Stream/aquifer relationships along the Big Blue River near Beatrice, Nebraska

In 1983, a research project, involving an area of 73 square miles, was initiated in order to study the relationships between the stream and aquifer system along the Big Blue River near Beatrice, Nebraska. The goal of this research was to describe and quantify stream/aquifer relationships and interactions as an aid to water management. A detailed hydrogeologic investigation of the area was conducted before the stream/aquifer relationship was analyzed. Through examination of over 300 test-hole logs and irrigation-well logs and conduct of various field activities during the course of this study, important hydrogeologic factors were defined or quantified. These include the aquifer geometry (bedrock and groundwater reservoir geology), aquifer properties (transmissivity and storage coefficient), aquifer conditions (confined, unconfined, and semi-confined), discharge, and recharge affecting the stream/aquifer system. Based on the hydrogeologic investigation of the area, the interrelationship between the stream and aquifer has been examined in detail. Significant clues toward a better understanding of the stream/aquifer relationship in the area were provided by an analysis of a major flood peak that occurred during the course of the study. Quantification of stream loss or gain could be assessed by using conventional methods such as seepage runs and baseflow separation of stream hydrographs. However at the times that the stream/aquifer system is under numerous types of stresses (evapotranspiration, pumpage, etc.), the conventional methods for quantification of a specific stress, such as impact of irrigation wells on the stream flow rates, are of little use. For the simulation of groundwater flow with relation to the streams and a better understanding of the impact of irrigation wells on the Big Blue River flow rates, a finite- element computer model of the stream/aquifer system of the area was used. The results of this part of the study shows that while the impact of a limited number of irrigation wells is negligible on Turkey Creek, the impact is mathematically detectable on the Big Blue River