches
There is a low amount of stable large wood within the Upstream Lazy C sub-reach due to historical stream
clearing and splash dam activities as well as the lack of channel migration that limits wood recruitment. Within
the main channel of the sub-reach (RM 2.4-3.3) there were six stable log jams identified during the 2020 field
survey (Figure 22) which is 14% of reference levels which were calculated based on the nearby Queets River
using data from Abbe and Montgomery, 1996. (Table 2). The existing log jams consist primarily of bank-attached
deflector jams and stable key piece snags that have been recruited to the channel from slumps/landslides on the
right bank hillslope. Where present, the jams are exerting some geomorphic influence on the stream by
sorting/aggrading sediment and forming small scour pools. Cut marks were observed on one large cedar key
piece snag (Figure 23).
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Figure 22. Stable large wood jams and large wood pieces within the project area. The stable large wood was
mapped in the field on 10/9/20.
Table 2. The frequency of stable log jams throughout the project area compared to reference conditions.
REACH LENGTH (MILES) STABLE LOG JAMS PER RIVER MILE
MAIN CHANNEL SIDE CHANNELS REFERENCE (QUEETS RIVER)1
Upstream Lazy C 0.9 7 0.0
49 Downstream Lazy C 0.4 18 0.0
Powerlines 1.4 9 6
1Stable log jams were identified in the field on 10/9/20 and reference conditions were derived from the nearby Queets River using data from Abbe and Montgomery, 1996.
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Figure 23. Cedar snag with cut marks in the Upstream Lazy C sub-reach. The snag is exerting geomorphic
influence on the channel by aggrading sediment and scouring a pool at the upstream end. The bole of the tree
was cut near the rootwad. Cutting snags decreases their stability. Photo is looking downstream, 10/9/20.
There is a greater amount of stable large wood within the Downstream Lazy C sub-reach (RM 2.4-2.0), although
the frequency is still well below reference levels (Figure 22 and Table 2). There were 7 stable log jams identified
in the sub-reach during the field survey which is 35% of reference levels. The stable log jams in this sub-reach
consisted of bank attached deflector jams, as well as a bar apex jam on the forested island near RM 2.2 and a
meander jam at the downstream end of the reach near RM 2.0 (Figure 24). One of the bank deflector jams was
located at the mouth of SC-1. There were also several pieces and accumulations of recently recruited large
wood, especially near the actively migrating left bank near RM 2.0, although none of that wood was deemed to
be stable during the field survey.
Figure 24. Examples of stable log jams within the Downstream Lazy C sub-reach. Photo A is of a bar apex jam
at the head of the forested island near RM 2.2. Photo B is of a meander jam on the left bank near RM 2.0.
Photos taken 10/9/20 looking towards the left bank. Flow in both photos is left to right.
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2.7.2 Powerlines Reach
There were 18 total stable large wood jams within the Powerlines reach during the field survey with 10 of the
jams in the main channel and 8 within side channels. The total wood frequency is 26% of reference conditions.
However, since almost half of the jams were identified as being stable within the existing side channels, the
actual frequency of stable jams is closer to that of only the main channel (14%) because those jams would likely
not be able to withstand the forces of the main channel if an avulsion occurs. A subset of the main-channel
stable log jams consisted of a large meander jam near RM 1.8 between SC-2 and SC-3, a large bar apex jam on
the left bank near RM 1.6, and a large channel spanning log jam complex within the downstream braid bar near
RM 1.2 (Figure 25). There were also many pieces of mobile wood that have accumulated on top of bar surfaces.
The amount of wood accumulation, especially within the downstream braid bar, is reflective of the depositional
qualities of the reach. The log jams within the side channels consisted of bank deflector jams and log steps
(Figure 26). The low level of stable large wood within the Powerlines reach compared to reference conditions is
likely due to historical stream cleaning and forest clearing activities, as well as the lack of mature riparian
vegetation capable of remaining stable once recruited into the channel.
Figure 25. Examples of stable log jams within the Powerlines Reach. Photo A is of a left bank meander jam
near RM 1.8. Photo B is of a left bank bar apex jam near RM 1.6. Photos C and D are of the channel spanning jam near RM 1.2. Photos taken 10/9/20.
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Figure 26. Examples of stable log jams within the side channels of the Powerlines Reach. Photo A shows a
bank attached deflector jam within SC-1. Photo B shows a log step jam within SC-2. Photos taken on 10/9/20.
2.8 Riparian and Wetland Communities
2.8.1 Lazy C Sub-reaches
Riparian vegetation communities within the Lazy C sub-reaches are characterized by mature mixed coniferous
and deciduous forested communities typical of wet forests within the Pacific Northwest. Clearing for timber
harvest, road, and home construction has altered much of the riparian community within the floodplain terraces
throughout the Lazy C sub-reaches. Riparian communities located directly adjacent to the riverbanks and on the
lower floodplain terraces are dominated by western red cedar (Thuja plicata), red alder (Alnus rubra), big-leaf
maple (Acer macrophyllum), and black cottonwood (Populus balsamifera) in the overstory, with vine maple (Acer
circinatum), salmonberry (Rubus spectabilis), and sword fern (Polystichum munitum) in the understory. The
overstory in these communities is primarily dominated by deciduous tree species, with multiple age class of
coniferous species growing within the understory (Figure 27). The higher, drier terraces within this reach
include Douglas fir (Pseudotsuga menziesii), grand fir (Abies grandis), and western hemlock (Tsuga heterophylla)
in the overstory, and snowberry (Symphoricarpos albus) in the understory.
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Figure 27. Riparian condition along Upstream Lazy C sub-reach. Photo looking upstream, 10/9/20.
In general, these vegetated lower floodplain terraces tend to be frequently flooded wet forests rather than
jurisdictional wetlands, but a site-specific wetland delineation would be needed to make that determination for
the study area. A single wetland feature is shown in the National Wetland Inventory (U.S. Fish and Wildlife
Service 2021) located on a low floodplain terrace near RM 2.8.
The Downstream Lazy C sub-reach includes low floodplain to both river left and river right. Much of the
vegetation to river right has been removed in association with the Lazy C I development except for a narrow
fringe of shrubs and small trees rooted directly in the riverbank (Figure 27). The typically sparse floodplain
vegetation within this area includes native black cottonwood, red alder, and big-leaf maple. The low floodplain
to river right supports a mosaic of flood channels with a forested community dominated by black cottonwood
and red alder in the overstory, and grand fir growing up within the understory. Shrub species include vine maple
and salmonberry, with sword fern in the understory. The mosaic of overflow channels is unvegetated and shows
signs of frequent flooding (I.e., debris and scour), and the vegetation shows a mix of flood-tolerant species.
Much of this area may be wet forest, rather than jurisdictional wetland. However, site-specific wetland
delineation would be needed to make that determination through an examination of soils, hydrologic indicators,
and vegetation.
2.8.2 Powerlines Reach
Riparian communities within the Powerlines reach are characterized by some of the tallest trees in the study
area (Figure 28) present in a mixed mature deciduous/coniferous forest on the higher floodplain terraces, and
by younger deciduous forest on the developing gravel bars. Few of these features appear to support wetland
communities, despite the frequent connection to flood flows. The higher flood terraces support an overstory of
a mixture of black cottonwood, big leaf maple, red alder, and grand fir, with an understory of vine maple,
salmonberry, snowberry, and sword fern. Sapling grand fir and western red cedar are also common within the
understory (Figure 29).
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Figure 28. Canopy height map of the project area. Canopy height was calculated using the highest hit digital
surface model (DSM) and bare-earth digital elevation model (DEM) from the 2018 Olympic Peninsula LiDAR
dataset. Canopy height is only shown within the valley-bottom for clarity.
Figure 29. Typical riparian conditions in the Powerlines Reach. Note mixed forest on higher terraces and
young deciduous forest on the gravel bars and lower terrace along the channel. Photo taken 10/9/20.
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The recently formed gravel bars within this reach support multiple age classes of red alder and black
cottonwood, with big leaf maple typically located on the higher elevations. Western red cedar and western
hemlock are common saplings within the understory, and large patches of invasive Himalayan blackberry (Rubus
armeniacus) dominate the understory in the younger forest areas. These gravel bars and young riparian
communities also support scattered patches of invasive butterfly bush (Buddleja davidii) and Scotch broom
(Cytisus scoparius), along with pockets of invasive knotweed (possibly Fallopia japonica).
Side channels are common through these floodplain areas. These open channels typically support Pacific willow
(Salix lucida), and salmonberry, along with red alder and cottonwood along the channel margins. One less than
approximately 0.5-acre wetland area was observed in the Powerlines reach located within the river left
floodplain at RM 1.0. This wetland has formed as a backwater alcove and is dominated by sapling red alders and
invasive reed canarygrass (Phalaris arundinacea) and is not identified in the National Wetland Inventory (NWI).
2.9 Aquatic Habitat Conditions, Salmonid Use, and Periodicity
2.9.1 Aquatic Habitat Conditions
The focal species in the Dosewallips River, fall Chinook and Hood Canal summer chum, spawn in the fall and
spend hours to months rearing in freshwater before outmigrating to estuarine and nearshore habitat. Both are
listed as federally threatened species under the Endangered Species Act. The life stages of these species most
affected by the quality, quantity, and diversity of aquatic habitats are spawning, incubation, emergence, and fry
rearing.
Within freshwater habitats, habitat diversity, channel stability and sediment load have been identified as the
elements most critical for restoration (Brewer et al. 2005). Loss of riparian forest has also been specifically
noted for the Dosewallips watershed. The floodplain in the lower reaches of the river, including the Lazy C I
portion of the study area, has been converted to agriculture, forestry, urban commercial and rural residential
uses (Correa 2003). These changes in land use have reduced the side channel and floodplain wetland habitat in
the study area. Diking along the Lazy C Reach to protect residential development was noted as limiting access to
the adjacent floodplain (Correa, 2003).
Aquatic habitat surveys in 2020 in the study area identified that riffle habitats made up 52% of the available
habitat in the Lazy C and Powerline reaches by area, and pools represented 28% of the channel area (Figure 30
and Appendix B). The percentage and area of pools was highest in the Powerline reach, with the Upstream Lazy
C I reach containing the lowest proportion of pools. The Upstream Lazy C sub-reach is much more confined,
lacks off-channel habitat and has lower habitat complexity (Burgess and Roni 2020). All three reaches had a
fairly even distribution of sediments in cobble, gravel and sand size classes. The Downstream Lazy C sub-reach
contained some side channel pools, while the Upstream Lazy C sub-reach did not.
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Figure 30. Typical habitat conditions within the project area. Photo A shows riffle habitat within the Upstream
Lazy C sub-reach which is the predominant habitat type in that sub-reach. Photo B shows an example of a
bedrock forced pool within the Powerlines Reach. Photo C shows typical habitat conditions within SC-1 and
photo D shows typical habitat conditions within SC-2. Photos taken 10/9/20. The flow direction of each photo
is as follows: A-Looking downstream, B- Looking upstream towards the left bank, C- looking downstream, D-
looking upstream.
Recent surveys in the Dosewallips watershed (Labbe et al. 2005) noted large wood as being an important factor
in creating pools and scour (LWD pieces was responsible for 60-80% of pools in the reaches surveyed). It was
also noted that large bar apex logjams (Abbe and Montgomery 2003) had a significant influence on habitat
formation, but that lack of “key” pieces (large tree boles) is limiting logjam formation. Key member recruitment
to the river is limited in the Lazy C reach by lack of bank erosion associated with channel confinement. In the
Powerlines reach it is limited by lack of big trees on the floodplain. In the downstream portion of the Powerlines
Reach there are few floodplain trees at all due to forest management beneath the Bonneville Power Lines.
