Standards and Procedures: Tread Maintenance
Basic tread maintenance, along with drainage maintenance, is the most important part of keeping our trails system in good condition. While not as exciting or glamorous as building structures, proper tread maintenance saves an enormous amount of time, energy, and resource value over the long term. If maintenance is neglected, trails can degrade to a point where they require heavy rehab work, or even complete relocation. It’s sad to look at heavily degraded trails, knowing that if only routine maintenance had been performed regularly, the problem would not exist. Relocation involves a long and drawn out process of NEPA, planning, design, and construction, which can easily take years. Let’s avoid this by giving basic maintenance the love it deserves!
Think about it like a personal vehicle. Sure, it’s impressive that a mechanic can completely rebuild your engine if it dies. But wouldn’t you rather follow your prescribed maintenance schedule, keep up with oil changes and minor tune-ups, and not have to drop a huge sum for major repairs?
Key Points:
- Maintain tread outslope to preserve sheet flow of water
- Maintain tread width to prevent tread creep
- Maintain obstacle-free tread to keep users off the edge
- Maintain effective full bench tread characteristics
- Avoid “artificial berms”
See Also:
- Summary/Takeaways
- Further Resources
Tread Outslope
Standards:
- All tread should be outsloped 2-5%, this should be gradual enough that the user does not notice the trail being sloped while walking on it. If the tread is outsloped too much, it will cause the user to drift toward the outside edge, leading to tread creep.
- Remember, the goal of tread outslope is sheet flow of water across the width of the trail, not down the length of the trail:
Procedures:
- Remove berms of soil and vegetation that form along the outside edge of the trail. Berms will channel water down the length of the trail if not removed periodically.
- Fix gullying/cupping early! If you notice an area is starting to trench out into a gully, the best solution is to reestablish a good bench with the 2-5% outslope.
- Simply filling the gully with soil is NOT a sustainable solution. Fill will not compact as well as the underlying natural soils and will wash away quickly.
- This means tread must be re-dug to the lowest level of the gully, establishing a new bench dug into the naturally compacted mineral soil layer which has been compacted by natural processes for tens of thousands of years.
Tread Width
Standards:
- Proper trail width depends on the prescribed class of trail, which is based on designed use and experience A wilderness trail will be different from a frontcountry trail, a hiking and biking only trail will be different from an equestrian trail, etc. Refer to Trail Fundamentals for trail class guidelines.
- Width should be consistent, and as wide as necessary to accommodate the designed use.
- Over time, sloughing from the trail backslope can result in a narrowing of the tread. If this narrowing goes unaddressed, it can eventually lead to tread creep as users are pushed to the outside edge of the tread.
Procedures:
- Restore original bench by removing sloughed soil from the inside edge (hinge) of the bench. You can generally identify sloughage as a hump on the inside edge where soil has gradually fallen from the backslope.
- Be careful not to overdig; dig only to the level of the original tread. If you overdig while removing sloughage you will create a channel for water on the inside of the tread, thus stopping sheet flow and leading to further gullying. If you accidentally overdig in this way, the entire bench must be re-dug to the lowest point of the gully (see above diagram from “Tread Outslope”)
Tread Roots, Rocks, and Obstacles
Standards:
- Obstacles or protrusions into the tread, such as exposed roots and rocks, can lead to tread creep over time as they encourage users to avoid the obstacle, often moving to the outside edge. This is commonly seen with sections of trail that have been pushed downslope due to exposed roots growing in from above.
- Exposed rocks, protruding branches, even old or improperly installed structures can all contribute to problems as well. Anything that causes the user to shift off the center of the tread (which often happens subconsciously) is likely to cause damage over the long term.
- Some obstacles may be desirable to some users. For example, mountain bikers may enjoy the challenge of an uneven tread, and hikers might enjoy scrambling over rocks on a summit trail. Consider these factors, but keep sustainability at the forefront. If an obstacle is starting to cause resource damage, better to fix the problem.
Procedures:
- The best way to deal with exposed roots where they are causing a problem is to remove them and reestablish a good bench, dug to the proper width and outslope.
- Do not fill over the roots with soil. As stated above in “Tread Outslope,” loose fill, even when compacted manually, does not hold the way underlying soils do, and will wash away quickly. Cutting away roots with loppers and pulaskis takes time and effort but it is the best way to solve the problem.
