Naturalizing Abandoned Trails (continued)

Check Dams

Check dams are used on pieces of abandoned, trenched tread to arrest further erosion and to hold material placed during site restoration. Sometimes check dams are appropriate for trails in active use. Check dams are intended to slow and hold surface water long enough to deposit transported sediment. They should be used with drainage structures to reduce overall erosion from the abandoned tread (Figure 74).

Figure 74—Check dams or retainer bars allow
soil to rebuild on eroded trails.

Check dams are best used as holding structures for fill used to recontour the old tread. The material used in the dam should be seated in an excavated footing that extends into the sides of the trench. As material behind the dam naturally builds up, successive levels can be added to the dam with enough batter to offer stability against the pressure of the fill. The top of the dam should be level or slightly higher than the trench walls. For watertightness, chinking and tamped fill should be used to complete the uphill face of the dam. Fill is then added behind the dam to finish the process. It generally takes a long time for these trenches to fill up. Most never do. If they do, add fill below the dam to finish the process.

Spacing between dams depends on the steepness of the old grade and the degree of restoration desired. If the check dam is intended only to slow down erosion, then relatively wide spacing is sufficient (every 20 m (65 ft) on a 25-percent grade). If the intent is for half of the old trench to be filled back in, the bottom of each dam should be level with the top of the next lower dam. On steeper grades the dams need to be closer together. If the intent is to approach complete recontouring of the trench, the dams should be closer still, especially on grades above 25 percent. A point of diminishing returns is reached on grades above 40 percent. Check dams would have to be built right on top of each other to retain soil at the full depth of the trench.

Revegetation

Revegetation can be accomplished passively or actively. Passive revegetation allows surrounding vegetation to colonize the abandoned trail. This works when erosion has been stopped, adequate precipitation occurs, and adjacent vegetation spreads and grows rapidly. Active revegetation ranges from transplanting onsite vegetation to importing genetically appropriate seed or propagated plants. Successful revegetation almost never happens in a single season. Plan carefully for best results.

There are no cookbook answers for returning abandoned trails to their natural condition. Each site should be evaluated for its potential to regrow and heal. On sites that are moist and relatively flat, it may be possible to block off the trail and allow rehabilitation to proceed naturally. Dry, steep sites will take a lot of work.

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