A large circular parking lot with a diameter of 400 feet is being constructed as overflow parking for the state fairgrounds. All stormwater will drain as sheet flow to the center, flow into a drop inlet, and travel through a pipe system to the nearest stream. The parking lot will be mowed grass (clay soil) with a slope of 2 percent toward the center. The 2-yr, 24-hr rainfall is 2.4 inches. Using SCS procedures to determine the time of concentration and the IDF curve in Figure 11.26, determine the 10-yr peak discharge that will be required to design the pipe system.

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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