Center for Environmental Excellence by AASHTO CENTER HOME  
skip navigation
CEE by AASHTO Home | Compendium Home | Online Compendium Help | Recent Updates | Inquiries | FAQs | State DOT Links
About Best Practices | Comment on Best Practices | Suggest A Best Practice | Volunteer to Vet Best Practices
Printer Friendly Version Print This Page    
« Back to Chapter 2 | Go to Chapter 4 »
Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.5. Culverts and Fish Passage

As long linear ecosystems, rivers and streams are particularly vulnerable to fragmentation. A number of human activities can disrupt the continuity of river and stream ecosystems, the most familiar of which are dams. There is growing concern about the role of road crossings - and especially culverts - in altering habitats and disrupting river and stream continuity. [N] On U.S. Forest Service and Bureau of Land Management land in Washington and Oregon alone, there are over 10,000 culverts on fish-bearing streams. [N] Based on an estimate from GIS analysis over 28,500 road and railroad crossings affect Massachusetts streams. [N] [N] Over half of the culverts assessed on U.S. Forest Service and Bureau of Land Management (BLM) lands in Oregon and Washington are considered barriers to juvenile salmonid fish passage. [N] Fish habitat and fish passage improvement projects undertaken by DOTs include installation of baffles or weirs in culverts, construction of berms or detention facilities, and installation of deck curbs, new culverts or jump pools for fish passage.


3.5.1 Forms of Stream Crossings
< back to top >

Stream crossing methods include bridges, fords, open-bottom or arch culverts, box culverts, and pipe culverts. Depending on the type of crossing, its size, method of installation, and maintenance, a road crossing may have many or relatively few adverse impacts on a river or stream ecosystem. It is generally believed that culverts are more detrimental to streams than are bridges; consequently, wildlife regulatory agency biologists routinely recommend installation of a bridge instead of a culvert. Culverts, however, are more economical than bridges; they often cost less to install, require less maintenance, and have a longer effective life. Culvert crossings tend to provide very little or no habitat within the culvert. Some habitat can be provided if the culvert is sufficiently embedded such that the substrate in the culvert resembles the natural streambed. Open-bottom or arch culverts and bridge crossings often maintain natural streambeds, although some habitat may be lost to footings, piers, and abutments. [N]

Resource agencies often prefer that structure types should be considered for use in the following order of preference: [N]

  • Bridge (with no approach embankment into the main channel).
  • Streambed simulation strategies using a Bottomless Arch or embedded culvert designs.
  • Streambed simulation strategies using embedded round metal or concrete box culvert designs.
  • Non-embedded culvert; placed at less than 0.5 percent slope.
  • Baffled culvert (various designs); placed at 0.5 percent to 12 percent slope or a structure with a fishway.


3.5.2 Bridges versus Culverts
< back to top >

Providing for larger structures that mimic natural streambeds requires a greater capital investment, but the return on such an investment can be accrued over the long term with reduced maintenance and/or replacement costs. [N]

NCDOT hypothesized that the impact of culverts on the stream bed is not uniform, but varies due to its design, and size and site specific factors and that construction and renovation practices may be refined to minimize the impact of crossing structures on surface waters and achieve a delicate balance between construction and maintenance costs and ecosystem integrity. Consequently, NCDOT is undertaking research, due in late 2005, that will compare the relative impact of culverts and bridges, and specific design attributes on freshwater mussel populations, in the interests of refining standard culvert designs to be more environmentally beneficial and acceptable to wildlife agency biologists. [N]

Through an initial assessment of the 51 study sites, the research team has observed that while each of the culvert sites is unique, a pattern seems to be emerging regarding their impacts on stream morphology. Many of the sites that seemed greatly affected by the installation of a culvert usually had one or more of the following characteristics. [N]

  • When the culvert was installed, many streams appeared to have been straightened and deepened in order to increase flow speed so that the culverts would be self cleaning. This altered habitats, destroyed stream sinuosity, and created long, slow pools that invite beaver dams.
  • When a culvert's width was near or less than the bankfull width, then the downstream bank incision usually was greater than upstream. Inversely, when a culvert was wider than the bankfull width, then the stream was able to use its floodplain and thus minimize the high velocities associated with the concentrated flow from most culverts.
  • When a culvert was installed in a stream with a coarse substrate, the stream banks seemed to resist the higher velocities below a culvert.

The team will identify crossing structure design attributes that may alter the physical or biological impact on streams and suggest where certain culverts are more appropriate for certain stream types. The study will be complete, and the final results documented for NCDOT and the project technical committee's review, by June 2005.


3.5.3 Potential Adverse Impacts of River and Stream Crossings
< back to top >

If not properly designed, crossing structures can block animal movements, delay migration (a process made worse where there are many crossings), and cause physiological stress as animals expend energy passing both natural and artificial obstacles. If crossing structures are not large enough, or lack banks or other dry passage, riparian wildlife may choose to cross over the road surface rather than pass through the structure. As barriers to animal movement, stream crossings for roads can reduce access to vital habitats. To the extent that road crossings act as barriers to animal passage, they can fragment and isolate populations, increasing vulnerability to genetic change and extinction due to chance events. Local extinctions can result from demographic chance events (e.g., change in sex ratio), natural disturbances, or human impacts. Barriers to movement can block the exchange of individuals among populations, eliminating gene flow and disrupting the ability of "source" populations to support declining populations nearby. Barriers to dispersing individuals also eliminate opportunities to re-colonize vacant habitat after local extinction events.

Culvert and embankment fill can cover up fish habitat on channel beds and banks. Flow concentration can raise velocities and increase erosion and sediment production and downstream deposition in the stream, increased slopes and flow velocities can block fish passage, and long culverts can discourage fish from entering if no light can be seen at the opposite end. Improper design or scour can result in a perched culvert which blocks fish passage.

  • Potential adverse effects of river and stream crossings that should be considered ineffective design for fish and wildlife include: [N]
  • Habitat Loss and Degradation
  • Alteration of Ecological Processes, including passage of large woody debris
  • Inlet or outlet drop. Elevation drops at either the inlet or outlet of a crossing structure can represent physical barriers to many animal species. Piping (water flowing through the fill material rather than the culvert) and scouring can result in culverts that are perched above the stream channel making passage impossible for most aquatic species.
  • Physical barriers. Animal movement can be blocked by clogged or collapsed culverts. Also, weirs or baffles associated with crossing structures can create barriers for some species.
  • Excessive water velocities. Water velocities can be too high to pass fish or other organisms during some or all of the year.
  • Absence of bank-edge areas. Passage by weak-swimming organisms can be inhibited or prevented by the absence of bank-edge areas within crossing structures.
  • Excessive turbulence. Flow contraction at the inlet can create turbulence that inhibits or prevents animal passage.
  • Insufficient water depth. Absence of a low-flow channel can result in water depths too shallow to allow passage for fish or other organisms.
  • Discontinuity of channel substrate. Crossing structures that lack any natural substrate or contain substrates (including riprap or other armoring) that contrast with the natural stream channel create discontinuities in streambed habitats. Many benthic (streambed-dwelling) organisms are confined to the streambed and can only move through appropriate substrates. Streambed discontinuities caused by crossing structures disrupt and fragment populations of these benthic organisms.


