Ask a Trail Builder: Grade Reversals

March 15, 2016
Erik Mickelson
New York-New Jersey Trail Conference


Ask a Trail Builder: Grade Reversals


The trail I maintain has issues with water channeling down the tread. What can be done to fix this?

It sounds like your trail has a lack of grade reversals. In one word, a grade reversal is all about drainage. The point is to keep soil on a trail, and get water off before it has enough energy to displace the soil. A grade reversal literally refers to a reversing, or changing the grade of a trail—going downhill to uphill, and then back downhill again (or vice-versa).

Ideally, when you lay out a trail, grade reversals are built in. Just how frequent these reversals occur is a subject of debate, and I won’t try to answer that here, but I will talk about two types of post-hoc, or post-construction, add-on grade reversals: grade dips and rolling grade dips. The idea of both reversals is to shed water off the trail before a rill (a shallow channel cut into the soil by erosion) becomes a gully, and the trail washes into, or becomes, a stream. 

A grade dip is the construction of a depression in the prevailing, or running, grade.

A rolling grade dip involves a grade dip as well as a “speed bump” of soil piled up on the downhill side of the dip. Ramp heights should be kept close to dip depths.

Grade dips with a half-circle shape are called “knicks.”

Rather than abrupt channels, grade reversals should be soft and smooth undulations that are almost unnoticeable while walking through them. Of course, achieving this is often easier said than done here in the rocky Northeast, where dips may be more practical than rolling grade dips. It’s important to also note that when grades start to exceed 15 percent, dips alone are more practical, as rolling grade dip ramps will only increase the steepness of the trail.