Given below are two statements: Assertion (A) and Reason (R). Assertion (A): Mechanical measures include contour bunding, contour cultivation and bench terracing. Reason (R): Mechanical measures consist of destruction of mechanical barriers across the line of flow of water.

Correct option is C

The correct answer is (C) (A) is correct but (R) is not correct.

Explanation:

Assertion (A) is Correct: Mechanical (or engineering) measures are structural modifications made to the land to control soil erosion. Contour bunding involves building small embankments across the slope, contour cultivation refers to plowing and planting across the slope rather than up and down, and bench terracing transforms steep slopes into a series of flat platforms.

Reason (R) is Incorrect: The goal of mechanical measures is the construction, not the destruction, of barriers. These barriers act as physical obstructions to the "line of flow," breaking the velocity of runoff water. By slowing down the water, these structures reduce its erosive power and give it more time to infiltrate into the subsoil.

Information Booster:

Slope Limits: Mechanical measures are usually adopted when the land slope is too steep (typically >2%) for biological measures (like crop rotation or mulching) to be effective on their own.

Hydrologic Impact: These structures change the land's hydrology by increasing the time of concentration—the time it takes for water to travel from the furthest point of the watershed to the outlet.

Additional Knowledge:

Contour Bunding: Most effective in low-rainfall areas with permeable soils where the primary goal is moisture conservation.

Graded Bunding: Used in high-rainfall areas to safely lead excess water away through a protected channel.

Bench Terracing: Typically required on very steep slopes (16% to 33%) to make the land suitable for intensive cultivation while preventing massive landslides or soil wash-off.