Hydraulic gradient

"The slope of the water surface in an aquifer. The hydraulic gradient indicates the direction of groundwater flow. Water always  flows from higher elevations to lower elevations. All other factors being equal, flow is greater when the hydraulic gradient is steeper." (Virginia Polytechnic Institute and State University, n.y.)


Virginia Polytechnic Institute and State University. "A Glossary  of Water-Related Terms", by Brian Benham. Publication 442-758