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DESIGN DOCUMENTATION REPORT
GREEN DUWAMISH RIVER ECOSYSTEM
RESTORATION – UPPER SPRINGBROOK
CREEK PROJECT
Prepared for
U.S. Army Corps of Engineers
Seattle District
4735 East Marginal Way South
Seattle, Washington 98134
Prepared by
Anchor QEA, LLC
1605 Cornwall Avenue
Bellingham, Washington 98225
May 2010
Design Documentation Report May 2010
Upper Springbrook Creek Project i 090202-01
TABLE OF CONTENTS
1 INTRODUCTION AND PURPOSE ....................................................................................... 1
2 DESIGN ANALYSIS ............................................................................................................... 2
2.1 Evaluation of Existing Conditions ...................................................................................2
2.2 Proposed Conditions Model Development .....................................................................4
2.3 Proposed Channel Realignment ......................................................................................4
2.3.1 Channel Design ..........................................................................................................4
2.3.2 Imported Sediment Grain Size Distribution Evaluation ..........................................6
2.3.3 Fish Habitat Evaluation ............................................................................................15
2.4 Proposed In-Channel Large Woody Debris Placement ...............................................20
2.4.1 LWD Log Quantities and Locations ........................................................................21
2.4.2 In-Channel LWD Placement Types ........................................................................22
2.4.3 LWD Stability and Expected Scour .........................................................................23
2.5 Proposed Floodplain Log Placements and Plantings ....................................................24
2.5.1 Floodplain Log Model Development and Analysis .................................................25
2.5.2 Floodplain Log Size Specification ............................................................................26
2.6 Proposed Culvert Replacement .....................................................................................26
2.6.1 Culvert Specifications ...............................................................................................26
2.6.2 Inlet/Outlet Design and Specifications ....................................................................29
2.6.3 Fish Passage Evaluation ............................................................................................30
2.6.4 Road Grade Replacement and Utility Relocation ...................................................31
2.6.5 Culvert Structural Requirements .............................................................................32
3 CONSTRUCTABILITY ANALYSIS ..................................................................................... 33
3.1 Recommended Construction Equipment ......................................................................33
3.2 Mobilization, Site Access and Staging, and Site Preparation .......................................34
3.3 Demolition ......................................................................................................................35
3.4 New Channel Construction ...........................................................................................36
3.5 Large Woody Debris Placements ..................................................................................37
3.5.1 In-Channel Large Woody Debris Placements ........................................................37
3.5.2 Floodplain Log Placements ......................................................................................39
3.6 Culvert Construction .....................................................................................................40
Table of Contents
Design Documentation Report May 2010
Upper Springbrook Creek Project ii 090202-01
3.7 Creek Flow Ramping and Fish Rescue and Recovery ..................................................42
3.8 Decommissioning of the Existing Channel ...................................................................43
3.9 Construction Decommissioning and Site Restoration .................................................43
3.10 Best Management Practices ...........................................................................................44
3.10.1 Spill Prevention ........................................................................................................44
3.10.2 Erosion and Sediment Control .................................................................................45
4 LIMITATIONS ..................................................................................................................... 46
5 REFERENCES ...................................................................................................................... 47
List of Tables
Table 1 Design Flow Hydrology ........................................................................................ 3
Table 2 Recommended Natural Sediment Distribution Ratios ....................................... 6
Table 3 WDFW Recommended Coho Spawning Sediment GSD ................................... 7
Table 4 Imported Channel Sediment GSD ..................................................................... 10
Table 5 Imported Channel Sediment GSD Specification ............................................... 10
Table 6 Spawning and Rearing Criteria .......................................................................... 15
Table 7 Spawning and Rearing Criteria, Model Summary (1) ....................................... 16
Table 8 Spawning and Rearing Criteria, Model Summary (2) ....................................... 20
Table 9 Recommended Natural Conditions LWD Quantities ....................................... 21
Table 10 Proposed LWD Quantities and Volumes ........................................................... 22
Table 11 HEC-RAS Lateral Weir Analysis Summary ...................................................... 25
Table 12 Replacement Culvert Specifications .................................................................. 28
Table 13 Culvert Adult Fish Passage Design Criteria ...................................................... 30
Table 14 Proposed Culvert Model Results ........................................................................ 31
Table 15 Recommended Construction Equipment .......................................................... 34
Table of Contents
Design Documentation Report May 2010
Upper Springbrook Creek Project iii 090202-01
List of Charts
Chart 1 Threshold Grain Size (48 cfs) .............................................................................. 7
Chart 2 Threshold Grain Size (88 cfs) .............................................................................. 8
Chart 3 Threshold Grain Size (121 cfs) ............................................................................ 9
Chart 4 Sediment Grain Mobility (48 cfs) ...................................................................... 11
Chart 5 Sediment Grain Mobility (88 cfs) ...................................................................... 12
Chart 6 Sediment Grain Mobility (120 cfs) .................................................................... 13
Chart 7 Sediment Transport Simulation ........................................................................ 14
Chart 8 Water Depth in Proposed Channel at Low Flows (3.2 cfs and 4.5 cfs) ........... 16
Chart 9 Velocities in Proposed Channel at Low Flows (3.2 cfs and 4.5 cfs) ................ 17
Chart 10 Habitat Model Results (3.2 cfs) ......................................................................... 18
Chart 11 Habitat Model Results (4.5 cfs) ......................................................................... 19
Chart 12 Habitat Model Results (10 cfs) .......................................................................... 19
List of Appendices
Appendix A HEC-RAS Proposed Hydraulic Model Results
Appendix B Floodplain Log Placement Specification Calculations
Appendix C Sediment Transport Analysis
Table of Contents
Design Documentation Report May 2010
Upper Springbrook Creek Project iv 090202-01
LIST OF ACRONYMS AND ABBREVIATIONS
BAGS Bedload Assessment for Gravel-bed Streams
BFW bankfull width
BMP best management practice
CDF controlled density fill
cfs cubic feet per second
cms cubic meter per second
Corps U.S. Army Corps of Engineers
cy cubic yard
D50
Dx
median grain size (sediment)
X% passing grain size (sediment)
EGL energy grade line
GSD grain size distribution (sediment)
H:V horizontal to vertical
HDPE high-density polyethylene
HEC-RAS Hydraulic Engineering Center’s River Analysis System
kN kilonewtons
LWD large woody debris
m meter
mm millimeter
Project Upper Springbrook Creek Project
PVC polyvinyl chloride
RI reference interval (discharge)
SR State Route
SWDM Surface Water Design Manual (King County 2005)
TESC Temporary Erosion and Sedimentation Control
WDFW Washington Department of Fish and Wildlife
WSDOT Washington State Department of Transportation
Design Documentation Report May 2010
Upper Springbrook Creek Project 1 090202-01
1 INTRODUCTION AND PURPOSE
The Upper Springbrook Creek Project (Project) is located within the City of Renton in King
County, Washington. Plan Sheets G-1 and C-1 illustrate the Project location and existing
condition, respectively. The Project will realign a portion of the existing stream channel
between the South 55th Street and State Route (SR) 167 crossings to provide a more naturally
functioning system and improve habitat conditions for salmonids and other fish species that
utilize the stream. The Project will also replace an existing 30-inch culvert that crosses
South 55th Street at the upstream end of the Project area. The proposed replacement culvert
will improve fish passage, increase hydraulic capacity, and allow for natural sediment
transport dynamics. Under existing conditions, the channel is primarily a linear, uniform
roadside ditch that runs parallel to South 55th Street on the north side of the roadway
through the Project extent. The proposed design will permanently relocate approximately
900 feet of the existing channel from its current channelized planform to a new
approximately 975-foot alignment through the floodplain to the north.
In addition to excavation of the proposed channel alignment, the Project will include
placement of large woody debris (LWD) in the channel, logs and plantings in the existing
floodplain, replacement of the South 55th Street culvert and associated headwalls, and
bioengineered stability measures upstream of the new culvert. These features will work
collectively to provide and maintain salmonid spawning and rearing habitat through the
Project site. Implementation of the Project is scheduled to occur during the summer of 2011.
Design Documentation Report May 2010
Upper Springbrook Creek Project 2 090202-01
2 DESIGN ANALYSIS
A variety of qualitative and quantitative evaluations were performed to formulate the Project
design and specifications. The following sections summarize the analyses performed as part
of the 95- and 100-percent design development including relevant supporting data and
calculations. The design analysis is divided into the following elements: evaluation of
existing conditions, development of a proposed conditions hydraulic model, design of the
proposed channel, design of in-channel LWD, design of floodplain log placements, and
design of a replacement culvert under South 55th Street.
2.1 Evaluation of Existing Conditions
Ground survey data collected in 2008 and 2009 (DHA 2008) and photogrammetric
topography data provided by the City of Renton were used to develop an existing conditions
surface of the Project area. Hydrology data including peak and low summer flows were
obtained from a previous study completed for replacement of the SR 167 culvert at the
downstream end of the Project area (DEA 2001). For low-flow hydrology both the “current”
and “future” (full build out) exceedance flows described in the 2001 report were evaluated
for the purposes of this design. The “current” flow describes the flows extracted from gage
records between 1988 and 1994 for the coho salmon migration period of October to
February. The “future” flow was determined by increasing the current flow by 40 percent to
reflect predicted increases in the 100-year flow from current conditions to future
development flows (DEA 2001). Additional design flows for the 1-year and 5-year flow
events that were not available in the report were estimated by the U.S. Army Corps of
Engineers (Corps) from the values presented in the 2001 Hydraulic Report (Hansen 2009).
Table 1 lists the design flows used in the hydraulic analysis. The Hydraulic Engineering
Center’s River Analysis System (HEC-RAS) model was used to evaluate hydraulic conditions
for existing and proposed site conditions (USACE 2008). Detailed information describing the
development of the HEC-RAS model geometry is available in the 35 Percent Design and
Constructability Report (Anchor QEA 2010a).
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 3 090202-01
Table 1
Design Flow Hydrology
Flow Event Discharge (cfs)
Low (current) 3.2
Low (future) 4.5
1‐year 48
2‐year 70
5‐year 84
10‐year 88
25‐year 99
50‐year 110
100‐year 121
Evaluation of the existing topography data indicate that the ground surface north of the
existing channel drops in elevation with increasing distance from the existing right channel
bank. This observation was consistent throughout the floodplain area north of the Project
site. The existing conditions HEC-RAS model shows that overtopping of the right bank
occurs throughout a majority of the Project area during a 2-year return interval
[approximately 70 cubic feet per second (cfs)], with slightly less overtopping occurring at a 1-
year return interval (approximately 48 cfs) (Appendix A). The 2001 Hydraulic Report
confirms that water overtopping the banks of Upper Springbrook Creek flows through the
north floodplain and ponds on the west side of SR 167 before eventually flowing north to No
Name Creek (DEA 2001). Observation of floodplain topography shows a depression west of
SR 167 approximately 1,400 feet north of the existing channel where water likely
accumulates.
Based on these findings, it is possible that significant volumes of water are currently lost to
the floodplain during flood events. These floodwaters may strand juvenile fish and
contribute to flooding off site. Understanding the complications of the existing conditions is
critical to alternatives evaluation and design development to minimize potential flooding and
fish stranding that may occur after Project implementation.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 4 090202-01
2.2 Proposed Conditions Model Development
The proposed conditions hydraulic model geometry was extracted from an AutoCAD Civil
3D surface incorporating the proposed channel realignment. The existing channel was
blocked at the upstream end of the model to simulate the blockage at this location, and the
proposed culvert and associated re-grading was incorporated into the model geometry. The
cross-sections were truncated at the Project limit and a lateral weir was built into the model
at the northern extent of the model to evaluate the effect of log placements in the floodplain.
The proposed model results were used to evaluate the suitability of the proposed channel and
floodplain improvements with respect to flow conveyance, floodplain connectivity, bank
overtopping, and depth-averaged velocities through the new channel and culvert. Sediment
transport dynamics were a key element in this evaluation. The existing and proposed models
were run with the same peak flow events and cross-section locations to allow comparison of
pre- and post-Project conditions, and to provide output to be used in the design analysis of
the proposed structural elements. The specific analyses performed for each design element
are discussed in detail within the following sections.
