Hydraulic gradient is the change in hydraulic head per unit distance of flow in a given direction and is expressed in units of length (elevation) per length (distance). Ground water velocity is a function of the hydraulic gradient. Most water in an unconfined aquifer moves slowly in undeveloped aquifers. However, an action such as pumping water from a well can steepen local hydraulic gradients. This results in acceleration of flow in toward the well, carrying any dissolved contaminants with it into the well. Appendix 7A gives a method calculating the hydraulic gradient in a water table aquifer.
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