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EXHIBIT C DRAINAGE DESIGN CRITERIA CHART The use of underground storm drain systems shall be required, when any of the following conditions exist: a. The limitations outlined in Table below. b. Future upstream development will cause drainage problems. c. The need for cross drainage of surface flow on arterial highway. d. Excess nuisance water in residential areas (surface flow maximum - 1000 feet). e. Median drainage is required. MAXIMUM ALLOWABLE STREET FLOODING Type of Street Frequency Storm Maximum Allowable Flooding Local 10 100 Top of curb At or below R/W line Arterial Highway 10 25 100 Parking lane plus 1/2 travel lane or 17 feet Top of curb At or below R/W line Sump Condition Same as above Same as above DESIGN STORM FREQUENCY 100 -Year Habitable structures protection. 25 -Year All open and underground channels and storm drains with drainage areas less than 640 acres and tributary to the Santa Ana River watershed. 10 -Year All open and underground channels and storm drains with drainage areas less than 640 acres and tributary to all other watersheds. ---PAGE BREAK---