Historically clearing of floodplain forests continues to impact habitat conditions and fluvial processes. And
historic splash damming flushed all wood through the river and certainly contributed to channel incision in the
Lazy C reach. Splash damming is believed to have reduced spawning gravel supply in the basin (WDFW and
PNPTT 2000). In the Upstream Lazy C sub-reach, large wood is lacking (see Section 2.7 and Appendix B),
indicating high flow velocities (Burgess and Roni 2020) and greater risk to redds and incubation from high flows
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in the fall and spring. This reach also offers very limited rearing habitat for juvenile Chinook, coho, and
steelhead. In the Downstream Lazy C sub-reach, floodplain habitat is disconnected from the channel due to the
Lazy C residential development. Wood noted in the reach is small and limited in geomorphic function.
The Powerlines reach contained higher quality aquatic habitat with little channel confinement, as well as more
common side and braided channel habitat (Figure 30). Large wood jams are most frequent in the upstream
portion of the Powerlines Reach, but still below reference levels. Logjams not only create pools but provide
complex cover that spawning adults and juveniles seek out. The Powerlines reach also has more pools, and
more large pools than the Lazy C reach, providing more holding habitat (refer to Figures 6, 9 and 13 in Appendix
B).
2.9.2 Habitat Use
Critical life stages for chum and Chinook have been identified as spawning, incubation and adult holding (Shared
Strategy 2007). Incubation and rearing success are driven by large wood and moderate peak flows, absence of
excessive fines in spawning gravels, moderate or low levels of scour, and access to off-channel and floodplain
habitats.
Chinook, as a larger species, require larger substrate for spawning and deep holding pools with cover for adult
migration. Egg incubation is affected by scour during high flows and excessive fine sediment which can smother
redds. Juvenile Chinook remain in the river for approximately 4 months (Table 3) and depend on low velocity
habitat and cover for rearing. The majority of juvenile Chinook in the Dosewallips and other coastal rivers
exhibit the ocean-type life history and out-migrate after about 4 months of rearing in freshwater, completing
the rest of their growth in estuarine or nearshore habitat. A small proportion of Chinook maintain a stream-type
life history, spending up to a year in fresh water before outmigration. The proportion of stream-type Chinook in
the Dosewallips is unknown but expected to be small. Low velocity habitat includes river margins, alcoves, back
waters, and side channels, where small fish can escape the force of the current, have sufficient hiding cover for
protection from predators, and be able to rest and feed.
Chum salmon have similar requirements for deep pools with cover for holding, but they use slightly smaller
gravels for spawning than Chinook. While most Chinook spawn in mainstem river channels, Chum are more
likely to spawn in lower velocity areas with smaller substrate, which may include mainstem habitat, smaller
creeks and side channels. Incubation for Chum is also limited by scour from high flows, perhaps to a greater
extent than Chinook based on the chum behavior of mass spawning and redd superimposition. Spawning
success for Chum is linked to suitable spawning gravel, adequate stream flows and water temperatures, as well
as habitat quality in the form of large wood for cover and holding pools for returning adults to rest. Excessive
fine sediment is also a concern for Chum eggs in terms of suffocation. Since Chum fry out-migrate upon
emergence (Table 3), their dependance on adequate riverine rearing habitat is less than that of Chinook, but
they still need safe pathways to out-migrate through the mainstem channel and have a higher need for
sufficient estuarine and nearshore habitat. Chum spawning in the Dosewallips is limited to the lower 4.3 miles
of river, with the greatest concentrations below RM 2.5 (Brewer et al. 2005), which includes the study area.
Current spawning conditions in the study area vary by reach with the highest level of spawning observed in the
Powerlines reach (see Section 2.8.1).
Coho salmon also spawn in the fall and have similar needs for spawning, incubation and fry rearing as Chinook.
However, Coho spend 1-2 years in freshwater habitat for rearing before outmigration (Table 3), so they are
more affected by the quality and duration of supportive riverine habitat conditions across multiple seasons.
Specifically, high flow refuge in the fall/winter, overwintering habitat, and summer low-flow rearing habitat are
necessary for coho to survive to become smolts. Like Chinook fry, Coho fry and juvenile life stages are most
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common in slower velocity habitat (3-6 cm/s) and moderate depths (up to 1 m). These areas are most often
found at the margins of mainstem channels, in side channels, backwaters, or floodplain channels.
Table 3 presents the periodicity of habitat uses for Summer Chum, Chinook and Coho in the Dosewallips River.
Additional salmonids which utilize the study area are described below.
Table 3. Periodicity of selected salmon in the Dosewallips River
2.9.3 Hood Canal Summer Chum ESU (Oncorhynchus keta)
Life History and Periodicity
The Dosewallips River supports an indigenous population of summer Chum. Summer Chum salmon in Hood
Canal are those that have a peak spawning migration before November 1 (WDFW and PNPTT 2000). Hood Canal
Summer Chum generally spawn from August to late October (Table 3). Fry emergence occurs between early
February and May with peak emergence in late March for Hood Canal (Ames et al. 2000 as cited in Brewer et al.
2005). Outmigration to salt water occurs quickly after emergence (hours to days).
Summer Chum spend a short amount of time in freshwater and adults spawn soon after entering freshwater in
the lower reaches of rivers and streams. This use of lower reaches may be an adaptation to spawning in low
flows. Fry often emerge at night and will move into estuarine waters within hours after emergence (Simenstad
2000). Fry do not likely feed significantly in freshwater systems during this rapid transition from fresh to saline
habitats. Estuaries and tidal marshes support Chum fry as they move along the shoreline once they have exited
the rivers.
Chum juveniles generally rear in nearshore habitats, often with eel grass where copepods are found, until they
are 40-50 mm. Following the nearshore rearing, Chum juveniles use deeper offshore habitats. Growth during
this estuarine phase is critical, often determining the chance of survival to later life stages. Although critical, this
stage is not long, and Chum have been noted to exit Hood Canal into the Pacific Ocean within 2 weeks of
emergence.
Limiting Factors
The Hood Canal Summer Chum Recovery Plan identifies the primary limiting factors affecting Chum salmon as
(Brewer et al. 2005):
Chinook Salmon Life History
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Spawning
Emergence
Rearing
Outmigration
Summer Chum Salmon Life History
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Spawning
Emergence
Rearing
Outmigration
Coho Salmon Life History
Spawning
Emergence
Rearing
Outmigration
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1. Climate related changes affecting streamflow patterns
2. Fishery exploitation
3. Habitat loss
Unfavorable stream flows in 1975 and 1976 caused a crash in Chum populations across Washington State, but
Hood Canal populations remained low while other populations recovered. High levels of fishing in the 1980s
had further impacts on the population and coincided with a shift in ocean conditions in 1986 to patterns less
favorable to Chum (Brewer et al, 2005).
Several factors have been identified in the Dosewallips River as affecting Hood Canal Summer Chum
populations. For spawning and incubation life stages, loss of channel complexity and floodplain access are key
factors (Brewer et al. 2005). Historically, much of the lower few miles of the river has been simplified, with the
construction of dikes, placement of riprap, splash damming and the removal of wood. The surrounding
floodplain in the area has also been converted to pastureland and residential development (Brewer et al. 2005).
Sediment aggradation is also noted as a problem for spawning and incubation due to sediment input from forest
roads, as well as channelization and diking. Logging of forests, specifically old growth areas, has resulted in loss
of recruitment sources for large wood into the river. Most trees in the riparian region below RM 4.5, including
in the study area, are 12 inches or less in diameter (Brewer et al. 2005) and up to 20% of the riparian zone has
been negatively affected by land use activities. The USFS rated the riparian conditions along the river as fair to
poor (Brewer et al. 2005). Loss of side channel habitat and channel instability have also been noted as limiting
factors for salmon habitat. Estuarine habitat degradation was also noted as a leading limiting factor for juvenile
Hood Canal Summer Chum rearing.
2.9.4 Puget Sound Chinook (Oncorhynchus tshawytscha)
Life History and Periodicity
The Mid-Hood Canal Chinook population is one of two historic and existing populations in the Hood Canal
Region listed under the Puget Sound Chinook Evolutionarily Significant Unit (ESU). In the Dosewallips River, fall
Chinook are known to spawn up to the barrier falls at RM 14.
Fall Chinook generally spawn in September through December and eggs incubate until January through March
(Table 3). Juvenile fall Chinook rear in freshwater for a variable time, typically a few weeks to months, and
outmigrate anywhere between January and August (Burgess and Roni 2020).
Limiting Factors
The factors most limiting Chinook production in the Dosewallips River are estuarine degradation, habitat
complexity and channel conditions, high water scour and fine sediment and floodplain disconnection. These
mostly occur in the lower reaches of the river and the estuary habitat since the upper watershed is less
developed (Shared Strategy 2007).
2.9.5 Coho (Oncorhynchus kisutch)
Life History and Periodicity
Coho generally return to their natal streams after three years in the ocean. After spawning, eggs incubate for 35
to 45 days before emergence. Juveniles use slow water habitats in streams and rivers such as ponds, off-
channel habitat and side channels and consume insects (Quinn 2018).
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Coho also enter the river in the fall but generally spawn in the winter, emerge in spring, and rear for a full year in
freshwater (Table 3). Based on their longer use of freshwater habitat, coho salmon are likely more dependent
on the aquatic habitat conditions in the Dosewallips River than either fall Chinook or Hood Canal Summer Chum.
Limiting Factors
Limiting factors for Coho generally relate to juvenile rearing habitat availability across multiple seasons. Since
Coho spend 1-2 years in freshwater, they need appropriate refuge and rearing habitat during both the winter
higher flow season and during summer low flows (Quinn 2018).
2.9.6 Pink / Humpback (Oncorhynchus gorbuscha)
Life History and Periodicity
Pink salmon have a slightly smaller body size than Chum salmon, but generally follow a similar life history
pattern with fall spawning, spring emergence, and rapid outmigration. Pink salmon spawn from late-June to
early October. Eggs incubate over the winter and emergence occurs in late winter or early spring. Fry migrate to
salt water immediately upon emerging from gravel (ADFG 2021).
Pink salmon have the shortest life cycle of all the salmon in North America, completing their development and
returning to spawn in just two years (ADFG 2020). Pink returns occur every two years, so they are affected by
habitat conditions every other year.
Pink salmon likely use the Dosewallips River for spawning (WDFW 2021), but like chum, outmigrate soon after
emergence to rear in estuarine and nearshore habitats. Pink salmon fry generally do not eat as the migrate
through freshwater, feeding on plankton, smaller fish, and invertebrates once they reach salt water (Quinn
2018).
Limiting Factors
Limiting factors for Pink salmon in freshwater are limited to spawning gravel, adequate spawning space, and
emergence. High flows can cause scouring of redds and excessive fines can smother eggs, reducing survival
from egg to the fry life stage.
2.9.7 Steelhead and Rainbow Trout (Oncorhynchus mykiss)
Life History and Periodicity
Steelhead and rainbow trout have identical life cycles and genetics, except that steelhead are anadromous,
outmigrating to the ocean and returning multiple times to spawn in freshwater, while rainbow trout remain as
resident freshwater fish for their entire life history.
Winter Steelhead are more common in coastal streams like the Dosewallips and return from the ocean ready to
spawn in between November and April. Summer Steelhead return earlier in the year than winter steelhead and
complete their development in freshwater before spawning. They generally return between May and October
and complete their spawning sometime in the spring.
Rainbow trout spawn in multiple seasons in freshwater streams rivers, and lakes. The eggs hatch in four to seven
weeks and remain in the alevin stage, feeding on a yolk sac for another two weeks. Fish grow from fry to
juveniles, or parr, and then to adults within freshwater (Quinn 2018).
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Limiting Factors
Factors for decline in Rainbow Trout and Steelhead populations include habitat degradation, invasive species,
diseases (such as whirling disease), overfishing, pollution, and hybridization with other species. Trout generally
feed on aquatic insects, but also may eat smaller fish. They will also eat fish eggs and terrestrial insects that fall
into the water. Steelhead, like Coho, rear in freshwater for 1-2 years and are thus highly dependent upon the
quality and quantity of instream and rearing habitat for their lifecycle.
