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

Correct Answer: (C) (A) is correct but (R) is not correct.

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 to reduce runoff, and bench terracing converts steep slopes into a series of flat platforms that slow water flow and prevent soil loss.

Reason (R) is Incorrect:
Mechanical measures involve the construction, not the destruction, of barriers across the line of flow of water. These barriers act as physical obstructions that reduce the velocity of runoff water. By slowing down the water flow, they decrease its erosive power and allow more time for infiltration into the soil.

Information Booster

Slope Limits:
Mechanical measures are usually adopted when the land slope is relatively steep (generally more than about 2%) and biological or agronomical measures alone are not sufficient to control soil erosion.

Hydrologic Impact:
These structures modify the land’s hydrology by increasing the time of concentration, meaning the time required for water to move from the farthest point of the field or watershed to the outlet. This reduces peak runoff and soil loss.

Additional Knowledge

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

Graded Bunding:
Used in high-rainfall areas to safely drain excess runoff through a protected channel.

Bench Terracing:
Adopted on steeper slopes (about 16–33%) to make the land suitable for cultivation while preventing severe soil erosion.