The County of San Mateo Planning and Building Department has developed a new Drainage Manual that applies to new and redevelopment in unincorporated portions of the County. The Drainage Manual conveys San Mateo County’s drainage requirements for development on private property and establishes the appropriate level of review based on project size and location.  

Compliance with Drainage Manual is enforced under the County's Stormwater Pollution Prevention Ordinance for all new planning and building permits. The Drainage Manual provides three levels of drainage review depending on the complexity of the project: Basic, Prescriptive, and Standard. Standard Drainage Review projects require a Civil Engineer to prepare a drainage report and drainage plan. The below chart provides a basic breakdown of which projects typically qualify for which review process – see the full Drainage Manual for details and more information.

Reminder: Drainage Review in San Mateo County is divided between private and public property. Projects that encroach in the public right-of-way (ROW) will also be reviewed and permitted by the County’s Public Works Department in a separate permitting process that is not included in the scope of this Manual. Projects that create a substantial amount of new impervious surface in the ROW may be subject to additional flow, velocity, and/or volume control requirements and should contact the County’s Public Works Department for more information.

Information about previously existing drainage review policies is available on the County’s Surface Water Management page. For more information about drainage review and the Drainage Manual, please contact us via email.