A cone of depression is the funnel-shaped fall in water level that forms around a pumped well, deepest at the well and shallower with distance.
A cone of depression is the funnel-shaped lowering of the water table or piezometric surface around a pumping well. It is deepest at the well and becomes shallower with distance. The steepening gradient toward the well is what drives water to it. The cone grows while pumping continues, until recharge or another source of water balances the pumping. The distance to its edge is called the radius of influence. In a confined aquifer the cone can spread for kilometres within days, because storativity is so small. In an unconfined aquifer it grows more slowly and stays nearer the well. Cones matter when they overlap. Neighbouring wells then lower each other's water levels, which raises pumping costs and can leave shallower wells dry. A cone can also reach a river and reduce its flow, a process called stream depletion. Near a coast it can draw in seawater, and near a polluted site it can pull a contaminant plume toward the supply well. For this reason, well spacing and protection zones around supply wells are based on the expected size of the cone.