Cave Detection using Electrical Resistance Tomography, 1992, Noel M. , Xu Biwen

The use of geophysical techniques in the detection of shallow cavities in limestone, MSc thesis, 1997, Walker, D. C.

Electromagnetic, resistivity and microgravity techniques were compared for their ability to delineate and resolve shallow natural cavity systems in limestone. Geophysical work was carried out at two field sites. Electromagnetic and resistivity constant-depth profiling surveys were carried out at Kitley Caves in Yealmpton, South Devon, with the purpose of determining the lateral extent of the already partially mapped system. Lower Long Chum Cave in Ribblesdale, North Yorkshire, was used as a control site for the testing of resistivity tomography and microgravity techniques. Several cavities had already been mapped at this site, and were known to be approximately cylindrical passages, with radii of 2-4m within a depth range of 5-20m, in the area to be surveyed.
At Kitley Caves, both the EM31 and resistivity surveys were carried out over a 20x30m grid, approximately 50m west of Western Ton's Quarry. The station interval for the EM31 survey was 2.5m, whereas resistivity readings were taken at 1m intervals. Both techniques identified a linear, low resistivity, anomaly orientated close to the primary joint direction. This feature is interpreted as a sediment-filled fissure, but excavation of the site would be required for verification.
The main Lower Long Chum Cave passage was also identified using EM mapping at 2.5m intervals. Four 155m lines were surveyed using resistivity tomography technique, with 32 electrodes at 5m spacing selected in a Wenner configuration. This survey successfully delineated Diccan Pot and Lower Long Churn caves in the locations and depth ranges expected, and also identified a previously unmapped feature that was interpreted as an air-filled cave or fissure 40m to the south of the main passage. The inversion process caused the features to be horizontally smeared to approximately twice their true dimensions, and in some cases anomalies from separate features were combined.
Lower Long Churn Cave was also successfully delineated using microgravity. Analysis of the residual Bouguer anomaly, combined with two dimensional forward modelling, implied a density contrast of 2.0g/cc, a radius of 2.1m and a depth of 5m. This agreed to within 2.5m with the depth given by resistivity. The position of the tunnel axis found using the two techniques differed by a maximum of 4m.
Resistivity tomography and microgravity were thus concluded to be techniques accurate in the delineation of shallow subsurface cavities. Future improvements in the latter method depend on the development of instruments that are sensitive enough to detect small changes in gravitational acceleration, whilst remaining relatively insensitive to background noise. Resistivity tomography is becoming an increasingly more valuable technique as refinements in the inversion process reduce smearing of anomalous features and improve the accuracy of the subsurface images produced.

Non-invasive investigation of polygonal karst features: Yorkshire Dales National Park. MSc thesis (Exploration Geophysics), 1999, Gullen T.

