USGS Grant Number:
Year Established: 2009 Start Date: 2009-09-01 End Date: 2012-08-31
Total Federal Funds: $117,847 Total Non-Federal Funds: $121,998
Principal Investigators: Roseanna Neupauer
Abstract: With growing populations and increased demand for water, it is necessary to ensure that increased pumping of aquifers does not reduce flows in rivers to levels that would limit the availability of water for drinking water supply, irrigation, and riparian habitat. Analytical solutions and numerical simulations have been used to quantify stream depletion, which is the change in stream flow due to pumping. Typically, in these approaches, the location of the pumping well is assumed to be known; thus they can be inefficient as a tool for siting new well locations. The goal of the proposed research is to develop an adjoint-based modeling approach that can be used in practice to quantify stream depletion due to aquifer pumping. In a single simulation of an adjoint model, stream depletion is calculated for a well at any location in the aquifer; thus, it is computationally efficient when the number of well locations or possible well locations is large. The new modeling approach will be developed so that it can be used with standard groundwater flow simulators, and therefore can be readily applied in practice. The proposed research includes rigorous development of the adjoint equation for calculating stream depletion in confined and unconfined aquifers with various models of groundwater/surface water interaction, numerical simulations to verify the adjoint equation, development of pre-processing codes to convert input files for standard groundwater flow simulations into input files for adjoint simulations, and development of training material and presentation of a training workshop to train groundwater modelers on the new methodology. The applications of the adjoint modeling approach to quantify stream depletion include management of surface water and groundwater resources, selection of locations of new groundwater withdrawal wells that limit the impact on stream flows, optimization of groundwater pumping rates at multiple wells to reduce the impact on stream flows, and determination of non-tributary groundwater.