Soil controls on recharge to aquifers

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Abstract
SUMMARY: Case studies are presented of the use of soil water measurements to determine the pathways, timing and quantities of natural recharge to groundwater at sites on the Chalk and Triassic Sandstone aquifers in England. Water content and potential have been monitored for several years at seven sites and unsaturated hydraulic conductivity measured in situ at three of the chalk sites. Recharge was estimated using a combination of the zero flux plane (ZFP) method and a simple water balance. Examples of the water balance are presented for three sites.It is shown that a shallow (∼1 m) depth of permeable drift and soil increased the annual drainage from the soil to the underlying formation by about 34% at a pair of sites on the Chalk aquifer. Effects upon drainage timing are equally dramatic. On thin soil directly on chalk, drainage responds quickly to rainfall and, once evaporation starts to exceed rainfall, declines rapidly. On drift‐covered sites, the drainage continues for a much longer period, as it does from the loamy soil overlying the sandstone site.