Stream Crossings

NYSDEC developed stream crossings guidelines to promote natural stream conditions and to allow animals to move unrestricted while balancing transportation demands. These guidelines have been incorporated into DEC’s Technical Guidance for the Review of Bridge and Culvert Projects in Nontidal Waters which further describes minimum design requirements and other considerations of the DEC, Division of Fish and Wildlife (DFW) during review of bridge and culvert projects requiring Protection of Waters permits. The guidance describes standards for maintaining stream continuity and reducing flood risk associated with bridge and culvert projects on regulated waters

Continuity for Healthy Stream Ecosystems

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:

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, cause scouring and erosion, high flow velocities, clogging and ponding. Can cause water to backup - pond - in areas upstream of the crossing when the structure is 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.

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

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.

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

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 Crossing structures, in descending order of preference:

1. Bridges and open bottom box culverts
2. Open bottom arch culverts
3. Four-sided box structures, arches with flat bottom (i.e., embedded floor)*
4. Elliptical/squash culverts*
5. Round culvert pipes*

* 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 or active channel, measured bank to bank at ordinary high water level or to the edges of terrestrial, rooted vegetation. An average of three measurements taken from an undisturbed section of the stream is recommended to determine natural channel bed width. 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.

Bridge and Culvert Technical Guidance

Technical Guidance for the Review of Bridge and Culvert Projects in Nontidal Waters Requiring a Protection of Waters Permit and a Water Quality Certificate (December 2024) (PDF) - DEC’s Division of Fish and Wildlife developed this Guidance with input from key agency personnel and various stakeholders. It provides additional details regarding the above guidelines and recommendations and is intended for Department staff involved with project permitting as well as to assist permit applicants. This Guidance has been developed to:

• Clarify DEC’s stream crossing guidelines described on this webpage and clarify permit issuance standards used by staff;
  • Incorporate climate change considerations into issuance of DEC permits as required by CRRA and CP-49; and
  • Promote and encourage statewide consistency and efficiency with both DEC staff and the regulated community.

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.