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Runoff Volume Equation:
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The runoff volume equation calculates the amount of water that flows off a surface during rainfall events. It's essential for stormwater management, drainage design, and flood prediction in civil engineering and environmental planning.
The calculator uses the runoff volume equation:
Where:
Explanation: The equation multiplies rainfall depth by surface area to get total water volume, then applies the runoff coefficient to account for infiltration, evaporation, and surface retention.
Details: Accurate runoff volume calculation is crucial for designing effective drainage systems, sizing retention ponds, managing stormwater infrastructure, and preventing urban flooding and erosion.
Tips: Enter rainfall in inches, area in square feet, and runoff coefficient as a decimal between 0 and 1. Typical runoff coefficients: pavement (0.8-0.95), grass (0.05-0.35), forest (0.01-0.20).
Q1: What is a runoff coefficient?
A: A decimal value between 0 and 1 that represents the fraction of rainfall that becomes surface runoff, accounting for infiltration, evaporation, and surface storage.
Q2: How do I determine the appropriate runoff coefficient?
A: Runoff coefficients depend on surface type, slope, soil conditions, and rainfall intensity. Standard engineering references provide coefficient values for different surfaces.
Q3: Why convert inches to cubic feet?
A: Rainfall in inches over area in square feet directly gives volume in cubic feet (1 inch over 1 sq ft = 0.0833 cu ft, but the calculator handles this conversion automatically).
Q4: Can this calculator be used for large watershed areas?
A: Yes, but for large areas, consider dividing into sub-areas with different coefficients and summing the results for better accuracy.
Q5: What are the limitations of this simple equation?
A: It doesn't account for rainfall intensity, duration, antecedent moisture conditions, or complex hydrological processes. More sophisticated models are needed for precise engineering designs.