Steelhead spawn in late fall and winter, so are likely more affected as spawners by high flows and scour during
peak flow events.
2.10 Summary of Impairments
Because the Dosewallips River is identified as a priority watershed for salmon conservation, restoration of the
processes which form and sustain aquatic habitat, as well as restoration of the river’s access to its floodplain
corridor are of critical importance. Although estuarine habitat is also critical to rearing success, this plan is
focused on the resiliency of freshwater habitat, and thus does not detail the health and threats to estuarine
habitat here.
While the study area reaches are in many respects still functional, the analysis completed as part of this project
points to several impairments which are affecting the formation and longevity of aquatic habitat, as summarized
below. Appendix E details the riverine processes, impairments, and potential actions to address the impairments
for the Lazy C I and Powerlines reaches.
2.10.1 Upstream Lazy C sub-reach
The Upstream Lazy C sub-reach is characterized by significant impairments in fundamental channel and
floodplain formation processes, floodplain connectivity, sediment transport, and channel migration which in
turn have caused impairments in large wood recruitment and retention, riparian and wetland habitat formation,
and in aquatic habitats supportive of anadromous salmonid use. As detailed in Appendix E, the following
impairments are present:
Channel and floodplain formation, connectivity, and sediment transport processes are impaired.
The river is confined to a straight, entrenched channel along the southside of valley with no right
bank floodplain and little left bank floodplain engagement.
Floodplain development limits potential for channel and floodplain formation and limits
opportunities for floodplain connectivity.
Incised and confined channel limits floodplain connectivity.
Localized bank protection along left bank is inhibiting formation of an inset floodplain.
Channel confinement increases sediment transport capacity and limits gravel retention and bar
formation.
Channel migration processes are impaired.
Channel confinement limits sediment deposition which reduces channel migration rates.
Ongoing and historical clearing of in-stream wood limits channel migration.
Localized bank protection limits channel migration.
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Large wood recruitment, riparian, wetland and aquatic habitat formation if impaired.
Lack of channel migration limits wood recruitment.
Ongoing and historical clearing of in-stream wood has reduced the quantity of instream large
wood.
Lack of overbank flooding limits the formation of floodplain wetlands.
Deciduous trees dominate the riparian zone due to historic forest clearing.
Formation of complex aquatic habitat is limited by lack of large wood, channel confinement, and
low degree of floodplain connectivity.
2.10.2 Downstream Lazy C sub-reach
The Downstream Lazy C sub-reach is similarly impaired by the development of the floodplain and the
consequent limited floodplain engagement. These impairments have in turn have caused impairments in large
wood recruitment and retention, riparian and wetland habitat formation, and in aquatic habitats supportive of
anadromous salmonid use. As detailed in Appendix E, the following impairments are present:
Channel and floodplain formation, connectivity, and sediment transport processes are impaired.
Floodplain development limits potential for channel and floodplain formation.
Localized left bank protection is inhibiting formation of an inset floodplain.
Development is inhibiting natural recovery of gravel retention, bar formation, and bank erosion.
Channel migration processes are impaired.
Localized bank protection and floodplain development limit up-valley channel migration.
Channel migration rates are increased above historical levels due to aggradation in Powerlines
reach and clearing of riparian vegetation.
Large wood recruitment, riparian, wetland and aquatic habitat formation if impaired.
Clearing of left bank riparian forest limits wood recruitment.
Reduction in channel migration rates due to floodplain development and bank armoring limits
wood recruitment.
Lack of channel migration limits wood recruitment.
Development and lack of overbank flooding limits the formation of floodplain wetlands.
Deciduous trees and immature riparian vegetation dominate riparian zone due to historic forest
clearing.
Formation of complex aquatic habitat is limited by lack of large wood, channel confinement, and
low degree of floodplain connectivity.
2.10.3 Powerlines Reach
The Powerlines reach, while not impaired by floodplain development, is affected by upstream factors, as well as
impairments caused by a lack of large wood which has adversely affected riparian and wetland habitat
formation and puts the existing aquatic habitats supportive of anadromous salmonid use at risk. As detailed in
Appendix E, the following impairments are present:
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Channel and floodplain formation, connectivity, and sediment transport processes.
Upstream channel confinement (e.g., Upstream Lazy C sub-reach, Wolcott Flats etc.) increased
sediment supply to this sub-reach.
Aggradation coupled with historical forest clearing has transformed the sub-reach from an
anabranching forested island morphology to a braided wide channel.
Frequent bed mobilization and sediment deposition in braided sections negatively impact
salmonid redds.
Channel migration processes are impaired.
Historical forest clearing and low levels of stable large wood have increased channel migration
rates above likely historical levels.
High channel migration rates increase risk of avulsion through side channels which will decrease
the amount of in-channel and side-channel habitat.
Large wood recruitment, riparian, wetland and aquatic habitat formation if impaired.
Historical forest clearing and instream wood removal have reduced levels of stable large wood
in the main channel and side channels.
Channel migration rates greater than historical levels are limiting the ability of riparian
vegetation to mature.
Increased sedimentation due to upstream channel confinement is encouraging the formation of
unstable morphologies (braided channels) which negatively impact salmonid habitat.
2.11 The Warming Climate
Scientific studies in the Pacific Northwest region have concluded that the frequency and magnitude of peak
flows will increase over the next 100 years while summer/fall low flows will diminish (Hamlet et al. 2013;
Mauger et al. 2016; Warner, Mass, and Salathé 2015; Hamlet and Lettenmaier 2007; Elsner et al. 2010). Impacts
from the warming climate on flooding are projected to occur in the coming decades, with increases in peak
flows modeled for the 2040s (inclusive of 2030-2059; Hamlet et al. 2013), 2050s (inclusive of 2040-2069; Mauger
et al. 2016), and beyond. Numerous studies for western Washington have indicated increases in peak flows as
early as the 2020s (inclusive of 2010-2039; Elsner et al. 2010, Mantua, Tohver, and Hamlet 2010). The warming
climate effects are therefore relevant to the consideration of all geomorphic and hydraulic processes related to
flow duration, frequency, and magnitude.
Projections for increased peak flow magnitudes with the warming climate are driven by projections for more
intense precipitation, particularly in the fall and winter months. Higher precipitation rates will increase the
magnitude of annual peak flows and contribute to increases in mass-wasting and sediment delivery to the river
network – both upstream and within the project area – which will impact flooding by raising bed elevations and
further increase the frequency of inundation by raising water levels. The increase in annual peak flow magnitude
will also contribute to increases in channel migration and erosion.
The warming climate will also result in lower base flows in the late summer and fall. This will diminish the
wetted channel area and depths that will decrease available habitat. Warmer air temperatures will also result in
warmer water in the river, further stressing fish (Mantua et al., 2010) and making riparian shade and in-stream
cover even more important for salmonids. While these changes were not quantitatively evaluated by the scope
of this study, they further underscore the importance of increasing the ecological resiliency of the project area.
In practice, this could be accomplished by increasing stream shade, the quantity of off-channel habitats and
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deep pools, as well as increased surface water/ ground water interactions through increased floodplain
connectivity and added roughness so that the predicted increases in stream temperature can be partially offset
by temperature decreases.
Looking to the future, the impact of the warming climate on river dynamics in the project area was analyzed by
projecting peak flow estimates into the future and modeling the resulting “climate change” flows. The discharge
estimates used for climate change floods are based on the work done by the Columbia Basin Climate Change
Scenarios (CBCCS) project (Hamlet 2010) and are included in Table 4. More details on how these discharge
values were estimated are included in Appendix D: Hydraulic Modeling.
Table 4. The magnitude of future peak flows 2070-2099 projected as result of warming climate.
RECURRENCE INTERVAL PRESENT DISCHARGE
ESTIMATE
(CFS)
PERCENT INCREASE DUE
TO CLIMATE CHANGE
FUTURE (2070-2099)
DISCHARGE ESTIMATE
(CFS)
1-year 2,100 18% 2,480
10-year 11,420 18% 13,480
100-year 17,120 23% 21,060
Flood risk is not significantly increased for low magnitude floods such as the one-year recurrence peak flow as
result of warming climate (Figure 31). Impacts increase with higher magnitude peak flows. For example, in the
Lazy C development the extent of flooding associated with the future 10-year recurrence peak flow will be
roughly equivalent to the present-day 100-year flood. The future 100-year flood will inundate almost every
parcel in the Lazy C development south of Palomino Lane, with some areas under 3-5 feet of water. Increases in
erosion are also expected with the increases in flood magnitude and frequency. These results underscore the
importance of developing a long-term resiliency plan for the project area to reduce flood damages and restore
habitat and river processes. Further detailed assessments of avulsion risk, flood risk, geological hazards, etc.
were outside the scope of this effort, but should be considered in any planning conducted to evaluate long-term
risks to the Lazy C development.
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Figure 31. Estimated depths for the 1-year (2,480 cfs), 10-year (13,480 cfs) and 100-year (21,060 cfs)
recurrence peak flows predicted by 2070-2099. The peak flow estimates were made by scaling the existing
recurrence intervals by their projected increases for the nearby Skokomish River developed by the Columbia
Basin Climate Change Scenarios (CBCCS) project (Hamlet, 2010). The Peak flows were scaled by the following
percentages: 1-year: 18%, 10-year: 18%, 100-year: 23%.
The peak flow estimates were made by scaling the existing recurrence intervals by their projected increases for
the nearby Skokomish River developed by the Columbia Basin Climate Change Scenarios (CBCCS) project (Hamlet
2010).
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3. PROJECT GOALS AND OBJECTIVES
The County and the Dosewallips River Collaborative worked with the NSD team to establish goals for the
Resiliency Plan project. The primary goals are to establish a better understanding of the historic changes, the
geomorphic and ecological processes that form and sustain salmon habitat and the extents of flood inundation
and erosion within the project area. Additional goals are to begin a planning template for building ecological
resiliency and reducing flood damages. This template presents short and long-term opportunities to achieve
these goals.
3.1 Resiliency Plan Assessment Goals
The goals for this assessment are to:
1. Describe the geomorphology of the Lazy C and Powerlines Reaches of the lower Dosewallips River,
including historic changes to geomorphic processes and habitat, and the existing and potential in-
channel, side channel, and floodplain-associated habitats relative to use by ESA-listed Hood Canal
summer chum and Puget Sound Chinook ESUs.
2. Describe current factors that limit the ‘normative river processes’ needed to create and sustain
salmonid habitat. These processes include channel migration, channel avulsions, landslides, recruitment
of in-stream wood and riparian forest conditions.
3. Determine opportunities to protect and restore riverine processes and in-channel, side channel, and
floodplain-associated habitats that support Hood Canal summer chum and Puget Sound Chinook
recovery, foster resiliency to climate change, and are sensitive to downstream shellfish habitat.
3.2 Resiliency Plan Assessment Objectives
A series of objectives were then established specifically tied to each of the goals. These objectives are reflected
in the data collection and analysis completed by NSD over the course of the project.
Goal 1: Describe the geomorphology of the Lazy C and Powerlines reaches of the lower Dosewallips
River, including historic changes to geomorphic processes and habitat, and the existing and potential
in-channel, side channel, and floodplain-associated habitats relative to use by ESA-listed Hood Canal
summer chum and Puget Sound Chinook ESUs.
Objective 1.1. map channel morphology, and floodplain conditions within the Lazy C and
Powerlines reaches.
Objective 1.2. map in-stream habitat conditions relative to potential for use by chum and
Chinook
Goal 2: Describe current factors that limit the ‘normative river processes’ needed to create and
sustain salmonid habitat.
Objective 2.1. Determine stressors of climate change for the Dosewallips River basin and
resiliency of river processes to these stressors.
Increased temperature (aquatic species stressor)
Increased precipitation and flooding (habitat and community stressor)
Increased sediment loading and mass wasting (habitat and community stressor)
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Objective 2.2. Determine impaired processes affecting in-stream, side channel, and floodplain-
associated habitats.