3.5.4 Stream Crossing Design Considerations
< back to top >

Research on culvert design considerations for fish passage is increasing with awareness of the issue and its importance for anadromous species on both the east and west coasts of the U.S. A cooperative research partnership with the Washington Department of Fish and Wildlife, WSDOT, Alaska , Oregon , California and FHW A is testing existing and new culvert retrofit designs that enable juvenile fish passage through culverts , complimenting work conducted by the Battelle Memorial Institute and Washington State University . Th e intent is to help define cost effective retrofit designs for thousands of culverts , particularly for salmonid species. The partners have constructed a test bed for research and results are expected in 2006. [N]

Collecting Adequate Survey Information

Adequate survey information should be collected, to help ensure proper design and avoid costly mistakes: [N]

  • The original site survey should have at least three durable reference points for location of all other site features and establishing additional references. Remote projects that are surveyed, then delayed for years, may lose reference points to vandalism, storm events or road maintenance activity. Site topography may also change, especially in stream channels due to flood events. Lost references have to be replaced. Existing culvert inverts and drill holes can be useful project references.
  • Preconstruction Survey. An early review of project plans in the field with the contract administrators and designers can help prevent surprises later on by answering specific questions and verifying that the design still fits if some site changes have occurred.
    • Enough references and data points should be surveyed to be able to locate the structure and reestablish the road surface and embankment geometry.
    • Assure the road surface is adequately described by existing survey information; otherwise, survey additional points to assure that super elevation, vertical curves, curve widening, or any other critical geometric elements can be reestablished. A straight road segment is easy to recreate with a minimum of survey data, but others such as a super-elevated "S" curve are not.
    • Examine site plans and design elevations carefully. The project site may not seem to match the site plan or stream profile. If survey points near the existing or new structure are not marked and the channel is very rough, this may lead to confusion and uncertainty as to design elevations and assumptions. A stream classification system may be helpful in describing channel conditions. This could be due to the software used to generate the contour map. Rough channels can be confusing unless it is known exactly what points were surveyed in the channel. The "stream channel elevation" used to design the new structure invert can vary a foot or even more depending on where the survey rod was placed originally. Was it held on top of a boulder or between boulders? Are boulders dominant? Do they seem to define elevation more than the spaces between boulders? Some additional surveying may be needed. The designer and administrator should communicate and verify design assumptions on the ground and during the contract as necessary to reduce potential questions such as these, and to prevent inappropriate "last minute" changes during construction. This is especially important when the decision affects the new structure elevation, orientation or gradient. Confusion may arise during construction surveys over contract drawings, survey points, elevations and design assumptions.

Designing for Target Species

When designing fish passage facilities, species of fish present, life stages to be impacted, and the migration timing of affected species/life stages should be considered. For example, in looking at non-anadromous trout in Virginia, researchers determined that culverts can be the best way to cross trout streams in Virginia, provided certain actions are taken. [N]

  • The culvert should be on the same slope as the streambed.
  • The slope of the stream should be less than 3 percent.
  • The flow velocity should not exceed 1.2 meters (4 feet) per second under normal flow conditions.
  • The culvert barrel should be properly countersunk at the outlet.
  • In addition, newly installed culverts should not use baffles to control stream flow, and concrete aprons should not be used at culvert outlets.
  • If these actions are not possible or feasible, then bridges should be constructed.

While in this case design is simplified by focus on one species, passage design for multiple species is normally based on the weakest species or life stage present that requires upstream access and should accommodate the weakest individual within that group. For fish, swimming ability is highly variable among species. While information exists on the swimming ability of stronger, migratory fish species, very little is known about the remaining. Even less is known about the swimming abilities of non-fish species that inhabit rivers and streams, [N] including aquatic salamanders, softshell and musk turtles, aquatic reptiles that rarely travel over land and are not strong swimmers (relative to migratory fish), though movement and population continuity is essential to the survival of their populations. [N] As a group the most vulnerable animal species in the U.S. are freshwater mussels. Over 70 percent of the 297 species native to the U.S. and Canada are endangered, threatened or of special concern. [N] Although adult mussels have a very limited capacity for movement, dispersal typically occurs when larvae (glochidia) attached themselves to host fish or salamanders. Therefore, survival and persistence of freshwater mussel populations is dependent on the capacity of host fish usually small, sedentary, and weak swimming, and therefore, highly vulnerable to movement barriers. [N] Many weak swimmers and crawling species take advantage of boundary zones along bank edges and the stream bottom where water velocities are much lower than in the water column. In addition to aquatic organisms, rivers and streams are used as travel corridors by riparian wildlife. To address these issues,

  • Maintenance of unfragmented stream bottom and bank edge habitats is the best strategy for maintaining continuous and interconnected populations for these species. [N]

Avoiding Channel Constriction

Channel constriction is often evident from undersized culverts. Channel constriction results in increased water velocity within and exiting the structure, creating a barrier to upstream fish passage. Where the streambed is not composed of bedrock or properly aproned with riprap, streambed elevation can be reduced. Sometimes this reduction is in the form of a pool and does not alter the ability of fish to enter the culvert. More commonly the culvert outlet becomes "perched" above the lowered streambed, creating a barrier to the upstream migration of smaller, less aggressive swimming fish. The effects of increased water velocity due to channel constriction can also be compounded as a result of excessively high culvert gradient and/or flow augmentation via ditch lines with improper road drainage. To avoid channel constriction, the following stewardship practices are recommended: [N]

  • Design and install road crossing structures that allow bankfull events to flow unimpeded. This requires larger culverts or alternative structures.
  • Where channel gradients exceed 2 percent, design structures for the upstream passage of fish, imitating natural roughness inside culverts.

Energy Dissipation at Culvert Exits

Energy dissipation at box culvert outlets is important for reducing harmful impacts to the receiving channel and for minimizing soil loss through scour and erosion. Dissipaters include riprap, vegetated ditches, concrete or steel baffles, and tiger teeth. Debris racks should be installed only when regular maintenance is possible. Raised culvert inlets are raised by constructing a dike around the culvert, or by installing a culvert elbow. They keep water on the land longer and promote infiltration. These inlets increase vegetation vigor and diversity, reduce flash flooding, create sediment barriers, and raise water tables.

Currently the only options available to roadway designers are riprap basins or rigid concrete structures requiring significant additional costs for concrete and steel and right-of-way. The Nebraska Department of Roads is evaluating three different low-cost energy dissipating methods for concrete box culverts: a sill wall placed in the downstream apron of the box culvert, a vertical drop structure with stilling pool or sill, and the feasibility of using concrete forms to increase the hydraulic roughness of the interior walls and floor of a concrete box. Research results will be due in early 2005. [N]

Other Hydraulic Considerations

Primary hydraulic considerations include the upper and lower flow limit. In general:

  • Acceptable hydraulic design of culverts includes selection of appropriate design flow from which the flow characteristics can be derived by hydraulic analysis. The low flow depth design should be based on the 2-year, 7-consecutive-day low flow discharge or the 95 percent exceedance flow for the migration period of the fish species of concern.
  • The high flow design discharge should be the flow that is not exceeded more than 10 percent (Q 10 percent) of the time during the months of adult migration.

