John Dunbar - Academia.edu (original) (raw)
Papers by John Dunbar
Water Resources Research, 2005
AGU Spring Meeting Abstracts, May 1, 2006
We applied field and laboratory electrical resistivity measurements to characterize seasonal wett... more We applied field and laboratory electrical resistivity measurements to characterize seasonal wetting and drying of a Texas Vertisol. Vertisols are complex soils characterized by high clay content (>30%), high shrink/swell potential, microrelief expression of subsurface soil dynamics (gilgai), and low hydraulic conductivity. A total of thirty-three multi-electrode resistivity profiling lines were taken along the same profile between April 27, 2005
Vadose Zone Journal, Aug 1, 2007
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
We integrate geoelectrical measurements with in-situ soil-moisture determination using core sampl... more We integrate geoelectrical measurements with in-situ soil-moisture determination using core sampling to assess changes in vadose zone properties induced by agricultural management practices in a Texas Vertisol. Two sites were established at the USDA research station, Riesel, Texas, where the underlying soils are cultivated soil for crop production and a soil in grass pasture. Center spread multielectrode resistivity data were collected on each site along the same profiles on February 22, May 7, and September 12, 2007. Data analysis involved inversion using a rapid least-square technique and temperature corrections. The results were calibrated against the in-situ soil-moisture values to generate apparent soil-moisture sections. Using the van Genuchten pedotransfer function, we used the apparent soil-moisture data to compute apparent distribution of pressure heads in the soil. The results for successive sections were then related to compute apparent soil-moisture flux over the intervals between each field survey. Significant variations in resistivity and soil-moisture dynamics between the two sites were observed in the upper 2 m of the soil, especially within the root zone. We show that, within the limitation posed by the problem of equivalence in data interpretation, management-induced changes in soil hydrologic properties can be characterized using the electrical resistivity method. Introduction Land management practices impact soils’ physical and chemical properties. Changes in physical properties (such as porosity and bulk density) manifest as changes in percolation rates and rooting depths of plants, and variations in depths to the water table (among others). Quantifying the effects of these practices is a major component of many ongoing conservation programs, e.g. Total Maximum Daily Load (TMDL) model (Torbert et al. 2005; Harmel et al. 2004). In the USDA Grassland Soil and Water Research Station (GSWRS), Riesel, Texas (Figure 1), hydrologic data have been collected since 1937. These data have been valuable in analyzing hydrologic properties of the soils for evaluating the effects of various management practices at the site (Torbert et al. 2005; Harmel et al. 2004, Harmel et al., 2006). For example, Harmel et al. (2006) used a comprehensive analysis of these data to establish a link between soil loss and erosion rate, and agricultural land use in the area. The authors also made quantitative comparisons of the earlier (pre-1964) and relatively recent (1982-2002) hydrologic data. The results show that conservation practices in recent times have helped minimize the impact of cultivated agriculture on the hydrologic properties of the soil. Geophysical surveying offer a potential alternative for quantifying the impact of agricultural land use on soils. Electrical-resistivity technique in particular can be useful in collecting spatial and temporal data to complement results of hydrological models. This method has the advantage that surveys can be carried out in 2D and 3D, and at various scales, which may be as small as centimetric scales (Samouelian et al. 2003). Besson et al. (2004) used this method to analyze structural heterogeneity of a tilled soil layer. The authors correlated resistivity distribution to variation in bulk density in the soil.
Environmental & Engineering Geoscience, May 1, 2013
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly ... more Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly variable sodium chloride loads originating from near surface evaporate deposits within the upper reaches of the contributing watershed. We investigate seasonal changes in salinity within Lake Whitney using the continuous resistivity profiling (CRP) method. From December, 2006 to October, 2007 we repeated a 30-km long profile along the axis of the reservoir six times. A 135-m long, 11-electrode, marine resistivity array was used to collect eight dipole-dipole readings at offsets from 5-120 m, at intervals of approximately 1 m along the profile. Each profile was collected in an 8 to 10 hour period to produce a “snapshot” of the salinity distribution. Starting from a well mixed and highly saline (3 ohmm/2,300 mg/L) state in early winter 2006, the reservoir became progressively fresher, due to the inflow of fresher water (4 ohm-m /1,700 mg/L) over the winter months. Spring rains, caused resistivity to rise and salinity to drop as layers of freshwater flowed out along the surface from north to south after each storm. The freshwater in these layers progressively mixed with deeper, more saline water as it moved south, raising the average resistivity of the reservoir. A second layer of cold freshwater flowed along the reservoir bottom in the north and out into mid-water depths as it moved south. The greatest contrast within the water column always occurred near the main tributary inlet and was least near the dam, suggesting progressive downstream mixing. We conclude that the CPR method can be used to delineate the depth and lateral extent of abnormally fresh and saline regions within water reservoirs and can resolve shallow and deep zones of contrasting salinity within the water column.
