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Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

CHAPTER 2 Literature Review

This section provides an overview of the most current published guidance documents focused on AOP design, construction, and monitoring practices by state and federal transportation agencies. This literature review serves as background information for the survey results and case examples.

2.1 Federal Agency Guidance Documents

2.1.1 FHWA

Culvert Design for Aquatic Organism Passage (HEC-26) (FHWA 2010) proposes a stream-simulation method that uses streambed sediment behavior as its surrogate parameter, with the hypothesis that aquatic organisms in the stream are exposed to forces and stresses similar to those experienced by the streambed material. The design goal is to provide a stream crossing that has an equivalent effect, over a range of stream flows, on the streambed material within the culvert compared with the streambed material upstream and downstream of the culvert.

The Aquatic Organism Passage Monitoring and Assessment Protocol (aopMAP) Field Manual (FHWA WFLHD 2024) provides guidance and tools for state DOTs and other agencies to perform long-term post-construction monitoring on AOP water crossing structures. The proposed monitoring protocol includes an as-built data collection protocol and a rapid geomorphic data collection protocol. Long-term data monitoring is proposed by the protocol to collect a variety of geomorphic field data intended to provide indicators of success for AOP water crossings. The aopMAP protocol includes a companion mobile data collection tool based on Esri ArcGIS Survey123 and a cloud-based database for data storage and sharing.

2.1.2 USFS

Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings by the USFS Stream-Simulation Working Group serves as a guide for the design and build of road-stream crossings aimed at promoting unimpeded movement and passage of aquatic species (USFS 2008). The methods described are intended to assist in the achievement of the project goal: the continuation of physical and biological robustness and quality of the stream systems under management. Stream-simulation structures in the guide have a sustained, uninterrupted streambed that imitates the slope, structure, and dimensions of a natural geomorphic streambed, thereby generating similar water velocities and depths and permitting a familiarity and ease of passage for aquatic species.

Stream Simulation (USFS 2008) includes chapters on assessing ecological conditions and connectivity, stream-simulation design, contract preparation, and construction. Once the ecological

Page 6 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

existing conditions assessments are completed, stream-simulation design guides the user to create a three-dimensional layout of the site, verify reaches and feasibility, and design selected stream feature geometry appropriate for the site. As part of the final design, the user considers structure type, materials and placement, crossing installation, and water quality. The stream-simulation construction chapter design directs the project engineer to produce a plan for pollution control, stormwater management control and stabilization, life-cycle costs and risk, environmental impacts, and construction timing and activities.

Stream Simulation (USFS 2008) provides design guidance, describes problems and their respective solutions, and offers installation recommendations to achieve passage for aquatic organisms from concept development to a project’s construction completion.

Technical Guide for Field Practitioners: Understanding and Monitoring Aquatic Organism Passage at Road-Stream Crossings (USFS 2020) is a proposed guide for assessing and prioritizing road-stream crossings that act as potential barriers to aquatic organisms. The guide provides methods for rapidly assessing conditions at a project site, suggests methods for detailed investigations, such as using FishXing software, and discusses a suite of biological-based options for effective monitoring of individual road-stream crossings.

2.1.3 National Marine Fisheries Service

NOAA Fisheries Guidelines for Salmonid Stream Crossings in WA, OR, and ID (NMFS 2023a) assists with improving conditions for salmonids that must migrate past barriers to complete their life cycle. The guidelines offer strategies to design crossings that maintain the ecological function of streams and pass flood flows, sediment, and wood; they also describe stream-simulation and hydraulic design methodologies.

NOAA Fisheries WCR [West Coast Region] Anadromous Salmonid Design Manual (NMFS 2023b) also focuses on improving conditions for salmonids that must migrate past barriers to complete their life cycle. It does not address water crossing culverts, rather it focuses on hydroelectric project barriers and fishways. The manual provides information on project development and informational needs as well as technical guidelines.

NOAA Fisheries WCR [West Coast Region] Guidance to Improve the Resilience of Fish Passage Facilities to Climate Change (NMFS 2023c) provides methods for incorporating future climate change into engineering designs of fish passage facilities and stream crossings. One of the goals of the document is to assist parties in satisfying National Marine Fisheries Service (NMFS) regulatory authorities and NMFS policy on the treatment of climate change in Endangered Species Act decisions. The document is part of a series NMFS recommends using when designing a fish passage project in the West Coast region, which encompasses California, Oregon, Washington, and Idaho.

NOAA Fisheries Guidelines for Salmonid Passage at Stream Crossings in California (NMFS 2023d) provides guidelines for designing stream crossings to aid upstream and downstream passage of migrating salmonids. The intent is to facilitate the design of a new generation of stream crossings and assist in the recovery of threatened and endangered salmon species. The document provides criteria, rationale, guidelines, and definitions for designing proper fish passage facilities in California.

NOAA Fisheries Pre-Design Guidelines for California Fish Passage Facilities (NMFS 2023e) provides a framework to assist in the development of facilities, fishways, and fish passage appurtenances, as well as the operational, monitoring, and maintenance plans necessary for the successful operation of such facilities. Within this framework approach, design factors are discussed, but specific engineering criteria for various fishways and fish passage appurtenances are generally not provided. For engineering criteria on facility fishways and fish passage appurtenances, see NOAA Fisheries WCR [West Coast Region] Anadromous Salmonid Design Manual (NMFS 2023b).

Page 7 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

2.2 State DOT Guidance Documents

The synthesis summarized state DOT guidance documents, shown in Table 1, by combining reference documents identified by state DOT participants in the online survey with additional findings from an internet search. States that did not participate in the online survey were included in this synthesis through the internet search. State DOTs were omitted from this synthesis in cases when the online survey and the internet search did not identify any AOP-specific guidance documents.

Table 1. State DOT guidance documents.

State DOT Sources	Summary
Alaska (ADFG 2024a) (ADFG 2024b) (Eisenman and O’Doherty 2014)	Alaska’s Anadromous Fish Act requires approval from the Alaska Department of Fish and Game for activities that could represent an impediment to fish passage (ADFG 2024a; 2024b). Fishways are required for dams and any other obstruction across a stream frequented by salmon or other fish. Under the Anadromous Fish Act, approval from the Alaska Department of Fish and Game is required “to construct a hydraulic project or use, divert, obstruct, pollute, or change the natural flow or bed” of an anadromous waterbody (ADFG 2024b). The Alaska Department of Fish and Game maintains the Fish Passage Inventory Database, and all Fish Passage Improvement Program projects are listed on its website. Eisenman and O’Doherty (2014) includes a guide to recording observations regarding fish passage in the field when developing the inventory for culverts. The guide contains a decision-support matrix that is used to provide a fish passage rating to inventoried culverts.
California (Caltrans 2007)	Three methods are proposed in Caltrans (2007) to design culverts for fish passage. The stream-simulation method replicates the culvert slope, cross-sectional size, and bed elevation after nearby stream reaches. Culverts should be embedded 30% to 50%, and the culvert width should be greater than or equal to the bankfull width in the stream-simulation approach. The stream-simulation method is typically used for streams with a slope of up to 6%. The active channel culvert design method involves installing a culvert at a level grade and a large enough size to encourage bedload movement. Under this approach, the culvert width should be greater than or equal to 1.5 times the active channel width with an upstream embedment of less than or equal to 40% and a downstream embedment of 20% to 40%. The active channel approach is typically used for streams with a slope of 3% or less. The hydraulic design method is similar to the conventional culvert design methods but uses the maximum average velocity within the culvert barrel as a design parameter as opposed to allowable headwater elevation. Existing culverts are retrofitted with roughness elements such as baffles or roughened channels within the culvert barrel. Rock or concrete weirs and roughened channel grade control structures are used at culvert outlets to enhance fish passage. Weir grade controls have a step-pool arrangement and are installed at slopes of 5% or less. Roughened channels consist of rocks that create small pools on the downstream side of rocks for fish to rest in and are installed typically at slopes of 6% or less. Fishways are typically used to improve fish passage for existing culverts as a “last resort” option. Fishways are used when a culvert outlet is high above the stream channel. Fishways pass only a portion of the flow (typically about 10%).

