Trails in Wet Areas

• Improving Drainage
• Geosynthetics
• Turnpikes
• Causeways
• Puncheon
• Subsurface Puncheon

Very few critters like to get their feet wet. There are a few exceptions, of course. Otters, beavers, goofy retriever dogs, motorcyclists, and most young children like to jump right in. But the rest of us—horses, llamas, and stodgy adult hikers—will often go to great lengths to avoid getting our feet wet or going for an unplanned swim. This section deals with a range of options for getting trail traffic from one side of wet ground to the other.

Because nearly every technique for fixing trails in boggy areas is expensive and needs to be repeated periodically, relocating the problem section of trail should be considered first. Scouting for suitable places to relocate trails and reviewing soil maps will be time well spent. The alternative route should bypass extensive boggy areas, be on a slope for better drainage, and have mineral rather than organic soil for its tread. Don't reroute a problem section of trail to another boggy piece of ground. If you do, the result will be two problem sections instead of one.

Sometimes, improved drainage will cure the problem. If so, this is a much less costly solution than other alternatives. Placing stepping stones is another technique for crossing bogs and streams. Stepping stones should be large, fairly flat on top, and partially buried in the streambed. Space the stones for the average stride, remembering that trails are for kids, too. It shouldn't be necessary to jump from stone to stone.

Moving up in cost and complexity, two types of structures—turn–pike and puncheon—are commonly constructed to provide dry trails through wet or boggy areas. Using geosynthetics in combination with these techniques can often result in a better tread with less fill. Rock and fill causeways are popular in some areas where hardened trails are needed to cross fragile alpine meadows.

In situations where long spans are needed high above the ground, or for crossing streams, a trail bridge is usually needed instead of puncheon. Bridges require special designs fitted to each application. Engineering approval is needed before constructing either a standard or special design bridge.

Boardwalks are common in some parts of the country, particularly parts of Alaska and in the Southeast. These can range from fairly simple structures placed on boggy surfaces, to elevated boardwalks over marshes or lake shores, as are sometimes found at interpretive centers (Figure 25).

Figure 25—This boardwalk relies on pilings for
support. Helical earth anchors can also support the structure.

Let's look at some of these alternatives in more detail.

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.

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