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The Duration Of Rainfall Given W-Index formula calculates the time duration of rainfall based on rainfall depth, runoff depth, and the W-Index infiltration rate. It provides a method to estimate how long a rainfall event lasted given these hydrological parameters.
The calculator uses the formula:
Where:
Explanation: The formula calculates rainfall duration by subtracting runoff depth from total rainfall depth and dividing by the uniform infiltration rate (W-Index).
Details: Accurate rainfall duration estimation is crucial for hydrological modeling, flood prediction, water resource management, and designing drainage systems and irrigation infrastructure.
Tips: Enter rainfall depth and runoff depth in centimeters, and W-Index in cm/h. All values must be positive, and rainfall depth should be greater than or equal to runoff depth for meaningful results.
Q1: What is W-Index in hydrology?
A: W-Index refers to the uniform rate of infiltration during a rainstorm after initial infiltration capacity has decreased, typically measured in cm/h.
Q2: How does this differ from φ-Index?
A: While both represent infiltration rates, W-Index specifically accounts for the uniform infiltration rate after the initial period, whereas φ-Index represents the average infiltration rate throughout the storm.
Q3: What are typical W-Index values?
A: W-Index values vary by soil type and conditions, typically ranging from 0.25 cm/h for clay soils to 2.5 cm/h or more for sandy soils under optimal conditions.
Q4: When is this calculation most useful?
A: This calculation is particularly useful in hydrological studies, flood forecasting, and designing stormwater management systems where rainfall duration needs to be estimated from measured parameters.
Q5: What are the limitations of this approach?
A: The calculation assumes uniform infiltration rate throughout the rainfall event and may not account for variations in soil moisture, vegetation cover, or changing rainfall intensity patterns.