Objective 2.3. Delineate channel migration zone and migration history and how it relates to the
current locations of aquatic habitats.
Objective 2.4. Develop a hydraulic model of flood conditions along the Dosewallips River
through the Lazy C and Powerlines reaches.
Objective 2.5. Describe flood, erosion, and landslide risks to the Lazy C I community and how
hydrologic changes associated with the warming climate will affect these hazards.
Goal 3: Determine opportunities to protect and restore riverine processes and in-channel, side
channel, and floodplain-associated habitats that support Hood Canal summer chum and Puget
Sound Chinook recovery, foster resiliency to climate change, and are sensitive to downstream
shellfish habitat.
Objective 3.1. Determine goals to improve habitat conditions for Hood Canal summer chum and
Puget Sound Chinook based on the limiting factors for these species in the Lazy C and
Powerlines reaches.
Objective 3.2. Determine location and extent of the highest functioning in-channel, side channel,
and floodplain-associated habitats, and associated parcels, as protection priorities.
Objective 3.3. Determine opportunities for maximum riverine process restoration, as well as
locations and extent of maximum chum and Chinook habitat restoration benefit.
Objective 3.4. Develop conceptual projects that address the highest benefit opportunities and
are sensitive to downstream shellfish habitat.
3.3 Resiliency Corridor
3.3.1 Reference Conditions
The fluvial landscape when the first Europeans arrived in the Dosewallips River watershed would have been
dominated by large old-growth conifers such as Douglas fir, western hemlock, Sitka spruce, western red cedar
and black cottonwood, with the anabranching channel network connected to a diverse range of floodplain
habitats including, but not limited to, perennial and ephemeral side channels, abandoned meander oxbow
wetlands, large logjams, and beaver ponds. The river would have freely migrated across the valley bottom
between glacial outwash terraces and valley hillslopes. Logjams and patches of mature forest would have
provided stability to the river channel banks (logjams by deflecting flow, roughening and strengthening banks
and mature trees through their extensive tree root systems). The mature trees were also a source of the “key
pieces” of large wood essential for forming stable logjams (e.g. Abbe and Montgomery 1996, 2003) and creating
an important ecosystem function referred to as the ‘floodplain large wood cycle’ in which stable logjams create
stable areas where trees can mature within areas of frequent channel migration (Abbe and Montgomery, 1996;
Collins et al., 2012; Montgomery and Abbe, 2006). The intimate connection between river and forest that
resulted from these conditions created a diverse range of complex aquatic, wetland, and floodplain habitats
which allowed aquatic organisms such as the region’s native salmonids to thrive.
One important characteristic of the historical fluvial landscapes that encouraged the persistence of the complex
diversity of habitat types was an adequate amount of physical space. Because river valleys were free from
development, the river had enough space to migrate freely amongst the old-growth forest and create and
sustain new habitats. Rivers were able to occupy the entirety of the alluvial valley bottom, allowing areas far
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from the active channel time to develop into stable habitats. Because there was a high density of stable log
jams and mature forest and flow was able to spread out frequently across the floodplain, the stream’s erosive
energy was diffused, and channel migration rates were moderated – allowing the forest time to mature. As
humans disturbed the historical conditions through development, logging, and wood clearing these beneficial
river/floodplain functions were reduced along with the space the river needs to maintain the complex fluvial
system.
Despite historical disturbances and current development pressure, examples of functioning anabranching
systems can still be found within the Dosewallips watershed (Figure 32). In the area of the watershed near RM
10, the river has occupied almost the entirety of the alluvial floodplain and has developed a multi-threaded
channel morphology where several perennial channels flow around forested islands. Because there is some level
of stable log jams and flood flows can spread out across the valley, the vegetation on the islands contains a
mixture of deciduous and conifer species and appears to be maturing. The maturing forest can shade the
channel network – providing high quality habitat for aquatic species.
Another example within the watershed is the Powerlines reach itself where the river has migrated to occupy the
valley bottom creating a network of perennial channels and a developing riparian forest. However, as discussed
in detail above, channel migration rates are higher than historical levels due to the lack of stable large wood in
the Powerlines reach – prohibiting the development of a fully mature forest and stable floodplain habitats. In
contrast, more confined reaches such as the Lazy C exhibit a simple plane-bed morphology with a low habitat
diversity because it is unable to freely migrate to create a diversity of habitat types.
Figure 32. Example of a reach of the Dosewallips River at RM 10 with anabranching channel morphology. Flow
is from left to right. The presented imagery is the 2019 NAIP.
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3.3.2 Ecological Resiliency
The core of our approach to the development of restoration concepts for the project reaches of the Dosewallips
River is the delineation of an ecological resiliency corridor, which estimates the minimum spatial footprint
required to sustain habitat-forming processes along the river corridor. The processes that form and sustain
aquatic habitat in a western Washington river system – lateral channel migration, channel avulsion (i.e., channel
switching), flow splitting, overbank inundation – are dynamic and require both sufficient space and a healthy
riparian forest to function (Collins et al., 2003; 2012).
NSD utilized an examination of the geomorphic parameters presented in Chapter 2 to define the Resiliency
Corridor for the study reach. The resiliency corridor was defined as the entire valley bottom throughout the
project reach based on the following:
1. The 100-year floodplain which includes areas frequently subject to flood inundation.
2. The channel migration zone
3. Floodplain topography and geomorphology, including areas with clear evidence of historical alluvial
channels.
4. The meander bend amplitude and frequency – particularly within the Powerlines Reach
The resulting resiliency corridor defines the space needed to create and sustain the diversity of aquatic habitat
types naturally found within unconfined alluvial valleys of the Dosewallips such as upstream near RM 10 (Figure
32).
The resiliency corridor is subdivided into areas with high flooding and erosion hazards and areas with moderate
hazards (Figure 33). Spatial areas at risk of flooding and erosion are also areas that tend to have high potential
for the restoration of aquatic and floodplain restoration. These areas are prone to fluvial processes of periodic
inundation, high groundwater tables, and channel migration. Because the high hazard areas are closer to the
current river corridor and subject to more frequent interactions with the river, they also have a high potential
for conservation and restoration. Floodplain areas farther from the current river corridor still have moderate
hazard potential due to their low lying position on the landscape and the future projected erosion trends. These
areas are also important for their future habitat restoration potential.
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Figure 33. Resiliency Corridor for the Lazy C and Powerlines Reaches.
Short-term and Long-term Resiliency Corridor
The high hazard resiliency corridor contains the current channel location, HMZ, and areas close to the current
channel that are most likely to be subject to habitat forming processes (e.g., erosion and avulsion) within the
next few decades due to the current location on the landscape and projection of continued sediment deposition
in the Powerlines Reach and subsequent upstream channel migration. These areas are also most likely to
experience flood inundation because of their proximity to the current channel and side channel network. The
high hazard resiliency corridor thus includes the properties along Appaloosa Drive within the Lazy C I
community.
The high hazard resiliency corridor concept can be utilized in conjunction with the flood and erosion hazard
assessment and channel migration zone mapping presented above to help increase resiliency of the Lazy C I
community over time. We envision that the County will be able to utilize this plan to identify specific properties
most at risk of flooding and erosion and to then work with the community to envision opportunities for
conservation easements and riparian zone restoration planting in the short-term, while the County could
consider potentially engaging in the longer-term work of considering programs to support moving people and
infrastructure out of harm’s way.
The moderate hazard resiliency corridor includes the remainder of the valley bottom, inclusive of the floodplain
currently occupied by the Lazy C I development, because of the channel migration patterns in the Powerlines
reach and the erodible material underlying the Lazy C I floodplain. The moderate hazard resiliency corridor is
intended to encompass and reflect the area needed for long-term habitat and species recovery benefits.
We recognize that the space needed to restore and sustain aquatic habitat formation can conflict with the needs
of landowners to maintain developed areas and to protect river-side structures. To allow time for a transition
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away from floodplain development, community resiliency actions could also include streambank stabilization
that introduces physical complexity and cover in areas where such actions could have immediate aquatic habitat
benefits. Such actions could support residents by slowing channel migration rates that provide additional time
for the community and the County to work together to advance restoration of the long-term resiliency corridor.
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4. RESILIENCY OPPORTUNITIES
Based on the analysis of geomorphic condition (Chapter 1) and in consideration of the goals and objectives
(Chapter 2), NSD determined that the study reaches are moderately impaired, particularly in the Lazy C Reach
(Upstream and Downstream). The impairments are typical of Pacific Northwest rivers and floodplains affected
by historical logging, development, and consequent disconnection of rivers and their floodplains.
Based on the impairments (Appendix E) as detailed above and the delineation of the resiliency corridor, NSD
considered restoration actions to meet the goals and objectives of the project and address both the critical
limiting factors for Hood Canal Summer Chum and Puget Sound Chinook in the Dosewallips River and the
opportunities and constraints presented by development in the Lazy C reach. Restoration actions were
considered from both a short-term perspective (I.e., actions which could be accomplished within approximately
2 to 5 years), and a longer-term perspective (I.e., actions which would require more than 5 years to accomplish).
4.1 Longer-Term Opportunities
The impairment of fundamental river processes such as channel migration in the Lazy C reach and large wood
inputs in both reaches has created a situation where restoration actions are necessary to restore the natural
riverine processes and large wood cycle so the river can create the range and complexity of habitats necessary
to support a diversity of aquatic species.
Longer-term opportunities center around community education, outreach, and engagement to all residents
within the Lazy C reach and with the private property owners in the Powerlines reach. The focus would be:
a. Education
i. flood and erosion hazards,
ii. habitat forming river processes,
iii. fish populations dynamics
iv. flood and environmental regulations
v. funding programs
b. Options available to landowners
i. acquisition,
ii. conservation easements,
iii. flood proofing,
iv. habitat restoration.
An additional longer-term opportunity to support the restoration of natural riverine processes and further
expand the protection and restoration of aquatic habitats is the expansion of the geomorphic analysis and
restoration planning presented herein to the reaches upstream and downstream of the Lazy C and Powerlines
reaches. While exploring this opportunity was outside the scope of this Resiliency Plan effort, it is an important
opportunity that could be pursued to expand the efficacy of the actions within the study area. Because
processes such as sediment delivery, floodplain engagement/flooding, and aquatic species spawning, rearing
and migration are directly influenced by conditions outside of the study area, it is important to consider and
restore conditions throughout the watershed and not solely within the confines of the Lazy C and Powerlines
reaches. For example, sediment delivery within the study area is likely higher than historical levels due to the
confinement (and loss of sediment storage) in upstream reaches such as Walcott Flats. Thus, by understanding
and restoring natural floodplain processes within upstream areas, habitat conditions can be further improved
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and the risk to local landowners potentially reduced within the Lazy C and Powerlines reaches. Additionally,
because salmonid species migrate through the downstream reaches to access spawning habitat within the study
area, and then utilize downstream rearing habitats, understanding and restoring estuarine habitat conditions
near Brinnon/Brinnon Flats can improve the overall resiliency of their populations. Similarly, additional analysis
is warranted to determine the CMZ and related flooding risks both upstream and downstream of the Lazy C and
Powerlines reaches to consider existing geomorphic processes, risks, and restoration opportunities in detail.
4.2 Education, Outreach and Engagement
Many residents living in floodplains are unaware of the flood and erosion hazards as well as the importance of
aquatic and riparian habitat to salmon and other species. While there are state and federal programs that offer
educational resources, few counties have budgets for outreach programs. The Dosewallips Resiliency Plan was
started with a grant with the intent to establish a better communication with local residents and setup a
framework to continue outreach work into the future working with other public, Tribal and non-profit
organizations.
Education is the critical first step to foster a shared understanding of the dynamic and ever-changing interaction
between rivers and their floodplains, and the inherent risks posed by living in their proximity. Thoughtful and
honest conversations between floodplain residents and the County will build trust and relationships to advance
a long-term vision for the resiliency corridor.
