Question

Given below are two statements regarding curve number method of runoff estimation
Statement I: Curve number method is also known as the Hydrologic Soil Cover Complex Method
Statement II: Curve number method is based on the recharge capacity of the watershed
In light of the above statements, choose the correct answer from the options given below

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

The Curve Number (CN) ranges from 0 to 100:
- CN = 100: Completely impermeable surface (all rainfall becomes runoff).
- CN \(\rightarrow\) 0: Highly permeable, vegetated soil (nearly all water infiltrates).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The USDA Soil Conservation Service Curve Number (SCS-CN) method is a widely used empirical model.
It is designed to estimate direct runoff volume from a storm event based on watershed characteristics.
Detailed Explanation:
Let us analyze Statement I:
The SCS-CN method is also formally known as the Hydrologic Soil Cover Complex Method.
The term "complex" refers to the unique combination of a hydrologic soil group (soil properties) and land use/cover.
This combination is used to assign a specific Curve Number (CN) to the watershed.
Thus, Statement I is true.
Let us analyze Statement II:
The curve number method is based on a water-balance hypothesis.
It assumes that the ratio of actual retention to potential maximum retention is equal to the ratio of actual runoff to potential maximum runoff: \[ \frac{F}{S} = \frac{Q}{P - I_a} \] The model calculates runoff based on parameters like soil type, land use, tillage practices, and antecedent soil moisture.
It is not designed based on the groundwater recharge capacity of the watershed.
Thus, Statement II is false.

Step 2: Final Answer:
Statement I is true, but Statement II is false.