Marin County, CA Environmental Rules: Erosion Control (2026)
Key Facts
- Governing section
- § 24.04.625, Erosion and sediment control
- Rainy season grading ban
- October 15 to April 15
- ESCP size trigger
- 10,000+ sq. ft. on 15%+ slope
- Watercourse buffer trigger
- 50-100 ft. depending on corridor
- Enforcement
- Agency-ordered stop-work by written notice
Summary
Marin County requires an approved erosion and sediment control plan for any project with a grading permit, or any building permit the County finds could cause significant erosion, under Section 24.04.625 of the County Code. Grading is barred outright between October 15 and April 15 without the Public Works Agency's prior approval.
(a)All disturbed surfaces, including, but not limited to, cut and fill slopes, building pads, driveways and areas cleared of vegetation, shall be protected against erosion and sediment discharges by measures that the agency determines to be appropriate to the site, phase of construction and time of year.(b)When required by the phase II stormwater permit or by the agency, a project shall have an erosion and sediment control plan (ESCP) which addresses erosion and sediment control, and pollution prevention during the construction phase, as well as final stabilization control measures... (d)Grading operations shall not be conducted during the rainy season (October 15 through April 15) without prior approval from the agency.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Municipal Code: Supplement 2026 Update 1).
Full Breakdown
625(a) requires every disturbed surface, cut and fill slopes, building pads, driveways, and cleared areas, to be protected against erosion and sediment discharge using measures the Agency finds appropriate to the site, construction phase, and time of year. 08, for any building or other permit the Agency determines could cause significant erosion or non-stormwater discharges, for grading disturbing more than 10,000 square feet on a slope over 15 percent, and for grading within 50 feet of a watercourse in the city-centered corridor or 100 feet in the inland rural corridor.
The ESCP must describe the project, list site-specific best management practices such as detention basins, erosion control blankets, hydroseed, and construction entrances, and note any outside permits needed, including a Clean Water Act Section 404 permit or a Fish and Wildlife 1600 Streambed Alteration Agreement. Subsection (d) bars grading during the rainy season, October 15 through April 15, unless the Agency approves a phasing plan showing no substantial risk of increased sediment discharge; when rainy-season grading is allowed, the exposed area and the time it stays exposed must both be minimized.
Projects may also need coverage under the State Water Resources Control Board's general construction stormwater permit, and the Agency can require financial security, a letter of credit, cash deposit, or bond, to guarantee the temporary controls stay in place during and after construction.
Violations & Fines
Working contrary to Section 24.04.625 lets the Agency order the work stopped by written notice; work must stay stopped until the Agency authorizes it to resume. Implementation of an approved ESCP is a standing condition of any building permit, grading permit, or other Agency permit issued for a covered project, so a lapsed or ignored ESCP puts the whole permit at risk, in addition to any civil or criminal remedies otherwise available under the Marin County Code.
Frequently Asked Questions
When is an erosion and sediment control plan required?
Can I grade during the rainy season?
What has to be in the ESCP?
What happens if erosion controls aren't maintained?
Sources & Official References
Other rules in Marin County
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