Question

In watershed hydrology, the 'Kirpich's Equation' is used to directly compute

• A. Surface runoff
• B. Time of concentration
• C. Watershed's lag time
• D. Base flow

Hint:

Kirpich's equation: $t_c = 0.01947 L^{0.77} S^{-0.385}$ (Minutes). Used to determine rainfall intensity duration for peak runoff estimation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Time of concentration (\(t_c\)) is the time required for storm runoff to travel from the hydraulically most remote point in the watershed to the outlet.
Key Formula or Approach:
\[ t_c = 0.01947 \cdot L^{0.77} \cdot S^{-0.385} \quad \text{(Kirpich's Formula in Metric Units)} \]
where \(t_c\) is in minutes, \(L\) is maximum channel flow length (m), and \(S\) is average channel slope (m/m).

Step 2: Detailed Explanation:
Kirpich (1940) developed an empirical equation based on small agricultural watershed data in Tennessee.
In metric units:
\[ t_c = 0.01947 \times L^{0.77} \times S^{-0.385} \]
It directly computes the Time of Concentration (\(t_c\)) of a watershed from channel length and slope parameters.

Step 3: Final Answer:
Therefore, Kirpich's equation is used to compute Time of concentration, corresponding to option (B).