Q, the flow rate in cubic feet per second, is equal to I, the intensity of rainfall in inches per hour, times A, the runoff area in acres, times c, a fudge runoff factor indicating how absorbent the ground is. A relatively impermeable area such as an asphalt parking lot or a rooftop would have a 'c' ranging from 0.90 to 1.00, whereas a grassy field
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