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Wetland and Stream Mitigation Report
Upper Hoh River Road Bank Stabilization Project
Jefferson County, Washington
Prepared for:
Federal Highway Administration
Western Federal Lands Highway Division
610 East Fifth Street
Vancouver, WA 98661
Contact: Steven Morrow/Kirk Loftsgaarden
FHAX0000-0242
Prepared by:
O. Gray Rand III
Sr. Biologist, PWS
David Evans and Associates, Inc.
14432 SE Eastgate Way, Suite 400
Bellevue, WA 98007
March 2018
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Executive Summary
The Western Federal Lands Highway Division (WFLHD) of the Federal Highway
Administration (FHWA), in partnership with Jefferson County (collectively referred to as
“Project Partners”), plans to construct bank stabilization and bridge and culvert improvement
projects in five locations along the Upper Hoh River Road (UHRR).
The proposed project will develop and implement cost-effective, long-term bank stabilization
solutions at three locations along the UHRR. The project will also replace or improve three
existing bridge or culvert locations. The roadway at these sites is at risk of washing away in a
large flood. The purpose of the proposed improvements is to prevent the road from washing
away at these locations, and to provide safe and consistent access to residents, businesses, and
Olympic National Park visitors via the UHRR.
The project area includes the UHRR between mileposts (MP) 3.7 and 10.2 and the general area
north and south of the road, including the Hoh River and its northern banks. The UHRR extends
generally east-west immediately north of the Hoh River, in unincorporated western Jefferson
County, Washington.
The proposed project will have unavoidable impacts to three wetlands. Wetland impact will total
0.036 acres (Table S-1). Most of the proposed project impacts occur to small, palustrine
emergent, Ecology Category III, wetlands that are previously disturbed. Most of these generally
low quality wetlands provide limited levels of hydrologic, water quality, and habitat functions.
Vegetated buffers around the impacted wetlands are generally disturbed by natural processes
(i.e., erosion along the Hoh River) or by disturbance from maintenance of the UHRR.
WFLHD staff took a watershed approach to mitigation by engaging local stakeholders and
regulatory agencies with the best knowledge of the aquatic habitat needs in the Hoh River and
identifying how the proposed project could best offset its impacts and meet long-term restoration
objectives in the watershed.
The compensatory mitigation will occur at two locations – a wetland creation area located at Site
C1 and an approximately 190-acre side channel of the Hoh River associated with Lindner Creek
between MP 6.7 and 7.3. The mitigation provides the following to compensate for project
impacts to wetlands and streams.
0.073 acres of wetland creation
187 acres of side channel habitat preservation to provide long term benefits to fish and
wildlife
WSDOT proposes to replace the impacted wetlands with a Category III created wetland
dominated by native trees and shrubs. The created wetland will provide improved flood flow
alteration and water quality function, and will add habitat function compared to the impacted
wetlands. Installation of channel plugs in high flow channels at the Lindner Creek side channel
complex will preserve the habitats in this area, protecting important salmon rearing and
spawning habitat, preserving a stand of mature forest, and allowing existing riparian forest to
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continue to mature. In addition to these proposed mitigation measures, all temporary impacts to
stream and wetland buffers will be restored by planting with native trees and shrubs.
The proposed mitigation site will be monitored for five years. Monitoring, contingency, and
management plans are described, and will be used to adaptively manage the mitigation site.
Table S-1. Summary of project wetland impacts and compensatory mitigation.
Township/Range/Section (impact) T27N, R12W, Section 25
T27N, R11W, Section2, 25, 27, 28 and 30
Permanent Wetland Impact 1,562 square feet; 0.036 acre
Temporary Wetland Impact 285 square feet; 0.01 acre
Permanent Hoh River Impact 50,193 square feet; 1.15 acres
Temporary Hoh River Impact 94,420 square feet; 2.17 acres
Permanent Tributary Stream Impact 8,572 square feet; 0.20 acre
Temporary Tributary Stream Impact 1,118 square feet; 0.03 acre
Permanent Wetland and Stream Buffer Impact 23,609 square feet; 0.54 acre
Temporary Wetland and Stream Buffer Impact 191,135 square feet; 4.39 acres
Mitigation Location (Wetland Creation) Adjacent to Hoh River at Site C1
(Side Channel Preservation) Lindner Creek Side Channel Complex,
Total Area of Mitigation Site 187 acres (Lindner Creek site only)
Area & Type of Mitigation 0.073 acre of Wetland Creation
Area & Type of Mitigation 49.9 acres of Mature Forest Preservation
Area & Type of Mitigation 84.6 acres of Early Successional Riparian Forest Preservation
Area & Type of Mitigation 30.0 acres of Early Successional Floodplain Preservation
Area & Type of Mitigation 22.5 acres of Wetland and Backwater Habitat Preservation
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TABLE OF CONTENTS
Introduction .............................................................................................................................. 1
1.1 Project Purpose and Need ........................................................................................ 1
1.2 Project Location ....................................................................................................... 2
1.3 Report Purpose ......................................................................................................... 4
Existing Conditions .................................................................................................................. 5
2.1 Environmental Setting ............................................................................................. 5
Terrestrial Environment .............................................................................. 5
Aquatic Environment .................................................................................. 5
Wetland and Stream Impact Assessment .............................................................................. 9
3.1 Wetland Impacts ...................................................................................................... 9
Wetland Buffer Impacts .............................................................................. 10
Jurisdictional Ditches .................................................................................. 11
Wetland Functions Affected ....................................................................... 11
3.2 Stream Impacts ........................................................................................................ 12
Stream Impacts ........................................................................................... 12
Stream Buffer Impacts ................................................................................ 13
Impacts to Stream Functions ....................................................................... 14
Mitigation Strategy .................................................................................................................. 17
4.1 Avoidance and Minimization of Wetland and Stream Impacts ............................... 17
4.2 Compensatory Mitigation ........................................................................................ 17
Compensatory Wetland Mitigation........................................................................................ 19
5.1 Goals and Objectives ............................................................................................... 19
5.2 Site Selection ........................................................................................................... 19
5.3 Site Design ............................................................................................................... 20
Compensatory Stream Mitigation .......................................................................................... 21
6.1 Goals and Objectives ............................................................................................... 21
6.2 Site Selection ........................................................................................................... 21
6.3 Site Design ............................................................................................................... 26
Mitigation Performance Standards ........................................................................................ 29
7.1 Performance Standards ............................................................................................ 29
Performance Standard 1 - Wetland Hydrology ........................................... 29
Performance Standard 2 - Wetland Plant Cover ......................................... 29
Performance Standard 3 - Invasive Species ................................................ 30
Performance Standard 4 - Movement of ELJ components ......................... 31
Performance Standard 5 – ELJ Wood Recruitment .................................... 31
Performance Standard 6 – Bank Restoration Area Vegetation Criteria ...... 31
Performance Standard 7 – Monitoring Streambed Composition ................ 32
Performance Standard 8 – Mitigation Site Channel Plug Movement and
Vegetation Establishment ........................................................................... 32
Monitoring and Maintenance ................................................................................................. 35
8.1 Contingency Plan ..................................................................................................... 35
8.2 Hydrology ................................................................................................................ 35
8.3 Vegetation ................................................................................................................ 35
8.4 Structure Movement ................................................................................................ 36
8.5 Site Management ..................................................................................................... 36
References .................................................................................................................................. 37
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LIST OF EXHIBITS
Figure 1. Vicinity Map ........................................................................................................................... 3
Figure 2. Proposed Aquatic Mitigation Concept – Lindner Creek Side Channel Engineered Log Jams
at MP 6.7 to 7.3 ........................................................................................................................... 22
Figure 3. Mitigation Site Habitat Types and Two Year Flood Channels. ............................................ 25
LIST OF TABLES
Table 1. Wetland Size, Classification, and Area Impacted by the Proposed Project. ............................ 9
Table 2. Permanent Palustrine Wetland Impact Summary by Classification. ..................................... 10
Table 3. Wetland Buffer Size and Area Impacted by the Proposed Project. ....................................... 10
Table 4. Ditch Wetland Size, Classification, and Area Impacted by the Proposed Project. ................ 11
Table 5. Impacted wetland functions. .................................................................................................. 12
Table 6. Stream Impact Table .............................................................................................................. 12
Table 7. Stream Buffer Impact (square feet) ........................................................................................ 13
Table 8. Checklist for Documenting Impacts to Stream Functions ..................................................... 14
Table 9. Habitat Types Preserved by Lindner Creek Side Channel Mitigation Project ....................... 23
Table 10. Wetland Revegetation Aerial Cover Standards ................................................................... 30
Table 11. Bank Restoration Aerial Cover Standards ........................................................................... 32
Table 12. Proposed Performance Standards for Wetland and Stream Mitigation................................ 32
APPENDICES
Appendix A: Wetland and Stream Buffer GIS Map Set
Appendix B: Wetland and Stream Impact Sheets
Appendix C: Wetland Mitigation Design Plans
Appendix D: Draft Hydraulics Report – Habitat Preservation Site
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Acronyms and Abbreviations
asl above sea level
BMP Best Management Practice
CWA Clean Water Act
dbh diameter at breast height
DEA David Evans and Associates, Inc.
Ecology Washington State Department of Ecology
ELJ engineered log jam/
ESA Endangered Species Act
FHWA Federal Highway Administration
FONSI Finding of No Significant Impact
HUC hydrologic unit code
IWWW In-water work window
LWD large woody debris
MP milepost
OHWM ordinary high water mark
ONP Olympic National Park
RM river mile
SEPA State Environmental Policy Act
UHRR Upper Hoh River Road
USACE U.S. Army Corps of Engineers
US 101 U.S. Highway 101
USFWS U.S. Fish and Wildlife Service
WDFW Washington Department of Fish and Wildlife
WDNR Washington Department of Natural Resources
WFLHD Western Federal Lands Highway Division
WRIA Water Resource Inventory Area
WSDOT Washington State Department of Transportation
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Introduction
The Western Federal Lands Highway Division (WFLHD) of the Federal Highway
Administration (FHWA), in partnership with Jefferson County (collectively referred to as
“Project Partners”), plans to construct bank stabilization and bridge and culvert improvement
projects in five locations along the Upper Hoh River Road (UHRR).
The UHRR is located in western Jefferson County, Washington, between U.S. Highway 101 (US
101) and the Hoh Rain Forest Visitor Center. The road is used to access the Olympic National
Park (ONP) and private properties along the road. The UHRR was likely built around 1938,
when the ONP was established, and is the primary western access to the park.
The UHRR extends in a generally east-west direction north of and in many places adjacent to the
Hoh River, an approximately 56-mile-long river originating from glaciers on Mount Olympus,
flowing through the Olympic Mountains, foothills, and emptying into the Pacific Ocean at the
Hoh Indian Reservation. The Hoh River Valley is relatively flat and broad with a complex
channel migration zone that supports a braided river channel and a wide variety of gravel bars,
side channels, and backwater areas. The Hoh River is also characterized by a wide range of
seasonal flow rates, with annual peak flows of more than 60,000 cubic feet per second.
The road varies in proximity to the Hoh River and, in certain areas, is within approximately 5
feet of the river, resulting in unstable banks and slides during high water or storm events. The
Project Partners have constructed several projects in recent years along the road, in order to
prevent road closures due to unstable slopes. Without the proposed project, these emergency
projects will continue to happen regularly.
1.1 Project Purpose and Need
The proposed project’s purpose is to develop and implement cost-effective, long-term bank
stabilization solutions at three locations along the UHRR in western Jefferson County,
Washington. The project will also replace three stream-crossing structures (i.e., bridges or
culverts). The UHRR at the bank stabilization and stream crossing sites is at risk of washing
away in a large flood event. Key design objectives are to protect the UHRR at certain locations
between milepost (MP) 3.6 and MP 10.2 from erosion, and to provide safe and consistent access
to residents, businesses, and ONP visitors between US 101 and the Hoh Rain Forest Visitor
Center.
The UHRR serves as the only access road for the residents and businesses located along this
roadway and for visitors entering ONP from US 101 from the west. In 2014, over 82,000
vehicles entered the park using the UHRR. In August of 2015 alone, 24,000 vehicles entered the
park using the UHRR. Visitor data for recent years indicate that an annual average of three
million people visit the park. The UHRR leads to the Hoh Rain Forest Visitor Center, which is
one of four year-round ranger stations in ONP and the only year-round ranger station with access
to the western side of the park.
Maintaining safe and consistent access along the UHRR has been increasingly difficult due to the
dynamic character of the adjacent Hoh River, a low-gradient river with frequently shifting
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braided channels. Additional challenges have recently exacerbated the character of the river
corridor. For example, vegetation removal in the Hoh River drainage combined with recent
changes in weather patterns (warmer temperatures and less snow) have contributed to the
magnitude and extent of the river’s channel migration. Often, this has caused flows to be
directed against the road embankment causing significant erosion and instability. Bank erosion
has occurred on sections of riverbank not protected by riprap revetments, heavy vegetation, or
boulder lag deposits. The bank erosion is caused by mid-channel sediment deposits and woody
debris shifting across the channel migration zone and redirecting flood flows at unstable bank
areas. Damage to the UHRR due to flooding has resulted in road or lane closures lasting for
several weeks in 1996, 1998, 2003, 2004, 2006, 2007, and 2014. A continuing trend of more
frequent flooding will increase the potential for interrupted access to US 101 and ONP for local
residents, business owners/patrons, park users, and other recreationists.