State DOT
Sources

Summary

Alaska
(ADFG 2024a)
(ADFG 2024b)
(Eisenman and O’Doherty 2014)

Alaska’s Anadromous Fish Act requires approval from the Alaska Department of Fish and Game for activities that could represent an impediment to fish passage (ADFG 2024a; 2024b). Fishways are required for dams and any other obstruction across a stream frequented by salmon or other fish. Under the Anadromous Fish Act, approval from the Alaska Department of Fish and Game is required “to construct a hydraulic project or use, divert, obstruct, pollute, or change the natural flow or bed” of an anadromous waterbody (ADFG 2024b). The Alaska Department of Fish and Game maintains the Fish Passage Inventory Database, and all Fish Passage Improvement Program projects are listed on its website. Eisenman and O’Doherty (2014) includes a guide to recording observations regarding fish passage in the field when developing the inventory for culverts. The guide contains a decision-support matrix that is used to provide a fish passage rating to inventoried culverts.

California
(Caltrans 2007)

Three methods are proposed in Caltrans (2007) to design culverts for fish passage. The stream-simulation method replicates the culvert slope, cross-sectional size, and bed elevation after nearby stream reaches. Culverts should be embedded 30% to 50%, and the culvert width should be greater than or equal to the bankfull width in the stream-simulation approach. The stream-simulation method is typically used for streams with a slope of up to 6%. The active channel culvert design method involves installing a culvert at a level grade and a large enough size to encourage bedload movement. Under this approach, the culvert width should be greater than or equal to 1.5 times the active channel width with an upstream embedment of less than or equal to 40% and a downstream embedment of 20% to 40%. The active channel approach is typically used for streams with a slope of 3% or less. The hydraulic design method is similar to the conventional culvert design methods but uses the maximum average velocity within the culvert barrel as a design parameter as opposed to allowable headwater elevation.

Existing culverts are retrofitted with roughness elements such as baffles or roughened channels within the culvert barrel. Rock or concrete weirs and roughened channel grade control structures are used at culvert outlets to enhance fish passage. Weir grade controls have a step-pool arrangement and are installed at slopes of 5% or less. Roughened channels consist of rocks that create small pools on the downstream side of rocks for fish to rest in and are installed typically at slopes of 6% or less. Fishways are typically used to improve fish passage for existing culverts as a “last resort” option. Fishways are used when a culvert outlet is high above the stream channel. Fishways pass only a portion of the flow (typically about 10%).

Page 8 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
Connecticut (CTDEP 2008)	The Connecticut DOT Stream Crossing Guidelines (CTDEP 2008), provided by the Connecticut Department of Environmental Protection, recommend the installation of clear span bridges and bottomless culverts. Guidelines have been established for situations in which barrel culverts are necessary. The invert of barrel culverts should be set at least 1 ft below the streambed elevation. For culverts larger than 10 ft in diameter, 20% of the pipe diameter should be below the streambed elevation. Culvert slopes should match the overall stream gradient but should not exceed 3%. The width of the culvert should be 1.2 times the bankfull width of the stream, while the length of the culvert should be minimized by using vertical headwalls at the inlet and outlet instead of fill slopes. The openness ratio (cross-sectional area of the culvert aboveground divided by the culvert length) should be greater than or equal to 0.25. To help retain streambed materials, corrugated culverts are preferred over smooth culverts (except for metal culverts because of rust concerns). Native streambed material should be placed in the culvert to replicate the cross section of the streambed. Many retrofitting techniques have been used, including gradient control weirs that use large boulders at the culvert outlet to back up water through the culvert or reduce a large drop at the culvert outlet. Additionally, interior baffles can be used but require periodic maintenance because they can increase debris accumulation. Fishways can be used as a retrofit when other retrofit solutions are not as viable. Seasonal culvert construction timing restrictions are in place for anadromous and inland fish species.
Delaware (DelDOT 2022)	The Delaware DOT (DelDOT) uses countersunk culverts as its AOP standard. Detailed drawings for precast concrete box culverts indicate that channel bed material should be installed within the culvert at a minimum depth of 12 in. and should transition to 4 in. of thickness at the ordinary high-water line or high-tide line for tidal areas.
Georgia (GDOT 2023a) (GDOT 2023b) (Georgia ACT 2021)	The Georgia DOT (GDOT) Drainage Design for Highways manual (GDOT 2023a) includes a section on AOP. The section references the design methods of the USFS stream-simulation method, the HEC-26 method (FHWA 2010), and the simplified method for designing culverts for AOP. The design guidelines in the manual (which resemble the simplified method) are included for compliance with the United States Army Corps of Engineers (USACE) Nationwide Permit AOP requirements under the Savannah District’s regional conditions. The general guidelines include installing culverts that maintain the existing bankfull cross-sectional area; embedding 20% of the culvert height; and maintaining the existing stream slope, depth, and width. The manual advises that multiple pipe culverts should not be used to convey base flows, but if an adjacent floodplain is available, an equalizer culvert at the floodplain elevation should be used to convey flows that exceed bankfull conditions. The manual also includes design guidelines for box culverts, and the GDOT details web page provides standard construction detail drawings of concrete veins (fish baffles) that can be included in embedded box culverts designed for AOP. The GDOT Perennial Stream Culvert Design Workflow document (GDOT 2023b) also recommends considering AOP at various stages throughout the preliminary evaluation and design process. The Georgia Aquatic Connectivity Team, a group of individuals from organizations and agencies interested in improving aquatic connectivity in Georgia, published Stream Crossings in Georgia: A Handbook for Connectivity and Resilience (Georgia ACT 2021). The handbook references an AOP barrier assessment methodology

