So you’ve got permission from the land owner, your financial ducks are in a row and now it is time to get some spades to start digging dirt. Building a trail is a creative and rewarding experience and Meurant Botha finds his best guideline is to try and envisage what people will think of the trail 10, 15 or 20 years down the line. Will it still be there? Will it still be solid and low-maintenance? Will people actually still use it because it is fun to ride? With that in mind here are the AmaRider tips to ensuring a successful trail build.
A great resource for trail construction is of course AmaRider’s USA-based parent body IMBA (The International Mountain Bicycling Association). The IMBA has a website packed with recourses, check it out at www.imba.com, and they’ve also produced a series of books on trail building.
The IMBA’s 3 main trail building goals:
- Limit environmental impacts.
- Keep maintenance requirements to a minimum.
- Avoid user conflicts.
The above is primarily achieved by building contour hugging trails that gently traverses a slope while continuous grade reversals in the design will ensure that water does not get the opportunity to collect and form a river, taking your trail with it down the slope. By ensuring that the tread surface is gently sloped the builder can achieve ‘sheet-flow’ where water continuously exits the trail off the downslope side, as per the diagram.
The diagram illustrates a retaining structure (in this case a treated pole), but I want to stress that this is only a requirement in certain environments.
On steep side slopes you often have no choice; achieving acceptable tread width could require extreme excavation. This is not only costly, but can destabilise the hillside too. Trust me, an undermined clay-based hillside will collapse, especially when waterlogged, with the potential of destabilising an entire ridge. Out in the backcountry the consequences might be limited to environmental damage, but when you’re faced with roads, cultivated lands or buildings in the vicinity above the excavation, things can get expensive and dangerous.
IMBA’s trail expert tips:
- Do everything you can to keep the water off the tread, and users on it.
- Build on the contour and use frequent grade reversals – surf the hillside.
- Follow the half-rule: A trail’s grade shouldn’t exceed half the grade of the side slope.
- Maximum grade should be 15 percent (except for natural or built rock structures).
- Average grade should stay under 10 percent (with grade reversals).
- Route trails to positive control points (viewpoints, water, and other attractions).
- Use bench-cut construction, and excavate soil from the hillside.
- For reroutes, reclaim old trail thoroughly – the visual corridor as well as the trail tread.
- For highly technical trails where grade will sometimes exceed 15 percent, use natural rock, rock armouring or other rock features to add challenge and improve sustainability.
Guidelines on slope percentages do change based on the soil type you are working on with but these are good guidelines to follow.
1) Avoid the fall line
While it is appealing to grab a rake and move a few pine needles out of the way, following the fall line straight down the forest is a temporary solution that will erode in no time.
I guess it looks cool on the freeride movies, but I promise you those trails are not built with sustainability in mind. An important thing to remember is that the average US freeride trail spends the winter under snow and does not see the year-round activity that a South African trail will.
2) Avoid flat, low lying areas
Flat areas are appealing from a build point of view as it is generally easy to make the track as there is little excavation to do. When you build through a flat area there is no place for water to go, so you can expect lots of trouble with puddles followed by mud or in dry times, a sandy sediment-rich deposit that can become unrideable. Raising the trail tread with a bridge or rock armouring is an expensive solution that can be avoided with proper initial design.
Again, the above should be treated as guidelines. Short sections of fall line on well binding clay-based soils are fun additions to the trail and can be managed. A short bridged section to cross a flat spot on the terrain can look nice and generally enhance the trail experience. As long as your main consideration is water management you should end up with a maintenance friendly trail that can stand the test of time.