The cost to repeatedly maintain safe access on the UHRR has increased substantially due to the
Hoh River’s character and its proximity to the UHRR. Over the past decade, the County and
WFLHD (through the Emergency Relief Program) have spent over $5 million on 13 projects to
maintain safe access on the 12-mile portion of the UHRR between US 101 and the ONP.
Built in 1983, the Tower Creek Bridge is in need of replacement, and does not meet current
seismic and design standards. The Hoh River’s migration toward the UHRR has shortened the
Tower Creek channel length, which has caused the Tower Creek channel to incise and scour the
bridge abutments. The other bridge replacement sites at MP 4.38 and Canyon Creek are
undersized, require frequent maintenance to remove debris and sediment, and are barriers to fish
passage at certain flows.
The proposed project will develop and implement cost-effective, long-term bank stabilization
solutions at three locations along the UHRR. The project will also replace or improve three
existing bridge or culvert locations. The roadway at these sites is at risk of washing away in a
large flood. The purpose of the proposed improvements is to prevent the road from washing
away at these locations, and to provide safe and consistent access to residents, businesses and
Park visitors via the UHRR.
1.2 Project Location
The project area includes the UHRR between MP 3.7 and 10.2 and the general area north and
south of the road, including the Hoh River and its northern banks. The UHRR extends generally
east-west immediately north of the Hoh River, in unincorporated western Jefferson County,
Washington. All six sites are located within the project area (Figure 1), a heavily forested and
rural area west of the Park.
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Figure 1. Vicinity Map
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Legal locations for the primary projects are as follows:
Site C1/C2 – Township 27N, Range 12W, Section 25 and Township 27N, Range 11W,
Section 30 (includes culvert at MP 4.38)
Site C3 – Township 27N, Range 11W, Section 28
Site C4 – Township 27N, Range 11W, Section 27
Site C5 – Township 27N, Range 11W, Section 25
All of the projects are located within sixth-field hydrologic unit codes (HUC) 171001010706
(Lower Hoh River) and 171001010705 (Owl Creek), both within the Sol Duc – Hoh Water
Resource Inventory Area (WRIA) 20. Public land owners and managers in the project area
include the Nature Conservancy, Jefferson County, the National Park Service (ONP), and the
State of Washington Department of Natural Resources (WDNR). Private individuals, Hoh
Rainforest Enterprises LLC, R.D. Merrill Company, and the Discovery Timber Company also
own land in the project area.
1.3 Report Purpose
This Wetland and Stream Mitigation Report (report) documents impacts to waters of the United
States, including wetlands and streams, due to construction of the proposed project and describes
a proposal to mitigate for unavoidable impacts to those resources.
This report has been prepared at the request of the U.S. Army Corps of Engineers (USACE) in
support of the Clean Water Act (CWA) Section 404 permit. It also provides information to
inform the applications for the following permits:
Washington State Department of Ecology (Ecology) Section 401 Water Quality
Certification
Washington State Department of Fish and Wildlife (WDFW) Hydraulic Project Approval
Washington State Department of Natural Resources (WDNR) Aquatic Lands Use
Authorization
State Environmental Policy Act (SEPA) determination (Jefferson County as lead agency)
Jefferson County Shoreline Substantial Development Permit and critical area assessment
This report does not describe the proposed project in detail, nor does it describe existing
condition of waters of the United States in the project area in detail. Please refer to the following
reports for more information on project description, existing conditions, and project impacts:
Final Environmental Assessment and FONSI (WFLHD 2017)
Biological Survey Report (DEA 2015a)
Wetland and Stream Delineation Report and Addendum (DEA 2015b and 2017)
Biological Assessment (DEA 2016)
Project Biological Opinion (USFWS 2017)
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Existing Conditions
2.1 Environmental Setting
The project area is located along the Upper Hoh River in the Hoh River Valley, west of the ONP
and east of US 101, in Jefferson County, Washington. The UHRR is the primary access to the
northwestern side of the ONP and the Hoh River Rainforest, one of the ONP’s most popular
destinations. UHRR is also the primary access to a few small enclaves of rural residences. Most
of the project area is characterized by undeveloped public and private forest land.
Terrestrial Environment
The project area consists primarily of a mix of public and private open forest land, with a few
scattered rural residences located near MP 6.0. Active logging is more common on the south
side of the valley where private land is more abundant. The Hoh River has an extremely active
channel migration zone and floodplain, with constantly changing meanders and side channels
forming and being destroyed. The active hydraulic nature of the river has led to a wide range of
seral riparian habitats along the river. Forest stands along the UHRR are generally mid-seral, but
several areas of old growth are present, particularly near Tower Creek.
Elevation in the project area ranges from about 500 feet above sea level (asl) adjacent to the Hoh
River, to about 3,200 asl at the ridgetops on the north side of the Hoh River valley.
Soils in the Hoh River drainage and minor tributaries are derived primarily from glacial outwash
and alluvium deposited in the valley floors and walls (NRCS 2016).
The project is located in the Westside Lowland Conifer-Hardwood Forest habitat type, as
described in Wildlife-Habitat Relationships in Oregon and Washington (Johnson and O’Neil
2000). Most of the project area is occupied by native upland and wetland forest vegetation,
except for the ditches and cleared areas adjacent to the roadside, where non-native species were
more common.
Aquatic Environment
The Hoh River is the primary waterbody affected by the project, along with three tributaries—
Tower Creek, Canyon Creek, and Stream S12 at the culvert at MP 4.38. Each of these
waterbodies is described in more detail below.
Hoh River
The Hoh River is a large, glacially influenced river with an extensive, active floodplain
associated with numerous spring-fed terrace tributaries (McHenry et al. 1996). The ONP
comprises 65 percent of the Hoh watershed, with the section of the Hoh River lying outside of
ONP boundaries extending from river mile (RM) 1.5 to 29.6. (The lower 1.5 miles of the river
are in the coastal unit of the ONP.) The headwaters lie within the ONP and drain to the Bailey
Range and the north slope of Mount Olympus (Phinney and Bucknell 1975). The Hoh River
flows from east to west and outlets directly into the Pacific Ocean. Average annual precipitation
varies significantly, with over 240 inches of precipitation along the ridge above Humes and Hoh
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Glaciers, down to 93 inches near the outlet. The entire watershed covers approximately 298
square miles in area, and a large portion of the watershed is administered within the ONP and has
therefore not been altered by timber harvesting practices. The South Fork Hoh is a major
tributary that joins the Hoh River at RM 30. Other known salmonid-producing tributaries
include Slide, Falls, Mt. Tom, Jackson, Taft, Snider, East Twin, Canyon, Spruce, Dismal, Pole,
Tower, Lindner, Clear, Willoughby, Elk, Alder, Winfield, Hell Roaring, Lost, Pins, Anderson,
Nolan, Braden, and Fossil Creeks.
The Hoh watershed provides habitat for coho, fall Chinook, spring/summer Chinook, chum
salmon, and winter and summer steelhead trout. Bull trout spawn in the North and South Fork
Hoh Rivers and utilize downstream areas as well. The Hoh watershed is believed to support the
largest char population on the coast (WDFW 1998). The Hoh spring/summer Chinook stock is
the largest population of early timed Chinook on the Olympic Peninsula, and this stock spawns
primarily within the ONP boundaries (McHenry et al. 1996).
Tributaries to the Hoh River
Construction of the proposed project will involve impacts to three tributaries to the Hoh River –
the unnamed tributary (designated as Stream S12) that flows into mainstem Hoh River through
the culvert at MP 4.38, Tower Creek, and Canyon Creek.
Stream S12 at MP 4.38 is a seasonal intermittent stream that drains a watershed of approximately
300 acres. The existing culvert at the UHRR is perched several feet on the downstream end
during most of the summer and fall. It is only accessible to fish during high water in the winter
and spring. It is possible that some fish may be able to access the stream at that time, but it is
unlikely given the high head pressures at higher water volumes. Also, several step pools
immediately upstream of the culvert would deter fish passage farther upstream. Stream substrate
in this stream is mostly cobble and large boulders.
Tower Creek is a swift flowing perennial tributary to the Hoh River at RM 23.3. It is
approximately 2.5 miles long and has a watershed of approximately 1,000 acres. Based on aerial
photointerpretation, approximately 50 percent of the watershed has been logged historically. It is
roughly 30 to 40 feet wide in the vicinity of the UHRR bridge crossing. Substrates consist of
boulders and large cobble. Within the project area the creek is confined in a very steep-sided
canyon, portions of which are vegetated. The creek appears to be eroding away at the west
canyon wall upstream of the bridge, leading to unvegetated slopes in places where earth and
vegetation have fallen into the creek. Extensive bank erosion occurs near the confluence of
Tower Creek and the Hoh River.
Canyon Creek is a swift flowing perennial tributary to the Hoh River at RM 26.4. It is
approximately three miles long and has a watershed of approximately 1,000 acres. It joins the
Hoh River at a large alluvial fan. Based on aerial photointerpretation, approximately 75 percent
of the watershed has been logged in the past. The actual location of the confluence likely
changes seasonally with high flows in the mainstem Hoh River. It is roughly 15 feet wide (at the
ordinary high water mark [OHWM] line) on the upstream side of UHRR. A large scour hole
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exists on the downstream side, where the creek is roughly 35 feet wide before narrowing back
down. Substrates consist of small boulders, cobbles, and gravels.
Wetlands
The project area supports numerous large wetlands and wetland complexes. Many of these are
associated with seeps and streams flowing off of the steep valley sidewalls. Many large wetlands
are present immediately adjacent to the north or uphill side of the UHRR. Development of these
wetlands was encouraged by the historic construction of a berm north of the road, which appears
in some cases to create a barrier to normal overland and subsurface flow, contributing to the
development of depressional wetland hydrology. Most of these wetlands outlet to ditches or
culverts that run underneath UHRR and then into the Hoh River after a short distance. Wetlands
in the project area are mostly forested, in some cases with mature forest overstory of conifers,
including Sitka spruce, western hemlock, and western red cedar.
Jurisdictional Ditches
The project area includes constructed ditches along portions of the UHRR roadway. Where
ditches are conveying a stream or adjacent to a wetland, these features are jurisdictional ditches.
Some of these areas develop wetland vegetation between instances of route maintenance
(vegetation clearing and sediment removal for drainage improvement) but were constructed and
maintained as part of the drainage system for the UHRR roadway. Impacts to jurisdictional
ditches will be addressed separately from other jurisdictional features. A jurisdictional ditch is
not considered a special aquatic site per the CWA and will be replaced in kind after construction
is completed.
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Wetland and Stream Impact Assessment
This section summarizes temporary and permanent impacts of the proposed project on wetlands
and streams in the project area, including an assessment of impacts to functions. It also discusses
impacts to vegetated ditch wetlands.
3.1 Wetland Impacts
The proposed project would result in unavoidable permanent or temporary impacts to five
palustrine wetlands (Table 1; Appendix A). Most of the proposed fill in jurisdictional wetlands
will occur because of the need to impact the slope adjacent to the river to install the engineered
log jams (ELJs). It is assumed that all of Wetland 1 and Wetland 5 will be removed by project
construction due to the need to create a nearshore access bench. Wetland 1 is being actively
eroded by the river at Site C1. Wetland 5 originates as a roadside seep adjacent to Site C2. A
portion of Wetland WC3-A will be removed by roadway improvements west of the Tower Creek
bridge. All of the permanently affected wetlands are previously disturbed and in close proximity
to the UHRR. All of the affected wetlands are assumed to be within USACE jurisdiction due to
downstream connections to other waters of the United States. Impacts to these wetlands are
described in Table 1 and Table 2 below.
Table 1. Wetland Size, Classification, and Area Impacted by the Proposed Project.
Wetland
Wetland Classification
Wetland
Size (acre)
Wetland Impact Area
(square feet)
CowardinA HGMD EcologyB Jefferson
CountyC Permanent
Percent
Perm.
Impacted
Temporary
1 PEM Slope III III 0.01 765 100 0
5 PSS Slope III III 0.01 458 100 0
WC3-A PFO Depressional III III 0.03 339 25 265
WC3-B PFO Depressional III III 0.02 0 <1 2
WC4-A PFO Slope III III 0.13 0 <1 18
Total 1,562 285
A. Cowardin et al. (1979) or National Wetland Inventory (NWI) Class based on vegetation.
PEM = Palustrine Emergent; PSS = Palustrine Scrub-Shrub; PFO = Palustrine Forested.
B. Ecology rating according to Hruby (2014).
C. Wetlands rated according to Jefferson County Critical Areas Ordinance.
D. HGM = hydrogeomorphic classification
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Table 2. Permanent Palustrine Wetland Impact Summary by Classification.
