CRP/CSP Profile 1001 N Line CW6 RESISTIVITY,
Transcript of CRP/CSP Profile 1001 N Line CW6 RESISTIVITY,
INTERPRETATIONS AND SUMMARY
F
Geophysical methods used to better characterize surface water, alluvial aquifer, and bedrock aquifer
interaction in the Cedar River Valley, IowaAdel E. Haj Jr.1, Eric A. White2, Lance R. Gruhn1, S. Mike Linhart1, and John W. Lane Jr.21: USGS Illinois-Iowa Water Science Center; 2: USGS Office of Groundwater Branch of Geophysics
• CRP and CSP methods delineate common
sub-bottom features across multiple survey
lines
• Shallow subsurface reflectors observed in
CSP correlate with resistive zones
observed in CRP.
• HVSR useful for interpreting depth to
bedrock in this area, with clear resonance
peaks for bedrock mapping in most
attempted surveys
• HVSR sensor coupling key to success
• ERT results match well to HVSR data
• Study area bedrock depths range from 5 to
28m
• ERT shows clear unconsolidated/bedrock
transition
• ERT shows some shallow high-resistivity
zones overlying less resistive materials
(attributed to saturation, grain-size, or
cementation differences)
• ERT and CRP resistivity ranges and
structures similar
• Results will be used to calibrate AEM
• Shallow CSP reflectors interpreted as hard
surface or fine/coarse transition
• Electrically resistive zones interpreted as
hard/cemented materials or coarse-grained
materials
• Results suggest possible buried valleys
and regions of bedrock connectivity
BACKGROUNDBetween July 2011 and February 2013, Iowa experienced severe
drought conditions (generally referred to as the 2012 drought)
that critically affected water availability throughout the state
where communities rely on alluvial aquifers to supply their water
needs. The City of Cedar Rapids saw pumping levels drop to
near cavitation levels in some wells. The City is interested in
evaluating prolonged drought condition water-supply availability
to determine if surface-water intakes need to be included in their
water-treatment capabilities.
The USGS Iowa Water Science Center is charged with building a
new groundwater model of the Cedar River alluvial aquifer that
can simulate stresses and drawdowns experienced during
extreme drought and demand. The new groundwater model
considers river connectivity to the aquifer, alluvial aquifer
connectivity to the bedrock aquifer, subsurface recharge sources
such as tributary inflows and buried valleys, and wetland and
oxbow lake connectivity to the alluvial aquifer. A suite of
geophysical methods is being employed to efficiently and non-
invasively map aquifer thickness and bedrock connectivity for
parameterization of this model. These geophysical methods
include waterborne and land-based seismic and resistivity surveys
and a forthcoming airborne electromagnetic survey.
BACKGROUND Future workFuture work
• Airborne electromagnetic
(AEM) survey spring 2017
• AEM will be calibrated to
previous geophysical
work and well data
• AEM will provide far
more comprehensive and
continuous data for an
improved model
• AEM will be
complemented with
additional land-based
seismic and ERT surveys,
as well as new boreholes
Example AEM
data from
Sioux Falls
aquifer study.
Warm colors
represent
more resistive
material,
preliminarily
interpreted as
quartzite.
