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Runoff Coefficient Formula:
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The Runoff Coefficient is a dimensionless coefficient that relates the amount of runoff to the amount of precipitation received. It represents the fraction of rainfall that becomes surface runoff rather than being absorbed into the ground.
The calculator uses the Runoff Coefficient formula:
Where:
Explanation: The formula calculates the ratio between the peak discharge and the product of precipitation intensity and drainage area, adjusted by the conversion factor 1/3.6.
Details: Accurate runoff coefficient calculation is crucial for hydrological modeling, flood prediction, urban drainage design, and watershed management. It helps in understanding how different surfaces respond to rainfall events.
Tips: Enter peak discharge in m³/s, mean intensity of precipitation in m/s, and drainage area in m². All values must be positive and valid for accurate calculation.
Q1: What is the typical range of runoff coefficients?
A: Runoff coefficients typically range from 0 (all water absorbed) to 1 (all water runs off). Different surfaces have different coefficients (e.g., paved areas: 0.8-0.95, grassy areas: 0.05-0.35).
Q2: Why is the 1/3.6 factor used in the formula?
A: The 1/3.6 factor is a conversion factor that accounts for unit consistency when working with different measurement units (mm/hr to m/s conversion).
Q3: How does land use affect runoff coefficients?
A: Impervious surfaces like concrete and asphalt have higher runoff coefficients, while permeable surfaces like grass and forest have lower coefficients due to better water absorption.
Q4: When is this calculation most important?
A: This calculation is particularly important in urban planning, stormwater management, flood control design, and environmental impact assessments.
Q5: Are there limitations to this equation?
A: The equation assumes uniform rainfall distribution and may not account for complex terrain, soil saturation levels, or varying infiltration rates during prolonged rainfall events.