Norwalk, CA Environmental Rules: Erosion Control (2026)
Key Facts
- Hillside trigger
- Natural slope 25%+ with cut/fill grading
- Project trigger
- 1+ acre disturbed, 10,000+ sq ft impervious
- State permit
- GCASP required over 1 acre disturbed
- Hillside home duty
- Divert roof/surface runoff to vegetation
- Permit gate
- No discretionary permit until Director confirms compliance
Summary
Norwalk requires an approved erosion and sediment control plan before a discretionary permit issues for hillside grading or any project disturbing an acre or more of land. New single-family hillside homes must specifically protect slopes and channels and route runoff to vegetation before discharge.
"Hillside" means property located in an area with known erosive soil conditions, where the development contemplates grading on any natural slope that is 25% or greater and where grading contemplates cut or fill slopes. ... A new single-family hillside home development project shall include mitigation measures to: (A) Conserve natural areas; (B) Protect slopes and channels; (C) Provide storm drain system stenciling and signage; (D) Divert roof runoff to vegetated areas before discharge unless the diversion would result in slope instability; and (E) Direct surface flow to vegetated areas before discharge, unless the diversion would result in slope instability.
Full Breakdown
040). The chapter's 'Construction' definition separately confirms that whenever grading or excavation disturbs more than one acre, coverage under the State of California's General Construction Activities Stormwater Permit is required. 105 designates such work a 'planning priority project': developments disturbing one acre or more and adding over 10,000 square feet of impervious surface, along with single-family hillside homes, must be conditioned on City approval of erosion and sediment mitigation before completion. i). D, E). F).
Violations & Fines
Failing to comply with an approved erosion/sediment mitigation plan, or with SUSMP requirements, is deemed a public nuisance under Section 18.04.110(A), abatable by the City with costs billed to the owner; false certification of BMP compliance is a separate violation. Enforcement can include civil injunctions, cost recovery and misdemeanor penalties under Chapter 1.16 of up to $1,000 and six months in jail, with each day a separate offense.
Frequently Asked Questions
Do I need an erosion control plan to grade a hillside lot in Norwalk?
How large does a construction project have to be to trigger Norwalk's erosion control rules?
What happens if I don't maintain the erosion control measures after a hillside home is built?
Sources & Official References
Other rules in Norwalk
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Erosion Control in Nearby Cities
How other cities in Los Angeles County handle erosion control.