When trails are located on primarily level terrain, water tends to pool on the trail tread. Building the trail surface slightly above grade allows water to move off the trail. Although this technique does increase initial construction costs, it decreases later maintenance expenses required to cope with pooled water and also provides a more convenient pathway for users during wet periods. Center crowning of the trail surface allows water to move to the sides of the trail. Hilly Terrain .
Erosion caused by water movement is a major concern when trails are built in hilly terrain.
Most such damage is caused by design and construction errors which allow water to build up volume and velocity. The key to reducing erosion created by water is to move the water off the trail surface as quickly as possible. This encourages water to flow perpendicular to, rather than along, the trail surface, thus directing the flow off the trail before erosion can occur. Section of a trail showing outsloped trail tread. This involves placing sections of logs 46 inches in diameter across the trail surface at a 300 angle.