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## Design For Fish Passage at Roadway - Stream Crossings: Synthesis Report## 8 Case Studies and Design Examples## How to use this chapter- Study worked out examples of culverts designs using selected design methods
- Review case studies for completed projects
## 8.1 Geomorphic simulation## 8.1.1 USFS Stream Simulation Design ExampleA survey of the existing channel, and a surface pebble count conducted on a representative reference reach, determined the following channel characteristics:
Channel width (W The culvert is sized assuming that bank margins are desirable.
Culvert bed width (W The culvert should span a minimum of 2.70 m (8.9 ft), which would be rounded up to 2.75 m (9 ft). Bed mix gradation includes D P=(d/D The Fuller-Thompson 'n' value can be varied approximately between 0.45 and 0.7 to control gradation until an appropriate proportion of fines (5-10%) has been attained. To start, compare the effects of an n value of 0.7 vs. and n value of 0.45. The results of these calculations have been plotted in Figure 8.1. Using n = 0.7 D
D Using n = 0.45 D
D
It can be seen that an n value of 0.45 will lead to gradation of approximately 12-13% fines (2 mm or less). Refining further, using n = 0.55
D
D This distribution is plotted in Figure 8.2
An n value of 0.55 leads to a bed mix gradation with between 5-10% fines (smaller than 2 mm). The following gradation should be used for design.
D ## 8.1.2 USFS Stability Check Design ExampleThe following stability check example is taken (almost verbatim) from Bates et al. 2006. It is included here for clarification of the USFS Stream Simulation Design.
Channel parameters are as follows:
D Determine whether the D
τ Find the average boundary shear stress in the reference reach at bankfull flow ( τ
τ Therefore, the D How well does the modified critical shear stress equation apply here? - D
_{84}/D_{50}= 2.3, which is much less than 30 - Slope < 5%
- Channel unit is a riffle
- D
_{84}particle size of 120 mm is between the range of 10 and 250 mm.
Conclusion: The modified critical shear stress equation is applicable to this stream
Find the critical unit discharge for D
Calculate b (which quantifies the range in particle sizes) using Equation 6.11.
Find critical unit discharge for D
Both D Is the Bathurst equation appropriate for this stream?
Slope > 1%
τ Find the upper critical shear stress for the D τ τ Find the lower critical shear stress for the D τ τ τ Summary: Both the modified critical shear stress and critical unit discharge equations predict that the D Judgment: D ## 8.1.3 WDFW Stream Simulation Design ExampleStream properties are determined from a channel survey and analysis of multiple representative cross sections.
Channel width (W Check Applicability S
Channel has been assessed to have little susceptibility to vertical changes Conclusion: WDFW Stream Simulation is applicable in this situation Culvert span is determined according to Equation 7.1. Culvert bed width (W Culvert should span a minimum of 3000 mm, which would likely be rounded up to 3048 mm (10 ft). Culvert bed configuration is based on slope scenarios. Since slope is less than 4%, design scenario I is employed, meaning that rock bands will be used to control the initial channel shape. This creates a situation that may be more adequately described as Hydraulic Simulation. Bands spacing should be the lesser of 5 ∙W 5 W
Therefore, spacing will be 9.75 m (32 ft). Bands are separated from the entrance and exit by the lesser of: 2W Therefore, spacing should be at least 3.9 m (13 ft) from culvert inlet and outlet. With a 30.5 m (100 ft) structure this leaves room for 3 rock weirs at a spacing of 9.75 m (32 ft) apart, and 5.5 m (18 ft) from the culvert entrance and exit. Sizing of rock band material is based on a surface pebble count of the reference reach.
D Rock bands are comprised of well-graded material within the following range. D Since channel slope is less than 4%, Paleohydraulic Analysis can be used to check the bed changing flow, ensuring that bed mix gradation is adequate.
