Measuring Resisitivity to Gauge Submarine Groundwater Discharge

Streaming Resistivity (Marine-based)

Electrical resistivity measurements can detect variations in the salinity (conductivity = 1/resistivity) regime of subsurface pore water and porous sediments. Resistivity data can be collected under two scenarios, 1) time series, and 2) streaming survey modes. In streaming survey mode, the 120 m 8-channel streamer system collects instantaneous dipole-dipole measurements at ~3 s intervals. The 120 m electrode cable, which is towed along the water's surface at a speed of about 3-4 knots, consists of two current-producing graphite electrodes and nine stainless steel electrodes spaced 10 m apart. The depth of penetration for such a system is roughly one-third of the total streamer cable length. By merging the ship's navigation (latitude, longitude and depth) and an in-situ hydrographic data stream (salinity, pH, conductivity, temperature) with the resistivity data, inversion models can be run to process resistivity cross-sections.

Time-series Resistivity (Land-based)

Time-series resistivity for our projects is collected using an advanced Geosciences SuperSting R8 resistivity receiver and a custom 112 m long high resolution underwater cable that consists of 56 graphite electrodes spaced 2 m apart in a dipole-dipole array. This cable is deployed along the shore face and seabed using a combination of electrode stakes and sandbags. Resolution of sharp salinity boundaries can be increased by using a starting model with the apparent resistivity pseudo-section overlain by water column data based on bathymetry and two conductivity, temperature, and pressure sensors. The best fitting layered model is then found by using an iterative least squares smooth model inversion method. Results from such time series resistivity measurements are compared relative to water levels.

Novel Geophysical and Geochemical Techniques Used to Study Submarine Groundwater Discharge in Biscayne Bay, Florida

Printable Version: Click on the image to the right to open USGS Report 2004-3117 in Adobe Reader. NOTE: PDF files may be viewed using Adobe Reader public domain software. If unable to access the PDF files, please contact aharrison@usgs.gov.

"Novel geophysical and geochemical techniques used to study submarine groundwater discharge in Biscayne Bay, Florida" is a four-page full-color discussion of new methods and tools being out to use in the study of submarine gorundwater dsicharge in Biscayne Bay, Florida. Among the new tools discussed are streaming resistivity profiling, electromagnetic seepage meters, and near-continous ²²²Rn surveys.

2004-3117 (1.16 MB PDF)

Novel geophysical and geochemical techniques used to study submarine groundwater discharge in Biscayne Bay, Florida http://sofia.usgs.gov/publications/fs/2004-3117/

Additional Links

To view a HTML accessible version of the report click on either the link below, or the link located beneath the image found on the right:

http://sofia.usgs.gov/publications/fs/2004-3117/

Click on the images below to open a printable version of the USGS Report in Adobe Reader.

OFR 2004-1226 (808 KB PDF)

Submarine ground water discharge and its role in coastal processes and ecosystems http://sofia.usgs.gov/publications/ofr/2004-1226/

OFR 2004-1369 (1.03 MB PDF)

An autonomous, electromagnetic seepage meter to study coastal groundwater/ surface-water exchange http://sofia.usgs.gov/publications/ofr/2004-1369/

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Measuring Resisitivity to Gauge Submarine Groundwater Discharge Streaming Resistivity (Marine-based) Electrical resistivity measurements can detect variations in the salinity (conductivity = 1/resistivity) regime of subsurface pore water and porous sediments. Resistivity data can be collected under two scenarios, 1) time series, and 2) streaming survey modes. In streaming survey mode, the 120 m 8-channel streamer system collects instantaneous dipole-dipole measurements at ~3 s intervals. The 120 m electrode cable, which is towed along the water's surface at a speed of about 3-4 knots, consists of two current-producing graphite electrodes and nine stainless steel electrodes spaced 10 m apart. The depth of penetration for such a system is roughly one-third of the total streamer cable length. By merging the ship's navigation (latitude, longitude and depth) and an in-situ hydrographic data stream (salinity, pH, conductivity, temperature) with the resistivity data, inversion models can be run to process resistivity cross-sections. Time-series Resistivity (Land-based) Time-series resistivity for our projects is collected using an advanced Geosciences SuperSting R8 resistivity receiver and a custom 112 m long high resolution underwater cable that consists of 56 graphite electrodes spaced 2 m apart in a dipole-dipole array. This cable is deployed along the shore face and seabed using a combination of electrode stakes and sandbags. Resolution of sharp salinity boundaries can be increased by using a starting model with the apparent resistivity pseudo-section overlain by water column data based on bathymetry and two conductivity, temperature, and pressure sensors. The best fitting layered model is then found by using an iterative least squares smooth model inversion method. Results from such time series resistivity measurements are compared relative to water levels.

	Figure 1. Stationary, time-series, multi-electrode resistivity profiles across a beach face as a function of water level. Inversion parameters were held constant for each time step. To highlight subsurface resistivity change at the land / sea interface, images reflect only the first 40 m of data. Inset graph of water level data collected from a Solinist Diver midway down cable, at electrode 28.
Novel Geophysical and Geochemical Techniques Used to Study Submarine Groundwater Discharge in Biscayne Bay, Florida Printable Version: Click on the image to the right to open USGS Report 2004-3117 in Adobe Reader. NOTE: PDF files may be viewed using Adobe Reader public domain software. If unable to access the PDF files, please contact aharrison@usgs.gov. "Novel geophysical and geochemical techniques used to study submarine groundwater discharge in Biscayne Bay, Florida" is a four-page full-color discussion of new methods and tools being out to use in the study of submarine gorundwater dsicharge in Biscayne Bay, Florida. Among the new tools discussed are streaming resistivity profiling, electromagnetic seepage meters, and near-continous ²²²Rn surveys.
		FS 2004-3117 (1.16 MB PDF) Novel geophysical and geochemical techniques used to study submarine groundwater discharge in Biscayne Bay, Florida http://sofia.usgs.gov/publications/fs/2004-3117/
Additional Links To view a HTML accessible version of the report click on either the link below, or the link located beneath the image found on the right: http://sofia.usgs.gov/publications/fs/2004-3117/


Print Publications: Reports Click on the images below to open a printable version of the USGS Report in Adobe Reader.

	OFR 2004-1226 (808 KB PDF) Submarine ground water discharge and its role in coastal processes and ecosystems http://sofia.usgs.gov/publications/ofr/2004-1226/	OFR 2004-1369 (1.03 MB PDF) An autonomous, electromagnetic seepage meter to study coastal groundwater/ surface-water exchange http://sofia.usgs.gov/publications/ofr/2004-1369/

Measuring Resisitivity to Gauge Submarine Groundwater Discharge

Streaming Resistivity (Marine-based)

Time-series Resistivity (Land-based)

Novel Geophysical and Geochemical Techniques Used to Study Submarine Groundwater Discharge in Biscayne Bay, Florida

Additional Links

Print Publications: Reports