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Scientific-Investigations Report 2009–5171

In cooperation with the Upper Elkhorn, Lower Elkhorn, Upper Loup, Lower Loup, Middle Niobrara, Lower Niobrara, Lewis and Clark, and Lower Platte North Natural Resources Districts

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

By Andrew P. Teeple, Joseph Vrabel, Wade H. Kress, and James C. Cannia

Abstract

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In 2005, the State of Nebraska adopted new legislation that in part requires local Natural Resources Districts to include the effect of groundwater use on surface-water systems in their groundwater management plan. In response the U.S. Geological Survey, in cooperation with the Upper Elkhorn, Lower Elkhorn, Upper Loup, Lower Loup, Middle Niobrara, Lower Niobrara, Lewis and Clark, and Lower Platte North Natural Resources Districts, did a study during 2006–07 to investigate the surface-water and groundwater interaction within a 79,800-square-kilometer area in north-central Nebraska. To determine how streambed materials affect surface-water and groundwater interaction, surface geophysical and lithologic data were integrated at four sites to characterize the hydrogeologic conditions within the study area. Frequency-domain electromagnetic and waterborne direct-
current resistivity profiles were collected to map the near-surface hydrogeologic conditions along sections of Ainsworth Canal near Ainsworth, Nebraska; Mirdan and Geranium Canals near Ord, Nebraska; North Loup River near Ord, Nebraska; and Middle Loup River near Thedford, Nebraska. Lithologic data were collected from test holes at each site to aid interpretation of the geophysical data. Geostatistical analysis incorporating the spatial variability of resistivity was used to account for the effect of lithologic heterogeneity on effective hydraulic permeability. The geostatistical analysis and lithologic data descriptions were used to make an interpretation of the hydrogeologic system and derive estimates of surface-water/groundwater interaction potential within the canals and streambeds.

The estimated interaction potential at the Ainsworth Canal site and the Mirdan and Geranium Canal site is generally low to moderately low. The sediment textures at nearby test holes typically were silt and clay and fine-to-medium sand. The apparent resistivity values for these sites ranged from 2 to 120 ohm-meters. The vertical and horizontal variability of the apparent resistivity data were consistently low. Low resistive variability indicates little lithologic heterogeneity for either canal site. The surface-water/groundwater interaction-potential estimates are in agreement with the narrow frequency distribution of resistivity, low apparent resistivities, low spatial heterogeneity, and test-hole grain-size ranges.

The estimated surface-water/groundwater interaction potential at the North Loup and Middle Loup River sites is moderate to moderately high. The sediment textures at nearby test holes were predominantly fine, medium, and coarse sand with some silt and silty to sandy clay. The apparent resistivity values for these sites ranged from 34 to 1,338 ohm-meters. The vertical variability of the resistivity data was moderately high. The horizontal variability at these sites is low to moderately low. The higher resistive variability at these sites indicates generally greater lithologic heterogeneity than at either the Ainsworth Canal site or the Mirdan and Geranium Canal site. The surface-water/groundwater interaction-potential estimates are in agreement with the generally moderate to high apparent resistivity, the greater spatial heterogeneity, and the variable lithologic texture. A higher interaction potential as compared to the canal sites is expected because of the higher subsurface resistivity and greater lithologic heterogeneity.

First posted September 29, 2009

For additional information contact:

Director, Nebraska Water Science Center
5231 South 19th Street
Lincoln, NE 68512-1271
(402) 328-4100

http://ne.usgs.gov/

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Suggested citation:

Teeple, A.P., Vrabel, Joseph, Kress, W.H., and Cannia, J.C., 2009, 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: U.S. Geological Survey Scientific Investigations Report 2009–5171, 66 p.



Contents

Abstract

Introduction

Methods for Continuous Resistivity Profiling

Methods for Estimating Surface-Water/Groundwater Interaction Potential

Apparent Resistivity and Estimated Interaction Potential of Surface Water and Groundwater

Summary

References Cited

Appendix 1. Sampling Delays and Widths used with the High-Resolution Time-Gate Sampling Rate for the Time-Domain Electromagnetic Soundings

Appendix 2. Inverse Modeling Results for Time-Domain Electromagnetic Soundings, North-Central Nebraska, 2006–07


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