Water withdrawal systems

Traditionally, a distinction is made between surface water intakes and groundwater catchments; in reality, however, situations can be less clear-cut. For example, a spring (a natural surface outlet) may be fed by real groundwater, subject to the laws of water movement in a porous medium, or, on the contrary, may simply be the open-air outlet of real underground rivers governed by the laws of free-surface flow. On the other hand, in many places, particularly on large alluvial plains, wells or boreholes are drilled in the immediate vicinity of river banks, with the water extracted coming almost directly from surface runoff.