1. What is a Drainage Spread Calculator?

Definition: This calculator estimates the width of water spread in drainage systems based on flow rate, slope, roughness coefficient, and cross-sectional area.

Purpose: It helps engineers and planners design effective drainage systems by predicting how water will spread across surfaces.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Spread — Width of water spread (meters, m)
• Q — Flow rate (cubic meters per second, m³/s)
• S — Slope (dimensionless, m/m)
• n — Manning's roughness coefficient (dimensionless)
• A — Cross-sectional area (square meters, m²)

Explanation: The flow rate is divided by the product of slope, roughness coefficient, and cross-sectional area to determine the spread width.

3. Importance of Spread Calculation

Details: Accurate spread calculation ensures proper drainage design, prevents flooding, and helps maintain infrastructure integrity.

4. Using the Calculator

Tips: Enter the flow rate in m³/s, slope (default 0.01), Manning's roughness coefficient (default 0.013 for concrete), and cross-sectional area. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is Manning's roughness coefficient?
A: It's an empirical value representing the channel/pipe surface roughness. Common values: 0.013 for concrete, 0.024 for grass, 0.03 for natural streams.

Q2: How do I measure the slope?
A: Slope is the vertical drop divided by horizontal distance (e.g., 1m drop over 100m = 0.01 slope).

Q3: What affects the cross-sectional area?
A: Channel shape and dimensions. For rectangular channels: width × depth. For circular pipes: π × radius².

Q4: How do I estimate flow rate (Q)?
A: Q = Rainfall intensity × Drainage area × Runoff coefficient. Or use flow measurement devices.

Q5: What if my spread is too wide?
A: Consider increasing slope, reducing roughness, or enlarging the channel cross-section.