Determine the 10-year peak discharge using the rational equation for a concrete parking lot that is 300 ft wide by 600 ft long. The longest flow path is 300 ft of sheet flow across the lot on a slope of 0.5 percent and 600 ft of shallow concentrated flow along the parking lot's length in a paved channel on a slope of 1.5 percent. Use SCS procedures to determine the time of concentration using a 2-yr, 24-hr rainfall of 2.4 in. Use Figure 11.26 for the rainfall intensity in the rational equation.

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25-yr average frequency 10-yr average frequency 2 4 -yr avcrage frequency 2-yr average frequency 2 0 10 20 30 40 50 60 70 80 9 100 110 120 Duration (min) Figure 11.26 Typical intensity-duration-frequency (IDF) curve