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For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit https://www.usgs.gov or call 1-888-ASK-USGS (1-888-275-8747).For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

This is the third and final report in a series describing the groundwater resources of the Hualapai Indian Reservation. These reports document the findings of a comprehensive groundwater study conducted on the reservation and adjacent areas from 2015 through 2018 by the U.S. Geological Survey in cooperation with the Bureau of Reclamation. The first report described the hydrologic framework and characterization of the Truxton aquifer on the Hualapai Indian Reservation (Bills and Macy, 2016). The second report described the hydrogeologic characterization of the Hualapai Plateau part of the reservation (Mason, Macy, and others, 2020). This report includes five chapters. Chapter A (this report) is a summary of this multichapter volume, including a brief description of the study area and hydrogeologic framework of the Truxton aquifer, description of the numerical groundwater-flow model developed to simulate groundwater levels in the aquifer, and estimates of simulated changes to groundwater levels in the aquifer based on projected groundwater withdrawals. Chapter B (Mason, Bills, and Macy, 2020) describes the geology and hydrology of the Truxton basin and Hualapai Plateau. Chapter C (Kennedy, 2020) describes the results of a gravity geophysical survey of the Truxton basin. Chapter D (Ball, 2020) describes the findings of an airborne electromagnetic survey of the Truxton aquifer and Hualapai Plateau. Chapter E (Knight, 2020) describes the results of a transient groundwater model created for the entire Truxton aquifer both on and off the reservation. The groundwater-flow model is used to estimate projected groundwater levels based on future groundwater withdrawal scenarios.

<p>A scripted development and deployment approach was used for developing the next-generation groundwater flow and land-surface subsidence model of the region surrounding Houston, Texas, USA.  The area has historically experienced substantial land subsidence resulting from groundwater use. Python scripts leveraging the FloPy and PyEMU packages were written to build and run the MODFLOW 6 model, perform very-high-dimensional parameter estimation and uncertainty analysis using PEST++, and process results. Automating these processes allowed for fast and repeated iterations through all or part of the modeling workflow for purposes including: troubleshooting input errors, testing hypotheses about the hydrologic system characteristics, evaluating the influences of structural model assumptions, and experimenting with different and increasingly complex formulations of the prior parameter distribution and likelihood functions in Bayesian sense. Automated generation and storage of processed output allowed easy comparison between iterations of the modeling workflow, and Git version control software provided a self-documented model repository with full-featured “undo” for returning to previous states of the workflow and investigating outcomes. The modeling team convened regularly (monthly to twice-weekly) to review results of the latest iteration and decide the next course of action. Model performance was improved steadily and incrementally by focusing on one new feature or problem per workflow iteration until modeling goals were met. This workflow style fostered a sense of predictability and confidence in the project outcome, a welcome departure from the “typical” numerical modeling process of panic and despair.</p>