Cedar Rapids
model area
(yellow) and
AEM survey
area (red)
FUTURE WORK
Passive Seismic Horizontal-to-Vertical Spectral Ratio (HVSR)
Electrical Resistivity Tomography
(ERT)
• Unit records ambient seismic wavefield
using 2-horizontal and 1-vertical
component; peak H/V frequency ratio is
resonant frequency (Fr) of surficial material
• Fr related to seismic shear wave velocity
(Vs) and depth to bedrock (Z) by the
equation 𝑉𝑠 = 4𝐹𝑟𝑍• Cedar River alluvium average Vs (300 m/s)
calculated from measurements at 5 wells
with known depth to rock
• Results depend on strong acoustic contrast
between sediment and bedrock, good
coupling of unit to ground surface, absence
of anthropogenic noise
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RESISTIVITY,IN OHM-METERS
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RESISTIVITY,IN OHM-METERS
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Distance (meters)
fr = 16.01 HzZ = 4.7 m
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RESISTIVITY,IN OHM-METERS
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Distance (meters)
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fr = 3.88 HzZ = 19.3
fr = 3.59 HzZ = 20.9
fr = 3.72 HzZ = 20.2
fr = 3.81 HzZ = 19.7
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RESISTIVITY,IN OHM-METERS
IN
Distance (meters)
S N
fr = 3.67 HzZ = 20.4 m
fr = 3.44 HzZ = 21.8 m
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RESISTIVITY,IN OHM-METERS
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Distance (meters)
fr = 3.02 HzZ = 24.8m
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RESISTIVITY,IN OHM-METERS
N SPipeline
f0 = 4.42 HzZ = 17.0 m
f0 = 3.99 HzZ = 16.8 m
f0 = 6.00 HzZ = 12.5m
Dep
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w g
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eter
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epth
bel
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Dep
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Distance (meters)
Line CW6
Line CW1
Seminole Valley Park
Line S10
Line CW3Dep
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LAND-BASED METHODS
Sample HVSR data:
(a) horizontal and
vertical component
frequency spectra,
(b) horizontal to
vertical frequency
ratio.
a
b
• Survey performed
with Supersting R8
• Used dipole-dipole,
Schlumberger, and
inverse Schlumberger
arrays
• Modeled resistivity ranges from 25 to
325 ohm-m
• Data affected by pipeline in line CW3Horizontal black lines indicate depth
to bedrock from HVSR measurements.
Land-based surveys help characterize the extent and geophysical properties
of floodplain sediments.Waterborne surveys provide information about channel sub-bottom, an area
inaccessible to other methods.
Space
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• 8-channel resistivity system and 11-electrode
streamer with 10-m spacing
• Subsurface penetration ~16m
• Resistivity range: 30 to 300 oh
• m-m
WATERBORNE METHODS
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RESISTIVITY,IN OHM-METERS
S
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CRP/CSP Profile 1000
L1000 S L1000 SNS
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CRP/CSP Profile 1001 NS
CRP/CSP Profile 1002 NS3D Composite of CRP data
AREAOFNOCRP
DATARECD
L1003A S L1003A S L1003B S L1003B S
CRP/CSP Profile 1003 NS
CRP/CSP Profile 1004 NS
FFf
EdgeTech Sub-bottom Profiler
• 4 - 24 kHz Chirp
system
• Subsurface
penetration ~5m
• Water bottom
multiples present in
all records
• 8-channel resistivity
system and 11-
electrode streamer
with 10-m spacing
• Depth of
investigation ~16m
• Resistivity range: 30
to 300 ohm-m
Continuous Resistivity Profiling
(CRP)
Continuous Seismic Profiling
(CSP)
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PROJECT AREA
References
Advanced Geosciences, Inc., 2005, Instruction manual for EarthImager 2D, version 1.9.0, Resistivity and IP inversion software: Advanced Geosciences, Inc.,134 p., accessed at http://www.agiusa.com/.
Day-Lewis, F., White, E., Johnson, C., Lane, J., and Belaval, M., 2006. Continuous resistivity profiling to delineate submarine groundwater discharge-example limitation, The Leading Edge, June, 724-728.
Loke, M.H., 2000, Electrical imaging surveys for environmental and engineering studies - a practical guide to 2D and 3D surveys, unpublished short course training notes: Penang, Malaysia, University Sains Malaysia, 67 p.
Reynolds, J.M., 2011, An introduction to applied and environmental geophysics, John Wiley and Sons, 712p.
Telford, W.M., Geldart, L.P., Sheriff, R.E., 1990, Applied geophysics, 2nd
edition, Cambridge University Press
Todd, D.K., 1980, Groundwater hydrology 2nd edition, John Wiley and Sons
REFERENCES
Black lines in CRP profiles indicate interpreted bedrock surface.
L1001 S L1001 S