D Using Table 6.5, slope (2.2%) and particle size 85 mm (0.28 ft) are used to find depth of flow Depth = 0.25 m (0.81 ft) With known depth, cross-sectional area can be computed from the proposed triangular cross section with 6:1 side slopes. (Area of a triangle is 0.5*base*height)
Area =0.5·Depth· (12·Depth) Using the proposed cross-sectional area, this corresponds to a flow of
Q=A·V ## 8.1.4 Unit Discharge Design ExampleWhen slopes are greater than 4%, the Unit-Discharge method is suggested for finding a stable bed material gradation. Necessary parameters include:
100 year exceedance flow (Q Solving for Critical Discharge (q q Using the Critical Discharge equation (6.16) to solve for D D So a D84 of 256 mm (0.84 ft) will create the necessary stability, and a gradation can be created based on D84. This can also be checked using the Paleohydraulic analysis shown above. ## 8.1.4.1 Paleohydraulic AnalysisD Using Table 6.5, find flow depth Depth = 1.6 ft (0.49 m) Using the proposed channel dimensions (6:1 side slope, triangular channel) Area = 0.5·Depth·(12·Depth) This is consistent with the trend of Co'ta's equation to predict smaller particle sizes than Bathu'st's equation at higher slopes (Bates et. al 2003). Both equations show this D ## 8.1.5 WDFW No-Slope Design ExampleStream Properties Needed Channel width (W Channel Type and Size
Culvert bed width (W Culvert should span a minimum of 2.44 m (8 ft). To check the applicability of No Slope Design, ensure that the product of channel slope times length is less than 0.2D.
L Since slope times length is > 0.2D, 0.67 m > 0.49 m (2.2 ft > 1.6 ft), No-Slope method is not applicable in this situation due to the inability to meet embedment requirements. ## 8.1.6 Embedded Pipe Case HistoryThe following example of stream simulation is taken from the USFS FishXing website (United States Forest Service 2006b), maintaining the format and content developed by the authors. It is reproduced here with permission from Mike Furniss of the USFS.
- Mad River Basin, Northern California
- Mather Creek
Project Type - Embedded Structural Plate Pipe
- Geomorphic Simulation
- Undersized Corrugated Metal Pipe (Overtopped at 5-yr flow)
- 1800 mm (6 ft) diameter CMP
- 41.1 m (135 ft) long at 0.4 % slope
- Cascade over rock apron at outlet
- 100-year Flow: 16.1 cms (570 cfs)
- Drainage Area: 4.4 km
^{2}(1.7 mi^{2}) - Bankfull Width: 3.4 m (11 ft)
- Provide access to 4.2 km (2.6 mi) of rearing habitat for coho salmon, steelhead and cutthroat trout. Upstream habitat is low gradient, marshy, and maintains good year-round flows.
- Culvert Diameter: 4.9 m (16 ft)
- Length: 32.0 m (130 ft)
- Depth Embedded: 0.6-0.9 m (2-2.5 ft)
- Slope of Bed in Culvert: 0.75 %
- Protecting buried water line
- Stabilizing side slopes during excavation to set culvert at desired depth for embedding
- Humboldt County
- California Dept. Fish and Game
- October, 2002
- $234,544
An embedded 4900 mm (16 ft) diameter culvert was selected as the replacement crossing. The new culvert is designed to pass a 100-year flood at Headwater-to-Diameter ratio (HW/D) of 0.6 and is 145% wider than the upstream bankfull channel. The appropriate slope and elevation for constructing the streambed within the culvert was determined from a 137 m (450 ft) long channel profile. Since the road was closed and no traffic bypass was needed during construction, the project took only four weeks to complete. This project experienced many construction challenges. Although originally designed to be embedded 1.8 m (6 ft), problems with buried utilities, groundwater and slope stability during excavation resulted in only embedding the culvert approximately 0.9 m (2.5 ft). ## 8.2 Hydraulic Simulation## 8.2.1 Culvert with Floodplain Relief Case HistoryThe following case history was provided by Andrzej ("Andy") Kosicki of the Maryland State Highway Administration.
- MD Route 25 over Beaverdam Run, Baltimore County, Maryland, USA
- Main channel Structure Plate Pipe Arch (SPPA)
- Floodplain culverts (one SPPa. and on SPP)
- Hydraulic Simulation
- Single span slab bridge with a 6.1 m (20 ft) long invert which was paved in the 1960s due to scour and poor structural condition. A single 3.05 m (10 ft) diameter structural plate pipe was added in 1972 after hurricane Agnes washed away a roadway approach on the north side. See Figures 8.5-8.7.
