Calgary Mountain Bike Alliance - Trail Care Construction and Maintenance

Trail Care

Trail Care Construction and Maintenance

Notes From IMBA Visits to Calgary 1999 / 2000
by Bob Scott

A general over-riding comment was that almost all trail damage is one of poor (or no) trail design and subsequent water erosion, and not a trail user erosion/damage situation.

General Guidelines

All trails should be built into a hillside, creating a bench, with a very gentle out-slope (3-5%), and not built on flat ground. This is done so that water can run across the trail (not along the trail) and continue down the hillside thus preventing any water from pooling on the trail or flowing along the trail.

Trails should be "contour trails" that mimic contour lines and work with the land.

Trails should not be built straight down the "fall line" of a slope, as water erosion can not be controlled.

Repairs to Existing Trails

For existing mud holes on flat terrain where there isn't sufficient side-slope to the ground to allow water to drain away, the options are limited. "Armoring" the mud hole is possible. Armoring is placing large, flat rocks into the hole, but first, all of the existing mud must be removed. The rocks must be large enough so that they are not moved by bicycles riding over them and the major cracks between rocks must run perpendicular to the line of travel to avoid wheels getting caught between the rocks. Re-routing the trail is the only other option.

Avoid using water bars (logs, rocks rubber conveyor mats) to channel water off of a trail. Water bars, used on steep trails to divert water off to the side of the trail are a band-aid and not a good long-term solution to prevent erosion. Use a "rolling grade dip" or "dishing". Remove a nick or chip out of the trail, a short section of dirt from the low side of existing trails so that water can flow off of the low side of the trail. It should be very subtle. The dish should not even be visually noticeable. If you can see the change in the terrain, then the change is likely too abrupt. Any changes made to the terrain during maintenance should be subtle. Once ground (dirt) is removed, it can not be replaced (and remain in place). The dirt from the dish can be thrown down the trail to form a small ramp.

Rain ruts can not be filled in with more dirt. Generally, the new dirt will simply be washed away by future rain. Ruts running along (parallel to) the trail, must de-bermed on the downhill side. Cut away the downhill side of the rut, down to the bottom (deepest point) of the rut, then gently angle (out-slope) the platform of the trail for future water to run off.

When trying to fill in an area with dirt, the dirt must be mineral soil and not contain any organic material (logs, moss, needles) as this material will decay and not remain in place.

All exposed tree roots that run parallel to line of travel should be removed. Selective pruning - removing roots that are exposed and have little or no dirt remaining under the root will not harm the tree. Cut the roots back to the point where they are covered by dirt. Roots with only the tops and part of their sides exposed should be left in place.

Replant vegetation on an old (closed) trail to cover it over. Also post signs to inform people of your intentions.

Designing a new section of trail

When planning and designing a trail or new section of trail, note all of the "control points" that the trail will encounter. These may be "Bad Points" - places to avoid. e.g. water holes, flat areas or "Good Points" - destination points - view points, picnic stops etc.

Cyclists like trails that are designed as "stacked loops", possibly with an initial practice loop.

Plan the trail to have an overall grade of 7% over its entire length.

The textbook maximum trail slope angle is 15%, but realistically, a 30% trail grade is tolerable, but only for a short (30 ft) sections or lengths of trail.
Always describe slope as a percent (not degrees).

100% = 45°

50% = 27° (a steep climb for an intermediate rider)

30% = 17°

15% = 9°

10% = 6°

Note, the degree value is approximately half of the percentage value.

When constructing a trail into a hillside (a full bench construction, as recommended), the trail slope angle (pitch or grade) should be no more than half of the slope of the hill which the trail is crossing e.g.) a trail cutting across a hill that has a 60% side slope, the trail grade should not exceed 30% at any point.

The bench itself should be constructed so that, if the hillside is 30%, the cut out downslope to the trail platform should be 60% (not vertical) and out-slope of the trail platform should be less than 8%.

Confused ? Diagrams help.

Design rolling, roller coaster type trails with natural grade dips ("grade reversals"), undulating trails.

Use "S" curves, avoid long straight sections of trail, to make the trail more interesting.

Avoid ridge tops, use the side of the ridge. Again hillside trails.

Transitions from high-speed sections to low speed sections should not be abrupt or riders will brake suddenly and skid their tires thus causing subsequent erosion. Add rocks and obstacles etc. to make trails technically challenging, as opposed to using steep pitches (fall lines) which will lead to erosion.

If a trail passes next to a tree, the trail should be placed on the high (up hill) side of the tree. Roots to the low side of the tree are more critical as they act as an anchor and support the tree.

Route trails that approach each side of a water drainage ditch, so as to minimize the crossing distance over the ditch. Avoid using structures, like bridges, on a trail as they required too much long-term maintenance. An alternative is a "Turnpike" or "Burrito" which is gravel wrapped in a textile fabric forming a tube structure. A bike is able to ride along the top of the tube and yet water can pass through the tube (turnpike). It is used to cross over standing water (which might form during the wet season in a marshy area) but not over running water, such as a stream.

If bridges are required they should

be built for the heaviest user (possibly an emergency rescue vehicle). Know your user groups.
have long site-lines approaching the bridge from either direction but have some means of cyclists reducing their speed before the bridge.
Span the entire distance to be crossed and not be made too short thus causing a drop down onto the bridge.
Use screws instead of nails.
Peel any bark off of logs to be used in construction.

Don't take away an existing trail from riders until you have provided them with a better (well engineered) trail. Their opinion on this changed in 2000.

When constructing a new section of trail

First, Place pin flags in the middle of where the trail is to be place, to mark the location for construction workers.

Trees on the trail path should be removed with their roots.

Branches should be removed ½ inch from the trunk, undercut them first, and then cut from the top to remove.

Remove all organic matter from the path and fling it down the hill.

Cut the bench.

The backslope should not be vertical. It should be blended in so that water stays on the ground. Don't create a waterfall onto the trail from the ground above the trail.

Outslope the tread 3-5%. There should not be any ankle roll due to excessive outslope. "Tread creep" occurs when people naturally take a lower line on a hillside trail, than the existing trail, because the trail has too much outslope.

There should be nothing on the downhill side of the tread.

Use large rocks (flagstone, armouring) where ever possible.

Avoid using culverts. If you must make them large so that they do not get plugged with debris (logs, brush, dirt). Cover the culvert with at least one foot of soil.

Climbing turns should have about a 10% grade (13% max) and have a grade dip above them to channel water off the trail above the turn.

Switchbacks ("Rolling Crowned") The turn should be about 16 feet in diameter and be built almost on a level platform, e.g. a deck or a crown. The lower tread should be outsloped. The upper leg (or tread) should have an inslope causing water to run off of the end of the turn. An object should be placed at the inside of the turn to discourage people from short-cutting the turn. Sometimes a retaining wall must be built to support the turn. One foot of vertical wall is needed for every 10% of sideslope. The wall should be built in tiers.