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Table of Contents

60.2

- Objectives

................................ ................................ ................................ ......................... 3 60.3

- Policy

................................ ................................ ................................ ................................ 3 60.6

- Referenc es

................................ ................................ ................................ ........................ 3 60.61

- Open

- Channel Flow

................................ ................................ ................................ .... 3 60.62

- Bridge Hydraulics

................................ ................................ ................................ ....... 4 60. 63

- Fords, Vented Fords, and Low

- water Bridges

................................ ............................ 5 60.64

- Geomorphic Design, Culvert Hydraulics, and Fish Passage

................................ ...... 5 60.65

- Webs ites

................................ ................................ ................................ ...................... 7 60.66

- Software

................................ ................................ ................................ ...................... 7 61
- CHANNEL DESIGN

................................ ................................ ................................ . 8 61.1

- Open

- Chan nel Hydraulics

................................ ................................ ................................ 8 61.11

- Flow States

................................ ................................ ................................ ................. 8 61.12

- Open

- Channel Flow Equations

................................ ................................ ................... 8 61.2

- Roadside and Trailside Design Features

................................ ................................ .......... 9 61.3

- Channel Modification

................................ ................................ ................................ ..... 10 61.4

- Channel Stabilization

................................ ................................ ................................ ...... 10 61.41

- Bank Stabilization Structures

................................ ................................ ................... 11 61.42

- Grade Control Structures

................................ ................................ .......................... 11 62
- BRIDGE DESIGN

................................ ................................ ................................ .. 11 62.1

- Bridge Location

................................ ................................ ................................ .............. 11 62.2

- Hydraulic Analysis

................................ ................................ ................................ ......... 11 62.3

- Scour

................................ ................................ ................................ ............................... 12 62.4

- Pier Design

................................ ................................ ................................ ..................... 13 62.5

- Abutment Design

................................ ................................ ................................ ............ 13 62.6

- Relief Structures

................................ ................................ ................................ ............. 14 63
- FORD AND LOW WATER CROSSING SELECTION AND DESIGN

.................... 14 63.1

- Fords

................................ ................................ ................................ ............................... 14 63.2

- Vented Fords

................................ ................................ ................................ .................. 15 63.3 Low

- Water Bridges

................................ ................................ ................................ ........... 16 64
- CULVERT DESIGN

................................ ................................ ............................... 16 64.1

- Location and Installation

................................ ................................ ................................ 16 64.2

- Site Surveys

................................ ................................ ................................ .................... 17 64 .3

- Culvert Type

................................ ................................ ................................ ................... 17 64.31

- Shape

................................ ................................ ................................ ........................ 17 64.32

- Materials

................................ ................................ ................................ ................... 17 64.33

- Number of Barrels

................................ ................................ ................................ .... 18 64.4

- End Treatments

................................ ................................ ................................ ............... 18 64.41

- Projecting Culverts

................................ ................................ ................................ ... 18 64.42

- Mitered or Beveled Culverts

................................ ................................ ..................... 18 64.43

- Headwalls and Wingwalls

................................ ................................ ........................ 19 64.5

- Culvert Hydraulics

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65
- AQUATIC ORGANISM PASSAGE DESIGN

................................ ......................... 19 65.1

- Design Priority:

................................ ................................ ................................ .............. 19 65.2

- Aquatic Organism Passage Design Methods

................................ ................................ .. 20 65.3

- Design Requirements for Aquatic Passage

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60.2
- Objectives To maintain stream channel integrity and fun ction, maximize structure life, minimize structure maintenance, and optimize user safety while providing for appropriate species passage. Address watershed characteristics that currently influence, or have potential to influence, stream crossings.
60. 3
- Policy To the extent possible, design bridges, culverts, and low

- water crossings to accommodate the natural passage of ice, woody debris, water, sediment , and aquatic species; accommodate passage of terrestrial species where such passage is necessary; provide for ecological connectivity; and meet the intent of applicable laws and regulations. Bridges, culverts, and low

- water crossings should minimize constriction, relocation, encroachment, and modification to stream channels, adjacent riparian veget ation, and floodplains. Where there are feasible opportunities, use channel and stream crossing designs to promote favorable stream channels and improve watershed conditions. Use an interdisciplinary process to develop site specific design criteria inc luding , but not limited to , project limits, structure type, structure material type, width , elevations, and skew angle. Identify upstream and downstream watershed influences, the current and most probable geomorphic stream setting, and species passage nee ds. Identify risks to the watershed and local stream conditions created by the structure and mitigation measures to reduce those risks.
60.6
- References
60.61
- Open
- Channel Flow 1. American Association of State Highway and Transportation Officials (A ASHTO). Highway Drainage Guidelines. Current e dition. AASHTO, 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 20001.
2. AASHTO. M odel Drainage Manual. Current e dition. AASHTO, 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 2 0001. 3. Chow, Ben Te. Open

- Channel Hydraulics. Current edition. McGraw Hill, Inc., 1221 Avenue of the Americas, New York, NY 10020.WO AMENDMENT 77 09. 56 b

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4. U.S. Department of Transportation, Federal Highway Administration ( DOT