- Fish blockages included an upstream earth and debris dam, a 0.15 m (6 in) drop at the downstream outlet, and a 0.025-0.05 m (1-2 in) flow depth under low flow conditions. No aquatic life has been observed within 15.2 m (50 ft) upstream of the bridge.
- 100-year Design Flow: 70.3 m
^{3}/s (2482 cfs) - High Flow Velocity: 3.05 m/s (10 ft/s)
- Mannings n: 0.034
- Drainage Area: 16.4 km
^{2}(5.9 mi^{2}) - Low Flow: 0.2 m
^{3}/s (7 cfs) - Low Flow Velocity: 0.58 m/s (1.9 ft/s)
- Mannings n: 0.030
- Department of Natural Resources stream classification is a Class III (Natural Trout Stream)
- 2-12'4"x7'9" Structural Plate Pipe Arches (SPPA)
- 1-10'0" Structural Plate Pipe (SPP) with end walls
- Culvert length: 10.76 m (35.5 ft)
- Culvert slope: 0.56%
- One of the two SPPAs was placed in the channel 0.6 m (2.0 ft) below the existing stream invert (low flow cell). The other SPPA and the round pipe were placed at bankfull elevations, approximately 0.9 m (3.0 ft) higher than the low flow cell.
- Buried riprap aprons, each 7.62 m (25 ft) long were placed at both upstream and downstream ends.
No formal monitoring program was set up since monitoring was not required by the permitting agency. Periodic field trips showed beneficial changes in the channel and within the structure: - Aquatic life that was not seen before
- Various water bugs and good sediment movement resulting in clear water, whereas the pre-1994 structure passed water that was dark and murky
- Side cells have displayed wildlife tracks (probably small mammals)
## 8.3 Hydraulic Design## 8.3.1 John Hatt Creek Case History
- FishXing Case Studies (United States Forest Service 2006b)
- Study from Sebastian Cohen P.E., California Dept. of Transportation
- Navarro River Watershed, Northern California, USA
- Culvert Rehabilitation with Metal Insert
- Corner Baffle Retrofit
- Hydraulic Design
- Placement of Concrete Weirs Below Outlet
- 1700 mm (5.5 ft) diameter CSP, 52.4 m (172 ft) long, at 2.4% slope
- Culvert distorted (out of round) and deteriorating
- Culvert bottom lined with concrete
- Concrete drop structure at culvert inlet
- Insufficient depth, high velocities, excessive leap (Figure 8.11)
- Partial barrier to adult steelhead trout
- Total barrier to juvenile salmonids
- Drainage Area: 1.6 km
^{2}(0.6 mi^{2}) - 2-year Peak Flow: 1.7 cms (60 cfs)
- Design Capacity (100-year Flow): 7.5 cms (266 cfs)
- Headwater-to-diameter ratio at 7.5 cms (266 cfs) = 2.5
- Adult Steelhead Passage Design Flows:
- Upper = 0.85 cms (30 cfs), 50% of 2-yr peak flow
- Lower = 0.08 cms (3 cfs)
- Juvenile Salmonid Passage Design Flows:
- Upper = 0.17 cms (6 cfs), 10% of 2-yr peak flow
- Lower = 0.03 cms (1 cfs)
- Provide access to 0.9 km (0.6 miles) of upstream spawning and rearing habitat for steelhead trout
- Insert a 9.6 mm (3/8 in) thick welded steel pipe, 1500 mm (5 ft) diameter and 52.4 m (172 ft) long into existing culvert
- Weld 43 steel corner baffles into pipe insert
- Baffles 0.21 m (8.3 in) tall at center and spaced 1.2 m (4 ft) apart
- 3 precast concrete weirs with wooden low-flow notches below culvert outlet
- 0.23 m (9 in) drops between concrete weirs
- Bedrock surrounding culvert made "jacking" a larger pipe through the fill impractical
- Existing culvert was out-of-round so smaller culvert had to be inserted
- Only 7.5 m (25 ft) right-of-way available below culvert outlet for grade control weirs
- Lack of rock armoring, and weirs not sufficiently keyed into banks resulted in flanking
- Wooden low flow notch in center of concrete weir causes plunging water to strike concrete lip at low flow.
