Watersheds and Catchment Management
This domain tests watersheds as hydrological units and the planning of catchment treatment. Expect questions on boundaries, runoff estimation, structural and non-structural measures, and upstream–downstream effects. Exam answers should name the outlet and the treatment sequence.
Core rules
- A watershed is an area draining to a common outlet; its boundary follows ridges, not administrative lines.
- Watershed management combines soil and water conservation, vegetation, check dams, farm ponds and drainage-line treatment.
- Plan from the ridge to the valley: treat upper slopes first, then gullies, then the outlet. Maintenance and community ownership are part of the design.
Worked example
A 500 ha watershed receives 700 mm rain. Total rainfall volume = 500 × 10,000 m2 × 0.7 m = 3.5 million m3. With a runoff coefficient of 0.25, runoff is 0.875 million m3. Thirty check dams storing 5,000 m3 each hold 150,000 m3, about 17% of runoff. That can recharge local wells but cannot eliminate downstream flow; the plan must leave environmental release.
Traps
- Drawing watershed boundaries along village or taluka boundaries.
- Counting only structures and ignoring maintenance.
- Capturing so much runoff that downstream users and ecosystems lose water.
- Assuming a check dam recharges all strata equally.