1. What is the Rainwater Runoff Equation?

The rainwater runoff equation estimates the volume of water that flows off a roof surface during rainfall. It's calculated by multiplying roof area, rainfall amount, and runoff coefficient to determine the total runoff volume.

2. How Does the Calculator Work?

The calculator uses the runoff equation:

Where:

• \( RR \) — Runoff volume (m³)
• \( A \) — Roof area (m²)
• \( R \) — Rainfall depth (m)
• \( C \) — Runoff coefficient (0-1)

Explanation: The equation calculates the total volume of rainwater that runs off a roof surface, accounting for the efficiency of water collection based on surface material and slope.

3. Importance of Runoff Calculation

Details: Accurate runoff calculation is crucial for rainwater harvesting system design, stormwater management, drainage system planning, and flood risk assessment.

4. Using the Calculator

Tips: Enter roof area in square meters, rainfall in meters, and runoff coefficient between 0-1. Typical runoff coefficients: metal roofs (0.95), tile roofs (0.9), flat roofs (0.8).

5. Frequently Asked Questions (FAQ)

Q1: What is a runoff coefficient?
A: The runoff coefficient represents the fraction of rainfall that becomes surface runoff rather than being absorbed or evaporated (0 = no runoff, 1 = all rainfall becomes runoff).

Q2: How do I measure roof area?
A: Calculate the horizontal projection area of the roof. For simple rectangular roofs: length × width. For complex shapes, break into smaller rectangles.

Q3: Why convert rainfall to meters?
A: Using consistent units (meters for all dimensions) ensures accurate volume calculations in cubic meters.

Q4: What affects runoff coefficient?
A: Roof material, slope, surface roughness, and rainfall intensity all influence how much water runs off versus being retained or evaporated.

Q5: Can this be used for other surfaces?
A: Yes, the same principle applies to other impervious surfaces, though runoff coefficients may differ based on surface type and condition.