Ground water is the water that flows through cracks in rocks, soil or sand etc. While some part of the water is stored, some quantity permeates through the layer or ducts called aquifers and gradually reaches the ground. Aquifers are porous materials consisting of gravel, stone,sandstone or fractured rock called limestone. The area occupied by the water in the aquifers is called the saturation zone and the top of this zone is called the water table. The depth of water table may vary from just a foot below to several feet underground. Ground water table is a relevant issue as water serves many necessary purposes beginning from drinking, irrigation etc. Efforts are needed in the direction of maintaining ground water table and maintaining purity. Hence organizations supporting the cause do raise awareness.
The rock below the Earth's surface is bedrock. Bedrocks contain many void spaces which allow the ground water to accumulate.Sedimentary rocks may als0 contain layers which allows water to permeate easily. Limestone is soluble in water which leads to formation of large cavities. The speed of groundwater flow is a function of the sizes and inter connectivity of the spaces. At greater depths in the bed rock the constituent material is dense and further percolation of water is not possible. These dense layers are situated below the porous layer and act as a confining layer preventing the vertical movement of water any further. From this point water tends to pool in the permeable layers and travels rather horizontally across aquifers until they reach an exposed surface body like a river or stream. This phenomenon can be compared to water flow in a pair of sponges. If a plastic sheet is put over one sponge moisture from one sponge will flow vertically until it hits the plastic sheet. After this point water flows in horizontal direction and gradually the first sponge gets saturated.
The ground water table rises due to heavy rains and melting snow. On the other hand massive pumping of ground water supplies leads to fall of water table. When water is pumped from the ground water system the water table is lowered and the direction of ground water movement is altered. In that case the amount the ground water that flows to the stream is reduced. Besides that some water can be taken from stream water to ground water system. Consequently the quantity of streamflow is less. Ground water is replenished during rainfall.During precipitation water travels by percolation to the ground. It then flows to the stream using the ground water flow system and so water table rises.
Two main problems concerning the ground water table are,
Ground water contamination:
This is due to infiltration of contaminants. The landsurface is contaminated with pollutants like pesticides,aerosols etc these may travel along with percolating water and infiltrate the water table. These travel as long as the discharge point is reached.
Pollutant seepage is higher when the layer above the aquifer is porous. Septic tanks, land fills etc may enter making water unfit for drinking.
Decline in water table may affect the ecosystem in the following ways,