HomeMy WebLinkAboutAttachment_F_UpperHoh-Bank_Stabilization_Habitat-Preservation_Hydraulics_Report1-combined 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 and the Park Rain 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 Park 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 Forest and the Park’s Hoh Rain Forest Visitor Center
for weeks at a time (and many months in 1996). Response to these storm events and maintenance of the
road in its current location has resulted in a continuing outlay of limited maintenance funds to maintain
safe access and to mitigate for adverse impacts those actions have on threatened and endangered fish
species.
In 1998 the Hoh Tribe requested the U.S. Bureau of Reclamation (BOR) prepare a geomorphic study to
better understand the existing and historical channel processes on the Hoh River, and how human
activities may have impacted those processes. The study, entitled Geomorphic Assessment of Hoh River
in Washington State, published in 2004, identifies areas 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. The report recommended more detailed data 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 roadway 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 Highway Division (WFLHD) completed for the County an
Upper Hoh Road Bank Failure Risk Reduction Study. The Study developed a comprehensive road
management strategy for mitigating high risk sites 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 sites (regardless of management jurisdictions),
development of a range of treatment options for each site, and initial cost estimates for each option
including construction, Preliminary Engineering (PE), Construction Engineering (CE), and ROW.
Treatment options developed represented a full range of types, costs, and environmental 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 Site) and MP 7.7 to 7.9 (MP 7.8 Site) (Fig. 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 dolosse ballast was
recommended for both sites. The design approach is the least expensive for effectively controlling bank
erosion. The wood buffer can accommodate a greater range of active flow channel migration and flow
impingement angles. The minimal channel bed excavation 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 buffer 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 stabilization. In the environmental permit application phase, the resource
agencies identified placing the wood buffer in the river channel as causing negative impacts 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. Recommendations for improving
the backchannel aquatic habitat survivability by reducing the channel migration and avulsion risk and
encouraging natural floodplain roughness to develop are presented. The work 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 encouraging future tree growth. Backchannel 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 can colonize in sufficient numbers
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 has 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 trees will likely provide adequate natural resistance. Large woody
debris lining the active channel edge deflects 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 (Photos 10 and 11). To simulate the large woody debris that lines the bank, install 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 to 37 inches in diameter, 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 rootwad. The rootwads will be placed on top of the log
bundles with rootwad in the upstream direction. Each channel plug will have 12 log piles and 8
Cottonwood boles evenly spaced along the downstream side of the log bundles 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 woody 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 flow away from the overbank area and achieving channel plug
stability. Care must be taken to pack bundles as densely 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 temporary construction access road is proposed constructed approximately
200 feet from the active river channel edge for minimizing disturbance of the vegetated floodplain.
Install the channel plugs on the side of the road nearest the river. Plant the temporary access road with
Douglas fir trees and cottonwood/willow poles. Do not disturb the existing vegetation between the
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. HECRAS 5.0 modeling results for the proposed 2-year flood flow
velocities and flow depths were used to help define the strategic locations at the head of flood scour
channels (Fig. 3 and 4). The results indicate the flow 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 scour the floodplain surface materials, creating new
flood scour channels. Scoured material will be deposited 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 indicate 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 immediately
in front of the wood channel plugs shows an increase in less than 0.5 feet/sec for the proposed conditions
(Fig. 13). A 100-year flood flow depth profile plot shows an increase in less than 0.2 feet for the
proposed conditions (Fig. 14). The results indicate flow depths and velocities in the active channel and
along the floodplain limit for the modeled proposed conditions will not be significantly different from
existing conditions.
Bank erosion occurs when the active flow channel migrates to the valley sides and directs flow at sharp
angles against erodible banks. Woody debris and gravel bars affect channel migration and flow
impingement angles. The wood channel plugs are not expected to restrict sediment and woody debris
transport and recruitment relative to existing conditions. Mid-channel and floodplain sediment deposition
is not expected to be noticeably different than current 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 channel avulsion along the wooded
floodplain, not prevent them. Aggressive bank migration 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 channel plugs to encroach into the
active channel is possible. The channel plug could 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. Access for construction is assumed down forest road and temporary construction access
road.
