GIS-BASED HYDROLOGIC AND ENVIRONMENTAL SYSTEMS ANALYSIS (HESA) FOR CHARACTERIZING GROUNDWATER FLOW SYSTEMS AT THE WATERSHED SCALE FOR WATER MANAGEMENT AND REGULATION: CASE HISTORY IN DELTA COUNTY, COLORADO, USA

Hydrologic and Environmental System Analysis (HESA), a GIS-based approach that integrates physical, chemical and biological information to derive a conceptual understanding or site model (CSM) of the various components of hydrological and environmental systems and their interactions, has been formulated and applied to develop a basic understanding of the surface water, and shallow and deep groundwater flow, both alluvial and bedrock systems, of Delta County, Colorado. HESA was used to develop a watershed scale understanding of the availability and sustainability of groundwater supplies; the vulnerability of the groundwater resource to contamination particularly Selenium and TDS; the interaction between groundwater and wetlands and streams; and the effects of energy development, mining operations, agriculture, and urbanization on the integrated groundwater and surface water systems. HESA relies on extensive field observation, is well suited for use in areas not subjected to previous groundwater investigations and lack the type, amount, and distribution of quantitative hydrologic data, and results in consistent, continuous county-wide GIS maps of various hydrologic and hydrogeologic characteristics with supporting databases.

Specifically, the Oak Mesa and Surface Creek/Leroux Creek Sections address hydrologic issues of southern Grand Mesa regarding connectivity between streams, topographically controlled glacial/alluvial aquifers, and regional bedrock groundwater systems. The North Fork River and Uncompaghre River/Gunnison River Sections address the interactions of glacial/fluvial aquifers and terraces overlying shale in areas of intensive agricultural and domestic water use with large-scale seasonally fluctuating rivers and streams, and include the source and mobility of Selenium and TDS, hydrologic input by large-scale diversions, and the ultimate connectivity of all Delta County hydrologic systems to the Gunnison River.