Manual cover

The County of San Mateo Planning and Building Department is in the process of developing a new Drainage Manual that will apply to new and redevelopment in unincorporated portions of the County. The intent of the Drainage Manual is to clearly convey San Mateo County’s drainage requirements for development on private property and establish the appropriate level of review based on project size and location.  

The Drainage Manual is currently in draft form and is implemented on a pilot-level basis 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.


chart for permit steps

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.