To collect water
Explanation
Contour barriers are a soil conservation measure implemented on slopes. They involve constructing barriers along the contour lines of the land using available materials such as stones, grass, or soil to intercept surface runoff.
Function of Trenches:
- Water Collection: Trenches are excavated immediately in front of the barriers. Their primary function is to trap rainwater flowing down the slope.
- Infiltration: By collecting the runoff, these trenches allow the water to settle and percolate into the ground, thereby increasing soil moisture and recharging groundwater levels.
- Erosion Control: By halting the speed of water flow, the trenches prevent the runoff from gaining enough velocity to wash away the fertile topsoil.
Analysis of Other Options:
- To grow crops To grow crops: Crops are cultivated on the land strips between the barriers, not inside the trenches designed for water retention.
- To stop wind To stop wind: Wind erosion is primarily mitigated using shelterbelts or windbreaks (rows of trees), not ground-level trenches.
- To mark field boundary To mark field boundary: While barriers may physically separate areas, their specific design purpose in this context is ecological conservation, not cadastral demarcation.
Key Takeaway:
In the contour barrier method, trenches are dug in front of the barriers specifically to collect water and facilitate its seepage into the soil.