1. What is Manning's Equation?

Manning's equation is an empirical formula that calculates the flow capacity in open channels and drainage pipes. It relates the flow rate to the channel/pipe geometry, roughness coefficient, and slope gradient.

2. How Does the Calculator Work?

The calculator uses Manning's equation:

Where:

• \( Q \) — Flow capacity (m³/s)
• \( n \) — Manning's roughness coefficient
• \( A \) — Cross-sectional area of flow (m²)
• \( R \) — Hydraulic radius (m)
• \( S \) — Slope or gradient (m/m)

Explanation: The equation calculates the volumetric flow rate based on the channel/pipe characteristics and flow conditions.

3. Importance of Flow Capacity Calculation

Details: Accurate flow capacity calculation is crucial for drainage system design, flood risk assessment, irrigation system planning, and wastewater management.

4. Using the Calculator

Tips: Enter the roughness coefficient (typical values: 0.012-0.015 for concrete, 0.013-0.017 for PVC), cross-sectional area, hydraulic radius, and slope. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What are typical Manning's n values for drainage pipes?
A: Concrete pipes: 0.012-0.015, PVC pipes: 0.013-0.017, Corrugated metal: 0.022-0.027

Q2: How is hydraulic radius calculated?
A: Hydraulic radius = Cross-sectional area / Wetted perimeter

Q3: What units should be used?
A: Use metric units: area in m², radius in m, slope in m/m, flow in m³/s

Q4: When is Manning's equation applicable?
A: For uniform, steady flow in open channels and partially full pipes with turbulent flow conditions

Q5: What are the limitations of Manning's equation?
A: Not suitable for pressurized flow, rapidly varied flow, or non-uniform channel conditions