ABSTRACT
Darcy was the first to introduce a useful law governing the general flow of water through geologic materials. In any experimental demonstration of Darcy's law, the presence of a geologic material slows the overall velocity of flow through the apparatus. Darcy's law is valid only for slow laminar flow characteristic of the movement of ground water through most earth materials. Turbulent flow is uncharacteristic of porous-media flow and should be treated by a fluid mechanics approach to flow through an open channel, or pipe. However, in the overwhelming majority of cases the movement of ground water is by slow laminar flow and Darcy's law applies. Most applications of Darcy's law require that seepage velocity be used rather than Darcy velocity. Seepage velocity is obtained by dividing Darcy velocity by porosity. It is recommended that any description of soils for hydrogeologic purposes should be made in terms of the Unified Soil Classification System.
