Surface Water Control

• Grade Dips
• Waterbars
• Maintaining the Drain
• Ponding

Diverting surface water off the trail should be near the top of your list of priorities. Running water erodes tread and support structures and can even lead to loss of the trail itself. Standing water often results in soft boggy tread or tread and support structure failure. Water is wonderful stuff—just keep it off the trail.

The very best drainage structures are those designed and installed during the original construction. These include outsloping the tread and grade dips. We've already discussed outsloping. Let's move on to the next best drainage choice, grade or drain dips. The classic mark of good drainage is that it is self maintaining, requiring minimal care.

Grade Dips

The best grade dips are designed and built during the original construction. These are also called terrain dips, Coweeta dips, and swales. Other versions, often called rolling grade dips, or drain dips, can be built on most sidehill trails or constructed to replace waterbars. The basic idea is to use a reversal in grade to force water off the trail without the need for any other structure.

Terrain dips use grade reversal to take advantage of natural dips in the trail. These need to be planned into the trail when it is first laid out. The grade of the trail is reversed for about 3 to 5 m (10 to 15 ft), then "rolled" back over to resume the descent. A trail that lies lightly on the land will take advantage of each local drainage to remove water from the tread (Figure 18) as the trail winds around trees and rocks. The terrain dip, which uses existing terrain as the control point for the grade reversal, is a natural part of the landscape.

Figure 18—Grade dips are much more effective than
waterbars and require less maintenance. Along with
outsloping, they are the drainage structure of choice.

The beauty of terrain dips is that water collected from the hillside is not intercepted and carried by the tread. These grade dips are the most unobtrusive of all drainage structures if constructed with smooth grade transitions, and they require very little maintenance. Be sure to protect the drain outlet by placing guide structures along the lower edge of the tread above or below the outlet.

 E-mail: wo_mtdc_webmaster@fs.fed.us