Improved parameterization of groundwater flow models using interferograms and adjoint sensitivity analysis

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Improved Parameterization of Groundwater Flow Models using Interferograms and Adjoint Sensitivity Analysis NSF #0943415 Radar interferometry provides for the acquisition of basin wide high precision vertical deformation data that reveal the spatially complex and structurally dependent nature of land subsidence in heavily pumped sedimentary basins. In Las Vegas Valley, for example, InSAR interferograms portray compartmentalized subsidence bowls bounded by basin-fill faults. Earth fissures are known to occur adjacent to many such faults where differential subsidence is observed from interferograms. Recovering water levels associated with reduced groundwater pumping during summer months and a rigorous ASR program during winter months have resulted in seasonal patterns of subsidence and rebound that are reflected in the InSAR time-series data. A new modeling strategy is proposed whereby these seasonal deformation patterns are coupled with observed water-level data to quantify the storage characteristics of the aquifer and confining units at a pixel resolution of the interferogram, or about 40m. Inverse models that use these observations are hindered by the fact that parameter zone distributions for storage and hydraulic conductivity are typically user defined and often formulated in an ad-hoc fashion. The objective of this proposed research is to develop an adjoint-based parameter estimation model that systematically produces the optimal storage and conductivity zone distributions that leads to a superior conceptual model and yields not only the best parameter distribution, but provides the details necessary to reflect the intricacies of the fault-bounded storage bowls observed in Las Vegas Valley. The broader impacts of this proposed research are significant because they address the socioeconomic and hydrogeologic problems facing Las Vegas Valley using a multi-disciplinary approach. The economic well being of Las Vegas Valley is dependent on long-term growth and management of developable land. This research will provide a high-resolution groundwater and subsidence model that can be used as a water-management tool well into the future. The adjoint-based parameter estimation model (APE) developed in this research automates zones used in inverse modeling. This new model provides a distinct advantage over techniques requiring analysis of numerous alternative models. This new modeling package will be made available to all modeling practitioners. An Outreach Coordinator will use the VT Museum of Geosciences to provide groundwater and water resources education to audiences that include pK-12 students, teachers, undergraduates and the general public. A physical groundwater model will be used during planned workshops to instruct teachers and demonstrate safe water practices. A poster and worksheet will be developed for high school classrooms and for the Museum to highlight Virginia Tech groundwater research in an effort to attract more future groundwater scientists.