< Erosion Control
Erosion Control

Preservation of the treadway is the most important task of the volunteer overseer. Trails that are allowed to erode, widen, and braid (the formation of multiple paths) not only are an eyesore in a pristine environment, but require substantial resources to repair or re-route. Most erosion can be minimized by good maintenance techniques (vegetation control, removal of obstacles, and the construction and care of water diversion devices). New maintainers are encouraged to attend an overseer workshop (or to work with an established trail crew), in order to learn these techniques.

Trails in Shenandoah National Park are typically either "sidehill" trails or routes that follow ridges and/or old road beds. Both types have specific erosion problems. Sidehill trails (routes that have been cut across the slope of the mountain) tend to "slip" over time, usually as a result of hikers following the outer edge of the path, in order to avoid obstacles, weeds, etc. As the trail widens and moves downhill, further erosion is encouraged (particularly when the path slips over cribwalls and downhill from waterbars and checkdams). Flat trails (routes that were built without the benefit of sidehill-style outsloping) become natural drainage paths and may channel heavy flows of run-off, following rain storms or snowmelt.


In order to prevent these problems, trail overseers construct and maintain erosion control devices, principally watebars, grade dips and check dams. Overseers should plan on visiting their trail sections at least twice a year to maintain erosion control devices. "Cleaning" waterbars is critical to ensure that they remain functional (and don't add to the erosion problem). For a complete discussion of waterbar/checkdam construction, refer to one of the books or videos available on the Resources page.

The following information is from the Trails Standards section of the PATC/SNP General Agreement:

Trail Tread (Erosion Control and Prevention)

Objective: Maintain or restore a trail tread (the footpath surface) which is safe for users and prevents the deterioration of the trail resources.

All maintenance activity expected to occur outside of the original footpath and associated water control features must have park-wide project clearance completed and approved. Use of natural materials is required in trail construction work; use of dimension lumber is discouraged and use of pressure-treated or creosote-treated lumber is not permitted.

General Standards:

  • Install grade dips or install waterbars on all slopes at a frequency sufficient to eliminate water from the trail before erosion occurs.
  • Install checkdams in badly eroded trails to retain sediment and restore tread. Checkdams are less effective than waterbars.
  • Keep culverts clear of silt and organic debris
  • Clear debris from streams downstream from trail crossing (to prevent damming and flooding on the trail).
  • Dig channels for small streams and channels for streams to cross the trail without travelling along the trail.
  • Remove accumulated silt and organic debris from waterbars in spring or when needed.
  • Remove loose stone and other debris which could cause hikers to trip or twist an ankle.
  • Discourage shortcutting of switchbacks by blocking shortcuts with branches and other debris. Heavy materials such as stumps or rocks might be used so that people do not remove them.

Standards for low-use Wilderness and Non-wilderness Blue-blazed trails

  • Annual maintenance may be sufficient; sections with unusual problems may require additional maintenance. The prevention of resource damage (erosion) should dictate the frequency of maintenance, with minimal amount of work.

Standards for moderate-use and high-use Wilderness and Non-wilderness Blue-blazed trails and for the Appalachian Trail

  • All waterbars should be cleaned and restored at least once each year due to erosion damage and wear from heavy foot.

Techniques:

  • Waterbar construction
    • Choose locations along the trail which naturally tend to allow water to run off the trail such as turns in the trail. Restore old waterbars if possible. Place waterbars near the top of a slope to prevent water from gaining momentum.
    • Construct a waterbar by digging a shallow trench at a 30-40 degree angle from the perpendicular of the trail and placing in it 10-12" rocks or a log. Strip bark from logs to slow rotting and use hardwoods like black locust. (Do not cut standing trees for this material!) Rocks or logs should protrude about 6" above the level of the tread on the downhill side (use a 10" to 12" diameter log). Cover rocks with small rocks and soil to create a mound. Secure logs with wooden stakes (natural stakes are preferable) or rocks on the downhill side. Cover stakes or rocks with soil and compact well. Another alternative is to construct a waterbar with well packed soil alone.
    • Slope the trail above the bar gently toward the bar to create a broad trench. The lowest point of the trench should be at the bar and should be below the level of the trail tread on the downhill side. Do not expose so much of the downhill side of the waterbar that it becomes undermined by erosion.
    • The waterbar should extend past the tread on both sides of the trail
    • The trench should extend beyond the waterbar and should be fanned out to assure that water is adequately dispersed and does not return to the trail
    • Drainage ditches alongside the trail may be used to move water to a suitable location for drainage away from the trail.
    • Compact waterbars well so that use will not damage them. Do not leave protruding rocks or stakes which could trip a hiker.
    • Fallen logs laying directly on the ground and which can be easily stepped over make good waterbars and checkdams.
  • Checkdam construction:
    • Where a drainage waterbar cannot be constructed due to high berms on both sides of the trail, construct a simple wood or rock dam perpendicular to the trail to collect silt and debris washing down the trail. Construction should be substantial enough to prevent hikers stepping on the dam from breaking it down.
    • When the area behind the dam is full, build another dam further down the slope.
  • Waterbar maintenance:
    • Remove all loose material from the trench; clear trench outside of tread to allow water to move away from the trail.
    • Dig or scoop out accumulated silt from the trench; put all accumulated soil on the backside of the waterbar. Do not throw the soil to the side of the trail. Soil is a precious commodity as evidenced by eroded trails. The bottom of the trench next to the bar should be slightly below the level of the tread on the downhill side of the bar.
    • If necessary, rebuild or repair the bar itself.
  • Obtaining tread material:
    • The following are good sources for tread fill material:
      • Deposited material from up-trail erosion (ie., waterbars, checkdams).
      • Material from the footpath.
      • Material may also be pulled from the banks or berms of the footpath area.
    • The source for tread material needs beyond the above must be approved by park staff. Borrow pits are not to be dug. Any disturbance of the soil beyond the trail tread, berms, and associated water control features itself must have project clearance.
  • Equipment:
    • Pick mattock, cutter-mattock, or Pulaski
    • Shovel,
    • Ax,
    • Saw,
    • Fire rake or McCleod.
  • New Trail Construction or Relocations
    • All proposed new trail constructions or relocations must be approved by the Superintendent and are subject to project clearance. Project clearance must be obtained anytime the soil is to be disturbed outside of the existing trail tread, berms, and associated water control structures. Any trail relocations and new trails are to be constructed in a manner promoting hiker safety and resource protection. No new trails will be constructed within designated Wilderness.

SEE ALSO: PATC OVERSEER'S MANUAL AND HOW TO BUILD A LOG WATERBAR