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Ground Water discharge is volumetric flow(upward or outward movement) rate of ground water through an aquifer.Discharge involves the upward movement and out-flux of groundwater from an aquifer.
Discharge is important aspects of the global hydrological cycle and are critical to the analysis of groundwater flow systems and water budgets. It is an opposite to recharge process. it means represents the upward outflow of groundwater from the subsurface that occurs naturally or as the result of human activity, Groundwater is induced to discharge from wells, and discharges naturally from the subsurface to oceans, springs, lakes, rivers (“gaining streams”), swamps, and other wetlands. Hence, groundwater discharge can represent a significant control over ecosystems.
Groundwater may also return to the atmosphere directly by evaporation within the soil and by transpiration through vegetation, but these processes are not formally considered as discharge. Without human intervention discharge rates often approximate to recharge rates, and hence a balance or equilibrium is achieved between influxes and outfluxes to the subsurface water budget.
However, “overdrafts” resulting from human exploitation of groundwater resources can lead to declining water levels (thereby raising pumping costs), hydrostatic pressure reductions, and other related problems such as land subsidence (earth holes)
Both groundwater recharge and discharge are usually spatially limited, and therefore may not be nearly as conspicuous as other aspects of the hydrological cycle.
Groundwater discharge occurs within unconfined aquifers where groundwater flow lines have a net vertical upward component as they emerge toward the Earth’s surface.
In confined aquifers the hydraulic head associated with these features is greater than that of the underlying aquifer , If the hydraulic head of the confined aquifer is greater than that associated with sinkholes, lakes, and reservoirs, the latter features become loci for groundwater discharge. But If the hydraulic head is greater in the confined aquifer than in the overlying or underlying aquifers, groundwater can flow through the confining layer to these aquifers.
Groundwater discharge is the volumetric flow rate of groundwater through an aquifer.
Total groundwater discharge, as reported through a specified area, is similarly expressed as:
where
Q is the total groundwater discharge ([L3·T−1]; m3/s), K is the hydraulic conductivity of the aquifer ([L·T−1]; m/s), dh/dl is the hydraulic gradient ([L·L−1]; unitless), and A is the area which the groundwater is flowing through ([L2]; m2)For example, this can be used to determine the flow rate of water flowing along a plane with known geometry.
