Trail Construction
These standards have been compiled from a number of trail manuals and are guidelines for enhancing a trail user's experience and for minimizing safety hazards. Width of clearing for the trail walking surface should be a minimum of 3 to 4 feet for most lightly used trails, with additional clearing of vegetation for 1 to 2 feet on each side of the walking surface. Fast growing brush species might also be cut back further to reduce the need for frequent maintenance. For trails that will receive heavy, or group use (eg interpretive trails), the cleared width for the walking surface should be a minimum of 6 to 8 feet. Equestrian and mountain bike trails should have a cleared width of at least 8 feet. If you will receive cost sharing for trail construction through the Stewardship Incentives Program (SIP), total right-of-way clearing should be 5 to 8 feet wide.
Where some type of surfacing material is added to the trail, the width of the surfaced tread should be at least: 18 to 24 inches for long distance trails with single-file traffic; 2 to 3 feet for bike trails; 2 to 5 feet for nature trails, depending on expected use; 6 feet for equestrian trails; and 4 feet of smooth tread surface for barrier-free trails that will be used by people with special needs.
Overhead clearance (hanging branches, vines, etc) should be at least 7 to 8 feet for hiking trails, 8 feet for bike trails and 10 to 11 feet over equestrian trails. Although most forest land in Florida has only gently sloping topography, if your land includes some steep grades, trail grade should be maintained at less than 10% except for very short pitches, as with spurs into large sinkholes or ravines. Steps may be necessary for such short steep grades to prevent soil erosion during heavy rains.
Other SIP specifications state that trails should follow the contour, minimize stream crossings and felling of large trees, and stay at least 35 feet from stream banks except at crossings. Areas cleared to expose scenic vistas may be no more than 100 feet in length, while areas cleared for access to riparian zones and waterways should be less than 8 feet wide.
Now it is time to implement all the preparation and planning. Trail layout involves marking the exact trail route, on the ground, so that construction can begin. The preliminary route selection should have left plastic flagging at distant intervals. Exact location of the complete trail is marked with additional brightly colored flagging. A compass and clinometer or Abney level may be used to relocate small portions of the trail or to locate the trail at the correct gradient if it traverses steep slopes. Your county forester can show you how to use the clinometer or Abney level.
Walk through the proposed route and hang flagging on live trees or branches or place brightly-colored stakes or flag pins frequently enough to make the route clearly visible. Even in open forest conditions the distance between stakes or flagging should probably be a maximum of 100 feet so that construction crews will always be able to see where they are headed. Once the complete trail is marked, rewalk the route from both directions to check visibility, aesthetics and all featured items, and move flagging if necessary. Have others walk the trail route to be sure it meets all your objectives. When you finish, remove all flagging or other markings except along the final selected route.
The following guidelines will be useful as you develop the exact route:
The initial preparation of the trail involves clearing trees and brush out of the trail right-of-way. Any of the cutting tools described previously can be used, but tools should be selected that will allow the task to be completed both efficiently and safely. First aid kits should always be immediately accessible to crews doing the clearing. Pine trees and other plants that will not sprout from stumps or roots can be cut flush with the ground line. Stumps and roots of plants that will sprout should be dug out of the ground if such excavation can be accomplished without substantially disrupting the trail surface. If vegetation outside the cleared part of the trail is so thick that visibility is restricted, you might selectively remove enough of it to facilitate hikers' views. Disperse cut materials away from, and out of sight of, the trail. Mechanized equipment can be used for the initial clearing, but the operator needs to avoid site disturbance and unsightly stumps and cut materials. SIP specifications allow cost sharing for clearing by hand labor, drum chopper or a rotary mower pulled behind a tractor.
Once the initial clearing is completed the trail can be used. However, additional preparation will enhance trail quality. Cut overhanging tree branches flush with tree trunks. Other overhanging vines and vegetation (especially poison ivy) should also be removed. Sections can be cut out of most fallen trees or logs, and loosely embedded rocks ought to be moved if they pose an obscured tripping hazard. However, the trail can also be detoured around, or over, large obstacles. Leaving a few such obstructions in the trail offers a challenge to hikers and serves as a deterrent to use of the trail by motorized vehicles. Small clearings or turnouts should be created near points of interest if the trail is to be used for group instruction. Whenever possible, try to avoid clearing more than the minimum necessary on both sides of the trail to keep trail users feeling "close" to the natural environment.
The last step in trail preparation involves installation of water drainage features, if necessary, and surfacing the tread on trails that will require more than the natural surface that is left after clearing. This can be the most time consuming and laborious stage in trail construction, but it may not be necessary for many nature trails in Florida's flat topography. Water drainage features will be discussed more completely in the next section since they are a critical method to prevent soil erosion from water that is channeled down a sloping trail. If non-native surface materials will be added to the tread, loose materials that might stick through the surfacing should first be raked from the tread surface. Mulch, chips, gravel or other surfaces can then be spread with a wheelbarrow and rake to meet the minimum tread specifications for your particular trail. Mowing may be all that is necessary where trails pass through grassy vegetation.
As previously mentioned, water drainage features are necessary to prevent erosion along trails on slopes and to avoid standing water on trails on flat ground. An important objective in designing any of these structures will be to minimize visual effects of construction efforts. The frequency, size and type of control structures depends on erosion potential of the soils under the trail. For example, sandy soils are less erodible than clay soils because of the large grain size and porosity of sands. Two other important factors include the velocity of water along the trail, which depends on the slope, and the length of time, or distance, running water is allowed on the trail. Most erosion control measures are designed to reduce the velocity and/or the distance of water running on the trail. SIP specifications for trail construction require that such measures be installed immediately after clearing.