Page 9 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	developed by the Southeast Aquatic Resources Partnership (SARP) that collects data for SARP’s online database, which is used to prioritize stream crossing replacement projects in the Southeast region of the United States. The handbook refers to the USACE Nationwide Permit Regional Conditions for the Savannah District for AOP guidance and includes additional recommendations for incorporating passage of terrestrial wildlife. The handbook also includes examples of AOP barriers, case studies of culvert replacements for AOP, and a list of federal and state regulations that influence AOP in the state.
Idaho (ITD 2021)	The Idaho Transportation Department Bridge Hydraulics Manual (ITD 2021) specifies that AOP regulatory requirements in the state vary depending on the stream being crossed and the resource agencies that have jurisdiction. The manual defers to HEC-26 and HDS-5 from FHWA (2010; 2012) and the stream-simulation document from USFS (2008) for AOP design.
Iowa (IDOT 2024)	The Iowa DOT specifies in its LRFD Bridge Design Manual (IDOT 2024) that any new or replacement pipe culvert of 48 in. in diameter or greater within specified waters of the United States must be embedded at least 12 in. below the natural streambed. Pipe culvert diameter should be increased by 6 in. to account for the loss of hydraulic capacity caused by embedding the culvert. Revetments that line the natural streambed should also be installed in new and replacement pipe culverts at the inlets and outlets to prevent upstream headcuts.
Kansas (USACE Kansas City District 2021)	The Kansas DOT’s 2021 Nationwide Permit Regional Conditions for the Kansas City District (USACE Kansas City District 2021) encourage the use of single culverts. The installation of culverts above the stream grade is prohibited, including other in-stream structures at the inlet that limit sedimentation in the culvert. The length of the culvert should be minimized to the greatest extent possible. The regional conditions define bankfull using the top of the high banks within a stream. The minimum percentage of the bankfull cross-sectional area that should remain open through the culvert varies depending on the stream type (85% for perennial, 50% for intermittent, and passage of low-flow conditions for ephemeral streams). Culverts larger than 48 in. in diameter must be embedded at least 1 ft on upstream and downstream sides. Culverts smaller than 48 in. in diameter must be embedded at or below grade. If there is a non-erodible streambed (bedrock or stable clay), the culvert can be placed flush with the streambed and does not need to be embedded. No monitoring or maintenance requirements are stipulated.
Maine (FHWA et al. 2017) (MaineDOT et al. 2016)	The MaineDOT User’s Guide for the Maine Atlantic Salmon Programmatic Consultation (MAP) (FHWA et al. 2017) is used for freshwater waterways populated by Atlantic salmon. The guide assists users with completing a project notification form and familiarizing them with state standard operating procedures for stream crossing projects. Programmatic Biological Assessment for Transportation Projects for the Gulf of Maine Distinct Population Segment of Atlantic Salmon and Designated Critical Habitat (MaineDOT et al. 2016) establishes three tiers of priority areas for watershed restoration on the basis of observed salmon populations. The programmatic biological assessment (PBA) contains design methods for stream crossing structure replacements and removals, culvert end resets and extensions, bridge scour countermeasures, bridge maintenance, and culvert rehabilitation. The PBA also includes avoidance and minimization measures (AMMs) for the construction methods used for

Page 10 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	stream crossing projects (e.g., timing restrictions for in-water work, cofferdam and bypass channel installation and removal methods, construction sequencing). A list of AMMs is also included in the appendices of FHWA et al. (2017) with turbidity-monitoring protocols for use during construction, underwater noise-monitoring plans, and fish evacuation protocols. Engineered streambed material is detailed in the design of culvert replacement projects under the PBA. Sizing of the streambed material is based on gradient, width, and flows and is not based on a survey of streambed materials from a reference reach. The PBA also proposes that Tier 1 priority areas should be designed with a culvert that matches 1.2 times the bankfull width in addition to streambank and substrate materials included within the culvert. Tier 2 priority areas are proposed to have a culvert with a diameter of 1.0 bankfull width.
Maryland (MDOT SHA Office of Structures 2011) (MDOT SHA 2023)	Maryland Code of Regulations 26.17.04.06: Bridges and Culverts (https://dsd.maryland.gov/regulations/Pages/26.17.04.06) specifies that culverts must have at least one cell placed 1 ft below the invert of the stream. Where bedrock foundations are present, the culvert should not have a concrete bottom unless measures are in place to ensure fish habitat and migration patterns are not adversely affected according to these regulations. The Maryland Department of Transportation (MDOT) State Highway Administration Manual for Hydrologic and Hydraulic Design (MDOT SHA Office of Structures 2011) includes in its culverts chapter an AOP section that as of 2024 is not fully developed with design approaches. The manual indicates that the Office of Structures is coordinating with FHWA and other state and federal agencies to develop these approaches. The Office of Structures is assessing AOP needs and designs on a project-by-project basis until updated design approaches are incorporated into the manual. The MDOT SHA Highway Drainage Manual (MDOT SHA 2023) recommends the designer consider AOP throughout the design process and defers to the Code of Maryland Regulations Section 26.17.04.06 for the specific AOP conditions to be met in non-tidal waters. MDOT SHA (2023) states that multiple-barrel culverts should be avoided where AOP is required unless one barrel is lowered to maintain low flows. MDOT SHA (2023) defers to FHWA’s HY-8 Culvert Hydraulic Analysis Program design software and HEC-26 (FHWA 2010) for energy dissipator designs for AOP culverts.
Minnesota (Hernick et al. 2019)	The Minnesota DOT (MnDOT) Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts (Hernick et al. 2019) presents multiple AOP design methods selected on the basis of stream characteristics determined from a site-specific assessment. The guide suggests using stream slope and the Rosgen system to assist with selecting the appropriate AOP design method (i.e., bridge spanning channel and banks, geomorphic simulations [USFS Stream Simulation], hydraulic simulation [FHWA HEC-26], embedded [initially filled], recessed [initially non-filled], and hydraulic design [species specific]). MnDOT considers bridge structures to be structures with an opening width greater than 10 ft (including three-sided and enclosed culverts). The geomorphic simulation design method outlined in the guide is based on Stream Simulation (USFS 2008) and aims to match channel conditions (slope, width, bed materials, and bedforms) with a nearby stable reference reach. The hydraulic design method is based on HEC-26 (FHWA 2010) and

