1. What is Stormwater Runoff Volume?

The stormwater runoff volume is the amount of water that flows over the land surface during and after precipitation events, calculated by subtracting losses (like infiltration and interception) from total rainfall and multiplying by the drainage area.

2. How Does the Calculator Work?

The calculator uses the runoff volume equation:

Where:

• \( Rainfall \) — Total precipitation (inches)
• \( Losses \) — Water lost to infiltration, evaporation, etc. (inches)
• \( Area \) — Drainage area (acres)

Explanation: The equation calculates the volume of water that doesn't infiltrate into the ground and instead flows over the surface.

3. Importance of Runoff Calculation

Details: Accurate runoff volume estimation is crucial for designing drainage systems, flood control measures, and stormwater management facilities.

4. Using the Calculator

Tips: Enter rainfall and losses in inches, area in acres. All values must be valid (rainfall ≥ 0, losses ≥ 0, area > 0).

5. Frequently Asked Questions (FAQ)

Q1: What are typical loss values?
A: Losses vary by soil type and land cover. Typical values range from 0.1-0.5 inches for impervious areas to 0.5-1.5 inches for pervious areas.

Q2: How do I convert the result to other units?
A: 1 acre-inch = 27,154 gallons = 102.8 cubic meters. Multiply your result by these factors for conversion.

Q3: What's the difference between rainfall and effective rainfall?
A: Effective rainfall is (Rainfall - Losses) - the portion that actually contributes to runoff.

Q4: Does this account for peak flow rates?
A: No, this calculates total volume only. Peak flow depends on rainfall intensity and duration.

Q5: How accurate is this simple formula?
A: It provides a reasonable estimate for small areas. For complex watersheds, more sophisticated models are needed.