Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : AMC-I represents the low runoff potential.
Reason (R) : The watershed soils are dry enough for satisfactory cultivation.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• B. Both (A) and (R) are true and (R) is the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember the three AMC levels:
- AMC-I: Dry soil \(\rightarrow\) High infiltration \(\rightarrow\) Low runoff.
- AMC-II: Average moisture condition.
- AMC-III: Saturated soil \(\rightarrow\) Zero/Low infiltration \(\rightarrow\) High runoff potential.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In the SCS Curve Number (SCS-CN) method, the Antecedent Moisture Condition (AMC) refers to the moisture content of the soil prior to a rainfall event.
AMC is categorized into three levels (AMC-I, AMC-II, and AMC-III) based on the total rainfall received in the preceding 5 days.

Step 2: Detailed Explanation:
Let us evaluate the Assertion and the Reason:
- Assertion (A): "AMC-I represents the low runoff potential."
This statement is correct. Under AMC-I, the soil is dry.
Dry soil has a high infiltration capacity, allowing most of the early rainfall to penetrate into the ground rather than flowing over the surface.
Consequently, the runoff potential is at its lowest level.
- Reason (R): "The watershed soils are dry enough for satisfactory cultivation."
This is the correct definition of the soil state under AMC-I.
Because the soil has low moisture, it is in a dry state suitable for tillage and cultivation activities.
Let us evaluate the relationship:
Because the watershed soils are dry enough for satisfactory cultivation (R), the soil has a high capacity to absorb water.
This high infiltration capacity directly results in low runoff potential (A).
Therefore, both (A) and (R) are true, and (R) is the correct explanation of (A).

Step 3: Final Answer:
The correct option is (B).