Erosion Control: Redwood City vs San Mateo
How do erosion control rules compare between Redwood City, CA and San Mateo, CA?
Redwood City and San Mateo have similar restriction levels.
Redwood City, CA
San Mateo County
San Mateo County Planning & Building Department requires submittal of an Erosion and Sediment Control Plan prior to issuance of any demolition, grading, or building permit that involves site disturbance. Standard BMPs include silt fencing, straw wattles, erosion control blankets, stabilized construction entrances, and covered stockpiles. Wet-season work (October 1 - April 30) triggers additional inspection requirements and may be restricted on steep slopes. SWPPP required for sites 1+ acre.
View full Redwood City rules →San Mateo, CA
San Mateo County
San Mateo requires Erosion and Sediment Control Plans for all projects requiring a demolition, grading, or building permit that involve site disturbance. Projects disturbing one acre or more require a state Construction General Permit with SWPPP. The city's hillside areas require particular attention to erosion prevention.
View full San Mateo rules →Key Facts Comparison
| Fact | Redwood City | San Mateo |
|---|---|---|
| ESCP Required | All ground-disturbing work | - |
| Wet Season | Oct 1 to Apr 30 | - |
| SWPPP | Sites 1+ acre | - |
| Stabilization | Within 14 days | - |
| Final Cover | 70% vegetation | - |
| Required | - | All construction with site disturbance |
| SWPPP Threshold | - | 1+ acres of disturbance |
| Rainy Season | - | October through April — high risk |
| Hillside Areas | - | Elevated erosion concern |
| Public Works | - | 650-522-7300 |
Highlighted rows indicate differences between cities.
Redwood City FAQ
Do I need erosion controls for a small addition?
Any project that disturbs soil — even a small addition or trench for utilities — requires basic BMPs like silt fence at the downslope edge and inlet protection on nearby storm drains. The County ESC Manual shows simplified standards for residential-scale projects. Your building plans must include an ESC sheet.
What happens if a storm washes sediment off my site into a creek?
You face enforcement from both the County (stop-work, fines) and the SF Bay RWQCB, which can assess up to $25,000/day under the Porter-Cologne Act. You'll also be responsible for cleanup costs and potential CDFW notification if fish habitat is affected. Maintain BMPs before every rain event.
San Mateo FAQ
Do I need an erosion control plan in San Mateo?
Yes. All projects with site disturbance requiring a demolition, grading, or building permit must submit an Erosion and Sediment Control Plan.
When is erosion risk highest in San Mateo?
The rainy season from October through April presents the highest erosion risk, especially on the western hillside areas.
What happens if sediment enters the storm drain?
Sediment discharge to storm drains is a violation of the city's NPDES permit and the federal Clean Water Act. State fines can reach $10,000 per day.
Compare other topics
See how Redwood City and San Mateo compare on other ordinance categories.
Want to add a third city?
Use our full comparison tool to compare up to three cities.
Open Comparison Tool