2009George Lightwood

Scott CraigDanny Lazzareschi

OverviewLocationPurposeMethodsResultsInterpretationsConclusions

LocationDry canal bank west of Fallon, NVLocal mapped units are Badlands

soil and Hawsley Sand. Typical resistivities for soils

consisting of predominantly of clay minerals containing brackish water: 1 to 100 Ω-m.

Soils consisting of sand and silt typically have a resistivity on the order of several hundred Ohm-meters

PurposeUse electrical methods to look for locations of

seepage and internal erosion of canal walls

Previous studies found these methods effective

Asch, T. H., M. Deszcx-Pan, B.L. Burton, and L.B. Ball, 2008, Geophysical Characterization of the American River Levees, Sacramento, California, using Electromagnetics, Capacitively Coupled Resistivity, and DC Resistivity, Open-File Report 2008-1109, U.S. Department of Interior, U.S. Geological Survey, Washington, D.C.

Panthulu, T.V., C. Krishnaiah, J.M. Shirke, 2001, Detection of seepage paths in earth dams using self-potential and electrical resistivity methods in Engineering Geology 59, pp 281-295.

Methods:MiniRes

•Wenner Array•A-spacings of 1, 1.47, 2.15, 3.16, 4.64, 6.81 and 10 meters•ρa=2πaΔV/I

•Thanks to L and R Instruments

SurveySoundings 1-9 in

canal bank profileSounding 10 on

playaSounding 11 at toe

of canal bankSoundings 12, 13 on

ReMi Line8 4.64 A-Spacing

Methods: VLFVery Low Frequency(15-

25Hz)Geonics EM16R Distant high power

sourcesFinds EM coupling with

conductors in the earthAnomalies perpendicular

to direction toward sourceSource in Jim Creek, WAMeasurements made at

locations of first 9 MiniRes

Results: Resistivity Soundings

Results- Resistivity profile

Interpretation: Resistivity Sounding

Resix to calculate resistivitites of layers

Resist to graph

Typical sounding at Station 8

Interpretation: Resistivity SoundingSounding 10 on Playa

Thinner resistive layerSounding 11 at toe of canal

bankOpposite layering

Interpretation: Resistivity Cross Section

Results:VLFApparent resistivity from 8 to 11 Ohm-m Phase angles from 34 to 38 degreesTried to construct a 2-layer model from the data Resistivity of the top layer was assumed to be on

the order of 10 to 30 Ohm-mnot successful at identifying contactmethod is poorly suited to defining the boundary

between a highly conductive layer overlying a layer of higher resistivity (Podder and Rathor, 1983)

Soil was at upper limit of conductivity senitivity

Podder, M. and B.S. Rathor, 1983, VLF Survey of the Weathered Layer in Southern India, Geophysical Prospecting, vol. 31, pp. 524-537.

ConclusionsCanal Bank consists of 3 layers- high

resistivity in between two low resistivity laversTop layer likely compacted clayMiddle layer likely sands excavated from the

canalBottom layer likely claysMiddle sand layer a likely conduit for fluid flow

MiniRes much more effective than VLF for detailed site study

ThanksQuestions?