Trails that follow an undulating contour rather than long steady grades will provide frequent points of water drainage and avoid increases in water velocity. Similarly, a trail that is descending a slope can be curved to follow the contour for a short distance before continuing down slope. At this "water curve" the trail tread is sloped outward so water will run off the trail into adjacent vegetation. On slopes less than 5 to 10%, the same effect is possible by sloping the trail tread to the outer (downhill) side, and/or by crowning the middle or inside of the trail so that the center of the trail is higher than the edges. The latter two measures will be more important on soils with clay than the very sandy soils of much of central Florida.
(Illustration of Water Curves)
Drainage dips can also be constructed on gentle slopes to reduce water flow along a trail. Dips are small trenches dug across a trail, usually at an angle toward the downhill side. Soil from the trench is mounded on the downhill side of the trench to be sure water running down the trail is directed into the trench and off the trail. The mound can be stabilized by burying logs or rocks under the mound. Rocks on the outflow end of the trench will prevent additional erosion as the water flows from the trench. Other small drainage ditches may be used to drain water from wet areas through which trails pass before a problem develops.
A waterbar is a larger version of the drainage dip, and is used on trails and roads that exceed 10% grade. As with drainage dips, the basic objective is to divert water off the trail without increasing erosion downslope from the trail. The number of waterbars on a particular slope will depend on the grade and soil type. Place the first waterbar close to the source of water that is entering the trail, and subsequent waterbars at distances that will prevent the development of any gullies in the trail. Rock, peeled logs or ties are angled 30 to 60 degrees across the trail, and are partially buried or anchored with soil, steel pins, reinforcing bar, wooden stakes or large rocks. Crowbars and shovels may be necessary for this construction. Logs should be at least 6 to 8 in. diameter at the small end, and stakes should be driven in at both ends of the log(s), as an inverted V, to hold the log in place.
The waterbar must extend 1 to 3 feet beyond the outside edge of the treadway to be sure water doesn't return to the trail. A ditch may be needed for this extension to ensure drainage off the trail. The trail on the upgrade side of the waterbar must be well below the top of the barrier to be sure water running down the trail does not run over it rather than being diverted off the trail. The downgrade trail tread can be built up with packed soil and rock to be flush with the top of the barrier. Install a rock spillway where water runs off the trail to disperse the erosive energy into surrounding vegetation.
Wherever trails cross small drainages, culverts located under the trail will channel water and prevent trail washouts. Corrugated metal, concrete pipe or wood boxes can be used as culverts, and they must be of sufficient size to handle the maximum anticipated flow. Culverts should be installed so that the bottom is at ground level, with a rock spillway on the downslope end to disperse the water as it exits the culvert.
On short steep grades, steps can be installed to control erosion, similar to waterbars, and to assist hikers climbing up and down the slopes. Steps are built with flat-sided rocks (at least 50 to 100 lbs each), treated wood or native logs. Logs need to be well anchored and buried at least one third of their diameter for stability. The top surfaces of each step must be rough, and should slope into the uphill side slightly to reduce slipping. Steps should extend beyond the edge of the trail to prevent erosion along the trail edge. The surface between steps should have a slight downhill slope to avoid water settling between the steps, and it should also slope to one side to reduce the effect of water cascading down the steps. Widely spaced steps may be installed above waterbars to prevent clogging the waterbars with sediments. Such steps should also be sloped to the outside of the trail to divert water off the trail. Steps ought to rise a maximum of 16 inches, but preferably less than 12 inches.
Without regular maintenance, trails will become overgrown and disappear in a few years in many of Florida's vegetation communities. Maintenance efforts will be minimized if done annually, probably during winter months when temperatures are cool and visibility is good. However, sprouting shrubs will be more easily controlled if cut in late spring or early summer, after they have leafed out and when starch reserves in the roots are at their lowest level. Maintenance activities include: clearing new vegetative growth; removing loose rocks, roots, or dead trees; replacing surfacing material if necessary; litter cleanup; and sign repair. It is especially important to remove dead trees or branches that could fall on trail users.
Trail width and clearance should be returned to original standards by pruning, cutting through or removing blowdowns, and removing new growth from the trail tread. As with initial clearing, select the right tool for the type of vegetation and clearing work, do not leave pointed stubs and stumps, and scatter (don't pile) cut material off the trail, out of obvious sight. Waterbars, ditches and other erosion control structures need to be cleaned out at least annually. Material excavated from above the waterbar can be placed on the mound below the bar to reinforce it.
Consider relocating trail segments that have become gullies or wide and muddy if the relocation will not create the same conditions elsewhere. Otherwise, use log mats (short logs laid side by side), the rock treadway in the next figure, or one of the methods described in the section on Bridges, Boardwalks and Other Wetland Crossings, to stabilize the trail. Whatever method is used, short drainage ditches into surrounding vegetation or one of the erosion control measures described previously should also be constructed to reduce the source of water that caused the problem.
Rock treadway across a poorly drained spot
(Courtesy of the Appalachian Mountain Club)
Gather wood, soil or rock materials used for maintenance from sites away from the trail and cover or fill those sites with brush and debris when finished.