DESIGN OF IRRIGATION WELLS
Generally, wells are designed for the purpose of irrigation, drainage, and domestic and industrial uses. The design of each type of well for each purpose requires particular attention, taking into account its purpose. Designing a water well involves selecting the proper dimensional factors for the well structure and choosing the materials to be used in its construction. Good design aims to assure an optimum, combination of performance, long service life and reasonable cost.
The hydraulic and (hydro-geological characteristics of aquifers vary greatly. Irrigation wells should be designed and constructed to take advantage of the natural conditions at a given location. When this is done, and the materials of construction are properly selected an economical and efficient well structure of long life can be achieved. Irrigation wells are usually designed to obtain the highest yield available from the aquifer, and the highest efficiency in terms of specific capacity. These factors bear directly upon operating costs. Two general principles influencing the design of both Open wells and tube wells are the water requirement of the crops to be irrigated and the location of well.
Water requirement: The yield potential of a well is evaluated on the basis of hydrological conditions of the area rainfall, runoff and recharge. When the yield potential of an area is not a limiting factor, a properly designed irrigation well should provide the required quantity of water to irrigate the entire area owned by the farmer, keeping in View the area to be irrigated, cropping pattern, and other needs such as domestic and livestock requirements.
When the yield potential of a well is more than the field water requirement of the farm under the control of the well owner, it is always economical to sell the additional yield to the neighbouring farmer, rather than limiting the capacity of the well to the requirement of a small or medium size folding. Often, it is not economical to have separate wells for individual small holdings. In an area with predominantly small holdings, it is essential that high discharge irrigation wells are owned jointly by a group of farmers or by a suitable public agency like the State Tube well Corporation.
Location of the well: The topography of the farm, the type of water conveyance system, the method of irrigation to be used, recharge possibilities of the area, safety of the pumping set and other installations are the main factors to be considered in deciding the location of the well. If the general slope of the farm does not exceed, 1 per cent and surface methods of water conveyance and distribution are to be employed, the well should be constructed at a higher elevation. If underground pipeline water distribution is to be used or sprinkler or drip irrigation are used. It is not necessary to locate the well at a high point. The location at a lower point of the farm usually facilitates better well yield.
Design of irrigation wells may be broadly divided into:
- (i) design of open wells in hard rock areas (consolidated formations) and unconsolidated, formations and
- (ii) design of tube wells in unconsolidated formations.
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Indian Council of Agricultural Research (2003). Vision of Water Research - Vision 2020. ICAR., New Delhi, P.45
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