Transactions of the ASAE, 2003
Journal of The American Water Resources Association, Oct 1, 2002
Geophysics, Jul 1, 2008
An important potential application of the electrical-resistivity method occurs in salinity studie... more An important potential application of the electrical-resistivity method occurs in salinity studies of lakes and water reservoirs. However, uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle (contrasts of a factor of two) and changes over short intervals of time (typically in hours or days). We carry out numerical modeling and inversion of synthetic data and field resistivity data from Lake Whitney, Texas, U.S.A., to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical-resistivity method. Our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs. The simulated freshwater target in the synthetic data effectively is realized from the inversion with root-mean-square (rms) error less than 10%. However, the resolutionof the inverted sections decreases with increasing noise. Inversions of the field apparent-resistivity data from three profiles in the lake, computed using estimated optimization parameters from the synthetic study, reveal the possible pattern of salinity distributions in the reservoir. For unconstrained inversion schemes, comparisons of the inverted and independently measured in situ water electrical-conductivity data yield an average rms error of 10.8%. This error value is reduced to approximately 5% with inclusions of a priori information on water resistivity in the inversion scheme. We observe an inverse relationship between error level and number of constraints on water resistivity. In general, results show that the electrical-resistivity method is a viable tool for mapping salinity variations in reservoirs. However, good data quality and inclusion of measured water conductivity as constraints in the inversion schemes are important to enhance accuracy of the inversion results.
Increasing land-use and a changing climate can drastically modify floodplain habitats along lowor... more Increasing land-use and a changing climate can drastically modify floodplain habitats along loworder streams in central Texas. Investigating stream response to these factors on the site-scale can be costly. In an effort to streamline future site-specific investigations, a near-surface geophysical method was used along Williams Creek in Axtell, Texas. A 2-D dipole-dipole resistivity reconnaissance study was employed to estimate depth to bedrock and locate buried channels in a partial-valley cross-section. Auger borings provided ground-truth along the resistivity profile, which confirmed depth to bedrock and the significance of varying resistivities. The 276 meter resistivity profile was completed across a flowing Williams Creek and a portion of its floodplain, revealing a number of different fluvial landforms. Hand-augering confirmed the presence of a coarse-grained paleochannel fill that corresponds with a high-resistivity zone (50-100 ohm-m). At one location, auger refusal at bedrock occurred 3.15 meters below ground surface, consistent with the observed change to lower resistivity values. This decrease in resistivity at the bedrock contact is associated with groundwater flow along the fissile marl bedding planes. These data suggest that resistivity and ground-truthing combined, provide a cost-effective foundation to guide future research on the effects of climate and land-use on Williams Creek.
Geological Society of America eBooks, 2013
Energies, 2020
Spectral induced polarization (SIP) is a non-intrusive geophysical method that collects chargeabi... more Spectral induced polarization (SIP) is a non-intrusive geophysical method that collects chargeability information (the ability of a material to retain charge) in the time domain or its phase shift in the frequency domain. Although SIP is a temporal method, it cannot measure the dynamics of flow and solute/species transport in the subsurface over long times (i.e., 10–100 s of years). Data collected with the SIP technique need to be coupled with fluid flow and reactive-transport models in order to capture long-term dynamics. To address this challenge, PFLOTRAN-SIP was built to couple SIP data to fluid flow and solute transport processes. Specifically, this framework couples the subsurface flow and transport simulator PFLOTRAN and geoelectrical simulator E4D without sacrificing computational performance. PFLOTRAN solves the coupled flow and solute-transport process models in order to estimate solute concentrations, which were used in Archie’s model to compute bulk electrical conductivi...
