Electrical resistivity investigation of fluvial geomorphology to evaluate potential seepage conduits to agricultural lands along the San Joaquin River, Merced County, California, 2012–13

Scientific Investigations Report 2016-5172
Prepared in cooperation with the Bureau of Reclamation
By: , and 

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Abstract

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydraulically connected to the river could act as seepage conduits, allowing rapid and widespread water-table rise during restoration flows. There is a need to identify the geometry and properties of these channel deposits to assess their role in potential increased seepage effects and to evaluate management alternatives for reducing seepage. Electrical and electromagnetic surface geophysical methods have provided a reliable proxy for lithology in studies of fluvial and hyporheic systems where a sufficient electrical contrast exists between deposits of differing grain size. In this study, direct-current (DC) resistivity was used to measure subsurface resistivity to identify channel deposits and to map their subsurface geometry. The efficacy of this method was assessed by using DC resistivity surveys collected along a reach of the San Joaquin River in Merced County, California, during the summers of 2012 and 2013, in conjunction with borings and associated measurements from a hydraulic profiling tool. Modeled DC resistivity data corresponded with data from cores, hand-auger samples, a hydraulic profiling tool, and aerial photographs, confirming that DC resistivity is effective for differentiating between silt and sand deposits in this setting. Modeled DC resistivity data provided detailed two-dimensional cross-sectional resistivity profiles to a depth of about 20 meters. The distribution of high-resistivity units in these profiles was used as a proxy for identifying areas of high hydraulic conductivity. These data were used subsequently to guide the location and depth of wells installed onsite for monitoring flow in the channel deposits. Estimates of the cross-sectional area of channel deposits from DC resistivity pseudosections can provide critical input for groundwater-flow models designed to simulate river seepage and evaluate seepage-management alternatives.

Suggested Citation

Groover, K.D., Burgess, M.K., Howle, J.F., Philips, S.P., 2017, Electrical resistivity investigation of fluvial geomorphology to evaluate potential seepage conduits to agricultural lands along the San Joaquin River, Merced County, California, 2012–13: U.S. Geological Survey Scientific Investigations Report 2016–5172, 39 p., https://doi.org/10.3133/sir20165172.

ISSN: 2328-0328 (online)

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Table of Contents

  • Abstract
  • Introduction
  • Methods
  • Observations and Data
  • Study Limitations
  • Summary and Conclusions
  • References Cited
  • Appendix 1

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Electrical resistivity investigation of fluvial geomorphology to evaluate potential seepage conduits to agricultural lands along the San Joaquin River, Merced County, California, 2012–13
Series title Scientific Investigations Report
Series number 2016-5172
DOI 10.3133/sir20165172
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center, Volcano Hazards Program, Volcano Science Center
Description vii, 39 p.
Country United States
State California
County Merced County
Other Geospatial San Joaquin River
Online Only (Y/N) Y
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