- FHWA). Design Charts for Open

- Channel Flow , Hydraulic Design Series No. 3 (HDS

- 3), FHWA

EPD

- 86

- 102. 1961.
Website: http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm

. 5. U.S. Department of Transportation, Federal H ighway Administration (DOT

- FHWA). Debris Control Structures Evaluation and Countermeasures, Hydraulic Engineering Circular No. 9 (HEC

- 9), FHWA

- IF

- 04

- 01. 2005.
Website: http://www.f

hwa.dot.gov/engineering/hydraulics/index.cfm

. 6

. U.S. Department of Transportation, Federal Highway Administration (DOT

- FHWA). Highways in the River Environment, Hydraulic Engineering Circular No. 16 (HE C

- 16), FHWA

- HI

- 90

- 016. 1990.
Website: http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm

. 7

. U.S. Department of Transportation, Federal Highway Administration (DOT

- FHWA)

. Bridge Scour and Stability Countermeasures Experien ce, selection, and Design Guidance, third edition, Hydraulic Engineering Circular No. 23 (HEC

- 23). FHWA

- NHI

- 09

- 111. 2009.
Website: http://www.fhwa.dot.gov/engineering/hydraulics/in dex.cfm

. 8 . U

. S

. D epartment of A griculture, F orest S ervice

. (USDA

– FS) "National Best Management Practices for Water Quality Management on National Forest Lands”. Volume 1: National Core BMP Technical Guide. The web address to order this publication is: http://www.fs.fed.us/biology/resources/pubs/watershed/index.html
60.62
- Bridge Hydraulics
1 . AASHTO. Highway Drainage Guidelines. Current Edition. AASHTO, 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 20001.
2. U. S. Department of Agriculture, Forest Service. (USDA

- FS). Bridge Scour Evaluation: Screening, Analysis, and Countermeasures. 7700

- Transportation Systems, September 1998, 9877 1207

- SDTDC. http://www.fs.fed.us/eng/techdev/sdtdc.htm

. 3. U.S. Department of Transportation, FHWA. Hydraulics of Bridge Waterways, Hydraulic Design Series No. 1 (HDS

- 1), FHWA

- EDP

- 86

- 101. 1978.
Website: http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm

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4. U.S. Department of Transportation, FHWA. Evaluating Scour at Bridges, Hydraulic Engineering Circular No. 18 (HEC

- 18). FHWA

- NHI

- 01

- 001. 2001.
Website: http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm

. 5. U.S. Department of Transportation, FHWA. Stream Stability at Highway Structures, 3rd Edition, Hydraulic Engineering Circular No. 20 (HEC

- 20). FHWA

- NHI

- 01

- 002. 2001. Website: http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm.
60.63
- Fords, Vented Fords, and Low
- water Bridges
1. U. S. Department of Agriculture, Forest Service. ( USDA

- FS) . Use of Precast Concrete Ramp Planks For Low

- Water Crossings, Engineering Field Notes, Volume 15, April

- June 1983. 4. USDA

- FS, Engineering Staff, P.O. Box 96090, Washington, DC 20090

- 6090.
2. U. S. Department of Agriculture, Forest Service. (USDA

- FS)

. Low

- Water Crossings: Geomorphic, Biological, and Engineering Design Considerat ions. Forest Service National Technology and Develo pment Program, 2006.
Website: http://www.f s.fed.us/eng/pubs/pdf/LowWaterCrossings 3. U.S. Department of Transportation, FHWA. Design and Construction of Low

- Water Stream Crossings, Executive Summary, FHWA

- RD

- 83

- 015. September 1983. The web address to order this publication is: http://www.fhw a.dot.gov/bridge/elibrary.htm

. 60.64
- Geomorphic Design, Culvert Hydraulics , and Fish Passage 1. AASHTO. Highway Drainage Guidelines. Current Edition. AASHTO, 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 20001.
2. AASHTO. Model Dr ainage Manual. Current edition. AASHTO, 444 North Capitol Street N.W., Suite 249, Washington, DC 20001. 3. American Iron and Steel Institute (AISI). Handbook of Steel Drainage and Highway Construction Products. Current edition. Published by AISI, 100 0 16th Street N.W., Washington, DC 20036.
4. Federal Interagency Stream Restoration Working Group

. 1988 Stream Corridor Restoration: Principles, Processes, and Practices. ISBN

- 0

- 934213

- 59

- 3

. 5. Watts, F. J. Design of Culvert Fishways. Current editio n. Available through the Water Resources Research Institute, University of Idaho, Moscow, Idaho 83843.WO AMENDMENT 77 09. 56 b

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6. Knighton, D. Fluvial Forms and Processes. New York: John Wiley and Sons. 383p

. 7. Montgomery, D. R. , & Buffington, J. M. 1997. Channel

- Reac h M orphology in M ountain D rainage B asins. Geological Society of America Bulletin. 109 p . 596

- 611

. 8 . Portland Cement Association (PCA). Handbook of Concrete Culvert Pipe Hydraulics. Current edition. PCA, 33 West Grand Avenue, Chicago, IL 60610.
9. R osgen, D. 1996. Applied River Morphology. Pagosa Springs, CO

