Tread (continued)

What causes tread creep? The answer is simple. Most livestock, two–wheeled traffic, and some people have a natural tendency to walk the outside edges of sidehill trails. Sloughing makes the edge the flattest place to walk. As the tread moves downhill, it also narrows, with the result that more traffic travels closer to the outer edge. Other causes of tread creep are constructing a trail that is too narrow or with cutslopes that are too steep. Your job is to bring the trail back uphill to its original location and keep it there (Figure 15).

Figure 15—Tread creep at work—
sloughing and soft fillslopes.

One of the best ways to do this is to take advantage of large stationary objects (guide structures) to prevent animals and people from walking the edge. Trees, log ends, rocks, and stumps left close to the downhill edge of the trail will keep animals walking closer to the middle. Guide structures should be no more than 500 mm (1 ft) high so they will not catch animals' packs.

Curb rocks need to be well anchored, and they should be placed at random distances so they don't look like a wall or trap water on the tread.

Tread between these anchors will creep downhill creating a situation where the trail climbs over every tread anchor and descends again. At the bottom of these "dips," water and sediment collect. This is the weakest portion of the tread and the most prone to catastrophic failure. The tread can be so soft that packstock may punch completely through the tread (called a step–through) or bicycles or dirt bikes may collapse the edge. The result can be a bad wreck.

Where soil is in short supply, you may have to install a short crib wall and haul in tread material. Thin tread on bedrock will not usually stay put without some support. If normal slough removal does not work on more substantial soils, the tread should be benched back into the slope in the original alignment. Guide structures should be installed on the outside edge of the tread to keep traffic toward the center.

A note on guide structures: If you use a rock, be sure it is big enough that at least one–third of it may be buried (so people and bears won't roll it away) and it will still be obtrusive enough that hikers and horses won't walk over it (Figure 16). Log ends should be sawed back at an angle if the top edge of the log is more than 500 mm (20 in) above the tread. If you have really substantial berm to remove, leave 1–m (3–ft) long portions at 3– to 5–m (10– to 15–ft) intervals with the ends feathered into the fillslope to serve as guide structures.

Figure 16—Guide rock properly installed
to help prevent tread creep.

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