Sonoma County Code Chapters 11 and 11A require construction-grading permits and Erosion Prevention and Sediment Control plans for almost any ground-disturbing work. During the October 15 - May 15 wet season, no more than 1 acre or 20% of the permitted work area (whichever is greater) may have erodible soil exposed at any time, and best management practices (BMPs) must be functional whenever the National Weather Service forecasts a 30% or greater chance of rain within 24 hours - in any season. Sonoma's hillside and vineyard/orchard grading rules (Chapter 36 VESCO) add further restrictions on slopes over 10%.
Chapter 11 of the Sonoma County Code (Construction Grading and Drainage) requires a construction-grading permit before any grading, land clearing, vegetation removal, or other ground disturbance not specifically exempted. Section 11.04.010 sets out permit thresholds; Permit Sonoma's GRD-011 Erosion Prevention and Sediment Control Notes are the standard plan-sheet requirement. During the County-defined wet season (October 15 through May 15) the area of erodible land exposed at any one time may not exceed 1 acre or 20% of the permitted work area, whichever is greater, and time of exposure must be minimized to the maximum extent practicable. Outside the wet season, BMPs (silt fence, fiber rolls, straw wattles, stabilized construction entrances, hydromulch or other surface protection) must be in place and functional on any day when the National Weather Service forecasts 30% or greater chance of rain within the next 24 hours. Chapter 11A (and where applicable Chapter 36, the Vineyard and Orchard Site Development Ordinance - VESCO) impose additional protections on hillside sites: any new vineyard or orchard on slopes 10-50% requires a VESCO erosion-control plan, water-quality and biotic-resource setbacks from streams (typically 25-200 ft depending on stream class), and post-construction vegetative cover. Slopes over 50% are generally prohibited from new vineyard/orchard development. The County coordinates inspections with the Regional Water Quality Control Boards under the MS4 permits and the State Construction General Permit (sites of 1 acre or greater also require a SWPPP filed with the State Water Board).
Grading without a permit, exceeding the 1-acre / 20% exposed-soil limit during the wet season, or failing to deploy BMPs before a forecasted rain event are violations of Chapter 11/11A. Penalties include stop-work orders, mandatory restoration, administrative civil liability under Sonoma County Code, and parallel Water Code Section 13350 fines up to $10,000 per day per violation if sediment reaches a waterway. Damage to streams, fisheries, or wetlands may also trigger California Fish and Game Code Section 1602 enforcement and federal Clean Water Act Section 401/404 penalties. Chapter 36 (VESCO) violations may result in permit revocation, replanting orders, and recorded notices of violation against the parcel.
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See how Sonoma County's erosion control rules stack up against other locations.
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