Certified Inspector of Sediment and Erosion Control (CISEC) Practice Exam 2026 – The All-in-One Guide for Exam Success!

Rill and gully erosion is described by a size-based progression: small, shallow channels called rills form from concentrated runoff, typically up to about 3 inches deep. When several rills converge, their erosive power combines and the channel deepens and enlarges, creating a gully, usually deeper than 3 inches. This distinction—rills being shallow and gullies forming from the convergence of multiple rills to greater depths—captures the practical progression engineers use to classify erosion features. The idea that gullies are simply any deeper feature or that rills are deeper than gullies doesn’t fit the observed process, and saying they’re the same thing ignores the clear difference in scale and formation. In practice, recognizing this helps determine appropriate stabilization measures: rills may be treated with stabilization and diversion sooner, while gullies indicate more advanced erosion needing more substantial remediation.