Water harvesting, storage and recycling.pptx

Water harvesting in dryland

1. Water harvesting, storage and recycling PRASAD P 2021004079

2. Water harvesting Water harvesting is a method to induce, collect, store and conserve surface runoff of the locality. This collected water can be used for agriculture and other purposes in arid and semiarid regions. Each and every water harvesting structure has a collection or catchment area and a command or utilization area . In dryland regions the catchment area is usually in higher proportion compared to command area .

3. CONT. This harvested water may be stored for future use or can be allowed percolate for recharging the ground water . The principle of collecting and using precipitation from a small catchment area is often referred to as rainwater harvesting . Harvesting excess water during periods of heavy rainfall and storing it in farm ponds and tanks not only saves water for future use but also helps to conserve water and soil from runoff losses .

4. Methods of water harvesting Macro catchment water harvesting First is a case of normal rainfall with high intensity on a few rainy days causing runoff . This runoff can be guided and collected in storage structures called farm ponds and reused for supplemental irrigation to crops suffering from moisture stress. Micro catchment water harvesting Total rainfall is less and soil storage is inadequate for supporting crop growth. Part of the land is left barren and uncultivated known as donor area and is treated as to increase runoff. The runoff from the donor strip is directed towards the lower adjacent strip to increase soil moisture storage used for raising crops .

5. Farm ponds Farm ponds are dug out ponds , usually square or rectangular in shape, harvest rainwater runoff and store in for future use . In undulating terrain, farm pond can be constructed and can be fed by diverted surface runoff (from terrace etc.) or by seepage of ground water or by diverted stream / spring flow . Sometimes it may be a combined structure made up by excavation of soil together with embankment by soil.

6. Farm ponds

7. Percolation ponds Percolation tanks are small water storage structures constructed in the natural paths of the runoff water or are constructed in the outlet of diversion channels or waterways where the land topography were flattened or depressed . The objective of the percolation pond is to raise the yield of wells situated in the downstream of the pond within a radius of 900 m (3000 feet) through better percolation effect as a result of which the extent under well irrigation is expected to be stepped upto increase the food production. Percolation ponds are beneficial only when situated in a government or community land or a large area farm with a well below the tank from which the water can be drawn. They collect and impound the surface runoff from the catchments of streams during monsoon rains and store it for longer time to facilitate infiltration and percolation of water into the soil substrata with a view to raise the ground water level in the zone of influence of the pond. The percolation pond also collect and detain the sediment.

8. Percolation pond

9. Checkdam Check dams are small barriers built across the direction of water flow on shallow rivers and streams for the purpose of water harvesting . The small dams retain excess water flow during monsoon rains in a small catchment area behind the structure. Pressure created in the catchment area helps force the impounded water into the ground. The major environmental benefit is the replenishment of nearby groundwater reserves and wells.

10. Purpose of checkdam It cuts off the runoff velocity and reduces erosive activity. The water stored improves soil moisture of the adjoining areas and allows percolation to recharge the aquifers . While constructing a series of check dams on along stream course, the spacing between two check dams should be beyond their water spread. The height of the check dam should be such that even during the highest flood, water does not spill over the banks . Check dams acts as a structure across a small river in order to break the flow of water during the monsoons, and allows it to seep into the soil.

11. Types of ponds Embankment ponds : These are suitable for hilly areas and areas with undulating topography. This involves construction of small length of dam or obstruction across a water course. Effective storage of rain water is possible in such ponds. Excavated ponds : These are suitable for flat areas and plains. These are dug out ponds or farm ponds. They are of multipurpose usage and the harvested water can be utilized for supplemental irrigation for crops, livestock, fishery etc. Percolation ponds : These are small water storage tanks / structures which are constructed across natural streams. They collect and impound the surface runoff from catchments and streams during monsoon rain. Thus they facilitate infiltration and percolation of water into subsoil strata thereby augmenting ground water recharge, which is the major objective.

12. Advantages of farm pond Harvested water can be used for protective irrigation to crops at critical stages Since runoff is properly guided through grassed water ways, erosion is checked Earth excavated from ponds can be used for bunding and levelling of fields Stored water can be used as drinking water for humans and animals, for spraying operations and for fish rearing. High value tree crops can be raised near farm ponds with protective irrigation A chain of farm ponds can recharge ground water in the region

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