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The underground water does not flow like a river. The water particle, flow in parallel paths. It is known as streamline flow. This flow takes place through interconnecting spaces in saturated rock material. It is called Percolation.
Water enters underground areas from higher areas by infiltration. Gravity makes the water flow down into valleys Water flows through the particles of the surface. It slows down the flow of the water because its energy is seduced by friction with water. This is why the underground water flows slowly.
During the rainy days, more water flows by filtration, so that the water table is raised but it is lowered during dry season. The water flows downwards due to gravity but rises near valley due to its tendency to flow parallel to water-level.
Three factors affect seeping process: permeability of rocks, the slope of water-table and the speed of flow of water.
When the water-table rises due to rain, the underground water is slowed down.
How to estimate the quantity of underground water? - It is necessary to know the amount of underground water because its correct estimate is helpful in maintaining water supply of a town, providing for irrigation and supplying water for various industries. The Following formula was used in the 19th century by Henry Darcy.
Q = P x i x A
Where Q = the amount of water in a unit time
P = The Permeability of soil
I = Slope of water-table
A = Cross-section of the area
Perched Water Table.
Many times water is available at such places, which are above the water-table. A layer of clay is found lying, over a water-table, will not allow water from seeping down because clay layers are impermeable. The water level thus prevented from falling is known as perched water table because this water-table is higher than the ordinary water-table.
In the desert and semi-desert areas, the perched water-table is found in the area affected by ice-sheet or glaciers of North America.
Next: Groundwater Topographic Features 1