Crossing Design

To maintain or restore the long-term viability of river and stream ecosystems, we must ensure that transportation systems are designed to protect habitat quality and ecosystem processes that maintain habitats and populations over time. When designing a road system, the first BMP is to carefully design the road system to minimize the number of river and stream crossings. Where crossings are necessary, a careful analysis of the area should be made so that they can be located away from sensitive areas (e.g. critical habitat, uncommon habitat types, areas particularly sensitive to disturbance). After minimizing the number of crossings and locating them away from sensitive areas, attention should be focused on the design of the crossing structure itself.

In order to preserve or restore all important elements of riverine ecosystems, crossing structures should be designed with the following objectives in mind:

Habitat quality: Avoid designs that will disrupt the natural hydraulic properties of the river or stream, and use of rip-rap or other armoring of channels or banks.

River and stream continuity: Maintain the continuity of the aquatic and benthic (stream bottom) elements of rivers and streams through the maintenance of appropriate substrates, water depths and flows. Provide appropriate bank-edge habitat for weak swimming and crawling animals.

Processes that maintain the channel and streambed: Maintain the natural slope of the stream bed and the capacity for sediment and woody debris to pass downstream through the crossing.

Fish and other aquatic organism passage: Facilitate movement for all fish species (including juvenile and relatively small resident fish) and other aquatic organisms such as amphibians, reptiles, and crayfish. Avoid physical barriers such as inlet or outlet drops, debris accumulation, weirs, baffles, or other structures that would block movement of aquatic organisms.

Wildlife passage: Facilitate movement of wildlife species including those primarily associated with river and stream ecosystems and others that may utilize riparian areas as movement corridors. Some species of wildlife, such as muskrat and stream salamanders, may benefit from the maintenance of river and stream continuity. Other species may require more open structures as well as dry passage along banks or within the streambed at low flow.

Hydraulic Design

The issues of road crossings and their effects on animal movement came to prominence because of the impact of passage barriers on migratory fish. Initially, the focus was on upstream passage of migratory fish, such as salmon and sea run trout. To allow fish passage, a culvert needed to meet certain specific hydraulic conditions (water depth, velocity, and turbulence) for target fish species. In the Pacific Northwest, many species migrate upstream during high flow periods. Therefore, a culvert could be designed by engineering it to meet specific standards for velocity, water depth, and turbulence at high flows.

Hydraulic culvert design can be an effective approach when designing for a small number of target species with similar requirements, and when the hydraulic requirements of those species are known. Some migratory fish are strong swimmers and good jumpers. Others, like sturgeons, may be capable of sustained movements, but are unable to leap over any but the smallest obstacles. Culverts that are designed by a hydraulic method to pass strong swimmers like salmon and trout are unlikely to accommodate smaller fish species, juvenile fish, and weak-swimming aquatic organisms that are important components of aquatic communities. We have reasonably good information on swimming performance for only a handful of fish species, unfortunately.

Because we lack specific information on the requirements of most aquatic organisms, hydraulic design is not particularly effective for facilitating movement for a broad range of species. Even if more information on swimming ability were available, hydraulic design for a diverse array of species would be a significant challenge. Species – and even different life stages within species – move at different times of the year, during different flow conditions. It would be impractical to design culverts to meet specific depth, velocity and turbulence requirements during high, low, and intermediate flow conditions.

Stream Simulation

An alternative to hydraulic design is to size and install culverts to avoid constricting the stream or river channel. Where they can be installed with the same slope as the natural streambed, non-constricting culverts will normally provide water depths, velocities, bottom substrates, and channel characteristics that are comparable to the natural stream. Well designed culverts can maintain the continuity of stream bottom and hydraulic conditions, thereby facilitating passage for aquatic organisms utilizing the stream.

Stream Simulation is an approach to culvert design that was developed in Washington State and is now being adapted for use elsewhere. It is a design process that both avoids flow constriction during normal conditions and creates a stream channel within culverts that resists scouring during flood events. Stream Simulation culverts are wider than the natural channel in order to simulate channel forming processes and the entire channel including margins and can be installed at the same slope or at slightly steeper slopes than the natural stream. Construction of a channel within the culvert insures adequate water depth during low-flow conditions. Particular attention is paid to construction of the streambed within the culvert, using bed material that interacts with the stream as a natural bed.

Designing culverts to avoid channel constriction and maintain appropriate channel conditions within the structure is an effective approach for accommodating the normal movements of aquatic organisms and preserving (or restoring) ecosystem processes that maintain habitats and aquatic animal populations. Where passage for riparian and terrestrial wildlife is desired, stream simulation structures should be adapted to meet minimum height and openness requirements.