Besides the upper and lower flow limit, other hydraulic effects need to be considered, particularly when installing a culvert:

  • Water surface elevations in the stream reach must exhibit gradual flow transitions, both upstream and downstream. Abrupt changes in water surface and velocities must be avoided, with no hydraulic jumps, turbulence, or drawdown at the entrance. A continuous low flow channel must be maintained throughout the entire stream reach.
  • In addition, especially in retrofits, hydraulic controls may be necessary to provide resting pools, concentrate low flows, prevent erosion of stream bed or banks, and allow passage of bedload material.
  • Culverts and other structures should be aligned with the stream, with no abrupt changes in flow direction upstream or downstream of the crossing. This can often be accommodated by changes in road alignment or slight elongation of the culvert. Where elongation would be excessive, this must be weighed against better crossing alignment and/or modified transition sections upstream and downstream of the crossing. In crossings that are unusually long compared to streambed width, natural sinuosity of the stream will be lost and sediment transport problems may occur even if the slopes remain constant. Such problems should be anticipated and mitigated in the project design.

Fish passage should be designed to be adequate for high and low discharge. When that cannot be accommodated, mitigation may be required.

Mitigating Fish Passage Effects through Culvert Design Modifications

Common DOT methods of assisting fish passage through culverts include lowering of culvert inlets, over-sizing and sinking a portion of the culvert to mimic streambeds. [N] The Alberta Department of Transportation has identified the following methods, in order of preference: [N]

  • Modify culvert design
  • Depress invert culverts
  • Replicate natural streams
  • Use baffled culverts

There are several alternatives for modifying a standard culvert design to satisfy fish passage requirements. Design options may vary as long as fish passage criteria can be met. Any culvert design should be thoroughly reviewed by a professional engineer to ensure that both fish passage and flood conveyance criteria are satisfied.

The following is a representative list of possible modification options. [N]

  • Culvert size. Culvert size may be increased to decrease water velocity.
  • Culvert shape. A different culvert shape (e.g., ellipse, culvert arch, or box culvert) may be chosen to achieve fish passage requirements.
  • Invert level. The invert level at an inlet or outlet is very important for managing flow effects at contractions (inlets), expansions (outlets), and flow regime in a culvert barrel. Invert levels affect habitat upstream and downstream of culverts. Lowering the invert may be necessary to allow the placement of natural substrate on the culvert bottom. Care should be taken to ensure a stable channel upstream and downstream of the culvert because erosion due to increased flow velocities can progress in both directions and create barriers to fish passage.
  • Roughness. Changes in culvert roughness may effectively decrease water velocities to acceptable levels. For example, corrugated circular culverts can be chosen with large, helical corrugations to provide greater overall roughness and provide for a larger low flow water depth suitable for fish. Concrete box culverts can be modified by using oversized aggregate or grouted riprap. The addition of energy dissipaters can control the hydraulic regime and thereby reduce velocities.
  • Grade Control. Artificial resting areas upstream or downstream of a culvert can mitigate many adverse conditions in the culvert barrel and at the inlet or outlet. Weirs or sills downstream of a culvert can be used to maintain adequate water depth and prevent scouring of a plunge pool. An upstream resting pool can trap sediment while allowing recuperation time for 7-10 migrants. Combined with proper instream cover, culverts may provide migrants some protection against predators.

Measures for Non-Embedded Culverts

Fish passage through existing non-embedded culverts may be improved through the use of gradient control weirs upstream or downstream of the culvert, interior baffles or weirs, or in some cases, fish ladders. While these measures are not a substituted for good fish passage design for new or replacement culverts, the following guidelines can be adapted for target species and local conditions: [N]

  • Hydraulic Controls - Hydraulic controls in the channel upstream and/or downstream of a culvert can be used to provide a continuous low flow path through culvert and stream reach. They can be used to facilitate fish passage by establishing the following desirable conditions: Control depth and water velocity within culvert, concentrate low flows, provide resting pools upstream and downstream of culvert and prevent erosion of bed and banks.
  • Baffles - Baffles may provide incremental fish passage improvement in culverts with excess hydraulic capacity that can not be made passable by other means. Baffles may increase clogging and debris accumulation within the culvert and require special design considerations specific to the baffle type. Culverts that are too long or too high in gradient require resting pools, or other forms of velocity refuge spaced at increments along the culvert length.
  • Fishways - Fishways are generally not recommended, but may be useful for some situations where excessive drops occur at the culvert outlet. Fishways require specialized site-specific design for each installation and resource agency specialists should be consulted.
  • Multiple Culverts - Retrofitting multiple barrel culverts with baffles in one of the barrels may be sufficient as long as low flow channel continuity is maintained and the culvert is reachable by fish at low stream flow. Additional culverts may be used to improve conveyance conditions for fish passage. For example, box culverts can be separated into multiple sections where part of the flow enters a plain section, and part of the flow is carried through a baffled section. Multiple culverts can also be "stacked" by placing the inverts at different elevations to provide sufficient fish passage conditions at different stream stages. However, the effectiveness of these types of solutions is questionable, because fish need to choose which section or culvert to enter. Fish have been observed choosing the culvert with the most flow and highest velocity; consequently, one large culvert may be preferable to two or more smaller ones. In general, it is better for fish passage to use fewer culverts. [N]

Other General Recommendations

  • Trash racks and livestock fences should not be used near the culvert inlet. Accumulated debris may lead to severely restricted fish passage, and potential injuries to fish. Where fencing cannot be avoided, it should be removed during upstream migration periods. Otherwise, a minimum of 9 inches clear spacing should be provided between pickets, up to the high flow water surface. Timely clearing of debris is also important, even if flow is getting around the fencing. [N]
  • Cattle fences that rise with increasing flow are highly recommended. [N]
  • Natural or artificial supplemental lighting should be provided in new and replacement culverts that are over 150 feet in length. Where supplemental lighting is required the spacing between light sources shall not exceed 75 feet. [N]
  • Comply with in-stream work windows in each watershed. Work in the active stream channel should be avoided during the times of year target species are present. Temporary crossings, placed in streams for water diversion during construction activities, should meet environmental stewardship guidelines or BMPs.


3.5.5 Design Methods for New and Replacement Culverts
< back to top >

High water velocity, shallow water depth within the culvert, excessive vertical drop at the culvert outlet and debris blockages are the most frequent causes of fish passage problems at culverts. These design methods can help prevent some of these problems: [N]

Active Channel Design Method

The Active Channel Design method is a simplified design that is intended to size a culvert sufficiently large and embedded deep enough into the channel to allow the natural movement of bedload and formation of a stable bed inside the culvert. Determination of the high and low fish passage design flows, water velocity, and water depth is not required for this method since the stream hydraulic characteristics within the culvert are intended to mimic the stream conditions upstream and downstream of the crossing. This design method is usually not suitable for stream channels that are greater than 3 percent in natural slope or for culvert lengths greater than 100 ft.

Structures for this design method are typical round, oval, or squashed pipes made of metal or reinforced concrete.