Wetland Classification Class
Wetland Impact
Area
(square feet)
Percent of Total
Wetland Area
USFWS
(Cowardin et al. 1979)
PEM 765 100
PSS 458 100
PFO 339 25
Total 1,562
Ecology
(Hruby 2014)
I 0 0
II 0 0
III 1,562 60.6
IV 0 0
Total 1,562
Jefferson County
(CAO)
I 0 0
II 0 0
III 1,562 60.6
IV 0 0
Total 1,562
Hydrogeomorphic
Class
Slope 1,223 100
Depressional Closed 339 25
Depressional Outflow 0 0
Riverine 0 0
Total 1,562
Wetland Buffer Impacts
Table 3 below lists anticipated wetland buffer impacts from the proposed project (Appendix B).
Wetland buffer impacts are not calculated for Wetlands 1 and 5 since they will be completely
removed by the project.
Table 3. Wetland Buffer Size and Area Impacted by the Proposed Project.
Wetland Jefferson County Wetland
Buffer (feet)
Wetland Buffer Impact Area
(square feet)
Permanent Temporary
1 80 0 0
5 80 0 0
WC3-A and WC3-B 80 1,211 6,968
WC4-A 150 1,627 5,662
Total 2,838 12,630
Wetland buffers that will be affected by the proposed project consist of herbaceous grass and
other plants near the maintained road edge with shrubs and native forest beyond. In all cases,
some portion of the wetland buffer is interrupted by the UHRR, sometimes significantly.
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Anticipated impacts to buffers on Wetlands WC3-A, WC3-B, and WC4-A are limited to portions
of the buffer immediately adjacent to the existing road and mostly dominated by herbaceous
species, particularly in the case of the permanent impacts. All permanent buffer impacts are due
to the realignment of the east and west road approaches to the Tower Creek Bridge.
Jurisdictional Ditches
Additional impacts will occur to vegetated ditches that have developed wetland vegetation and
are part of the road prism and the constructed road drainage system (Table 4). Ditch wetlands
are maintained on an as-needed basis by Jefferson County. Some of these ditches carry water
routed from nearby streams to the Hoh River.
Impacts to ditch wetlands will affect, primarily, water quality and hydrology functions. These
ditches transport road runoff to local waterbodies. Specifically, Ditch DC3-A transports runoff to
Wetland WC-3B. Ditch DC4-A collects a small area of runoff and directs it to Tower Creek.
Ditch DC4-B transports road runoff from the eastern road approaches to Tower Creek Bridge to
Wetland WC4-A. These ditches have herbaceous plants that can provide some treatment of
runoff prior to reaching local waterbodies.
Table 4. Ditch Wetland Size, Classification, and Area Impacted by the Proposed Project.
Ditch
Wetland
Ditch Wetland
Classification
Ditch Wetland Size
(acre)
Ditch Wetland Impact Area
(square feet)
Permanent Percent Perm.
Impacted Temporary
DC3-A PEM 0.01 432 100 60
DC4-A PEM 0.01 55 100 0
DC4-B PEM 0.03 630 25 466
Total 1117 526
Wetland Functions Affected
Table 5 below describes wetland functions affected by impacts described above. Wetland 5 is a
small sparsely vegetated bench wetland with little habitat value and limited opportunity to
provide hydrologic or water quality functions. It is also within the active erosional zone of the
river. Wetland 1 is a roadside swale that leads to a seep that flows down the riverbank to the Hoh
River. Wetland 1 supports only palustrine emergent vegetation, so habitat function is limited, but
its location immediately adjacent to UHRR provides opportunity for water quality treatment of
pollutants in road runoff. Wetlands WC3-A and B are small isolated depressional wetlands west
of Tower Creek that support better habitat than Wetlands 1 and 5 and could also treat road runoff.
Wetland WC4-A is the largest of the impacted wetlands, with the highest habitat quality as well
as good hydrologic and water quality function.
Wetland buffer impacts are limited to the three wetlands in proximity to Tower Creek. These
buffer impacts include permanent impacts due to realignment of the road, and temporary impacts
due to regrading of the road slopes. All wetland buffer impacts are to that narrow portion of the
buffer between the wetlands and the existing road.
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Table 5. Impacted wetland functions.
Function/Value Wetland Ditches 1 5 WC3-A WC3-B WC4-A
Flood Flow Alteration - - - - - -
Sediment Removal X - X X X X
Nutrient and Toxicant Removal X - X X X X
Erosion Control & Shoreline Stabilization - - - - - -
Production & Export of Organic Matter - - - - X -
General Habitat Suitability - - X X X -
Habitat for Aquatic Invertebrates - - - - X -
Habitat for Amphibians - - - - X -
Habitat for Wetland-Associated Mammals - - X X X -
Habitat for Wetland-Associated Birds - - X X * -
General Fish Habitat - - - - - -
Native Plant Richness - - X X + -
Educational or Scientific Value - - - - - -
Uniqueness and Heritage - - - - - -
Notes: “-” means that the function is not present,
“X” means that the function is present and is of low quality, and
“+” means the function is present and is of high quality.
3.2 Stream Impacts
Stream Impacts
Table 6 describes permanent and temporary impacts to the mainstem Hoh River and its
tributaries from the proposed project (Appendix A).
Table 6. Stream Impact Table
Waterbody Impact Type Area of Impact (square feet)
Hoh River Permanent 50,193
Hoh River Temporary 94,420
Stream S12 at MP 4.38 Permanent 534
Stream S12 at MP 4.38 Temporary 1118
Tower Creek Permanent 5,908
Tower Creek Temporary --
Canyon Creek Permanent 2130
Canyon Creek Temporary --
Total Permanent Impact 58,765
Total Temporary Impact 95,538
Permanent impacts in the Hoh River are related mostly to the placement of ELJs into the river.
This impact number represents the footprint of all 30 of the ELJs to be installed, along with a
portion of the bank area that will be permanently regraded behind each ELJ and a 10-foot
hydraulic buffer around each structure. While these areas are counted as permanent impacts,
they will still be an active part of the river, and they will likely provide improved fish habitat as
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well as large woody debris recruitment (see stream function discussion below). Permanent
impacts to Stream S12 at MP 4.38 are from the installation of a larger culvert, which will occupy
part of the existing channel. Permanent impacts at Tower Creek are related to the portion of the
stream channel that will be regraded and widened for the new bridge, and receive treatment with
scour protection rock. Similarly, permanent impacts at Canyon Creek are related to the portion
of the existing channel that will be regraded and receive new scour protection rock after
installation of the new bridge.
Temporary stream impacts in the Hoh River were calculated by assuming a buffer of
approximately 20 feet around all of the installed ELJs, as well as assuming that most of the area
between the structure and the existing OHWM will be affected by construction of a temporary
construction access path along the shoreline. This construction will involve laying the existing
banks back and creating a bench near the existing water level to support large construction
equipment. Since the ELJs will be constructed from the shore, it is likely that the temporary
impacts shown in Table 6 above are a worst-case scenario. All temporarily impacted areas will
be restored following construction.
Indirect impacts to streams on the site could include impacts from the proposed project that
happen later in time. For example, long-term changes to river flow, morphology, and fish habitat
could occur from placement of the ELJs. Hydraulic modeling of the proposed project has
demonstrated that any hydraulic changes related to the proposed ELJs would be localized to the
immediate vicinity of the structures. The structures will be monitored for a period not less than
five years after installation to determine how the structures move and flex, as well as what
hydraulic conditions develop around each one.
Stream Buffer Impacts
The majority of the proposed project occurs within aquatic habitat or within stream buffers.
Along Sites C1 and C2, only a narrow band of riparian habitat exists between the river and the
UHRR. Impacts to these riparian areas along the Hoh River are unavoidable in order to install
the ELJ/dolosse units from the streambanks. Up to 325 trees within stream buffers are
conservatively assumed to be removed by the proposed project. The vast majority of these trees
are small deciduous trees (mostly red alder). Approximately 20 large (>18 inch diameter)
conifer trees may be removed by the project. Vegetation removal in general is estimated to occur
over a total area of approximately 187,000 square feet (4.2 acres), approximately 75 percent of
which is within stream buffers, either of the Hoh River or of one of its tributaries (Table 7;
Appendix B).
Table 7. Stream Buffer Impact (square feet)
Stream Buffer (feet) Estimated Permanent Buffer Impact
(square feet)
Estimated Temporary Buffer Impact
(square feet)
Hoh River 150 4,010 142,153
Stream S12 150 349 7,107
Tower Creek 150 6,777 15,594
Canyon Creek 150 4,058 13,651
Total 15,194 178,505
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Impacts to Stream Functions
Table 8 describes the potential effects of the proposed action on stream functions in the Hoh
River and its tributaries. This table is modified from Table 11 in the project Biological
Assessment.
Table 8. Checklist for Documenting Impacts to Stream Functions
Diagnostics/
Pathways/Indicators
Hoh River and Affected Tributaries
Existing
Conditions Effects of the Action
Water Quality
Temperature FAR Minor impact from removal of riparian vegetation; long term maintain by
mitigation plantings.
Sediment/Substrate FAR Short-term impacts from construction-related suspended sediment and
turbidity in Hoh River due to direct placement of ELJ components in water.
Very minor impacts in tributaries due to complete work area isolation.
Localized changes in sediment movement around ELJs – deposition in lower
velocity areas between, behind and below ELJs, with added scour waterward
of ELJs.
Chemical Contamination/Nutrients PF No change.
Habitat Elements
Physical Barriers FAR Will improve fish passage at Canyon Creek and Culvert 4.38. In the case of
Canyon Creek, opening up more than a mile of available fish habitat.
Substrate Embeddedness FAR Short-term impacts from construction-related suspended sediment and
turbidity; long-term maintenance of indicator.
Large Woody Debris FAR Short-term impact from removal of riparian trees; long term improve by
installation of ELJs, additional LWD recruitment, and riparian plantings.
Pool Frequency and Quality FAR Improve. Anticipate eddy pools forming below ELJs in Hoh River.
Large Pools PF No change.
Off-channel Habitat PF No change.
Refugia PF Improve. Anticipate near bank refugia created by ELJs in Hoh River. No
change in tributaries.
Channel Condition and Dynamics
Width to Depth Ratio FAR Maintain in mainstem Hoh. Improve in tributaries by widening of structures
and associated channel width.
Streambank Condition FAR Improve through repair and stabilization of failing streambanks, which will
allow longer development of riparian development.
Floodplain Connectivity FAR Improve at Canyon Creek by removal of blocking culvert.
Flow/Hydrology
Change in Peak/Base Flows FAR No change.
Drainage Network Increase FAR No change.
Watershed Conditions
Road Density and Location FAR No change.
Disturbance History FAR No change.
Riparian Conservation Areas FAR Short-term impacts from removal of riparian trees; long term maintain by
riparian plantings and improved stability for streambanks. Also, mitigation
program will improve long-term stability of important side channel complex.
PF = properly functioning; FAR = functioning at risk; NPF = not properly functioning, LWD = large woody debris
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The proposed action is likely to maintain or improve current stream functions in the Hoh River
and its tributaries in the long term. Some short-term impacts will occur to some indicators, due
primarily to in-water installation of the ELJ/dolosse units. The ELJ/dolosse units would provide
long-term protection for UHRR without creating more hard armoring that would further degrade
water quality and streambank conditions along the river. These units would also provide
improved fish habitat along the river. The interstitial spaces within the dolos/log structures can
provide over 10 times the interstitial space as other engineered log jams and over 100 times that
of traditional rock structures (Abbe, 2017). Monitoring results for ELJs installed in the Elwha
River indicate that they have a measurable and significant effect on primary productivity,
secondary productivity and juvenile fish populations (McHenry et al. 2007). Similarly, at the
Elwha project, development of large scour pools were observed at almost every ELJ.
During construction, there would be temporary and localized degradation of water quality in the
Hoh River. The project would implement a variety of erosion and sediment control techniques to
minimize sedimentation, including working during low water, staging equipment on dry gravel
bars, use of gravel berms to keep equipment off the native streambed, etc. Work on Tower
Creek, Canyon Creek, and Culvert 4.38 would likely be conducted using dewatering and
diversion techniques. Combined with appropriate implementation of erosion and sediment
control techniques, this would avoid and minimize stream sedimentation to keep impacts short-
term and localized. Dewatering would avoid sedimentation and other in-water impacts during
construction, but there may be a minor pulse of sediment downstream when the stream
diversions are removed.
Effects to Listed Species
The project’s effects to listed species are evaluated in the project Biologist Assessment and
Section 4.6 of the Draft and Final Environmental Assessment. Overall, the project is anticipated
to have potential short-term direct impacts to bull trout rearing in the Hoh River due to direct
disturbance and increased sedimentation from construction. The U.S. Fish and Wildlife Service
(USFWS) concluded in its Biological Opinion (USFWS 2017) that the action, as proposed, is not
likely to jeopardize the continued existence of bull trout and is not likely to adversely modify or
destroy designated critical habitat for bull trout.
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Mitigation Strategy
The mitigation strategy described in this chapter involves avoidance, minimization of wetland
and stream impacts, and compensatory mitigation for unavoidable wetland and stream impacts.