The actions described below require consistent, honest, and supportive community education and engagement
before any actions could be planned for or accomplished. Community outreach to date indicates residents may
be unaware of the inherent risks to their property of the river’s migration and likely continued upstream
meandering; they may similarly be unaware of the actions that can be taken in the reach to support salmon
recovery. Mapping of erosion hazards and channel migration zones is both essential to flood damage reduction
and is a valuable element for the community. The CMZ and hydraulic model results presented herein can serve
as a starting point for those discussions.
It is also important to respect and acknowledge issues of environmental justice and social equity in considering
public education, outreach, and engagement. The Lazy C community includes affordable housing options for
long-time permanent residents and any County efforts to engage landowners will need to be sensitive to the
economic and social equity issues inherent in finding affordable housing solutions for populations at risk from
environmental hazards.
4.3 Development of Programs and Options for Landowners
The costs of flood damage to lives and property, along with environment and economic benefits of restoring
floodplains, has led local, state, and federal government agencies to implement major land acquisition and
relocation programs across the country (e.g., Conrad et al. 1998, FEMA 2009, Polefka 2013, Mechler et al 2014,
Schiff et al. 2015, Frendenberg et al. 2016, ELI 2017, Patterson 2018, Salvesen et al. 2018, Siders 2019, Johnson
et al. 2020). More locally, Pierce County has implemented very successful buy-out programs in floodplains of the
Puyallup and Carbon Rivers.
Helping people get out of harm’s way not only protects their lives and properties but can save taxpayers millions
of dollars in flood relief. Managed retreat from increasingly hazardous areas, such as the purchase of flood
prone property, will become an unavoidable situation as climate change effects intensify (see Jay et al, 2018 in
https://nca2018.globalchange.gov/). The federal government shares responsibility for flood recovery and there
is increasing interest in assisting state and local governments with reducing community flood risk.
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A comprehensive list of federal flood resilience and risk reduction assistance programs is provided in a recent
2019 Congressional Research Service report, https://crsreports.congress.gov, report number R45017. There are
also several other federal resources to assist the County in developing the programs and supports necessary to
provide the Lazy C reach landowners with viable options for relocation, including but not limited to:
Repetitive Loss Program: Using FEMA’s Cost-Benefit Calculator, “beneficial” actions for repetitive
loss properties (more than 1 FEMA insurance claim) can be identified. This opens funding
opportunities and reduces community insurance premium costs (including for floodplain residents).
Hazard Mitigation Grant Program: This program funds buyouts for homes and businesses that meet
the cost-benefit ratio. https://www.fema.gov/hazard-mitigation-grant-program
The federal government is increasingly pushing for communities to commit to buy-out programs in
chronic flood-prone areas (Mach et. al 2019). In a recent federal policy change, funding partially
administered by the U.S. Army Corps of Engineers for flood protection and climate adaptation can
be contingent on local governments agreeing to use eminent domain to purchase properties whose
owners are unwilling to voluntarily sell:
https://www.nytimes.com/2020/03/11/climate/government-land-eviction-
floods.html?action=click&module=Top%20Stories&pgtype=Homepage.
Such policies and initiatives promote a process to identify the risks and impacts on community resilience to
natural hazards, including those associated with climate change, and direct Federal agencies to support climate
resilient infrastructure, including a Hazard Mitigation Assistance (HMA) program by FEMA, which provides
funding for flood and erosion mitigation strategies rooted in restoring ecological process and function. See:
https://www.fema.gov/media-library-data/1487161136815-
ecad1c0312eda2111ffa28735a4d06ad/FSR_Fact_Sheet_Feb2017_COMPLIANT.pdf
Other actions the County could pursue in support of landowner relocation support could include:
Establish funding for immediate acquisition of flood prone properties that come up for sale.
Develop preliminary criteria for prioritizing acquisitions, including utilizing the risk prioritization
identified in Figure 33.
In many locations, the current cost of floodplain land acquisition is 3 to 5 times less than future
flood damages (Johnson et al, 2020).
Develop long-term plans for moving interested residents to safe ground, including considerations
such as:
Establish outreach program to assist landowners who want to stay in community but move out
of flood prone areas.
Ensure adequate services and access to state highways in plans for relocation.
Local government action guides exist which provide detailed guidance and resources for
developing a floodplain acquisition program which maximizes ecological benefits and minimizes
risk as projects are planned and completed (ELI 2017).
Consider social and environmental equity and the location of the County’s low income housing
and business sectors within the 100-year floodplain and even delineated floodways.
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4.4 Conservation Easements, Acquisition and Relocation Actions
4.4.1 Upstream and Downstream Lazy C Reach
The most effective long-term flood protection is to remove structures from flood hazard areas, which also allows
habitat restoration of these ecologically valuable areas. To do this the property can be purchased through at-
will participation. Relocation grants allow willing landowners to move to a safer property in the area while
ownership of the flood prone property is transferred to Jefferson County, a land trust or other public entity.
Smaller-scale actions such as shoreline setbacks, riparian zone restoration, and even excavation of floodplain
benches could be interim actions accomplished with conservation easements, and such actions can build
community support. However, developing a program for gradual property acquisition from willing sellers over
the long term is the most beneficial action to restore the river’s resiliency corridor and the aquatic habitats in
the Upstream and Downstream Lazy C reach.
Priorities Based on Risk
Parcels along the riverside edge of the Lazy C I and Mossy Lane developments are at the highest risk from
erosion, flooding, and channel migration as they lie within or adjacent to the floodway. These areas also have
the greatest negative impact on habitat conditions by restricting access to the historical floodplain (Figure 34).
These parcels are within the high hazard resiliency corridor presented in Figure 33. Acquisition of these parcels
from willing sellers would enable the construction of streambank and apex ELJs with aquatic habitat benefits
and would provide the space necessary for the river to create areas of new and reconnected floodplain.
Affordable housing and social equity considerations will need to be factored into any planning and support
programs for property acquisition to equitably relocate willing sellers to affordable options away from the
hazards of the channel migration zone.
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Figure 34. Private and public parcels relative to risk from erosion and channel migration. Public ownership
largely lies within the High Hazard area.
The moderate hazard parcels within the interior of the Upstream Lazy C reach would be the next highest priority
for acquisition or easement because these parcels are still at risk of erosion and flooding even though they are
not along the current shoreline. Full acquisition of these parcels would allow for significant aquatic habitat
enhancement actions in a section of the river currently largely devoid of habitat complexity and would expand
the availability of floodplain habitat for the river to create and sustain new and diverse habitat types.
Restoration actions such as excavation of floodplain benches, riparian restoration, and construction of ELJs
would directly address the impairments within the reach and could be enacted aggressively if flood and erosion
risk to the landowners were reduced. Affordable housing and social equity considerations will similarly need to
be factored into any planning and support programs for property acquisition of moderate hazard parcels to
equitably relocate willing sellers to affordable options away from the hazards of the channel migration zone.
As discussed in detail above, the risks to these properties are projected to increase as the channel continues to
migrate upstream and peak flows increase with climate change, and thus, acquiring parcels from willing sellers
as they become available will gradually increase resiliency over time. Acquisition also has an added benefit to
water quality when current septic systems in the river floodplain are decommissioned.
Powerlines Reach
Key to the Powerlines reach is implementing strategies to establish more mature floodplain forest while taking
actions in the short-term to increase the number of deep pools and cover. It would be necessary to work with
Bonneville Power Administration, and the right and left bank property owners (i.e., Jefferson County, and
private landowners, to establish a strategy to provide better forest cover or a means of providing shade under
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the powerlines. Conservation easements or property acquisition from willing sellers of the remaining privately
owned parcels within the Powerlines reach floodplain should be pursued in conjunction with the short-term
priority Lazy C reach parcels because they represent areas of quality existing habitat including one of the reach’s
four side channels (SC-1; Figure 12). Protecting via easements or acquiring these parcels would allow for valley-
scale restoration to occur within the Powerlines reach and ensure that the necessary space for the river to
sustain a well-functioning and diverse ecosystem exists. Protecting intact floodplain and side channel habitat
through conservation easements in the Powerlines reach is an action supportive of the long-term resiliency
corridor if acquisition is not feasible. Continuing to protect County- and State Parks-owned properties in the
Powerlines reach from future development will also help achieve this goal, as will careful consideration of the
longevity and sustainability of any new recreational and infrastructure (e.g., trails) in the resiliency corridor.
Similarly, continued protection of publicly owned parcels, both within and outside of the resiliency corridor, is
also recommended to protect the processes and habitats of the adjacent uplands.
4.5 Short-Term Opportunities
Informed by the analysis of existing conditions, shorter-term opportunities focus on actions to support
restoration of a functioning floodplain large wood cycle within the Powerlines reach. These actions include both
restoration of a mature riparian forest and complimentary actions to slow channel migration rates closer to
historical levels through the placement of ELJs so that the recovering forest can mature before being eroded.
Although the functional capacity of the Powerlines reach is the highest, actions to enhance instream habitat in
the mainstem and add complexity in the side channels though large wood placement would also support aquatic
habitat stability for chum spawning, and rearing for coho, Chinook and steelhead. Floodplain reconnection and
restoration of riparian forests are short-term actions that support the greatest long-term habitat expansion
benefits for chum and Chinook in the study area.
Shorter-term actions center around:
1. Riparian restoration to support the formation of a mature riparian forest that will stabilize banks and
provide a source of stable large wood for long-term recruitment into the stream, and
2. Placement of large wood to reduce channel migration rates, encourage development of velocity refuges,
support spawning gravel storage, and encourage floodplain connection.
Sufficiently reducing channel migration rates in the short term within the Powerlines reach is essential so that
riparian forests have enough time (~100 years) to mature so they can remain stable when eventually recruited
to the river. Placement of large wood to encourage development of velocity refuges, spawning gravel storage,
and floodplain reconnection would benefit coho, steelhead and rainbow, and Chinook, as well as pink and chum
for spawning habitat. This strategy will eventually allow the river system to sustain itself and accomplish the
habitat forming processes necessary to sustain healthy aquatic ecosystems.
4.5.1 River and Riparian Restoration
Riparian planting and management actions include a suite of strategies to restore the riparian forest and the
related ecological and geomorphological functions of a mature riparian forest consistent with reference
conditions. The strategies include planting young riparian areas to restore mixed coniferous/deciduous forest,
removal of invasive species (e.g., Himalayan blackberry) and noxious weeds such as knotweed and butterfly
bush, installing floodplain roughness structures to rack debris and protect riparian plantings, conifer
underplanting in existing riparian forests, and thinning of deciduous species to promote accelerated
establishment of conifers.
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4.5.2 Bank Alcoves
Bank alcoves are wide spots in the river channel that provide velocity refuge for juvenile salmonids and other
organisms. The upstream end of the Lazy C reach has a natural alcove in the left bank at RM 2.9 (Figure 30). They
are created by excavating a concentric depression in the existing bank down to the elevation of the adjacent
riverbed or lower. Stable wood structure in the alcove will further enhance habitat by creating complex cover.
Because the alcove will be an area of lower velocities during high flows, they can trap finer suspended sediments
such as sand along their banks, creating nice spots for both people and wildlife.
4.5.3 Engineered Log Jams and Large Wood Placement
Engineered log jams are intended to mimic the geomorphic functions of natural log jams by increasing flow
resistance, slowing flow velocities, raising water surface elevation, aggrading, and sorting sediment, and
connecting the channel to side channels and the adjacent floodplain (Abbe and Montgomery, 2003;
Montgomery et al., 2003). Log jams provide critical habitat functions such as triggering and sustaining the
formation of deep pools, retaining spawning gravels, and providing in-stream cover. The goal of implementing
engineered log jams is to re-initiate these habitat-forming processes in the near-term until natural wood
recruitment from the restored riparian forest sustains those processes in the long-term.
