"A flux is a process that moves water between pools, like evaporation, precipitation, discharge, recharge, or human use." (U.S. Geological Survey, 2022). "The rate of discharge of groundwater per unit area of a porous medium measured at right angle to the direction of flow" (Lohman et al 1972)
U.S. Geological Survey (USGS). "Water Cycle Glossary Terms". USGS Water Science School. (2022). Link: https://www.usgs.gov/glossary/glossary-water-cycle-terms
Drescher, W.J.,Jr., Ferris, J.G., Johnson, A.I., McGuinness, C.L., Piper, A.M., Rorabaugh, M.I., Stallman, R.W., and Theis, C.V., 1972, Definitions of selected ground-water terms—Revisions and conceptual refinements: U.S. Geological Survey Water-Supply Paper 1988.