THE ELKHORN-LOUP MODEL STUDY: PROACTIVE NEBRASKA DECISION MAKERS INITIATE SCIENCE-BASED INTEGRATED WATER MANAGEMENT

Natural Resources Districts (NRDs) in Nebraska are local agencies responsible for management of natural resources including ground-water resources. Critical issues for NRDs include long-term availability of the ground-water resource, the effect of ground-water withdrawal on surface water, and management of the integrated system, which in some areas is mandated by recently enacted legislation. Though the NRDs mission is to study and maintain the ground-water resource, much of Nebraska's agriculture is supported by ground-water irrigation, so the NRDs do not unnecessarily restrict ground-water usage or development.

The Elkhorn-Loup Model is a product of a cooperative study by the USGS, Nebraska Department of Natural Resources, the Lower Loup NRD, Upper Loup NRD, Lower Elkhorn NRD, and Upper Elkhorn NRD, to study the surface- and ground-water system of a 30,800 mi2 area in north-central Nebraska. The area includes the Elkhorn and Loup River basins, the primary rivers flowing from the Nebraska Sand Hills, which overlie more than half of the area. The Sand Hills are an important area for regional ground-water recharge, and generally overlie aquifers hundreds of feet thick. Primary aquifers include the Tertiary-age Ogallala Group and Quaternary-age alluvial aquifers.

Phase 1 of the study included basic data compilation as well as construction and calibration of a regional ground-water flow model. This model was used for a few system analysis runs but detailed analysis was postponed until late in phase 2. Phase 1 analysis runs include calculation of 50-year stream depletion based on theoretical well pumping, simulation of the effects of past ground-water pumping on future surface-water resources, and simulation of the effects of current ground-water pumpage on future surface-water resources. Phase 2 enhances the initial study with four new supporting efforts: to measure streamflow, update the aquifer base map, collect geophysical data, and construct and calibrate a rainfall-runoff simulation. Data and analysis from these efforts will be used to refine the Phase 1 ground-water flow model. The refined ground-water flow model will be used for additional analysis, possibly through optimization approaches to identify best management strategies to balance competing demands on water resources.