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Stream Crossings

NYSDEC developed the stream crossings guidelines to promote natural stream conditions and to allow animals to move unrestricted while balancing transportation demands. Special considerations for the life requirements of invertebrates, fish, amphibians, reptiles, mammals, and birds have been considered while developing these guidelines. Depending on the project, additional engineering design may be necessary to ensure structural integrity and appropriate hydraulic capacity.

Continuity for Healthy Stream Ecosystems

Image of stream running through culvert
Photo by Scott Jackson

Streams are long, linear ecosystems that are uniquely vulnerable to fragmentation through the development of stream crossings, like bridges and culverts. Designing effective crossings to keep stream continuity is imperative to protect the core functions of these diverse ecosystems and the animals they support. Poorly designed stream crossings act as barriers to natural communities and they can affect the overall health of the stream and its connection to riparian and upland areas that comprise the greater stream ecosystem.

A species biological fitness - the ability to survive and produce viable offspring - can be negatively impacted by the design of a stream crossing. Throughout a species life, their success can be determined by certain factors, such as:

1. Natural Dispersal - Access to breeding, spawning, and nursery areas

Natural dispersal -- the movement of a species from their native area -- is critical to a ensure a healthy, productive environment. Dispersal is an important step to help restore a stream after it has been damaged by a major event, like flooding, severe drought, or pollution. Barriers and restrictions, like stream crossings, can prevent adult fish from traveling to spawning areas and offspring from dispersing into juvenile and adult habitat. Additionally, when animals are prevented from traveling in and along stream corridors, they may be subject to increased predation and mortalities. This reduces the overall chance to repopulate an area, which in turn can have impact on ecosystem health and services.

2. Optimal temperatures and oxygen levels - Access to coldwater habitats

During the summer, species such as brook trout travel to and congregate in cold water sections of streams and tributaries. If fish are prevented from reaching these areas, they can become susceptible to heat stress and mortality. Limited travel may also cause overcrowding, which can make fish vulnerable to disease and predators.

3. Good cover and access to feeding areas

Different habitats provide various feeding opportunities throughout a day or season and species regularly travel to take advantage of these resources. Restricting access to prime feeding areas can affect a variety of species.

4. Natural substrates

Poor crossing design and installation can result in degradation of natural substrates, which can adversely affect native plants and animals. In undersized crossings, high water velocities may scour natural substrates in and downstream of the crossing, resulting in habitat degradation for fish and other wildlife. The substrate in or under a crossing should match the natural substrate of the surrounding stream in order to maintain natural conditions.

5. Optimal hydrological conditions - water depth and flow

Inefficient stream crossings can alter the natural flow of a stream, which may have a serious impact on a species' fitness; fish and other aquatic organisms need sufficient water depth to move through a stream crossing.

  • Low flow can impede passage and may also lead to stagnant conditions within the crossing.
  • High flow caused by a constricted crossing can degrade wildlife habitat and weakens the structural integrity of a crossing overtime.
  • High water velocities and related flow alterations may also erode stream banks.

Recognizing Problems

Stream crossings should be properly sized, placed, and installed. They should be large enough to allow easy passage of fish, wildlife, and floods while preserving natural flows and velocities. Approved designs should contain an open bottom or be embedded into the stream bed so that substrate and water depth are similar to the surrounding stream.

Identifying poor crossing structures and installations is an important step in evaluating whether they should be fixed or replaced. The following types of crossings demonstrate common design flaws that can create barriers for fish and wildlife.

Undersized Crossings: Restrict natural flow, scouring and erosion, high flow velocities, clogging and ponding. Can cause water to backup - pond - in areas upstream of the crossing when clogged by woody debris, leaves, and other material or during seasonal high water and flood events. Clogging can occur year-round or may intensify the effect of floods and make a crossing impassable to wildlife. Ponding can also lead to property damage, road and bank erosion, and severe changes in upstream habitat. As a result, undersized crossings typically require frequent and costly maintenance.

undersized stream crossing

Shallow Crossings: Water depths are too low for many organisms to move through and the bottom may lack appropriate stream bed material.

Image of shallow crossing

Perched Crossings: Low flow, unnatural bed material, scouring and erosion, ponding. In perched culverts, scour pools often develop downstream of the culvert and eventually undercut the culvert and impede upstream passage.

Image of perched crossing

Double Culverts: Restriction of natural flow, clogging with debris, ponding and flooding.

picture of double culvert stream crossing

Stream Crossings: Guidelines and Best Management Practices

The following recommendations are to assist in designing, installing, and replacing stream crossings to protect stream continuity and to maintain healthy habitat for fish and wildlife. Structures should consider the pre-installation stream conditions and be thoughtfully designed and installed to retain the natural flow and substrate of the stream. Additional engineering may be necessary to ensure structural integrity and hydraulic capacity.

Types of Crossings, in descending order of preference:

  1. Bridges and open bottom box culverts
  2. Open bottom arch culverts
  3. Box culverts*
  4. Arch or elliptical/squash culverts*
  5. Circular culverts*

* Box and pipe culverts (#3-5), if used, must be installed level only in flat streambeds, where the slope is not steeper than 3% and be embedded to at least 20% of the culvert height at the downstream invert.

Design and Installation Recommendations:

  • Width of the crossing should be 1.25x the normal width of the streambed, measured bank to bank at ordinary high water level or to the edges of terrestrial, rooted vegetation. An average of three measurements is recommended to determine natural channel bed width: 1.) at project site, 2.) and 3.) straight sections upstream and downstream from the crossing. Additionally, the overall capacity needs to accommodate expected high flows to ensure stream continuity.

  • Side slopes should be as steep as possible without compromising stability to minimize the length of the culvert. Note: A side slope grade of 2:1 is typically the steepest that can be vegetated.
  • Installation should take place in the dry to facilitate construction and reduce effects of turbidity and sedimentation downstream. This may require piping or pumping the stream flow around the work area and the use of cofferdams. The duration of dewatering should be kept to a minimum and the flow downstream should be equal to that upstream from the work site.
  • Erosion and sediment control, such as rip rap, silt fencing and/or straw bales, and revegetation is important to limit disturbance to the streambed and banks.
    • Rip rap should be used as head wall protection to prevent scouring and erosion from high flows around the inlet and outlet of the culvert.
    • Silt fencing and/or straw bales, should be installed parallel to the stream to prevent downstream impacts and should be depicted on project plans.
    • Affected bank and bed areas should be restored to pre-project conditions following installation and banks should be revegetated with native plants and covered with mulch to accelerate plant growth.
  • Natural substrate used in the crossing should match those found up and downstream and resist displacement from natural flows and during levels of high water or floods. Metal and concrete are not appropriate materials for species that travel along the streambed.
  • Timing restrictions may be imposed to protect fish spawning. In general, instream work should occur during low flow conditions, typically between June and September, to minimize impacts to fish and water quality.
  • Maintenance of structures is recommended to be completed at least once annually, preferably before high spring flows.

Required DEC Permits for projects involving:

  • All streams with a classification of AA, A or B, or with a classification of C with a standard (T) or (TS). The Environmental Resource Mapper can be used to identify protected streams based on their classification and create simple maps needed as part of the permit application process.
  • All navigable waters.
  • NYSDEC regulated freshwater wetlands outside of the Adirondack Park.

Other Potential Permits

Adirondack Park Agency regulates wetlands within the park and may have jurisdiction on stream crossings within the park.
U.S. Army Corps of Engineers regulates activities involving dredging, excavation, placement of fill, or construction of certain structures in Waters of the United States.