4.1 Avoidance and Minimization of Wetland and Stream Impacts
The Project Partners have avoided and minimized impacts to wetlands and streams and their
buffers to the greatest extent practicable. Total avoidance was not possible because of the
project’s need to place bank stabilization in the river itself, as well as required activities to
replace the bridges and culverts at Tower Creek, Canyon Creek, and the Stream S12 at MP 4.38.
Impacts were minimized primarily through site-specific design techniques including the
following:
Delineation and mapping of all streams and wetlands in the project area, including
resources on the north side of UHRR and in the vicinity of mitigation areas, so that
project design could avoid streams and wetlands where possible;
Use of retaining walls where appropriate to minimize impacts at the bridge locations;
Placement of access roads and staging areas to maximize use of previously disturbed
areas (e.g., the Jefferson County equipment yard at Tower Creek and the abandoned
Willoughby Creek campground site);
Selecting the most environmentally preferable design for bank stabilization (ELJs) in
order to maximize aquatic habitat benefits compared to more engineered solutions such
as riprap and rock groins;
Modeling the hydraulic effects of the ELJs in order to minimize use of dolosse for ballast
(including advanced physical modeling in national lab);
Avoiding critical spawning periods for sensitive fish species, particularly steelhead and
spring Chinook salmon; and
Preparation of a Water Quality Maintenance and Monitoring Plan;
4.2 Compensatory Mitigation
During the environmental permitting phase of the project, resource agencies voiced concerns that
placing the ELJ/dolosse units into the river channel would cause negative effects to fish and
aquatic habitat. As a result of these concerns and of the National Environmental Policy Act
(NEPA) process, including agency consultation and public comment, WFLHD concluded that the
proposed project would require compensatory mitigation to offset unavoidable impacts to the
aquatic ecosystem. Compensatory mitigation for unavoidable impacts will be provided through a
combination of wetland creation and preservation of important side channel habitat in the
mainstem Hoh River, and is described in more detail in Section 5.0.
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Compensatory Wetland Mitigation
5.1 Goals and Objectives
In compliance with Jefferson County Code Section 18.22.350, the Project Partners have the
following goals and objectives related to wetland mitigation:
1. Follow appropriate mitigation replacement ratios (in this case, a creation ratio of 2:1 for
Category III wetlands);
2. Provide for long-term protection of the mitigation site;
3. Provide in-kind, on-site mitigation;
4. Follow appropriate order of preference for selection of mitigation sites:
a. Filled, drained, or cleared sites which were formerly wetlands and where appropriate
hydrology exists; and
b. Upland sites, adjacent to wetlands, if the upland is significantly disturbed and does
not contain a mature forested or shrub community of native species, and where the
appropriate natural hydrology exists.
5.2 Site Selection
WFLHD considered “on-site” in the case of the proposed project to include areas within
proximity of one of the proposed project activities (Sites C1 through C5). Within these areas,
very few disturbed sites exist that are potentially appropriate for wetland mitigation. Most of the
wetlands on the project are located north of the Upper Hoh Road and are in good condition.
Two sites were originally considered for compensatory wetland mitigation, both of which were
considered for wetland creation, one at Site C1 and one at the aquatic habitat mitigation site near
MP 6.7. These two sites had the following characteristics:
Site C1
o Upland area adjacent to Wetland 5;
o Site would be cleared by ELJ installation, and wetland could be created before,
during, or immediately after ELJ construction;
o Appropriate natural hydrology is available in outflow of Stream 9;
o Stream 9 is not fish passable due to a vertical drop of approximately 10 feet where it
meets the Hoh River;
o Site is dominated by second growth forest; and
o Site will be protected from future bank erosion by the ELJs.
MP 6.7
o Existing wetlands are present adjacent to the existing access road to the river;
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o Some of these wetlands have been disturbed by human activities, and could be
enhanced or wetland could be created adjacent to them;
o Hydrology at this site is problematic. Existing wetlands are supported by
precipitation that perches on non-permeable soils. To reach dependable groundwater,
created wetland would have to be excavated approximately five feet deep; and
o Site is exposed to occasional high flows from the river and could be damaged or
destroyed in the future.
Based on the more dependable natural hydrology source, and the fact that the site will be
disturbed by construction in any case, WFLHD chose Site C1 for wetland mitigation.
5.3 Site Design
At this location, WFLHD will construct a bench wetland (similar to Wetland 1) approximately
3,200 square feet in size, offsetting permanent impacts of 1,562 square feet at a creation ratio of
at least 2:1. Hydrology will be provided by flow from Stream 9 and groundwater seepage from
large wetlands on the north side of the road. Water will be allowed to pond in the created
wetland area prior to joining the Hoh River. The overall site will be graded to match the existing
elevation of the stream channel.
The mitigation site will be planted with a combination of native shrubs and trees that are
common in adjacent wetlands, including, but not limited to, the following:
Slough sedge
Skunk cabbage
Lady fern
Small-fruited bulrush
Water parsley
Red alder
Salmonberry
Western red cedar
Sitka spruce
This vegetation structure will be a significant improvement over current vegetation in Wetlands 1
and 5.
See Appendix C for wetland mitigation design plans.
5.4 Site Protection
The stream and wetland mitigation sites will be held in a permanent conservation status,
protected in perpetuity from future development. The wetland mitigation site will extend to the
legal extent of the County defined wetland buffers. The stream mitigation is part of a larger
property managed by The Nature Conservancy (TNC) for conservation purposes. This mitigation
will be retained as a part of the TNC or other managing conservation organization. The sites will
be posted with appropriate signage once planting is completed.
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Compensatory Stream Mitigation
6.1 Goals and Objectives
The goal of compensatory stream mitigation is to offset temporary and permanent aquatic habitat
effects of the proposed project. Specific objectives of this aquatic habitat mitigation include the
following:
Offset potential loss of rearing and spawning habitat for steelhead and Chinook salmon
from placement of ELJs over approximately one acre of the mainstem Hoh River; and
Offset temporary loss of stream buffer habitat, and associated impacts to functions like
detritus input, wildlife habitat, large woody debris recruitment, etc.
6.2 Site Selection
Four stream mitigation options were discussed with involved agencies, including mitigation
options at Canyon Creek crossing, Spruce Creek Bridge, Spruce Creek/Canyon Creek at MP 9.8,
and Lindner Creek Side Channel at MP 6.7. Each mitigation option considered is described in
detail in the project 404(b)(1) analysis. Ultimately, after extensive agency consultation and
numerous coordination meetings, the mitigation option that was chosen is habitat preservation at
Lindner Creek Side Channel (MP 6.7).
The extent and permanency of high-value side channel aquatic habitat has been limited in recent
years in the Upper Hoh River basin due to frequent channel migration and avulsions. During the
permitting process, WDFW identified high-value side channel aquatic habitat immediately
downstream of MP 7.8 (see Figure 2). Lindner Creek and several other creeks flow into a major
side channel of the Hoh River at this location, which formed approximately 15 years ago when
the main channel of the river migrated to the south side of the channel migration zone.
Mitigation will involve placing ELJs at the edge of the floodplain, in order to improve the side
channel aquatic habitat survivability by reducing the channel migration and avulsion risk and
encouraging the development of natural floodplain roughness. The aquatic side channel habitat
is best preserved where the floodplain vegetation is oldest and has become large and dense
enough for resisting channel migration and avulsion.
Increasing the floodplain roughness along the floodplain boundary is recommended for
protecting the side channel aquatic habitat and encouraging natural succession from an alder
forest to a conifer-dominated forest. Side channel aquatic habitat is created when the channel
migrated or avulses, leaving water-filled pools that are isolated from the main river flow. They
persist when alder and conifer trees are able to colonize in sufficient numbers and grow large
enough to create a high floodplain roughness that inhibits channel migration and avulsion. Most
of the site’s floodplain area has only sparse small willows and alder trees. The trees will not
provide enough floodplain roughness for resisting expected channel migration and avulsion. If
left to grow, the trees will likely provide adequate natural resistance. Large Woody Debris
(LWD) lining the active channel edge will deflect high velocity flow away from overbank areas,
reducing the overbank flow velocity, increasing fine-grained sediment deposition, and allowing
alder and conifer trees to grow.
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Figure 2. Proposed Aquatic Mitigation Concept – Lindner Creek Side Channel Engineered Log Jams at MP 6.7 to 7.3
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Tributaries to the Hoh River, such as Lindner Creek, and the high-water channels that cross
the wooded floodplain between the Hoh River upstream and the large side channel near MP
6.7 provide important rearing and high-water refuge habitat for fish species such as steelhead,
Chinook salmon, coho, and bull trout. Many of the high-water channels have emerged during
relatively minor flood events (e.g., less than 10-year flood flow) since the 1990s, due to the
increasingly erratic nature of the Hoh River’s migration across the river meander belt. Figure
3 shows the finger- and overflow-channels that emerge on the floodplain ‘peninsula’ during a
two-year flood event.
Lindner Creek, the large main channel, and the high-water channels on the ‘peninsula’
comprise a side channel complex. Long-term preservation of this side channel complex
would result in the following benefits to aquatic and forest resources, which are important to
stakeholder resource managers such as WDFW and the Hoh Tribe:
Preservation and maintenance of vital rearing and high-water refuge habitat for
steelhead, Chinook salmon, coho, and bull trout;
Preservation of nearby priority steelhead spawning areas, which could potentially
undergo modification during the next channel migration event;
Protection of the remaining mature forest stand south of the UHRR;
Encouragement of riparian forest development in the area surrounding the side
channel complex by preventing a future channel migration (this area provides
important forage and cover for Roosevelt elk, particularly in the spring); and
Preservation of the configuration of small overflow channels in the ‘peninsula’ area
that currently exist as small, finger- and overflow-channels, rather than having them
develop into larger channels, or join the main channel, if a river migration occurs.
In addition to the side channel benefits listed above, this mitigation project will encourage
long-term preservation of rearing and spawning habitat on the mainstem Hoh River by
increasing channel stability. Table 9 displays areas of various habitat types preserved by this
mitigation plan. These preserved habitat types, along with the extent of preserved two-year
flood channels, is shown on Figure 3.
Table 9. Habitat Types Preserved by Lindner Creek Side Channel Mitigation Project
Habitat Type Area Preserved Within Side
Channel Complex (acres)
Early successional floodplain 30.3
Early successional forest 84.6
Mature forest 49.9
Perennial wetlands/flooded backwater 22.5
Total Habitat 187.3
Total 2 year Flood Channels* 64
*Two year flood channels overlap various habitat categories
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The goal of preservation is to allow the continued succession and development of these
habitat types into the mature forest that is present on part of the site, at least on a longer time
span that the current avulsion event timeline on the Hoh River. Preservation will also
maintain the perennial wetland/flooded backwater habitat type. This habitat type includes
those areas where active flow from Lindner Creek (combined with groundwater expression
and backwater from the Hoh River downstream of the side channel) maintains inundated
habitat for most of the year. Inundated habitat is critical to support rearing and foraging for
important fish species like bull trout, coho, steelhead and Chinook salmon. The proposed
mitigation does not include “administrative” land protection mechanisms, which are
unneccesary at this property, which is currently owned by a combination of the U.S. Forest
Service, The Nature Conservancy, and the Washington DNR, and maintained for recreation
and river floodplain protection.
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Figure 3. Mitigation Site Habitat Types and Two Year Flood Channels.
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6.3 Site Design
Twenty-four ELJs will be installed at the head of flood scour channels near the active channel
edge, which will simulate the LWD that currently lines the bank in this area. They will be
installed between approximately MP 6.7 and MP 7.3 of the UHRR, west of Site C3 (Tower
Creek) and in an area and owned or managed by the U.S. Forest Service, the Nature
Conservancy, and the WDNR (see Figure 2, and Figure 2 in Appendix D). The 24 ELJs will be
installed in an arc, extending approximately 0.8 mile south and west from MP 7.3 of the UHRR,
crossing the lower section of the side channel complex (see Figure 2, and Figure 2 in Appendix
D). Each ELJ will consist of four log bundles and five root wads. The log bundles are made of
three logs, 20 to 22 feet long, 18 to 37 inches in diameter, with total log volume 110 to 150 cubic
feet, and without attached root wads. Each log bundle is wrapped with a steel chain. Because
the side channel has lower flow depths and flow velocities than the main channel of the Hoh
River, woody debris anchored to the buried cottonwood “posts” provides sufficient ballast
without dolosse. Appendix D has further details of the log bundle design. Between the ELJs, the
bank would be planted with cottonwood, bank willow, and emergent willow. In addition, the
bank would be stabilized with a mixture of gravel and cobble.
Installation of the ELJs will require limited clearing and temporary improvements to an existing
un-graded side road off the UHRR. This unimproved road, which is currently used for drift boat
access to the river, will be improved and temporarily extended beyond its existing terminus for
construction access. The extended portion will be decompacted and replanted with dense native
shrubs and trees when ELJ installation is complete. Up to one acre of clearing will be required
for the temporary 20-foot-wide access road, located approximately 200 feet from the active river
channel edge. Vegetation clearing for the newly extended access road will be limited to young
alders and willows averaging less than 10 inches diameter of breast height (dbh).
