WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2002NE5B
Title: Investigation of Directional Hydraulic Conductivities of Streambeds and Evaluation
Project Type: Research
Focus Categories: Hydrology, Groundwater, Models
Keywords: Standpipe method, Streambed, Directional hydraulic conductivity, Stream-aquifer connectivity
Start Date: 03/01/2002
End Date: 02/28/2003
Federal Funds: $16,446
Non-Federal Matching Funds: $44,782
Congressional District: First District
University of Nebraska-Lincoln
James W. Goeke
University of Nebraska-Lincoln
In groundwater irrigation areas of the High Plains states, one common concern regarding water resources is streamflow depletion. Development of optimal management models for ground water and stream water is of interest to federal, state and local agencies. In modeling of stream-aquifer interactions, one of the most critical databases is of streambed conductivity, discussions of which are very scarce in the literature and earlier investigations of stream systems. Consequently, investigation of streambed conductivities is theoretically and practically important to understanding stream-aquifer interactions.
This study includes three objectives: 1) utilization of the developed standpipe methods for determination of in-situ streambed hydraulic conductivities in new locations in Nebraska's key rivers and their tributaries; 2) collection of streambed hydraulic gradients (their upward or downward directions and magnitude) in various river reaches for determination of the losing/gaining river segments; and 3) development of a stream-aquifer model to evaluate the role of streambed hydraulic conductivity in streamflow depletion. The standpipe consists of two PVC pipes and a joint. Based on the availability of PVC joints in hardware stores, we have designed a series of standpipes with angles of, 90, 115, 135, 157.5, and 180 degrees between the two pipes in an earlier investigation.
During tests in river channels, one pipe will be pushed into the streambed and the other pipe will remain vertical, and water will be poured into the vertical pipe. Because there is a hydraulic gradient between the stream stage and the vertical pipe, water in the vertical pipe migrates through the sediment column which has filled the other segment of the standpipe. The water-level readings from the PVC pipes will be collected for calculating the streambed hydraulic conductivities. Standpipe tests will be conducted perpendicular, parallel, and with various oblique angles to the streambed surface. Analysis of the data from the streambed tests will mostly be based on the theories developed by Hvorslev (1951) and Chen (2000).
Study sites will be selected in the Republican and Platte rivers, as well as a number of their tributaries. The study locations will be selected in those areas where aquifer tests have been conducted and the hydraulic properties of the alluvial aquifers have been evaluated, so that results from stream and aquifer tests can be compared. For each location, tests will be conducted along one or more transects across the river so that spatial variations can be detected for sediments in the middle and near the bank of the river. Most streambed tests will be conducted to determine the vertical hydraulic conductivity. Tests for horizontal and oblique conductivities will be determined at random locations to construct the streambed conductivity ellipses. Streambed hydraulic gradients will be measured prior to, during and after irrigation season.
We will then use the USGS MODFLOW to design stream-aquifer models to analyze stream-aquifer interactions due to groundwater extraction in nearby aquifers. A pre- and post-processor will be developed to manage the input data and output results for the models. Modeling will consider both irrigation and non-irrigation seasons. The modeling results will demonstrate the importance of the information on the streambed conductivities and anisotropy to the development of an optimal conjunctive water-use plan.