VARIOUS FORMS OF UNDER-GROUND SOURCES INFILTRATION GALLERY
Infiltration gallery or horizontal or nearly - horizontal tunnels constructed at shallow depths (3-5m) along the bank of the river through the water bearing strata as shown in the figure. They are sometimes called as horizontal wells.
These galleries are constructed of masonry walls with concrete roof slab and derive their water from the aquifer by various drain pipes. These pipes are generally covered with gravel so as to prevent the entry of sand particles into the pipe. These tunnels are laid at a slope and water collected in them, is taken into a sump from where it is pumped to the treatment plant and distributed to the public. These are very helpful when sufficient quantity of water is available just below the ground level or so.
In order to obtain large quantity of water, a series of shallow wells are sunk in the banks of the river. The wells are constructed of brick masonry with open joints and are closed at top and open at the bottom. The water infiltrates through bottom sand bed and gets purified to some extent. For inspection a manhole cover is usually provided in roof slab.
These various infiltration wells are connected to a common sump well by porous drain pipes. This sump well is called JACK WELL. The water from this jack well is lifted to the treatment plant.
A natural outflow of ground water at the earth surface is said to form a spring a pervious layer sandwiched between two impervious layers gives rise to a natural spring. The springs are generally capable of supplying very small quantities (amounts) of water and therefore generally not regarded as sources of water supply.
YIELD AND SPECIFIC YIELD
The volume of ground water extracted by gravity drainage from the saturated water bearing material is known as YIELD and when it is expressed as the ratio of the volume of water that can be drained by the gravity to the gross volume of the soil then it is known as SPECIFIC YIELDA Therefore
= volume of water obtained by gravity / drainage gross volume of the soil.
Values of specific yield are dependent on soil' particle size, shape and distribution of pores and degree of compaction of the soil.
AQUIFER = An Aquifer is an water bearing stratum or formation capable of transmitting water in quantities sufficient to permit development.
AQUICLUDE = It is an impermeable stratum that may contain large quantities of water but whose transmission rates are not high enough to permit effective development.
CLASSIFICATION OF WELLS
The wells may be classified as Open wells, Tube wells