. Wildland 8. Hydrology.
10. Somon, A. 1989

. A M odel of C hannel R esponse in D isturbed A lluvial C hannels. Earth Surface Process and Landforms. 14 p. 11

- 26

. 11. Rosgen, D. 2001. The Cross

- Vane, W

- Weir and J

- Hook Structures: Their Description, Design and Application for Stream Stabilization and River Restoration.
12. U. S. Department of Agriculture, Forest Service. (USDA

- FS). The Water/Road Interaction Series. San Dimas Technology Dev elopment Center. 1997. http://fsweb.mtdc.wo.fs.fed.us/search
13. U. S. Department of Agriculture, Forest Service. (USDA

- FS). Stream Simulation: An Ecological Approach to Providing Passage for Aqu atic Organisms at Road

- Stream Crossings, Forest Service Stream

- Simulation Working group, Forest Service National Technology and Development Program, 2008. http://www.fs.fed.us/eng/pubs/pdf /StreamSimulation/
14. U. S. Department of Agriculture, Forest Service. (USDA

– FS). Keeping Beavers From Plugging Culvert Inlets, Engineering Field Notes, Volume 18. January

- February 1986. USDA

- FS, Engineering Staff, P.O. Box 96090, Washington, DC 20 090

- 6090.
15. U.S. Department of Transportation, Federal Highway Administration (DOT

- FHWA). Hydraulic Design of Highway Culverts, Hydraulic Design Series No. 5 (HDS

- 5), FHWA

NHI

- 01

- 020. 2005. http://www.fhwa.dot.gov/engineering/hydraulics/index.cfm.
16. U.S. Department of Transportation, Federal Highway Administration (DOT

- FHWA). Culvert Design for Aquatic Organism Passage, Hydraulic Engineering Circular No. 26 (HEC

- 26). FHWA

- HIF

- 11

- 008. 2010

. http://www.fhwa.dot.gov/engineering/hydraulics/index.cfmWO AMENDMENT 77 09. 56 b

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60.65
- Webs ites
1. FHWA

- Hydraulic Engineering Website: http://www.fhwa.dot.gov/engineering/hydraulics/inde x.cfm

. 2. FHWA

- Western Federal Lands Website: http://www.wfl.fhwa.dot.gov/resources/hydraulics/fishpassage/bibliography.htm

. 3. NRCS

- Hydraulics and Hydrolo gy Website: http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/H&H_home.html

. 4. U.S. Army Corps of Engineers

– Hydrologic Engineering Center (HEC) Website: http://www.hec.usace.army.mil/

. 5. U.S. Department of Agriculture Forest Service, Stream Systems Technology Center Website: http://www.stream.fs.fed.us/

. 6. U.S. Department of Agriculture Fo rest Service, National T&D Publications Website: http://fsweb.mtdc.wo.fs.fed.us/search/

. 7. U.S. Geological Survey, Office of Surface Water Website: http://water.usgs.gov/osw/techniques/indirect.html

. 8. U.S. Geological Survey, Water Resources Website: http://water.usgs.gov/

. 60.66
- Software 1. U.S. Army Corps of Engineers. Hydrologic Engineeri ng Centers River Analysis System (HEC

- RAS). http://www.hec.usace.army.mil/software/hec

- ras/

. 2. U.S.D

. A

- FS. Stream Systems Technology Center, WinXSPRO: A Channel Cross

Section Analyzer. http://www.stream.fs.fed.us/publications/winxspro.html

. 3. DOT

- FHWA. HY

- 7, Bridge Waterways Analysis Model, Micro Computer Software, FHWA

- WSPRO. Current version. http://www.fhwa.dot.gov/engineering/hydraulics/software/softwaredetail.cfm#hy7

. 4. DOT

- FHWA. HY

- 8, FHWA Culvert Analysis, Micro Computer Software, FHWA

HY

- 8. Current version

. http://www.fhwa.dot.gov/engineering/hydraulics/software/hy8/

. 5. U.S. Geological Survey. National Streamflow Statistics Program. http://water.usgs.gov/software/NSS/

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61
- CHANNEL DESIGN Channels should be designed to use a combination of geomorphic and hydraulic principles and approaches. Use the same hydraulic principles to analyze both natural stream and manmade channels through structures or channel section to be restored relative to water surface profiles, flow and velocity distributions, lateral and vertical stability of the channel, sediment mobility/stability, flood risk, and the potential reaction of the stream to c hanges in alignment, shape, or slope.
61.1
- Open
- Channel Hydraulics
61.11
- Flow States Determine appropriate flow states using criteria and equations outlined in "Open

- Channel Hydraulics" (Chow) (sec. 60.6). Open

- channel flow is usually classified as one or a combination of: 1. Steady or unsteady flow, or
2. Uniform or non

- uniform flow, or 3. Subcritical or supercritical flow.
See the z ero c ode of this h andbook for definitions of flow states. Steady and uniform flow seld om occurs in nature. Howe ver, E ngineers generally use the simplifying assumption of steady and uniform flow to simplify hydraulic calculations. This assumption would not be valid for flow during a dam failure or breach where steady and uniform flow obviously does not occur. Stea dy, but non