Design and placement of ELJs and smaller instream wood placements need to both meet geomorphic and
habitat objectives while not increasing flooding or erosion hazard risks to adjacent landowners (as well as
upstream and downstream) and fitting in with the floodplain management of the river system. Through the
project reach, the Dosewallips River is categorized as a Special Flood Hazard Area which includes a regulatory
Zone AE floodplain with floodway by the National Flood Insurance Program (NFIP). Jefferson County code,
Section 15.15.080, describes the limitations to development (referred to as encroachments) within regulatory
floodways and requires that “the proposed encroachment would not result in any increase in flood levels during
the occurrence of the base flood discharge (Section 15.15.080(4)).”
Floodplain regulations require that a hydrologic and hydraulic analysis be conducted on the proposed project
actions to assess if the water surface elevations during a 100-year flood event (referred to as the Base Flood
Elevation) would be increased because of the proposed actions. If proposed restoration actions are shown to
increase the Base Flood Elevation (BFE) in the project reach, a Conditional Letter of Map Revision (CLOMR)
would need to be obtained from FEMA to document the proposed changes to the BFE and the 100-year
floodplain before the project actions could be implemented. In addition, no increase in BFEs can impact an
insurable structure as defined by the NFIP. Once the project is completed, a Letter of Map Revision (LOMR)
would need to be reviewed and approved by FEMA. The time frame for receiving a CLOMR and LOMR can be on
the order of 6-12 months and 3-6 months, respectively, and thereby can significantly increase the design
timeline for restoration actions. The floodplain management regulations, as well as the feasibility of pursuing
the CLOMR/LOMR pathway, will need to be factored into the prioritization and design development of
restoration actions in the project reaches.
Key Piece Placement or Small Engineered Logjams
The placement of Key-sized logs and smaller “side channel’ ELJs is intended to improve existing habitat
conditions within less hydraulically active sections of the floodplain to improve local habitat conditions and
increase stable wood loading within the reach. These structures are suitable for locations where hydraulic forces
(velocity and shear stress) are lower than the main channel and construction access is limited. Placement of
these smaller structures is designed to add hydraulic roughness and complexity to the side channel and
floodplain, sort and store mobile sediment, and rack mobilized small woody debris during floods. Natural snags
that are deposited in the river should be protected from cutting. A big western red cedar snag observed in 2020
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at RM 2.8 in the upstream Lazy C reach initiated a bar apex logjam that formed a mid-channel pool and island,
but the tree’s bole had been cut.
Apex Engineered Log Jams
Apex ELJs are intended to mimic the geomorphic functions of natural bar apex log jams and will be placed in the
middle of the channel and on existing gravel bars within the project reach. Apex ELJs are intended to split flow
around the structures and to stabilize existing bar and/or floodplain surfaces – reducing overall bed mobilization
frequency and providing refugia for spawning redds. The structures are designed to aggrade sediment in their
lee (behind them) – eventually encouraging the development of forested islands by reducing hydraulic forces so
that vegetation can establish and flourish. Because the structures are often placed in areas with high hydraulic
forces, deep pools are often scoured at the front face of the jam. Apex ELJs are often constructed as a group of
multiple structures so larger island areas can form and so the structures can ‘protect each other’ by reducing the
overall hydraulic forces within a particular region of the river corridor.
Deflector Engineered Log Jams
Deflector ELJs, which include log jams installed adjacent to the channel margin, are intended to mimic the
geomorphic functions of natural flow deflection or meander bend log jams. The structures are primarily
constructed along a bank and, as their name states, are intended to deflect flow from one area of the river
corridor to another. Deflector ELJs can be used to slow channel migration rates to historical levels on a particular
portion of bank by deflecting flow away from the bank, as well as cause an increase in frequency of side channel
inundation by deflecting flow towards the side channel inlet. Because they are often placed in areas with high
hydraulic forces (such as the outside of an actively migrating meander bend), large scour pools develop at the
head of the structures which can provide important holding habitat for salmonids. Deflector ELJs can also be
used to protect developing riparian vegetation located behind the structures by reducing the rates of future
channel migration and erosion. The structures can be placed in groups to treat larger areas such as the entirety
of a meander bend.
Channel Spanning Engineered Logjams
The huge timber characteristic of the Olympic Peninsula Channel had a major influence on the river. A 200 ft
tree more than six feet in diameter would easily span the Dosewallips River. When these trees fell into the river
because of bank erosion or landslides, they would have created large logjams spanning the river, raising water
levels and creating a mosaic of channels as river flow found pathways around the wood. Within the Powerlines
Reach there is an opportunity to create channel spanning engineered logjams (ELJs) are intended to mimic the
geomorphic functions of the large old-growth log jams that likely spanned large portions of the valley under
historical conditions. The structures are designed to cross the entirety of the active channel corridor to maximize
the geomorphic and hydraulic influence of the jam. Channel spanning ELJs are intended to raise water elevations
for several channel widths upstream – increasing floodplain connectivity and sediment aggradation for broad
regions of the reach. Because the structures greatly reduce the hydraulic forces within them, the channels that
develop through the ELJs can provide high quality spawning habitat with high amounts of cover as well as slow
water refugia for juveniles. Channel spanning ELJs are often placed in areas where wood is naturally depositing
and can be built by supplementing the existing wood to increase its overall stability.
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5. PRIORITIZATION AND SEQUENCING
5.1 Prioritization Framework
A prioritization framework was developed by applying a hierarchical implementation of restoration strategies
(watershed scale process prioritization) adapted from Roni et al. (2002) and Beechie et al. (2008), which results
in the logical sequencing of restoration actions based on their probability of “success, response time, and
longevity.” Using this approach, we applied the following priority order to restoration opportunities in the three
reaches of the study area:
1. Protect intact habitat
2. Restore impaired processes
3. Restore riparian zone
4. Enhance instream habitat
Using this framework, opportunities were scored by reach/location based on their ability to meet project goal #3
(i.e., Determine opportunities to protect and restore riverine processes and in-channel, side channel, and
floodplain-associated habitats that support Hood Canal summer chum and Puget Sound Chinook recovery, foster
resiliency to climate change, and are sensitive to downstream shellfish habitat) and its related objectives for
maximum improvement in aquatic habitat, extent, and durability of anticipated biological benefits. Long-term
and short-term actions were not considered separately as they can and should be evaluated and conducted in
parallel to make progress on longer-term goals like community engagement, conservation easements, and
acquisition from willing sellers, while shorter-term actions are being planned, designed, and implemented.
Higher scores and thus higher ranking were given to actions that provided protection of intact, naturally
functioning habitat in a more expedient manner (e.g., through conservation easement rather than through
acquisition) and to actions which could provide improvement of a targeted impaired process and immediate
improvements in aquatic habitat. A greater range of scores was ascribed to the riparian restoration and ELJ and
large wood placement criteria to account for the priority placed on actions which would address impaired
processes identified in each reach and the limiting factors for Hood Canal Summer chum and Puget Sound
Chinook (i.e., lack of velocity refuges, spawning gravel storage, and floodplain connection/rearing habitat).
Table 5 presents the opportunity identified, and its score for the prioritization criteria considered. Criteria were
scored as follows:
Habitat Protection
1– Long-term potential for restoration
2- High potential for habitat restoration due to degraded conditions and high flood hazards. Protection
of high-quality naturally functioning habitat on private property would require property acquisition.
3 –Currently has good habitat attributes and high potential for habitat enhancement.
Riparian Restoration
1 – The existing riparian buffer is primarily mature mixed conifer and deciduous forest, with minor
opportunities for riparian enhancement.
2 - The existing riparian buffer is moderately disturbed with small areas (approximately 0.5 - 2 acres)
available for riparian enhancement, either on public land or requiring conservation easements.
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3 - The existing riparian buffer is moderately disturbed with large contiguous opportunities
(approximately 2 or more acres) available for riparian enhancement, either on public land or requiring
conservation easements.
ELJs and Large Wood Placement
1- Protect natural snags that form (e.g., Cedar snag in upstream Lazy C reach, RM could not be placed
without permission of adjacent property owners or acquisition of effected properties.
2- ELJs and/or large wood could be placed for immediate habitat benefit and to reduce channel
migration to historical rates with private property conservation easements while property acquisition
process is occurring. Scale and nature of structures could require CLOMR or LOMR process with FEMA.
3- ELJs and/or large wood could be placed for geomorphic process and immediate habitat benefit
without private property conservation easements. Scale and nature of structures would not require
CLOMR or LOMR process with FEMA.
Table 5 illustrates the opportunities for shorter-term restoration actions in the Powerlines reach given the
advantages inherent to working largely on publicly owned land where easements are not required for access
and construction actions. The Powerlines reach also offers gravel bar and similar construction access
opportunities and more easily accessible areas for invasive removal and riparian planting.
Table 5. Scoring and Prioritization of Restoration Opportunities by Reach.
HABITAT PROTECTION VIA
CONSERVATION EASEMENTS OR PROPERTY ACQUISITION*
RIPARIAN
RESTORATION
ELJS AND LARGE
WOOD PLACEMENT
TOTAL SCORE
Upstream Lazy C 1 1 1 3
Downstream Lazy C 2 2 2 6
Powerlines 3 3 3 9
*longer-term actions which can be pursued in parallel with shorter-term actions.
In contrast, opportunities for implementing riparian restoration and/or ELJ and large wood placement actions in
the Lazy C sub-reaches in the shorter-term are constrained by the need to make further substantive progress in
landowner outreach and engagement and the need for both construction and conservation easements. These
reaches also pose larger challenges for construction access and staging given the lack of work areas outside the
active channel, which adds cost and complexity to actions in these reaches. Finally, the Lazy C sub-reaches also
offer more limited habitat restoration potential within the river channel, unless aggressive actions to fully
engage the floodplain can be pursued. Such actions cannot be pursued in the near term due to the proximity of
homes to the channel and the risk of exacerbating the current erosion and flood damage risks to the Lazy C I
development.
Thus, we recommend opportunities for shorter-term restoration actions in the Powerlines reach be pursued
first, while the County continues to make progress in landowner outreach and engagement with the Lazy C
reach landowners and homeowners association.
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5.2 Action Sequencing
There are sometimes opportunities for actions to be combined with one another to maximize benefits and gain
cost efficiencies. By combining and sequencing complimentary actions, impacts to landowners and the public
can be reduced, permitting and funding can be streamlined, and disruption to the aquatic and terrestrial
environments minimized.
Given the high score of actions in the Powerlines reach, we recommend geomorphically related ELJs and riparian
planting actions in proximity to each other be combined into a group of actions that could be spun off as an
individual project. Design and permitting could occur for a project in the Powerlines reach concurrently with
landowner and community engagement to support subsequent complementary actions in the Upstream and
Downstream Lazy C sub-reaches. Sequencing restoration actions in this manner, starting first with the
Powerlines reach and then expanding to actions in the Lazy C reach, can build community support by
demonstrating forward progress. Community support in turn can further support the County in acquiring grants
for continued restoration efforts and for potentially developing a program to support relocation of willing land
owners from high risk floodplain areas.
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6. CONCEPTUAL RESTORATION DESIGN
Following the prioritization of restoration opportunities and engagement with the project stakeholders, NSD
developed a series of restoration concepts looking at both short-term and long-term restoration actions in the
Upper and Lower Lazy C and Powerlines reaches. Short-term restoration actions focused on design elements
that address key reach impairments and improve existing habitat quantity and quality while remaining feasible
to implement under the current level of occupancy and floodplain management in the valley.
In addition to the short-term restoration concepts, a long-term restoration vision was developed looking at a
potential restored valley-scale floodplain and channel condition if the valley were unoccupied and publicly
owned. This “future full valley restoration” concept was developed for illustrative purposes to show long-term
restoration potential in the project reach if the County were to develop a program to work with willing
landowners in the Lazy C and gradually relocate homes and infrastructure out of the floodplain.
