Unit 6
Tube Well Irrigation
Occurrence of ground water:-During the rain or if water is collected on the surface of soil, then this water is goes downward till the hard strata is came. The moisture/water is then becomes static and collected in zones of soil which may be saturated or unsaturated zone .this water collected is then called occurrence of ground water in that zone.
Water table:-The upper most surface level of the zone of saturation is called a water table. When the rain water is collected in pound, then the water will goes downward due to seepage from unsaturated soil to saturated soil. This water is stopped by hard strata or rocks. So the seepage water is collected in saturated zone of soil layer. This water table is thus called underground water table.
Radius of influence:- The radial distance from the centre of a wellbore hole to the point where there is no lowering of the water table is known as the radius of influence.
Depression head:- When the water is pumped out from the wall, then the level of the well is reduced, then the difference in levels between original water level in the well is called depression head.
Cone of depression:-A cone of depression are occurs in aquifers when ground water is pumped out from a well. In the unconfined aquifers the cone of depression is a reduction in pressure head surrounding the pumped well.
Aquifers:-It is a wet underground layer of water bearing permeable rocks (gravels, silts or sand).these are saturated regions of the subsurface that produce economical quantity of water to lift irrigation by tube well or well.
Unconfined aquifers:- Those aquifers which contains water table in their upper boundaries. This area contains almost all the ground water table. These aquifers cannot contain by any impervious layer.
Confined aquifers:- It is the aquifer which is confined by an impervious stratum at the top. That the water is contained between the hard strata around it just like as water is flowing through pipe.
Yield of well:- When the water is lifted from the well contineously. Then the water level goes decreasing and there will be contribution of water from the surroundings layer into the well. If the lifting / water taken is increasing then the drawdown of water will be increasing and the fine silt /sand also entered into the well will started from the previous strata of the soil. At this stage water structure become unstable . due to this drawdown is always kept
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