2.3 Proposed Channel Realignment
2.3.1 Channel Design
The proposed channel alignment is approximately 975 linear feet. The typical cross-sectional
geometry is trapezoidal with 3 horizontal to 1 vertical (3H:1V) side slopes, a 6-foot bottom
width, and an average bank full depth of approximately 1.5 feet. The channel will be over-
excavated to allow for the placement of imported sediments along the channel bottom and
sides. The planform of the channel is sinuous and the channel alignment primarily follows
low areas within the existing topography within the 100-foot-wide drainage easement,
minimizing cut volumes and grading activities through the floodplain. The proposed
channel alignment effectively relocates the channel reach away from South 55th Street,
enhances salmonid habitat, enhances and protects riparian conditions, and is feasible in
terms of constructability and cost. Plan Sheets C-2 through C-5 and C-8.0 through C-9.5
show the proposed channel design details.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 5 090202-01
Plan Sheet C-2 illustrates the proposed channel alignment. The new channel alignment
begins in an existing pool at the downstream end of the existing culvert (Existing Culvert 3)
at the east end of the Project reach. The pool elevation roughly establishes the upstream
grade of the new channel and the discharge invert elevation of the replacement culvert. The
proposed channel alignment gradient (slope) is approximately 1.40 percent from
approximately Station 0+00 to 7+31 and 1.82 percent from approximately Station 7+30 to the
downstream end of the culvert. The proposed channel gradient is similar to the average
grade of the existing channel and roughly tied into existing bed elevations at the upstream
and downstream ends of the proposed alignment.
The cross-sectional geometry of the channel was designed to mimic the geometry of a more
naturally functioning segment of the creek upstream of the Project site, and to effectively
contain lower peak flow hydrology with adequate flow depths and velocities that are
consistent with salmonid habitat criteria. The channel sinuosity and alignment within the
existing floodplain promotes hydraulic complexity, minimizes the removal of mature
riparian vegetation, and reduces the volume of earthwork required by following low areas
within the existing topography.
The bankfull channel depth is limited to 1.5 feet through the majority of the new channel
extent. This is due to the low existing floodplain topography and existing bed elevations at
the upstream (Existing Culvert 1) and downstream (Existing Culvert 3) culverts. However,
this configuration will allow for good floodplain connectivity. Model results for the
proposed conditions show overtopping of the banks begins to occur near the 1-year
recurrence discharge throughout a majority of the Project reach. Concerns related to the loss
of bankfull flows to the lower floodplain areas north of the site will be minimized by
incorporating logs and live plantings into the floodplain, discussed in Section 2.5.
Coir fabric will be installed along the banks of the new channel below the imported channel
sediment and extend upland of the new channel as shown in the plans. Long-term
stabilization of the channel banks will be established by riparian plantings.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 6 090202-01
2.3.2 Imported Sediment Grain Size Distribution Evaluation
Imported sediment for the proposed channel is intended to enhance spawning and rearing
habitat for salmonids while maintaining acceptable channel stability. This evaluation
involved an analysis of relative sediment mobility under various design flows and
conformance to recommendations from government agencies. The selected sediment needs
to be sufficiently mobile such that it will provide clean spawning substrate but not
excessively mobile so as to require undue spawning sediment augmentation.
Recommendations from government agencies included both general stream sediment
distribution ratios and specific grain sizes for habitat function. Table 2 shows recommended
natural stream sediment distribution ratios. These values are intended to provide a starting
point for development of a synthetic grain size distribution (GSD) for stream beds. The
lower portion of the gradation is intended to sufficiently fill the interstices to promote
surface flow during low flow. The upper portion of the gradation is intended to provide bed
surface diversity.
Table 2
Recommended Natural Sediment Distribution Ratios
Distribution Ratio Recommended Value
D84/D100 0.4
D84/D50 2.5
D84/D16 8.0
Source: WDFW (2003)
In addition to general sediment distribution ratios, specific GSD recommendations are
provided for target species habitat function. Table 3 shows a recommended GSD for
spawning sediment used by coho.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 7 090202-01
Table 3
WDFW Recommended Coho Spawning Sediment GSD
Grain Size Class Size (mm) Size (in)
D100 150 5.9
D97 100 3.9
D74 50 2.0
D31 13 0.51
D08 2 0.08
Source: WDFW (2004)
The threshold sediment grain size was evaluated along the proposed channel based on
hydraulic conditions provided by the HEC-RAS model and a slope based relationship for the
grain mobility reference shear stress. See Appendix C for a technical explanation regarding
reference shear stress. Chart 1 shows the model-predicted channel bed shear stress for each
cross-section for the 1-year recurrence interval discharge and the corresponding threshold
grain size.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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(lb
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Th
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Si
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)
River Station (ft)
Sediment Grain Stability
Q = 48 cfs (1.36 cms), 1‐year RI
Threshold Grain Size
Channel Shear Stress
Reference shear stress is based on EGL slope.
Notes: Q = discharge flow
RI = recurrence interval
Chart 1
Threshold Grain Size (48 cfs)
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 8 090202-01
Chart 2 shows the model-predicted channel bed shear stress for each cross-section for the 10-
year recurrence interval discharge and the corresponding threshold grain size.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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Th
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Gr
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Siz
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(in
.
)
River Station (ft)
Sediment Grain Stability
Q = 88 cfs (2.49 cms), 10‐year RI
Threshold Grain Size
Channel Shear Stress
Reference shear stress is based on EGL slope.
Chart 2
Threshold Grain Size (88 cfs)
Chart 3 shows the model-predicted channel bed shear stress for each cross-section for the
100-year recurrence interval discharge and the corresponding threshold grain size.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 9 090202-01
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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(l
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Th
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Gr
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Si
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(i
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River Station (ft)
Sediment Grain Stability
Q = 121 cfs (3.41 cms), 100‐year RI
Threshold Grain Size
Channel Shear Stress
Reference shear stress is based on EGL slope.
Chart 3
Threshold Grain Size (121 cfs)
The proposed culvert under South 55th Street is located between Stations 10+50 and 11+00 of
the new channel alignment (Plan Sheet C-5). The downstream end of the new channel will
connect to the existing channel near Station 0+76 (Plan Sheet C-3). No imported sediment
will be placed downstream of that location. Additionally, no imported sediment will be
placed upstream of the extents required to place and protect the culvert.
Overall, the evaluation of threshold grain sizes shows that for the 1-year discharge a grain
size of approximately 2.0 inches would be stable for a majority of the cross-sections. For the
10-year discharge a grain size of approximately 2.5 inches would be stable for a majority of
the cross-sections. For the 100-year discharge a grain size of approximately 3.0 inches would
be stable for a majority of the cross-sections, with a grain size closer to 4.0 inches required at
some cross-sections.
Because of differing objectives and constraints in various locations within the Project area,
imported stream sediment was separated into two different specifications. Type 1 sediment
will be placed within the culvert and along portions of the channel bank where erosion is
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 10 090202-01
not desirable. This sediment specification is designed to be immobile for discharges up to the
100-year recurrence interval event. Type 2 sediment will be placed along channel banks and
bed to a minimum thickness of 1 foot (Plan Sheets C-3 through C-5). This sediment is
designed to be slightly mobile at the 1-year recurrence interval discharge and moderately
mobile at the 10-year recurrence interval discharge. Type 2 sediment will serve as spawning
substrate for coho and other native fish species. As the stream evolves and becomes
dynamically stable this sediment will become sorted as riffles develop a coarser mobile armor
layer and finer fractions are deposited in scour pools and other low shear stress areas of the
channel. Table 4 shows the GSD for each sediment specification. Table 5 shows the GSD
specification tolerances for construction.
Table 4
Imported Channel Sediment GSD
Use
Type 1 Type 2
Culvert Fill, Bank
Stabilization
Riffles, Spawning Areas,
Channel Banks, and Bed
Median Grain Size, D50 (in) 5 1.3
100% Passing, D100 (in) 24 10
84% Passing, D84 (in) 10 3.5
16% Passing, D16 (in) 1.5 0.44
5% Passing, D05 (in) 0.1 0.08
D84/D100 0.4 0.35
D84/D50 2 2.3
D84/D16 6 8
Table 5
Imported Channel Sediment GSD Specification
Sediment Type
Type 1, Culvert Fill Bank
Stabilization
Type 2, Riffles, Spawning
Areas, Channel Banks and Bed
Standard Sieve Size Percent Passing Range Percent Passing Range
24 in 98 – 100 100
12 in 85 – 93 100
10 in 80 – 88 98 – 100
6 in 55 – 63 95 – 100
5 in 45 – 53 92 – 98
3 in 25 – 34 76 – 88
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 11 090202-01
Sediment Type
Type 1, Culvert Fill Bank
Stabilization
Type 2, Riffles, Spawning
Areas, Channel Banks and Bed
Standard Sieve Size Percent Passing Range Percent Passing Range
1‐1/2 in 10 – 18 45 – 55
3/ 4 in 5 – 10 20 – 31
7/16 in 3 – 7 12 – 20
#10 1 – 3 1 – 8
#200 0 – 2 0 – 2
Relative sediment mobility for the selected import sediment types and the recommended
Washington Department of Fish and Wildlife (WDFW) spawning gravel (Table 3) was
evaluated at each cross-section in the proposed conditions model. Relative sediment
mobility is expressed as the ratio of the channel shear stress to the grain mobility reference
shear stress. Relative shear stress values less than 1.0 indicate insignificant sediment motion
(stable sediment). Relative shear stress values greater than 1.0 indicate sediment motion
(mobile sediment).
Chart 4 shows the relative shear stress condition for a 1-year recurrence interval discharge
along with the corresponding channel shear stress.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.1
1
10
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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(τ /τ r )
River Station (ft)
Relative Sediment Mobility ‐Springbrook Creek
Q = 48 cfs (1.36 cms), 1‐year RI
5 in., D50 1.3 in., D50
0.94 in., D50 Channel Shear Stress
Insignificant sediment motion
Significant sediment motion
Reference shear stress is based on EGL slope.
Sediment Classes in inches, 5"Type1, 1.3" Type 2, 0.94" WDFW Coho Redds.
Chart 4
Sediment Grain Mobility (48 cfs)
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 12 090202-01
Chart 5 shows the relative shear stress condition for a 10-year recurrence interval discharge
along with the corresponding channel shear stress.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.1
1
10
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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(τ /τ r )
River Station (ft)
Relative Sediment Mobility ‐Springbrook Creek
Q = 88 cfs (2.49 cms), 10‐year RI
5 in., D50 1.3 in., D50
0.94 in., D50 Channel Shear Stress
Insignificant sediment motion
Significant sediment motion
Reference shear stress is based on EGL slope.
Sediment Classes in inches, 5"Type1, 1.3" Type 2, 0.94" WDFW Coho Redds.
Chart 5
Sediment Grain Mobility (88 cfs)
The model results indicate that Type 1 sediment (5-inch, D50) is stable for the modeled cross-
sections at the 10-year discharge. The Type 1 sediment was also evaluated to be stable at the
100-year discharge (see Chart 6). The Type 2 sediment (1.3-inch, D50) is only slightly mobile
at the 1-year discharge and moderately mobile at the 10-year discharge. This will allow for
spawning gravel cleaning and refreshment without losing significant quantities from the
restoration reach. The increase in shear stress and turbulence associated with the rootwads
on LWD configurations will maintain pools excavated during construction. Cover within
the pools will also provide valuable hydraulic refuge areas.
Chart 6 shows the relative shear stress condition for a 100-year recurrence interval discharge
along with the corresponding channel shear stress. Type 2 sediment is clearly mobile at all
cross-sections for the 100-year discharge. Type 2 sediment has a maximum relative shear
stress of approximately 0.8; below the reference shear stress.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 13 090202-01
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.1
1
10
0+00 2+00 4+00 6+00 8+00 10+00 12+00
Sh
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Re
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(τ /τ r )
River Station (ft)
Relative Sediment Mobility ‐Springbrook Creek
Q = 121 cfs (3.41 cms), 100‐year RI
5 in., D50 1.3 in., D50
0.94 in., D50 Channel Shear Stress
Insignificant sediment motion
Significant sediment motion
Reference shear stress is based on EGL slope.
Sediment Classes in inches, 5"Type1, 1.3" Type 2, 0.94" WDFW Coho Redds.
Chart 6
Sediment Grain Mobility (120 cfs)
For all discharges, the WDFW coho sediment GSD (0.94-inch, D50) shows slightly higher
mobility compared to the Type 2 sediment GSD. This increased mobility is not desirable in
the proposed channel because of the unknown influx of sediment supply from upstream of
the site. The selected Type 2 GSD is still within the acceptable range for spawning gravels.
