Nebraska Water Science Center
Elkhorn-Loup Model: Phases one, two, and three
The Upper Elkhorn Natural Resources District, the Lower Elkhorn Natural Resources District, the Upper Loup Natural Resources District, the Lower Loup Natural Resources District, the Middle Niobrara Natural Resources District, the Lower Niobrara Natural Resources District, the Lewis and Clark Natural Resources District, and the Lower Platte North Natural Resources District (herein referred to collectively as NRDs) are collecting data and developing tools to assist with water resource planning. Critical planning issues in the Elkhorn River and Loup River basins are focused on the availability of the ground-water resource, the effect of anthropogenic stresses on the ground-water resource, and the interaction of groundwater and surface water (view detailed map of study area). Specifically, the NRDs and the Nebraska Department of Natural Resources (NDNR) are concerned with the effect of ground-water withdrawal on the availability of surface water and the long-term effects of ground-water withdrawal on the ground-water resource.
The Elkhorn-Loup Model, a multi-phase project, is a study of surface-water and groundwater resources in the Elkhorn River basin upstream from Norfolk, Nebraska, and the Loup River basin upstream from Columbus, Nebraska. The study area covers approximately 30,800 square miles, and extends north to the Niobrara River and south to the Platte River. The eastern boundary coincides with the approximate location of the westernmost extent of glacial till in eastern Nebraska. The study, conducted by the U.S. Geological Survey in cooperation with NDNR and the NRDs, was designed to assist NDNR and the NRDs by characterizing the ground-water system within the study area and by providing a regional groundwater-flow model.
The first phase of the study began with construction of a groundwater-flow model usin gpreviously collected data. The model was constructed with a single layer vertically to represent the aquifers of the Tertiary-age Ogallala Group and Quaternary-age alluvial deposits, with a uniform node spacing of 2 miles. The model was calibrated to measured groundwater levels and estimated groundwater discharge to streams for the pre-groundwater-development period (approximately 1940) and the simulation of the 1940-2005 period was calibrated to measured groundwater-level changes. The calibrated groundwater-flow model was used to assess current and future impacts of groundwater pumping on surface water, and could be used to provide information to the NRDs for groundwater-management planning.
Continuation of the study, phase two, was part of a larger, ongoing effort to enhance the current knowledge of hydrogeology, improve the understanding of stream-aquifer interactions, and compile reliable data describing hydrogeologic properties such groundwater recharge, groundwater pumpage for irrigation, and groundwater discharge to evapotranspiration in the study area. This study extension, hereinafter referred to as phase two, included updates to the groundwater-flow simulation using newly collected data, supporting analyses done in 2007 and 2008, improved simulation calibration methods, and additional approaches for analyzing the effects of agricultural irrigation using the simulation. Newly collected data include revisions to the base-of-aquifer map using test-hole drilling and surface and borehole geophysics (McGuire and Peterson, 2008), synoptic base-flow measurements along stream reaches (Peterson and Strauch, 2007), a runoff-recharge watershed model to estimate long-term patterns of recharge (Strauch and Linard, 2009), and geophysical mapping of resistivity patterns in canals and streams (Teeple and others, 2009). In addition to enhancing the data to the simulations, parameter-estimation techniques were used for phase-two simulation calibration, providing a more robust calibration. Other enhancements to the simulations included refining the grid discretization, using time-variable recharge from precipitation, time-variable base-flow estimates, improved estimates of groundwater withdrawals for irrigation, and refined delineation of active evapotranspiration grid cells.
The third phase of the study, phase three, continues to use new methods and data to refine the groundwater-flow model developed in phases one and two. Implementation of these new methods and data will increase the understanding of the availability of groundwater and the effect of anthropogenic stresses on the groundwater and surface-water resources in the Elkhorn and Loup River basins. Phase-three objectives include an investigation of the phase-two model sensitivity to recharge using the Soil-Water-Balance (SWB) model, newly developed by USGS. SWB will help assimilate readily available public data (climate, soils, land use, etc.) to estimate the spatial and temporal patterns of recharge. Another major objective is continued collection of geologic data to better characterize the aquifer. The combination of test-hole drilling, bore geophysical logging, and surface geophysical surveys will provide a more detailed picture of the aquifer units and base of the aquifer. Additionally, monitoring wells will be installed in test-hole drilling locations to give NRDs better information on water levels. The final objective is spatial and temporal refinement of the groundwater-flow model. This includes re-discretization of the model grid to ½-mile-cell spacing and the refinement of stress periods from an annual time step to at least seasonal so that the model can represent input changes that occur within one model year. Finally, the results of the phase-three model will undergo calibration via parameter estimation similar to the calibration done for phase two, as well as the completion of additional analysis runs.
Phase-One ELM Publications
Simulation of Ground-Water Flow and Effects of Ground-Water Irrigation on Base Flow in the Elkhorn and Loup River Basins, Nebraska Scientific Investigations Report 2008-5143
Phase-Two ELM Publications
Simulation of Groundwater Flow and Effects of Groundwater Irrigation on Stream Base Flow in the Elkhorn and Loup River Basins, Nebraska, 1895–2055—Phase Two Scientific Investigations Report 2010-5149
Base of Principal Aquifer for the Elkhorn-Loup Model Area, North-Central Nebraska Scientific Investigations Map 3042 (revised)
Apparent Resistivity and Estimated Interaction Potential of Surface Water and Groundwater along Selected Canals and Streams in the Elkhorn-Loup Model Study Area, North-Central Nebraska, 2006–07 Scientific Investigations Report 2009-5171
Streamflow Simulations and Percolation Estimates Using the Soil and Water Assessment Tool for Selected Basins in North-Central Nebraska, 1940-2005 Scientific Investigations Report 2009-5075
Phase-Three ELM Publications
Hydrostratigraphic Interpretation of Test-Hole and Surface Geophysical Data, Elkhorn and Loup River Basins, Nebraska, 2008 to 2011 Open-File Report 2012-1227
Base of the upper layer of the phase-three Elkhorn-Loup groundwater-flow model, north-central Nebraska Scientific Investigations Map 3259
U.S. Geological Survey Groundwater Modeling Software: Making Sense of a Complex Natural Resource Fact Sheet 2009-3105
groundwater, integrated resource management tool, flow model, cooperative effort, state and local agencies
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