Private Property Impacts
A 100-year flood flow velocity profile plot along the 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 conditions (Fig. 14). Based on the HECRAS modeling, the wood
channel plugs are not expected to noticeably increase flooding or bank erosion 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 flow 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 revetments, 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 redirecting 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 downstream from the MP 7.8 Bank Stabilization Site and
occupies a wooded floodplain area on the inside bank of a river 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 avulsion occurred between 2006 and 2009 when a relatively
consistent down-valley channel translation abruptly avulsed into a new channel, leaving the 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 best preserved where the floodplain vegetation is oldest and has
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 boundary. 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 width 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 valleys 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 preservation 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 are present. Mean annual precipitation reported by USGS StreamStats is 168
inches. The watershed lies mostly within the Olympic National Park and Olympic 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.
6
Memo to: Kirk Loftsgaarden, WFLHD Project Manager
September 7, 2017
Peak flood discharges were estimated with the weighting equation in USGS WRIR 97-4277 for ungagged
sites on gaged streams. Peak discharges for the ungaged sites were estimated using USGS StreamStats
regression equations. The regression equation estimates were then improved by weighting with the
weighted estimates for the USGS 12041200 gage station (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 precipitation 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 February, March, April, 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 were estimated using the Hydrologic Engineering Center
River Analysis System HEC-RAS 5.0, a computer 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 models for the existing conditions and proposed design options.
LIDAR terrain data was obtained from Puget Sound 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 models by merging the LIDAR terrain data with the surveyed river
cross sections and ground topography data. Each channel plug was placed in the model 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 meshes 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. Predicted 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 12. The 100-year flood flow
velocities and flood flow depths were used for designing the channel plug features and 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 16. 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 intention of the associated regulations is to avoid, to the 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 possible, the policies require appropriate consideration of methods to minimize
adverse impacts.
The sites are located within Zone A identified on the Federal Emergency Management Agency (FEMA)
Flood Insurance Rate Map (FIRM) 5300690600B and 5300690625B. Zone A is an area of 100-year
flood not determined. Jefferson County 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 estimates are provided in Table 2. Assumed stabilization length is 1,900 feet.
Temporary construction access road is 3,500 feet long. The estimates assume logs with root wads cost
$1,100 and logs without root wads cost $600 each. Flow diversion is assumed not needed. The costs
presented include 7 percent mobilization and 10 percent contingency.
attachments: Tables 1 and 2
Figures 1 to 17
Site Photographs 1 to 12
Sheets H.1 to H.5
Estimate Drainage Annual
Method Area (mi2) Precip 2 10 25 50 100
MP 7.8 ‐ Streamstats 210 170 28,400 44,700 52,500 59,300 66,700
USGS 12041200 PEAKFQ 32,660 52,390 61,460 67,890 74,060
USGS 12041200 Tab. 2 32,200 51,100 59,700 65,700 71,400
weighted Tab.2 32,000 51,000 59,600 65,700 71,200
MP 7.8 ‐ Design 210 26,960 42,968 50,213 55,352 59,986
Notes:
1. USGS - USGS Regression Equations, “Magnitude and Frequency of Floods in Washington”,
WRIR 97-4277, 1998.
Table 1. Peak Discharges (ft3/sec)
Recurrence Intervals (years)
Table 2. Cost Estimates
Site:
Wood Fence with Slash Stabilization Length 1900 feet
Unit Quantity Unit Cost Total Cost
Mobilization 7% of construction cost LS 1 42,224$ 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
Im
a
g
e
f
r
o
m
G
o
o
g
l
e
E
a
r
t
h
P
r
o
,
i
m
a
g
e
d
a
t
e
8
/
1
9
/
2
0
1
6
.
N Large Woody Debris Along Active Channel Edge
0
2000
F
e
e
t
FIGURE 2 HABITAT PRESERVATION SITE MAP
Ho
h
R
i
v
e
r
FlowMP 7.8 Bank Stabilization Site
Up
p
e
r
H
o
h
R
i
v
e
r
R
o
a
d
Channel Migration Area Limits
Ba
c
k
c
h
a
n
n
e
l
A
q
u
a
t
i
c
Ha
b
i
t
a
t
A
r
e
a
Proposed Wood Channel Plugs, 24
Ba
c
k
c
h
a
n
n
e
l
A
q
u
a
t
i
c
Ha
b
i
t
a
t
A
r
e
a
Sp
a
r
s
e
S
m
a
l
l
T
r
e
e
A
r
e
a
De
n
s
e
L
a
r
g
e
T
r
e
e
A
r
e
a
Pr
o
p
o
s
e
d
T
e
m
p
o
r
a
r
y
A
c
c
e
s
s
Ro
a
d
w
i
t
h
P
l
a
n
t
i
n
g
s
,
3
,
5
0
0
F
e
e
t
Active Channel Edge
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
3
PROPOSED CHANNEL PLUGS 2-YR FLOW VELOCITYLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
4
PROPOSED CHANNEL PLUGS 2-YR FLOW DEPTHLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
5
EXISTING CONDITIONS 100-YR FLOW VELOCITYLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
6
PROPOSED CHANNEL PLUGS 100-YR FLOW VELOCITYLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
7
EXISTING CONDITIONS 100-YR FLOW DEPTHLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
8
PROPOSED CHANNEL PLUGS 100-YR FLOW DEPTHLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 500 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Pr
o
f
i
l
e
t
a
k
e
n
1
5
f
e
e
t
d
o
w
n
g
r
a
d
i
e
n
t
o
f
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
.
