Res21 16010 final - Laserfiche WebLink

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2021 Multijurisdictional Local Hazard Mitigation Plan Source/Location Drainage Area (square miles) Discharge (cubic feet/second) 10-Percent 2-Percent 1-Percent 0.2- Percent At Pope Street d d d 730 d Combined Middlefield Road and Pope Street Overflows d d d 1,154 d South of Highway 101 d d d 1,154 d North of Highway 101 d d d 570 d San Mateo Creek At mouth (City of San Mateo) d d d 1,0177 d At downstream side of S. Humboldt St. and E. Third Ave. d d d 1,4937 d 400 feet downstream of Crystal Springs Road 33.3 d d 2,124 d Woodhams Creek At Esmeralda Terrace 0.7 220 340 390 480 At confluence with La Honda Creek 0.9 270 520 480 600 Note: All locations are at mouth unless otherwise noted. Locations do not include jurisdictional boundaries. a. Capacity of Atherton Creek box culvert b. 1,750 cfs spilled upstream of study area during the 1-percent annual chance flood event c. 170 cfs spilled to Redwood City during the 1-percent annual chance flood event d. Data not available e. 170 cfs spilled to Redwood City during the 1-percent annual chance flood event f. Flows reduced due to overflow into San Carlos and Redwood City g. Flows reduced due to upstream spill h. Values do not include overland flow from Belmont Creek i. Inflow to low area west of track; 1-percent annual chance outflow is 170 cfs. j. Flows limited by culvert capacity, ponding, and pump capacity k. Value reflects spills from the channel into Palo Alto Source: San Mateo County FIS, FEMA 2019 Coastal Flooding The frequency and severity of coastal flooding are based on storm surge height, which is the height of water accounting for waves. The 2019 FEMA FIS for San Mateo County mapped 59 transects along the Pacific Ocean, identifying 10-, 50-, 100- and 500-year still-water elevations for each transect. Table 11-7 summarizes the high, low and mean elevations observed for each return interval along the Pacific Ocean coastline, representing the steady state water depth not accounting for breaking waves. These are the projected elevations of floodwaters in the absence of waves resulting from wind or seismic effects. 11-18 San Gregorio Creek At upstream limit of study 9.3 1,800 3,000 3,500 4,500 Upstream of confluence with La Honda Creek 9.5 1,800 3,000 3,600 4,600 Downstream of confluence with La Honda Creek 21.3 3,300 4,800 6,900 9,300 Downstream of State Highway 84 21.8 3,300 4,800 6,900 9,300 At downstream limit of study 22.4 3,500 6,100 7,200 9,700 San Vicente Creek At upper study limit 1.4 340 570 660 880 At Etheldore Street 1.7 400 670 780 1,000 At Pacific Ocean 1.9 430 720 840 1,100 Spruce Branch At Colma Creek 1.5 540 770 810 830