Three Elements of Sustainable Trails
There are three essential elements for creating good sustainable trails. Good trails that withstand use and weather. Good trails that are easy and pleasant to use. Good trails that minimize maintenance and fight off the greatest trail evil – erosion:
- Outslope – A trail’s tread should always be slightly higher on the uphill side so that water can easily drain off. A gentle outslope of at least 2%, preferably 5%, is recommended. Trails without this outslope catch, hold, and channel water, helping erode and destroy the trail. Proper outslope encourages water to sheet across and off the trail.
- Proper Grade – Harkening back to your high school geometry, Grade = rise/run, or the elevation gain between two points always expressed as a percentage. When applied to trails, there are 3 aspects of grade to watch for:
- The average grade of the trail overall should not exceed 10% (8% is better).
- Limit the maximum grade, the steepest parts, to 20% (15% is better), and only for short sections less than 50 linear feet.
- Follow The Half Rule – A trail’s grade shouldn’t exceed half the grade of the sideslope. In other words, a trail should be less than half as steep as the slope it traverses.
- Rolling Dips – Rolling Dips, aka “Grade Reversals,” are little drops in a trail that forces water to drain at the low spot. Rolling dips are subtle downhills, just 10′ to 50′ in length, that prevent water from gaining volume, momentum, and erosive power. They also should be frequent – every 20′ to 50′ depending on soil and water conditions. Rolling dips replace water bars on good trails. (Rolling dips good, water bars bad.) Rolling dips also make a trail more enjoyable, providing variety and relief.
Good trails will simultaneous incorporate all of these principles. When you come across a trail in poor shape, you will see that these features have not been incorporated. When not planned for, water will always win and end up destroying trails! Ignore these elements on a trail and plan on significant maintenance requirements for that trail.
Other Elements of Good Trail Design
A few other guidelines to remember: Follow natural contours. Connect positive control points (viewpoints, water, other attractions). Use bench-cut construction and excavate soil from the hillside. For highly technical trails where grade will sometimes exceed 15 percent, use natural rock, rock armoring or other rock features to add challenge and improve sustainability. And don’t guess at grade. Use an inclinometer.
Building sustainable trails decreases time and money demands while increasing user enjoyment and resource protection.
- USFS Trail Construction and Maintenance Notebook
- IMBA Trail Building and Design
- American Trails Design and Construction
- CCCMB Build Skills
Building Sustainable Trails Videos