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Aquifer recharge, deep percolation, and water-table interactions

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Aquifer recharge is water that moves from the land surface or from the vadose zone into the saturated zone. Quantitative estimation of recharge rate contributes to the understanding of large-scale hydrologic processes. It is important for evaluating the sustainability of groundwater supplies, though it does not equate with a sustainable rate of extraction. Where contamination of an aquifer is a concern, estimating the recharge rate is a first step toward predicting solute transport to the aquifer. Recharge often occurs episodically in response to storms and other short-term, high-intensity inputs. For a given amount of infiltration, such temporal c oncentration enhances recharge because it entails shorter residence times for water in the portions of the soil from which evapotranspiration takes place. Similarly, a larger fraction of infiltrated water will become recharge if it is concentrated in narrow channels such as fingers or macropores, not only because this tends to hasten its passage through the unsaturated zone, but also because the water then occupies less of the volume of soil from which evapotranspiration takes place. Artificial recharge by ponding or injection is becoming a widely-used means of water storage.

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