• Kirpich Equation for Watershed Time of Concentration:
• In hydrology, the Kirpich (1940) equation expresses the time of concentration ($T_c$) in minutes for small agricultural watersheds:

where:

• $L$ is the maximum length of flow along the main channel (meters)
• $S$ is the dimensionless average slope of the watershed channel ($H / L$)
• Conclusion: 0.0195 L^0.77 S^-0.385 (Option 1).

Correct option: (1) 0.0195 L^{0.77} S^{-0.385}