SEG Technical Program Expanded Abstracts 1984, 1984
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010, 2010
Increasing land-use and a changing climate can drastically modify floodplain habitats along lowor... more Increasing land-use and a changing climate can drastically modify floodplain habitats along loworder streams in central Texas. Investigating stream response to these factors on the site-scale can be costly. In an effort to streamline future site-specific investigations, a near-surface geophysical method was used along Williams Creek in Axtell, Texas. A 2-D dipole-dipole resistivity reconnaissance study was employed to estimate depth to bedrock and locate buried channels in a partial-valley cross-section. Auger borings provided ground-truth along the resistivity profile, which confirmed depth to bedrock and the significance of varying resistivities. The 276 meter resistivity profile was completed across a flowing Williams Creek and a portion of its floodplain, revealing a number of different fluvial landforms. Hand-augering confirmed the presence of a coarse-grained paleochannel fill that corresponds with a high-resistivity zone (50-100 ohm-m). At one location, auger refusal at bedrock occurred 3.15 meters below ground surface, consistent with the observed change to lower resistivity values. This decrease in resistivity at the bedrock contact is associated with groundwater flow along the fissile marl bedding planes. These data suggest that resistivity and ground-truthing combined, provide a cost-effective foundation to guide future research on the effects of climate and land-use on Williams Creek.
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly ... more Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly variable sodium chloride loads originating from near surface evaporate deposits within the upper reaches of the contributing watershed. We investigate seasonal changes in salinity within Lake Whitney using the continuous resistivity profiling (CRP) method. From December, 2006 to October, 2007 we repeated a 30-km long profile along the axis of the reservoir six times. A 135-m long, 11-electrode, marine resistivity array was used to collect eight dipole-dipole readings at offsets from 5-120 m, at intervals of approximately 1 m along the profile. Each profile was collected in an 8 to 10 hour period to produce a “snapshot” of the salinity distribution. Starting from a well mixed and highly saline (3 ohmm/2,300 mg/L) state in early winter 2006, the reservoir became progressively fresher, due to the inflow of fresher water (4 ohm-m /1,700 mg/L) over the winter months. Spring rains, caused resistivity to rise and salinity to drop as layers of freshwater flowed out along the surface from north to south after each storm. The freshwater in these layers progressively mixed with deeper, more saline water as it moved south, raising the average resistivity of the reservoir. A second layer of cold freshwater flowed along the reservoir bottom in the north and out into mid-water depths as it moved south. The greatest contrast within the water column always occurred near the main tributary inlet and was least near the dam, suggesting progressive downstream mixing. We conclude that the CPR method can be used to delineate the depth and lateral extent of abnormally fresh and saline regions within water reservoirs and can resolve shallow and deep zones of contrasting salinity within the water column.
SEG Technical Program Expanded Abstracts 2007, 2007
As demands for freshwater resources continue to rise, there are critical needs for improved techn... more As demands for freshwater resources continue to rise, there are critical needs for improved techniques for water quality assessment in lakes and water reservoirs. Because conventional methods of water reservoir studies largely involve point-based water and sediment sampling, obtaining spatial data for improved characterization of salinity variations in lakes and water reservoir remains a challenge. We explore the potential of using CRPmeasured resistivity data to determine accurately true resistivity distribution in water reservoirs. Our objective is to advance the method as a tool in limnological research for mapping freshwater zones within impacted lakes and water reservoirs.
Journal of Paleolimnology, 2008
Page 1. ORIGINAL PAPER Late Tertiary paleoclimatic interpretation from lacustrine rhythmites in t... more Page 1. ORIGINAL PAPER Late Tertiary paleoclimatic interpretation from lacustrine rhythmites in the Gray Fossil Site, northeastern Tennessee, USA Aaron J. Shunk Æ Steven G. Driese Æ John A. Dunbar Received: 12 December ...
Journal of Hydrology, 2011
GEOPHYSICS, 2008
An important potential application of the electrical-resistivity method occurs in salinity studie... more An important potential application of the electrical-resistivity method occurs in salinity studies of lakes and water reservoirs. However, uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle (contrasts of a factor of two) and changes over short intervals of time (typically in hours or days). We carry out numerical modeling and inversion of synthetic data and field resistivity data from Lake Whitney, Texas, U.S.A., to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical-resistivity method. Our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs. The simulated freshwater target in the synthetic data effectively is realized from the inversion with root-mean-square (rms) error less than 10%. However, the resolutionof the invert...
