Installation of Stream Crossings
NOTE: Stream Channel Alteration Permit required.
- Minimize stream channel disturbances and related sediment problems during road construction and stream crossing structure installation.
- Time construction activities to protect fisheries and water quality.
- Do not place erodible material into stream channels. Remove stockpiled material from high water zones.
- Locate temporary construction bypass roads in locations where the stream course will have minimal disturbance.
- When using culverts to cross small streams, install those culverts to conform to the natural stream bed and slope on all perennial streams and on intermittent streams that support fish or that provide seasonal fish passage.
- Place culverts slightly below normal stream grade to avoid culvert outfall barriers. Do not alter stream channels upstream from culverts, unless necessary to protect fill or to prevent culvert blockage.
- Install culverts to prevent erosion of fill. Compact the fill material to prevent seepage and failure. Armor the inlet and/or outlet with rock or other suitable material where needed.
- Consider dewatering stream crossing sites during culvert installation.
- Use I foot minimum cover for culverts 18 to 36 inches in diameter, and a cover of one-third diameter for larger culverts to prevent crushing by traffic.
Construction of stream crossings has the greatest potential to cause immediate sediment pollution. Complete the work as fast as possible during a time of year when the least damage can occur. This photo sequence shows a typical culvert installation.
The temporary channel in the foreground carries stream water. The dewatered stream channel is being cleared for the culvert foundation and trench walls must be free of logs, stumps, limbs, or rocks that could damage the pipe.
The culvert bed is graded to the appropriate slope to conform with the natural stream bed. The bed is either rock-free soil or gravel. Bedding should provide even distribution of the load over the length of the pipe.
Alignment is critical for the culvert to function properly. Culverts set at an angle to the channel can cause bank erosion. Skewed culverts can develop debris problems. Culvert alignment must fit the natural stream channel.
Place culvert slightly below the natural streambed. Water should drop slightly as it enters the culvert. The natural rock bed of this stream serves to control water velocity and protect the culvert as water enters the Inlet.
Start to backfill over one end of the culvert. Then cover the other end. Backfill material must be free of limbs, rocks, and other debris that could dent the pipe or allow water to seep around the culvert.
Once the ends are secured by backfill, the center is covered. Pour backfill material over the to of the pipe. This allows finer soil particles to flow around under culvert sides. Larger particles roll to the outside. Fine soil particles close to the culvert compact more easily.
Closing Statement BMP's
The need to safeguard the future of our water resource is essential. With the cooperation of all forest users, and the application of the information on these pages, we can protect the water quality of Idaho's forestlands.
Please be aware the BMP's can and probably will change. Our knowledge of the forest will increase over time. Forest managers will have new techniques, new equipment, and different needs. To help you keep up to date with BMP changes, Idaho's BMP education program includes workshops, videos, and literature. You are encouraged to participate in this program.
Thank you for doing your best to put BMP's to work in the forest.
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