Ephemeral Drainage-Line Assessments: Indicators of Stability

Abstract

In chapter 15 we describe eight indicators that inform restoration practitioners (RPs) about hether a drainage line is still active or is becoming stabilized. Here, we are referring to drainage lines that flow occasionally, that is, ephemeral drainages, such as gullies running down a hillslope rather than permanently flowing creeks, streams, or rivers. Ephemeral drainage lines on hillslopes in undisturbed landscapes are smoothly concave in cross-section (no sharp edges), receive diffuse overland flow, and gently drain water from the surrounding slopes. (See figure 15.1.) These undisturbed landscapes do not have high rates of runoff or erosion. Landscapes that have a history of disturbance, however, often have hillslopes here drainage lines have become incised. (See figure 15.2.) If erosion cuts a channel deeper than 0.3m, the drainage line is defined as a gully; if the cut is less than 0.3m, it is called a rill.