Methods and Indicators for Assessment of Regional Ground Water Conditions to Monitor the Sustainable Use of Ground Water Supplies

Sustainable management of water resources requires that scientists, planners, and water managers be aware of the status and trends in the availability of ground-water supplies.  The general public also has a stake in understanding the changing conditions of ground-water availability, especially in the semi-arid southwestern United States where much of the water used by municipalities and agriculture comes from the subsurface.  Unlike surface-water indicators such as stage or discharge, ground-water conditions may be more difficult to assess and visualize.  Individual well observations represent aquifer conditions only in a limited area.  Wells may be screened over single or multiple aquifers, further complicating single-well interpretations.  Additionally, changes in ground-water conditions may involve time scales ranging from days to many decades depending on the timing of recharge, soil and aquifer properties, and depth to the water table.  The lack of an easily identifiable ground-water feature indicative of current conditions combined with differing time scales of water-level changes makes the presentation of ground-water conditions a complex task, particularly on a regional basis.  One approach is to present several indicators of spatial ground-water conditions that address different time scales and attributes of aquifer systems. 

 

Several methods and indicators were developed as part of this project for demonstrating differing aspects of ground-water conditions using water-level observations from existing datasets.  The indicators of ground-water conditions developed in this study include locations of wells experiencing water-level decline and water-level rise for both historic and recent time periods, recent trends in ground-water levels, and current depth to ground water.  Computer programs were written to create these indicators of ground-water conditions and display them in an interactive geographic information systems (GIS) format.  Results are illustrated through analyses of ground-water conditions for selected alluvial basins in the Lower Colorado River Basin in Arizona, available in an online interactive map (http://montezuma.wr.usgs.gov/website/azgwconditions).