To provide an estimate of the quantity of sediment mobilized through the proposed channel
during a typical 1-year recurrence interval discharge event, a sediment transport simulation
was conducted. The transport simulation used the empirical transport relations of Parker
(1990) and Wilcock and Crowe (2003). These transport relations were developed for use in
gravel bed systems and have been shown to be relatively reliable. The U.S. Forest Service’s
Stream Systems Technology Center BAGS (Bedload Assessment for Gravel-bed Streams)
software was used to run the simulations. See Appendix C for additional information
regarding the use of BAGS. Additionally, a full explanation of the functionality of BAGS can
be found in the BAGS Users Manual (Pitlick 2009). In short, the model used the proposed
typical channel cross-section geometry and normal flow assumptions to calculate channel
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 14 090202-01
shear stress for a specified range of discharges. The specified sediment GSD was then used to
calculate the sediment transport stage and corresponding mass transport rate.
Chart 7 shows the results of a simulation over a single 1-year recurrence interval discharge
event. The measured hydrograph is from the King County stream gage Springbrook Creek
03b (decommissioned) (King County 2010). This measured hydrograph was used to develop
the synthetic hydrograph used for the simulation. The synthetic hydrograph has a peak of 48
cfs for 6 hours.
0
2
4
6
0
10
20
30
40
50
60
Se
d
i
m
e
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t
Vo
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(c
y
d
s
)
Di
s
c
h
a
r
g
e
(c
f
s
)
Simulation Time
Springbrook Creek ‐Sediment Transport Simulation
Simulated 1 yr RI Event, 48 cfs for 6 hrs.
Measured Discharge
1 yr RI Event Threshold
Synthetic Hydrograph
Cumulative Sed. Transport (1.1" D50)
Cumulative Sed. Transport (1.3" D50)
Cumulative Sed. Transport (1.5" D50)
Empirical transport relations from Wilcock 2003 and Parker 1990 are based on an assumed surface GSD and normal flow conditions.
Chart 7
Sediment Transport Simulation
The simulation shows that for the synthetic hydrograph and a 1.3 inch surface median grain
size sediment (represents Type 2 imported channel sediment), approximately 4 cubic yards
(cy) of sediment may be transported through the system. If the surface grain size is
decreased to 1.1 inches the cumulative transport volume may increase to nearly 5 cy. It is
more likely, however, that the surface grain size may increase over time. As this occurs the
expected transport volume of gravel sediment for a 1-year event is anticipated to
dramatically decrease. The simulation shows that if the surface median grain size is
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 15 090202-01
increased to 1.5 inches the cumulative transport volume may decrease to roughly 2.5 cy.
This bounded calculation of cumulative sediment transport indicates that an upstream supply
of sediment in the range of 2.5 to 4 cy per 1-year event would be sufficient to prevent
significant channel degradation. If this sediment supply is not satisfied, degradation may be
expected without additional sediment augmentation. Based on the volume of sediment
currently present upstream of the existing culvert, it appears that a sufficient sediment load is
present in the system to supply the sediment necessary to prevent degradation.
2.3.3 Fish Habitat Evaluation
Proposed channel conditions for low flows during the typical coho migration period
(October through February) were obtained from the 2001 Hydraulic Report and used to
evaluate recommended spawning and rearing criteria (DEA 2001). The criteria used in this
evaluation are summarized in Table 6.
Table 6
Spawning and Rearing Criteria
Description
Depth (ft) Velocity (ft/s)
Lower Bound Upper Bound Lower Bound Upper Bound
Riffle 0.33 0.82 0.98 1.80
Pool 1.64 4.00 0.30 0.79
Spawning criteria provided by Jackels (2009)
Results from the proposed HEC-RAS model within the realigned channel (downstream of
the replacement culvert) were compared to the recommended criteria for stream riffles for
the two lower discharges. These results are summarized in Table 7 and shown in Charts 8
and 9. Average water depth in the channel during the 3.2 cfs flow was approximately 0.6
inches less than the lower bounding criteria for riffles. The water depth was just below the
lower bound depth throughout a majority of the proposed channel for this discharge
(Chart 1). Average depths during the 4.5 cfs flow met the lower bound criteria for depth
through a majority of the channel with some localized areas that were below the specified
depth.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 16 090202-01
Table 7
Spawning and Rearing Criteria, Model Summary (1)
Flow
Event
Discharge
(cfs)
Depth (ft) Velocity (ft/s)
Minimum Average Maximum Average
Current 3.2 0.23 0.29 1.76 1.59
Future 4.5 0.25 0.35 2.65 1.81
See DEA 2001 for explanation of hydrology values.
0.0
0.2
0.4
0.6
0.8
1.0
1+00 3+00 5+00 7+00 9+00
Fl
o
w
De
p
t
h
(f
t
)
HEC‐RAS Station (ft)
Upper Bound Criteria
Lower Bound Criteria
4.5 cfs
3.2 cfs
Chart 8
Water Depth in Proposed Channel at Low Flows (3.2 cfs and 4.5 cfs)
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 17 090202-01
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1+00 3+00 5+00 7+00 9+00
Av
e
r
a
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Fl
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Ve
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c
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(f
t
/
s
)
HEC‐RAS Station (ft)
Upper Bound Criteria
Lower Bound Criteria
4.5 cfs
3.2 cfs
Chart 9
Velocities in Proposed Channel at Low Flows (3.2 cfs and 4.5 cfs)
Cross-section averaged channel velocities for both flows were higher than the lower bound
criteria; however, average velocities are within the range of recommended velocities
throughout a majority of the proposed channel (Chart 2). The cross-section averaged
channel velocities for the 3.2 cfs flow remain below the upper bound value. Just
downstream of the proposed culvert, and at five cross-section locations near the downstream
end of the proposed channel where it appears the water depth is more shallow, velocities are
slightly higher than the upper bound criteria for velocities for the 4.5 cfs modeled discharge.
It is important to note that these results are for the relatively plain trapezoidal channel
configuration without the inclusion of LWD or placed gravel bars.
To examine the effect of micro-topography (pools and riffles) on hydraulic conditions for fish
habitat, a second, more detailed HEC-RAS model was developed. This habitat model was
developed to include the placement of LWD, scour pools, and gravel bars. The model
examines a section of the stream that is representative of the proposed LWD configurations.
The area obstructed by LWD configurations and the proposed initial pool extents were
incorporated into the model geometry. The cross-section geometry and LWD configurations
are roughly shown on Plan Sheets C-8.0 and C-8.1. Modeled discharges included the
existing and future conditions low flow as well as a typical high flow (10 cfs) in the fish
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 18 090202-01
migration period. The high flow value represents a typical high flow during the period
between October and November based on 5 years of gage data (King County 2010).
Charts 10 through 12 show the relevant output from the habitat model with respect to the
model station. For LWD location comparison purposes the model station is approximately 76
feet greater than the proposed channel alignment station. Each chart shows and labels the
upper and lower bound criteria values for pool velocity and depth, respectively.
‐1.0
‐0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
28
33
38
43
48
5+00 5+20 5+40 5+60 5+80 6+00 6+20 6+40 6+60 6+80 7+00
Fl
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De
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(f
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& Ve
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(f
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El
e
v
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t
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(f
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HEC‐RAS Station (ft)
LWD Detail Model, Long Profile
Q = 3.2 cfs , Lower Bound Low Flow
Min. Channel Elv.W.S. Elev
Max. Flow Depth Avg. Velocity
0.79 ft/s
1.64 ft
Chart 10
Habitat Model Results (3.2 cfs)
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 19 090202-01
‐1.0
‐0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
28
33
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43
48
5+00 5+20 5+40 5+60 5+80 6+00 6+20 6+40 6+60 6+80 7+00
Flo
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(f
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& Ve
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(f
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El
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(f
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HEC‐RAS Station (ft)
LWD Detail Model, Long Profile
Q = 4.5 cfs , Upper Bound Low Flow
Min. Channel Elv.W.S. Elev
Max. Flow Depth Avg. Velocity
0.79 ft/s
1.64 ft
Chart 11
Habitat Model Results (4.5 cfs)
‐1.0
‐0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
28
33
38
43
48
5+00 5+20 5+40 5+60 5+80 6+00 6+20 6+40 6+60 6+80 7+00
Fl
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(f
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El
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(f
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HEC‐RAS Station (ft)
LWD Detail Model, Long Profile
Q = 10 cfs , Fish Flow
Min. Channel Elv.W.S. Elev
Max. Flow Depth Avg. Velocity
0.79 ft/s
1.64 ft
Chart 12
Habitat Model Results (10 cfs)
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 20 090202-01
Table 8 summarizes the habitat model results relevant to the coho spawning and rearing
criteria. Results are averages over the extent of the habitat model for the specific channel
feature type (riffle or pool). The model shows that spawning and rearing criteria are satisfied
for a discharge of 3.2 cfs in both the pools and riffles. For a discharge of 10 cfs the model
shows that depth criteria are satisfied but the velocity criteria are slightly exceeded on
average.
Table 8
Spawning and Rearing Criteria, Model Summary (2)
Description
Depth (ft) Velocity (ft/s)
3.2 cfs 10 cfs 3.2 cfs 10 cfs
Riffles 0.3 0.7 2.0 2.4
Pools 1.7 2.0 0.79 1.5
Although the habitat model captures the basic geometry of the LWD configurations and
pools, inherent limitations of the one-dimensional model do not capture complex variations
in velocity around LWD, margin areas, and in pools. Therefore, it is likely that there will be
areas that satisfy the velocity criteria at a discharge of 10 cfs.
2.4 Proposed In‐Channel Large Woody Debris Placement
Placement of LWD in the proposed channel includes three configurations: a channel center
log configuration (Type 1), a bank log configuration (Type 2), and a bend stabilization log
configuration (Type 3). In-channel LWD placement locations are shown on Plan Sheets C-3
through C-5, and detail sections are shown on Plan Sheets C-8.0 and C-8.1. LWD has been
placed throughout the channel such that it encourages a natural pool and riffle spacing while
exceeding the key piece requirements for the 75th percentile of key pieces in natural systems
according to recommendations by Fox and Bolton (2007). The proposed LWD placements
are a vital component in the maintenance of fish habitat. The logs will increase hydraulic
variability, promote accumulation of other debris, and enhance fish habitat by providing
holding areas with cover and refuge, aeration of surface water, and localized scour and
deposition of channel material (micro-topography). The Type 3 placement will also aid in
the stabilization of the outer right bank bends and minimize the potential for lateral channel
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 21 090202-01
migration to the north. In addition, the hydraulic roughness provided by the rootwads will
dissipate hydraulic energy that may otherwise cause erosion of the banks.
2.4.1 LWD Log Quantities and Locations
The proposed quantity of in-channel LWD is based on recommendations for wood loading of
key pieces to the 75th percentile of natural conditions according to criteria established by
Fox and Bolton (2007). Over time, it is expected that additional LWD (smaller pieces in
particular) will accumulate within the channel contributed from upstream or from the
surrounding riparian vegetation as the result of natural mortality, windfall, and other causes,
leading to a total LWD quantity of large and small pieces similar to natural systems. Table 9
summarizes the recommended quantities of LWD and key pieces for a 0- to 6-meter bankfull
width (BFW) channel in the Western Washington region. Key pieces are defined as having
an adequate size such that the wood is stable and functional with the ability to retain other
pieces of organic debris. While the typical individual log volume proposed is slightly less
than the value recommended by Fox and Bolton (2007), the LWD will be stabilized with
mechanical soil anchors and partially buried in the bank. Therefore, the proposed logs will
remain stable and function to accumulate additional wood over time.
Table 9
Recommended Natural Conditions LWD Quantities
BFW (meter)
LWD Pieces per 100 meters Key Pieces per 100 meters
75th Percentile Median 25th Percentile 75th Percentile Median 25th Percentile
0‐6 > 38 29 < 26 > 11 6 < 4
Fox and Bolton (2007)
The proposed channel alignment downstream of the South 55th Street culvert crossing is
approximately 975 feet long, or 297 meters. For the purposes of this assessment it is assumed
that the channel is 300 meters long. As summarized in Table 10, the design proposes
approximately 13 pieces of in-channel LWD for every 100 meters throughout the new
alignment when all individual log placements with rootwads are included, which exceeds the
recommended 75th percentile guideline of 11 key pieces presented by Fox and Bolton (2007).
