by Randy Stemler
November 15, 1999

Rolling Dips
Rolling dips excavated into the roadbed along a distance of 100 feet or more prevent rilling. Constructed at an acute angle of 30-45 degrees to the road alignment, they’re as deep as 4-5 inches at the uphill end, and 16 inches at discharge, depending on the road grade.

Culverted Crossings
Stream crossings commonly use culverts to convey water under roads. Serious problems develop if culvert size isn’t adequate during peak flows. Preferably, culverts should be set at grade (in the bottom of the channel). Extensions can be attached to prevent discharge onto erodible fill. To reduce the likelihood of a culvert's inlet plugging, a fence post can be pounded in just upstream of the culvert to catch debris. Rocks, logs, and vegetation at the culvert outlet serve to dissipate the energy of water and reduce erosion. A rock-surfaced road is hardened for better traction, and doesn’t rill easily.

Critical Dips
When a culvert becomes plugged, a low spot constructed in the road called a critical dip keeps the creek confined to the channel (perhaps washing out the crossing), but more importantly prevents diversion down the road that could result in erosion several orders of magnitude greater.


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Table of Contents for Mattole Restoration Newsletter, Issue 14 - Winter/Spring 2000