Water Resources Research, 2005
AGU Spring Meeting Abstracts, May 1, 2006
We applied field and laboratory electrical resistivity measurements to characterize seasonal wett... more We applied field and laboratory electrical resistivity measurements to characterize seasonal wetting and drying of a Texas Vertisol. Vertisols are complex soils characterized by high clay content (&amp;amp;gt;30%), high shrink/swell potential, microrelief expression of subsurface soil dynamics (gilgai), and low hydraulic conductivity. A total of thirty-three multi-electrode resistivity profiling lines were taken along the same profile between April 27, 2005
Vadose Zone Journal, Aug 1, 2007
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
We integrate geoelectrical measurements with in-situ soil-moisture determination using core sampl... more We integrate geoelectrical measurements with in-situ soil-moisture determination using core sampling to assess changes in vadose zone properties induced by agricultural management practices in a Texas Vertisol. Two sites were established at the USDA research station, Riesel, Texas, where the underlying soils are cultivated soil for crop production and a soil in grass pasture. Center spread multielectrode resistivity data were collected on each site along the same profiles on February 22, May 7, and September 12, 2007. Data analysis involved inversion using a rapid least-square technique and temperature corrections. The results were calibrated against the in-situ soil-moisture values to generate apparent soil-moisture sections. Using the van Genuchten pedotransfer function, we used the apparent soil-moisture data to compute apparent distribution of pressure heads in the soil. The results for successive sections were then related to compute apparent soil-moisture flux over the intervals between each field survey. Significant variations in resistivity and soil-moisture dynamics between the two sites were observed in the upper 2 m of the soil, especially within the root zone. We show that, within the limitation posed by the problem of equivalence in data interpretation, management-induced changes in soil hydrologic properties can be characterized using the electrical resistivity method. Introduction Land management practices impact soils’ physical and chemical properties. Changes in physical properties (such as porosity and bulk density) manifest as changes in percolation rates and rooting depths of plants, and variations in depths to the water table (among others). Quantifying the effects of these practices is a major component of many ongoing conservation programs, e.g. Total Maximum Daily Load (TMDL) model (Torbert et al. 2005; Harmel et al. 2004). In the USDA Grassland Soil and Water Research Station (GSWRS), Riesel, Texas (Figure 1), hydrologic data have been collected since 1937. These data have been valuable in analyzing hydrologic properties of the soils for evaluating the effects of various management practices at the site (Torbert et al. 2005; Harmel et al. 2004, Harmel et al., 2006). For example, Harmel et al. (2006) used a comprehensive analysis of these data to establish a link between soil loss and erosion rate, and agricultural land use in the area. The authors also made quantitative comparisons of the earlier (pre-1964) and relatively recent (1982-2002) hydrologic data. The results show that conservation practices in recent times have helped minimize the impact of cultivated agriculture on the hydrologic properties of the soil. Geophysical surveying offer a potential alternative for quantifying the impact of agricultural land use on soils. Electrical-resistivity technique in particular can be useful in collecting spatial and temporal data to complement results of hydrological models. This method has the advantage that surveys can be carried out in 2D and 3D, and at various scales, which may be as small as centimetric scales (Samouelian et al. 2003). Besson et al. (2004) used this method to analyze structural heterogeneity of a tilled soil layer. The authors correlated resistivity distribution to variation in bulk density in the soil.
Environmental & Engineering Geoscience, May 1, 2013
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly ... more Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly variable sodium chloride loads originating from near surface evaporate deposits within the upper reaches of the contributing watershed. We investigate seasonal changes in salinity within Lake Whitney using the continuous resistivity profiling (CRP) method. From December, 2006 to October, 2007 we repeated a 30-km long profile along the axis of the reservoir six times. A 135-m long, 11-electrode, marine resistivity array was used to collect eight dipole-dipole readings at offsets from 5-120 m, at intervals of approximately 1 m along the profile. Each profile was collected in an 8 to 10 hour period to produce a “snapshot” of the salinity distribution. Starting from a well mixed and highly saline (3 ohmm/2,300 mg/L) state in early winter 2006, the reservoir became progressively fresher, due to the inflow of fresher water (4 ohm-m /1,700 mg/L) over the winter months. Spring rains, caused resistivity to rise and salinity to drop as layers of freshwater flowed out along the surface from north to south after each storm. The freshwater in these layers progressively mixed with deeper, more saline water as it moved south, raising the average resistivity of the reservoir. A second layer of cold freshwater flowed along the reservoir bottom in the north and out into mid-water depths as it moved south. The greatest contrast within the water column always occurred near the main tributary inlet and was least near the dam, suggesting progressive downstream mixing. We conclude that the CPR method can be used to delineate the depth and lateral extent of abnormally fresh and saline regions within water reservoirs and can resolve shallow and deep zones of contrasting salinity within the water column.