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
L
o
c
a
t
i
o
n
N FIGURE
9
FLOODPLAIN 100-YEAR FLOW VELOCITY DIFFERENCE
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Ch
a
n
n
e
l
P
l
u
g
s
We
s
t
E
n
d
East End
Pr
o
f
i
l
e
t
a
k
e
n
1
5
f
e
e
t
d
o
w
n
g
r
a
d
i
e
n
t
o
f
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
.
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
L
o
c
a
t
i
o
n
FIGURE
1
0
FLOODPLAIN 100-YEAR FLOW DEPTH DIFFERENCE
We
s
t
E
n
d
East End
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
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
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 300 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
1
2
PROPOSED CHANNEL PLUGS 100-YR FLOW DEPTH CLOSEUPLeft Bank Floodplain
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0 300 feet
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
Ba
c
k
c
h
a
n
n
e
l
H
a
b
i
t
a
t
A
r
e
a
N FIGURE
1
3
RIGHT BANK 100-YEAR FLOW VELOCITY DIFFERENCE
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Ch
a
n
n
e
l
P
l
u
g
s
Do
w
n
s
t
r
e
a
m
Upstream
Pr
o
p
o
s
e
d
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
N FIGURE
1
4
RIGHT BANK 100-YEAR FLOW DEPTH DIFFERENCE
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Ch
a
n
n
e
l
P
l
u
g
s
Do
w
n
s
t
r
e
a
m
Upstream
Pr
o
p
o
s
e
d
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
N FIGURE
1
5
LEFT BANK 100-YEAR FLOW VELOCITY DIFFERENCE
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Ch
a
n
n
e
l
P
l
u
g
s
Do
w
n
s
t
r
e
a
m
Upstream
Pr
o
p
o
s
e
d
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
N FIGURE
1
6
LEFT BANK 100-YEAR FLOW DEPTH DIFFERENCE
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Ch
a
n
n
e
l
P
l
u
g
s
Do
w
n
s
t
r
e
a
m
Upstream
Pr
o
p
o
s
e
d
W
o
o
d
C
h
a
n
n
e
l
P
l
u
g
s
LI
D
A
R
t
e
r
r
a
i
n
d
a
t
a
o
b
t
a
i
n
e
d
f
r
o
m
P
u
g
e
t
S
o
u
n
d
L
I
D
A
R
C
o
n
s
or
t
i
u
m
,
L
I
D
A
R
m
a
p
p
i
n
g
s
u
r
v
e
y
e
d
A
p
r
i
l
1
4
a
n
d
2
1
,
2
0
1
2
.
N FIGURE
1
7
HABITAT PRESERVATION HECRAS 2-D MODEL
Te
r
r
a
i
n
S
u
r
f
a
c
e
Mo
d
e
l
G
r
i
d
L
i
m
i
t
s
Le
f
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
Fl
o
o
d
p
l
a
i
n
Ri
g
h
t
B
a
n
k
F
l
o
o
d
p
l
a
i
n
Right Bank Floodplain
Do
w
n
s
t
r
e
a
m
B
o
u
n
d
a
r
y
Upstream Boundary
Wo
o
d
C
h
a
n
n
e
l
P
l
u
g
s
0
1
0
0
0
f
e
e
t
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
u
r
_
f
t
2
D
[
c
:
\
m
y
f
i
l e
s
\
p
w
_
p
r
o
d
u
c
t
i o
n
\
d
0
3
3
2
3
5
4
\
H
.
X
X
_
v
5
_
H
a
b
i
t
a
t
p
r
e
s
e
r
v
a
t
i
o
n
_
T
y
p
i
c
a
l _
f
l o
o
d
f
e
n
c
e
_
B
S
_
S
u
r
_
f
t
2
D
.
d
g
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