MODELING THE STREAM-AQUIFER DYNAMICS USING STREAMBED FIELD DATA IN THE LOWER PLATTE RIVER BASIN, NEBRASKA

Streambed hydraulic conductivity (Kb) is one of the most important factors controlling the interaction between streams and groundwater. Kb, however, is rarely properly determined, thus causing high uncertainty in stream-groundwater modeling. In this study, a three-dimensional numerical groundwater flow model was developed and streambed field data was used in the model to simulate the stream-aquifer dynamics. The model covers an area of 1713 mi² in the Lower Platte River Basin, Nebraska. Stream-groundwater interactions along the Platte River between Duncan and Ashland were simulated with the River Package. Streambed properties were determined through series of streambed sediment cores collected by Geoprobe's direct-push techniques in the Platte River. Kb was estimated through permeameter tests on the sediment cores. The Geoprobe direct-push method was also used to generate electrical conductivity logs of streambeds for determination of hydrostratigraphic units. The streambed hydrogeological information was proved to be very useful for our stream-groundwater model calibration. The effects of agricultural irrigation wells, as well as other types of pumping wells, were considered in the model. Hydrostratigraphic units and their hydraulic properties were determined based on lithology of registered wells and the Nebraska statewide test holes. Over 200 observation wells were calibrated through the trial-and-error method. A computer interface based on Microsoft Visual Basic 2010 was developed to assist calibration. The model can quantitatively depict the stream-groundwater interaction and the agricultural irrigation impact and is useful for integrated management of stream and groundwater resources.