- Need for inspection by personnel familiar with fish passage design concepts and objectives
Baffles were designed to satisfy, as best as possible, State and Federal velocity and depth criteria for fish passage while avoiding excessive turbulence. Hydraulics of corner baffles at fish passage flows were modeled using empirical equations developed by Rajaratnam and Katopodis (1990) and provided by WDFW (2003). The energy dissipation factor (EDF) was calculated as a measure of turbulence.
A total of 43 corner baffles were welded into the pipe prior to insertion. Baffles constructed of 9.6 mm (3/8 in) thick steel and spaced 1.2 m (4 ft) apart. The 0.23 m (9 in) tall baffles were rotated 15 degrees from horizontal, resulting in the low and high sides of the baffle located 0.11 m and 0.39 m (4.3 and 15.2 in) above the invert, respectively. The gap between the existing and new pipes was filled with concrete slurry to prevent seepage. The existing culvert outlet was perched nearly 0.5 m (1.5 ft) above the downstream water surface and the channel below the culvert was steep. To improve fish passage conditions at the outlet, three precast concrete weirs were installed within the 7.5 m (25 ft) right-of-way below the outlet. The concrete weirs were spaced 2.5 m (8 ft) apart with 0.23 m (9 in) drops. The weirs were keyed into the bank approximately 0.6 m (2 ft). Although facing class rock was to be placed on both banks between the weirs for scour protection, the contractor only placed rock on the left bank.
Rock was only placed on the left bank below the outlet which allowed for rapid bank erosion, resulting in flanking of the weirs. The bank was rocked later to prevent further erosion. Placing rock along both banks, as designed, and keying the weirs further into the banks may have prevented flanking. A design problem with the wooden low-flow notch was also discovered. The wood is not set flush with the downstream edge of the weir. Instead of plunging directly into the downstream pool at low flows, the water strikes the lip of the concrete weir. Installing a steel low-flow notch flush with the downstream edge of the concrete weir would create the desired plunging conditions at low-flow. A steep slab of existing concrete at the culvert inlet was to be removed as part of the project. However, it was left in place. Using inspectors familiar with the project's fish passage objectives may have avoided some of these problems.
- October 2003
- Construction: $140,000
## 8.3.2 WDFW Roughened Channel Design ExampleStream properties needed: Channel width (W Slope ratio
This is a situation where slope ratio exceeds 1.25 (typical upper range for Stream Simulation Design in Washington). Culvert span is an iterative parameter beginning with channel bed width. Width of Culvert Bed (W Culvert bed configuration by U.S. Army Corps of Engineers Riprap Design, requiring computation of unit discharge as follows:
q = 1.66 m This allows the D
D Note - it may be pertinent to increase the factor of safety (1.25) since rock sizing is greater than 152 mm (0.5 ft). Use D D This particle size is checked to ensure that it does not exceed 1/4 of the culvert span
4·D A gradation can now be created based on D ## 8.3.2.1 Fish Passage VelocityFish passage velocity is now calculated to ensure that fish are able to traverse the structure. In this case, design is for juvenile Coho salmon, and velocity cannot exceed 4 ft/s according to WDFW Hydraulic Design criteria (based on 90 ft structure). Additional parameters required include fish passage velocity and hydraulic radius: Allowable Velocity (V For use with Limerinos and Jarrett's equations, velocity will be based on a Manning's n value, and will be calculated according to Equation 7.7.
Limerinos equation is solved as follows (Equation 6.2)
which can be used into Equation 7.7 to solve for velocity
V So, according to the Limerinos equation, this would be an acceptable velocity Jarrett's equation is solved as follows n =0.32·S Using n to solve for velocity
V Mussetter's equation utilizes the Darcy-Weisbach friction factor, and is solved according to Equation 6.4.
For this equation D
Channel depth is also needed, taken from analysis based on a 6:1 triangular channel at the fish passage design flow. depth = 1.1 ft
V ## 8.3.2.2 TurbulenceTurbulence is then checked through the calculation of channel EDF. EDF = γQ EDF = 2.13 ft·lb/(ft
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Updated: 09/22/2014 |