Stormwater and drainageGuide

When you need a county permit to change drainage

By The Downspout · Updated Oct 11, 2026 · 1 min read Share

In unincorporated Sonoma County, a drainage permit is required before any drainage improvement. Grading over 50 cubic yards needs a grading permit.

This covers land the county governs. Cities such as Santa Rosa and Petaluma have their own rules. Ask your city.

You need a grading permit if

• You cut or fill more than 50 cubic yards.
• A cut or fill is deeper than 3 feet.
• A cut makes a slope over 5 feet high and steeper than 2 to 1.
• Fill over 1 foot deep supports a structure, or sits on ground steeper than 15 percent.
• You place fill in a flood hazard area.

Exemptions exist in Chapter 11 of the Sonoma County Code. Routine farming is not counted as grading.

Drainage permit

• It is required before any drainage improvement or related work, including site clearing and soil disturbance.
• You need a separate permit for each site.
• New drainage features need a drainage report. It must show no harm to structures or neighbors.
• For regular grading, the owner may prepare the report. Engineered grading needs a civil engineer.

What to expect

• Do not start before the permit is issued. Doing so violates county code and can bring fines.
• Most grading permits cost roughly $2,000 to $4,000, per Permit Sonoma.
• Staff aim to send first comments within six weeks of a complete application.
• A permit lasts three years. A final inspection is required.

The Resource Conservation District adds that permits may be needed for retaining walls, cisterns over 5,000 gallons, outlets to creeks, and runoff sent onto a neighbor's land.

Who to call

Permit Sonoma Engineering: (707) 565-2268. General: (707) 565-1900.

Related: slow it, spread it, sink it.

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