Page 11 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	specifies that natural sediment should be placed within an embedded culvert underlain by oversized sediment for bed stability at peak flow. The hydraulic design method attempts to maintain through the culvert flow depth and velocities that match upstream and downstream conditions. The guide recommends embedded and recessed culvert design approaches for less complex stream crossing sites where streambed characteristics and roughness through the culvert must be maintained. For this approach, the slope of the culvert is recommended to match the stream slope, and the width of the culvert is recommended to equal the bankfull width. The guide also provides recommendations for multiple-barrel culverts, such as embedding a primary barrel to handle base flow conditions and vertically offsetting other barrels (above base flow channel but below bankfull elevation) to handle peak flows. The guide recommends applying the hydraulic design method to retrofit situations. In this method, baffles and weirs are selected to create target depths and velocities within a culvert. Frequent inspections (at least annually) and maintenance are recommended for baffles and weirs. To improve roughness in the culvert, the guide recommends using loose or grouted rocks or boulders, incorporating formed roughness into a concrete overlay, or placing mussel spat rope through culverts. The guide also considers installing downstream grade controls as a retrofit to increase the water depth within a culvert. Case design examples and a list of recommended construction practices are included in the guide.
Missouri (USACE St. Louis District 2021)	The Missouri DOT 2021 Nationwide Permit Regional Conditions for the St. Louis District (USACE St. Louis District 2021) encourage the use of single culverts. Installing culverts above the grade of the stream, including other in-stream structures at the inlet that limit sedimentation in the culvert, is prohibited. The length of the culvert should be minimized to the greatest extent possible. The regional conditions define a bankfull using the top of the high banks within a stream. The minimum percentage of the bankfull cross-sectional area that should remain open through the culvert varies depending on the stream type (85% for perennial and 50% for intermittent). Culverts larger than 48 in. in diameter must be embedded at least 1 ft on upstream and downstream sides. Culverts smaller than 48 in. in diameter must be embedded at or below grade. If there is a non-erodible streambed (bedrock or stable clay), the culvert can be placed flush with the streambed and does not need to be embedded. No monitoring or maintenance requirements are stipulated.
Montana (MDT 2023)	The Montana Department of Transportation’s (MDT) Hydraulics Manual (MDT 2023) has an AOP section that sizes culverts to pass design flood criteria and span the bankfull width but increases the size of the culvert as necessary to match the flow velocity through the culvert with upstream and downstream velocities at the 2-year return flow event (HEC-26; FHWA 2010). MDT embeds its culverts below the streambed and installs Class I riprap within the culvert. Streambed material can be added to fill in the voids of the riprap, or the voids can be left in place to allow for natural recruitment of streambed material. MDT also adds a low-flow channel inside the culvert to maintain seasonal low-flow channel depths.

Page 12 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
New Hampshire (New Hampshire 2024)	New Hampshire state regulations 482-A:1, Fill and Dredge in Wetlands, and Chapter Env-WT 900, Stream Crossings; Certified Culvert Maintainer Program, establish rules on the installation, replacement, and repair of stream crossings permitted by the New Hampshire Department of Environmental Services. According to the New Hampshire Stream Crossing Initiative web page (New Hampshire 2024), these regulations ensure that geomorphic compatibility, hydraulic capacity, and AOP are maintained or enhanced for new and modified stream crossings. The New Hampshire Stream Crossing Initiative is a multi-agency group that collaboratively works to align resources and improve management of stream crossing infrastructure across the state. The initiative provides the tools needed for stakeholders to make data-driven decisions when targeting investments in projects that support transportation, stream connectivity, fish and wildlife habitat, and flood resilience.
New Jersey (NJDOT 2006) (NJDOT 2015) (NJTA 2020)	The New Jersey DOT (NJDOT) Drainage Design Manual (NJDOT 2006) and New Jersey Turnpike Authority Design Manual (NJTA 2020) indicate that Category One waters, designated by New Jersey Administrative Code 7:9B, Surface Water Quality Standards, receive special protection for exceptional fisheries. For streams with a drainage area greater than 50 acres, the stream encroachment permit requires culverts to provide fish passage in at least one box culvert for multi-cell systems. NJDOT encourages engineers to refer to the New Jersey Department of Environmental Protection’s Technical Manual for Land Use Regulation Program, Bureau of Inland and Coastal Regulations, Stream Encroachment Permits, and a chart detailing functional low-flow fish passage for stream crossings for the latest acceptable methods for providing fish passage in all proposed box culvert installations. The chart categorizes fish species and drainage structure configurations, characterizing each practice as preferred, questionable, acceptable, obsolete, or unacceptable. Additionally, the NJDOT Roadway Design Manual (NJDOT 2015) refers to the New Jersey Department of Environmental Protection Division of Fish and Wildlife’s Connecting Habitat Across New Jersey, a tool for the identification of key areas, road barrier impacts, species, and guidance for proper habitat management.
New York (NYSDOT 2021)	The New York State DOT (NYSDOT) Highway Design Manual (NYSDOT 2021) presents design guidelines for hydraulic and hydrologic systems (structural and natural) with consideration for AOP in quantitative design elements such as culvert and channel geometrics and alignment. To maintain the consistency of the environment and facilitate colonization of species, NYSDOT recommends original streambed material be collected and relocated to the new stream channel. General environmental considerations are characterized as low-flow channel design, velocity control, pool-to-riffle ratios, shading, stabilization techniques, and methods and timing of construction for temporary and permanent fish and wildlife passage. Suggested practices include limiting the removal of riparian vegetation, crossing streams at right angles rather than bends or pools, establishing species spawning timing restrictions, and installing soil erosion and sediment control features to reduce turbidity to waterbodies. NYSDOT indicates that culverts designed for fish

Page 13 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	passage should be placed in locations where adequate foundational support is present. Where good foundational support exists, an open-bottom arch shaped culvert may be used to maintain the natural streambed. However, in locations with poor foundational material, an oversized depressed culvert may be installed with natural streambed material placed inside, such as a reinforced concrete box culvert with a “V-” or dish-shaped floor set at least 8 in. below the natural streambed elevation. NYSDOT recommends that culverts be installed between August and September during low-flow conditions. The NYSDOT Engineering Division, Office of Environment, provides further information for users regarding habitat assessment and management, regulatory programs, species information, and software and learning systems for fish passage through culverts.
North Carolina (NCDOT 2022)	North Carolina DOT’s Guidelines for Drainage Studies and Hydraulic Design (NCDOT 2022) includes a section on anadromous fish passage within the coastal plain region and for perennial and intermittent streams. AOP design guidelines in this section include embedding the invert of box culverts at least 1 ft below the existing streambed. The guidelines state that the opening of the structure should be able to pass historical spring flow or bankfull flow without adversely altering the flow velocity. To help terrestrial wildlife passage (as a co-benefit), perennial streams serving watersheds greater than 1 mi² must have at least 4 ft of additional opening width. For additional guidance on AOP, the guidelines refer to HEC-26 (FHWA 2010). North Carolina has a time-of-year restriction for in-stream activities during spring migration periods.
North Dakota (NDDOT 2023)	The North Dakota DOT Design Manual (NDDOT 2023) recommends that existing bridges replaced with reinforced concrete box culverts countersink the bottom of the structure 1 ft below the existing channel bottom grade to provide AOP. NDDOT provides suggestions to minimize adverse stream impacts, including maintaining existing bridge abutments by constructing new abutments behind existing structures, spanning as much of the stream and associated wetlands as feasible, and covering a portion or all riprap with suitable bed materials such as gravel. Additional guidelines are provided for temporary traffic bypass culvert sizing and drainage maintenance. The manual references the United States Fish and Wildlife Service (USFWS) National Wetland Inventory maps as a resource for historical wetland data.
Oregon (ODOT 2024)	The Oregon DOT (ODOT) established two culvert repair programmatic agreements (2015–2017 and 2018–2022) with the Oregon Department of Fish and Wildlife (ODFW) to improve fish passage to culverts in western Oregon (ODOT 2024). The culvert repair reports from these programmatic agreements are available on the ODOT website (ODOT 2024). The ODFW Fish Passage Program established through the Fish Passage Administrative Rules, Division 412, and the Fish Passage Statutes in Oregon Revised Statute 509. The state fish passage regulations established the Fish Passage Task Force, which advises ODFW on criteria for fish passage and sets waiver, exemption, and protest conditions for fish passage. The ODFW Fish Passage Program maintains an inventory of fish passage barriers and a priority list, has a pilot fish passage mitigation bank, and provides a checklist for design plans that meets the Fish Passage Task Force requirements (ODOT 2024).

