Runoff estimation using Khosla’s empirical formula For catchment runoff estimation by Khosla’s formula Qy = Py − K (1.8 Ty + 32), what is the mean recommended value of the constant K?

Introduction / Context:
Several empirical relations are used for quick runoff estimation when detailed hydrologic data are scarce. Khosla’s formula introduces a constant K to account for temperature and catchment losses in converting precipitation to annual runoff.

Given Data / Assumptions:

• Qy = Py − K (1.8 Ty + 32), where Qy is annual runoff (cm), Py is annual precipitation (cm), and Ty is mean annual temperature (°C).
• “Mean value” of K is requested for general use.
• Catchment has no extreme anomalies in infiltration/evaporation beyond empirical calibration range.

Concept / Approach:
K is a correction factor capturing combined effects of evapotranspiration and catchment abstractions tied to temperature. Standard references suggest a representative mean K near 1.23, used where local calibration is unavailable.

Step-by-Step Solution:
Identify the formula structure and the role of K.Recall the commonly adopted mean value for Indian catchments: K ≈ 1.23.Select the closest matching option: 1.23.

Verification / Alternative check:
Worked examples in introductory hydrology texts frequently employ K = 1.23 for preliminary estimates before basin-specific calibration.

Why Other Options Are Wrong:

• 1.21, 1.25, 1.27, 1.31 are not the standard “mean” choice; they may apply to specific local calibrations but are not the default mean value.

Common Pitfalls:
Using a generic K without validating against local streamflow records; always calibrate when data are available to reduce error.

Final Answer:
1.23