The following section describes the conceptual restoration actions in each reach, presents a discussion of their
opportunities to address reach impairments and key habitat limitations, presents design constraints given the
current landownership and floodplain management, and presents a conceptual level construction cost estimate.
Conceptual restoration drawings are included in Attachment B.
6.1 Short Term Actions in Lazy C Reach
Short term restoration actions in the Upstream and Downstream Lazy C sub-reaches were developed to address
the reach impairments discussed in Chapter 2.8 and further elaborated upon in Appendix E. In general, short
term restoration actions focused on increasing stable wood structures that are activity engaged in the channel,
slowing upstream migration rates in the Downstream Lazy C sub-reach, restoring riparian vegetation
communities, and pursuing a simple habitat pilot project in the existing tributary located to the north of the Lazy
C community (see Figure 14 for tributary location).
6.1.1 Upstream Lazy C sub-reach
As described in Chapter 2, the Upstream Lazy C sub-reach is characterized by a confined channel with limited
floodplain connectivity and low levels of stable wood. The reach functions as sediment transport reach and the
low levels of stable wood and lack of floodplain connectivity limit the ability to store and retain gravels and limit
the available rearing habitat for salmonids. The primary restoration action to address these impairments, while
not increasing the current levels of flooding and erosion risks to adjacent landowners, is the installation of small
groups of low-profile log jams located in the channel and deflector jams located along the left bank (Error!
Reference source not found.).
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Figure 35 Low-Profile and Deflector Log Jam Concept in Upstream Lazy C sub-reach
The low-profile jams split flows in the middle of the channel and create localized scour along the front of the jam
while promoting sediment deposition behind the jams to build and maintain gravel bars. These effects add to
the hydraulic complexity of the sub-reach, promoting sediment storage, and increases in stable large wood. The
bank-based deflector jam structures are positioned to shift flows away from the left bank, create scour pools,
and produce areas of slower water or “hydraulic shadows” downstream of the jams (Figure 36). Together, these
two structure types increase hydraulic complexity in the sub-reach and can lead to the development of a more
defined low flow channel, as well as providing areas of slow water within the reach. The resulting hydraulic
complexity provides varying areas of fast- and slow-moving water which increases holding areas for migrating
adult salmonids and rearing juveniles. The increase in stable wood and development of associated scour pools
also increases complex cover for adult migrating chum and Chinook. To minimize an increase in risk to left bank
landowners, this design strategically places deflector jams to intercept split flows from the low-profile jam and
redirect it back toward the channel. To minimize impacts to water surface elevations during the 100-year design
event, the low-profile jams would be designed to be overtopped during large flows thereby reducing their
impact of flood elevations.
6.1.2 Downstream Lazy C sub-reach
Similar to those for the Upstream Lazy C, restoration concepts for the Downstream Lazy C sub-reach focus on
increasing stable wood actively engaged with the channel to increase hydraulic complexity and habitat diversity.
In contrast to the Upstream Lazy C sub-reach, two existing side channels in this reach offer opportunities to
enhance these existing habitat features by stabilizing and revegetating these islands and providing increased
wood loading and habitat complexity in the side channels. Additionally, in the lower portion of the reach, the
Dosewallips River has been actively migrating upstream, increasing erosion risk to the Lazy C community, and
resulting in the placement of riprap armoring to stabilize the bank. In this area, larger deflector structures are
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proposed to stabilize the bank location while producing deep scour pools with complex, woody cover thereby
improving habitat conditions in the reach.
To stabilize and enhance the existing side channels, a variety of wood structures are proposed. At the head of
the existing mid-channel islands, an apex jam proposed to maintain flow into the side channel and support
ongoing fluvial processes. The apex jam also serves to stabilize existing wood accumulations, as well as to
capture and retain transported large wood during flood events, further stabilizing the island. Apex jams will be
planted with riparian species (e.g., willows) to encourage the development of mature trees on these features
over time. Within the side channel, smaller low-profile jams are placed to increase wood loading and provide
additional habitat complexity. Along the left bank, deflector jams are placed to maintain the current left bank
location. The proposed restoration actions associated with the existing side channels in the reach will increase
the available Chum spawning habitat by promoting sediment sorting and increasing stable large wood for cover.
An example of the proposed layout at the existing side channel at RM 2.3 is shown in Figure 36.
Figure 36 Apex and Associated Jams along existing Side Channel at RM 2.3
To address the ongoing upstream migration of the existing meander bend at RM 2.0, a series of large deflector
structures are proposed to maintain the existing bank alignment while developing deep scour pools with
associated woody cover. Similar to the smaller deflectors proposed for the Upstream Lazy C sub-reach, the large
deflector will produce zones of hydraulic shadowing along the bank, slowing velocities adjacent to the banks and
reducing erosion. The deflectors will also redirect flows away from the bank, shifting the thalweg away from the
bank and producing scour pools. The deep scour pools and associated complex cover will increase holding
habitat for both adult chum and Chinook salmon and areas of hydraulic shadowing along the bank will also
provide slow water refugia for juveniles. The proposed large deflector jam layout in this section of the sub-reach
is shown in Figure 37.
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Figure 37 Large Deflector Jams along Left Bank near RM 2.0
At the existing meander at RM 2.0, a small tributary enters the Dosewallips River to the north of Palomino Lane
(Figure 38). This tributary formally traversed the Lazy C floodplain prior to joining the Dosewallips River but was
shifted to the north and channelized during the development of the Lazy C community and currently has
degraded aquatic habitat conditions. A “pilot project” is proposed in this reach consisting of single key log
placements and simple large wood structures that would both serve to improve habitat conditions, mainly by
increasing available slow water refugia for juvenile Chinook and serve as an example to the community of
restoration actions focused on improving aquatic habitat conditions.
6.1.3 Design and Construction Considerations in Lazy C Reach
Restoration opportunities and proposed actions within the Upstream and Downstream Lazy C sub-reaches are
constrained by a variety of factors related to the presence of the Lazy C community within the 100-year
floodplain and associated floodplain management regulations. The Lazy C community is located within the
regulatory 100-year floodplain and these sub-reaches are additionally classified as in either a high or moderate
geomorphic risk setting as described in Section 3.3. Both classifications speak to the existing level of risk the
community is under from large floods and related erosion. Consequently, any short-term design actions will
require not increasing risk to the community.
Much of the active channel of the Dosewallips River within the Lazy C reach is classified by FEMA and Jefferson
County as a regulatory floodway which limits the allowable hydraulic impact from any proposed restoration
actions. Per Jefferson County Code, Chapter 15.15.080, any proposed structures or “encroachments” within the
floodway cannot increase the 100-year flood water surface elevation, referred to as the Base Flood Elevation
(BFE) (Jefferson County 2020). If the proposed project actions are unable to achieve a “no-rise” condition during
the base flood event, the project can pursue a Conditional Letter of Map Revision (CLOMR) through FEMA,
which would document any proposed changes to the 100-year floodplain and resulting BFE. However, a critical
condition of pursuing the CLOMR pathway is that the BFE is not increased at any insurable structures, e.g.
residences within the Lazy C community. Given the very close proximity of many residences to the active
Dosewallips channel, it seems unlikely that the CLOMR route is feasible in this reach. Proposed actions that
result in an increase in the BFE would likely also impact insurable structures therefore eliminating the potential
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to pursue a CLOMR. Therefore, it is highly likely the design of short-term restoration actions within the Lazy C
reach will have to meet the “no-rise” requirements of Jefferson County floodplain management to be permitted
and constructed. This regulatory condition limits how “aggressive” the restoration actions can be within this
reach.
To impart a desired geomorphic and hydraulic effect on the channel, the proposed log jams are designed to split
and redirect flows and can cause localized impacts on water surface elevations. These hydraulic changes are
desirable from a habitat and river processes perspective; however, they can also result in increasing the already
existing risk to landowners by potentially shifting flows toward the floodplain and increasing water surface
elevations during large design events. To achieve the balance between floodplain management and risk
constraints and desired habitat outcomes, the proposed design approach is to construct low-profile jams,
coupled with small deflectors along the left bank. The low-profile jams would be designed to be overtopped at
the 1- to 2-year flow, while also remaining stable during the 100-year flow. By designing these structures to be
overtopped, their relative obstruction to the 100-year flood event will be reduced, while still imparting desired
hydraulic and geomorphic impacts at the lower- and channel-forming discharge events. The small deflector jams
on the left bank will intercept redirected flows from the low-profile jams and serve to reduce velocity and shear
forces along the bank while also producing scour pools and increased woody cover for salmonids.
Construction considerations for the conceptual restoration actions in the Lazy C reach primarily relate to the
management of water during construction and the methodology for anchoring the structures to resist the
hydraulic forces imparted during the 100-year flood event. Both water management and structure anchoring
can be potentially simplified by designed log jams that are supported by driven timber piles. In this style of
structure design, both lateral (drag and impact) forces and vertical (buoyant) forces are resisted by timber piles
driven into the channel bed below anticipated scour depths. As opposed to post or ballast support structures,
minimal excavation for the structure is required, reducing the need to excavate large “pits” to place vertical
posts and begin structure construction.
While management and diversion of river flows will be needed for both pile and post structure types, by
reducing the need to excavate a large pit, management of subsurface flows can be minimized with a pile
supported structure. A primary drawback to pile-based structure designs is the inherent uncertainty in the pile
driving conditions and the ability to achieve the design pile embedment depths needed for structure stability. A
key constraint for driving piles can be the presence of bedrock layers underneath the alluvial substrate which
can limit pile embedment depths. Uncertainty in pile driving conditions can be reduced both through
geotechnical investigations within the project reach and/or driving test piles during the test phase to determine
feasible driving depths and factor that information back into the structure design process.
6.1.4 Conceptual Construction Cost for Lazy C
A conceptual level construction cost estimate (Appendix F) was developed for the restoration actions shown in
the Lazy C reach and are estimated to be within the range of $1.4M to $1.6 in construction costs. Cost estimates
were developed on a unit cost basis for the types and sizes of proposed log jams, as well as additional costs
associated with mobilization, access and staging, temporary erosion and sediment control, and site isolation
related to the construction of log jams within the active channel. Estimated construction costs will be further
refined during future design phases.
6.2 Short Term Actions in Powerlines Reach
NSD developed short term restoration actions in the Powerlines reach to address the reach impairments
discussed in Chapter 2.8 and further elaborated upon in Appendix E. Reach conditions in the Powerlines reach
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are substantially different than the upstream Lazy C sub-reach, offering increased opportunities for habitat- and
geomorphic-focused designs to improve upon the existing habitat features in the reach.
In general, short term restoration actions in the Powerlines reach are focused on creating hardpoints through
the active channel to encourage the development of stable channel islands, reducing channel migration rates
and avulsions risks, and enhancing riparian vegetation communities by removing invasive species and
interplanting native conifers to, over time, increase floodplain stability and restore the large wood cycle. For the
purposes of discussion, proposed restoration actions are divided into groupings based upon their geomorphic
setting within the active, unvegetated channel, existing side channels, or the low-lying, vegetated floodplain.
6.2.1 Dosewallips Active Channel Restoration Actions
Restoration actions within the active Dosewallips channel focus on installing large log jams to create hardpoints
in the channel to reduce the rates and frequency of channel migration and encourage the development of stable
forested islands. Reducing the rates and frequency of channel migration within the active channel will help
decrease the frequency of redd scour increasing the egg to fry survival rates of chum and Chinook.
To achieve these goals, arrays of large and smaller apex jams would be placed on active gravel bars, as well as
integrated with existing accumulations of large wood, to provide additional stability and increase the likelihood
of these natural wood features persisting and recruiting additional mobile wood. Figure 38 illustrates an
example of an apex array proposed at the upstream end of the Powerlines reach near RM 1.9. The array consists
of a single large apex jam at the head of an existing mid-channel gravel bar. Three smaller apex structures are
proposed further downstream along the outer edges of the gravel bar. Together, these structures will split flows
around the gravel bar, helping to “lock in” the bar location, as well as providing scour pools and complex woody
cover around the upstream edges of the jams. The apex jams will also be planted with riparian species such as
willows to promote the development of stable vegetation communities along the gravel bars, increasing long-
term bar stability and leading to the development of a stable mid-channel island over time.
