1. What is W-Index?

W-Index refers to the uniform rate of infiltration during a rainstorm after initial infiltration capacity has decreased. It represents the steady infiltration rate that occurs once the soil surface has become saturated, typically measured in mm/min or cm/h.

2. How Does the Calculator Work?

The calculator uses the W-Index formula:

Where:

• \( W \) — W-Index (mm/min)
• \( I \) — Intensity of Rainfall (mm/min)
• \( C_r \) — Runoff Coefficient (dimensionless)

Explanation: The W-Index represents the portion of rainfall that infiltrates into the soil after accounting for surface runoff. It's calculated by multiplying rainfall intensity by the complement of the runoff coefficient.

3. Importance of W-Index Calculation

Details: Accurate W-Index calculation is crucial for hydrologic modeling, flood prediction, irrigation planning, and stormwater management. It helps determine how much rainfall will infiltrate into the soil versus how much will become surface runoff.

4. Using the Calculator

Tips: Enter rainfall intensity in mm/min and runoff coefficient as a decimal between 0 and 1. The runoff coefficient represents the fraction of rainfall that becomes surface runoff (0 = no runoff, 1 = all runoff).

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for W-Index values?
A: W-Index values typically range from 0 to the rainfall intensity value, depending on soil type, land cover, and antecedent moisture conditions.

Q2: How does W-Index differ from infiltration capacity?
A: W-Index represents the steady infiltration rate after initial surface saturation, while infiltration capacity refers to the maximum rate at which soil can absorb water at any given time.

Q3: What factors affect the runoff coefficient?
A: Runoff coefficient is influenced by soil type, slope, vegetation cover, land use, and antecedent soil moisture conditions.

Q4: When is this calculation most useful?
A: This calculation is particularly useful for stormwater management, flood control design, and agricultural irrigation planning during rainfall events.

Q5: Are there limitations to this equation?
A: The equation assumes uniform rainfall distribution and doesn't account for temporal variations in infiltration rates or complex watershed characteristics.