Total Storm Runoff Given W Index Calculator

Formula Used:

\[ R = P - I_a - (W \times t_e) \]

Total Storm Precipitation (P):

Depression and Interception Losses (I_a):

W-Index (W):

Duration of Rainfall Excess (t_e):

hours

Total Storm Runoff (R):

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1. What is Total Storm Runoff?

Total Storm Runoff is rain that flows off building rooftops, driveways, lawns, streets, parking lots, construction sites, and industrial storage yards. It represents the portion of precipitation that does not infiltrate into the ground and instead flows over the surface.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R = P - I_a - (W \times t_e) \]

Where:

\( R \) — Total Storm Runoff (cm)
\( P \) — Total Storm Precipitation (cm)
\( I_a \) — Depression and Interception Losses (cm)
\( W \) — W-Index (cm)
\( t_e \) — Duration of Rainfall Excess (hours)

Explanation: The equation calculates runoff by subtracting losses (depression storage, interception, and infiltration) from total precipitation.

3. Importance of Storm Runoff Calculation

Details: Accurate runoff estimation is crucial for urban drainage design, flood prediction, water resource management, and environmental impact assessment of development projects.

4. Using the Calculator

Tips: Enter all values in appropriate units (cm for precipitation, losses, and W-Index; hours for duration). All values must be non-negative.

5. Frequently Asked Questions (FAQ)

Q1: What is W-Index?
A: W-Index is the average infiltration rate during the time when the rainfall intensity exceeds the infiltration rate.

Q2: What are Depression and Interception Losses?
A: These represent the portion of precipitation that is returned to the atmosphere through evaporation from plant surfaces and stored in surface depressions.

Q3: When is this formula most applicable?
A: This formula is particularly useful for urban hydrology and small watershed analysis where detailed infiltration data is available.

Q4: What are the limitations of this approach?
A: The method assumes constant infiltration rates and may not accurately represent complex watershed behavior during extreme storm events.

Q5: How does this relate to other runoff calculation methods?
A: This is a simplified approach that complements more complex methods like the SCS Curve Number method or unit hydrograph analysis.