Intensive groundwater development: A water cycle transformation, a social revolution, a management challenge
Groundwater is associated with a large water storage in the pores, fissures and voids of the terrain. It flows slowly from recharge (inflow) areas to discharge (outflow) areas. In recharge areas, often extensive ones, rain, snowmelt, runoff and losing streams – besides anthropic-generated irrigation return flows and leakages – infiltrate and increase water storage in the ground. Discharge areas can be both diffuse and concentrated, and they appear in a small part of the territory as springs, along streams, at the sea and lakes coasts, as more or less permanent wetland areas and lagoons, and as shallow water tables. Discharge means a depletion of storage (reserves) that is continuously or discontinuously compensated by recharge. The large water storage smoothes out recharge variability –whichmay be almost constant for deepwater tables – and produces a discharge that is much less variable than recharge. Average renewal time of water in aquifers is typically from several years in small, highly perme-
able formations, up to many millennia in large ones; especially in deep, confined aquifer systems (see Insert 1). This means a slow and delayed aquifer response to external actions (extractions, land use modifications, surface water alteration, climate and global changes) that is beyond the common experience of human beings, which is at the scale of daily to monthly, at most a few years scale.