  • Culvert Width - The minimum culvert width should be equal to, or greater than, 1.5 times the active channel width.
  • Culvert Slope - The culvert should be placed level (0 percent slope).
  • Embedment - The bottom of the culvert should be buried into the streambed not less than 20 percent of the culvert height at the outlet and not more than 40 percent of the culvert height at the inlet.

Stream Simulation Design Method

The Stream Simulation Design method is a design process that is intended to mimic the natural stream processes within a culvert. Fish passage, sediment transport, flood and debris conveyance within the culvert are intended to function as they would in a natural channel. Determination of the high and low fish passage design flows, water velocity, and water depth is not required for this option since the stream hydraulic characteristics within the culvert are designed to mimic the stream conditions upstream and downstream of the crossing.

This approach to culvert design both avoids flow constriction during normal conditions and creates a stream channel within culverts that resists scouring during flood events. [N] Since the streambed longitudinal profile and cross section in the pipe are similar to the natural channel, water velocities and depths at flows up to bankfull are also similar, and the crossing should be essentially invisible to migrating aquatic organisms.

Culverts designed for stream simulation are sized wide enough to include either channel margins or banks. The most basic stream simulation culvert is a bottomless culvert placed over a natural streambed. Other culverts are filled with a sediment mix that emulates the natural channel and adjusts similarly during most flows. In steep channels, the bed may be designed to resist erosion during very large floods. [N] These culverts contain a streambed mixture that is similar to the adjacent stream channel.

Stream simulation culverts require a greater level of information on hydrology and geomorphology (topography of the stream channel) and a higher level of engineering expertise than the Active Channel Design method.

  • Culvert Width - The minimum culvert width should be equal to, or greater than, the bankfull channel width. The minimum culvert width shall not be less than 6 feet.
  • Culvert Slope - The culvert slope shall approximate the slope of the stream through the reach in which it is being placed. The maximum slope shall not exceed 6 percent.
  • Embedment - The bottom of the culvert should be buried into the streambed not less than 30 percent and not more than 50 percent of the culvert height. For bottomless culverts the footings or foundation should be designed for the largest anticipated scour depth.

Certain channel features cannot be duplicated directly or can be simulated only partially in a culvert. Examples include channel-spanning wood, embedded wood, bank vegetation, cohesive bank stability, debris jams and rigid bed forms. Bank vegetation stabilizes most natural streambanks. Large wood that spans the channel provides roughness and complexity, as do bedrock exposures and other rigid bedforms. Debris embedded in the natural channel may anchor bed material and in some cases control all of the elevation change. Bank vegetation cannot grow inside a pipe; trees will not fall into them; and large, woody debris is difficult and risky to install. While vegetation and large wood are often critical to channel stability, it is usually possible to replace these functions with large rock to create a stable streambed inside a pipe. [N]

It is essential to understand what stream functions are critical at a site, as well as the consequences to the stream of placing a culvert and interrupting them to some degree. Riparian functions such as overbank flooding, side channel construction, and nutrient and debris exchange between stream and floodplain are not simulated within the culvert. The impact of floodplain contraction on up- and downstream floodplains may be reduced with a larger culvert, additional culverts in the floodplain, and/or overflow dips in the road. At any given flow, slope is an important factor affecting water velocity in culverts. Culvert size also affects velocities, especially when a structure is considerably undersized and a head (pooling above culvert) is developed. [N]

  • If any of these functions cannot be adequately simulated by the design, other road alignments and/or crossing structures should be considered.
  • Gradients (slope) for non-embedded, non-baffled culverts should not exceed 0.5 percent unless a tailwater situation exists to backwater the culvert to a suitable depth for its length. Properly baffled or weired culverts are appropriate for steeper gradients depending on design. Structures with fishways (i.e., fish ladders or culverts with weir-type baffles) generally will be required where culvert gradients exceed 5 percent and streambed simulation is not employed.
  • Corrugated metal culverts should generally be used over smooth-surfaced culverts. Deep corrugations are preferred over shallow corrugations.
  • Bottomless arches and all styles of embedded culverts should be placed at or near the same gradient as the natural streambed and should be at least as wide as the active stream channel (i.e., no lateral encroachment on the active stream channel). All embedded culverts (round or arch) must be embedded one foot deep or at least 20 percent of its height, whichever is more.
  • When deciding between bottomless arch and embedded culvert designs, the primary consideration is foundation substrate. If considerable bedrock is present, an open bottom arch is generally the appropriate choice; embedding a culvert would require extensive excavation. Where deep unconsolidated gravel and cobble is present, failure (undermining) of a bottomless arch foundation is a major concern.
  • Hydraulic controls may be required to 1) improve culvert entrance and exit conditions (e.g. using a beveled inlet configuration; providing resting pools at culvert entrance and exit), 2) concentrate low flows, 3) prevent erosion of stream bed and banks, or 4) allow passage of bedload material. The need for, and design of, these project features should be developed in consultation with the resource agency.
  • If water-crossing structures are placed in spawning areas, they should incorporate mitigation measures, as necessary, to achieve no-net-loss of spawning area.
  • Trash racks are discouraged at culvert inlets, but if necessary, these should be installed only above the high passage flow water level.

Hydraulic Design Method

The Hydraulic Design method is a design process that matches the hydraulic performance of a culvert with the swimming abilities of a target species and age class of fish. This method targets distinct species of fish and therefore does not account for ecosystem requirements of non-target species. There are significant errors associated with estimation of hydrology and fish swimming speeds that are resolved by making conservative assumptions in the design process. Determination of high and low fish passage design flows, water velocity, and water depth are required for this option.

The Hydraulic Design method requires hydrologic data analysis, open channel flow hydraulic calculations, and information on the swimming ability and behavior of the target group of fish. This design method can be applied to the design of new and replacement culverts and can be used to evaluate the effectiveness of retrofits of existing culverts.

  • Culvert Width- The minimum culvert width should be 3 feet.
  • Culvert Slope- The culvert slope shall not exceed the slope of the stream through the reach in which it is being placed. If embedment of the culvert is not possible, the maximum slope shall not exceed 0.5 percent.
  • Embedment - Where physically possible, the bottom of the culvert should be buried into the streambed a minimum of 20 percent of the height of the culvert below the elevation of the tailwater control point downstream of the culvert. The minimum embedment should be at least 1 foot. Where physical conditions preclude embedment, the hydraulic drop at the outlet of a culvert shall not exceed the limits specified above.
  • High Fish Passage Design Flow - The high design flow for adult fish passage is used to determine the maximum water velocity within the culvert.
  • Low Fish Passage Design Flow - The low design flow for fish passage is used to determine the minimum depth of water within a culvert.
  • Maximum Hydraulic Drop - Hydraulic drops between the water surface in the culvert and the water surface in the adjacent channel should be avoided for all cases. This includes the culvert inlet and outlet. Where a hydraulic drop is unavoidable, its magnitude should be evaluated for both high design flow and low design flow and shall not exceed 1 foot for adults or 6 inches for juveniles. If a hydraulic drop occurs at the culvert outlet, a jump pool of at least 2 feet in depth should be provided.