Transactions of the ASAE, 2003
Journal of The American Water Resources Association, Oct 1, 2002
Geophysics, Jul 1, 2008
An important potential application of the electrical-resistivity method occurs in salinity studie... more An important potential application of the electrical-resistivity method occurs in salinity studies of lakes and water reservoirs. However, uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle (contrasts of a factor of two) and changes over short intervals of time (typically in hours or days). We carry out numerical modeling and inversion of synthetic data and field resistivity data from Lake Whitney, Texas, U.S.A., to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical-resistivity method. Our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs. The simulated freshwater target in the synthetic data effectively is realized from the inversion with root-mean-square (rms) error less than 10%. However, the resolutionof the inverted sections decreases with increasing noise. Inversions of the field apparent-resistivity data from three profiles in the lake, computed using estimated optimization parameters from the synthetic study, reveal the possible pattern of salinity distributions in the reservoir. For unconstrained inversion schemes, comparisons of the inverted and independently measured in situ water electrical-conductivity data yield an average rms error of 10.8%. This error value is reduced to approximately 5% with inclusions of a priori information on water resistivity in the inversion scheme. We observe an inverse relationship between error level and number of constraints on water resistivity. In general, results show that the electrical-resistivity method is a viable tool for mapping salinity variations in reservoirs. However, good data quality and inclusion of measured water conductivity as constraints in the inversion schemes are important to enhance accuracy of the inversion results.
Increasing land-use and a changing climate can drastically modify floodplain habitats along lowor... more Increasing land-use and a changing climate can drastically modify floodplain habitats along loworder streams in central Texas. Investigating stream response to these factors on the site-scale can be costly. In an effort to streamline future site-specific investigations, a near-surface geophysical method was used along Williams Creek in Axtell, Texas. A 2-D dipole-dipole resistivity reconnaissance study was employed to estimate depth to bedrock and locate buried channels in a partial-valley cross-section. Auger borings provided ground-truth along the resistivity profile, which confirmed depth to bedrock and the significance of varying resistivities. The 276 meter resistivity profile was completed across a flowing Williams Creek and a portion of its floodplain, revealing a number of different fluvial landforms. Hand-augering confirmed the presence of a coarse-grained paleochannel fill that corresponds with a high-resistivity zone (50-100 ohm-m). At one location, auger refusal at bedrock occurred 3.15 meters below ground surface, consistent with the observed change to lower resistivity values. This decrease in resistivity at the bedrock contact is associated with groundwater flow along the fissile marl bedding planes. These data suggest that resistivity and ground-truthing combined, provide a cost-effective foundation to guide future research on the effects of climate and land-use on Williams Creek.
Geological Society of America eBooks, 2013
Energies, 2020
Spectral induced polarization (SIP) is a non-intrusive geophysical method that collects chargeabi... more Spectral induced polarization (SIP) is a non-intrusive geophysical method that collects chargeability information (the ability of a material to retain charge) in the time domain or its phase shift in the frequency domain. Although SIP is a temporal method, it cannot measure the dynamics of flow and solute/species transport in the subsurface over long times (i.e., 10–100 s of years). Data collected with the SIP technique need to be coupled with fluid flow and reactive-transport models in order to capture long-term dynamics. To address this challenge, PFLOTRAN-SIP was built to couple SIP data to fluid flow and solute transport processes. Specifically, this framework couples the subsurface flow and transport simulator PFLOTRAN and geoelectrical simulator E4D without sacrificing computational performance. PFLOTRAN solves the coupled flow and solute-transport process models in order to estimate solute concentrations, which were used in Archie’s model to compute bulk electrical conductivi...