Page 14 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	The Division 412 rules list design requirements for fishways, bridges, and culverts and recommend using Stream Simulation (USFS 2008) for bridges and culverts. Division 412 also states that the width for bridges and culverts should be greater than or equal to the active channel width multiplied by 1.2 plus 2 ft, the slope should be equal to the slope of the existing surrounding stream, a minimum of 3 ft of vertical clearance should be maintained from the active channel width elevation and the inside top of the structure, and the average water depth and velocities through the structure should match that of the existing surrounding stream. Furthermore, streambed material under bridges and culverts should be maintained over time, consist of natural streambed material or supplemented to address bed retention and hydraulic shadow, contain partially buried oversized rock, be installed mechanically, be installed at a depth 20% of the structure height (except for oversized rock), be stable at the 100-year flood flow, and contain a low-flow thalweg. The Division 412 rules also establish that ODFW can require monitoring and reporting of fish passage structures to determine whether they are functioning as intended and that such structures be maintained by the owner or operator of the structure to provide fish passage of native migratory fish at all times.
Pennsylvania (PennDOT 2022) (PennDOT 2024)	The Pennsylvania DOT (PennDOT) Design Manual (PennDOT 2024) provides the department’s recommended procedure for the design of fishable stream channel construction and low-flow fish passage through highway culverts. Drainage guidance for the selection of features is provided in the PennDOT Drainage Manual (PennDOT 2022). For culvert locations with continuous flow, a hydrologic and hydraulic report must be provided, including comments regarding fish habitat and environmental concerns as well as stream classification per 25 Pa. Code Chapter 93. PennDOT design guidelines require the normal flow depth of culverts to be greater than 3 in. The guidelines also require a stable condition, including choked riprap at the inlet and outlet ends of a culvert for aquatic fish passage, measurement of the streambed slope suitable for the waterbody and the fish species, the selection of a structure dependent on the site conditions and ease of installation and maintenance, and consideration of slow water zones for fish rest. General guidance design for culverts and fish baffles, as well as alternative methods to accommodate fish passage in low-flow highway culverts, is provided. Satisfactory culvert installation practices for fish passage designated by PennDOT include open-bottom culverts, culverts supported on spread footings, culvert sizes maintaining natural stream velocities, and a foundation of rock or scour-resistant material.
South Dakota (SDDOT 2011) (USACE Omaha District 2012) (USACE Omaha District 2021)	The USACE Omaha District published a Nationwide Permit Regional Conditions document (USACE Omaha District 2021) to ensure projects result in no greater than minimal adverse impacts to the aquatic environment. A recommended design practice set forth by the USACE Omaha District is the countersinking of culverts, such that the culvert invert is set below the natural stream channel flow line where the minimum distance lowered is based on the culvert type and drainage area size.

Page 15 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	The South Dakota DOT (SDDOT) Drainage Manual (SDDOT 2011) has a chapter on culverts that provides guidelines for the consideration of fish passage during the facility design. Suggested drainage practices entail maintenance of low flows and the flattening of culvert slopes to induce sedimentation. The guide directs users to a hydraulic design procedure for culverts with inverts below the streambed within HEC-26 (FHWA 2010), the FHWA’s HY-8 software for buried inverts for common culvert shapes, and the AASHTO Model Drainage Manual for hydraulic design guidance on alternative sill-type fishways, such as ladders, if fish passage cannot be accommodated via a depressed invert. Fish passage guidelines within the SDDOT Drainage Manual provide a user design guide for culverts to avoid impacting fish movement. The manual contains a drainage design procedure that outlines tasks such as the identification of culverts, culvert hydraulic geometry, and their respective stream flow lines. The design procedure and documentation guidelines encourage users to assemble data and project files, including environmental constraints such as fish migration and wildlife passage, and perform a risk assessment for environmentally sensitive areas such as fisheries and wetlands.
Texas (TxDOT 2019)	The Texas DOT (TxDOT) Hydraulic Design Manual (TxDOT 2019) details channel environmental mitigation measures for its “no net loss” policy, such that habitat loss is acceptable when combined with mitigation measures that prevent habitat damage. Enhancement and surface water reconstruction practices are described and include incorporating sinuosity into a straight stream reach, relocating the channel to avoid contamination, adjusting flow depth and width, encouraging overhanging banks, and improving riparian vegetation. However, the manual does not detail design guidance for such measures. The manual states that an arch culvert shape benefits fish passage by maintaining the natural stream bottom. Users are encouraged to consider the USFWS requirements and recommendations to avoid, minimize, or compensate for adverse effects to wildlife habitat.
Utah (UDOT 2018)	The Utah DOT (UDOT) Drainage Design Manual of Instruction (UDOT 2018) sets forth drainage design requirements and criteria as a minimum standard of practice and encompasses methods for culvert and channel hydrology and hydraulics design, regulations and permits, responsibilities, and training. The UDOT manual includes recommendations for coordination between roadway and structural engineers, flood control districts, the Federal Emergency Management Agency’s (FEMA) Special Flood Hazard Areas (SFHAs) for hydraulic and hydrologic design, and UDOT environmental staff to determine the requirements for passage of aquatic organisms. Culvert design requirements are characterized by flow-type characteristics: on-site flows only, natural stream channels, natural stream channels in FEMA SFHAs, and regulated irrigation flows. UDOT directs users and project engineers to use design procedures described in HEC-26 (FWHA 2010) as well as embedding the bottom of box culverts 1 ft into the channel bed for culverts that require an AOP as dictated by UDOT’s environmental staff.