Structural Design and Flood Capacity

All culvert stream crossings, regardless of the design option used, should be designed to withstand the 100-year peak flood flow without structural damage to the crossing. The analysis of the structural integrity of the crossing should take into consideration the debris loading likely to be encountered during flooding. Stream crossings or culverts located in areas where there is significant risk of inlet plugging by flood borne debris should be designed to pass the 100-year peak flood without exceeding the top of the culvert inlet (Headwater-to-Diameter Ratio less than one). This is to ensure a low risk of channel degradation, stream diversion, and failure over the life span of the crossing. Hydraulic capacity must be compensated for expected deposition in the culvert bottom.


3.5.6 Culvert Evaluation for Fish Passage and Ranking for Remediation Efforts
< back to top >

Various methods for fish habitat and passage evaluation have been developed. The following sample ranking method assigns scores or values for the following five parameters: [N]

  1. Species Diversity - Number of target species currently present ( or historically present which could be restored ) within the stream reach at each crossing location. Score - For each federally or state listed salmonid species; Endangered = 4 points; Threatened or Candidate = 2 points; not listed = 1 point. Consult state resource agency or NOAA for historic species distribution and listing status information.
  2. Extent of Barrier - Over the range of estimated migration flows, assign one of the following values from the "percent passable" results generated with FishXing . GREEN crossings are considered 100 percent passable for all fish, while RED crossings are considered 0 percent passable for all fish. Do this for adult anadromous, resident, and target species for each culvert. Score - 0 = 80 percent or greater passable; 1 = 79-60 percent passable; 2 = 59-40 percent passable; 3 = 39-20 percent passable; 4 = 19 percent or less passable; 5 = 0 percent passable ( RED ) . For a total score, sum the values for all three.
  3. Habitat Value - Multiply habitat quantity score by habitat quality score. Habitat Quantity - Above each crossing, length in feet to a sustained 8 percent gradient or field identified limit of anadromy. Score: 0.5 points for each 500 feet of stream ( example: 0.5 points for <500 Ν ; 1 point for 1,000 Ν ; 2 points for 2,000 Ν ; and 5.5 points for 5,500 Ν ) . The maximum possible score for Habitat Quantity is 10.
  4. Habitat Quality - For each stream, assign a score of quality after reviewing available habitat information. Consultation with local state resource agency biologists to assist in assigning habitat quality score is recommended. Score: 1.0 = Excellent - Relatively undeveloped, with pristine watershed conditions. Habitat features include dense riparian zones with mix of mature native species, frequent pools, high-quality spawning areas, cool summer water temperatures, complex instream habitat, floodplain relatively intact. 0.75 = Good - Habitat is mostly intact but erosional processes or other factors have altered the watershed with a likelihood of continued occurrence. Habitat includes dense riparian zones of native species, frequent pools, spawning gravels, cool summer water temperatures, complex instream habitat, floodplain relatively intact. 0.5 = Fair - Erosional processes or other factors have altered the watershed with negative affects on watershed processes and features, with the likelihood of continued occurrence. Indicators include: a) riparian zone lacking mature conifers, b) infrequent pools, c) sedimentation evident in spawning areas (embeddedness ratings of 3), d) summer water temperatures periodically exceed stressful levels for target species, e) sparse instream complex habitat, and floodplain intact or slightly modified. 0.25 = Poor - Erosional processes or other factors have significantly altered the watershed. There is a high likelihood of increased erosion and apparent effects to watershed processes. Habitat impacts include riparian zones absent or severely degraded, little or no pool habitat, excessive sedimentation evident in spawning areas (embeddedness ratings of 4), stressful to lethal summer water temperatures common, lack of instream habitat, floodplain severely modified with levees, riprap, and/or residential or commercial development.
  5. Sizing ( risk of failure ) - For each crossing, assign one of the following values as related to flow capacity. Score: 0 = sized for at least a 100-year flow, low risk; 1 = sized for at least a 50-year flow, low/moderate risk; 2 = sized for at least a 25-year flow, moderate risk of failure; 3 = sized for at least a 10-year flow, moderate/high risk of failure; 4 = sized for less than a 10-year flow, high risk of failure; 5 = sized for less than a 5-year flow, extreme risk of failure.
  6. Current Condition - For each crossing, assign one of the following values. Score: 0 = good condition; 1 = fair, showing signs of wear; 3 = poor, floor rusting through, crushed by roadbase, etc.; 4 = extremely poor, floor rotted-out, severely crushed, damaged inlets, collapsing wingwalls, slumping roadbase, etc.

For each stream crossing, enter criteria values into a spreadsheet, sum the ranking criteria values, and compute the total scores. Then sort the list of crossings by total scores to determine a first-cut ranking for the project area. The results of the ranking matrix provide a rough, first-cut evaluation. There are other important factors that should be considered when deciding the exact scheduling of remediation efforts. The following list provides guidance that should assist in rearranging the first-cut ranking. On a site-specific basis, some or all of these factors should be considered:

  • Presence or absence of other stream crossings - In many cases, a single stream may be crossed by multiple roads. If migration barriers exist at multiple stream crossings, a coordinated effort is required to identify and treat them in a logical manner, generally in an upstream direction starting with the lowest crossing in the stream.
  • Fish observations at crossings - Sites where fish are observed holding during migration periods should receive high consideration for remediation. Identify the species present, count the number of fish, and record failed versus successful passage attempts. Consider the potential for predation and/or poaching. Sites with holding fish are areas where immediate recolonization of upstream habitat is likely to occur.
  • Amount of road fill - At stream crossings that are undersized and/or in poor condition, consider the volume of fill material within the road prism. This is material which is directly deliverable to the stream channel if the crossing were to fail. Also determine if there is a potential for water to divert down the road if the crossings capacity is overwhelmed.
  • Remediation project cost - The range of treatment options and associated costs must be examined when determining the order in which to proceed. In cases where federal or state listed fish species are present, costs must be weighed against the consequences of not providing unimpeded passage.
  • Opportunity - Road managers should consider upgrading all migration barriers during road maintenance activities. The ongoing costs of maintaining an undersized or improperly installed culvert may exceed the cost of replacing it with a properly sized and installed crossing. When undersized or older crossings fail during storms, road managers should be prepared to install properly-sized crossings that provide unimpeded passage for all species and life stages of fish.


3.5.7 DOT Practice and Design Guidance for Culvert Installation, Design, and Prioritization for Fish Passage
< back to top >

The following state agency links contain installation guidance and stewardship practices for the listed culvert and stream crossing measures. Practices cover the designs, construction and maintenance of both temporary and permanent stream crossings, including culverts:

Research is increasing in the area. For example, WSDOT published research in 2006 comparing baffle and no-baffle culvert designs and cubic flow per second (cfs). WSDOT found that for the configuration without baffles, salmonids were able pass successfully about 40 percent of the time at 1.5 cfs, about 70 percent of the time at 3 cfs, and less than 10 percent at 12 cfs. [N]

Several DOTs have developed programmatic approaches to Fish Passage improvements, as detailed below.