The quantity for every 100 meters becomes approximately 22 pieces when all logs, including
those within multiple-log formations, are totaled.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 22 090202-01
Table 10
Proposed LWD Quantities and Volumes
Design Element
Average Pieces per
100 meters
Total Pieces
Proposed
Individual Log Placements 13 40
Multiple Log
Structures
Pieces with
Rootwads 5 16
All pieces including
stringer logs 9 27
Total LWD placements 22 67
The proposed locations for in-channel LWD were developed in an effort to maximize habitat
complexity by encouraging the formation of natural stream features. The placement spacing
is intended to provide a relatively even and geomorphically consistent distribution of pool
and riffle features along the proposed channel. Project stations and channel positions for the
LWD configurations are listed in Plan Sheets C-9.0 and C-9.1.
2.4.2 In‐Channel LWD Placement Types
Type 1 log configurations will be placed in straight portions of the proposed channel with
the rootwad facing upstream (Plan Sheet C-8.0). The configuration will provide hydraulic
variability along the length of the corresponding riffle. These logs will be partially buried in
the gravel substrate and a pool will be excavated around the rootwad. The pool is intended
to provide increased flow depths at low flow simulating natural conditions. The pool is
anticipated to be naturally maintained by the turbulence caused by the rootwad placement.
Type 2 log configurations will be placed on alternating channel banks (Plan Sheet C-8.0).
The configuration will encourage alternating pool, bar, and riffle features. During placement
of the Type 2 logs a pool will be excavated around the rootwad to a minimum depth of 1.0
feet below the rootwad. The pool will be lined with imported channel sediment, Type 2.
The pool is anticipated to be naturally maintained by the turbulence induced by the rootwad
placement. Between the alternating bank placements, riffles are likely to form. Placement
in series along the outside of meanders will tend to decrease bank erosion by deflecting the
high energy current away from the bank.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 23 090202-01
Type 3 configurations will be placed on the right bank (north side) of selected meanders
(Plan Sheet C-8.1). This configuration will provide pool habitat and minimize the potential
for lateral migration of the proposed channel to the north. These placements will be
accompanied by placement of Type 1 imported channel sediments. The Type 3 LWD
configurations will be bedded into the imported sediment and partially covered as shown in
the plans. This coarser sediment will provide additional protection against bank erosion and
lateral channel migration. During placement of the Type 3 configurations a pool will be
excavated around the rootwads to a minimum depth of 1.0 feet below the rootwads. The
pool is anticipated to be naturally maintained by the turbulence induced by the rootwad
placement.
2.4.3 LWD Stability and Expected Scour
Mechanical soil anchors will be used to secure the LWD configurations in place. Details and
specifications for the soil anchors and their connection to the LWD configurations are shown
on Plan Sheets C-8.0 and C-8.1. The load capacity of the soil anchor and connections to the
log is based on the expected maximum buoyancy and drag forces exerted on an exposed log
during a 100-year flow event. The net buoyancy and drag force calculated for an exposed log
in the center of the channel during a 100-year event is 500 pounds [2 kilonewtons (kN)]. All
soil anchors will be proof tested to a load of 1,000 pounds, per Project specifications, which
provides a stability factor of safety of 2. The stability factor of safety provides additional
protection against uncertainties such as subsurface conditions, unexpected high flows, and
unexpected accumulation of debris, thereby increasing the drag forces exerted on the log
placement. All portions of the mechanical soil anchor to LWD connection will have a rated
load capacity that exceeds the proof test load. Although a factor of safety has been
considered for the mechanical soil anchors and log cabling, this factor of safety does not
protect the installation from unexpected scour and undermining of the mechanical soil
anchor.
Pools excavated during placement of the LWD will be naturally maintained due to the local
turbulence inflow caused by each rootwad at higher discharges. Although fine sediments
may be deposited in the pools following small flood events it is anticipated that the sediment
will then be scoured out during subsequent larger flow events. These deposition and scour
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 24 090202-01
cycles will help maintain sufficient pool habitat depths especially around LWD rootwads.
The proposed pool volume excavation is based on maintaining a similar cross-sectional flow
area, below BFW, at LWD placement locations compared to locations without LWD. The
depth and extent of the pools was based on professional judgment and experience with
similar LWD installations.
2.5 Proposed Floodplain Log Placements and Plantings
Log poles will be placed in a linear continuous structure at an approximately east-west
orientation along the northern boundary of the Project area in the existing floodplain. Each
log pole will be buried to one-half the diameter, as shown on Plan Sheet C-12.1. Offsetting
the logs from the channel bank will allow floodplain connectivity to the extent possible
(within the Project extents), while retaining flows in the vicinity of the proposed channel.
The floodplain log pole structure specified will contain flows within the Project area
approximately up to a 10-year event (assuming no leakage between logs of the structure),
with a minor amount of flow overtopping the logs at greater flows. Individual logs with
rootwads will be placed, angled upstream of the floodplain log pole structure, to provide low
velocity refuge areas and additional floodplain roughness, thereby increasing the ability to
trap overbank sediments and build up a natural berm over time. The individual rootwad logs
do not affect the containment of floodwaters; therefore, the sizing of these logs will likely be
dependent upon availability of materials. The floodplain log placements will be partially
backfilled using onsite spoils. The placement extents and typical section for backfill is shown
on the plans. Approximately 100 cubic yards of spoil material from project activities will be
placed in conjunction with the floodplain log placements.
Size (diameter and length) specifications for the floodplain log pole structure were
determined by modifying and running the proposed hydraulic model in an iterative manner
to establish the appropriate height to contain floodwaters at various peak flow events. It
should be noted that the calculations performed to estimate log diameters assume a vertical,
non-porous structure located at the northern boundary of the Project area. Therefore, small
volumes of water that may seep through spaces between the logs are not accounted for in the
estimation. However, floodplain plantings of vertical willow stakes are expected to
contribute flow retention in addition to the log structure. Additionally, the HEC-RAS model
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 25 090202-01
was run as a steady-state condition; the results of the model only simulate the cross-sectional
averaged water surface elevation at the peak of a high flow event, rather than a dynamic
scenario such as a multiple day- or hour-long storm event.
2.5.1 Floodplain Log Model Development and Analysis
To model the floodplain log placements a lateral weir was incorporated into the HEC-RAS
model at the Project limit and the flow optimization option was chosen to calculate the
amount of flow (cfs) overtopping the weir and leaving the Project area. Because of the low
topography north of the site, it was assumed that this flow permanently leaves the site and is
unable to re-enter the Upper Springbrook Creek channel. To develop an initial estimate at
the height required to retain flows, the crest height of the lateral weir was set to well above
the expected water depth at the Project limit. Because this configuration retains all flow in
the floodplain, this height is likely an overestimate as flow does not leave the domain. From
this initial estimate, the height of the weir was stepped down in 0.05-foot increments until at
least 99.5 percent of flow was retained at the 100-, 50-, 25- and 10-year flows. Calculation
tolerances of the weir split flow were set to converge to within 0.5 percent of total discharge
(the default is 2 percent). Table 11 summarizes the results of the lateral weir split flow
sensitivity analysis.
Table 11
HEC‐RAS Lateral Weir Analysis Summary
Flow Event
100%
Contained
Total
Discharge
(cfs)
Discharge Over Weir
(cfs)
Discharge In‐Channel
(cfs)
Average Height of
Weir Above Existing
Floodplain Grade (ft) 10 25 50 100 10 25 50 100
10‐year 88 0.1 1.2 4.6 9.9 87.9 97.8 105.4 111.0 1.14
25‐year 99 0.0 0.1 0.8 3.4 88.0 98.9 109.2 117.6 1.20
50‐year 110 0.0 0.0 0.1 0.6 88.0 99.0 109.9 120.4 1.25
100‐year 121 0.0 0.0 0.0 0.0 121.0 110.0 99.0 88.0 1.35
Discharge values rounded to nearest one‐tenth cfs.
The results of the lateral weir sensitivity analysis show that a weir height that contains a 10-
year flow event also retains approximately 92 percent of the 100-year flow. Based on these
results, as well as discussion with WDFW and the Corps, it is assumed that the minor
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 26 090202-01
amount of flow that would leave the site during a 100-year flow event is likely a significant
improvement upon current flooding conditions. Therefore, floodplain logs poles were
specified to contain the 10-year peak flow discharge (while allowing for some leakage
between log poles).
2.5.2 Floodplain Log Size Specification
A log diameter was calculated for a half-buried log using the water depth at the Project limit
at each HEC-RAS cross-section where bank overtopping occurred. The calculated diameter
was rounded up to the nearest typical log diameter (e.g., 12-inch, 18-inch, 24-inch, and 30-
inch). In order to simplify the floodplain log pole specifications, average log length was
assumed to be approximately 35 feet with a 5-foot overlap on each side, and the calculated
log diameters (to the nearest typical size) were grouped with the output from adjacent cross-
sections to determine the minimum log diameter necessary at that location. The typical log
diameters determined at each cross-section were broken up into groups of at least two logs
(approximately 50 feet in length) to simplify specifications and construction actions.
Floodplain log pole specification calculations are presented in Appendix B. The specified
diameters shown in Plan Sheets C-9.0 and C-9.1 were placed in the floodplain by super-
imposing the geo-referenced HEC-RAS cross-sections onto a base map of the site.
2.6 Proposed Culvert Replacement
2.6.1 Culvert Specifications
The existing 30-inch-diameter corrugated steel culvert (Existing Culvert 3) at the east end of
the Project area will be removed and a new culvert installed. The existing culvert conveys
Upper Springbrook Creek under South 55th Street into the channel segment to be realigned
as part of the Project. The replacement culvert will be installed along a similar alignment as
the existing culvert. Culvert details are shown on Plan Sheets C-10.0 through C-10.4.
Design of the replacement culvert was based on the stream simulation design option methods
from the WDFW Design of Road Culverts for Fish Passage (Culvert Design Manual; WDFW
2003) and criteria from the King County Surface Water Design Manual (SWDM; King
County 2005). Additional design criteria was also developed based on site-specific
limitations including physical constraints and expected fish passage requirements in the new
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 27 090202-01
culvert. Physical limitations include the existing channel grade on the upstream end of the
culvert, the presence of underground utilities (sewer mains and structures), and the design
grade of the proposed channel realignment at the downstream end of the culvert.
Providing improved hydraulic conditions for fish passage was a primary goal of culvert
replacement. The existing culvert presents a considerable fish passage barrier because its
downstream invert is perched approximately 3 feet above the channel bed elevation. The
design of the new culvert focused on providing appropriate hydraulic conditions for fish
passage over a range of stream flows within the physical constraints of the site. These fish
passage conditions were achieved using the methods given in the stream simulation design
option (WDFW 2003, Chapter 6).
The design flows used for culvert design and analysis are as follows:
Fish passage design flow of 3.2 cfs to 4.5 cfs, the 10 percent exceedance flow (Table 1)
Conveyance design flow of 121 cfs, the 100-year return period flow (Table 1)
Required conveyance through culverts for the 100-year flood event is regulated by the
SWDM (King County 2005, Section 4.3.1.1) and is based on a maximum rise in headwater of
1.5 times the culvert rise.
Based on the above described design criteria and the presence of the sewer line within the
roadway prism, a 10-foot-span, 5.25-foot-rise concrete box culvert was selected as the
replacement culvert. The alignment, longitudinal profile, and cross-section of the proposed
culvert are shown on Plan Sheets C-10.0 through C-10.4. Culvert specifications including
vertical alignment, counter sink depth, length, and clearance over the sewer line are shown
in Table 12. Details for protection and modifications to the existing sewer main are shown
on Plan Sheets C-11, and discussed further in Section 3.6.
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 28 090202-01
Table 12
Replacement Culvert Specifications
Description Culvert
Width, Inside (ft) 10.0
Rise, Inside (ft) 5.25
Upstream Invert (ft) 41.02
Downstream Invert (ft) 40.03
Depth of Gravel Fill, Average (in) 12 (Min. 9)
Length (ft) 53.8
Longitudinal Slope (ft/ft) 0.0182
Clearance Over Sewer (ft) 0.0
The proposed culvert slope of 1.82 percent meets the slope ratio requirements (WDFW 2003,
Chapter 6) that the culvert’s slope be less than or equal to 1.25 times the slope of the channel
upstream of the culvert. For this culvert the upstream channel slope is approximately 4.0
percent. The existing channel slope downstream of the culvert (1.6 percent) results in a
slope ratio is 1.14, also within the limit.
