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The following factors shall be utilized for calculating the CVWD 100-year-plus design standard for regional storm water facilities:

A. One-Hundred-Year Flood. The 100-year flood should be estimated using long-term streamflow records within the watershed where available. For streams with no gauges or inadequate length of record, the 100-year flood will be determined from rainfall-runoff (hydrologic) modeling. CVWD standards for rainfall depth, depth area reduction factors (DARFs) and guidelines for rainfall-runoff modeling are given within the CVWD Development Design Manual.

B. Freeboard for Incised Channels. An incised channel is one where the adjacent ground elevation is higher than the 100-year flood water surface elevation within the channel. Incised storm water channels shall be designed to convey the 100-year flood with a minimum of three feet of freeboard above the design water surface elevation. CVWD may require additional freeboard based on the size and location of the watershed and the associated flood hazard potential.

C. Freeboard for Leveed Channels. A leveed condition is one where the 100-year flood water surface elevation is higher than the adjacent ground elevation. Levees shall be designed with a minimum of four feet of freeboard from the levee crest elevation to the 100-year flood water surface elevation. CVWD may require additional freeboard based on the size and location of the watershed and the associated flood hazard potential. (Ord. 1234.2 § 2, 2017)

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