Alaska Programmatic Agreement for Fish Passage Improvements

The Alaska Department of Transportation and Public Facilities (ADOT and PF)and the Alaska Department of Fish & Game(ADF&G) developed a Memorandum of Agreement (MOA), signed in August 2001, to improve fish passage through culverts and to streamline the review process for the increasing number of fish habitat permits processed annually for culvert work. The MOA is the result of more than 15 years of fish passage research by state agencies and the University of Alaska Fairbanks, in addition to extensive discussions with fish and wildlife and transportation counterparts in Washington and Oregon State, the Federal Forest Service, and the National Marine Fisheries Service (now NOAA Fisheries). Prior to development of the MOA, permitting decisions were often ad hoc, resulting in inconsistencies, unpredictability, and unnecessary tension and conflict in the permitting process. Now, the MOA provides a consistent, state-wide basis for evaluating and approving culvert structures.

Alaska's Memorandum of Agreement (MOA) applies to both new culvert installation and reinstallation of culverts during maintenance activities, where the ADF&G and/or the ADOT&PF have determined that culverts are the appropriate structure. Key to the agreement is a tiered approach to the culvert design. The level of information necessary for the permit depends on the "Tier." Opting for Tier 1 requires simulation of a natural stream, but requires minimal interagency design review and permitting paperwork and leads to faster approvals. Under the MOA, ADOT&PF's senior Regional Hydraulic Engineer reviews all proposed fish passage structures, including those proposed by Maintenance and Operations, for compliance with the design criteria contained in the MOA. ADF&G provides relevant information early in the design process, and if additional information from ADOT&PF is needed, requests such in a timely manner and in a consolidated form. The MOA also provides ADF&G reasonable opportunity to inspect culverts in the field and to review "as-built" plans prior to project shutdown, demobilization, or release of the contractor(s), in order to ensure that all culverts are installed in accordance with permit terms and conditions.

ADF&G and Alaska Department of Transportation and Public Facilities ADOT&PF believe the agreement is leading to more timely approval of permit applications for culvert installations, as well as improved passage for anadromous and resident fish populations through drainage structures, when migrating to spawning, rearing and over-wintering grounds. As their agreement represents current knowledge and state of the practice, ADF&G and ADOT&PF will meet annually to review the MOA and to amend it appropriately to accommodate new information and proven fish passage techniques.

Maine DOT's Fish Passage Policy and Design Guide

In early 2002, the Maine Department of Transportation issued guidance establishing a policy, process, and design guide for fish passage at Maine DOT projects with water-crossing structures such as bridges, struts, culverts, pipes, or pipe arches. In the past, case-by-case evaluation of crossings and the associated regulatory approvals added unpredictability to project timelines and budgets. The new guidance establishes consistent expectations and procedures, facilitating planning and budget estimation. A second edition of Maine's Fish Passage Policy and Design Guide (July, 2004) is now available on-line.

To reach agreement on how best to achieve interagency goals, representatives from Maine DOT and resource agencies met over several months to discuss the issues involved with fish passage and establish a protocol considering the need for passage and the feasibility of improvement, given site conditions and other potentially limiting factors. The team developed guidance that provide a framework and tools to evaluate crossing projects by balancing a variety of needs at a site (including regulatory requirements and resource needs) while delivering safe, cost effective, and timely projects.

When examining whether fish passage and associated habitat issues are compatible with new stream crossing structures or improvements to existing structures, Maine DOT considers the following goals:

  • Maintain or replicate natural stream channel or flow conditions, as appropriate.
  • Pass peak flows in accordance with Maine DOT drainage policy.
  • Comply with existing regulations on passing fish.
  • Consider potential impacts to rights-of-way, utilities and traffic.
  • Meet appropriate standards and safety requirements.
  • Provide reasonable life cycle costs.
  • Consider the least environmentally damaging solutions.

In addition to including a clear protocol for the nature and timing of agency coordination, the new guidance facilitates Maine DOT use of new and developing technologies. Currently Maine DOT addresses deficient culverts by rehabilitating a culvert through insertion of a smaller diameter pipe inside the existing culvert, placing a concrete lining at the inverts or throughout the entire length, or by replacing the culvert. This rehabilitation allows a culvert to be repaired in place, usually with less streambed disturbance and lower project cost than replacement would entail.

Oregon DOT Culvert Retrofit and Replacement Program Agreement

In 2001, the Oregon Department of Transportation (ODOT) and the state Department of Fish and Wildlife (ODFW) signed a Memorandum of Understanding (MOU) acknowledging that repairing or modifying ODOT-maintained culverts is a priority for the agencies that will take decades to resolve. The Oregon Department of Fish and Wildlife completed culvert inventories for the entire state of Oregon in 1999 and found that 96 percent of the barriers identified were culverts associated with road crossings. The project also identified high priority culverts for fish passage remediation.

ODOT has an ongoing program of culvert installation and maintenance, with the goal of making all ODOT culverts passable to fish. After research monitoring results demonstrated the effectiveness of baffle and weir designs in culverts, ODOT modified their culvert replacement programs to use these designs, significantly reducing the cost of improving fish passage at ODOT culverts. The designs improve fish passage by slowing water velocity and raising stream elevations to reduce entry jump heights or backwater culvert outlets. Use of retrofit designs are allowing culverts that are otherwise in good physical condition to be retrofitted until their service integrity is compromised, at which time they will be replaced with designs that more fully meet fish passage criteria and standards. Use of retrofits will thus allow many more culverts to be remediated each year, increasing the scope and pace of ODOT's contribution to salmon recovery in Oregon. The baffle and weir retrofits also provide ODOT an alternative to fish ladders, which have become increasingly problematic for ODOT from a maintenance standpoint.

According to the MOU, ODOT will continue internal education regarding the needs and requirement of fish passage, and prioritize its resources and culvert modification needs on an annual basis, demonstrating good faith in addressing culvert passage problems. On replacement culvert projects, ODOT will strive to simulate a natural stream and will determine if changes in culverts result in flows detrimental to fish passage. ODFW is supporting ODOT's efforts by providing the master inventory of culverts that do not provide adequate passage, along with technical assistance on educational activities, design, and construction techniques.

WSDOT Fish Passage Improvements on a System and Project-by-Project Basis

WSDOT is trying to tailor transportation investments in restoration and mitigation to mesh with state and community watershed restoration and enhancement goals. To that end, WSDOT has been pursuing watershed characterization research to better understand how watersheds store water naturally (e.g., wetlands, riparian areas, floodplains) and then identify where land use has resulted in the loss of natural storage capacity. So far, the agency has found that investments in watersheds with lower areas of impervious surface may yield greater marginal benefits than mitigation sited close to impact areas. Hence, WSDOT has directed mitigation investments to restoring natural, self-maintaining systems that provide many other valuable watershed functions such as groundwater recharge, water quality treatment and fish and wildlife habitat, along with aesthetic, recreational, and educational values to residents.

WSDOT's watershed approach aims to direct transportation mitigation and conservation dollars toward high priority watershed needs, including recovery of native fish species. Access to good quality habitat is a key factor in the recovery of listed salmon stocks and culverts can create fish passage barriers that fragment habitat. Common problems with older culverts include high water velocity, inadequate water depth, and large culvert outfall drops. Once these problems are corrected, the benefits to fish habitat are real and immediate; in many cases, fish have been observed upstream of improved culverts within weeks of restoring access.

