AgdaPkt 2025.10.27 Joint SA PFA - Laserfiche WebLink

Browse Search

Redwood City Stormwater Roadmap Preparing for Climate Change September 2025 5-1 Schaaf & Wheeler 5 Preparing for Climate Change To strengthen its resilience to future flood risks, Redwood City should update its municipal codes and infrastructure design standards in accordance with recommendations from recent regional and local planning studies. 5.1 Lowest Floor Elevation Requirements Currently, the City requires the lowest floor of residential and nonresidential construction to be constructed at or above base flood elevation, according to Section 41.24 of City Code. However, the City adopted the 2022 California Building Code (CBC) in Section 9.40 which requires most new development to be constructed one foot above the base flood elevation. The Base Flood Elevation (BFE) is the computed elevation to which floodwater is anticipated to rise during a base flood, commonly defined as the 1-percent annual chance (100-year) flood. BFEs are determined through detailed hydrologic and hydraulic modeling of watershed and floodplain conditions, accounting for rainfall, topography, conveyance capacity, and tidal or shoreline influences. BFEs are established and published by the Federal Emergency Management Agency (FEMA) as part of the Flood Insurance Study (FIS) and Flood Insurance Rate Maps (FIRMs). These maps are the official regulatory documents used by local jurisdictions to enforce floodplain management standards and by the National Flood Insurance Program (NFIP) to set insurance requirements and are publicly available at the FEMA Map Service Center. The Sea-Level Rise Vulnerability and Adaptation Planning Study recommends that shoreline protection infrastructure, including levees, public facilities, and other at-risk assets, be designed to accommodate up to 3.5 feet of sea-level rise, which corresponds to projected water levels by 2050 – 2070 under a medium-high risk aversion scenario (ESA, 2024). This guidance is consistent with the California Sea-Level Rise Guidance (Ocean Protection Council, 2024), which encourages local governments to incorporate sea-level rise projections into capital project planning, permitting, and design, especially for long-term infrastructure. Accordingly, the City should consider updating finished floor elevation requirements to a minimum of one foot above the base flood elevation for new development as described in the CBC 2022 and ASCE 24-24. Additionally, the City should consider updating finished floor requirements to include the effects of sea level rise for new development and public infrastructure not protected by shoreline protection. An additional study is recommended to determine zones in which raising the finished floor minimum to include sea level rise projections would be appropriate or feasible from a constructability standpoint. 5.2 Stormwater Infrastructure Capacity Requirements The City’s Storm Drain Design Criteria requires new closed conduits to convey the runoff volume and peak flow generated from 100-year storm event and allows pressurized flow conditions provided the hydraulic grade line (HGL) remains at least 0.5 feet below the inlet rim elevation. The Eastern Low-Lying Area Drainage Master Plan evaluated seven closed conduit systems in downtown Redwood City and found that none met the 100-year design capacity. Two systems had capacity for the 30-year storm, and four systems had capacity for the 10-year storm (Wood 11.A. - Page 22 of 53 453