1. What is Rainwater Flow Rate?

Definition: This calculator estimates the flow rate of rainwater runoff based on rainfall intensity and catchment area.

Purpose: It helps engineers, architects, and planners design proper drainage systems and rainwater harvesting solutions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Flow rate (cubic meters per second)
• \( i \) — Rainfall intensity (millimeters per hour)
• \( A \) — Catchment area (square meters)

Explanation: The formula converts rainfall intensity over an area into a volumetric flow rate, with 3600 converting hours to seconds and millimeters to meters.

3. Importance of Flow Rate Calculation

Details: Accurate flow rate estimation ensures proper sizing of gutters, downspouts, drainage pipes, and storage systems to prevent flooding and water damage.

4. Using the Calculator

Tips: Enter the rainfall intensity in mm/h and catchment area in m². Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Where can I find rainfall intensity data?
A: Check local meteorological data or use design standards for your region (e.g., 100-year storm values).

Q2: What's included in catchment area?
A: Include all surfaces that direct water to your collection point (roofs, paved areas, etc.).

Q3: Why is the result in m³/s?
A: This is the standard SI unit for flow rate in engineering calculations.

Q4: Should I consider runoff coefficient?
A: This basic formula assumes 100% runoff. For more accuracy, multiply result by a runoff coefficient (0.8 for roofs, 0.3-0.5 for lawns).

Q5: How do I convert to other units?
A: 1 m³/s = 1000 L/s = 15,850 gpm (gallons per minute).