If you’ve ever driven down a forest road, you’ve probably seen those wide spots along the road that look like places to pull over. In many cases, those are ‘ditch-outs,’ a road building technique to protect nearby streams and wetlands while helping roadside ditches to drain properly.
Well-constructed ditches are key to proper drainage of forest roads. Washington State’s forest practices rules are designed to reduce the chances that these roads–installed to access forest resources, such as timber–will cause harmful erosion or other damage to nearby streams and wetlands. The rules describe how to build ditches along roads so that water will collect there before flowing to the forest floor or other vegetated areas.
Ditch-outs or relief culverts at regular intervals can keep ditches from overflowing. Relief culverts allow ditch water to move under a road and onto the forest floor. When the terrain allows the ditch water to be drained away from the road on the same side the ditch is on, it’s wise to use a ‘ditch-out.’
You’ll see ditch-outs most often on ridge tops and switchbacks. Ditch-outs should not be used where they would allow water to drain toward an unstable slope or directly into a stream or wetland where it could bring sediment that might harm fish or other species living in the stream.
See an overview of about these and other important rules for forestry and other forest practices in DNR’s Forest Practices Illustrated.
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