PARSING OUT SMALLER HYDRAULIC PROVINCES FROM REGIONAL AQUIFER SYSTEMS

Regional aquifer systems, such as the Edwards-Trinity Aquifer in south-central Texas, are often treated as singular hydrologic provinces when characterized and numerically modeled. This treatment has been motivated by the designation of region-scale hydraulic boundaries to define the aquifer domain. Recent studies based on water-chemistry data, dye-tracer results, subsurface imaging, water-budget assessments, and hydraulic analyses, however, suggest that internal hydraulic boundaries exist and that these boundaries can be sufficiently characterized to allow smaller regimes within the regional aquifer systems to be conceptualized as separate hydraulic provinces. The Devils River watershed is an example of a smaller hydraulic province in the central portion of the regional-scale Edwards-Trinity Aquifer. Conceptual and numerical models for this sub-basin have been successfully developed in recent years using multiple lines of evidence. Preliminary assessment of adjoining sub-basins suggests that these hydraulic regimes can also be conceptualized and modeled as separate hydraulic provinces. Parsing this large regional aquifer system into several smaller-scale hydraulic provinces allows for more accurate numerical representations provided sufficient data are available to support the conceptualization and that the internal hydraulic boundaries do, in fact, exist. Characterizing systems into smaller-scale hydraulic provinces allows for greater refinement of numerical grids and meshes to capture the behavior of key hydraulic features.