DETERMINATION OF CANAL LEAKAGE POTENTIAL USING CONTINUOUS RESISTIVITY PROFILING TECHNIQUES IN WESTERN NEBRASKA

In the North Platte River Basin, a ground-water model is being developed to evaluate the effectiveness of using leakage of water from selected irrigation canal systems to enhance ground-water recharge. For the ground-water model to accurately simulate ground-water and surface-water conditions in the North Platte River Valley, input of leakage values along the canals is imperative. The U.S. Geological Survey, in cooperation with the North Platte Natural Resources District, used capacitively coupled and water-borne direct-current continuous resistivity profiling techniques to map the lithology of the upper 8 meters and to interpret the relative canal leakage potential of 110 kilometers of the Interstate and Tri-State Canals in western Nebraska.

Qualitative lithologic descriptions from 25 test holes were used to evaluate the effectiveness of both techniques for mapping near-surface lithology and to develop an interpretive color scale that symbolized resistivity features found to be associated with coarse-grained sediments as warmer colors and fine-grained sediments as cooler colors. Resistivity values for each geographic (x,y) location were vertically averaged, yielding a single resistivity value that was used to represent the overall resistivity of the canal at that location. At the test hole sites, the average resistivity was compared to the lithologic descriptions and found to be a reasonable interpretation of the lithologic data. The average resistivity was interpreted to classify areas of the canal as having either high, moderate, or low canal leakage potential.

Both continuous resistivity profiling techniques, in comparison to the lithologic descriptions, were determined to be effective at differentiating coarse-grained sediments from fine-grained sediments. Both techniques were useful for producing independent, similar interpretations of canal leakage potential.