Use of Modflow's Groundwater-Management Process for Managing the Effects of Groundwater Pumping and Artificial Recharge On Surface Waters

Groundwater pumping and artificial groundwater recharge can affect surface waters and associated aquatic ecosystems and riparian vegetation. Groundwater pumping depletes surface-water flows, often during times of the year when flows are most needed to support aquatic habitats. Artificial groundwater recharge, on the other hand, can enhance surface-water flows and the health of riparian vegetation if the timing and location of recharge is correctly managed. In both cases—groundwater pumping and artificial groundwater recharge—numerical simulation coupled with mathematical optimization can be used to manage the magnitude, timing, and location of streamflow depletions and (or) accretions that result from these two types of groundwater stresses. The Groundwater-Management (GWM) Process for MODFLOW-2000 and MODFLOW-2005 is one of the simulation-optimization tools now available to hydrologists for managing the effects of groundwater pumping and artificial recharge on surface waters. GWM is based on the widely used response-matrix approach to solve several types of linear, nonlinear, and mixed-binary linear groundwater-management problems, including conjunctive management of groundwater and surface-water systems.

GWM can be used to design time-varying pumping and artificial-recharge schedules for one or more supply wells and (or) recharge basins that are constrained by water-supply demands, minimum streamflow requirements specified for certain stream segments within a groundwater basin, and many other types of physical and regulatory constraints. An important application of GWM is the determination of trade-off curves between alternative streamflow requirements and optimal levels of groundwater withdrawals. Such curves provide neutral information to help decision makers determine how much groundwater can be optimally withdrawn for a specified level of flow reduction.

This presentation will provide examples of how GWM can be applied to managing the effects of groundwater pumping and artificial recharge on surface waters.