Page 16 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
Vermont (Austin et al. 2013) (Bates and Kirn 2009) (VANR 2003) (VANR 2005a) (VANR 2005b) (VDEC and VFWD 2016) (VFWD 2009)	The Vermont Fish and Wildlife Department’s (VFWD) Guidelines for the Design of Stream/Road Crossings for Passage of Aquatic Organisms in Vermont (Bates and Kirn 2009) provides technical guidance for the design and implementation of stream and road crossings for which AOP has been identified. The document describes a concept-to-construction approach for which ecological demands or conditions, regulatory obligations, and aquatic resource objectives are identified. Identified parameters are addressed during the hydraulic design phase and constructed according to the guidelines. Design for passage of fish and other aquatic organisms is categorized by three options: low slope, stream simulation, or hydraulic approaches. Design approaches and bed materials vary by fish species because VFWD indicates that certain structures may have a more significant impact on specific aquatic species. Users are instructed to determine procedures and parameters for their project site through the Vermont Agency of Natural Resources Vermont Stream Geomorphic Assessment Protocols—Vermont Stream Geomorphic Assessment Handbook: Phase 1, Watershed Assessment; Phase 2, Rapid Stream Assessment; and Phase 3, Survey Assessment (VANR 2003, 2005a, 2005b) and agency websites. Treatments for Aquatic Organisms Passage (VFWD 2009) sketches provide engineers with design profile and plan views of suggested techniques and AOP features for channels, streams, and culverts set forth in Bates and Kirn (2009). Conserving Vermont’s Natural Heritage (Austin et al. 2013), VFWD’s guidance manual, provides direction to state conservation planning that prioritizes the quality and maintenance of Vermont’s fish, wildlife, and biodiversity via the examination of studies and practices suitable for various climates, geologic conditions, and landscape types. For AOP, attention is paid to the analysis of wetlands, connecting habitats, and riparian and aquatic habitats where conservation mapping, strategies, and development are evaluated. Additional state aquatic organism and structure information includes up-to-date specific regulation requirements, permit applications, and a contact list for the department’s fish biologists to assist in the identification of aquatic resource issues associated with a stream crossing project.
Virginia (Fitch 1995) (Mudre, Ney, and Neves 1985) (VDOT 2023)	The Virginia DOT (VDOT) Drainage Manual (VDOT 2023) sets stormwater structure design guidelines to meet state technical standards. Chapter 8 discusses culvert design and practices, special culvert installations that minimize the disruption of the movement of aquatic life, features for culverts on bedrock and culverts on steep terrain that include partial countersinking of the inlet end of the culvert, construction of a stone step or pool structure, use of river rock or native stone, or construction of low rock weirs to generate pools. According to the Drainage Manual, culvert inverts should be set below the flow line and at a grade no steeper than that of the stream. The manual refers to Fitch (1995) and Mudre, Ney, and Neves (1985) for additional design criteria. Analysis of Impediments to Spawning Migrations of Anadromous Fishes in Virginia Rivers (Mudre, Ney, and Neves 1985) outlines technical considerations for fish passage facilities by structure,

State DOT
Sources

Summary

Vermont
(Austin et al. 2013)
(Bates and Kirn 2009)
(VANR 2003)
(VANR 2005a)
(VANR 2005b)
(VDEC and VFWD 2016)
(VFWD 2009)

The Vermont Fish and Wildlife Department’s (VFWD) Guidelines for the Design of Stream/Road Crossings for Passage of Aquatic Organisms in Vermont (Bates and Kirn 2009) provides technical guidance for the design and implementation of stream and road crossings for which AOP has been identified. The document describes a concept-to-construction approach for which ecological demands or conditions, regulatory obligations, and aquatic resource objectives are identified. Identified parameters are addressed during the hydraulic design phase and constructed according to the guidelines. Design for passage of fish and other aquatic organisms is categorized by three options: low slope, stream simulation, or hydraulic approaches. Design approaches and bed materials vary by fish species because VFWD indicates that certain structures may have a more significant impact on specific aquatic species. Users are instructed to determine procedures and parameters for their project site through the Vermont Agency of Natural Resources Vermont Stream Geomorphic Assessment Protocols—Vermont Stream Geomorphic Assessment Handbook: Phase 1, Watershed Assessment; Phase 2, Rapid Stream Assessment; and Phase 3, Survey Assessment (VANR 2003, 2005a, 2005b) and agency websites.

Treatments for Aquatic Organisms Passage (VFWD 2009) sketches provide engineers with design profile and plan views of suggested techniques and AOP features for channels, streams, and culverts set forth in Bates and Kirn (2009). Conserving Vermont’s Natural Heritage (Austin et al. 2013), VFWD’s guidance manual, provides direction to state conservation planning that prioritizes the quality and maintenance of Vermont’s fish, wildlife, and biodiversity via the examination of studies and practices suitable for various climates, geologic conditions, and landscape types. For AOP, attention is paid to the analysis of wetlands, connecting habitats, and riparian and aquatic habitats where conservation mapping, strategies, and development are evaluated. Additional state aquatic organism and structure information includes up-to-date specific regulation requirements, permit applications, and a contact list for the department’s fish biologists to assist in the identification of aquatic resource issues associated with a stream crossing project.

Virginia
(Fitch 1995)
(Mudre, Ney, and Neves 1985)
(VDOT 2023)

The Virginia DOT (VDOT) Drainage Manual (VDOT 2023) sets stormwater structure design guidelines to meet state technical standards. Chapter 8 discusses culvert design and practices, special culvert installations that minimize the disruption of the movement of aquatic life, features for culverts on bedrock and culverts on steep terrain that include partial countersinking of the inlet end of the culvert, construction of a stone step or pool structure, use of river rock or native stone, or construction of low rock weirs to generate pools. According to the Drainage Manual, culvert inverts should be set below the flow line and at a grade no steeper than that of the stream. The manual refers to Fitch (1995) and Mudre, Ney, and Neves (1985) for additional design criteria.

Analysis of Impediments to Spawning Migrations of Anadromous Fishes in Virginia Rivers (Mudre, Ney, and Neves 1985) outlines technical considerations for fish passage facilities by structure,

