what is recharging in depletion water table
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Recharge
Ground water recharge includes recharge as a natural part of the hydrologic cycle and human-induced recharge, either directly through spreading basins or injection wells, or as a consequence of human activities such as irrigation and waste disposal. Artificial recharge with excess surface water or reclaimed wastewater is increasing in many areas, thus becoming a more important component of the hydrologic cycle.
Natural recharge to the water table can be diffuse or localized. Diffuse recharge is the widespread movement of water from land surface to the water table as a result of precipitation over large areas infiltrating and percolating through the unsaturated zone. Localized recharge refers to the movement of water from surface water bodies to the ground water system and is less uniform in space than diffuse recharge. Most ground water systems receive both diffuse and localized recharge. In general, the importance of diffuse recharge decreases as the aridity of a region increases.
Typically, most water from precipitation that infiltrates does not become recharge. Instead, it is stored in the soil zone and eventually returned to the atmosphere by evaporation and plant transpiration. The percentage of precipitation that becomes diffuse recharge is highly variable, being influenced by factors such as weather patterns, properties of surface soils, vegetation, local topography, depth to the water table, and the time and space scales over which calculations are made. Recharge to the water table can occur in response to individual precipitation events in regions having shallow water tables. In contrast, unsaturated zone water in some desert regions is estimated to have infiltrated the soil surface as long as tens of thousands of years ago.
Magnitudes of recharge fluxes are generally quite low and difficult to measure directly. Measurement of fluxes can be exacerbated by preferential flow (i.e., macropore flow) in the unsaturated zone, although preferential flow paths are of greatest concern as potential conduits for rapid contamination of aquifers. The above factors, in addition to temporal and spatial variability, greatly complicate the estimation of basin-wide recharge rates. Estimation methods include use of water budgets, tracers, geophysics, and simulation models. Because of the inherent uncertainties in any method, it is often advisable to apply multiple techniques for any study.
Water levels in many aquifers follow a natural cyclic pattern of seasonal fluctuation, typically rising during wetter, cooler months and declining during drier, warmer months. Superimposed on natural, climate-related fluctuations in ground water levels are the effects of human activities that alter natural rates of ground water recharge or discharge. For example, deforestation and draining of wetlands can expedite surface runoff and reduce ground water recharge. Agricultural tillage, the impoundment of streams, and creation of artificial wetlands can increase ground water recharge. Urbanization may either increase or decrease recharge. For example, built-up and paved areas promote runoff and inhibit infiltration. The enhanced runoff, however, may be channeled to a retention basin or infiltration gallery, resulting in relocation of recharge areas and the transition from slow, diffuse recharge to rapid, localized recharge. The effects of human-induced changes on ground water recharge commonly are incremental, and the cumulative effects may not become evident for many years
Ground water recharge includes recharge as a natural part of the hydrologic cycle and human-induced recharge, either directly through spreading basins or injection wells, or as a consequence of human activities such as irrigation and waste disposal. Artificial recharge with excess surface water or reclaimed wastewater is increasing in many areas, thus becoming a more important component of the hydrologic cycle.
Natural recharge to the water table can be diffuse or localized. Diffuse recharge is the widespread movement of water from land surface to the water table as a result of precipitation over large areas infiltrating and percolating through the unsaturated zone. Localized recharge refers to the movement of water from surface water bodies to the ground water system and is less uniform in space than diffuse recharge. Most ground water systems receive both diffuse and localized recharge. In general, the importance of diffuse recharge decreases as the aridity of a region increases.
Typically, most water from precipitation that infiltrates does not become recharge. Instead, it is stored in the soil zone and eventually returned to the atmosphere by evaporation and plant transpiration. The percentage of precipitation that becomes diffuse recharge is highly variable, being influenced by factors such as weather patterns, properties of surface soils, vegetation, local topography, depth to the water table, and the time and space scales over which calculations are made. Recharge to the water table can occur in response to individual precipitation events in regions having shallow water tables. In contrast, unsaturated zone water in some desert regions is estimated to have infiltrated the soil surface as long as tens of thousands of years ago.
Magnitudes of recharge fluxes are generally quite low and difficult to measure directly. Measurement of fluxes can be exacerbated by preferential flow (i.e., macropore flow) in the unsaturated zone, although preferential flow paths are of greatest concern as potential conduits for rapid contamination of aquifers. The above factors, in addition to temporal and spatial variability, greatly complicate the estimation of basin-wide recharge rates. Estimation methods include use of water budgets, tracers, geophysics, and simulation models. Because of the inherent uncertainties in any method, it is often advisable to apply multiple techniques for any study.
Water levels in many aquifers follow a natural cyclic pattern of seasonal fluctuation, typically rising during wetter, cooler months and declining during drier, warmer months. Superimposed on natural, climate-related fluctuations in ground water levels are the effects of human activities that alter natural rates of ground water recharge or discharge. For example, deforestation and draining of wetlands can expedite surface runoff and reduce ground water recharge. Agricultural tillage, the impoundment of streams, and creation of artificial wetlands can increase ground water recharge. Urbanization may either increase or decrease recharge. For example, built-up and paved areas promote runoff and inhibit infiltration. The enhanced runoff, however, may be channeled to a retention basin or infiltration gallery, resulting in relocation of recharge areas and the transition from slow, diffuse recharge to rapid, localized recharge. The effects of human-induced changes on ground water recharge commonly are incremental, and the cumulative effects may not become evident for many years
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