Hydraulic modeling of the Lindner Creek Side Channel mitigation project was conducted
(Appendix D) and shows that for the proposed 2-year flood, flow will be maintained to the side
channel aquatic habitat. See Figures 3 and 4 in Appendix D, which show the flows and depths,
respectively, for the 2-year flood event with this mitigation approach.
For the 100-year flood, modeling showed that flow velocity and flow depth will decrease in the
sparsely vegetated floodplain area (Figures 5, 6, 7, and 8 in Appendix D), which should
encourage natural vegetation growth. Figures 11 and 12 in Appendix D show that the presence
of the ELJs with the 100-year flood scenario will result in a decrease in flow and depth across the
floodplain by dissipating the river’s energy across the floodplain, and lessening the potential for
main channels to form. Photos 1 through 12 in Appendix D show examples of pools that form
when channels avulse and the differences in vegetation growth and ground surface over time,
after avulsion.
The model also showed that the flow depths and velocities in the active channel and along the
floodplain limit for the model 100-year proposed conditions will not be significantly different
than existing conditions. The ELJs are intended to inhibit bank erosion and channel avulsion
along the wooded floodplain. Flooding or bank erosion impacts to private property adjacent to
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the project site above current levels was not shown in the modeling to noticeably increase due to
the ELJ placement. Impacts on the river and stream processes are discussed in more detail in
Appendix D.
Appendix D includes Channel Habitat Preservation (Sheets 1-4) and Channel Plug Details,
which display and explain details about the placement, configuration, and construction of the
ELJs and the temporary construction access road.
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Mitigation Performance Standards
The proposed mitigation site will be monitored for five years to demonstrate that the intended
goals and objectives are established. Performance measures and performance standards describe
specific on-site characteristics that indicate a function is being provided. Performance measures
are used to guide management of the mitigation site. Performance standards are used to evaluate
compliance with regulatory permits in the final year of monitoring. Contingency plans describe
what actions can be taken to correct site deficiencies.
The Project Partners use the adaptive management process to improve mitigation success.
Adaptive management involves learning from monitoring and implementing management
activities, such as implementing parts of the site management or contingency plans. Information
from monitoring is used to direct subsequent site management activities. As part of the adaptive
management process, mid-course corrections may necessitate a change in vision for the site if
nature takes its course and things turn out differently than planned. A change in vision may
require renegotiation with regulators for a new set of performance standards.
7.1 Performance Standards
The performance standards described below provide benchmarks for measuring achievement of
the goals and objectives of the mitigation sites. Mitigation activities are intended to meet these
performance standards within a specified time frame. The mitigation site will be deemed
successful after achieving the approved performance standards described below and in Table 12.
A baseline evaluation should be conducted and will represent a baseline of conditions after
mitigation is implemented (i.e. construction is competed). Results of annual monitoring will be
compared with these standards.
The following performance standards are based on conditions at and around the proposed
mitigation site and project sites. Methods to monitor each performance standard are described in
general terms.
Performance Standard 1 - Wetland Hydrology
Performance Standard (Years 1, 2, 3, 4, and 5)
Within the wetland creation area at Site C1, the soil will be saturated, or a water table will be
present, within 12 inches of the soil surface for at least 30 consecutive days during the growing
season in years when rainfall meets or exceeds the 30-year precipitation average.
Performance Standard 2 - Wetland Plant Cover
Performance Standard (Year-1)
One hundred percent survival of all installed native trees and shrubs one-year post installation.
At least two species of native tree and three species of native shrubs will be present in the
mitigation area.
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Performance Standard (Year-2)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 20
percent in the mitigation area. At least two species of native trees and three species of native
shrubs will be present.
Performance Standard (Year-3)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 30
percent in the mitigation area. At least two species of native trees and three species of native
shrubs will be present.
Performance Standard (Year-4)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 40
percent in the mitigation area. At least two species of native trees and three species of native
shrubs will be present.
Performance Standard (Year-5)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 60
percent in the mitigation area. At least two species of native trees and three species of native
shrubs will be present.
Table 10. Wetland Revegetation Aerial Cover Standards
Year of Monitoring Percent Coverage
Year-2 20 percent
Year-3 30 percent
Year-4 40 percent
Year-5 60 percent
Performance Standard 3 - Invasive Species
Performance Measure (Years 1, 2, 3, 4, and 5)
Washington State-listed or county-listed noxious weeds observed in any area of the mitigation
site must be eradicated. (Eradicating weeds means getting rid of the plants altogether, including
plant roots). All occurrences shall be reported to the site manager. Class B and C weed species
designated for mandatory control in Jefferson County include the following:
Yellow archangel (B) (Lamiastrum galeobdolon)
Scotch broom (B) (Cytisus scoparius)
Butterflybush (B) (Buddleja davidii)
Reed canarygrass (C) (Phalaris arundinacea)
Common fennel (B) (Foeniculum vulgare)
Knotweeds (B) (Polygonum spp.) (non‐native)
Poison hemlock (B) (Conium maculatum)
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Tansy ragwort (B) (Senecio jacobaea)
Perennial sowthistle (C) (Sonchus arvensis)
Common teasel (C) (Dipsacus fullonum)
Ravenna grass (C) (Saccharum ravennae)
Designated noxious weeds or other species of concern will include less than 10% cover in all
intended wetland zones. Other weeds of concern include Himalayan blackberry, herb Robert,
English ivy, and Canada thistle.
Performance Standard 4 - Movement of ELJ components
Individual dolos/timber units in the ELJ will not move significantly outside the design footprint,
particularly in such a way as to present a danger to members of the public that may be boating on
the river. Visual inspection of the ELJs will be conducted on an annual basis to determine
compliance with this performance standard. Using photo points of ELJs from GPS fixed
locations, Jefferson County and WFLHD will conduct annual monitoring and reporting to
monitor for movement and to confirm that the ELJs and their constituent pieces have not shifted
in such a way to present a danger to water users. In the event an individual dolo breaks away
from the ELJ and rotates out into the river such that it potentially becomes a navigation hazard,
the dolo will be retrieved and attached back to the ELJ mass. Monitoring may be conducted
using drone technology.
Performance Standard 5 – ELJ Wood Recruitment
Performance Measure (Years 1, 2, 3, 4, and 5)
ELJs are having a net positive effect for wood recruitment (more wood is being recruited than is
being lost from the structure). WFLHD will conduct monitoring in Years 1, 3 and 5 to determine
how the ELJs are functioning to recruit and maintain large woody debris. Visual inspection will
be conducted from fixed observation points on the upstream ends of the ELJs. The width and
height of the racking material accumulated at each of the in-channel ELJs will be measured and
recorded, noting newly recruited pieces greater than 12 inches in diameter and 10 feet in length.
Performance Standard 6 – Bank Restoration Area Vegetation Criteria
Following installation of ELJs, the bank between the Upper Hoh River Road and the river will be
revegetated using a combination of pole plantings and willow bundles.
Performance Standard (Year-1)
One hundred percent survival of all installed native trees and shrubs one-year post installation.
Performance Standard (Year-2)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 20
percent in the mitigation area.
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Performance Standard (Year-3)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 30
percent in the mitigation area.
Performance Standard (Year-4)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 40
percent in the mitigation area.
Performance Standard (Year-5)
Cover of native wetland trees and shrubs combined (planted and volunteer) will be at least 60
percent in the bank restoration area.
Table 11. Bank Restoration Aerial Cover Standards
Year of Monitoring Percent Coverage
Year-2 20 percent
Year-3 30 percent
Year-4 40 percent
Year-5 60 percent
Performance Standard 7 – Monitoring Streambed Composition
ELJs will lead to a net gain in finer grain materials in nearshore areas due to reduced scour.
Current streambed materials are generally characterized by large cobble and boulders due to high
scour in the thalweg along the toe of the bank. Monitoring will include photo-point monitoring
of specific locations. Monitoring would likely occur at representative locations in the gaps that
will remain between ELJs. Photographs will be taken from the same vantage point at as-built
stage and then Year 1, Year 3 and Year 5.
Performance Standard 8 – Mitigation Site Channel Plug Movement and
Vegetation Establishment
Channel plugs at Lindner Creek mitigation site will remain intact and structurally functional
during monitoring period. Visual inspection will be conducted to document that key deflector
pieces remain anchored, and that restoration plantings downstream of structures and within the
structures are growing.
Table 12. Proposed Performance Standards for Wetland and Stream Mitigation
Performance Standards Monitoring Methods Monitoring
Intervals
1. Wetland hydrologic characteristics present Inundation at the soil surface or at least saturation
within 12 inches of soil surface at least 30
consecutive days during the growing season, in
years when rainfall meets or exceeds the 30-year
precipitation average.
Year 5
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Performance Standards Monitoring Methods Monitoring
Intervals
2. Wetland Plant Cover. Annual monitoring for
cover of all installed plants. Volunteer native
plants in mitigation area will be included.
Shrub and tree plant cover: 100%
survival in Year 1
Shrub and tree plant cover: 30%
by Year 3, 50% by Year 5.
At least 3 native herbaceous
plants shall be present in the
mitigation area
Percent cover of installed plants shall be measured
by an approved monitoring technique such as line
intercept method and/or sample plots. Year 1 is
measured as percent survival.
Tally species in restoration areas
Years 3, and 5
Years 1, 3 and 5
Years 1, 3 and 5
3. No more than 10% cover of non-native or
other invasives, e.g., Himalayan blackberry,
evergreen blackberry, reed canarygrass, scots
broom, English ivy, morning glory, etc.
Percent cover of non-native or invasive species
shall be measured by an approved monitoring
technique such as line intercept method and/or
sample plots.
Years 1, 3, and 5
4. Movement of ELJ Components Visual inspection of the ELJs will be conducted on
an annual basis.
All years.
5. ELJ wood recruitment Visual inspection will be conducted from fixed
observation points on the upstream ends of the
ELJs.
Years 1, 3 and 5
6. Bank restoration vegetation monitoring
Performance Standard (Year-1)
100% survival of all installed native
trees and shrubs
Performance Standard (Year-3)
30% cover of native wetland trees and
shrubs combined (planted and
volunteer)
Performance Standard (Year-5)
60% over of native wetland trees and
shrubs combined (planted and
volunteer)
Percent cover of installed plants shall be measured
by an approved monitoring technique such as line
intercept method and/or sample plots. Year 1 is
measured as percent survival.
Years 1, 3, and 5
7. Monitoring streambed composition Monitoring method to be determined in consultation
with regulatory agencies, but could include visual
assessment at low water, substrate sampling, etc.
Years 1, 3 and 5
8. Mitigation Side Channel Plug Movement and
Vegetation Establishment
Visual inspection of the channel plugs will be
conducted on an annual basis from fixed photo
points to document structural integrity and
vegetative regeneration from cottonwood poles..
All years.
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Existing upland vegetation around the proposed mitigation area will be left intact with existing
vegetation. No buffer vegetation performance criteria are proposed.
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Monitoring and Maintenance
The wetland and stream mitigation sites will be monitored for a minimum of five years. Formal
monitoring procedures will be performed in years one, two, three, four, and five after initial
acceptance of the mitigation construction. The site should be evaluated for baseline conditions
the summer following plant installation to evaluate survival rates and document the presence of
non-native invasive species. A baseline monitoring report should document post construction
conditions and characteristics. As built, baseline and monitoring reports will be submitted to the
USACE, Ecology, WDFW, and Jefferson County for review and comment. Monitoring reports
will be completed by December of each monitoring year. Mitigation success will be measured
by the attainment of performance standards.
The actual monitoring methods used to monitor the site will be determined and documented in
annual monitoring reports.
8.1 Contingency Plan
It is anticipated that the mitigation goals will be accomplished with the construction and
installation of the mitigation design as shown on the grading and planting plans. Contingency
actions, however, may be needed to correct unforeseen problems. Contingency revisions
typically require coordination with the permitting agencies. These coordinations will be the
responsibility of Jefferson County, as the applicant land management agency.
8.2 Hydrology
Hydrologic problems occurring on a wetland mitigation site are typically the result of either
insufficient water or excessive water. Insufficient water can occur seasonally during drought
conditions or can be a long-term problem. Long-term problems can be the result of altered
surface water flows for mitigation sites reliant on surface water flows as the primary source of
hydrology. For groundwater driven mitigation sites, typical long-term hydrologic problems that
result in either excessive or insufficient hydrology can occur from a design based on insufficient
groundwater data, the establishment of incorrect final grade elevations, or an unperceived soil
condition that alters groundwater flows. Hydrologic contingency measures will be implemented
based on observed conditions or monitoring data. Steps to address insufficient or excessive
hydrology are:
Clearly identify the source of the problem.
Consult with the mitigation design team and the resource agencies to determine an
appropriate course of action.
Adjust elevations or install water management structures to achieve appropriate
hydrologic conditions.