- uniform flow generally occurs at restrictions in the channel, such as at some bridge locations. Use engineering judgment to ensure that the use of simplifying assumptions will not result in inaccurate calculations.
Stable natural stream chann els should always exist in subcritical flow conditions. Supercritical flow is only experienced with isolated hydraulic situations such as hydraulic jumps, channel obstructions, and constrictions. Design channels should mimic these subcritical flow condi tions.
61.12
- Open
- Channel Flow Equations As appropriate, use the following basic equations from "Open

- Channel Hydraulics" (Chow) and "Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains" (FHWA TS

- 84

- 204) (sec. 60. 6) to determine flows for the hydraulic design of open

- channels:
1. Manning's Equation . Use Manning's Equation to make uniform flow and gra dually varied flow calculations and to calculate normal depth in an open channel. (Normal depth is the depth of fl ow for uniform flow for a given cross

- section, roughness, andWO AMENDMENT 77 09. 56 b

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slope.) The most dif

ficult part of using Manning's E quation is selecting the appropriate channe l roughness coefficient, "n". Always validate numeric outputs for realistic values. Average stab le channel conditions are always in a subcritical flow scenario, and most stream channels will have bankfull velocities ranging from 3

- 6 fps. If realistic values are not generated, the roughness coefficient or perhaps other variables should be adjusted. Use actual discharge measurements to back calculate M annings to calibrate flow models and perform a Froude number check to validate subcritical flow regime.
2. Energy Equation . Use the Energy Equation, or results derived from it, for calculating gradua lly varied flow in channels, for determining backwater elevations, and for calculating headwater for culverts in outlet control.
3. Momentum Equation . Use the Momentum Equation, or results derived from it, for calculating rapidly varied flow in the desig n of energy dissipaters.
4. Continuity Equation . Use the Continuity Equation, or results derived from it, for calculating all types of flow conditions in channels and for determining backwater elevations and upstream effects due to storage. Use commerci ally available charts and computer programs (available from the F ederal Highway Administration, S tate highway departments, and private vendors) to simplify and speed calculations using these equations. For additional procedures see "Design Charts for Open

- Channel Flow" (FHWA HDS

- 3) (sec. 60.6).6.11

- Stage Discharge Curves. Use a stage discharge curve to display the elevations of the water surface at a particular cross

- section for different discharges. Develop a stage discharge curve to find channel free board, to predict flo oding, or to determine culvert t ailwater elevations.
61.2
- Roadside and Trailside Design Features Ditches along the side of the traveled way either prevent water from reaching the traveled way or drain water that would otherwise coll ect on the traveled way. Design ditches to car ry flows commensurate with the Road Management O bj ectives (RMOs, FSM 7714) and Trail Management O bjectives (TMOs). Ensure that side features are stable for the selected flows.
Ditches and associated struct ures should be designed and maintained to be disconnected from the natural stream system with adequate buffer distances and/or devices to eliminate or reduce sediment delivery to streams. This is best achieved through frequent cross drains that discharge onto stable areas of the forest floor allowing water to infiltrate into the ground. Design cross drain alignment to maintain sediment transport to the extent possible by skewing and sloping. Sediment buffering devices, such as low

- profile slash filter wi ndrows, coir rolls, straw bales, and so forth, should be used at the outlets of cross

- drains to trap sediment when sediment has the potential to be delivered to a stream or wetland. For further information on traveled way drainage, see FSH 7709.56, s ec tion 44.WO AMENDMENT 77 09. 56 b

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61.3
- Channel Modification Streams are dynamic and extremely powerful; attempts at stream modification are expensive, frequently create unintended consequences , and are often only temporary. Every attempt should be made to move the route and struct ure to a stable location rather than manipulate the stream. Channel modifications should only be attempted with an interdisciplinary team as a last resort and should not be manipulated beyond natural geomorphic ranges of profile, pattern, and dimension. When manipulated beyond natural geomorphic ranges, streams that have been stable for years frequently can respond by several outcomes such as head

- cutting, straightening, widening, meandering, down cutting, or aggrading. Perform a geomorphic assessment to identify the critical design information required for channel modifications.
61.4
- Channel Stabilization Use interdisciplinary expertise to characterize and properly identify stabilization issues and remedies. Assure that both causal and symptomatic me chanisms of the instability are understood and addressed by performing a geomorphic assessment. Avoid placing roads, trails, or structures across or immediately adjacent to unstable or braided channels, across debris flow or avalanche paths or on alluvial fans. Channel stabilization designs should be developed by an experienced interdisciplinary team. Check upstream and downstream stability at any proposed stream crossing by identifying potential bank sloughing, head cutting, aggradation , or down cutting

. Where stream stabilization may be necessary, all design components should be designed to address identified failure mechanisms such as, but not limited to, flanking, channel down cutting, local scour, or systemic down cutting. Consider the stabilizatio n method relative to efficacy of bot h local and systemic dynamics. Localized spot stabilization may fail or be expensive to maintain if they are located within long reaches of unstable channels. Understand the dynamics of discontinuous grades above and b elow the stream crossing. When replacing a culvert with a bottomless structure, assure that adequate grade control is used to avoid head cutting through the structure. Select stabilization measures based on an evaluation of the slope, velocity, shear str ess on the channel and bank, projected scour, grain size of the bed load, bed and bank material, design flood water surface elevations, volume and type of debris, whether the channel is horizontally or vertically unstable, and experience with stabilization efforts in the area. Every attempt should be made to adjust the structure to the natural or most probable stable long profile elevation of the stream channel. Attempts to change a streams elevation beyond natural geomorphic ranges for the valley and loc al setting controls are expensive and frequently temporary.WO AMENDMENT 77 09. 56 b

