Water harvesting is the technique of collecting runoff during periods of heavy rainfall in storage tanks, ponds, and other similar structures. It is the process of collecting runoff water from treated or untreated land surfaces, catchments, or roof tops and storing it for irrigation or drinking purposes in an open farm pond, closed water tanks/reservoirs, or in the soil itself (in situ moisture storage).
Runoff farming and rainwater harvesting agriculture are interchangeable expressions that describe farming in dry places using runoff from a catchment. Runoff farming is a type of water collection technology that is used to provide supplemental or life-saving irrigation to crops, particularly during seasons of low soil moisture. It is a method to induce, collect, store and conserve local surface runoff for agriculture in arid and semiarid regions.
Water harvesting is the process of collecting rainstorm-generated runoff from a specific region in order to produce water for human, animal, or crop consumption.
The water collected can be used right away, such as for irrigation, or it can be stored for later use in aboveground ponds, subterranean reservoirs, or shallow aquifers. As a result, water harvesting is an old tradition that has allowed some communities to thrive in semiarid and arid regions where other fresh water sources (lakes or aquifers) are scarce or unavailable.
In situ water harvesting with simple technologies allows for better water infiltration, temporarily impounds water on the soil surface to improve infiltration opportunity time, extends the availability of moisture to the crop, and allows the crop to survive in changing rainfall situations. Good in situ soil and water conservation practices improve soil porosity, increase infiltration and consequently increase soil water storage and promote crop growth.
The amount and distribution of rainfall, slope and soil type, depth and texture, especially clay content and clay type, all influence water holding capacity and hydraulic conductivity, affecting runoff and soil erosion, and all influence the selection of appropriate soil and water conservation measures for a location.
Runoff water induced by the following methods
– Land Alterations: Runoff can be increased by removing rocks and vegetation and compacting the soil surface. Land change, on the other hand, may cause soil erosion unless the slope is reduced. Property alteration can be a very cost effective approach to gather rain water in arid places where erosion is not extensive and low-cost hillside land is accessible.
– Chemical Treatment: Treating soils with chemicals that fill pores or make soil water resistant is a promising strategy for gathering rain water. Silicon salts, latexes, asphalt, and wax are some of the components employed in this process.
Methods of Water Harvesting
The catchment area should offer enough water for the crop, and the sort of farming used should maximize water use. Perennial crops, in general, are suited because they have deep root systems that can use runoff water that is held deep in the soil and is not lost to evaporation.
– Water Spreading: The meagre rainfall in desert places comes in the form of short, severe storms. Water quickly drains into gullies before flowing into the sea. Water penetrates the region, and floods induced by the storm’s quick discharge can be destructive to places that were previously unaffected. In this circumstance, water spreading is a straightforward irrigation method to apply.
Flood waters are diverted from their usual paths and dispersed across surrounding plains. Ditches, dikes, minor dams, and bush barriers redirect or slow the flow of water. Crops are grown in the wet flood plains or valley floods.
– Micro catchments: If a rain water catchment basin is made around a plant, it can grow in a place with insufficient rainfall for survival. A 40-centimeter-deep basin is dug at the lowest point within each micro catchment, and a tree is planted in it. The micro catchment runoff is stored in the basin. Traditional water harvesting systems: Tanka, Nadi, Khadin are the important traditional water harvesting systems of Rajasthan.
– Tanka: It’s an underground tank or cistern used to collect and store runoff water from a natural or intentionally prepared catchment, as well as from a roof top. The vertical walls are made of stone masonry or cement concrete, with a 10 cm thick concrete base. The tank’s capacity ranges from 1000 to 6,00,000 liters.
– Nadi or village pond: It is constructed for storing water from natural catchments. The capacity of Nadis ranges from 1200 m 3 to 15000 m 3.
– Khadin: It is a unique land use system where in runoff water from rocky catchments are collected in valley plains during rainy season. Crops are grown in the winter season after water is receded in shallow pond on the residual moisture.
– Dug Wells: Hand dug wells have been used to collect and store underground water and this water is lifted for irrigation. The quality of water is generally poor due to dissolved salts.
– Tanks: On the plains, runoff water from hill sides and forests is collected in tanks. Catchment area, storage tank, tank bund, sluice, spill route, and command area are the components of a typical tank system. With the use of a bund, runoff water from the catchment area is collected and stored in a storage tank on the plains. Spillways are constructed at one or both ends of the tank bund to dispose of excess water and prevent the tank bund from being breached. The sluice is located in the tank bund’s center region and allows for a regulated flow of water into the command area.
– Percolation Tanks: Water from the pond’s percolates into the soil, raising the region’s water table. Percolation tanks are employed for supplemental irrigation because the water level in the wells has improved.