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District updates FEMA floodplain mapping and winter outlook; University Creek LOMR approved, FEMA final determination possible by Sept. 2026
Summary
District staff said FEMA CTP4 mapping covers about 36 miles of streams and that the University Creek LOMR was approved in November 2025; staff also reported mixed snowpack signals with low snow-water equivalent despite above-average accumulated precipitation and brief La Niña conditions continuing into spring.
District staff told the Board on March 9 that FEMA Community Technical Partner mapping work is progressing and that recent winter storms produced mixed hydrologic signals that affect flood-season risk.
Eric Griffin, the District’s development review coordinator, said CTP4 mapping — conducted with Wood Rodgers — analyzes hydrology and hydraulics for roughly 36 miles of Placer County streams. Griffin said the initial CTP4 submittal was made in Summer 2025 and staff is finalizing responses for final submittal; he also noted the University Creek Letter of Map Revision (LOMR) was approved in November 2025. Griffin summarized CTP3 milestones, including comment and appeal periods, and said FEMA may issue a Letter of Final Determination as soon as September 2026.
A director asked whether blue lines on the CTP4 exhibits mean areas are unmapped; staff explained the District and its Technical Advisory Committee prioritize which streams are mapped in each CTP cycle and that member agencies may request restudies where substantial changes have occurred. The District also described FEMA’s separate LOMR process to update mapping outside the CTP schedule.
Brad Brewer presented a winter-season update, saying the UC Berkeley Central Sierra Snow Lab (CSSL) reported total accumulated precipitation at 114% of average as of March 4, 2026, and the California Department of Water Resources’ northern Sierra 8-station precipitation index was 109% of average as of March 6. However, Brewer said SWE at the lab was 53% of average (Mar. 6) and DWR’s overall Sierra SWE was 58% of normal for Mar. 6 and 54% of the April 1 average, a decline attributed in part to recent high-elevation rain-on-snow events. Brewer noted the five-day snow-depth measurement for the February storm cycle was the third snowiest five-day period at the lab since 1970. He said NWS/NOAA short-term forecasts indicate continued weak La Niña conditions through summer with a 50–60% chance of a new El Niño late in 2026, and that the region is projected to see below-average precipitation and above-average temperatures through March–May 2026.
When asked whether below-normal precipitation is preferable from a flood-control perspective, Brewer said normal precipitation is better for statewide water distribution and that gradual precipitation helps reservoirs and reduces flood risk compared with intense storms.