Page 17 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	existing conditions, and fish species. Technical considerations focus particularly on the dissipation of energy and velocity reduction in fishways, suggesting that features should be designed with the weakest species in mind or the most minimal individual jump height or obstacle. The document also highlights the different impediments that roadway culverts can present when altering factors such as water depth, velocity, flow type, and streambed gradients. Culvert material, size, and streambed material are discussed, and the document concludes that corrugated metal arch culverts that do not disturb the stream bottom present the fewest issues for migrating fish, while road corrugated metal pipe culverts are the least desirable for passage. Recommendations entail sinking the bottom of the culvert or having it flush with streambed grade to prevent a vertical drop, avoiding oversizing culverts to maintain a desirable water level, and installing culverts where the streambed gradient is near zero. Non-Anadromous Fish Passage in Highway Culverts (Fitch 1995) addresses the impact on trout species from water parameter changes. The findings reveal that culverts can be the primary option for crossing non-anadromous trout streams where the culvert is placed on the same slope as that of the streambed, the slope of the stream is less than 3%, the flow velocity does not exceed 1.2 m per second under typical flow conditions, and the barrel of the culvert can be properly countersunk at the outlet to prevent perching. Culvert parameters and maximum flow conditions are set forth in an effort to maintain a habitat and near natural path for passage to both anadromous and non-anadromous species.
Washington (Barnard et al. 2013) (WDFW 2019) (WSDOT 2024a) (WSDOT 2024b) (WSDOT 2024c) (WSDOT 2024d) (WSDOT and WDFW 2023)	The Washington State DOT (WSDOT) web page links to information regarding the federal court injunction for fish passage (WSDOT 2024a), a treaty-based duty resting on the State of Washington requested by 21 northwest Washington Tribes to preserve fish runs and repair culverts that impede salmon migration. Issued in 2013, the permanent injunction requires the state to increase its effort for removing state-owned culverts that negatively infringe on the habitat for salmon and steelhead by 2030. WSDOT Fish Passage Performance Report (WSDOT and WDFW 2023) details WSDOT’s culvert correction and habitat connectivity progress as of June 2023. The monitoring approach outlined in the report entails four types of monitoring time periods: post-construction inspection, Year-1 evaluation, long-term evaluations (5 to 10 years after construction), and additional monitoring at the discretion of the WSDOT biologist. Monitoring parameters vary depending on the time period and typically include culvert and streambed geometric measurements and condition, stormwater events, and repair or action required. In addition, as defined in the state’s 2030 Fish Passage Project Delivery Plans (WSDOT 2024c), on larger highway projects, WSDOT will correct barriers within project boundaries. On WSDOT’s website, users can view an interactive map containing information on corrected and uncorrected barriers, delivery plan sites, and drainage structures with and without fish use. Fish passage work prioritization is based on the principles of habitat gain, partnership opportunities, culvert condition, downstream barriers (on which a high value is placed), project readiness, and geographic bundling and public impacts or a secondary benefit, and Tribal input.

State DOT
Sources

Summary

existing conditions, and fish species. Technical considerations focus particularly on the dissipation of energy and velocity reduction in fishways, suggesting that features should be designed with the weakest species in mind or the most minimal individual jump height or obstacle. The document also highlights the different impediments that roadway culverts can present when altering factors such as water depth, velocity, flow type, and streambed gradients. Culvert material, size, and streambed material are discussed, and the document concludes that corrugated metal arch culverts that do not disturb the stream bottom present the fewest issues for migrating fish, while road corrugated metal pipe culverts are the least desirable for passage. Recommendations entail sinking the bottom of the culvert or having it flush with streambed grade to prevent a vertical drop, avoiding oversizing culverts to maintain a desirable water level, and installing culverts where the streambed gradient is near zero.

Non-Anadromous Fish Passage in Highway Culverts (Fitch 1995) addresses the impact on trout species from water parameter changes. The findings reveal that culverts can be the primary option for crossing non-anadromous trout streams where the culvert is placed on the same slope as that of the streambed, the slope of the stream is less than 3%, the flow velocity does not exceed 1.2 m per second under typical flow conditions, and the barrel of the culvert can be properly countersunk at the outlet to prevent perching. Culvert parameters and maximum flow conditions are set forth in an effort to maintain a habitat and near natural path for passage to both anadromous and non-anadromous species.

Washington
(Barnard et al. 2013)
(WDFW 2019)
(WSDOT 2024a)
(WSDOT 2024b)
(WSDOT 2024c)
(WSDOT 2024d)
(WSDOT and WDFW 2023)

The Washington State DOT (WSDOT) web page links to information regarding the federal court injunction for fish passage (WSDOT 2024a), a treaty-based duty resting on the State of Washington requested by 21 northwest Washington Tribes to preserve fish runs and repair culverts that impede salmon migration. Issued in 2013, the permanent injunction requires the state to increase its effort for removing state-owned culverts that negatively infringe on the habitat for salmon and steelhead by 2030. WSDOT Fish Passage Performance Report (WSDOT and WDFW 2023) details WSDOT’s culvert correction and habitat connectivity progress as of June 2023. The monitoring approach outlined in the report entails four types of monitoring time periods: post-construction inspection, Year-1 evaluation, long-term evaluations (5 to 10 years after construction), and additional monitoring at the discretion of the WSDOT biologist. Monitoring parameters vary depending on the time period and typically include culvert and streambed geometric measurements and condition, stormwater events, and repair or action required. In addition, as defined in the state’s 2030 Fish Passage Project Delivery Plans (WSDOT 2024c), on larger highway projects, WSDOT will correct barriers within project boundaries. On WSDOT’s website, users can view an interactive map containing information on corrected and uncorrected barriers, delivery plan sites, and drainage structures with and without fish use. Fish passage work prioritization is based on the principles of habitat gain, partnership opportunities, culvert condition, downstream barriers (on which a high value is placed), project readiness, and geographic bundling and public impacts or a secondary benefit, and Tribal input.

Page 18 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	WSDOT’s Hydraulics Manual (2024b) provides an expansive guide to discussing design procedures, features, references, and methodology for fish passage project staff. The manual lists specific sources for reference on Manning’s roughness coefficient for river, stream, and culvert design for AOP based on surface material. The manual also directs users to obtain a Fish Passage and Stream Restoration Design certificate number and WSDOT Scour Certification Record to work on WSDOT fish passage and stream restoration design specialty reports. Training modules and a comprehensive exam are available through the WSDOT hydraulics and hydrology training website (2024d). Approved software for design of water crossings is limited to the Bureau of Reclamation’s Sedimentation and River Hydraulics–Two Dimension (SRH-2D) model. The Hydraulics Manual references the Washington Department of Fish and Wildlife (WDFW) Water Crossing Design Guidelines (Barnard et al. 2013) and has incorporated experience-based advice and alterations based on the 2013 Permanent Injunction Regarding Culvert Correction. WSDOT’s water crossings chapter provides detailed guidelines for designers to follow in assessing existing conditions, land use and cover, geological conditions past and present, risk, and bankfull geometry. Following the assessment, project staff are directed to incorporate such parameters into an analysis of bank stability, threshold of motion, hydraulic analysis (SRH-2D), and a meander belt assessment. References and links guiding the user to data sources for historical maps, elevation data, and aerial photos are readily available to counteract developments that may have shortened or straightened fish passage channels. WSDOT’s fish passage feature recommendations, depending on project site attributes, include meander bars, boulder features, and scour countermeasures. Fish passage improvement structures are discerned as roughened channel design, roughened rock ramp design, structure retrofit, or hydraulic culvert designs that mimic natural channel processes and facilitate unimpeded passage. A performance management process description provides project managers with guidance for the maintenance and upkeep of fish passage structures and features. In coordination with the Hydraulics Manual’s water crossings chapter, the pipe classifications and woody material chapters detail materials and design procedures that can positively affect migrating fish species and habitat connectivity. The Hydraulics Manual provides protocols for a broad application to ensure efficiency and consistency of post-project monitoring processes for fish passage projects. It describes four types of monitoring: post-construction compliance inspection, Year-1 inspection, long-term evaluation, and additional monitoring. The first step WSDOT suggests is to collect historical information on the site, including permit drawings and as-builts. Suggested post-construction monitoring parameters are culvert or bridge span, culvert rise, culvert or bridge type, streambed mix, streambed shape, streambed slope, and other features identified in the design. The main purpose of Year-1 inspections is to assess the site after the first winter to evaluate the effects of higher seasonal flows at the structure. Specific metrics include streambed material, channel thalweg, channel location, channel width, and hydraulic drops.

