EAS446lec6 - EAS 44600 Groundwater Hydrology Lecture 6...

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EAS 44600 Groundwater Hydrology Lecture 6: Darcy’s Law and Hydraulic Conductivity Dr. Pengfei Zhang Darcy’s Law We discussed Darcy’s experiment in last lecture and now let us go back to Darcy’s law: = = dl dh KA L h h KA Q b a (6-1) The quantity dh represents the change in head with distance, dl . The negative sign is a convention such that the direction of flow is toward lower hydraulic head . The essence of groundwater flow is that groundwater moves from areas of higher hydraulic head to areas of lower hydraulic head. However, this says nothing about the rate of flow. The rate of flow is controlled by the hydraulic conductivity of the subsurface. Hydraulic conductivity has units of length per time (L/T). It represents both the properties of the porous medium as wells as the properties of the fluid flowing through the porous medium. It is obvious that a viscous fluid like motor oil would move more slowly through a sand than would water. To separate the properties of the porous medium from the properties of the fluid, a new parameter is introduced to represent the size and interconnectedness of the pores in the porous medium. This parameter is called intrinsic permeability , k i , which has the units of length squared (L 2 ). Using the intrinsic permeability, we can put the hydraulic conductivity in terms of the
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This note was uploaded on 12/29/2010 for the course EAS 44600 taught by Professor Pengfeizhang during the Spring '10 term at CUNY City.

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EAS446lec6 - EAS 44600 Groundwater Hydrology Lecture 6...

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