The proposed 10-foot culvert span meets the culvert width requirements stated in the
Culvert Design Manual (WDFW 2003, Chapter 6) that the culvert’s width be greater than or
equal to 1.2 times the existing downstream BFW plus 2 feet. Because it is difficult to
determine an appropriate “natural” BFW due to modification of the Upper Springbrook
channel, a regression relationship based on drainage area and average annual precipitation
was used to determine the BFW (Barnard 2010). This relationship has been developed by
WDFW representatives using measured data from several relatively small, high gradient
(greater than 2 percent), coarse-bedded stream systems in the region. Based upon this
method the estimated BFW is 6.7 feet, making the required culvert width 10.0 feet. A width
of 10 feet is expected to be adequate based on observed BFW for the modified stream system
downstream of the culvert.
The culvert counter sink (average depth of gravel fill) depth of 12 inches meets the culvert
fill requirements (WDFW 2003, Chapter 6) of 30 percent to 50 percent of the hydraulically
required culvert rise (approximately 3 feet). The culvert will be filled with Type 1 imported
channel sediment. The sediment specification conforms to the design methods in the
Design Analysis
Design Documentation Report May 2010
Upper Springbrook Creek Project 29 090202-01
Culvert Design Manual (WDFW 2003) for stream simulation. The sediment provides a stable
bed capable of transporting sediment delivered from the upstream reach through the culvert.
A low flow channel will be provided by alternating the locations of large rock clusters along
the culvert sides. Additionally, one large rock sill and two log sills will provide grade control
and encourage the development of small pools and low velocity areas within the culvert at
low flow. The placement plan for sediment in the culvert is shown on Plan Sheet C-10.4.
The plan shows locations of the rock and log sills, rock clusters, and the low flow channel
alignment.
This culvert configuration will provide flood conveyance up to the 100-year flow without
exceeding the SWDM headwater rise criteria of 1.5 times the culvert rise. The culvert will
have an interior freeboard of approximately 1.5 feet during the 100-year flow with no
appreciable headwater rise. The culvert rise for this design was determined from municipal
maintenance access requirements. The sediment sill depth was based on the required culvert
rise for passage of the 100-year flow and recommended minimum depths from WDFW.
2.6.2 Inlet/Outlet Design and Specifications
Wingwalls, headwalls, and other stabilization measures at the ends of the new culvert will
direct flow through the culvert while stabilizing the road prism and channel banks near the
culvert. Plan Sheets C-10.2 and C-10.3 show proposed wingwalls and headwalls at the ends
of the culvert outside the design road clear zone.
Wingwalls and headwalls will be precast concrete sections joined to the culvert with
manufacturer recommended methods. At the outlet of the culvert the ends of the wingwalls
will be blended into the channel banks using select placement of larger rocks derived from
Type 1 imported channel sediment. Additionally, the stream bed immediately downstream
of the culvert will be lined with Type 1 imported channel sediment to provide erosion
protection and a natural transition out of the culvert. Plan Sheet C-10.4 shows the extents
and details of Type 1 imported channel sediment in and around the culvert.
The existing channel bed at the culvert inlet will be graded to match the proposed sediment
fill invert elevation. In addition to wingwalls at the culvert inlet, the toe of the left bank will
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Upper Springbrook Creek Project 30 090202-01
be stabilized by the placement of log poles secured into the bank and coir fabric (see Plan
Sheet C-10.4).
2.6.3 Fish Passage Evaluation
As described in the Culvert Design Manual (WDFW 2003), fish passage criteria for
construction of new culverts includes maximum velocities, minimum water depths, and
maximum hydraulic drop depths in the fishway, as shown in Table 13. Critical species
present in Upper Springbrook Creek include coho salmon; therefore, the fish passage criteria
for adult Chinook, coho, sockeye, or steelhead from Table 5-1 in the Culvert Design Manual
were used in the analysis. These criteria are valid for culverts between 10 feet and 60 feet
long.
Table 13
Culvert Adult Fish Passage Design Criteria
Description Design Criteria
Maximum Velocity 6.0 ft/s
Minimum Water Depth 1.0 ft
Maximum Hydraulic Drop 1.0 ft
To verify that the proposed culvert will meet fish passage criteria, a detailed HEC-RAS model
geometry of the culvert bed including low flow channel and roughness elements was
developed. The culvert was analyzed for fish passage by comparing the results of the model
to acceptable values for fish passage criteria (WDFW 2003). Table 14 shows the HEC-RAS
model results relevant to the adult fish passage design criteria.
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Upper Springbrook Creek Project 31 090202-01
Table 14
Proposed Culvert Model Results
Description
Discharge
(cfs)
Maximum
Velocity
(ft/s)
Maximum
Depth (ft)
WDFW Passage Criteria N/A 6.0 1.0
Lower Bound Low Flow 3.2 1.9 0.6
Upper Bound Low Flow 4.5 2.2 0.7
1‐year Recurrence Interval 48 4.5 1.8
10‐year Recurrence Interval 88 5.5 2.3
100‐year Recurrence Interval 121 6.2 2.7
The results of the detailed culvert model show that for discharges up to nearly the 100-year
recurrence interval the culvert meets the hydraulic criteria for adult coho fish passage.
Juvenile fish passage at target flows was assumed to be possible based on the culvert design
adherence to the Culvert Design Manual (WDFW 2003) stream simulation approach. This
assumption was agreed upon by relevant agency representatives and design team members
during the January 2010 Project meeting (Anchor QEA 2010b).
2.6.4 Road Grade Replacement and Utility Relocation
Road grade replacement and utility relocation will be conducted in accordance with all
applicable regulations and design standards. Vertical road alignment will be adjusted as
necessary to provide sufficient road thickness over the culvert. The sanitary sewer manhole
elevation may need to be adjusted in conjunction with road re-grading. Manhole rim
elevation adjustments may be made with riser rings and conform to all applicable regulations
and design standards. A telecommunications conduit, owned by Qwest Communications
International Inc., will likely be permanently relocated during culvert placement and
replaced in accordance with line owner specifications. Details and specifications for road
grade replacement and utility relocation can be found on Plan Sheets C-12.0 and C-12.1, and
in the specifications package.
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Upper Springbrook Creek Project 32 090202-01
2.6.5 Culvert Structural Requirements
The proposed culvert shall meet all applicable structural design requirements. The culvert
manufacturer will be responsible for meeting all applicable codes and specifications. These
requirements include:
AASHTO LRFD bridge design specifications (5th edition), live load type HL-93.
WSDOT bridge design manual, M 23-50.02, current edition (supplements AASHTO
LRFD bridge design specifications)
WSDOT local agency guidelines, M 36-63.06, chapter's 34 and 42
Satisfaction of geotechnical engineering requirements will be the responsibility of the pre-
cast manufacturer, and the contractor during construction. Structural design elements will
be required to be submitted as shop drawings per the project specifications.
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3 CONSTRUCTABILITY ANALYSIS
Construction of the Project is currently scheduled for the summer of 2011, pending Project
permit acquisition and contractor selection, among other factors. Potential challenges to the
construction of the Project, which may affect the schedule and cost, include:
Unforeseen or unknown utility conflicts during channel excavation and culvert
construction
Ingress and egress of vehicular traffic on South 55th Street during construction of the
replacement culvert
Construction actions and consideration are discussed in the following sections and include:
Recommended construction equipment
Mobilization, site access and staging, and site preparation
New channel construction
In-channel LWD and floodplain log placements
Culvert construction
Creek flow ramping and fish rescue and recovery
Decommissioning of the existing channel
Construction decommissioning and site restoration
Best management practices (BMPs)
3.1 Recommended Construction Equipment
The construction site is within an existing wetland and natural drainage area where soils are
typically silty and saturated. These conditions limit the type of heavy construction
machinery that can be used safely and efficiently.
It is recommended that equipment used for the Project include only tracked equipment, as
rubber-tired equipment may experience limited traction and maneuverability. The Project
site is heavily vegetated in some areas and minimal disturbance to vegetation is desired;
therefore, smaller, lighter, and more maneuverable equipment may be the most efficient.
Machinery recommended for use in construction of the Project is listed in Table 15.
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Upper Springbrook Creek Project 34 090202-01
Table 15
Recommended Construction Equipment
Excavation
and Fill
Material
Transport
LWD
Placement
Culvert
Construction
Preferred Machinery
Tracked
Excavator
(120‐series)
Tracked
Dumper
(Morooka)
Tracked
Log Loader
Excavator or
Backhoe
Loader
Alternate Machinery
Tracked
Excavator
(200‐series)
Tracked
Loader
Tracked
Excavator N/A
3.2 Mobilization, Site Access and Staging, and Site Preparation
Mobilization of the Project site involves the transport and delivery of construction
equipment, tools, material, and supplies. Mobilization length of time is dependent upon the
contractor’s scheduling, availability of equipment/materials/supplies, and the areas available
for staging and access. Mobilization also includes the acquisition of any and all construction
permits and preparation and implementation of construction plans, such as a Temporary
Erosion and Sedimentation Control (TESC) Plan, Care of Water Plan, Traffic Control Plan,
Stormwater Pollution Prevention Plan and others as necessary. Utility locating is necessary
prior to the start of construction activities.
Site access is provided at each end of the new channel alignment and two staging areas are
proposed, as shown in Plan Sheet C-6. Disturbance to existing conditions within access and
staging areas will be limited to the extent practicable, and the removal and disturbance of
riparian vegetation will be limited or avoided to the extent possible. Local and state
jurisdictions may require temporary construction easements. Permission to access private
property for culvert replacement and associated construction actions will require the
acquisition of a Temporary Work Area (TWA) easement, as well as the establishment of a
Perpetual Environmental Easement to encompass permanent structures to be built upstream
(south) of the right-of-way limit. Temporary improvements for access and staging areas may
be required, however the installation of rock entrances has not been proposed due to the
typical silty, muddy conditions of the site. Measures will be required to provide erosion and
sediment control.
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Site preparation will involve light clearing and grubbing only as necessary for the movement
of equipment along the access and staging areas, and to prepare for excavation of the new
channel and other design elements. Less than 1 acre is expected to be disturbed, which
includes the new channel alignment and temporary site access and staging areas. Other site
preparation work includes the installation of fish exclusion screens in the existing channel
upstream and downstream of the Project site (Sheet C-7 and C-14). Site preparation should
include identifying potential hazards such as overhead utilities, underground utilities, and
areas where shoring protection will be required for construction.
TESC measures will be employed during site preparation to limit the amount of erosion on-
site, as well as off-site transport of sediment from construction activities. TESC measures
proposed include a silt fence along the extent of the Project limits, and erosion and sediment
management at access points and staging areas. Typical silt fence details are shown on Sheet
C-14.
Plan Sheet C-6 illustrates the locations of proposed site access, staging, and TESC measures.
The plans show two access routes that cross over the existing channel. The access route over
the existing channel at the west end of the project will require temporary measures to cross
the existing channel while providing care of water in accordance with permit requirements.
The access route over the existing channel at the east end of the project will become a
permanent fill in the existing channel. During construction this access route will also need
to comply with all permit requirements.
3.3 Demolition
Minimal demolition is required for the Project. Demolition includes the removal of the
following existing features, which are shown in the Plans (Sheets C-3 through C-5):
A derelict culvert headwall located upstream of the existing culvert to be replaced.
Asphalt and subgrade removal for replacement culvert and installation of sewer
casing pipe.
An existing culvert under South 55th Street (see Section 3.6, below).
A small sandbag berm located north of the existing channel.
An abandoned staff gage near the downstream end of the existing culvert.
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Upper Springbrook Creek Project 36 090202-01
Miscellaneous refuse and debris encountered within the Project area (natural debris is
not included).
A 4-inch diameter ductile iron water main located immediately upstream of the South
55th Street culvert; the main has been unofficially identified as abandoned. The
option to remove the feature shall be coordinated by the Corps and the City with the
Utility Owner.
All demolished materials shall be removed from the Project site and disposed of in an
approved disposal site meeting all local, state, and federal regulations. Natural debris
(boulders, logs, stumps, etc.) will be dispersed on-site within the floodplain.
3.4 New Channel Construction
Approximately 975 linear feet of new channel will be created as part of the Project within a
100-foot-wide drainage easement that encompasses a vegetated wetland/floodplain.
Excavation of the new channel will require heavy machinery. Table 15 lists recommended
and alternate construction equipment.
Approximately 1,067 cy of excavation is expected for the construction of the new channel.
Of the total excavation volume, 506 cy is over-excavation of the channel followed by backfill
of imported channel sediment (Type 2). Spoils may be used in other design elements such as
floodplain log placements, provided the spoils meet standards for those uses. The remaining
spoils will be transported off-site and disposed of in an approved disposal site.