MA Crossing Standards

The Massachusetts River and Stream Crossing Standards were developed by the River and Stream Continuity Partnership with input from an Advisory Committee that included representatives from UMass Amherst, MA Riverways Program (nos Mass DER), Massachusetts Watershed Initiative, Trout Unlimited, The Nature Conservancy, the Westfield River Watershed Association, ENSR International, the Massachusetts Highway Department, and the Massachusetts Departments of Environmental Protection and Conservation and Recreation.

In developing the standards, the Partnership received advice from a Technical Advisory Committee that included representatives of the US Fish and Wildlife Service, USGS BRD, US EPA, US Army Corps of Engineers, MA Division of Fisheries and Wildlife, American Rivers, Connecticut River Watershed Council, Connecticut DEP, a hydraulic engineering consultant, as well as input from people with expertise in Stream Simulation approaches to crossing design. The standards are intended to serve as recommended standards for permanent crossings (highways, railways, roads, driveways, bike paths, etc.) on fish-bearing streams and rivers, and as guidelines for upgrading existing crossings when possible. These standards seek to achieve, to varying degrees, three goals:

Fish and other Aquatic Organism Passage: Facilitate movement for fish and other aquatic organisms, including relatively small, resident fish, aquatic amphibians & reptiles, and large invertebrates (e.g. crayfish, mussels).
River/stream continuity: Maintain continuity of the aquatic and benthic elements of river and stream ecosystems, generally through maintenance of appropriate substrates and hydraulic characteristics (water depths, turbulence, velocities, and flow patterns). Maintenance of river and stream continuity is the most practical strategy for facilitating movement of small, benthic organisms as well as larger, but weak-swimming species such as salamanders and crayfish.
Wildlife Passage: Facilitate movement of wildlife species including those primarily associated with river and stream ecosystems and others that may utilize riparian areas as movement corridors. Some species of wildlife such as muskrats and stream salamanders may benefit from river and stream continuity. Other species may require more open structures as well as dry passage along the banks or within the streambed at low flow.

These Crossing Standards adopt a “Stream Simulation” approach for crossing design in order to better protect river and stream ecosystems. Stream Simulation is a design approach that avoids flow constriction during normal conditions and creates a stream channel that maintains the diversity and complexity of the streambed through the crossing. Crossing structures that avoid channel constriction and maintain appropriate channel conditions (channel dimensions, banks, bed, and bed forms) within the structure should be able to accommodate most of the normal movements of aquatic organisms, and preserve (or restore) many ecosystem processes that maintain habitats and aquatic animal populations. The goal is to create crossings that present no more of an obstacle to movement than the natural channel and that are essentially “invisible” to aquatic organisms.

These guidelines are for general use to address issues of river and stream continuity, fish passage and wildlife movement. In some cases, site constraints may make strict adherence to the standards impractical or undesirable. For example, in some situations the road layout and surrounding landscape may make it impossible or impractical to achieve the recommended standards for height and openness. These standards may not be appropriate for highly degraded streams where stream instability may be a serious concern. Site-specific information and good professional judgment should always be used to develop crossing designs that are both practical and effective.

Here are some important considerations to keep in mind when using these standards.

They are intended for permanent river and stream crossings. They are not intended for temporary crossings such as skid roads and temporary logging roads.
They are generally intended for fish-bearing streams. However, these standards may be useful in areas where fish are not present but where protection of salamanders or other local wildlife species is desired. Further, the standards are not intended for drainage systems designed primarily for the conveyance of storm water.
These standards were developed with the objective of facilitating fish and wildlife movement and the preservation or restoration of river/stream continuity. They may not be sufficient to address drainage or flood control issues that must also be considered during design and permitting of permanent stream crossings.
These standards are not prescriptive. They are intended as conceptual performance standards for river and stream crossings. They establish minimum criteria that are generally necessary to facilitate fish and wildlife movement and maintain river/stream continuity. Use of these standards alone will not satisfy the need for proper engineering and design. In particular, appropriate engineering is required to ensure that structures are sized and designed to provide adequate capacity (to pass various flood flows) and stability (bed, bed forms, footings and abutments).
The design of any structure must consider the channel type and long profile and must account for likely variability of the stream or river for the life of the structure.
In urbanizing environments there is greater potential for land use changes to result in stream instability. Wherever there is potential for stream instability it is important to evaluate stream adjustment potential at the crossing location and to factor this into the design of the structure.

Click on the following link to download a copy of the Massachusetts River and Stream Crossing Standards.

Massachusetts River and Stream Crossing Standards