1. What is the Runoff Coefficient Formula?

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.

2. How Does the Calculator Work?

The calculator uses the Runoff Coefficient formula:

Where:

• \( C_r \) — Runoff Coefficient (dimensionless)
• \( Q_p \) — Peak Discharge (m³/s)
• \( A_D \) — Drainage Area (m²)
• \( i \) — Intensity of Rainfall (m/s)

Explanation: The formula calculates the ratio between the peak discharge and the product of drainage area and rainfall intensity, providing a measure of how much rainfall becomes surface runoff.

3. Importance of Runoff Coefficient Calculation

Details: Accurate runoff coefficient calculation is crucial for hydrological modeling, urban drainage design, flood prediction, and stormwater management systems. It helps engineers design appropriate drainage infrastructure and predict potential flood risks.

4. Using the Calculator

Tips: Enter peak discharge in m³/s, drainage area in m², and rainfall intensity in m/s. All values must be valid positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for runoff coefficients?
A: Runoff coefficients typically range from 0.05 for permeable surfaces like lawns to 0.95 for impervious surfaces like paved areas and roofs.

Q2: How does land use affect the runoff coefficient?
A: Urban areas with more impervious surfaces have higher runoff coefficients, while rural and vegetated areas have lower coefficients due to greater infiltration capacity.

Q3: Why is the runoff coefficient important in civil engineering?
A: It's essential for designing drainage systems, stormwater management facilities, and flood control structures by estimating the amount of runoff generated from rainfall.

Q4: Can the runoff coefficient change over time?
A: Yes, runoff coefficients can change due to urbanization, land use changes, soil compaction, and seasonal variations in vegetation.

Q5: How accurate is the runoff coefficient method?
A: While useful for preliminary design and estimation, the method has limitations and should be used with other hydrological methods for critical applications.