The proposed channel alignment will cross over the alignment of an existing sanitary sewer
line near the confluence with the existing channel, shown in Plan Sheet C-3 (WRA 1978).
Based on calculations of maximum scour depth it has been determined that sufficient
clearance exists above the sewer line at this location. No special actions will be required at
this crossing to protect the sanitary sewer line.
It is recommended that construction of the new channel includes the use of two equipment
teams; each team consisting of one tracked excavator and one tracked dumper. In an effort
to reduce haul distances and minimize impact and disturbance to the Project site, it is
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Upper Springbrook Creek Project 37 090202-01
recommended that excavation of the new channel occur simultaneously at each end of the
new channel and continue toward the middle of the channel. Once excavation of the new
channel is completed, one team of equipment may begin construction of the floodplain
improvements and another equipment team may begin placing imported channel sediment
and in-stream LWD placements from the middle of the proposed channel alignment and
continue work towards the downstream end of the Project. Once the floodplain
improvements are completed, an equipment team may complete the placement of imported
channel sediment and in-stream LWD from the middle of the channel alignment, working
towards the upstream end of the new alignment.
Approximately 5 cy of existing material will be left in place at the upstream end of the new
channel to temporarily prevent the potential of inflow of water from the existing channel
Sheet C-7. The existing channel will be undisturbed during excavation of the new channel.
This upstream material will be removed sequentially when flow is diverted from the existing
channel to the new channel as discussed in Section 3.7.
Following construction of the new channel, coir fabric will be installed along the banks of
the new channel from the toe of slope, underneath the imported channel sediment, to the
top of slope and extend upland of the new channel as necessary to stabilize areas disturbed
during construction of the new channel (Plan Sheets C-9.0 and C-9.1). Coir fabric will be
installed in accordance with the manufacturer recommendations in addition to the Project
specifications (Sheet C-14).
3.5 Large Woody Debris Placements
LWD placements are proposed in two areas of the Project area: within the proposed channel
and along the northern boundary of the Project area in the floodplain. These areas are
discussed in Sections 3.5.1 and 3.5.2. The locations of LWD are shown in Plan Sheets C-9.0
and C-9.1.
3.5.1 In‐Channel Large Woody Debris Placements
The placement of LWD in the proposed channel (in-stream) includes three configurations:
two single log placements and a multiple-log bank stabilization structure. Each
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configuration involves attaching the wire rope to a mechanical soil anchor, driving the
anchor(s) below the channel bottom to a design depth, load locking the anchor and proof
testing to a specified load, drilling the log(s), and securing the wire rope to the log(s).
Placement of the LWD will require the use of machinery (see Table 15 for recommended
equipment) and installation of the mechanical soil anchors may be performed with light
machinery or other means approved by the manufacturer.
Type 1 single log configurations involve placement of the log in the middle of the channel
with its rootwad facing upstream. A shallow trench will be excavated to place the log with
approximately the top one-third diameter of the log above final grade. One mechanical soil
anchor, installed into the channel subgrade and affixed to the bole downstream of the
rootwad mass, will stabilize the log. During placement of the Type 1 logs a small pool will be
excavated around and underneath the rootwad. The pool will be lined with imported
channel sediment, Type 2. Plan Sheet C-8.0 shows the configuration of this LWD
placement.
Type 2 single log configurations will be placed on alternating channel banks. The log bole
will be buried into the bank a minimum of 2/3 its length with the top of the log flush with
the top of the bank. One mechanical soil anchor, installed into the bank subgrade and
affixed to the bole behind the rootwad mass, will stabilize the log. During placement of the
Type 2 logs a small pool will be excavated around and underneath the rootwad. The pool
will be lined with imported channel sediment, Type 2. The excavated sediment will be
placed as a bar deposit immediately downstream of the LWD placement. Plan Sheet C-8.0
shows the configuration of this LWD placement.
The multiple-log bank stabilization structure is a continuous log structure along the outside
bends of the right bank in the new channel. Logs with rootwads will be placed
perpendicular to flow at the top of the right bank with rootwads protruding into the channel
and the pole ends buried into the right bank. Log poles will be placed parallel to the channel
between the perpendicular logs. The logs will then be tied together using wire rope to create
a continuous structure. As illustrated in Plan Sheet C-8.1, mechanical soil anchors will be
installed into the bank subgrade and affixed to the structure minimizing the likelihood of the
structure becoming mobilized. During placement of the Type 3 configurations a pool will be
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Upper Springbrook Creek Project 39 090202-01
excavated around and underneath the rootwads. Topsoil and vegetation removed for
placement of the logs into the right bank will be set aside and replaced following backfill of
the logs.
3.5.2 Floodplain Log Placements
Placement of LWD in the floodplain includes construction of a linear, continuous log pole
structure and individual rootwad logs (Plan Sheet C-13). These placements require the use of
equipment similar to that required for in-channel placement of LWD (see Table 15). Work
required for construction of the floodplain log placements should be completed prior to
completion of the new channel construction and prior to revegetation efforts, which are
expected to occur under a separate contract following completion of the Project.
Revegetation efforts include floodplain plantings (live stakes along the floodplain log pole
structure), as well as additional riparian plantings along the new channel and in the
floodplain.
The floodplain log pole structure will require clearing and excavation of a shallow trench
excavation to partially bury the log poles to a depth approximately one-half the diameter of
each log pole placed. The logs will be placed at the existing floodplain elevation. Access for
machinery to place the floodplain logs is shown in Plan Sheet C-6. All efforts will be made
to minimize the amount of disturbance of the floodplain to complete this portion of the
Project. Areas disturbed by the use of machinery for the placement of floodplain logs will be
temporarily stabilized with the use of straw, coir fabric, or other measure. Log poles placed
in the structure, with the exception at the ends of the structure, will overlap adjacent log
poles by approximately 5 feet and the overlapped portion of adjacent logs will require tight-
fitting tolerances. The log placements will be partially backfilled using onsite spoils. The
placement extents and typical section for backfill is shown on Plan Sheet C-13.
Approximately 100 cubic yards of material will be placed in conjunction with the floodplain
log placements.
The individual rootwad log placements in the floodplain will be located and oriented as
shown in Plan Sheets C-9.0 and C-9.1. Placement of the rootwad logs will require minimal
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Upper Springbrook Creek Project 40 090202-01
clearing and grading, each will be placed in a shallow trench and buried to approximately
one-half the diameter of the bole end.
3.6 Culvert Construction
Existing Culvert 3 will be replaced with a concrete box culvert. The replacement culvert and
concrete headwalls will be installed as shown on Plan Sheets C-10.0 through C-10.4.
Prior to commencing culvert replacement, creek flow will need to be temporarily routed
outside of the replacement culvert footprint and into the existing channel. The creek will be
diverted into a flexible high-density polyethylene (HDPE) pipe that is capable of conveying
the entire creek flow. In addition to the temporary pipe, temporary revetments will be
necessary to isolate creek flow, both upstream and downstream of the replacement culvert,
for installation of the replacement culvert. These temporary flow diversions will remain in
place as long as is necessary to construct the replacement culvert, which is expected to last
less than 2 weeks. Construction of the replacement culvert and removal of the existing
culvert will be done in a no-flow condition to the extent practicable, referred to below as “in
the dry.” Sequencing of events for construction of the replacement culvert includes:
1. Commence the road cut. The road will be excavated along the replacement culvert
alignment to the footprint and elevation suitable to construct the replacement culvert
to its design elevation. Shoring and trench protection will be employed as necessary.
2. Relocate any utility lines as necessary following applicable standard practices and
specifications for the particular utility. Any modification of existing utilities will
require coordination between the Contracting Officer, Contractor, and Utility
Owner.
3. Install a temporary flow bypass. The flow bypass may include temporary bypass pipe
installed from upstream of the replacement culvert construction footprint to the
existing channel downstream of the replacement culvert construction footprint. The
pipe or other bypass method will have sufficient capacity to convey the entire
anticipated creek flow without causing significant backwater (Sheet C-7).
4. Dewatering methods, including pumping, will be required within the replacement
culvert footprint. Additional methods will include flow revetments upstream and
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Upper Springbrook Creek Project 41 090202-01
downstream of the replacement culvert to convey and bypass the creek flow in order
to construct the replacement culvert (Sheet C-7).
5. Demolish, remove, and dispose of the existing culvert.
6. Expose and protect the existing 12-inch diameter polyvinyl chloride (PVC) sanitary
sewer main. Install a steel casing pipe over the sewer main. Encase the sewer and
casing in CDF as shown in the plans (Sheet C-11).
7. Construct the replacement culvert; dewater culvert footprint as necessary. Install in-
culvert channel sediment.
8. Remove the temporary flow bypass to allow creek flow through replacement culvert.
9. Replace any utility lines as necessary following applicable standard practices and
specifications for the particular utility. Adjust sanitary sewer manhole frame and
cover as necessary according to the specifications.
10. Repair the road cut according to the applicable jurisdictional standards and
requirements (C-12.0 and C-12.1).
11. Commence flow ramping and fish rescue and recovery. See Section 3.7 below.
Construction sequencing for the replacement culvert and temporary flow diversions are
shown on Plan Sheet C-7. Construction of the replacement culvert will require the use of
heavy machinery (Table 15) and will involve the removal of a section of the asphalt roadway,
shoulders, and road subgrade above the replacement culvert and a trench to the extent of the
steel casing pipe. The removal will affect an area approximately 15 feet wide by 50 feet long
and extends the entire width of the roadway.
Placement and connection of the culvert headwalls and wingwalls may require welding and
joint grouting per manufacturer recommendations.
Permanent utility relocation is anticipated for the known communication conduit that
crosses the culvert. There also remains the potential for encountering underground utilities
that are unknown or are located differently than shown on the Project survey. A second
communication utility is known but it has not been identified in the survey. Overhead
power lines are present within the Project site and will be avoided. Underground utility
locating will be done prior to the start of the culvert replacement.
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Temporary closure of South 55th Street due to the construction of the replacement culvert
will be minimized to the extent possible, and local access will be required during
construction. Traffic control will be conducted as necessary to limit the interruption of
vehicular traffic within the Project site.
Approximately 40 cy of Type 1 imported channel sediment will be placed at a minimum
depth of 9 inches along the inside of the culvert bottom and a depth of 12 inches
immediately upstream and downstream of the culvert as shown on Plan Sheet C-10.4. The
substrate may be placed using an excavator, by hand or by other means as necessary. Rock
and log sills within the culvert may be placed by hand or by other means necessary, such as
by using an industrial conveyor belt. Placement of individual large rocks will be directed
on-site by the Contracting Officer to be in accordance with configurations shown on the
plans. It is anticipated that professional engineering staff will be onsite to assist the
Contracting Officer with the placement of these materials.
3.7 Creek Flow Ramping and Fish Rescue and Recovery
Once the new channel and replacement culvert is completed, transfer of flow from the
existing to the new channel will commence. Prior to the release of water into the new
channel, temporary fish exclusion screens will be placed upstream of the culvert within the
existing channel and downstream of the confluence of the existing and new channels to
exclude fish during the ramping process. Flow from the existing creek will be slowly and
sequentially diverted to the new channel in an effort to closely monitor water quality
conditions, stability of the new channel, and to perform fish rescue and recovery within the
existing creek. Flow rates will be increased in small increments by removal of the existing
material at the upstream end of the new channel to allow for these efforts to be conducted
successfully. It is anticipated that transfer of the entire flow into the new channel may take
as long as 8 hours. It is anticipated that flow ramping from the existing channel to the new
channel will be sediment-laden. To mitigate turbid flow in the new channel, a temporary
shallow trench or pool will be excavated downstream of the confluence of the new and
existing channels, where the turbid water will be pumped into the floodplain. This effort is
expected to last a short time, yet is dependent upon site conditions and permit requirements
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Upper Springbrook Creek Project 43 090202-01
for water quality. Should the creek flow remain turbid for an extended period of time, other
measures will be employed to maintain creek flows.
3.8 Decommissioning of the Existing Channel
Once flow has been successfully diverted into the new channel, decommissioning of the
existing channel may commence. Decommissioning the existing channel involves removal
of temporary flow conveyance pipe and temporary fill, followed by placement and
compaction of the permanent fill area at the upstream end of the existing channel, shown on
Plan Sheet C-9.1. The upstream fill will require the use of heavy machinery (Table 15).
Approximately 19 cy of material is proposed for placement of the upstream fill.