State DOT
Sources

Summary

WSDOT’s Hydraulics Manual (2024b) provides an expansive guide to discussing design procedures, features, references, and methodology for fish passage project staff. The manual lists specific sources for reference on Manning’s roughness coefficient for river, stream, and culvert design for AOP based on surface material. The manual also directs users to obtain a Fish Passage and Stream Restoration Design certificate number and WSDOT Scour Certification Record to work on WSDOT fish passage and stream restoration design specialty reports. Training modules and a comprehensive exam are available through the WSDOT hydraulics and hydrology training website (2024d). Approved software for design of water crossings is limited to the Bureau of Reclamation’s Sedimentation and River Hydraulics–Two Dimension (SRH-2D) model.

The Hydraulics Manual references the Washington Department of Fish and Wildlife (WDFW) Water Crossing Design Guidelines (Barnard et al. 2013) and has incorporated experience-based advice and alterations based on the 2013 Permanent Injunction Regarding Culvert Correction. WSDOT’s water crossings chapter provides detailed guidelines for designers to follow in assessing existing conditions, land use and cover, geological conditions past and present, risk, and bankfull geometry. Following the assessment, project staff are directed to incorporate such parameters into an analysis of bank stability, threshold of motion, hydraulic analysis (SRH-2D), and a meander belt assessment. References and links guiding the user to data sources for historical maps, elevation data, and aerial photos are readily available to counteract developments that may have shortened or straightened fish passage channels. WSDOT’s fish passage feature recommendations, depending on project site attributes, include meander bars, boulder features, and scour countermeasures. Fish passage improvement structures are discerned as roughened channel design, roughened rock ramp design, structure retrofit, or hydraulic culvert designs that mimic natural channel processes and facilitate unimpeded passage. A performance management process description provides project managers with guidance for the maintenance and upkeep of fish passage structures and features. In coordination with the Hydraulics Manual’s water crossings chapter, the pipe classifications and woody material chapters detail materials and design procedures that can positively affect migrating fish species and habitat connectivity.

The Hydraulics Manual provides protocols for a broad application to ensure efficiency and consistency of post-project monitoring processes for fish passage projects. It describes four types of monitoring: post-construction compliance inspection, Year-1 inspection, long-term evaluation, and additional monitoring. The first step WSDOT suggests is to collect historical information on the site, including permit drawings and as-builts. Suggested post-construction monitoring parameters are culvert or bridge span, culvert rise, culvert or bridge type, streambed mix, streambed shape, streambed slope, and other features identified in the design. The main purpose of Year-1 inspections is to assess the site after the first winter to evaluate the effects of higher seasonal flows at the structure. Specific metrics include streambed material, channel thalweg, channel location, channel width, and hydraulic drops.

Page 19 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	Fishway evaluation, miscellaneous obstruction, non-culvert crossing, and Level A and B culvert assessment field forms are available to evaluate the passability and condition of features detailed in the Fish Passage Inventory, Assessment, and Prioritization Manual (WDFW 2019). The methods described have been widely used since the late 1990s by WDFW, Tribes, local governments, the Salmon Recovery Funding Board, regional fisheries enhancement groups, and others. It should be noted that the methods provided are for assessing no-slope or hydraulic design culverts and are not set up to assess fish passage in-stream simulation AOP crossings. Example calculations are provided for the user to follow as are inspection and condition forms to assess the status of existing AOP structures. The manual describes a protocol similar to the one adopted by the Alaska Department of Fish and Game, breaking assessments into two levels of analysis. Similar to the Alaska approach, Level A analyses are typically assessed by biologists or interns and look at field-based metrics. Table 3.1 in the manual relates culvert characteristics to the % passage rate for aquatic species. Level B analyses build on the Level A analysis and are typically conducted by a hydraulic engineer. The Level B analysis assesses characteristics such as water depths and velocities during key fish passage flows and compares them to passability criteria developed for culverts. Passability criteria were developed for hydraulic designed culverts and therefore do not apply to AOP or stream-simulation crossings. In addition to barrier assessment, the manual provides criteria and metrics to assess the quality of habitat based on species present and characteristics such as substrate size, stream gradient, and in-stream cover. The manual also provides a fish passage priority index used to prioritize the sequence for which crossings are replaced to have the greatest benefits to fish.
West Virginia (WVDOT 2015)	The West Virginia DOT (WVDOT) Division of Highways, Engineering Division, Hydraulic and Drainage Unit Drainage Manual (WVDOT 2015) contains an Accommodating Aquatic Life Movements section. The directs manual projects to adhere to USACE Section 404, Nationwide Permit General Conditions for Aquatic Life Movements, so that no project activity may substantially disrupt the necessary life-cycle movements of aquatic life species indigenous to a waterbody, including migratory species. West Virginia Water Quality Certification Special Conditions for Nationwide Permit 14, Linear Transportation Projects, state that culvert barrels must be properly countersunk at the outlet to avoid impeding aquatic fish passage. Drainage guidelines state the designer must list aquatic organisms present within site boundaries and consider aquatic life movement if the stream supports aquatic life. Additional resources, including the FHWA Design for Fish Passage at Roadway-Stream Crossings: Synthesis Report (2007), are provided.
Wisconsin (WDNR and WisDOT 2021) (WisDOT 2024)	A memorandum of understanding on aquatic connectivity at road stream crossings (WDNR and WisDOT 2021) maintains a cooperative agreement between the Wisconsin DOT (WisDOT) and the Wisconsin Department of Natural Resources (WDNR) to formally recognize the importance of aquatic connectivity (ACONN) and provide economic and efficient transporting systems. The agreement states that evaluation for potential ACONN concerns and accommodations may apply to special waterway designations, wild rice waters, priority navigable waters, special natural resource interest areas, and areas containing the presence of endangered, threatened, or otherwise listed species.

Page 20 Bookmark

Suggested Citation: "2 Literature Review." National Academies of Sciences, Engineering, and Medicine. 2025. Design, Construction, and Monitoring Practices for Aquatic Organism Passage. Washington, DC: The National Academies Press. doi: 10.17226/29054.

State DOT Sources	Summary
	Per the Facilities Development Manual (WisDOT 2024), project engineers are directed to engage WDNR for a field review during the project scope phase for drainage facilities that may affect AOP. Project engineers are also directed to consult with the state drainage engineer for AOP coordination. Specific policy regarding the scope and design of projects that affect AOP is currently being authored.

State DOT
Sources

Summary

Per the Facilities Development Manual (WisDOT 2024), project engineers are directed to engage WDNR for a field review during the project scope phase for drainage facilities that may affect AOP. Project engineers are also directed to consult with the state drainage engineer for AOP coordination. Specific policy regarding the scope and design of projects that affect AOP is currently being authored.