What Is a Sustainable Trail?


For several years the Ranger staff and volunteers have been replacing old, poorly designed trails using sustainable
trail design standards. The phrase “sustainable trails” is commonly used, but what does it mean? A sustainable trail
should have as little impact on the surrounding environment as possible; this is done with proper planning, design,
construction and maintenance. A trail built with these four elements in mind will last for generations and will blend in
with the natural surroundings.

This is The National Park Service’s definition of a sustainable trail:

• Supports current and future use with minimal impact to the area’s natural systems.
• Produces negligible soil loss or movement while allowing vegetation to inhabit the area.
• Recognizes that pruning or removal of certain plants may be necessary for proper maintenance.
• Does not adversely affect the area’s animal life.
• Accommodates existing use while allowing only appropriate future use.
• Requires little rerouting and minimal long-term maintenance.

From the National Park Service,
Rocky Mountain Region, January 1991

Well-constructed trails will withstand erosion and are more enjoyable to use. Poorly designed trails will create an
unpleasant experience for trail users as well as a financial and volunteer resource drain.

Erosion is the key issue leading to trail failure. Erosion, if left alone can destroy a trail tread and also harm the
surrounding environment.

There are three types of trails on Ken-Caryl Ranch, those being, hard (cement, asphalt), soft (crusher fines) and
natural (dirt). Over two-thirds of the trails on the Ranch are of the natural variety and while we look at drainage on our
hard surface trails this is mainly to try and keep ice off of them in the winter months, not to keep them from washing
away. When we plan a natural surface trail every element of the planning is meant to keep water on the trail for as
short a time/distance as possible.

The International Mountain Bikers Assoc. lists these as the five essential elements of sustainable trails:
1) The Half Rule: A trails grade should not exceed half the grade of the side slope the trail is traversing.

2) The Ten Percent Average Grade: Generally, the trails’ average grade should be maintained at sustainable grade of
10 percent or less.

3) Maximum Sustainable Grade: Maximum grade, usually around 15 to 20 percent, is the steepest allowable grade
based on several site-specific factors such as: Half Rule, Soil Types, Annual Rain/Snowfall, Grade Reversals (a short
dip followed by a rise forces the water to drain off the trail), Types of Users, Number of Users, and Difficulty Level.

4) Grade Reversals: A grade reversal is a spot at which a climbing trail levels out for about 10 to 50 feet before
raising again, this allows water to exit the trail tread at the low point of the grade reversal.

5) Outslope: As the trail contours across a hillside, the downhill or outer edge of the trails tread should be slightly
lower than hillside, or inside edge by five percent. Outslopes encourage water to sheet across the trail rather than
traveling down the trails center.

On Ken-Caryl Ranch Open Space, sustainable design standards have been used on re-routes of Bradford, Colorow
and Shaffer Trails. Lost Canyon was also designed and built using these widely accepted standards. In fact, recently
adopted county regulations borrow heavily from sustainable design standards. I hope this gives all of you a better
understanding of the standards the Ranger staff is looking for in future trail projects. Let’s all be good stewards of the
beautiful place in which we are privileged to live, work and play. See you on the trails!

by Mike Rogers, KCRMA Open Space Ranger

Ken-Caryl Ranch