Woody plants should be dug out, roots and all.
Safety is paramount in any kind of trail work. Sharp tools, difficult ground, weather, fatigue and natural hazards can cause injuries. Trail crews should wear sturdy boots and gloves. Long pants and long-sleeve shirts are recommended. Eye protection and hard hats are a good idea too.
Crew leaders should know the location of the closest medical facility and who will go for help. When an accident happens far a field, time is critical. Create an emergency plan before heading out. Make sure everyone knows his or her responsibility during an emergency.
Start each workday with reminders about tool safety and the emergency plan. Cover these points:
Woody plants should be dug out, roots and all. |
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The trail corridor should be at least twice as wide as the tread width. This can vary with the terrain and type of user the trail is designed for. Leave grasses and trees when they're outside of the tread. Get approval from the land manager if there is any question about tree removal. There may be a size limit for cutting. When small trees and bushes are within the tread, don't cut them flush with the ground. They must be dug out, roots and all, or they'll become "pungee sticks" when the trail compacts around them. Cutting them at waist level leaves a handle for levering them out. Fill the resulting hole to match the tread.
When trimming tree branches, always cut just outside the branch junction. The resulting nub helps prevent disease from infecting the tree, and the cut will heal quicker. When removing larger branches, start by making a partial cut underneath. Then when the branch falls it won't strip protective bark.
Put cut trees and branches at least 10 feet from the corridor. Lay them with the butt end pointing away.
Clear an area equal to the planned tread width. Also clear four feet downhill from the tread's lower edge. Next, rake the duff and debris from the tread area onto the uphill side. It can be used later to cover dirt removed from the bench cut and give the trail a more finished look. If it's too steep to rake uphill, rake downhill into large piles. Scatter dirt removed from the bench cut over the downhill area. Cover it with the duff and leaf litter.
When possible, excavate down and into the hillside to put the entire tread width on mineral soil. This is called full bench tread construction. It creates a consistent and stable tread. It takes more time to build, but it lasts longer and needs less maintenance.
Not recommended: A portion of the tread width is excavated and placed on the downhill side of the tread. This forms an incomplete or partial bench. The tread rarely compacts consistently, and eventually it begins slipping down the hill (tread creep). Partial bench construction usually results in an unsustainable trail if it gets substantial use.
When essential roots or impenetrable rock make it impossible to establish a full bench trail, a retaining wall can be built to support the downslope side of the tread. This crib wall holds in soil, stopping the tread from creeping downhill. It's important for the top of the wall to be lower than the tread so water can sheet across. The construction cost of a crib-walled tread is usually at least twice that of a standard full bench tread. On sideslopes of 100 percent or greater, a partial bench supported by a crib wall will reduce the height of the backslope and the trail's impact on the hillside
The uphill side of the tread where it blends into the slope above the trail (the backslope) is called the back-cut. Often, the first rough cut of a full bench tread produces a vertical back-cut. If left vertical, water can undercut the backslope, which eventually sloughs off onto the tread. That's why it's very important to blend the back-cut into the grade of the hill. It lengthens the trail's life by preventing water from cascading onto the tread.
Trail tread should have a subtle tilt (3-5 percent) in the direction of the fall line. This is known as outslope. It's the most important part of the tread because water won't sheet without it. Depending on soil type, newly constructed tread can have up to an 8-percent outslope to compensate for settling. To estimate, stand a Mcleod on the tread to see if the handle leans into or away from the hillside, and at how much of an angle. To measure precisely, use a digital level or clinometer
Throw excavated topsoil several feet downhill, away from the trail. If topsoil is left near the edge, it can settle and become a berm that interrupts sheet flow, causing water to puddle or flow down the trail. The ground beyond the edge of the tread should slope away, if possible. This might require digging and removing vegetation.
This depends on who the primary trail users will be. For more technical trails, leave natural obstacles such as rocks and roots that aren't a safety hazard and won't contribute to erosion.
On a bench-cut trail, remove rocks on the inside edge. If you don't, they'll force users to the outside of the tread and cause the edge to break down. On the other hand, obstacles on the outside edge will keep users in the center of the trail. Remove logs that are parallel to the tread on the downhill side so they won't act as gutters.
