water wells consisting of pipes ranging in size from 6 to 45 cm in diameter and sunk into an aquifer . Tubewells are constructed by installing a pipe below the ground surface passing through different geological formations comprising water-bearing and non-water-bearing strata. Blind pipes (casing pipes) are placed in the non-water-bearing layers and well screens are placed in the water-bearing layers . Several tubewells have been and are being installed worldwide for meeting water demands in domestic,agricultural and industrial sectors. The type of tubewell to be constructed depends on the type of geological formation, intended use of the well and the availability of fund. their construction,development and maintenance Tubewells are also classified based on the depth, method of construction, entry of water into
the wells and the type/nature of the aquifer . As mentioned above, based on the depth of the well, tubewells are classified as shallow tubewells or deep tubewells. Shallow tubewells are of low capacity and their average depth is normally less than 35 m. They mostly tap one aquifer. Deep tubewells are of high capacity and their depth usually ranges from 60 to 300 m . They often tap two or more aquifers. Based on the method of construction, tubewells are classified as bored tubewells, drilled tubewells, driven tubewells and jetted tubewells; they are described in Tubewells in unconsolidated formations generally consist of blind pipes, strainers and gravel pack (if necessary). However, tubewells in hard-rock formations are known as borewells, because the borehole remains stable for most of its depth and the tube is placed only in the upper weathered soil zone No strainer/screen or gravel pack is required for borewells. https://www.maridia.com.mx/perforacion-de-pozos-de-agua
Moreover, tubewells are also classified as fully penetrating tubewells or partially penetrating tubewells depending on whether the well screen penetrates the saturated thickness of the aquifer fully or partially. In some special hydrogeologic situations, the drilled hole is terminated at the top of the confined aquifer without penetrating it, and hence no strainer is required; such wells are called cavity wells or non-penetrating wells which are described below. In coastal areas, partially penetrating wells with controlled rate of pumping are used expediently to „skim‟ the upper layer of fresh water overlying the saline water. Such tubewells are popularly known as skimming Wells
Cavity well is a shallow tubewell drilled in an alluvial formation. If a relatively thin impervious formation consisting of stiff clay, conglomerate or stone is encountered at a shallow depth underlain by an extensive thick sandy confined aquifer, then it is an excellent location for constructing a cavity well. A hole is drilled using the hand boring set, and casing pipe is lowered to rest firmly on the stiff clay layer. Water enters the cavity well through the bottom only and screens are not used in such wells. Thus, the cavity wells do not penetrate the aquifer, and hence they are also known as non-penetrating Wells
