Costa Mesa, CA Environmental Rules: Flood Zones (2026)

Article 10 of the zoning code, sections 13-77 through 13-82, creates Costa Mesa's floodway and floodplain districts to keep the city eligible for FEMA flood insurance and to prevent development that would raise flood levels for neighboring property. Under section 13-79(a), any parcel shown in a designated flood hazard area on the Orange County countywide Flood Insurance Rate Map, dated August 9, 2002 and any later revision, is subject to this article on top of its underlying zoning. The development services director serves as floodplain administrator and reviews every project in Zone A for compliance, including confirming that permits required from other agencies, such as a Clean Water Act section 404 permit, have been obtained.

Within the regulatory floodway itself, section 13-80(a) allows only flood-control channels, levees and spreading basins, general agricultural uses without permanent structures, public utility transmission lines, and open-space recreation uses like parks, trails and golf courses without permanent structures. Section 13-80(b) prohibits the reverse: permanent structures and buildings other than those conveying floodwater or utilities, all dwelling units, and any landfill, excavation or encroachment that would obstruct flood flow, raise the flood elevation at any point, or broaden the floodplain. A property owner who wants a use not on either list can seek a conditional use permit, but the planning commission or city council cannot approve it unless engineering studies from a registered professional engineer or architect show the project will not endanger public safety, restrict the floodway's carrying capacity, or increase flood heights or velocity.