Basin Lag For Mountainous Drainage Areas Calculator

Basin Lag Formula:

\[ Basin\ Lag = 1.715 \times \left( \frac{Basin\ Length \times Distance\ along\ Main\ Water\ Course}{\sqrt{Basin\ Slope}} \right)^{0.38} \]

Basin Lag:

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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 is an important parameter in hydrology for understanding the timing of runoff response in a watershed.

2. How Does the Calculator Work?

The calculator uses the Basin Lag formula for mountainous drainage areas:

\[ Basin\ Lag = 1.715 \times \left( \frac{Basin\ Length \times Distance\ along\ Main\ Water\ Course}{\sqrt{Basin\ Slope}} \right)^{0.38} \]

Where:

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

Explanation: This formula calculates the basin lag time based on the physical characteristics of the watershed, including its length, water course distance, and slope.

3. Importance of Basin Lag Calculation

Details: Accurate basin lag calculation is crucial for flood forecasting, watershed management, and designing hydraulic structures. It helps in predicting the timing of peak flows and understanding the hydrological response of mountainous drainage areas.

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 significance of the 1.715 coefficient?
A: The coefficient 1.715 is an empirical constant derived from regression analysis of mountainous drainage areas data.

Q2: Why is the square root of basin slope used in the formula?
A: The square root of basin slope accounts for the non-linear relationship between slope and flow velocity in mountainous terrain.

Q3: What are typical basin lag values for mountainous areas?
A: Basin lag values vary significantly but typically range from a few hours to several days depending on watershed characteristics.

Q4: Are there limitations to this equation?
A: This equation is specifically designed for mountainous drainage areas and may not be accurate for flat terrain or urban watersheds.

Q5: How does basin length affect the lag time?
A: Longer basin lengths generally result in longer lag times as water has to travel greater distances to reach the outlet.