This photo shows a prime example of how roots can lead to tread creep. A second “lane” has developed to the left of the original tread, which is now completely overtaken by roots.
Effective Full-Bench Trail Characteristics
Standards:
- Full-bench sidehill trail, sometimes called contour trail, is the standard for modern sustainable trail construction.
- Tread outsloped 2-5%
- Tread dug to appropriate width (see above section “Trail Width”)
- Tread dug to the level of solid, geologically compacted mineral soil.
- Backslope cut 45 degrees, or to meld with the hill slope.
- All excavated soil is broadcast far down the hill to prevent creating a berm and allow vegetation to come back up on the downhill side.
- Do NOT build partial-bench trail, which consists of piling and compacting loose fill on top of the existing slope to build out your edge. This requires less digging overall but does not create a long-lasting trail. As stated numerous times in this document, loose fill does not compact enough to be sustainable. Full-bench is the way to go. Build it well the first time and there will be fewer problems in the long run.
The Berm is the Enemy: A Note on Structures
The sections above articulate the most important elements of sustainable trails and how to maintain these elements to keep a trail in good shape over the long term. One common pitfall to avoid in trail maintenance is the construction of “artificial berms.”
Sustainable Trails, Not “a Path to Grandma’s House”
As described above, berms often develop naturally on the outside edge of the trails as a result of sediments accumulating over time, often accelerated by the growth of vegetation on the outside edge. Removing this berm periodically and reestablishing proper outslope is important to maintaining good sheet flow of water which is the key to a sustainable trail.
A problem can develop when “artificial berms” are created by lining the outside edge of a trail with logs or rocks. This is often a well-intended effort to retain soils and stop erosion, or to keep users on the trail. However, these measures should not be necessary on a well constructed trail, and can actually make the situation worse by acting like a berm and channeling water down the length of the trail - exactly what we strive to avoid when we build sustainable sidehill trail. In their comprehensive manual Trail Solutions, IMBA uses the phrase “A Path to Grandma’s House” to describe this common error of lining the trail with logs or rocks.
Outsloping on Cribbing
This is not to say that cribbing/retaining wall is never needed to shore up especially steep or unstable slopes. Keep in mind that when you build a crib wall, the tread surface should still have a 2-5% outslope. The cribbing should not form a berm that can trap water and prevent sheet flow.
Summary/Takeaways
Good Tread:
- Free of berms
- Maintains 2-5% outslope
- Smooth, flat surface
- Consistent width appropriate for class
- Preserves sheet flow of water!
Poor Tread:
- Gullied/cupped
- Artificial berms made by lining trail with logs
- Pushes users to the outside edge
- Channels water down the trail
- Rapidly leads to further trail damage
Tool and PPE Guidelines
Tools:
- Rogue hoe/hazel hoe - this is a great tool for tread maintenance, lighter and more efficient than a pick mattock for light digging.
- Pick Mattock - in heavier, rockier soils, this tool will be more useful than a hoe.
- Pulaski - especially useful for chopping out roots where they are a tread problem, plus it can handle light digging, too. Avoid using it for heavy digging in rocky soil as the head can come loose.
-McLeod - excellent tool for finish work, grading, smoothing tread, removing berms, and compacting soil. It's largely ineffective in heavy, rocky soil so it shouldn't be your first choice for major digging.
-Shovel - generally useful to have, both for moving excavated soil and for shaping, digging, etc.
- Fire rake - can be a useful tool for broadcasting excavated soil downhill when undertaking larger stretches of tread maintenance or redigging.
- Loppers/hand saw - always useful to have for removing roots while digging, or for removing roots that are compromising the tread surface.
PPE:
- All required PPE should be worn, including hard hat, boots, gloves, and eye protection.
Additional Resources
- USFS Trail Class Guide - useful excerpt from the USFS Trail Fundamentals and Trail Management Objectives manual, which covers the differences between Trail Classes 1-5 and how they affect the design parameters on trails for different users. The parameters include tread width and surface characteristics. Also see the Pisgah Trail Academy page on Trail Class Specifications for more details.
- PRD Trail Class List - PDF list of all the trails in the Pisgah Ranger District, along with their corresponding Trail Class.