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61.41
- Bank Stabilization Structures Many types of stabilization structures exist. Consult with appropriate resource specialists to decide which structures best accommodate the channel relat ive to the remedy and the risk. Harden or protect banks only to a level of protection necessary to address the desired risk and public safety. Incorporate vegetation whenever possible. Avoid activities that remove or retard natural bank vegetation and de ep rooting strengths. If stream banks are unstable and horizontal movement and erosion must be retained, utilize natural materials whenever possible and minimize the extent of hardened structures. When hardened structures are used, use natural channel de sign techniques that work with natural stream processes and cross

- section hydraulics whenever possible.
61.42
- Grade Control Structures Use grade control structures as needed to avoid or control vertical instability, head cutting, and undermining of st ructure components. Understand and design for the causal mechanism of vertical instability in both local and systemic contexts. Utilize structures that provide for natural flow and sediment transport hydraulics. Natural channel design techniques will in most cases be the desired approach. Design structures in context to reduce the risk of identified potential failure mechanisms such as flanking, local scour, and down cutting. If techniques other than natural channel design approaches are used, assure t he grade control structure(s) do not interfere natural flow hydraulics or with passage requirements for aquatic organisms.
62
- BRIDGE DESIGN Hydraulic design of bridges is site specific and varies by geographic and geomorphic area. Use the following gen eral requirements, modified as necessary by Regions and Forest guidance.
62.1
- Bridge Location
Direction on b ridge location is found in c hapter 20 of this Handbook

. 62.2
- Hydraulic Analysis Perform hydraulic an alyses of the design discharges for roa d and trail bridges and Aquatic Organism Passage structures to determine the: 1. Headwater elevation just upstream from the bridge. 2. Water surface profile upstream from the bridge, with and without the proposed bridge.
3. Freeboard clearance

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4. Dep th of overtopping of the road or trail and the associated design discharge. 5. Velocity of flow transitioning upstream, through the bridge opening, and downstream

. Bridge openings should not restrict the bankfull stream width. Consider sloping abutment fills to create spill through openings to improve flow efficiency and reduce scour potential. The bridge opening should also account for freeboard above the maximum design flood event’s upstream water surface elevation. A minimum freeboard of three fee t is recommended for most structures. If large floating debris is possible, half a typical root wad, or half a typical log should be added to the minimum three foot freeboard to provide clearances. A minimum freeboard to accommodate boat, canoe , and floa ter r ecreation use should be five feet.
Use the HEC

- RAS, “Hydrologic Engineering Center

– River Analysis System” or a similar program that may be available to model the water surface pro file through the bridge opening

. Bridge openings should be sized to pass the 100

- year flood event with an appropriate freeboard and considering debris and sediment passage and blocking if applicable. The hydraulic model should consider debris blockage in the analysis. If site specific debris data is not available, a 3 0

- 50 percent blockage of the bridge opening using ineffective flow areas can account for debris blockages. Debris blockage should be considered if there is history or probability of transported debris or high intensity wildfire. Modeling contraction an d expansion coefficients should be 0.1 and 0.3 for most channels and 0.3 and 0.5 for the cross sections nearest the bridge. The 2

- year flood flow event , bankfull or the flow corresponding to the clear Ordinary High Water (OHW) geomorphic indicators should be used to determine the OHW surface elevation. This design elevation should be confirmed with existing OHW or bankfull at the site as validation of the design discharges. If elevations of predicted and existing OHW or bankfull are not similar , then fur ther refinement of the design discharges is necessary. Temporary construction detour drainage structures should be sized to pass the 2

- year flood flow , bankfull flow or the peak flow anticipated during the time of year construction will occur based
on a hydrologic analysis of the site and nearby stream gages, unless provisions are in place to remove the structure during seasonal high

- water.
62.3
- Scour For details on estimating and reducing scour, see the following:
1. “Bridge Scour Evaluation: Scree ning, Analysis, and Cou ntermeasures” (USDA

- FS) (sec. 60.6).
2. "Evaluating Scour at Bridges" (FHWA HEC

- 18) (sec. 60.6).WO AMENDMENT 77 09. 56 b

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3 . "Highways in the River Environment" (FHWA HEC

