Lag Time Of 1-h Unit Hydrograph Calculator

Formula Used:

\[ T_{p1} = \frac{1.56}{\left(\frac{Q_{pd}}{A}\right)^{0.9}} \]

Lag Time of a 1-h Unit Hydrograph (T_p1):

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1. What is the Lag Time of a 1-h Unit Hydrograph?

The Lag Time of a 1-h Unit Hydrograph is the time interval from the midpoint of the rainfall excess to the peak discharge in a unit hydrograph. It is a crucial parameter in hydrological modeling for predicting the timing of peak flows in watersheds.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ T_{p1} = \frac{1.56}{\left(\frac{Q_{pd}}{A}\right)^{0.9}} \]

Where:

\( T_{p1} \) — Lag Time of a 1-h Unit Hydrograph (Hour)
\( Q_{pd} \) — Peak discharge of a D-h Unit hydrograph (m³/s)
\( A \) — Area of Catchment (m²)

Explanation: The formula calculates the lag time based on the ratio of peak discharge to catchment area, raised to the power of 0.9, and scaled by the constant 1.56.

3. Importance of Lag Time Calculation

Details: Accurate lag time estimation is essential for flood forecasting, watershed management, and designing hydraulic structures. It helps in understanding the response time of a catchment to rainfall events.

4. Using the Calculator

Tips: Enter the peak discharge in cubic meters per second (m³/s) and the catchment area in square meters (m²). Both values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a unit hydrograph?
A: A unit hydrograph represents the direct runoff response of a watershed to a unit depth of excess rainfall over a specific duration.

Q2: How does catchment area affect lag time?
A: Generally, larger catchments have longer lag times due to the greater distance water must travel to the outlet.

Q3: What factors influence peak discharge?
A: Peak discharge is influenced by rainfall intensity, catchment characteristics, soil type, land use, and antecedent moisture conditions.

Q4: Can this formula be used for any catchment?
A: This formula is specifically designed for certain hydrological conditions and may not be universally applicable without calibration.

Q5: What are typical values for lag time?
A: Lag time varies widely depending on catchment size and characteristics, ranging from minutes for small urban catchments to hours or days for large river basins.