WSDOT's environmental procedures manual describes their environmental retrofit program for construction and maintenance as retrofitting state highway facilities as appropriate to reduce existing environmental impacts. [N] This commitment extends beyond the agency's work in performing appropriate avoidance, minimization, and environmental mitigation as a part of all other highway system projects. The Washington State Highway System Plan update sets a 20-year goal for correction of all state highway culvert barriers. Expenditures for barrier removal in the current biennium are approximately $7 million, and estimates show that this spending level would have to double to complete correction of all culvert barriers on the highway system in 20 years. Consequently WSDOT has developed and funded a research strategy to improve understanding of how road crossings can become barriers to fish and the best approaches to correcting barriers, enabling retrofit projects to be prioritized so that those culvert barriers that promise to yield the greatest habitat benefits are corrected first.

The WSDOT fish passage barrier retrofit program is inventorying highways to locate impassable culverts, rating the potential habitat to be gained from fixing them, and prioritizing the fixes. WSDOT and the Washington Department of Fish and Wildlife jointly manage a statewide database for this inventory with over 900 identified culvert barriers, many of which have been added under more stringent criteria adopted in the past few years. Culverts associated with 2,000 of the 7,000 miles in the state highway system have been inventoried. Since 1991, 27 barriers have been corrected in the course of highway projects, and another 42 barriers have been corrected through the special retrofit program. WSDOT maintenance personnel also correct or at least improve some fish barriers during routine culvert maintenance.

WSDOT's Environmental Retrofit Program also includes:

  • Noise Barriers - Adding noise mitigation along state highways where neighborhoods are exposed to unacceptable noise levels as defined by federal statute.
  • Stormwater Discharge - Constructing new stormwater treatment facilities to treat runoff from existing untreated pavements.

MDSHA Incorporates Stream Morphology Concepts in Culvert Design

In 1992, the Maryland State Highway Administration (SHA) initiated new design procedures to limit the impact of constructing culverts and bridges in streams. Elements of the new procedures included studies to define the characteristics of Maryland streams regarding bankfull widths, depths, and discharges; training of engineers in basic and advanced courses in stream morphology; and updating the MDSHA culvert design manual to address consideration of stream morphology, fish passage, and other environmental features. The revised design procedure emphasized the need to identify all appropriate objectives at the start of the design process so the best overall solution can be determined. The design concept is to construct a stream system that is stable and that neither scours nor aggrades. Elements of this approach include maintaining the consistency of dimension, pattern, and profile of the stream with particular attention given to maintaining bankfull width and width/depth ratio. Initial efforts to construct culverts using stream restoration methodologies and to relieve the hydraulic load on the main channel culvert in some cases to limit downstream scour and erosion were quite successful; MDSHA concluded that it was practical to consider stream morphology concepts in culvert design. [N]

Alberta Transportation Practices and Measures for Protection of Fish & Aquatic Ecosystems

Practices and measures for fisheries and aquatic ecosystems have been established in Canada, and include the following:

  • Crossings of a waterbody that provide fish habitat at any time of the year should be designed, constructed, operated and maintained such that no new barriers to fish passage, including physical, chemical or flow impediments (including maintaining minimum flows and depths), are created so that fish can pass and the ability for fish to pass is not reduced over time, unless authorized by the appropriate resource agency.
  • If highway construction must proceed during a period when fish are moving between different areas of their habitat, their safe passage shall not be restricted for an unreasonable amount of time. The relevant period should be determined by a qualified fisheries biologist, for the target species/community, in consultation with the appropriate resource agency.
  • Fish screens, guards, netting or other barriers should be installed and maintained across any water intake withdrawing water from any waterbody that contains fish (e.g. for the purposes of water-taking, dewatering, bypass pumping, etc.) or across the entrance to any channel constructed for the purposes of conducting water temporarily from any waterbody that contains fish so as to prevent fish access until the water intake or diversion has been decommissioned.
  • Any area of a waterbody containing fish that is temporarily isolated by guards, screens or other barriers should be inspected for the presence of fish, and all fish should be captured using appropriate means and released unharmed in adjacent fish habitat beyond the barriers. This fish transfer should be conducted under the direction of a qualified fisheries biologist, with the appropriate permit.
  • Fish shall not be harmed in any manner unless authorized by the appropriate resource agency. Fish species, or parts or derivatives of fish species listed as extirpated, endangered or threatened shall not be killed, harmed, harassed, captured, taken, possessed, collected, bought, sold or traded except under a valid Permit.
  • No harmful alteration, disruption or destruction of fish habitat is permitted unless authorized the appropriate resource agency. Destruction of any part of the critical habitat of any listed endangered or threatened aquatic species, or an extirpated species where a recovery strategy recommends reintroduction of that species to the wild, is not permitted.
  • Where a harmful alteration, disruption or destruction of fish habitat is authorized by the appropriate resource agency. Appropriate compensation should be developed by a qualified fisheries biologist, to ensure no net loss of the productive capacity of the habitat occurs.
  • Where the use of explosives is required during construction in the vicinity of a waterbody that contains fish, they should be used in such a manner as to ensure no harmful effects to fish occur.
  • No substance of any type that is deleterious should be deposited in water frequented by fish, or be released or placed such that the deleterious substance could enter the water.
  • Plans and specifications for highway construction that may affect fish habitat should be provided to Ministry of Natural Resources and Fisheries and Oceans Canada, and modified as required.
  • Where a substance is released and/or deposited into water such that fish and/or their habitat could be harmed, it should be reported to the appropriate agencies (Ministry of Natural Resources, Fisheries and Oceans Canada, Ministry of the Environment).
  • Where a substance is released and/or deposited into water such that fish and/or their habitat are harmed or likely to be harmed, all reasonable measures to remedy the situation should be undertaken as soon as possible.


3.5.8 Resource Agency and Other Design Guidance for Fish Passage
< back to top >

A number of agencies have guidance for design of culverts for fish passage, including:

  • Improving Stream Crossings for Fish Passage: Final Report (2004 NOAA Fisheries) Final report of a multiyear research project investigating passage conditions for anadromous salmonids at numerous steam crossings within Northwestern California. The project evaluated the effectiveness of current fish passage guidelines. A main focus of the study was relating observed migration of adult and juvenile salmonids fish passage to existing and proposed design flows. The study also evaluated the leaping success of different size classes of fish at various culvert outlets and examined hydraulic conditions within various culvert types.
  • California Salmonid Stream Habitat Restoration Manual , (2003) Commonly called "The Green Book" this California Division of Fish and Game manual details many aspects of stream restoration and watershed monitoring and is the de facto standard (in California) for in-channel and in-stream structures for fisheries habitat improvement. The 3rd Edition contains a new section: "Part IX Fish Passage Evaluation at Stream Crossings," added to the manual in April 2003. The primary authors of this section were Ross N. Taylor and Michael Love. This section addresses fish passage evaluations at stream crossings (roads, bridges, etc.) and Data Collection for evaluations using the FishXing software.
  • Design of Road Crossings for Fish Passage (2003) Comprehensive engineering manual by the Washington State Department of Fish and Wildlife detailing the design of manual permanent, new, retrofit, or replacement road crossing culverts without harmful impact to salmonid migration.
  • Washington State DOT Fish Passage Barrier Removal Program
  • Oregon DOT Water Quality and Habitat Guide, Best Management Practices (July 1999)
  • Fish-stream Crossing Guidebook, British Columbia Ministry of Forests (2002)
    Culvert design manual for culverts, fords and low water bridges. Generally directed toward range and wild land roads.
  • Geomorphologic Impacts of Culvert Replacement and Removal (2003) by the Oregon Department of Fish and Wildlife.
  • DRAFT National Inventory and Assessment Procedure For Identifying Barriers to Aquatic Organisms at Road-Stream Crossings USDA Forest Service, San Dimas Technology and Development Center.
  • Juvenile and Resident Salmonid Movement and Passage Through Culverts (1998) Washington State Transportation Center (TRAC), Univ. of Wash.
  • Stream Characteristics and Hydrology - Design for Fish Passage and Aquatic Organisms (BLM)
  • FishBase is a Searchable relational database with information to cater to different professionals such as research scientists, fisheries managers, zoologists and many more. Available on CD and on the web, it contains over 28,000 fish species, data on habitat range, swim speeds, references, research photos and much more.
  • FishXing software and learning systems for the analysis of fish migration through culverts has added features for hydraulic analysis of culverts and expanded biological references, as of Spring 2004. FishXing gives detailed profiles of hydraulic conditions and fish performance inside a variety of culvert shapes.
  • HydroCulv is an Excel-based macro that performs culvert hydraulic calculations to determine water surface profiles through culverts based on culvert geometry data and boundary conditions. Output includes key results such as freeboard, head loss, inlet and outlet velocities, as well as depth and velocity profile information throughout each culvert. Profile plots are available for each pipe and boundary condition.
  • Flow Pro is a Windows-based program that computes steady-state water surface profiles for many prismatic open channel shapes, including circular, rectangular, trapezoidal, triangular, U-shaped, and tubular. It handles both subcritical and supercritical flow types, and flow through weirs, orifices, and underflow gates. Flow Pro also computes many useful flow and channel properties including critical depth and slope, hydraulic radius and wetted perimeter, normal depth, and channel roughness. It uses Manning's equation and numerical integration, and accepts both English and SI units of measure.
  • CulvertMaster is a Windows-based program intended for use in design and analysis of culverts at road-stream crossings. The program uses FHWA Design of Highway Culverts (HDS-5) methodology to perform inlet control and outlet control computations, including pressurized flow conditions and hydraulic jumps. The software can model hydraulics for most commonly used culvert shapes. It allows the user to input the tailwater elevation or it can generate a tailwater rating curve based on a downstream cross-section. Additionally, the user is able to input road surface elevations to check overtopping conditions. CulvertMaster also contains a hydrology module that allows the user the ability to calculate peak design flows using the Rational Method or SCS Graphical Peak Method. It provides tabular and graphical output and can generate reports. The program accepts both English and SI units of measure.
  • HEC-RAS is produced by the Army Corps of Engineers, Hydrologic Engineering Center. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) is designed to perform one-dimensional hydraulic calculations for a full network of natural and constructed channels. HEC-RAS allows the user to perform one-dimensional steady and unsteady flow calculations within a graphical user interface. The steady flow component of the modeling system is intended for calculating water surface profiles for steady gradually varied flow. The system can handle a full network of channels, a dendritic system, or a single river reach. The steady flow component is capable of modeling subcritical, supercritical, and mixed flow regimes water surface profiles. The unsteady flow component was developed primarily for subcritical flow regime calculations.
  • WinXSPro uses a resistance-equation approach (e.g., Manning's equation) to single cross-section hydraulic analysis, and is capable of analyzing both the geometry and hydraulics of a given channel cross-section. WinXSPRO was specifically developed for use in high-gradient streams and supports three alternative resistance equations for computing boundary roughness and resistance to flow. The program allows the user to subdivide the channel cross-section so that overbank areas, mid-channel islands, and high-water overflow channels may be analyzed separately. The program also allows input of variable water-surface slope so that is may be varied with discharge to reflect natural conditions.
  • PEAKFQ from the U.S. Geological Service is a DOS based program that performs flood-frequency analysis based on the guidelines delineated in Bulletin 17B, published by the Interagency Advisory Committee on Water Data in 1982. The program is interactive and contains the code from the WATSTORE program J407. PEAKFQ uses the method of moments to fit the Pearson Type III distribution to the logarithms of annual flood peaks. The skew that is used may be a user-developed generalized skew for a region, from the Bulletin 17B skew map, computed from the data, or weighted between the generalized skew and station skew computed from the data. Adjustments can be made for high and low outliers and historic information. Qualification codes may be used to censor data from the analysis.
  • CTE Literature Survey on Impacts of Culverts on Anadromous and Non-Anadromous Fish Passage (December 2002)
  • FISHPASS program for culvert installations - Alaska Department of Fish and Game
  • Fish Protection Screens:


3.5.9 Post-Construction Evaluation and Long Term Maintenance and Assessment
< back to top >

Post-construction evaluation is important to assure the intended results are accomplished, and that mistakes are not repeated elsewhere. There are three parts to this evaluation: 1) Verify the culvert is installed in accordance with proper design and construction procedures. 2) Measure hydraulic conditions to assure that the stream meets these guidelines. 3) Perform biological assessment to confirm the hydraulic conditions are resulting in successful passage. Staff and resource agency biologists may assist in developing an evaluation plan to fit site-specific conditions and species. The goal is to generate feedback about which techniques are working well, and which require modification in the future. These evaluations are not intended to cause extensive retrofits of any given project unless the as-built installation does not reasonably conform to the design guidelines, or an obvious fish passage problem continues to exist. [N]

Any physical structure will continue to serve its intended use only if it is properly maintained. Hence the following practices should be employed.

  • Ensure timely inspection and removal of debris for culverts to continue to effectively move water, fish, sediment, and debris.
  • Inspect all culverts should be inspected at least annually to assure proper functioning. Summary reports should be completed annually for each crossing evaluated. An annual report should be compiled for all stream crossings and submitted to the resource agencies. A less frequent reporting schedule may be agreed upon for proven stream crossings. Any stream crossing failures or deficiencies discovered should be reported in the annual cycle and corrected promptly addressed.


< back to top >
Continue to Section 3.6 »
Table of Contents
Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.1 Beyond Mitigation: Projects to Achieve Environmental Goals
3.2 Context Sensitive Design/Solutions
3.3 Avoiding Impacts to Historic Sites
3.4 Designing to Accommodate Wildlife, Habitat Connectivity, and Safe Crossings
3.5 Culverts and Fish Passage
3.6 Stream Restoration and Bioengineering
3.7 Design Guidance for Stormwater and Erosion & Sedimentation Control
3.8 Drainage Ditches, Berms, Dikes, and Swales
3.9 Design for Sustainable, Low Maintenance Roadsides
3.10 Designing to Reduce Snow, Ice, and Chemical Accumulation
3.11 Designing to Minimize Air Quality Problems
3.12 Design and Specification for Recycling
3.13 Designing to Minimize Noise
3.14 Lighting Control/Minimization
3.15 Design for Sustainability and Energy Conservation
3.16 Safety Rest Areas, Traveler Services, and Parking Area Design
Lists: Examples | Tables | Figures
Website Problems Report content errors and/or website problems
PDF Document Download Adobe Acrobat Reader