- 16) ( sec. 60.6).
4. "Stream Stability at Highway Structures" (FHWA HEC

- 20) ( sec. 60. 6). Validate predicted scour with existing channel information. Evaluate the longitudinal profile and sediment size and mobility in the reference channel reaches to provide a check of scour depth that occurs naturally in the stream. Investigate local ma ximum scour depths in the existing channel, realizing that substrate deposition during recession of the peak flood commonly occurs, which reduces the measured maximum scour. Placement of structure elements in dynamic stream channels commonly has greater s cour potential at flood flows than the natural stream because of greater flow constriction and higher shear stresses.
62.4
- Pier Design Eliminate piers when possible. Consider the following when piers must be constructed:
1. Pier Width and Length . Mi nimize the area a pier presents to the flow to decrease backwater and local scour.
2. Pier Shape . Streamline the pier so that it produces less backwater and scour potential and so that it catches less debris.
3. A lignment . Align piers with the m aximu m design flood flow to produce less backwater and scour and to catch less de bris. Use geomorphology, aerial photographs and other available site specific data to determ ine appropriate pier alignment. Avoid using multiple pier bents that are not aligned t o the stream flow since they catch debris, which in turn increases local scour and backwater.
4. Location . Pier location affects the debris catching characteristics of a bridge. Avoid placing piers in the center of streams that carry a large amount of d ebris where velocity and debris concentration is highest. Consider alternatives, such as using a three

- span bridge with two short spans and one long central span or using two unequal spans to avoid placing a pier in the center of the stream.
62.5
- Abutme nt Design
Choose either a ver tical or spill

- through abutment depending on economic and structural considerations and in accordance with the following conditions:
1. Spill through abutments is preferred and may minimize scour impacts.
2. Vertical abutmen ts should have wing walls to improve scour resistance.
3. Align abutments with the flow to reduce backwater and to avoid excessive scour.WO AMENDMENT 77 09. 56 b

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4. L ocate spill

- through abutments so that the toe of the embankment is equal to or greater than bank full width and does not constrict the main channel.
5. Design riprap or other appropriate countermeasures based on maximum design flood flow velocities and shear with debris blockages that may accelerate flows. If the channel and banks are stable, riprap or other ap propriate countermeasures should be installed within areas of channel and bank disturbance. Riprap mat thickness must be a minimum of twice the average rock size of the r iprap class/gradation or D50. A layer of geotextile may be placed under the riprap l ayer. 62.6
- Relief Structures Consider using relief structures on wide floodplains with large amounts of overbank flow. Relief structures allow floodplains to drain without using lateral channels along the upstream embankment slope. Relief structures also distribute the flow across the floodplain, reducing constriction losses and increasing the efficiency of the structures. Relief structures reduce abutment scour described in section 62.3.
63
- FORD AND LOW WATER C ROSSING SELECTION AN D DESIGN
Use th ese structures only when their installation is consistent with the RMOs and TMOs. Consider the need for depth markers to warn of dangerous crossing conditions. Install fords or low

- water structures if traffic can be interrupted during floods and the stru cture can be built to prevent frequent severe damage. Designs must meet aquatic organism passage requirements including low flow depth needs and minimum jump limits. Consult U.S. Department of Agriculture, Forest Service. Low

- Water Crossings: Geomorphic , Biological, and Engineering Design Considerations. Forest Service National Technology and Development Program, 2006.
63.1
- Fords Use paved or natural fords under the following conditions: 1. Traffic can be interrupted during periods of mild to sever e flooding. 2. Fisheries and water quality requirements allow vehicles to enter the stream. 3. The normal daily flow is less than 6 inches deep.
4

. When there is extreme variation in normal flow to flood flow levels

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If a stream has a flat slope and a rock or gravel bottom, construct a natural ford by merely dropping the grade to the stream bottom. On streams with steep slopes, or with rough, rocky, or soft sandy bottoms, level the bottom with coarse gravel. Except in very low gradients, a grade step will occur at the ford site. To dissipate flow energy and provide for aquatic organism passage when it is necessary, construct one or more grade control features downstream to evenly transition the downstream grade with the ford. Use paved fords for sit es similar to those of natural fords, but where a more permanent structure requiring less maintenance is desirable. Extend the paved ford horizontally to a point above the high water for a specified design flood frequency. Base slab thickness on the desi gn wheel load and the foundation strength. Use vertical cutoff walls on the downstream side of paved fords to prevent undermining of the slab. The depth of the cutoff wall below the streambed depends on the streambed material. Large gravel and cobble st reams normally require only 1

- foot depth, while a sandy streambed may require a deeper cutoff wall.
Build fords at the same elevation as the streambed.
63.2
- Vented Fords Use a vented ford under the following conditions:
1. Traffic can be interrupted during flooding.
2. Fishery and water quality requirements do not allow vehicles to enter the stream.
3. Fish passage is not required.
4. Normal daily low flow can pass through one or more small culverts.
5. The type and volume of bed load in the st ream is unlikely to clog the culverts. Vented fords obstruct the stream channel and are subjected to large drag and lift forces. Reinforce and tie all parts of the structure together so the weight of the entire structure will resist the drag and lift for ces. Use culverts as large as possible within the height restrictions for the vented ford; because large culverts are less likely to clog than small ones. Use as many culverts as are needed to pass the low flow in the stream.WO AMENDMENT 77 09. 56 b

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63.3 Low
- Water Bridges
Use a low

- water bridge under the following conditions:
1. Traffic can be interrupted during periods of moderate to severe flooding.
2. Normal daily flow cannot pass economically or effectively through a vented ford.
3. It is necessary to provide aquatic or ganism passage and associated natural bottoms. Design low