8.3 Vegetation
Problems related to vegetation include plant mortality, and poor growth resulting in low plant
cover. These problems could be the result of insufficient site management, particularly watering
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in the first few growing seasons, animal browse, competition from invasive species, incorrect
plant selection, altered site conditions, and vandalism. Contingencies for plant mortality and
poor plant cover may include:
Plant replacement – Additional planting may be required to meet plant survival and plant
cover requirements. Plant species will be evaluated in relation to site conditions to
determine if plant substitutions will be required.
Weed control – Control of non-native invasive species may be required to meet survival
and plant cover requirements. Weed control methods could include mechanical or hand
control, mulching, or herbicide application.
Review and revise performance criteria with permitting agency agreement.
8.4 Structure Movement
Movement of constituent elements of ELJs and mitigation site channel plugs will be monitored
by visual inspection from fixed points with known GPS locations. Visual inspection may be
conducted by sight or may be conducted using a remotely-controlled drone or similar method.
All visual inspections will be documented with photographs or video footage. Movement of key
elements will be documented and reported to the Corps, WDFW, Ecology, and others as
appropriate.
8.5 Site Management
The applicant (Jefferson County) or its agent will manage the site annually for the first 5 years.
Site management activities shall include noxious weed control and may include mulching,
fertilizing, supplemental watering, browse control, maintaining access, correcting erosion or
sedimentation problems, or litter pickup. The first year of plant establishment includes
supplemental water and care of all replacement plants installed during the first year.
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References
Abbe, T. 2017. Personal communication from Tim Abbe, Natural Systems Design, with Gray
Rand, Biologist, David Evans and Associates, Inc., October 6, 2017.
Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of Wetlands and Deepwater
Habitats of the United States. Office of Biological Services, Fish and Wildlife Service, U.S. Dept. of
the Interior, FWS/OBS-79/31.
David Evans and Associates, Inc. (DEA). 2015a. Biological Survey Report. Upper Hoh River
Road Project. April 2015.
———. 2015b. Wetland Delineation Report. Upper Hoh River Road Project. July 2015.
———. 2016. Upper Hoh River Road Project Biological Assessment. March 2016.
———. 2017. Upper Hoh River Road Project Wetland Addendum. June 2017.
Hruby, T. 2014. Washington State Wetland Rating System for Western Washington: 2014 Update.
Publication No. 14-06-029. Olympia, Washington: Washington Department of Ecology.
Johnson, D.H., and T.A. O’Neil. 2000. Wildlife-Habitat Relationships in Oregon and
Washington. Oregon St0, ate University Press. Corvallis, Oregon.
McHenry, M., J. Lichatowich, and R. Kowalski-Hagaman. 1996. Status of pacific salmon and
their habitats on the Olympic Peninsula, Washington. Report to the Lower Elwha S’Klallam
Tribe, Port Angeles, Washington.
McHenry, M., G. Pess, T. Abbe, H. Coe, J. Goldsmith, M. Liermann, R. McCoy, S. Morley, and
R. Peters. 2007. The physical and biological effects of engineered log jams (ELJs) in the
Elwha River, Washington. Elwha River Engineered Log jam Monitoring Report. April 1,
2007.
Natural Resource Conservation Service. 2016. Web Soil Survey. Soil characteristics queried by
G. Rand on January 28, 2016 . http://websoilsurvey.nrcs.usda.gov/app/.
Phinney, D., and Bucknell. 1975. A catalog of Washington streams and salmon utilization. Vol.
2 Coastal Region. Washington Department of Fisheries, Olympia, Washington.
U.S. Fish and Wildlife Service. 2017. Biological Opinion for Upper Hoh River Road Bank
Stabilization Project. Consultation #01EWFW00-2016-F-0643. June 1, 2017.
Western Federal Lands Highway Division (WFLHD). 2017. Finding of No Significant Impact
(FONSI) and Final Environmental Assessment for the Upper Hoh River Road Project. June
2017.
Washington Department of Fish and Wildlife (WDFW). 1998. Salmonid Stock Inventory.
Appendix Bull Trout and Dolly Varden. Olympia, Washington 437 pp.
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APPENDIX A
WETLAND AND STREAM BUFFER GIS MAP SET
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Upper Hoh River Road Mitigation Report
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DigitalGlobe, GeoEye, Earthstar Geographics,
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Upper Hoh River Road Mitigation Report
Figure 1b
Stream and Wetland Buffers
Wetland Delineation Features
Wetland
Wetland outside study area
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D D D D D
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Pond
Culvert
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Creek (USGS NHD)
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DigitalGlobe, GeoEye, Earthstar Geographics,
CNES/Airbus DS, USDA, USGS, AeroGRID,
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Upper Hoh River Road Mitigation Report
Figure 1c
Stream and Wetland Buffers
Wetland Delineation Features
Wetland
Wetland outside study area
Wetland/OHWM outside study area
D D D D D
D D D D D
D D D D D Wetland
Ordinary High Water Mark (OHWM)
Stream/OHWM
Ditch - OHWM
Ditch - Wetland
Pond
Culvert
""Culvert
!!.Upland Ditch End
Stream Buffer
Wetland Buffer
Engineered Log Jam (ELJ)
Existing Road
New Road
Creek (USGS NHD)
Riprap ´0 350 700Feet
D D D D D
D D D D D
D D D D D
D D D D
D D D D
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D D D D D D D D D D D D D D
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D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
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Stream SC4-Bextends outside study area
Wetland WC4-Cextends outside study areaWetland WC4-Aextends outside study area
Ditch DC4-B
C1
C2
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C5
Upper Hoh Rd
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DigitalGlobe, GeoEye, Earthstar Geographics,
CNES/Airbus DS, USDA, USGS, AeroGRID,
IGN, and the GIS User Community
Upper Hoh River Road Mitigation Report
Figure 1d
Stream and Wetland Buffers
Wetland Delineation Features
Wetland
Wetland outside study area
Wetland/OHWM outside study area
D D D D D
D D D D D
D D D D D Wetland
Ordinary High Water Mark (OHWM)
Stream/OHWM
Ditch - OHWM
Ditch - Wetland
Pond
Culvert
""Culvert
!!.Upland Ditch End
Stream Buffer
Wetland Buffer
Engineered Log Jam (ELJ)
Existing Road
New Road
Creek (USGS NHD)
Riprap ´0 200 400Feet
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RoadtoQu
arry
Upper Hoh Rd
Beaver Pond
C1
C2
C3 & C4
Lindner Ck
Mitigation Site
C5
Upper Hoh Rd
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Service Layer Credits: Source: Esri,
DigitalGlobe, GeoEye, Earthstar Geographics,
CNES/Airbus DS, USDA, USGS, AeroGRID,
IGN, and the GIS User Community
Upper Hoh River Road Mitigation Report
Figure 1e
Stream and Wetland Buffers
Wetland Delineation Features
Wetland
Wetland outside study area
Wetland/OHWM outside study area
D D D D D
D D D D D
D D D D D Wetland
Ordinary High Water Mark (OHWM)
Stream/OHWM
Ditch - OHWM
Ditch - Wetland
Pond
Culvert
""Culvert
!!.Upland Ditch End
Stream Buffer
Wetland Buffer
Engineered Log Jam (ELJ)
Existing Road
New Road
Creek (USGS NHD)
Riprap ´0 150 300Feet
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APPENDIX B
WETLAND AND STREAM IMPACT SHEETS
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APPENDIX C
WETLAND MITIGATION DESIGN PLANS
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APPENDIX D
UPPER HOH RIVER ROAD BANK STABILIZATION
HABITAT PRESERVATION MITIGATION
DRAFT HYDRAULICS REPORT
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Memorandum
Western Federal Lands Highway Division
610 E. Fifth Street
Vancouver, WA 98661-3801
UPPER HOH RIVER ROAD BANK STABILIZATION
HABITAT PRESERVATION MITIGATION
DRAFT - HYDRAULICS REPORT
To: Kirk Loftsgaarden, WFLHD Project Manager
From: Sven Leon, P.E., WFLHD Hydraulics Engineer
Date: September 7, 2017
Project: Upper Hoh River Road Bank Stabilization – WA JEFF 91420(1)
Background
One of the major roads leading into Olympic National Park (Park), Washington, is the Upper Hoh Road
located off of US Highway 101 on the far western side of Olympic National Park. The road is the only
entryway into the Hoh Rain Forest an d the Park R ain Forest Visitor Center. The Upper Hoh Road is
approximately 18 miles in length. Jefferson County (County) owns and maintains the portion of the road
from the junction with US 101 to the OLYM boundary, approximately 12 miles. The Par k owns and
maintains the remaining 6 miles.
Management of the road to provide constant safe access to residents, business, and Park visitors, has
become increasingly difficult over the past 20 years. Portions of the Upper Hoh Road are located within
and adjacent to the Hoh River’ s channel migration zone. The location combined with the increasing
frequency and severity of winter storm events (most recently in 2004, 2006, 2007, and 2009) has resulted
in an increasing number of roadway washouts which either completely prevents access or creates unsafe
roadway conditions for visitors, Park personnel, and local residents. In some cases the damage resulted in
road closures, allowing no access to the Hoh Rain For est and the Park’s Hoh Rain Forest Visitor Center
for weeks at a time (and many months in 1996). R esponse to these storm events and maintenance of the
road in its current location has resulted in a continuing outlay of limited maintenance funds to m aintain
safe access and t o mitigate for adverse im pacts those actions have on threatened and endangered fish
species.
In 1998 the Hoh Tribe requested the U.S. Bureau of Reclamation (BOR) prepare a geo morphic study to
better understand the exis ting and hist orical channel processes on the Hoh River, and how hum an
activities may have impacted those processes. The study, entitled Geomorphic Assessment of Hoh River
in Washington State, published in 2004, identifies ar eas of risk for further lateral erosion in the historic
channel migration zone and provided some general management considerations to deal with these areas of
concern. T he report re commended more detailed da ta collection and analysis for developing a
management approach at any specific particular location.
In 2009, the Park published a report entitled Olympic National Park, Road Hazards and Solutions Report.
This report examined two methods to address roadwa y locations, vulnerable to damage from severe storm
events, within the Park. The two different methods evaluated included a site-specific approach versus a
natural systems engineering approach. The report concluded that a natural systems engineering approach
would likely provide a more long-term fix while improving the ecological conditions. Six sites along the
Upper Hoh River Road within the Park were included in this evaluation.
2
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
September 2013 Western Federal Lands Highwa y Division (WFLHD) completed for the County an
Upper Hoh Road Bank Failure Risk Reduction Study. The Study developed a com prehensive road
management strategy for mitigating high risk s ites along the Upper Hoh Road. WFLHD used the
information from the two earlier reports and from site visits for developing the road management strategy.
The WFLHD study included the prioritization of s ites (regardless of management jurisdictions),
development of a range of treatment options for each site, and initial cost estimates for each option
including construction, P reliminary Engineering (PE), Construction Engine ering (CE), and ROW.
Treatment options developed represente d a full range of types, costs, and environm ental impacts. All
treatment options where expected to provide a similar level of road failure risk reduction.
Selection and refinement of treatment options were completed March 2016 for two sites, road mile post
(MP) 3.7 to 4.1 (MP 4.0 Si te) and MP 7.7 to 7.9 (MP 7.8 Site) (Fi g. 1). The County selected these sites
for the project as having the highest priority for needing bank stabilization.
Two bank stabilization design options were evaluated;
Stream barbs with mitigation logs.
Wood buffer with dolosse ballast.
MP 4.0 Site has 2,570 feet of proposed bank stabilization. MP 7.8 Site has 500 feet of proposed bank
stabilization. Each design options was evaluated on controlling bank erosion, cost, disrupting existing
habitat, reducing flow velocity, preserving stream processes, and minimizing private property impacts.
Based on the hydraulic analysis and cost estimates, installation of wood buffer with dol osse ballast was
recommended for both sites. The desi gn approach is the least expensive for effectively controlling bank
erosion. The wood buffer can acco mmodate a greater range of active flow ch annel migration and flow
impingement angles. The minimal channel bed ex cavation and ability to place the wood and dollose
directly into flowing water is least disruptive to environment. The approach does not appear to noticeably
increase flooding or bank erosion on private property adjacent to the project sites. It does not appear to
negatively affect stream processes. The wood buffe r provides the greatest flow velocity reduction and
habitat complexity. The approach is most adaptable to changing field conditions.
WFLHD is currently developing final designs and construction contract documents for the wood buffer
with dolosse ballast bank stabiliza tion. In the environm ental permit application phase, the resource
agencies identified placing the wood bu ffer in the rive r channel as causing negative im pacts to fish and
aquatic habitat.
Washington Department of Fish and Wildlife (WDFW) has identified high- value backchannel aquatic
habitat immediately downstream of MP 7.8 site (Fig. 2). Frequent channel migration and avulsions limits
the extent and permanency of high-value backchannel aquatic habitat. Reco mmendations for improving
the backchannel aquatic habitat survivabilit y by re ducing the channel m igration and avulsion risk and
encouraging natural floodplain roughness to develo p are presented. The wor k is proposed as mitigation
for the project’s environmental impacts.