Coir fabric installation upland of the new channel, including the extent of the upstream fill
of the existing channel will provide short-term stabilization, while riparian plantings will
provide long-term stabilization once the vegetation becomes established.
3.9 Construction Decommissioning and Site Restoration
Construction decommissioning includes demobilization and removal of temporary
construction measures. Items requiring decommissioning include removal of site access and
staging measures, maintenance or removal of the silt fence, and removal of construction
fencing and tree protection measures.
Site restoration within the Project area includes restoring areas disturbed by construction as
necessary. Landscape planting, including planting within the existing channel and
floodplain plantings associated with the floodplain log placements, is expected to be
conducted under a separate contract following construction completion. Areas disturbed by
construction include the temporary site access and staging areas (including pavement
surfaces), the banks along the new channel, and the fill area(s) placed within the existing
channel. Restoration of these areas may include seeding, mulching, placement of coir fabric,
and pavement resurfacing.
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3.10 Best Management Practices
BMPs are guidelines to prevent the introduction of pollutants and minimize the effect of
pollutants to surface water. Pollutants include solids, chemicals, and changes in water
temperature, among others. For the purpose of this Project, the BMPs outlined in the
sections below are recommended for use on-site to prevent spills, minimize erosion, and
control sediment transport.
3.10.1 Spill Prevention
The potential for spills occurring during the Project may be prevented, minimized, and/or
greatly mitigated by using refueling containment systems, petroleum alternatives in
machinery hydraulics, and careful attention paid by operators and staff working in or nearby
surface water. BMPs include:
Each piece of machinery shall be checked daily for leaks, and any repairs shall be
done prior to work in or near water.
All refueling of machinery shall be done in the staging areas with appropriate spill
containment measures in place and ready to employ.
Fueling procedures must be approved by the local fire department and comply with
local and state fire codes, including departments of transportation.
The driver/operator must be present and maintain constant observation/monitoring
during refueling.
The driver/operator must be trained in spill prevention, cleanup measures, and
emergency procedures.
All employees must be made aware of the significant liability associated with fuel
spills.
Spill cleanup materials must be maintained in all fueling vehicles including non-water
absorbents capable of absorbing 15 gallons of diesel and conventional fuel.
Drip pans including absorbent pads will be present at each construction location
during all working activities.
If a power generator is used during construction, the generator should be placed out
of the creek channel (above the ordinary high water level) within a spill containment
unit.
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3.10.2 Erosion and Sediment Control
Erosion and sedimentation during construction activities should be minimized by limiting
the amount of disturbance to the creek channel, banks, and the top of slope. In order to
minimize the potential for erosion and transport of sediment into the creek system, the
following actions are recommended:
A silt fence installed to the extent shown on the plans to minimize transport of
sediment beyond the active construction area. A high-visibility silt fence may aid in
marking access routes and clearing limits.
Rock check dams to reduce flow velocity over steep slopes and/or straw bale dams to
filter sediment in low-velocity, low-flow areas.
Clearing limits that are marked and visible during construction reduce impacts and
disturbance within the Project area.
Equipment washing stations located near surface streets to remove sediment from
equipment prior to movement of equipment onto surface streets and/or use of street
sweepers or hand sweeping of surface streets to remove sediment and debris
transported off site. These methods shall be performed in accordance with local
requirements as provided in the specifications.
All efforts will be made to locate storage and staging areas in flat areas above the
ordinary high water line with appropriate erosion and sediment control measures,
such as gravel pads.
The number of trips made through the Project site by heavy equipment will be
minimized.
Following construction completion, all disturbed areas that result in bare earth
surfaces will be covered with straw or other TESC measure to reduce the potential for
erosion and sediment transport.
Excavation requiring the temporary removal of top soil and usable vegetation within
the site should be set aside from other excavation spoils and be used to top-dress bare-
cut surfaces following grading work completion.
Revegetation and rehabilitation of disturbed areas is expected to occur following
construction completion and will be completed under a separate contract.
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4 LIMITATIONS
This report has been developed for the Corps for use in documenting design and
constructability analyses for the 95- and 100-percent design phase of the Project. Conditions
within the Project site may change both spatially and with time, and additional scientific
data may become available. Significant changes in site conditions or the available
information may require re-evaluation. Within the limitations of scope, schedule, and
budget, our services have been executed in accordance with generally accepted scientific and
engineering practices in this area at the time this report was prepared.
Design Documentation Report May 2010
Upper Springbrook Creek Project 47 090202-01
5 REFERENCES
Anchor QEA. 2010a. 35% Design and Constructability Report; Green Duwamish River
Ecosystem Restoration – Upper Springbrook Creek Project. Prepared for U.S. Army
Corps of Engineers, Seattle, Washington. Anchor QEA, LLC. March 2010.
Anchor QEA. 2010b. Upper Springbrook Creek Restoration Project – Documentation of
Additional Planned Changes to 35% Design and January 14, 2010 Meeting Notes.
Prepared for U.S. Army Corps of Engineers, Seattle, Washington. Anchor QEA, LLC.
January 2010.
Barnard, Robert. 2010. Documentation of channel width and drainage area regression
relationship provided via email correspondence with Tracy Drury. January 19, 2010.
DEA. 2001. Hydraulic Report – State Route 167 Culvert Replacement, Upper Springbrook
Creek, MP 23.6, King County. Prepared for Washington State Department of
Transportation, Northwest Region, Seattle, Washington. David Evans & Associates,
Inc. September 2001.
DHA. 2008. Upper Springbrook Creek – Topographic Survey, Contract No. W912DW-05-
D-1030, Task Order No. 0044. Additional survey collected November 2009. Prepared
for the U.S. Army Corps of Engineers. Duane Hartman & Associates, Inc. July 2008.
Fox, M. and Bolton, S. 2007. A Regional and Geomorphic Reference for Quantities and
Volumes of Instream Wood in Unmanaged Forested Basins of Washington State.
North American Journal of Fisheries Management. Vol. 27 pp. 342-359.
Hansen, P. 2009. H&H for Springbrook Creek. Documentation provided via email by Paul
Hansen, Hydraulic Engineer, U.S. Army Corps of Engineers. October 14, 2009.
Jackels, C. 2009. Upper Springbrook Design Criteria for Coho Spawning and Rearing.
Documentation provided by Chemine Jackels, Biologist, U.S. Army Corps of
Engineers. December 10, 2009.
King County. 2005. King County Surface Water Design Manual. King County, Washington.
King County. 2007. King County Road Design and Construction Standards. King County,
Washington.
References
Design Documentation Report May 2010
Upper Springbrook Creek Project 48 090202-01
King County. 2010. Springbrook Creek Gage 03b (1988-1994).
http://green.kingcounty.gov/wlr/waterres/hydrology/GaugeMetaData.aspx?G_ID=67
King County, Washington.
Mueller E. R., Pitlick J., Nelson J. M. 2005. Variation in the reference Shields stress for bed
load transport in gravel-bed streams and rivers. Water Resources Research, 41, 04006
Parker, G. (1990). Surface-based bedload transport relation for gravel rivers. Journal of
Hydraulic Research, 28(4), 417-436
Parker, G., Dhamotharan, S., and Stefan, H. 1982a. Model experiments on mobile, paved
gravel bed streams. Water Resources Research, 18(5), 1395–1408.
Parker, G., and Klingeman, P. C. 1982b. On why gravel bed streams are paved. Water
Resources Research, 18, 1409–1423.
Pitlick, John; Cui, Yantao; Wilcock, Peter. 2009. Manual for computing bed load transport
using BAGS (Bedload Assessment for Gravel-bed Streams) Software. Gen. Tech. Rep.
RMRS-GTR-223. Fort Collins, CO: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station. 45 p.
USACE. 2008. HEC-RAS River Analysis System. Version 4.0.0. U.S. Army Corps of
Engineers. March 2008.
USACE. 2009. HEC-GeoRAS GIS Tools for Support of HEC-RAS Using ArcGIS. Version
4.2. U.S. Army Corps of Engineers. September 2009.
WDFW. 2003. Design of Road Culverts for Fish Passage. Washington Department of Fish
and Wildlife.
WDFW. 2004. Stream Habitat Restoration Guide Lines. Washington Department of Fish
and Wildlife.
Wilcock, P. R., & Crowe, J. C. (2003). Surface-based transport model for mixed-size
sediment. Journal of Hydraulic Engineering, 129(2), 120-128
Wilcock, P. R. 1988. Methods for estimating the critical shear stress of individual fractions
in mixed-size sediment. Water Resources Research, 24(7), 1127–1135.
References
Design Documentation Report May 2010
Upper Springbrook Creek Project 49 090202-01
WRA. 1978. Cascade Sewer District – Sewer Plan & Profile, ULID No. 34. Sewer as-built
drawings at Springbrook Creek site. Provided by City of Renton. Prepared for the
Cascade Sewer District. Williams, Roth & Associates. December 1978.
APPENDIX A
HEC‐RAS PROPOSED HYDRAULIC MODEL
RESULTS
HE
C
‐RA
S
Pr
o
p
o
s
e
d
Hy
d
r
a
u
l
i
c
Mo
d
e
l
Re
s
u
l
t
s
Hi
g
h
Fl
o
w
s
Q To
t
a
l
M
i
n
Ch
El
W
.
S
.
El
e
v
C
r
i
t
W.
S
.
E
.
G
.
El
e
v
E
.
G
.
Sl
o
p
e
V
e
l
Ch
n
l
F
l
o
w
Ar
e
a
T
o
p
Width
(c
f
s
)
(
f
t
)
(
f
t
)
(
f
t
)
(
f
t
)
(
f
t
/
f
t
)
(
f
t
/
s
)
(
s
q
ft
)
(
f
t
)
11
4
3
.
7
1
1
‐ye
a
r
4
8
4
5
.
2
2
4
6
.
2
9
4
6
.
2
9
4
6
.
4
9
0
.
0
2
7
8
3
2
3
.
9
2
1
8
.
6
8
5
3
.
1
3
0
.
8
8
11
2
1
.
9
7
3
1
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a
r
4
8
4
3
.
8
6
4
5
4
5
4
5
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3
7
0
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3
4
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7
4
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9
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1
11
1
5
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6
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8
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5
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6
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1
3
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4
4
0
.
8
9
11
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3
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8
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2
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5
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2
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6
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3
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1
7
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3
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8
4
0
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0
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2
2
3
.
3
8
1
4
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1
9
1
0
.
6
7
0
.
5
2
10
5
8
C
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l
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10
5
6
.
4
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1
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0
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2
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1
9
0
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6
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7
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7
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2
3
1
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6
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4
5
10
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7
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4
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7
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7
3
98
2
.
1
1
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4
8
3
9
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5
6
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5
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.
1
6
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3
9
0
.
7
6
95
0
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a
t
St
r
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92
7
.
1
6
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5
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7
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3
3
9
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9
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0
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9
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9
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1
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0
5
3
2
.
8
6
0
.
7
7
86
8
.
2
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1
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a
r
4
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3
7
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4
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3
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3
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5
3
3
9
.
0
1
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0
1
3
5
9
8
3
.
6
3
1
3
.
2
1
1
3
.
9
8
0
.
6
6
81
2
.
4
3
2
1
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a
r
4
8
3
6
.
6
9
3
7
.
8
6
3
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8
6
3
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1
0
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0
1
9
6
6
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4
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0
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6
.
1
3
5
1
.
0
4
0
.
7
8
75
5
.
3
2
4
4
1
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a
r
4
8
3
5
.
9
3
6
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8
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3
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0
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0
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3
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5
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7
70
9
.
8
8
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3
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4
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3
5
.
2
5
3
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3
7
3
6
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1
3
3
6
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4
3
0
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0
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2
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6
2
.
5
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3
5
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1
2
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1
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9
5
0
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5
67
6
.
0
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3
4
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3
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3
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1
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1
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1
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64
4
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1
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7
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62
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6
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6
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7
.
1
7
5
5
1
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a
r
4
8
3
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3
3
3
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1
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3
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3
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9
1
7
3
.
7
9
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7
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9
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6
9
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9
.
5
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a
r
4
8
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1
.
8
8
3
2
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8
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3
2
.
7
9
3
2
.
9
7
0
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0
1
8
2
5
2
3
.
8
5
2
6
.
4
7
6
9
.
9
3
0
.
7
5
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3
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3
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0
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a
r
4
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3
1
.
3
7
3
2
.
3
3
2
.
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4
3
2
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1
0
.
0
1
6
0
6
2
3
.
4
1
2
9
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6
7
7
8
.
