Exploring groundwater recoverability
Creators: name: Thompson, Justin Cameron
name: 0000-0001-5644-790X
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: Groundwater recoverability
Yield optimization
Well capacity
Pumping costs
Depth-to-water

description: Where the depth of groundwater increases, recoverability—the relative ease of pumping—decreases. Understanding how recoverability changes with planned or unplanned changes in depth-to-water is a critical issue for groundwater managers, policymakers, and stakeholders. However, recoverability is generally not well understood, poorly quantified, and detached from local-level groundwater planning and management where decisions are often based on depth-to-water over time. Currently, Texas’ best estimates of recoverability are derived from arbitrary storage volume constraints, rendering unknown the impacts of variable storage and use conditions, or management decisions. Using hydrogeologic and economic constraints to better calculate recoverability, the topic of this dissertation, could provide a more comprehensive approach for long-term water planning. New modeling methods for quantifying recoverability are developed to capture the complex relationship among aquifer storage conditions, well infrastructure, and recoverability by connecting groundwater drawdown solutions with comprehensive cost components (drilling, equipment, and lifting energy). Partially penetrating well effects, which have direct ramifications for both the capacity and economic elements of recoverability, are used to create a novel approach for optimizing well infrastructure that maximizes long-term recoverable yields. In this way, the model has the flexibility to quantify recoverability for deterministic (user specified or existing) well infrastructure or to explore the limits of recoverability with yield-optimized infrastructure. Single well model results reveal that groundwater stored in shallow and unconfined conditions is highly recoverable; physical constraints are more likely than economic considerations to bind yields. Alternatively, recoverability of groundwater stored in deep and confined conditions is more likely bound by economic constraints than physical limitations; yields may be restricted where the cost of dewatering saturated thickness is prohibitively expensive. Yield-optimized infrastructure is then integrated with spatially distributed aquifer data to model maximum recoverable yields for the Carrizo-Wilcox Aquifer in Texas at an initial depth-to-water and a planned change in depth-to-water in order to assess how yields differ between the two. Results show that the capacity constraints upon regionally recoverable yields correlate strongly with aquifer saturated thickness, economic limitations correlate strongly with aquifer depth, and recoverable yields in shallow and unconfined settings are highly sensitive to changes in depth-to-water. Using a unique approach, recoverability solutions developed here are then linked with three disparate data sets providing aquifer characteristics, existing well infrastructure, and user attributes to quantify the socioeconomic impact to existing users (domestic, livestock, and irrigation) of a planned change in depth-to-water. Important disparities are illuminated by specifying the types of these impacts and allocating them to specific user groups. For example, 84% of study area wells designated for domestic use bear only 58% of the total modeled increase in regional pumping costs, while 5% of study area wells designated for irrigation use bear 19% of these costs. Additionally, while affordability of domestic water supply for the majority of the study area population is unimpeded by the planned change in depth-to-water, results suggest that low-income communities may be disproportionately impacted. Finally, results indicate that the distribution of the types of costs (drilling, equipment, and lifting energy) present at initial groundwater production do not necessarily correspond to the socioeconomic impacts of a planned change in depth-to-water. While drilling costs are found to compose 83% of all study area pumping costs at initial production, 56% of the increase in future pumping costs are driven by lifting energy costs. Thus, policy interventions designed to mitigate these impacts are more likely to meet their objectives if they apply these or similar methods, rather than rely on initial production costs