Recommendations
Increasing the floodplain roughness along the floodplain boundary is recommended for protecting the
backchannel aquatic habitat and enc ouraging future tree growth. Backch annel aquatic habitat is created
when the channel migrates or avulses, leaving water-filled pools that are isolated from the main river flow
(Photos 1, 2, 3, 4, and 5). They persist when alder and conifer trees c an colonize in sufficient num bers
3
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
and grow large enough to create a high floodplain roughness that inhibits channel migration and avulsion
(Photos 6 and 7). Most of the site floodplain area ha s only sparse small willows and alder trees (Photos 8
and 9). The trees will not provide enough floodplain roughness for resisting expected channel migration
and avulsion. If left to grow, the tree s will likel y provide adequate natural r esistance. Large woody
debris lining the active channel edge deflects high velocity flow away from overbank areas, reducing the
overbank flow velocity, increasing fine grained sedim ent deposition, and allowing alder and conifer trees
to grow (Photos 10 and 11). To simulate the large woody debris that lines the bank, i nstall twenty-four
wood plugs at the head of flood scour channels near the active channel edge ( Sheets H.1, H.2, H.3, and
H.4).
Each wood plug consists of four log bundles and five rootwads (Sheet H.5). The log bundles are made of
three logs, 20 to 22 feet long, 18 t o 37 inches in di ameter, total log volume 110 to 150 ft3, and without
attached rootwads. Each log bundle is wrapped with a steel chain. Each rootwad is 20 to 22 feet long, 18
to 37 inches in diameter, and has an attached root wad. The rootwads will be placed on top of the log
bundles with rootwad in the upstream direction. Each channel plu g will have 12 log piles and 8
Cottonwood boles evenly spaced along the downstream side of the log bundl es for increasing slippage
resistance. Log piles are 20 feet long, 12 to 18 inches in dimeter, and 15 feet embedment. Set the log pile
top 5 feet above the floodplain ground surface (100-year flood flow depth). Cottonwood boles are 10 feet
long, 12 to 18 inches in dimeter, and 5 feet embedment. Embed the log piles and cottonwood boles with a
track hoe-mounted vibratory hammer. Each channel plug is covered with coarse wood y debris; even
mixture of branches, limbs, trunks, and vegetation.
Initial placement of the log bundles and logs with root wads should be as shown on Sheet H.5.
Orientation is critical for deflecting fl ow away from the overbank area and achieving channel pl ug
stability. Care must be taken to pack bundles as de nsely as possible and to place the bottoms in close
contact with the floodplain ground surface for effectively controlling erosion under the bundles.
Do not remove or modify the existing vegetation and large woody debris lining the active channel edge
(Photo 12). A 20 feet wide tem porary construction access road is proposed c onstructed approximately
200 feet fro m the active river chann el edge for mini mizing disturbance of the vegetated floo dplain.
Install the channel plugs on the side of the road n earest the river. Plant the tem porary access road with
Douglas fir trees and cott onwood/willow poles. Do not disturb the existing vegetation between th e
temporary construction access road and active channel edge.
Stream Processes Impacts
The wood channel plugs are not intended to prevent water from flowing from the river to the backchannel
aquatic habitat. They are also not intended to manipulate the river flow in a way that unnaturally deflects
the river flow towards a bank. The wood channel plugs increase roughness at strategic locations along the
edge of the wooded floodplain. HE CRAS 5.0 mode ling results for the pr oposed 2-year flood fl ow
velocities and flow depths were used to help define the strategic locations at the head of flood scou r
channels (Fig. 3 and 4). The results i ndicate the fl ow will be maintained to the aquatic backchannel
aquatic habitat.
Modeling results for the 100-year flood flow velocities and flow depths are presented in Figures 5, 6, 7,
and 8. A velocity profile plot 15 feet behind the wood channel plug alignment shows a decrease in flow
velocity behind each channel plug and an increase between the channel plugs (Fig. 9). Higher flow
velocities along the wood channel plugs sides will sc our the floodplain surface materials, creating new
flood scour channels. Scoured material will be de posited on the floodplain gravel bars, building their
elevation. A depth profile plot shows only a 0.2 to 1 foot decrease in flow depth behind the channel plugs
(Fig. 10). Close-up plots are shown in Figures 11 and 12. They show how the overbank flow is deflected
4
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
around the wood channel plugs and where the flow velocity increases occur. The results i ndicate flow
velocity and flow depth is reduced in the sparsely vegetated floodplain area. This should help encourage
natural vegetation growth.
A 100-year flood flow velocity profile plot along the right (looking downstream) bank line imm ediately
in front of the wood channel plugs shows an incr ease in less than 0.5 feet/sec for the proposed conditions
(Fig. 13). A 100- year flood flow depth profile plo t shows an increase in less than 0.2 feet for the
proposed conditions (Fig. 14). The results indicate fl ow depths and velocities in the active channel an d
along the floodplain lim it for the modeled proposed c onditions will not be significantl y different from
existing conditions.
Bank erosion occurs when the active flow channel migr ates to the valley sides and directs flow at sharp
angles against erodible banks. Woody debris and gravel bars affect ch annel migration and flow
impingement angles. The wood channe l plugs are not expected to restrict sediment and wood y debris
transport and recruitment relative to existing conditions. Mid-channel and fl oodplain sediment deposition
is not expected to be noticeably different than curre nt trends. Current natural active channel migration
and bank erosion levels beyond the proposed habitat preservation is expected to continue.
The wood channel plugs are intended to inhibit bank erosion and channe l avulsion along the wooded
floodplain, not prevent them. Aggressive bank m igration or full channel avulsion is still possible when
enough sediment or large woody debris is deposited in the active channel to deflect the river flow towards
the habitat preservation area. Entangling enough woody debris on the ch annel plugs to encroach into the
active channel is possible. The channel plug co uld become large enough to deflect flow towards the left
bank, significantly increasing the bank erosion.
Installing the wood channel plugs requires minor excavation into the floodplain gravel bar surface. No
flow diversion or work area dewatering is needed.ve. Turbidity release is expected to be limited in extent
and duration. Ac cess for construction is assumed down forest road and te mporary construction access
road.
Private Property Impacts
A 100-year flood flow vel ocity profile plot along t he left bank line shows an increase in less than 0.2
feet/sec for the proposed conditions (Fig. 15). A 100-year flood flow depth profile plot shows an increase
in less than 0.2 feet for the proposed conditi ons (Fig. 14). Based on the HECRAS modeling, the wood
channel plugs are not ex pected to noticeably increase flooding or bank er osion on private property
adjacent to the project site above current levels. Woody debris entangling on the channel plugs and
encroaching into the active channel could deflect fl ow towards the left bank, significantly increasing the
bank erosion.
Site Conditions
The river is braided with dramatically shifting active flow channels. Bank erosion is observed at all bank
areas not protected by riprap revetmen ts, heavy vegetation, or boulder lag deposits. The bank erosion is
caused by mid-channel sediment deposits and woody debris shifting across the braid plain and redirecting
flood flows at unstable bank areas. Erosion is severest where flow is directed at sharp angles against an
erodible bank. Large woody debris appears to play a significant role in deflecting and redir ecting flood
flows. Cobbles and small boulders naturally armoring the toe and large trees growing in the stream bank
inhibits the bank erosion.
5
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
The habitat preservation site is 2,000 feet downs tream from the MP 7.8 Bank Stabilization Site and
occupies a wooded fl oodplain area on the inside ba nk of a ri ver bend (Fig. 2). Based on historical
satellite imagery (Google Earth, 1994, 2006, 2009, 2011, 2013, and 2016), the area has experienced
aggressive channel avulsions. The latest avulsi on occurred between 2006 an d 2009 when a relatively
consistent down-valley channel translation abruptly avulsed into a new channel, leaving th e old channel
as new aquatic backchannel habitat (Photos 1, 2, 3, 4, and 5). The active channel near the habitat
preservation site has remained relatively unchanged since the avulsion.
The aquatic backchannel habitat is be st preserved where the floodplain vegetation is ol dest and ha s
become large and densely-spaced enough for resisting channel migration and avulsion (Photos 6 and 7).
Large woody debris lining the bank also help deflect overbank flow from floodplain area, slowing flow
velocities and allowing sediment deposition and abundant large diameter tree growth (Photos 10 and 11).
Areas with smaller, sparsely spaced vegetation is at greater risk of experiencing aggressive bank erosion
and a channel avulsion (Photos 8 and 9).
An erosion resistant poorly consolidated alluvium terrace deposit limits river bend migration to the north.
The terrace deposit represents the HCMZ right bou ndary. Width of the HCMZ is approximately 2,500
feet. The Upper Hoh River Road embankment coincides with the HCMZ right boundary. Upstream the
active channel width is 300 to 600 feet. Downstream widt h is 500 to 700 feet. At the site the width is
300 to 500 feet. Sand, gravel, and small boulders comprise the stream bed material. Gradation analysis
indicates the bed material ranges from sands to 12 inches with a D50 of 7 inches.
Analysis
Analysis completed by WFLHD includes hydrologic and two-dimensional hydraulic modeling.
Hydrology
The Hoh River drains the western slope of the Olympic Mountains. The river originates on the slopes
surrounding Mount Olympus and adjacent mountain peaks at an elevation of 7,800 feet (NAVD88) and
flows approximately 41 miles through relatively -wide, moderately high-relief, glacial valley s before
discharging to the Pacific Ocean. Elevations at the MP 7.8 project site and the habitat preservation site is
approximately 300 feet. MP 7.8 site is at river mile 24.6 to 24.9. The habitat pr eservation site is at river
mile 24.2 to 24.4.
MP 7.8 site and the habitat preservation site drainage area, including Tower Creek, was determined using
USGS StreamStats version 3.0 to be approximately 210.0 mi2. Approximately 70 percent of the
watershed is heavily timbered and 20 percent is exposed bedrock. Four small glaciers, White, Blue, Hoh,
and Hubert, are found in the higher elevations and occupy approximately 7 mi2 (3 percent) of the drainage
area. Only small lakes ar e present. Mean annual precipitation reported by USGS StreamStats is 168
inches. The watershed li es mostly within the Ol ympic National Park and Oly mpic National Forest.
Development is sparse, primarily light rural residential. No diversions for irrigation occur upstream.
The USGS maintains a stream gage station (12041200) on Hoh River, near the State Highway 101
Bridge, river mile 15.4. The gage has 54 years of record, beginning 1961 and ending 2014. Hydrology
for the gage station is presented in Magnitude and Frequency of Floods in Washington: U.S. Geological
Survey Water-Resources Investigations Report 97-4277 (Sumioka, S.S., Kresch, D.L., and Kasnick, K.D.,
1998). Annual peak stream flow for the gage station is presented in Figure XX. The gage station has not
experienced floods greater than the 50-year event. Largest floods of record occurred in 2004 (62,100 cfs)
and 2007 (60,700 cfs). Both were approximately equal to the 25-year flood event.
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Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
Peak flood discharges were estimated with the wei ghting equation in USGS WRIR 97-4277 for ungagged
sites on gaged streams. Peak discharges for the ung aged sites were estimated using USGS StreamStats
regression equations. The regres sion equation estimate s were then improved by weighting with the
weighted estimates for the USGS 1204120 0 gage st ation (Table 2, USGS WRIR 97-4277). Peak
discharge estimates are presented in Table 1.
Maritime weather dominates. Storms and moderate to heavy precipitation occurs year round. Storms are
more frequent and precipit ation is heavier September through January. September through November
have the heaviest recorded rainfall. Snow occurs frequently during winter months, but melts after a few
days. Lowest flows occur in Februar y, March, Apr il, July, and August. Winter season snowfall ranges
from 10 to 30 inches in the lower elevations and between 250 to 500 inches in the higher mountains. In
the lower elevations, snow melts rather quickly and depths seldom exceed 6 to 15 inches. In midwinter,
the snowline is between 1,500 and 3,000 feet above sea level. The higher ridges are covered with snow
from November until June.
Hydraulic Modeling
Water surface elevations and flow velocities wer e estimated using the H ydrologic Engineering Center
River Analysis System HEC-RAS 5.0, a co mputer program that performs two-dimensional unsteady
steady flow calculations. Two–dimensional flow models provide a more thorough understanding of how
the design options effect water surface elevations and flow velocities.
WFLHD developed HEC-RAS 5.0 flow m odels for the existing conditions and proposed design options.
LIDAR terrain data was o btained from Puget S ound LIDAR Consortium. The LIDAR mapping was
surveyed April 14 and 21, 2012. The LIDAR data does not have topography of the channel bed beneath
the water surface and cannot be used directly to accurately model flow conditions. WFLHD surveyed
topography and cross sections of the river channel at the MP 7.8 bank stabilization site. Terrain data was
developed for the existing condition m odels by merging the LIDAR terrain data with the surve yed river
cross sections and gr ound topography data. Each channel pl ug was placed in the m odel at design
locations. The blocking effect of the channel plugs were simulated by assigning a Manning’s Roughness
Coefficient to the channel plug areas of 10.
Meshes with 10 feet by 10 feet grid spacing encompassing the flow areas were generated for each model.
Floodplains and areas with higher flow roughness were delineated on the m eshes from aerial imagery.
