RECREATIONAL TRAILS: EROSION CONTROL DESIGN/REPAIR TECHNIQUES
AND RATIONALE FOR SINGLE-USE TRAILS
Suzanne Mittenthal, Ph.D.

A. SINGLE-USE TRAILS SERVE USERS MOST EFFICIENTLY.
     At present, the nation's trails aren't being used, they're being used up! Trail conditions are deteriorating in public forests all over the U.S. Conflicts between users are erupting, as use levels on the nation's park and forest back country trails exploded in the last century. Management has been on a laissez-faire basis, with historically little or no maintenance. A multiple-use management policy allowing high-impact users such as horseback, mountain bike, and ATV riders on most trails has caused widespread damage on a majority of trails.
     Impact (consumption) varies greatly according to user type. Hiking has the lowest impact of all uses, is the least "consumptive" or erosive of soil and trail surface, and serves the greatest number of users with the least maintenance cost. Mountain bike use has much higher impact: bike wheels leave a continuous track and dig deep when ascending or braking, and bikers tend to go around protruding stone or wood water diversion devices in their desire to speed down trails. Horses dig divots in all but the hardest surfaces, creating deep pock-marking in wet weather. Except on rock, horses pulverize tough, dry surfaces, which turn to mud when wet. Horses add pollution in the form of wastes and alien seeds--and hikers are asked to "leave no trace." Horse trails are very high maintenance (Boone).
     User conflicts are inevitable as a result of crowding and the growing awareness that the high-impact users are the source of the destruction. They are not just the result of user antipathy. Lack of maintenance and non-separation of users results in deflection of dissatisfaction to users from managers, who really bear the responsibility for degraded conditions.
     User groups have different, incompatible, goals for use of forest trails.
· Bike users: physical challenge, aerobic workout, and thrill of a sport, in a natural setting. Eroded trails can be considered part of the challenge (Bjorkman).
· Horse users: enjoyment of riding, Western culture, natural setting for the sport. Eroded trails can be considered part of the culture, may not interfere with the view from the horse.
· Hikers: require a more direct, close-up interface with nature, experience the forest for its own sake; bad trails ruin the experience, impede their progress, or actually endanger them.
     Asymmetry of Aggravation Principle Mandates Single-Use Trails: High-impact users aggravate all, but are harmed by none; low-impact users aggravate none, but are harmed by all. ATVs destroy trail surfaces and forest peace for all other users. Multiple-use trails unfairly impact hikers, destroying the footbed and vegetation close to the trail. With hikers' goals unattained; they are accused of being selfish if they complain or ask for single-use trails.
     An outcomes-based approach to trail management must be taken. Campaigns to "educate" users to accommodate to deteriorating trail conditions and declarations that "multiple-use"--one size fits all--trails should satisfy all users are not sufficient. Proper maintenance of high-impact sport trails is expensive, and requires regular maintenance. Horse and bike miles should be reduced to the number of sustainable trail miles. Managers have a responsibility to provide users access to trails only if they are able to protect the resource and not diminish other users' enjoyment. Wider, hardened trails, usually requiring machine maintenance, are treatments that distance hikers from the natural experience. For these reasons, single-use trails are the only justifiable management plan.

B. APPROACH TO COST-BENEFIT ANALYSIS OF TRAIL PROBLEMS
     Recreational trail planners and users must acknowledge the different needs and trail installation and maintenance costs of the three user groups: hiker, horseback rider, and biker.
1. Analyze the Source of Trail Problems.
     · Effects of specific users
     · Poor design: too-steep grades? improper drainage?
     · Lack of maintenance
2. Assess Amount of Use: Numbers, Types, Trips/Hours.
3. Identify Cost of Maintenance Per Mile Per User for Each Type of Use and Impact.
4. Analyze the Function of Each Trail in the System.
     · Determine which trails receive highest use from each user group. "L.A.C." teams are useful for making political decisions, but are not appropriate for this evaluation of trail functions. Some may serve as "access" routes to destinations for all groups, and require overlapping "multi-use" for some distance.
5. Develop a Cost-Benefit-Based Rehabilitation and Maintenance Plan.
     · Allocate trails to single-use systems, on basis of function survey, condition, and cost of expected repairs and maintenance.
     · Ensure that methods adopted suit both terrain and users; this requires surveillance and feedback. Using gravel on trails that users (horses) won't walk on is counterproductive.
     · Repair existing trails before destruction is irreversible; close trails if necessary until repaired.
     · Stop practice of abandoning ruined trails; this sets wrong example and encourages development of additional user trails. Limiting miles of high impact use enables managers to concentrate funds and volunteer efforts on maintenance. The goal is the preservation of the natural resource, the primary goal of the resource planner and manager.

