Geology Of GroundWater Occurence

Water Table

Water table lies in between the zone of aeration and zone of saturation in the capillary zone of zone of saturation.water table lies above the confined aquifer.As long as water does not crosses the water table it serves as the groundwater boundary but it flows such as percolating water reaches to water table the flow lines are no longer parallel the surface as an impermeable boundary.

Infiltration

The process of penetrating of water in soil is called infiltration.The rate of infiltration is influenced by condition of soil surface,vegetation cover and soil properties including hydraulic conductivity,porosity as well as moisture content.the infiltration rate f is the rate at which water enters the soil surface expressed in in/hr or cm/hr.the potential infiltration rate f is the rate when water is ponding occurs the actual rate is less than that of potential rate.the cumulative infiltration f is the accumulated depth of water infiltrated which can be written as

F(t)=F(a)da which determines the infiltration rates

Soil Moisture

soil moisture is the key variable in controlling the exchange of water and heat energy within the land surfaces and atmosphere through the transpiration and evaporation.Soil moisture plays a very important role in development of wather pattern and the production of precipation generaally the soil moisture is the water that is held in the space between the soil particles .The surface soil moisture is the water that is in the upper 10cm of soil,whereas root zones of soil moisture is vthe water that is available in plants in upper 200cm of soil.The remote sensing is done to detect different types of defect with in soil.only the moisture at top few cm can be detected.

Permeability of sediments

The ability of rock or soil to tranmit afluid is called permeability.This is of medium and independent of fluid properties.for the practical work in groundwater hydrology water is the prevailing fluid,hydraulic conductivity k has benn employed.A medium is generally called unit hydraulic conductivityif it trnsmit unit volume of water in unit time.At prevailing kinematics viscocity,cross section of unit area is measured right angles to direction of flow.The rate at which water is prevailing kinematics viscocity which is transmitted through unit widthof aquifer under unit hydraulic gradient is transmitivity.It is mostly employed in groundwater hydraulics.the hydraulics conductivity of soil or rock depends on the physical factors including porosity,particle size,distribution,shape of particles,arrangement of particles etc.mainly clay materials exhibit low values of hydaulic conductivity of sand and gravels display high values.The two uniformly sieved sands sample were taken which were mixed in varying proportions and corresponding hydraulic conductivitieswere again determined.Results shows mixture of two sands display a conductivity less than interpolated value and smaller grainsoccupy larger fraction of space than uniform grains of either size.

Aquifers

Grounwater are found in many forms among them aquifers are the most important one.Aquifers is the formation which contain sufficient saturated permeable materials to yield significant quantities of water to wells and springs.The best example of aquifers are sand and gravels.the aqufers consists of unsaturated portions of permeable unit.Aquifer are extensive and overlain and underlain by confined bed,which is relatively impermeable materials significantly adjacent to one or more aqufers.The different types of confing of bed are as follows:

Aquiclude

A saturated relatively impermeable materials which do not yield appreciable quantities of water of wells.example:-clay

Aquifuge

A relatively impermeable formation which neither transmit nor contains water.example:-solid granite

Aquitard

A saturated poorly permeable stratum which impeded groundwater movement and does not yield water freely to wells which transmit appreciable water to form adjacent aquifers.It consistute important groundwater storage zone.Example:-sandy clay

Types of Aquifers

Most of the aquifers are large areal extent and may visualized as groundwater storage reservoirs.Eg:-Edwards aquifer.water enter groundwater from both natural as well as artificial recharge.groundwater flow by the action of gravity or can be extacted from wells.normally, the annual volume of water removed or replaced is a small fraction from total storage capacity.aqufers can be classified as confined or unconfined aqufer on the basis of presaence or absence of water table and leaky aqufer consists of combination of both aquifers.different types of aquifers are as follows:-

Unconfined aquifers:

In unconfined aquifer,water table varies in undulating form and in slope,depending on areas of recharge and discharge,pumping from wells and permeability.The rise and fall in water table correspond to change in volume of water stored with in a aquifer.contour maps and profiles of water can be prepared from elevations of water in wells and tapped the aquifer and determined the qualities of water available,their distribution and movement.In the special unconfined aquifer perched water bodies are involved which occur whereever a groundwater body is separated from the main groundwater by relatively impermeable stratum of small area extend zone of aeration above main body of groundwater.In sedimentary deposits clay lenses have swallow perched water bodies overlying them.

Confined aquifers:

It is also known as artesian or pressure aquifers,which occur where groundwater is confined under pressure greater than atmospheric by overlying impermeable strata.In well penetrating aquifer,the water level rise above bottom of confing bed,shown by artesian wall and flowing well.The water enter to the confined aquifer in an area through the confing bed which rise to the surface where confing bed enters to the groundwater where aquifer become unconfined.A region which supply water to the confined aquifer is called as recharge area.water may enter through leakage in confing bed.The rise and falls of water in penetrating confined aquifers results primarily change in pressure rather changes in storage and volumes.we can say confined aqufers display small change in storage and serve primarily as conduits for convoying water from recharge areas to locations of natural as well as artifical discharges.The piezometric surface or petentiomtric surface of confined aquifer is an imaginary surface coinciding with hydristatic pressure level of the water with in the aquifer.the water level in well penetrating a confined aquiferdefines elevations of piezometric surface at the point.the peizometric surface should lie above groundwater from which a flowing well results.the contour maps and profiles of piezometric surface can be prepared from well data similar to the water table in confined aquifer.the confined aquifer becomes unconfined when the piezometric surface falls below the bottom of upper confing bed.we can say commonly unconfined aquifer exits above a confind one.

Leaky aquifers:-

The aquifers that may be completely confined or unconfined occur less frequently than leaky known as seniconfined aquifers.They are mostly found in alluvial valleys,plains or former lake basins where a permeable stratum is overlain or underlain by semipervious aquitard or semiconfining layers.The pumping in wells of leaky aquifer are by horizontal flow within the aquifer and vertical flow through aqutard in aquifar.

Idealized aquifers:-

In mathematical calculations of storage and flow of groundwater,aquifers are frequently assumed as homogenous as well as isotropic.A homogenous aquifer posses hydrologic properties which are identical eveywhere.An isotropic properties are independent in the different directions which are not exit.The good quantitative approximations can be obtained by assumptions,where average aquifer conditions are employed on a large scale.