In this article we will discuss about the design of deep and shallow wells with the help of suitable diagrams.
Classification of open wells is deep and shallow wells. It is according to the mode of water contribution to the well from the sub-soil. A shallow well is that well which does not encounter mota formation. Mota is an impervious patch of small thickness situated in pervious soil mass. A shallow well derives water from the underground pervious rock or soil formation through the bottom or sides of the well depending upon the nature of construction.
A deep well is that well which goes below the water table and finally finds its foundation in the mota formation. The mota formation is a local impervious patch. To derive the water from the soil a bore (15 to 23 cm in diameter) is drilled in the mota formation to tap the water of underlying pervious soil mass. (See Fig. 8.5).
The water which enters the well through the bore first brings fine sand along with it because of high velocity and pressure of the incoming water. Progressively a hollow space is formed below the bore and when the rate of discharge from the well equals the rate of entry of the incoming water only clear water enters the well.
The presence of a perfect mota layer with high outcrop below the water table may create artesian conditions. If a hole is drilled in the mota layer a water jet may enter through the bore in the open well (See Fig. 8.6).