C. CONSTRUCTION OF EROSION CONTROL MEASURES: DRAINAGE
     Protection of recreational trails involves two factors: limiting the impact of users on trail surfaces, and limiting the erosive effects of water on trails. Both can be controlled somewhat by managing--directing or diverting water drainage--on trail surfaces.
1. General Design Principles:
· Build drainage features into trails as they are constructed; don't plan to add later when problems develop.
· All drainage design principles apply to all user types.
· Surfaces require much more hardening for the high-impact users, greater width, and usually machine-maintenance.
· Water-diverting designs involve trail dips, tilts, or reverse grades which actually route the trail and water off the slope, then redirect the trail back up.
· Water bars are no longer advised: placed in the "fall line" of the trail, they fill up with leaves or silt; newer deep trench types get cut through. Both eventually become ineffective if not cleared or repaired. Trail/water-diverting designs need little/no maintenance.
· Modifying existing straight-line trails with drainage dips is time-consuming. The pay-off is, of course, that such improvements extend the life of trails by decades.
· Drainage concepts are simple, but application requires training. Different grades and types of slopes demand different techniques. It takes practice to develop one's eye to see where to apply drainage dips, side sloping of the trail, reverse grades, or switchbacks with water channels at the turns, and how to apply these principles to open grassy slopes as well as forest.
2. Tread Wear on Flat Surfaces: Some tread wear is inevitable. Ways to prevent the wearing of deep ditches over time on flat surfaces:
· Locate trails on edges of slopes, so the tread can deepen slowly without ditching. · Locate trails at edge of meadows, if at all possible.
· Artificial underlays or graveling may be necessary, as soil pulverized in dry weather on a flat surface becomes mud when it rains.
· Line cross-path drain channels with logs; keep channel free of gravel for passage of water.
3. Trails on Slopes.
· Out-slope trail surface (angled slightly sideways), so water drains off to the side instead of being channeled down the trail. Do not line edges of trails with cribbing. Trails tend to deepen and channel with wear over time; out-sloping may need renewal over the years.
· Switchbacks are used to wind a trail across and down a slope, to lengthen it and reduce the grade. On grassy slopes, turns should be designed to occur at rock outcroppings, bushes, or any structure to prevent short-cutting and keep hikers on the trail. The number of turns in the switchback should always be kept to a minimum, to reduce short-cutting.
4. Diverting Water OFF Trail:
· Install drains at bend of switchback above turn to channel water off the trail, using stone, treated timber or available logs. This results in a step down at the turn for the user. Stone or strong timbers anchored with rebar must be used for horse trails. Sometimes slope allows water to fan off the bend.
· Use self-cleaning Reverse Grade dips, 5-foot diversions of the trail stepped down slope then 5 feet back up again. Water leaves the trail as the trail is stepped back up. Send the trail around a tree, or disguise the dip with a pile of rocks and a fern.
· Grade dips: lowering of trail below grade for 10 feet, with a tilt down slope. Watch for naturally occurring dips, which can be accentuated, to drain water off long, straight trails.
5. Cross Drains: Prevent, divert, or slow water drainage across trail from up the slope.
· Pack gullies above the trail with logs across the flow to slow water moving across the trail; pack the gully below the trail with cross-wise log sections to prevent undercutting.
· Pave the trail with rock slabs to prevent water from washing it away. Rock surface must be flat, not tilted downhill or it will be hazardous.
6. Slow the Movement of water on the trail where keeping it off is impossible. Water bars or weirs--log or rock-- across the direction of flow may have to be installed in sections of trail where no other drainage option is possible, in old road beds with high sides, for example. Just slowing the flow can help to control damage. Downed trees may be trimmed and left in place to slow rain flow, and also interfere with and slow any unauthorized uses of trail.

References

Bjorkman, Alan W., Off-Road Bicycle and Hiking Trail User Interactions: A Report to the Wisconsin Natural Resources Board, Wisconsin Department of Natural Resources, Bureau of Parks and Recreation, 101 S. Webster, Madison, Wisconsin 53707 (606/266-2181).

Boone, Tony, Arrowhead Trails, Inc. (www.mountain-bikes.com (303)258-7425, personal communication May 1, 2000.

This paper is a condensation of remarks presented at the National Association of Recreation Resource Planners conference in Albuquerque on May 4-5, 2000.