Basin Lag For Foot Hill Drainage Area Calculator

Basin Lag Formula:

\[ \text{Basin Lag} = 1.03 \times \left( \frac{L_{\text{basin}} \times L_{ca}}{\sqrt{S_B}} \right)^{0.38} \]

Basin Lag (tp):

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1. What is Basin Lag?

Basin Lag is the elapsed time between the occurrences of the centroids of the effective rainfall. It represents the time delay between rainfall and runoff response in a watershed.

2. How Does the Calculator Work?

The calculator uses the Basin Lag formula:

\[ \text{Basin Lag} = 1.03 \times \left( \frac{L_{\text{basin}} \times L_{ca}}{\sqrt{S_B}} \right)^{0.38} \]

Where:

\( L_{\text{basin}} \) — Basin Length measured along the watercourse from the basin divide to the gauging station (km)
\( L_{ca} \) — Distance along Main Water Course from the gauging station to a point opposite to the watershed centroid (km)
\( S_B \) — Basin Slope of the catchment under consideration

Explanation: This formula calculates the basin lag time using geometric characteristics of the watershed, including length measurements and slope.

3. Importance of Basin Lag Calculation

Details: Basin lag is crucial for flood forecasting, hydraulic design, and watershed management. It helps determine the time response of a watershed to rainfall events and is essential for designing drainage systems and flood control measures.

4. Using the Calculator

Tips: Enter basin length and distance along main water course in kilometers, and basin slope as a dimensionless value. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range of basin lag values?
A: Basin lag values typically range from a few hours to several days, depending on watershed size, shape, and characteristics.

Q2: How does basin slope affect the lag time?
A: Steeper slopes generally result in shorter lag times as water flows more quickly through the watershed.

Q3: What are the limitations of this formula?
A: This formula is specifically designed for foot hill drainage areas and may not be accurate for other terrain types or extreme watershed conditions.

Q4: How accurate is this calculation method?
A: The formula provides a reasonable estimate for preliminary design purposes, but field measurements may be needed for critical applications.

Q5: Can this formula be used for urban watersheds?
A: This formula is primarily designed for natural foot hill drainage areas and may require modification for urban watersheds with significant impervious surfaces.