- water bridges similar to conventional bridges, but allow for overtopping. When inundated, these bridges may be subjected to significant scour. Design low

- water bridges to resist scour and lateral stream flow forces.
64
- CULVERT DESIGN When designing culverts, use the direction outlined in this section in conjunction with direction in FSH 7709.56 , s ection 44 along with guides and design charts available from culvert manufacturers.
64.1
- Loca tion and Installation
Consult c hapter 20 for direction in locating bridges and culverts. See U.S. Department of Agriculture, Forest Service. Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road

- Stream Crossings , "Handbook of Steel Drainage and Highway Construction Products" (AISI) and "Highway Drainage Guidelines" (AASHTO) ( see sec. 60.6) for guidance in locating and installing all types of culverts. In addition, consider the following: In flat country where t he stream leaves its banks during high wate r and spreads over a wide flood plain, flow must be accommodated in the active main channel, as well as flood swales, side channels and sometimes along the floodplain for continuous, long embankments. In low grad ient streams and where sediment and debris transport are an extremely low occurrence or probability, placing multiple adjacent culverts can be considered. Avoid concentrating water in one place due to the danger of scour and upstream aggradation.
Ident ify and provide for proper functions of all side channels adjacent to the primary channel. For wetland drainage or drainage of the floodplain it is extremely important to ensure that the culvert invert is not placed lower than the primary surface elevatio n of the wetland or floodplain as head cutting and lowering of the water table can result. See U.S. Department of Agriculture, Forest Service. Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road

- Stream Crossings f or methodology to determine vertical, horizontal alignment of structure with the stream and cross sectional and streambed attribute necessary for design.WO AMENDMENT 77 09. 56 b

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64.2
- Site Surveys
Directi on on site surveys is found in c hapter 30 of this Handbook

. 64.3
- Culvert Type Consider the shape, material, and number of barrels when selecting culvert types and base selection on accommodating the desired stream width, total annual cost, local availability, flow capacity and desired headwater depths, flow capacity relative to counter

- sinking depth, service life, and fill height.
64.31
- Shape Use one of the following culvert shapes:
1. Circular . Circular culverts are the most common. They cost less because of their efficient use of material and ease of construction. T o gain maximum desired width of the channel , they may require relatively deep counter

- sinking depths, which may limit desired flow capacity.
2. Pipe Arch . Use pipe arch culverts when there are fill height limitations. Pipe arch culverts are not as struc turally strong as circular culverts, require mor e intensive construction inspection for the backfill, and are usually more expensive for equal hydraulic capacity. However, for stream simulation design, they are commonly preferred to maximize stream width accommodation relative to culvert rise and flow capacity.
3. Rectangular . Rectangular box

- shaped culverts are the most efficient in reducing headwater elevations for a given culvert cross sectional area, but they are poor for fish passage unless they are counter

- sunk. They are generally more expensive than circular or arch pipes.
4. Arch (Without Bottom) . Avoid restricting bankfull flow when using open bottom arch pipes. Locate footings on rock or below the estimated scour depth. Scour depth is diffi cult to estimate inside an arch because the flow is non

- uniform and highly turbulent.
64.32
- Materials Culverts are usually made of reinforced concrete, corrugated steel, corrugated aluminum, and polyethylene. Evaluate the following variables when choos ing culvert material:
1. Abrasion . When evaluating abrasion potential, consider the water velocity and the size, shape, and quantity of the streambed material that can be transported. Provide additional protective measures for metal pipe to avoid loss o f culvert material when the average flow velocity in the culvert exceeds 7 feet per second and the bed load consists of sharp, angular rock.WO AMENDMENT 77 09. 56 b

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2. Corrosion . Evaluating corrosion is complex and involves appraising abrasion and factors that cause chemicals t o erode the culvert surface. Use the performance of existing structures in the same channel as the primary design criterion. The "Handbook of Steel Drainage and Highway Construction Products" (AISI) ( see sec. 60.6) contains values for corrosion indicat ors for different types of soils. Use these values as guidelines only.
64.33
- Number of Barrels Avoid using multiple barrels in stream channels with the exception being where vertical alignment cannot be raised due to right

- of

- way, paving, grade contr ol po ints, or environmental issues. Keep in mind that multiple culvert openings are more susceptible to debris and ice clogging than a larger single opening.
64.4
- End Treatments Consult "Hydraulic Design of Highway Culverts" (FHWA HDS

- 5) ( see sec. 60.6 ) for information on culvert end treatments. The following are four common types of end treatments: projecting culverts, mitered or beveled culverts, and headwalls and wingwalls.
64.41
- Projecting Culverts Use this type for the smaller diameter culver ts and where projecting inlets and outlets will not be visually objectionable. This type of treatment will have the least first cost.
64.42
- Mitered or B eveled Culverts A mitered culvert is formed when the culvert is cut to conform with the plane of t he embankment slope. Use this treatment with large metal culverts to improve the appearance of the culvert ends. Cutting corrugated metal pipe significantly reduces its strength and rigidity, making the inlet end susceptible to damage by hydraulic forces during large flows. When stream flows depths will not exceed one half the height of the miter, hydraulic pressures can generally be ignored. Horizontal earth pressures on the mitered section of the pipe should be considered in the design. Sharp skews on a structure can result in uneven loading from the structure fill, so contours at the inlet and outlet may need to be adjusted to balance the earth pressures. In general, miters not exceeding 6 feet in length (along the axis of the pipe) are not in jeo pardy of earth pressure failure. Mitered, or bevels exceeding 6 feet in horizontal length should be structurally evaluated.WO AMENDMENT 77 09. 56 b