SEG Technical Program Expanded Abstracts 1984, 1984
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010, 2010
Increasing land-use and a changing climate can drastically modify floodplain habitats along lowor... more Increasing land-use and a changing climate can drastically modify floodplain habitats along loworder streams in central Texas. Investigating stream response to these factors on the site-scale can be costly. In an effort to streamline future site-specific investigations, a near-surface geophysical method was used along Williams Creek in Axtell, Texas. A 2-D dipole-dipole resistivity reconnaissance study was employed to estimate depth to bedrock and locate buried channels in a partial-valley cross-section. Auger borings provided ground-truth along the resistivity profile, which confirmed depth to bedrock and the significance of varying resistivities. The 276 meter resistivity profile was completed across a flowing Williams Creek and a portion of its floodplain, revealing a number of different fluvial landforms. Hand-augering confirmed the presence of a coarse-grained paleochannel fill that corresponds with a high-resistivity zone (50-100 ohm-m). At one location, auger refusal at bedrock occurred 3.15 meters below ground surface, consistent with the observed change to lower resistivity values. This decrease in resistivity at the bedrock contact is associated with groundwater flow along the fissile marl bedding planes. These data suggest that resistivity and ground-truthing combined, provide a cost-effective foundation to guide future research on the effects of climate and land-use on Williams Creek.
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2008, 2008
Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly ... more Lake Whitney, Texas is an example of many reservoirs whose water quality is controlled by highly variable sodium chloride loads originating from near surface evaporate deposits within the upper reaches of the contributing watershed. We investigate seasonal changes in salinity within Lake Whitney using the continuous resistivity profiling (CRP) method. From December, 2006 to October, 2007 we repeated a 30-km long profile along the axis of the reservoir six times. A 135-m long, 11-electrode, marine resistivity array was used to collect eight dipole-dipole readings at offsets from 5-120 m, at intervals of approximately 1 m along the profile. Each profile was collected in an 8 to 10 hour period to produce a “snapshot” of the salinity distribution. Starting from a well mixed and highly saline (3 ohmm/2,300 mg/L) state in early winter 2006, the reservoir became progressively fresher, due to the inflow of fresher water (4 ohm-m /1,700 mg/L) over the winter months. Spring rains, caused resistivity to rise and salinity to drop as layers of freshwater flowed out along the surface from north to south after each storm. The freshwater in these layers progressively mixed with deeper, more saline water as it moved south, raising the average resistivity of the reservoir. A second layer of cold freshwater flowed along the reservoir bottom in the north and out into mid-water depths as it moved south. The greatest contrast within the water column always occurred near the main tributary inlet and was least near the dam, suggesting progressive downstream mixing. We conclude that the CPR method can be used to delineate the depth and lateral extent of abnormally fresh and saline regions within water reservoirs and can resolve shallow and deep zones of contrasting salinity within the water column.
SEG Technical Program Expanded Abstracts 2007, 2007
As demands for freshwater resources continue to rise, there are critical needs for improved techn... more As demands for freshwater resources continue to rise, there are critical needs for improved techniques for water quality assessment in lakes and water reservoirs. Because conventional methods of water reservoir studies largely involve point-based water and sediment sampling, obtaining spatial data for improved characterization of salinity variations in lakes and water reservoir remains a challenge. We explore the potential of using CRPmeasured resistivity data to determine accurately true resistivity distribution in water reservoirs. Our objective is to advance the method as a tool in limnological research for mapping freshwater zones within impacted lakes and water reservoirs.
Journal of Paleolimnology, 2008
Page 1. ORIGINAL PAPER Late Tertiary paleoclimatic interpretation from lacustrine rhythmites in t... more Page 1. ORIGINAL PAPER Late Tertiary paleoclimatic interpretation from lacustrine rhythmites in the Gray Fossil Site, northeastern Tennessee, USA Aaron J. Shunk Æ Steven G. Driese Æ John A. Dunbar Received: 12 December ...
Journal of Hydrology, 2011
GEOPHYSICS, 2008
An important potential application of the electrical-resistivity method occurs in salinity studie... more An important potential application of the electrical-resistivity method occurs in salinity studies of lakes and water reservoirs. However, uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle (contrasts of a factor of two) and changes over short intervals of time (typically in hours or days). We carry out numerical modeling and inversion of synthetic data and field resistivity data from Lake Whitney, Texas, U.S.A., to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical-resistivity method. Our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs. The simulated freshwater target in the synthetic data effectively is realized from the inversion with root-mean-square (rms) error less than 10%. However, the resolutionof the invert...