0
7
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.
6
9
Ri
v
e
r
St
a
t
i
o
n
P
r
o
f
i
l
e
Froude # Chl
D
e
s
i
g
n
D
o
c
u
m
e
n
t
a
t
i
o
n
R
e
p
o
r
t
U
p
p
e
r
S
p
r
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n
g
b
r
o
o
k
C
r
e
e
k
P
r
o
j
e
c
t
A ‐1
May 2010 090202-01
HE
C
‐RA
S
Pr
o
p
o
s
e
d
Hy
d
r
a
u
l
i
c
Mo
d
e
l
Re
s
u
l
t
s
Hi
g
h
Fl
o
w
s
Q To
t
a
l
M
i
n
Ch
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W
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S
.
El
e
v
C
r
i
t
W.
S
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v
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.
G
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o
p
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V
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l
Ch
n
l
F
l
o
w
Ar
e
a
T
o
p
Width
(c
f
s
)
(
f
t
)
(
f
t
)
(
f
t
)
(
f
t
)
(
f
t
/
f
t
)
(
f
t
/
s
)
(
s
q
ft
)
(
f
t
)
Ri
v
e
r
St
a
t
i
o
n
P
r
o
f
i
l
e
Froude # Chl
38
2
.
6
4
7
9
1
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a
r
4
8
3
0
.
6
6
3
1
.
4
1
3
1
.
3
3
3
1
.
5
2
0
.
0
2
1
0
9
8
3
.
8
1
2
7
.
9
2
6
3
.
5
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7
9
33
9
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2
9
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4
8
3
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0
6
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7
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1
2
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3
5
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9
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4
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4
.
7
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5
6
30
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.
4
4
4
1
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r
4
8
2
9
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5
1
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0
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2
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1
6
3
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6
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.
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1
7
5
4
2
3
.
2
8
3
2
.
7
7
8
5
.
2
8
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7
1
27
6
.
5
5
5
4
1
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a
r
4
8
2
9
.
1
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May 2010 090202-01
HE
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HE
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A ‐8
May 2010 090202-01
HE
C
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Pr
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Hy
d
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c
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Width
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P
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c
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A ‐9
May 2010 090202-01
HE
C
‐RA
S
Pr
o
p
o
s
e
d
Hy
d
r
a
u
l
i
c
Mo
d
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Re
s
u
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t
s
Hi
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Fl
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s
Q To
t
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Ch
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Ar
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a
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p
Width
(c
f
s
)
(
f
t
)
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f
t
)
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f
t
)
(
f
t
)
(
f
t
/
f
t
)
(
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t
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)
(
s
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)
(
f
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)
Ri
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St
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P
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f
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Froude # Chl
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5
6
.
4
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A ‐10
May 2010 090202-01
HE
C
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Width
(c
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A ‐11
May 2010 090202-01
APPENDIX B
FLOODPLAIN LOG PLACEMENT
SPECIFICATION CALCULATIONS
Floodplain Log Placement Specification Calculations
Ground Elev. at
Proj. Limit
Right Overbank
Reach Length WSEL
Depth at
Project Limit
Diameter to
Contain Flow
Typical Log
Spec.
Grouped Log
Spec.
Distance Between
Sections
Total Group
Length
(ft) (ft) (ft) (ft) (in) (in) (in) (ft) (ft)
1143.71 NA 27.59 46.49 NA NA NA NA 28 NA NA NA
1121.973 NA 6.19 45.4 NA NA NA NA 6 NA NA NA
1115.626 NA 6.68 45.05 NA NA NA NA 7 NA NA NA
1103.83 NA 5.39 44.14 NA NA NA NA 5 NA NA NA
1099.468 NA 55.24 44.26 NA NA NA NA 55 NA NA NA
1056.481 NA 10.48 42.59 NA NA NA NA 10 NA NA NA
1047.451 NA 39.32 42.41 NA NA NA NA 39 NA NA NA
1029.764 NA 41.15 42.17 NA NA NA NA 41 NA NA NA
982.1165 NA 68.64 40.98 NA NA NA NA 69 NA NA NA
927.1654 39.4 40.77 40.14 0.74 17.76 18 18 41 41 1.6 2
868.2409 39.1 52.55 39.15 0.05 1.2 12 53
812.432 37.7 48.84 38.13 0.43 10.32 12 49
755.3244 36.2 44.19 37.14 0.94 22.56 24 44
709.8883 35.6 27.19 36.64 1.04 24.96 30* 27
676.08 35.3 21.57 36.3 1 24 24 22
655.6738 35.2 9.98 36.05 0.85 20.4 24 10
644.5648 35.2 9.98 35.91 0.71 18 18 10
635.4199 35 10.72 35.69 0.69 18 18 11
628.682 34.8 11.35 35.59 0.79 18.96 24 11
617.9985 34.6 23.31 35.5 0.9 21.6 24 23
594.9594 34.1 22.26 35.12 1.02 24.48 30 22
576.3321 33.8 18.55 34.82 1.02 24.48 30 19
560.3003 33.5 16.42 34.57 1.07 25.68 30 16
547.5794 33.2 6.86 34.27 1.07 25.68 30 7
534.9249 33.1 4.98 34.14 1.04 24.96 30 5
522.4411 33 11.13 34.01 1.01 24.24 30 11
507.5188 32.9 20.46 33.67 0.77 18.48 24* 20
487.1755 32.8 25.21 33.39 0.59 14.16 18 25
469.5943 32.3 24.59 33 0.7 16.8 18 25
433.3106 31.8 47.37 32.47 0.67 16.08 18 47
382.6479 30.9 47.15 31.64 0.74 17.76 18 47
339.2951 30 27.92 30.99 0.99 23.76 24 28
300.444 29.7 24.21 30.5 0.8 19.2 24 24
276.5554 29.5 25.02 30.22 0.72 17.28 18 25
252.3564 29.3 29.53 29.93 0.63 15.12 18 30
219.4787 29 46.7 29.4 0.4 9.6 12 12 47 47 1.9 2
170.3751 28.5 47.01 29.08 0.58 13.92 18 47
122.1461 27.9 31.12 28.71 0.81 19.44 24* 31
71.26093 NA 24.86 27.8 NA NA NA NA 25 NA NA NA
48.34139 NA 8.14 27.4 NA NA NA NA 8 NA NA NA
38.71117 NA 6.91 27.38 NA NA NA NA 7 NA NA NA
HEC‐RAS Model Output (10‐Year Flow Contained) Floodplain Log Specifications
Number of Logs (25
ft Sections)
Number of Logs
(Nearest Whole)
12
River
Station
101 4.1 4
24 158 6.3 6
30 80 3.2 3
18
24 52 2.1 2
165 6.6 7
18
18 78 3.1 3
55 2.2 2
Design Documentation Report
Upper Springbrook Creek Project B-1
May 2010
090202-01
Floodplain Log Placement Specification Calculations
Ground Elev. at
Proj. Limit
Right Overbank
Reach Length WSEL
Depth at
Project Limit
Diameter to
Contain Flow
Typical Log
Spec.
Grouped Log
Spec.
Distance Between
Sections
Total Group
Length
(ft) (ft) (ft) (ft) (in) (in) (in) (ft) (ft)
HEC‐RAS Model Output (10‐Year Flow Contained) Floodplain Log Specifications
Number of Logs (25
ft Sections)
Number of Logs
(Nearest Whole)
River
Station
30.64652 NA 6.74 27.38 NA NA NA NA 7 NA NA NA
20.40138 NA 7.12 27.32 NA NA NA NA 7 NA NA NA
8.486752 NA 7.05 27.24 NA NA NA NA 7 NA NA NA
1.548412 NA 5.09 26.97 NA NA NA NA 5 NA NA NA
MINIMUM 0.05 1.20 12.00 TOTAL 31.1 31
AVERAGE 0.79 18.93 22.14
MAXIMUM 1.07 25.68 30.00
Note:
*Log diameter to contain flow greater than grouped diameter specification. This difference does not exceed 1.5 inches.
Design Documentation Report
Upper Springbrook Creek Project B-2
May 2010
090202-01
APPENDIX C
SEDIMENT TRANSPORT ANALYSIS
Design Documentation Report May 2010
Upper Springbrook Creek Project C-1 090202-01
APPENDIX C
Sediment Transport Analysis
This appendix provides additional explanation of the sediment mobility and transport
evaluations. This appendix is intended to be a primer on basic terminology and relationships
and not a comprehensive explanation of sediment transport theory and practice.
A majority of sediment mobility and transport evaluations are based on two system
parameters. One is the shear stress exerted on the sediment grains by the water. The second
is the size of the sediment grains composing the bed.
Shear stress on the bed for normal open-channel flow conditions is often approximated by
Equation 1. Where ρ is water density, g is gravitational acceleration, R is the hydraulic
radius (flow area over wetted perimeter), and S is the slope of the energy grade line (equal to
the bed slope for normal flow).
(1)
The bed shear stress can be normalized by sediment grain size and water weight, Equation 2,
to produce the dimensionless form of grain shear stress (τ*). Where τ is bed shear stress, ρs is
sediment grain density, ρ is water density, g is gravitational acceleration, and D is grain size.
(2)
The dimensionless form of shear stress can be used to establish a value called the reference
shear stress (τr). The value for reference shear stress is defined to produce a small but
measurable dimensionless transport rate (W*, Equation 3) of 0.002 (Parker et. al.
1982a,b;Wilcock 1988). Where Qs is the volumetric sediment transport rate, s is the
sediment grain specific gravity, and B is the transport width.
(3)
gDs)(*
gRS
B
gsQW
s
s
2/3/
)1(*
Appendix C
Design Documentation Report May 2010
Upper Springbrook Creek Project C-2 090202-01
This dimensionless transport rate is roughly equivalent to mass sediment transport rate of 1
ounce/feet/second for gravels.
The reference dimensionless shear stress (τr*) that produces the specified dimensionless
transport rate varies depending on several system parameters and can range between 0.025
and 0.10 with a typical value near 0.04. Recent work has shown that the reference shear
stress varies considerably based on the channel slope. Equation 4 is a relationship for this
variation in dimensionless reference shear stress with respect to channel slope (S) as defined
by Mueller et. al. (2005).
(4)
Using the calculated values of dimensionless grain shear stress (τ*) and dimensionless
reference shear stress (τr*) the transport stage (θ) can be defined as shown in Equation 5.
(5)
The sediment transport stage is used as the primary variable in several common coarse
sediment transport models. Depending on the model, the transport stage can be specified for
either for the grain size distribution (GSD) as a whole or for individual grain size classes.
The two models used to evaluate sediment transport for this project (Parker 1990; Wilcock
and Crowe 2003) are capable of modeling individual grain size classes, although only the
aggregate transport rate was presented in the report. Both models employ a similar non-
linear function for transport rate with respect to transport stage. Explanations of the models
basis and functionality can be found in the respective references for each model and many
other related publications.
The U.S. Forest Service’s Stream Systems Technology Center BAGS (Bedload Assessment for
Gravel-bed Streams) software was used to run transport rate simulations using both the
021.018.2*Sr
r**
Appendix C
Design Documentation Report May 2010
Upper Springbrook Creek Project C-3 090202-01
Parker (1990) and Wilcock (2003) models. A full explanation of the functionality of BAGS
can be found in the Manual for computing bed load transport using BAGS (Pitlick 2009).
Input to the model included information regarding channel cross-section, slope, floodplain
boundaries, surface grain size distribution, and water discharge range. An example input
data set is shown in Figure 1.
Figure 1
Example BAGS Input Data
The output provided by the software included data regarding the aggregate bedload transport
rate, the transport stage, maximum water depth, hydraulic radius, and the grain size class
bedload transport rate. An example output data set is shown in Figure 2. As shown in the
report, output data sets were then used to calculate transport rate over synthetic hydrographs
and examine system sensitivity to changes in GSD.
Channel bed slope 0.0140
Bankfull width N/A
Min. water discharge 0.09 cms
Max. water discharge 3.43 cms
Main channel Manning's n0.045 Size (mm) % Finer
Left floodplain boundary 9.14 m 200 100
Left floodplain Manning's n0.1 80 84
Right floodplain boundary 13.72 m3250
Right floodplain Manning's n0.1 10 16
55
11
Lateral distance (m) Elevation (m) 0.8 0.5
0 0.4572 0.5 0
9.144 0.4572
10.5156 0
12.3444 0
13.716 0.4572
18.288 0.4572
Cross‐Section
Surface Grain Size
Distribution
Appendix C
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