November 28, 2012

Trail Science 102: Keeping water off the tread

“The whole point of trail work is to get dirt where you want it and to keep it there. Water is the most powerful stuff in your world. Gravity is water's partner in crime. Their mission is to take your precious dirt to the ocean. The whole point of trail work is to keep your trail out of water's grip.” – Trail Construction and Maintenance Notebook
Trail with water
Trail with water (Photo credit: Wikipedia)

So, water is the great nemesis of trail development and preservation. Two ways to keep water off a trail are frequent grade reversals and outsloping the entire tread.

Water flows down a hill in sheets, referred to as sheet flow. To keep these sheets crossing the tread of a trail without puddling or running down the length of the trail, frequent grade reversals are needed. This simply means that a will designed trail should have its ups and downs. According to the forest service, a trail should have frequent grade reversals that extend for 10-15 feet.

An outsloped tread is one that is lower on the downhill side of the trail than it is on the inside or bankside. Outsloping lets water sheet across the trail naturally. A trail’s tread should be outsloped at least 5 percent, but not so much that it is awkward to walk on. Maintaining a trail’s outslope is key to keeping water from puddling.

Next: Tread

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