Stream crossings represent the point at which a forest road or skid trail comes in contact with a waterbody. Consequently, some type of planned crossing is necessary to protect water quality. Careful consideration should be given to determining the type of crossing to be used, and in constructing the project. The principal objectives of a stream crossing are to provide a dry surface crossing even during periods of stormflow, and to provide adequate conveyance of flow beneath the road fill so that impounding of flow does not occur. BMPs for stream crossings are provided below.
BMPs for Stream Crossings
In General
- Minimize the number of crossings on a given stream, and cross streams perpendicular to the flow at the most narrow section. This minimizes the area of disturbance and simplifies construction.
- Any erodible fill material or other areas normally exposed to flowing water should be stabilized with rip-rap, vegetation or other appropriate material following construction.
- Avoid planning construction of crossings for wet periods - avoid construction during high water conditions.
Culverts
The use of a culvert is the most common method for constructing stream crossings associated with forestry activities. Culverts are well suited for crossing both perennial and intermittent streams as well as other wet areas. However, several other types of stream crossings are also well suited for forestry related stream crossings under certain conditions.
- Place culverts in a section of the stream channel that is relatively straight and free from curves, meandering or major obstructions.
- Place the bottom of the culvert at the same elevation as the bottom of the stream, and at approximately the same slope.
- Keep the height of the entire structure (culvert plus fill) as low as possible to reduce the potential for impounding large areas of water.
- Use a culvert diameter that is sufficient to carry the normal flow expected. Culvert sizing for permanent installations should be based on the size and nature of the stream channel being crossed, or on the size and nature of the watershed above the crossing. Appendix 9 provides two possible methods for determining culvert diameter.
- When crossing broad channels or wetlands, several small culverts, spaced
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