Soil and Water Conservation Engineering and Irrigation
Soil and Water Conservation Engineering and Irrigation deals with erosion control, rainwater management and efficient water application. Questions cover erosion types, conservation structures, irrigation scheduling and efficiency, with local relevance to Assam’s high rainfall, sloping land and flood-prone areas.
Core rules
- Sheet, rill and gully erosion form a sequence; contour bunds, contour trenches, terracing and check dams slow runoff and trap soil.
- Vegetative measures and conservation tillage protect the surface; structural measures are used where runoff concentration is high.
- Irrigation water requirement is often expressed as depth (delta) over the command area. Volume = area × depth.
- Duty is the area irrigated per unit discharge over a season; higher duty means more efficient use of water.
- Efficiency chain: conveyance × distribution × application. Drip and sprinkler usually raise application efficiency compared with flood irrigation.
- Schedule irrigation from soil moisture, crop stage and evapotranspiration rather than fixed calendar dates.
Worked example
A 2 ha field needs 5 cm of irrigation. Volume = 2 × 10,000 m² × 0.05 m = 1,000 m³. A pump delivers 20 L/s = 0.020 m³/s. Running time = 1,000 ÷ 0.020 = 50,000 s = 13.9 hours. If application efficiency is 75%, the water actually needed at the field edge is 1,000 ÷ 0.75 = 1,333 m³, and pumping time rises to about 18.5 hours. Reasoning: convert depth to metres and litres to cubic metres before dividing.
Traps
Do not confuse delta (depth) with duty (area per discharge). Do not add efficiencies; multiply them. A 1 cm depth over 1 ha is 100 m³, not 1 m³. In erosion questions, remember that gully control comes after runoff diversion; treating a gully without checking upstream flow often fails.