Large, stable, round rocks are good for the tread surface. So are reasonably square or rectangular rocks with ledges. But sharp, pointy rocks tend to force users off trail. Remove them as well as loose rocks that are likely to work free and create holes.
During construction, take out most roots with a diameter larger than a pencil. This is especially necessary for roots running parallel to the tread. They will channel water and may force cyclists off-trail. Sometimes large roots that are perpendicular to the tread offer an appealing challenge. But they might force cyclists to the low side of the trail, causing widening (tread creep). It depends on the nature of the trail and whether leaving roots exposed will cause significant damage to the tread or tree. Cutting large feeder roots near the downhill side of a tree may kill it and cause it to fall across the trail. Sometimes it's better to build a small crib wall and fill over large roots.
Two types of turns are used to reverse direction on hillsides in order to gain elevation in a short distance. A climbing turn on the existing grade doesn't have a constructed turning platform or landing. A switchback turn reverses direction with the help of a relatively level constructed landing. Both turns take skill to locate and are difficult and expensive to build and maintain. Think of them as a last resort. Whenever possible, it's better to gain elevation by maximizing long contour trail sections.
Climbing turns are used on shallow slopes that don't exceed a grade of about 7 percent. To control cyclists' speed and prevent skidding, climbing turns should be free flowing and gentle. Keep the turn radius as wide as possible, ideally 30 feet.
Minimize erosion by having a short uphill section or grade reversal just above the turn. A grade reversal diverts water off the trail before it reaches the fall-line section. Climbing turns are best used on elevated ridges or slopes where water accumulation is minimal.
Because climbing turns include a section of trail on the fall line, they aren't as durable as well-constructed switchbacks.
Switchbacks are difficult to build but are more durable on steep slopes. They will last longer than climbing turns if properly designed. We recommend a version called the "rolling crown" switchback. It's carefully engineered for good drainage.
Build a crib wall (retaining wall) when you need to shore up the turning platform. It's better to use rocks instead of logs, and better to use large rocks (at least 50 pounds) than small ones. If you can lift the rock by yourself, it's probably not big enough. Ideally, many of them will weigh at least 150 pounds and be rectangular, not round. Excavate the footing, then place large, well-anchored foundation rocks. The wall should tilt into the slope - described as the wall's "batter." Batter should never be shallower than 4:1, defined as an inward tilt of one foot for every four feet of height. A 2:1 batter is better. Building large crib walls is difficult, so enlist the help of someone who has experience.
A water crossing doesn't always have water. It's also the site of a potential conduit for water. Every crossing is important for two reasons:
When water from two sources join, it's called hydrologic connectivity. An example is a trail that collects water and channels it into a stream. Runoff from trails may carry soil that causes sedimentation, which can harm aquatic plants and animals. A well-designed water crossing minimizes the trail's negative impact on water quality and the riparian corridor (the habitat along the edge of a river or stream). Good design minimizes hydrologic connectivity by building gentle grades near water crossings to direct flow off the trail. Never design a trail with fall-line sections oriented toward water crossings. This encourages land erosion and sedimentation.
When crossing a waterway, also consider how it may affect the trail. Will water be diverted by the tread? What will happen when the waterway floods? Even desert trails require careful consideration when intersecting with possible drainages. What seems like a perennially dry gulch could channel a roaring torrent following a cloudburst.
These are the most common solution for water crossings. By putting the trail above the water, you minimize the impact each has on the other. Make the bridge high enough so the approach is on a gentle grade (if not level). Proper height also helps avoid flood damage. Make the bridge and adjoining trail have good flow (no awkward transitions).
Before beginning work, consult an experienced bridge builder or at least check with the U.S. Forest Service for its construction guides.
Bridges can be expensive and may require a lengthy permitting process. So consider an alternative - the armored ford. This lets users pass through water but minimizes sedimentation. The approach to a ford is similar to one for a bridge. Use care to prevent sediment runoff from the trail to the water. Place stone to make a hard surface for the entrances and crossing. This prevents trail users from degrading the banks or stirring up silt. Consult the land manager before disturbing any creek or streambed.
A culvert is a large pipe that allows water to flow beneath the trail bed. This is an appealing solution thanks to low cost and easy installation.