Napa County regulates erosion control through Napa County Code Chapter 18.108 (Conservation Regulations) and Chapter 13.15 (Grading Control). Any agricultural earthmoving, grading, or vineyard replanting on slopes over five percent requires an approved Erosion Control Plan from the Napa County Conservation Division before work begins.
Napa County Code Chapter 18.108 defines an erosion hazard area as any portion of a parcel with slope over five percent. Under Section 18.108.060, no agricultural earthmoving, grading, or improvement may begin on slopes over five percent until an Erosion Control Plan (ECP) complying with Section 18.108.080 has been submitted to and approved by the Conservation Director. Replanting an existing vineyard on slopes greater than five percent also triggers ECP review. ECPs require winter cover crops, sediment basins, road and culvert design, riparian setbacks, and prohibition of work in the wet season unless specifically allowed. Chapter 13.15 (Grading Control) provides the underlying grading permit framework, with thresholds and engineered drainage requirements that intersect Chapter 18.108 on hillside parcels. Chapter 18.108.025 imposes additional intermittent and perennial stream setbacks, particularly important after the 2017 Atlas and 2020 Glass Fires increased post-burn erosion risk.
Agricultural earthmoving, grading, or vineyard replanting on slopes over five percent without an approved Erosion Control Plan violates Napa County Code Chapter 18.108 and can trigger stop-work orders, restoration requirements, civil penalties, and discretionary permit revocation. Sediment discharges into a watercourse can also draw state enforcement under California Water Code 13385, with civil liability up to $10,000 per day. Repeat violators face escalating administrative fines.
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