US Department of Agriculture, USDA Forest Service, Technology and Development Program Banner with Logos.
Images from various aspects of the T&D Program.
HomeAbout T&DT&D PubsT&D NewsProgram AreasHelpContact Us
  T&D > T&D Pubs > Trail Construction and Maintenance Notebook T&D Publications Header

Trail Construction and Maintenance Notebook

Natural Forces at Work

Nature will have the last word. It's best to consider natural forces before moving dirt.

Dirt, Water, and Gravity

Dirt, water, and gravity are what trail work is all about. Dirt is your trail's support. Terra firma makes getting from point A to point B possible. 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 (figure 8).

Photo of a trail on a hillside that has been eroded by water.
Figure 8—Water and gravity join forces to
erode trail tread.

It's much more important to understand how the forces of water and gravity combine to move dirt than it is to actually dig dirt. If you put in many years building trails, you will see hundreds of examples of trails built with little understanding of the forces at hand. You will save time, money, and your sanity if you get grounded in the basic physics.

Water in the erode mode strips tread surface, undercuts support structures, and blasts apart fill on its way downhill. The amount of damage depends on the amount of water involved and how fast it is moving.

Water has carrying capacity. More water can carry more dirt. Faster water can carry even more dirt. You need to keep water from running down the trail! When and where you can do that determines the sort of water control or drainage structure you use.

Signs of Success

You have mastered dirt, water, and gravity when you can:

  • Keep surface water from running down the trail.
  • Keep tread material on the trail and keep it well drained.

Water also can affect soil strength. While the general rule of thumb is that drier soils are stronger (more cohesive) than saturated soils, fine, dry soils may blow away. The best trail workers can identify basic soils in their area and know their wet, dry, and wear properties. They also know plant indicators that tell them about the underlying soil and drainage.

Critter Effects

Gravity has a partner—the critter. Critters include packstock, pocket gophers, humans, bears, elk, deer, cows, and sheep. Critters burrow through the tread, walk around the designated (but inconvenient) tread, tightrope walk the downhill edge of the tread, shortcut the tread, roll rocks on the tread, chew up the tread, or uproot the tread.

Gravity waits in glee for critters to loosen up more soil. If you recognize potential critter effects (especially from humans, deer, elk, domestic livestock, and packstock), you can beat the system for awhile and hang onto that dirt:

  • Don't build switchbacks across a ridge or other major "game route."
  • Don't let tread obstacles like bogs or deeply trenched tread develop.
  • Make it inconvenient for packstock to walk the outer edge of your tread.

Your trail strategies are only as good as your understanding of the critter's mind.