Chapter 4--Designing Trail Elements--Continued
The choice of tread surface treatment affects the speed at which horses and mules can travel. For example, fine aggregate and dry woodchips provide relatively good traction and are conducive to safe cantering. Hard surfaces, such as large flat rocks, offer poor traction, and for safety reasons, limit travel to a walk. Consult Chapter 6--Choosing Horse-Friendly Surface Materials for more information.
Tread obstacles, including tree roots, waterbars, holes, or projecting objects, present tripping hazards and should be removed. Whenever possible, construct edges flush on either side of the trail tread without rocks, curbs, or other delineating materials. Stock may encounter curbs and other low objects, especially in highly developed areas. Most horses and mules navigate them successfully, but it is better to avoid them when possible. If curb cuts and grades are designed to meet accessibility guidelines and are at least as wide as the trail tread, the curbs usually are passable.
Alignment is a major consideration when locating trails. Alignment--horizontal and vertical--affects trail users' satisfaction and the trail's longevity. Alignment also affects sight distance and the speed at which trail users travel. The ideal trail matches the route to the ground, following the contours of the land and providing the best view (figure 4-8). The most enjoyable trails take advantage of natural features, such as drainages, winding around trees and rocks.
Horizontal alignment is the way the trail looks from above, as on a map. The best horizontal alignment includes simple curves rather than straight sections with sharp turns. Vertical alignment is the way the trail climbs and descends slopes. The vertical alignment determines not only how steep the trail is, but also how it channels water. Erosion from runoff is one of the most destructive forces affecting a trail. For information regarding trail alignment, refer to Appendix B--Trail Libraries, Trail Organizations, and Funding Resources and Appendix C--Helpful Resources.
Steepness--or grade--determines how challenging a trail is. In the English measurement system, grade is the amount of rise in 100 feet (30.5 meters) expressed as a percentage. A trail that climbs 5 feet (1.5 meters) over a distance of 100 feet has a 5-percent grade. Grade directly affects how a trail needs to be designed, constructed, and maintained to establish and retain solid tread.
Generally it is easier for stock to maintain their balance when they are traveling uphill rather than downhill. This is because most of their weight is over their forelegs. Descents require stock to shift more weight to the forelegs. Table 4-3 shows suggested design grades for horse trails. Surface water runoff can be controlled on all of the grades listed in the table. On grades nearing 50 percent, erosion cannot be controlled.
The best contour trails have grades, slopes, and turns that are comfortable for all trail users, not just horses and mules. Following contours helps reduce erosion and minimize trail maintenance. Keep trail segments between slope breaks--or running grades--as short as possible. Do so by following land contours, as opposed to cutting across or going straight up and down contours. Incorporate periodic short grade reversals as needed to remove surface water from the trail. Because water gains speed as it runs downhill, the potential for erosion increases greatly as the running grade becomes longer.
Horses and mules easily can master steady grades steeper than 10 percent--even 20 percent. However, as the grade increases, so does the potential for runoff to harm the trail's surface. In areas where grades are steeper than 10 percent, consider using one or more switchbacks to gain elevation (figure 4-9). Refer to Trail Switchbacks in this chapter for more information.
On running grades steeper than 5 percent, add 6 to 12 inches (152 to 305 millimeters) of extra tread width as a safety margin where possible. This helps a trail animal regain its footing if it accidentally steps off the downhill side of the trail. Benches or trail sections that are at least 100 feet (30.5 meters) long without a running grade can serve as resting areas for stock that are out of condition, large groups, and packstock. The larger, relatively flat area means an entire group can rest together at one time.
In areas where grades exceed 10 percent, trail steps are common (figure 4-10). Most horses and mules navigate steps successfully, but steps sized for humans may present difficulties for stock. Some stock hesitate at steps, and some riders don't like the jostling that occurs when they're forced to navigate steps on horseback. Figure 4-11 shows a ford that incorporates a step up to the trail. The landing is too small, causing some stock to balk. Soils at the approach and landing areas of steps or staircases may erode quickly, leaving a gap that can catch an animal's hoof. Stock can negotiate steps with risers that are 16 inches (406 millimeters) high or higher, but many riders prefer steps with risers that are no higher than 12 inches (305 millimeters).
Figure 4-10--Experienced trail stock readily
travel these steps to a bridge crossing. The
risers are 8 to 12 inches tall, and the landings
are 6 to 8 feet deep. The trail tread is about 3 feet
wide. Trees and rocks along the sides direct stock
onto the bridge.
Flowing water follows the path of least resistance, which may be directly down a poorly constructed trail. An outslope--also known as a cross slope-- helps shed water from the trail (figure 4-12). Grading with an outslope leaves the outside edges of a hillside trail slightly lower than the inside edge. Table 4-4 shows suggested slope ranges for outslopes for horse trails.
|5 to 10||5||2 to 5|
Over time, trails tend to drift downhill as trail users step to the tread's outside edge and wear it away. As running grades increase and outslopes become extreme, stock may find it difficult to maintain their balance and stay in the center of the tread. To protect the edges of the trail, make trails wider as the outslope becomes steeper. When trails have outslopes of 4 to 5 percent, widening the trail an additional 6 to 12 inches (152 to 305 millimeters) helps stock stay in the center. An alternative is to create wide spots where obstacles might force riders and packstock to the outer edge of a trail. Berms sometimes build up on the edges of trails, preventing water from flowing off the tread. Proper maintenance removes these berms, preventing erosion.
Trail animals can slip on smooth, hard surfaces, especially if they are outsloped. Where trails intersect solid rock ledges, asphalt, concrete, or other hard surfaces, keep the outslope to 5 percent or less to reduce the possibility of slipping. Add texture to hard surfaces at trail crossings. Evaluate surface treatments carefully where trails make a transition to pavement--loose material may end up on the hard surface and reduce traction further. Consult Chapter 6--Choosing Horse-Friendly Surface Materials for additional information.