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Trail Construction and Maintenance Notebook

Trails in Wet Areas (continued)

Improving Drainage

Although an area may appear perfectly flat, often it will have a slight gradient and flow of water. Drainage ditches and culverts can help ensure that water drains off the trail.

Generally, ditches are at least 300 mm (12 in) deep, have flat bottoms, and side slopes of 1:1. In many cases, the ditch can be extended beyond the wet area to capture water that might flow onto the trail (Figure 26).

Figure 26—Ditches are a simple and effective way to drain
wet areas. Slope angle and depth vary with soil and
water conditions.

The simplest way to get water across a trail is to cut a trench across it. These open-top cross drains (Figure 27) can be reinforced with rocks or treated timbers to help keep them from caving in. These structures are not usually a good alternative because people and stock stumble on them. One way to reduce this risk is to make the ditch wide enough, at least 600 mm (2 ft), so stock will step in it rather than over it (Figure 28).

Figure 27—Open-top cross drains of culverts are not
often chosen because they are a hazard to
livestock, hikers, and bikers.

Figure 28—Wide cross drain and causeway

An open drain can be filled with gravel. This is called a French drain. Start with larger pieces of rock and gravel at the bottom, topping off with smaller aggregate (Figure 29). French drains are often used to drain a spring or seep from under a trail bed.

Figure 29—Wrapping French drains with geotextile
helps prevent clogging. These are used to drain
low-flow springs and seeps.

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