Floods occurring 2004 and 2006 approximately equaled the 25-year event. Existing condition model was
calibrated by adjusting the Manning’s Roughness Coefficients until the 25-year flood flow water surfaces
approximately equaled observed high water marks and debris limits. Manning’s Roughness Coefficient
of 0.040 was selected for the main channel 2D flow areas. Manning’s Roughness Coefficient of 0.15 was
selected for the floodplain areas. Figure 17 shows the two-dimensional model setup. Normal flow depth
with 0.01 feet/feet friction slope was set for the downstream boundary condition. A 10-hour duration, 1-
minute interval hydrograph, stepping through the 2, 10, 25, 50, and 100-year flood flows was used for the
upstream boundary condition. Each model uses the full momentum equation set, 15 second computation
interval, and 2-hour initial condition time.
Predicted 2-year flood flow velocities are presented in Figure 3. Predicted 2-year flood flow depths are
presented in Figure 4. Pr edicted 100-year flood flow velocities are presented in Figures 5, 6, and 11.
Predicted 100-year flood flow depths are presented in Figures 7, 8, and 1 2. The 100-year flood flow
velocities and floo d flow depths were used for designing the channel plug features an d evaluating
potential effect on stream processes. Differences between the existing condition and proposed habitat
preservation models for the 100-year flood flow velocities and flood flow depths are presented in Figures
9, 10, 13, 14, 15, and 1 6. The 100- year flood flow velocity and flood flow depths differences help
7
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
identify potential private property flooding, private property bank erosion, and natural stream processes
impacts.
Floodplain and Flood-rise Limitations
Executive Order 11988, Floodplain Management, established federal policies for protecting floodplains
and floodways. The inte ntion of the associated regulations is to avoid, to t he extent practical, adverse
impacts to floodplains; minimize the impact of floods to human safety, health, and welfare; and avoid
supporting land use development that is incompatible with the natural and beneficial floodplain values.
When avoidance is not po ssible, the policies require appropriate consideration of methods to m inimize
adverse impacts.
The sites are located within Zone A ide ntified on the Federal Emergency Management Agency (FEMA)
Flood Insurance Rate Map (FIRM) 530069 0600B and 5300690625B. Zone A is an area of 100- year
flood not determined. Jefferson Count y is the local floodplain administrator. Both federal and local
regulations require increases in the 100-year water surface elevation for Zone A to be less than one foot.
Cost Estimates
Construction cost esti mates are provided in Tabl e 2. Assumed stabilization length is 1,900 fe et.
Temporary construction access road is 3,500 feet long. The estimates assume logs with root wads cos t
$1,100 and logs without root wads cost $600 each. Flow diversion is assu med not needed. The costs
presented include 7 percent mobilization and 10 percent contingency.
attachments: Tables 1 and 2
Figures 1 to 17
Site Photographs 1 to 12
Sheets H.1 to H.5
Estimate Drainage Annual
Method Area (mi2) Precip 2 10 25 50 100
MP 7.8 ‐ Streamstats 210 170 28,400 44,700 52,500 59,300 66,700
USGS 12041200 PEAKFQ 32,660 52,390 61,460 67,890 74,060
USGS 12041200 Tab. 2 32,200 51,100 59,700 65,700 71,400
weighted Tab.2 32,000 51,000 59,600 65,700 71,200
MP 7.8 ‐ Design 210 26,960 42,968 50,213 55,352 59,986
Notes:
1. USGS - USGS Regression Equations, “Magnitude and Frequency of Floods in Washington”,
WRIR 97-4277, 1998.
Table 1. Peak Discharges (ft3/sec)
Recurrence Intervals (years)
Table 2. Cost Estimates
Site:
Wood Fence with Slash Stabilization Length 1900 feet
Unit Quantity Unit Cost Total Cost
Mobilization 7% of construction cost LS 1 42,224$ 42,224$
Remove Existing Revetment LF - -$ -$
Flow Diversion LS 1 5,000$ 2,000$
Wood Buffer
Exc./Place Conserved SBM CY 480 8$ 3,840$
18" dia. X 20' Logs w/out rootwads EA 288 600$ 172,800$
18" dia. X 20' Logs w/ rootwads EA 120 1,100$ 132,000$
Chain, 5/8" HDG Grade 43 FT 1,920 10$ 19,200$
18" dia. X 20' Log Piles EA 288 700$ 201,600$
18" dia. X 10' Cottonwood Boles EA 192 200$ 38,400$
Pole-plantings, cottonwood EA 240 4$ 960$
Pole-plantings, willow EA 3,600 2$ 7,200$
Coarse Woody Debris CY 1,680 15$ 25,200$
Per ELJ Unit
ELJ Width 80 feet
ELJ Unit No.24
Exc./Place Conserved SBM 20 CY
18" dia. X 20' Logs w/out rootwads 12 No.3 per
18" dia. X 20' Logs w/ rootwads 5 No.
18" dia. X 20' Log Piles 12 No.3 per
18" dia. X 10' Cottonwood Boles 8 No.2 per
Chain, 5/8" HDG Grade 43 80 feet 20 per
Log Bundles 4 No.
Pole-plantings, cottonwood 10 No.
Pole-plantings, willow 150 No.
Coarse Woody Debris 70 CY
Cost per ELJ Unit
Total Construction Cost without Contingencies 645,424$
Contingency 10% of construction cost 64,542$
Total Construction Cost 709,966$
CE and PE 30% of construction cost 212,990$
ROW -$
TOTAL Capital Cost Cost/Foot 486$ 922,956$
Annualized Capital Cost Discount rate, i 0.07125 67,936$
Service life, n 50 years
CFR 0.0736071
Habitat Mitigation - Channel Preservation
25,050$
Project Site Locations
Project Area Location
Map printed from National Geographic TOPO
MP 4.0
N
Habitat
Preservation
Site
0 1 mile
FIGURE 1
HABITAT PRESERVATION
SITE LOCATION
MP 7.8
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N Large Woody Debris Along Active Channel Edge
0
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FIGURE 2 HABITAT PRESERVATION SITE MAP
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N FIGURE
3
PROPOSED CHANNEL PLUGS 2-YR FLOW VELOCITYLeft Bank Floodplain
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N FIGURE
4
PROPOSED CHANNEL PLUGS 2-YR FLOW DEPTHLeft Bank Floodplain
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N FIGURE
5
EXISTING CONDITIONS 100-YR FLOW VELOCITYLeft Bank Floodplain
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N FIGURE
6
PROPOSED CHANNEL PLUGS 100-YR FLOW VELOCITYLeft Bank Floodplain
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N FIGURE
7
EXISTING CONDITIONS 100-YR FLOW DEPTHLeft Bank Floodplain
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0 500 feet
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N FIGURE
8
PROPOSED CHANNEL PLUGS 100-YR FLOW DEPTHLeft Bank Floodplain
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B
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d
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P
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0 500 feet
Ba
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b
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A
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a
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N FIGURE
9
FLOODPLAIN 100-YEAR FLOW VELOCITY DIFFERENCE
Te
r
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a
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S
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Mo
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Fl
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Ri
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F
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d
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n
Right Bank Floodplain
Do
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B
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y
Upstream Boundary
Ch
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P
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s
We
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d
East End
Pr
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1
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W
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FIGURE
1
0
FLOODPLAIN 100-YEAR FLOW DEPTH DIFFERENCE
We
s
t
E
n
d
East End
LI
D
A
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a
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d
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1
4
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2
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2
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1
2
.
N FIGURE
1
1
PROPOSED CHANNEL PLUGS 100-YR FLOW VEL. CLOSEUPLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
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d
p
l
a
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Wo
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C
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a
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l
P
l
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g
s
0 300 feet
Ba
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H
a
b
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a
Ba
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1
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N FIGURE
1
2
PROPOSED CHANNEL PLUGS 100-YR FLOW DEPTH CLOSEUPLeft Bank Floodplain
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F
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0 300 feet
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N FIGURE
1
3
RIGHT BANK 100-YEAR FLOW VELOCITY DIFFERENCE
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Right Bank Floodplain
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Upstream Boundary
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N FIGURE
1
4
RIGHT BANK 100-YEAR FLOW DEPTH DIFFERENCE
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Right Bank Floodplain
Do
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Upstream Boundary
Ch
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N FIGURE
1
5
LEFT BANK 100-YEAR FLOW VELOCITY DIFFERENCE
Te
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B
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F
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Right Bank Floodplain
Do
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Upstream Boundary
Ch
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N FIGURE
1
6
LEFT BANK 100-YEAR FLOW DEPTH DIFFERENCE
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Right Bank Floodplain
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.
N FIGURE
1
7
HABITAT PRESERVATION HECRAS 2-D MODEL
Te
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y
Upstream Boundary
Wo
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0
1000 feet
Habitat Preservation Area
PHOTO 1
PHOTO 2
PHOTO 3
2/15/2017
Backchannel aquatic habitat.
Pool formed when river channel avulsed.
Newer habitat, created with 2006
avulsion.
Backchannel aquatic habitat.
Upper Hoh River Road Bank Stabilization
Pool formed when river channel avulsed.
Newer habitat, created with 2006
avulsion.
Pool formed when river channel avulsed.
Newer habitat, created with 2006
avulsion.
Backchannel aquatic habitat.
Habitat Preservation Area
PHOTO 4
PHOTO 5
PHOTO 6
2/15/2017
Backchannel aquatic habitat.
Pool formed when river channel avulsed.
Older habitat, created in earlier
avulsions.
Main bank stabilization site - looking
upstream.
Pool formed when river channel avulsed.
Older habitat, created in earlier
avulsions.
Older floodplain with more established
vegetation.
Trees larger and type varies, ground
surface rougher.
Upper Hoh River Road Bank Stabilization
Habitat Preservation Area
PHOTO 7
PHOTO 8
PHOTO 9
2/15/2017
Older floodplain with more established
vegetation.
Newer floodplain with less established
vegetation.
Trees larger and type varies, ground
surface rougher.
Vegetation smaller with fewer types,
ground surface smoother.
Newer floodplain with less established
vegetation.
Vegetation smaller with fewer types,
ground surface smoother.
Upper Hoh River Road Bank Stabilization
Habitat Preservation Area
PHOTO 10
PHOTO 11
PHOTO 12
2/15/2017
Vegetation lining active channel edge.
Vegetation limits bank erosion and must
be preserved.
Large woody debris lining active channel
edge.
Older, naturally anchored woody debris
deflects flow away from overbank area.
Woody debris protects vegetation on
floodplain. Woody debris and vegetation
limits bank erosion and must be
preserved. Trees smaller and younger.
Large woody debris lining active channel
edge.
Upper Hoh River Road Bank Stabilization
Older, naturally anchored woody debris
deflects flow away from overbank area.
Woody debris protects vegetation on
floodplain. Woody debris and vegetation
limits bank erosion and must be
preserved. Trees larger and older.
OHW
Deflector log bundle
Deflector log bundle
Defector rootwad, 5
Deflector log bundle, 4
DETAILS
CHANNEL PLUG
7.
6.
5.
4.
3.
2.
1.
5
STATE PROJECT
NUMBER
SHEET
]
U
S
_
S
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t
2
D
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:
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d
0
3
3
2
3
5
4
\
H
.
X
X
_
v
5
_
H
a
b
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_
T
y
p
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f
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o
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S
_
S
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2
D
.
d
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n
WA JEFF 91420(1)
1
2
:
3
6
P
M
1
6
A
u
g
u
s
t
2
0
1
7
-
-
/
-
-
-
-
-
-
/
-
-
-
-
C
h
e
c
k
e
d
b
y
:
D
e
s
i
g
n
e
d
b
y
:
Log pile
space between fill logs and deflector logs.
vegetation, 1-inch to 8-inch diameter, tightly pack into void
Coarse woody debris; even mixture of branches, limbs, trunks,
Deflector log bundle; 110 to 150 ft3 total log volume.
Space log pile and cottonwood boles 4' o.c.
Cottonwood bole; 10-foot min. trunk, 12 to 18-inch diameter.
attached rootwad.
Log pile; 20-foot min. trunk, 12 to 18-inch diameter without
attached rootwad.
Deflector rootwad; 20-foot min. trunk, 18 to 37-inch diameter with
attached rootwad.
Deflector log; 20 to 22-foot trunk, 18 to 37-inch diameter without
NO SCALE
Flow
Wrap each log bundle
trunk with chain
Wrap each log bundle
trunk with chain,
center in log bundle
20'-0"
4
'
m
i
n
.
Do not disturb existing vegetation
Do not disturb
existing vegetation
NOTE:
100-year W.S.
TYPICAL SECTION
Existing channel bottom
over deflector logs
Placed coarse woody debris, min. 1'
A
A
Temporary access road
random spacing
3 per channel plug,
Doug fir planting,
3' random spacing
method,
single group
Pole planting,
Deflector rootwad
DETAIL
TYPICAL DEFLECTOR LOG BUNDLE
80'-0"
PLAN
5
'
m
i
n
.
excavate as needed for setting flush on subgrade
Set deflector log bundle on channel bottom,
1
5
'
m
i
n
.
2'-0"
4'-0"
Log piles, 12 Cottonwood boles, 8