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Mitered ends may be on a continuous slope from the top to the bottom of the culver t, or with a vertical step on the bottom, or wit h vertical steps on both the top and bottom. The ends with steps are referred to as step mitered or step beveled. Stabilize fill slopes, paying particular attention to the inlet end, with riprap or other erosion control methods. Riprap placement should be monitored to prevent damage to the pipe.
64.43
- Headwalls and Wingwalls Headwalls and wingwalls are usually vertical walls that are commonly reinforced concrete. Headwalls and wingwalls are typically constructed on the ends of culvert barrels to reta in the fill material, reduce erosion of the embankment , and improve hydraulic efficiency. Although headwalls are sometimes skewed to the culvert barrel to fit the embankment slope, aligning them with the direction of flow provides a more hydraulically e fficient opening. Where feasible, warp the fill slope to accommodate this more favorable orientation.
64.5
- Culvert Hydraulics Hydraulic capacity design of culverts must accommodate aquatic organism passage and natural substrate within the c ulvert. S ee the references in s ection 60.6 for detailed information. In most instances, headwater depths should not exceed the height of the structure in order to avoid back water conditions and assure proper transport of flow, sediment, and debris. For the desir ed design discharge, designs should accommodate headwater to depth ratios of 0.8 for maximum hydraulic efficiency.
65
- AQUATIC ORGANISM PASSAGE DESIGN This guidance sets expectations for aquatic organism passage (AOP) design for new structures and replac ement structures at road or trail stream crossings. Priority setting, design, and monitoring must be accomplished as part of an interdisciplinary process.
65.1
- Design Priority: Aquatic organism passage and ecological connectivity is the goal and is sec ond only to user safety in design priority for crossing streams that provide habitat for aquatic life. The other design considerations include, in order of importance:
1. Minimizing the consequences of plugging and overtopping, including the ability to p revent stream diversion;
2. Hydraulic capacity, including the requirement that headwater depth does not cause pressurized flow at the maximum flood; and
3. Maximize benefits while minimizing life cycle cost.WO AMENDMENT 77 09. 56 b

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65.2
- Aquatic Organism Passage Design Methods Consider route realignment to avoid crossing the stream where possible. Temporary structures that span the stream may be desirable on roads with intermittent use. If a permanent crossing is necessary, the following alternatives for stream crossings sho uld be considered in order of preference:
1. Stream simulation strategies

. Bridges, arches or embedded culverts provide stream simulation. The USDA Forest Service stream simulation guidance should be used when possible.
2. Geomorphic

- based Channel Desi gn . Re connects the upstream and downstream channel while meeting most fish and other aquatic organism movement and habitat needs.
3. Hydraulic design

. Designs based primarily on hydraulic capacity should be limited to low stream gradients, where the cul vert is constantly partially submerged. Baffled culverts or structures designed with a fishway are discouraged and should be used as a last resort, especially if they also hinder terrestrial organism passage. Note , in some limited circumstances , a fishwa y hydraulic design for a high gradient stream may be required to meet limited fish passage only objectives. The design method must respond to the site specific conditions found at the crossing, a combination of design methods may be needed. New and repla cement structures will use the most preferred design method possible or as much of the preferred design methods as possible. Document the design rationale especially when variance from this guidance is planned. Document the specific nature of any varianc e, along with biological and/or hydrologic rational to support the alternative approach.
65.3
- Design Requirements for Aquatic Passage Aquatic habitat stream crossings, regardless of the design option used, must be designed to accommodate the peak floo d flow (100 year in most cases) plus debris and bed load without structural damage to the crossing or diversion of the stream. Hydraulic capacity must compensate for expected deposition in the culvert bottom. Structure opening width, as a minimum, should not constrict the stream or accelerate velocity at bankfull flow (bankfull width).
Stream form and substrate within the structure should conform to the reference channel cross

section, provide a thalweg for low flow conditions, and avoid continuous str eam flow along the structure wall. The natural stream gradient and substrate material should be simulated through the structure and should be restored whenever possible. Consider the need for terrestrial organism passage in the design of materials placed in and around structures.WO AMENDMENT 77 09. 56 b

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Conduct geomorphic and hydrologic assessments to determine design parameters, feasibility, and watershed risk. All structures should be evaluated for appropriate regrading and grade control measures to avoid head cutting through and above the structure. Hydraulic analysis designs should be done in a manner to ensure bed and bed form stability. They should also evaluate ecological process (large woody debris transport) and associated failure risk (flood history). Baffles, wei rs, and other mechanical devices inside culverts and artificial instream structures below culverts should only be employed when stream simulation or use of natural stream features is not physically possible or practical. Before using these devices, seek a dvice from the Regional Bridge Engineer.