EAS446lec5 - EAS 44600 Groundwater Hydrology Lecture 5...

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EAS 44600 Groundwater Hydrology Lecture 5: Hydraulic Head and Fluid Potential Dr. Pengfei Zhang Darcy’s Experiment The first studies of the movement of water through rock and sediment were performed by the French engineer Henry Darcy. Darcy used a column filled with sand to perform the experiments. The column had an inlet ( influent ) and an outlet ( effluent ) through which water was introduced and released from the column. The column also had two ports connected to two vertical tubes, called piezometers . The water level in the tubes rose to heights that reflected the energy of the water in the pipe at the location of the port (Figure 5-1). h a h a -h b h b A B L Figure 5-1. Horizontal pipe filled with sand to demonstrate Darcy’s experiment. Darcy found that the discharge of water, Q , through the pipe was proportional to the difference in the height of the water in the two “ piezometers ”, and was inversely proportional to the flow length, L . The flow was also proportional to the cross-sectional area, A , of the pipe, and was proportional to the ability of the sand to transmit water. This ability to transmit (or conduct) water is referred to as the hydraulic conductivity , K , of the sand. These observations were summed up as Darcy’s Law : = = dl dh KA L h h KA Q b a (5-1) where dh / dl is known as the hydraulic gradient .
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