1. What is Runoff Volume Calculation?

Runoff volume calculation estimates the amount of water that flows off a surface during rainfall events. It's essential for drainage design, flood control, and stormwater management in civil engineering and environmental planning.

2. How Does the Calculator Work?

The calculator uses the runoff volume formula:

Where:

• \( Rainfall \) — Depth of rainfall in feet
• \( Area \) — Surface area in square feet
• \( Runoff\ Coefficient \) — Decimal representing the fraction of rainfall that becomes runoff

Explanation: The runoff coefficient accounts for surface characteristics - impervious surfaces have higher coefficients (0.8-0.95) while pervious surfaces have lower coefficients (0.05-0.35).

3. Importance of Runoff Volume Calculation

Details: Accurate runoff volume estimation is crucial for designing drainage systems, sizing retention ponds, preventing flooding, and managing stormwater in urban and rural development projects.

4. Using the Calculator

Tips: Enter rainfall depth in feet, surface area in square feet, and appropriate runoff coefficient (0-1). All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical runoff coefficient values?
A: Asphalt/concrete: 0.8-0.95, Lawns: 0.05-0.35, Forest: 0.01-0.20, Roofs: 0.75-0.95 depending on material.

Q2: Why use feet instead of inches for rainfall?
A: Using consistent units (feet for all dimensions) ensures volume is calculated in cubic feet. Convert inches to feet by dividing by 12.

Q3: How does slope affect runoff volume?
A: Steeper slopes generally increase runoff coefficients as less water infiltrates and more runs off quickly.

Q4: When is this calculation most accurate?
A: For small drainage areas with relatively uniform surface characteristics and moderate rainfall intensities.

Q5: Are there more complex methods available?
A: Yes, for larger watersheds, methods like the Rational Method or NRCS Curve Number method provide more sophisticated analysis.