Colusa County, CA Environmental Rules: Erosion Control (2026)

40, exists specifically because construction on steep ground can induce soil erosion, result in excessive grading, and increase wildfire danger and slope instability. 010 triggers the chapter for all grading and development of slopes exceeding 15 percent average natural slope anywhere in the unincorporated county, regardless of the underlying base zone. 050, Grading Standards: grading must respect the natural contour of the existing terrain wherever possible, is limited to building pads and access drives, and cuts over 16 feet from top to toe shall be discouraged.

Where cutting is unavoidable, cut slopes cannot exceed a two horizontal to one vertical ratio unless a soils or geologic study calls for something shallower, and the code directs that graded slopes be rounded and shaped to simulate the natural terrain and screened from public view. 050(E) requires graded slopes to be revegetated with a mixture of grass seeds, shrubs, or other native vegetation as recommended by the Director, though the Director can waive planting where rocky slopes will not support growth. These standards apply on top of, not instead of, Chapter 70 grading rules in the California Building Code and Chapter 9 (Land Grading and Leveling) of the Colusa County Code.

060 reinforce the same goal, requiring drainage facilities to be designed to minimize soil erosion and holding any off-site drainage increase to no more than a 10-year storm's peak rate until permanent facilities are completed. The Community Development Department reviews grading plans for compliance before issuing a building or grading permit.