Figure 38 Apex Jam Array within Active Channel
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Additional objectives for the active channel zone in the Powerlines reach are the stabilization of existing
accumulations of large wood to promote the longevity of these features and increase the presence of
hardpoints within the channel. Similar to the apex arrays described above, increasing the stability of the existing
wood accumulations will promote the development of mid-channel islands and aid in the reduction of channel
migration and redd scour in the reach. Stabilization of the existing wood accumulations will be achieved by
placing apex jams adjacent to and integrated with these existing features.
6.2.2 Side Channel Restoration Actions
Within the existing four side channels in the Powerlines reach, restoration actions focus on increasing stable
wood loading to provide increased hydraulic complexity and woody cover (Figure 39). In the case of side
channels 1 and 3 (SC-1 and SC-3), the proposed restoration actions also focus on increasing hydraulic roughness
to reduce the risk of the mainstem Dosewallips River occupying these potential avulsion pathways. A channel
avulsion through either SC-1 or SC-2 would greatly reduce the main channel length in the reach and destroy
existing functional side channel habitat reducing the overall habitat complexity of the Powerlines reach. To
reduce the risk of avulsion within SC-1 and SC-3, larger and more densely placed log jams are proposed to
increase the obstructions to flow, reducing flow velocities, and partitioning shear stresses that act upon the
channel bed. Collectively, these actions serve to maintain the current active channel planform as the
preferential route for main channel flows and reduce the risks to aquatic habitats of an avulsion through either
of these channels.
Figure 39. Proposed Side Channel Enhancements in SC-1
6.2.3 Floodplain Restoration Actions
Floodplain restoration actions outside of the active Dosewallips River channel and side channels consist of
proposed roughness jams along the low, vegetated floodplain and enhancement to the existing vegetation
communities in these areas. Collectively, the goal of the proposed floodplain roughness jams and riparian
enhancement is to facilitate the restoration of the natural large wood cycle where stable riparian forests can
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grow and develop to key sized trees so that when these trees are naturally recruited to the river, they can
contribute to stable hardpoints in the reach (Figure 40).
Figure 40. Potential example of future conditions in a riverine floodplain with a functional large wood cycle
recruiting large conifers as stable hard points.
The floodplain roughness structures will also recruit and retain smaller woody debris transported along the
floodplain and can encourage the deposition of floodplain sediments by reducing flow velocities. The clustering
of these jams will increase topographic variability on the floodplain surfaces, which in turn increases the overall
complexity of floodplain channel and floodplain and can support an increased diversity of riparian and floodplain
vegetation throughout the valley floor.
6.2.4 Design and Construction Considerations in Powerlines
The Powerlines reach offers a less constrained environment for restoration actions to address impaired
processes and promote a process-based restoration approach. Much of the Powerlines reach is publicly owned
and on those parcels that are privately held there are no structures located within the floodplain. While there is
no public or private infrastructure within the reach, the proposed restoration actions must consider any effects
on the upstream Lazy C community, including erosions risks and increases to flooding magnitude and frequency.
A major design constraint within the Powerlines reach is the designation of much of the active channel and
adjacent floodplain as a regulatory floodway, which as described above, requires that any proposed restoration
actions within the floodway meet a “no-rise” criteria at the 100-year flood event. An alternative to meeting the
strict “no-rise” condition required by FEMA and Jefferson County regulations, is to pursue a Conditional Letter of
Map Revision (CLOMR) through FEMA, which would document any proposed changes to the 100-year floodplain
and water surface elevations, referred to as the Base Flood Elevation (BFE), because of the proposed actions. A
condition of the CLOMR pathway is that any increase in BFE cannot impact an insurable structure, which in this
case would be homes in the Lazy C community. Given the wide active channel area in this reach and the need for
larger scale Apex and Deflector jams, it is likely that the proposed restoration actions currently shown would
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produce a rise in the BFE and would require pursuing the CLOMR pathway to permit and construct the project.
Hydraulic modeling conducted in future design phases would be necessary to assess the increase in BFE and
would be used to refine the log jam design and evaluate the feasibility of pursuing the CLOMR pathway.
Construction considerations in the Powerlines reach are similar to the Lazy C reach and primarily center around
log jam structure anchoring methodology and water management, with an additional complexity of establishing
access through the reach to facilitate construction of the proposed restoration elements. As discussed for the
Lazy C reach, pile supported structures offer an advantage to meeting structural stability requirements and
reducing the magnitude of water management actions associated with constructing the structures. The
feasibility of driving timber piles to required embedment depths is contingent on appropriate subsurface
conditions in the reach, however given the history of aggradation in the Powerlines reach, the likelihood of
encountering bedrock seems lower than in the Upstream Lazy C sub-reach.
Establishing access to the proposed log jam locations would involve multiple channel crossings, requiring long
span bridges to transport construction equipment and logs to the jam locations. Within the side channels, small
log structures could be placed and constructed via helicopters, minimizing the need to develop temporary
access to those locations. Construction access can potentially be simplified for the smaller side channel
structures, by placing key logs and simple side channel structures via helicopter rather than by ground-based
equipment. The feasibility of helicopter-based construction, including cost implications and constraints posed by
the existing powerline corridor, will be evaluated along with overall construction access during a subsequent
design phase.
The conceptual restoration actions envisioned for the Powerlines reach include 52 log jams, ranging in size from
small low-profile jams to large apex jams, spread through the active and side channels of the Dosewallips River,
an additional 30-40 floodplain roughening jams, and 37 acres of riparian enhancement. This large suite of
restoration actions can be phased or sequenced to facilitate the development and implementation of short-term
actions while building toward a cohesive restoration vision for the Powerlines reach. Proposed actions can be
phased in a variety of ways such as by geographic location, geomorphic setting, access points, or regulatory and
landownership boundaries. Evaluation of project phasing approaches would occur in subsequent design phases
based upon feedback from stakeholders, prioritization of restoration actions, and anticipated levels of
construction funding in future years.
6.2.5 Conceptual Construction Cost for Powerlines
A conceptual level construction cost estimate (Appendix F) was developed for the full suite of restoration actions
shown in the Powerlines reach and is estimated to be within the range of $3.4M to $4.0M in construction costs.
Cost estimates were developed on a unit cost basis for the types and sizes of proposed log jams, as well as
additional costs associated with mobilization, access and staging, temporary erosion and sediment control, and
site isolation related to the construction of log jams within the active channel. The restoration costs in the
Powerlines reach are driven primarily by the high number of proposed log jams structures within the active and
side channels, 51 structures, as well as the related access requirements to reach the structure locations and the
site isolation work needed to install the log jams in the active channel. Future design efforts in the Powerlines
Reach will evaluate phasing or sequencing of the discrete groups of log jams and other proposed restoration
actions to further refine construction costs.
6.3 Future Full Valley Restoration Concept
NSD developed the future full valley restoration concept presented in Attachment B to conceptually illustrate a
scenario that meets all the goals and objectives for full restoration of the geomorphic and aquatic habitat
processes and in which river has restored access to the full resiliency corridor. This concept is a long-term vision
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for the resiliency corridor and lays out restoration actions dependent on the premise that all residents have
willingly moved out of the floodplain and related structures, roads, etc. can be removed. This concept also
integrates the premise that the floodplain has been entirely acquired by public entities (or permanent
conservation easements are established on private parcels).
The future full valley restoration concept would address the documented impairments in both the Lazy C and
the Powerlines reaches through a series of actions similar to those applicable for shorter-term restoration
projects but applied at a larger scale and more aggressively. These actions center on increasing the frequency of
overbank flows and hydraulic connectivity between the river and the Lazy C reach, encouraging channel
migration into the Lazy C reach, promoting the development of a multi-threaded planform and forested island
network, and restoring a mixed coniferous and deciduous forest to the floodplain in both reaches. Together,
these actions are intended to restore the processes necessary for the river to create and sustain a diverse range
of complex aquatic, wetland, and floodplain habitat types in perpetuity.
Specifically, the future full valley restoration concept includes the same restoration actions presented above for
the Powerlines reach and the following additional restoration actions within the Lazy C reach:
1. Excavation of the inset floodplain benches to allow for increased frequency of overbank flows along the
left bank Lazy C floodplain, improving floodplain connectivity and encouraging channel migration into
the floodplain.
2. Construction of Apex Jams to obstruct flow in the existing mainstem channel, encouraging overbank
flows into the left bank Lazy C floodplain and promoting channel migration into the floodplain.
3. Construction of a variety of Apex and Floodplain Roughness Jams along with conifer and riparian
revegetation to increase roughness throughout the floodplain and promote the development of a multi-
threaded channel planform and forested island network.
4. Restoration of a mixed coniferous and deciduous forested condition in the floodplain, through conifer
underplanting and invasive species management.
The suite of restoration actions could be phased or sequenced in a variety of ways such as by geographic
location, geomorphic setting, access points, or regulatory and landownership boundaries. Evaluation of phasing
approaches would be a point of discussion with the County and regional restoration stakeholders and would be
best based on a prioritization of needs and associated restoration actions and anticipated levels of design and
construction funding available at the future point in time in which this concept looks to be possible.
6.4 Stakeholder Engagement and Selection of Preferred Design Concepts
6.4.1 Stakeholder Engagement
Since before the onset of the Resiliency Plan project, the County has been working with the Dosewallips
Collaborative Group to consider the condition of the larger Dosewallips River system and work to support
aquatic species recovery and habitat restoration. The Collaborative Group has been meeting monthly with NSD
providing updates to the group after completion of the background data collection, field data collection,
hydraulic modeling, impairments analysis, prioritization, and conceptual design development components, as
documented herein. The Collaborative Group meetings have occasionally been attended by local community
members and residents of the Lazy C community, but are generally more regularly attended by a variety of
Tribal, federal, state, County, and non-profit stakeholders interested in the river and aquatic species recovery,
including but not limited to representatives of the following:
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Jefferson County Public Health, Parks and Recreation, and County Commissioners
Hood Canal Coordinating Council
Hood Canal Salmon Enhancement Group
Wild Fish Conservancy
Jamestown S’Klallam Tribe
Port Gamble S’Klallam Tribe
Skokomish Indian Tribe
Washington State Parks
Washington Department of Natural Resources
U.S. Forest Service
U.S. Geological Service
As a result of these meetings, the County has tasked NSD with creating a landowner outreach letter which the
County can send to residents in the Lazy C to further determine interest in engaging in discussions about short-
and long-term aquatic habitat restoration opportunities. NSD is also supporting the County in discussions with
County Commissioners regarding the channel migration zone, riverine processes, community risks, and
restoration opportunities. Finally, NSD is supporting the County with input regarding relocation program
development support through various federal funding and grant programs.
6.4.2 Selection of the Preserved Design Concepts
NSD presented the conceptual design alternatives (Attachment B) to the Collaborative Group at the May 2021
meeting. Feedback generally centered around the complexities associated with both the long-term and the
short-term actions in the Lazy C reach. The Collaborative Group discussed the challenges considering the density
of development, the existing flood and erosion hazard risks, and the need for more direct outreach to the Lazy C
community to increase understanding of existing risks, as well as the potential habitat benefits associated with
the suite of viable short-term actions identified in the Upstream and Downstream Lazy C sub-reaches.
NSD participated in the June Collaborative meeting where the focus of discussion was on the short-term actions
possible in the tributary stream at the downstream end of the Lazy C reach and in the Powerlines reach as
possible components to advance to Preliminary Design. The County and NSD will collaborate further to select a
suite of actions to combine into a viable project to advance to Preliminary Design.
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