Resistivity, refraction and resistivity tomography methods were used to ascertain the dimensions of any sediment body present within solution dolines. Fieldwork was undertaken at two sites within the Yorkshire Dales National Park: High Mark [SD920 679] northeast of Malham Tarn, and on Ingleborough, northeast of Clapham Bottoms [SD765 722].
Results of previous studies of doline fill have been inconclusive. It has been hypothesised (Howard, unpublished) that if dolines do contain significant amounts of sediment, the fill could provide a complete palaeoenvironmental record of the Quaternary.
Resistivity studies undertaken at High Mark used an Offset Wenner array, and field data were inverted to produce a 1-D image of the subsurface. The profiles were located at the base of the doline, in the area believed to contain the greatest sediment thickness. Results suggest that the fill comprises two layers. An upper layer approximately 1 m thick is composed of poorly consolidated clayey sand with an apparent resistivity of 166m. The second layer reaches a depth of 5.6m and is more clay-rich, with an apparent resistivity of 60m. These interpretations are supported by evidence from augering. The upper 10m of limestone below the sediment has been altered during doline formation, weathering and fracturing, and has a resistivity of 220m compared to 440m for the unaltered bedrock.
Refraction profiles were undertaken at High Mark, using the hammer and plate method with a 2m geophone spacing. Profiles were located on the base, flanks and interfluves of the doline. Ground conditions prevented the acquisition of very long offset shots (>10m), and lack of these data hindered interpretation. Profiles undertaken at Ingleborough used an explosive shot placed in a 45cm-deep hole, and a 5m geophone spacing was used. Profiles were located at the base of the dolines.
Results at High Mark suggest that the limestone is overlain by 4m of sediment. The upper layer has a velocity of approximately 0.50m/ms, whereas that of the second layer is 1.19m/ms. Alteration of the upper 6m of the bedrock is indicated by a velocity of 2.00m/ms, compared to 2.99m/ms for the unaltered limestone. The bedrock surface is undulatory, possibly indicating the effects of preferential dissolution or glacial activity.
Results of the refraction surveys at Ingleborough indicate that the limestone is overlain by a single 4m-thick layer of sediment with a velocity of 0.52m/ms. Beneath this, the upper 13m of limestone is altered, with a velocity of 2.45m/ms, which increases to 3.75m/ms in the unaltered limestone below. Velocities obtained are lower than expected, but reliable imaging of the limestone was ensured by siting the profiles close to observed rock exposures. Refraction interpretations indicate that the centre of the doline is not coincident with the position predicted from observation of the surface morphology.
Resistivity tomography profiles were undertaken at the base of the dolines at both sites. A fully automated system employing a Wenner array with 25 electrodes at 5m spacings was used, and six levels were recorded. The field data were inverted and the results suggest that there are about 12.5m of sediment in the High Mark doline. The sediment is underlain by 2m of altered limestone and the bedrock base of the doline is relatively smooth.
In contrast, the thickness of sediment fill in the Ingleborough dolines is 7.5m, but the depressions are bounded by a greater thickness of altered limestone (10m). In places the limestone imaged appears to reach the surface, but is not observed in the field, indicating that minimal sediment cover is not imaged. The surface of the limestone is pitted by smaller sediment-filled depressions, possibly a feature of glacial scour.
Two profiles were forward modelled to test the reliability of the inversion model. The models were similar, but features were displaced to the right of the true section. Synthetic models were constructed to test geological hypotheses concerning the composition of the dolines. The models suggested that the dolines are relatively shallow (<12m) and are underlain by significant thicknesses of altered limestone (~10m).
The combination of results obtained suggests that dolines are not filled by significant quantities of sediment and, consequently, they cannot be used as palaeoenvironmental indicators of the Quaternary.
Jobling A. 2000. Resistivity tomography survey over a topographic depression, West Yorkshire.
BSc thesis (Geophysical Sciences), School of Earth Sciences, University of Leeds, Leeds, LS2 9JT, UK.
Three resistivity profiles were completed across a topographic depression near Garforth, West Yorkshire. The depression is roughly circular, with a radius of approximately 20m. Two profiles ran through the centre of the depression, with a third profile lying outside it. Data from these three profiles were processed, and graphs and pseudosections were compiled. The data were also inverted.
The pseudosections and inversions both showed a large, negative resistivity anomaly centred approximately beneath the surface depression. This anomaly had a resistivity difference of between 600m and 700m compared to that of the surrounding rock.
The most likely reason for this anomaly is dissolution of limestone causing development of a doline or sinkhole. The chance of the depression being an old coal mine or sand mine working has been dismissed due to the location of the site and the nature of the resistivity anomaly.

Thesis Abstract: Resistivity tomography survey over a topographic depression, West Yorkshire, 2000, Jobling A.

Reliability of dipole-dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes, 2000, Zhou W. , Beck B. F. , Stephenson J. B. ,

Resistivity tomography survey over a topographic depression, West Yorkshire. BSc Thesis,, 2000, Jobling, A.

Three resistivity profiles were completed across a topographic depression near Garforth, West Yorkshire. The depression is roughly circular, with a radius of approximately 20m. Two profiles ran through the centre of the depression, with a third profile lying outside it. Data from these three profiles were processed, and graphs and pseudosections were compiled. The data were also inverted.
The pseudosections and inversions both showed a large, negative resistivity anomaly centred approximately beneath the surface depression. This anomaly had a resistivity difference of between 600m and 700m compared to that of the surrounding rock.
The most likely reason for this anomaly is dissolution of limestone causing development of a doline or sinkhole. The chance of the depression being an old coal mine or sand mine working has been dismissed due to the location of the site and the nature of the resistivity anomaly.

Road and bridge construction across gypsum karst in England, 2002, Cooper Ah, Saunders Jm,

Gypsum karst problems in the Permian and Triassic sequences of England have caused difficult conditions for bridge and road construction. In Northern England, the Ripon Bypass crosses Permian strata affected by active gypsum karst and severe subsidence problems. Here, the initial borehole site investigation for the road was supplemented by resistivity tomography studies. The roadway was reinforced with two layers of tensile membrane material within the earth embankment. This will prevent dangerous catastrophic collapse, but will allow sagging to show where problems exist. The River Ure Bridge was constructed across an area of subsidence pipes filled with alluvial deposits. It was built with extra strength, larger than normal foundations. If one pier fails, the bridge is designed for adjacent arches to span the gap without collapse. The bridge piers are also fitted with electronic load monitoring to warn of failure. In the Midlands area of England, road construction over Triassic gypsum has required a phase of ground improvement on the Derby Southern Bypass. Here, the gypsum caps a hill where it was formerly mined; it dips through a karstic dissolution zone into an area of complete dissolution and collapse. The road and an associated flyover were built across these ground conditions. A major grouting program before the earthworks began treated the cavities in the mine workings and the cavernous margin of the gypsum mass. Within the karstic dissolution zone, gypsum blocks and cavities along the route were identified by conductivity and resistivity geophysical surveys, excavated and backfilled. In the areas of complete dissolution and collapse, the road foundation was strengthened with vibrated stone columns and a reinforced concrete road deck was used. (C) 2002 S. Yamamoto. Published by Elsevier Science B.V on behalf of NERC. All rights reserved

Effective electrode array in mapping karst hazards in electrical resistivity tomography, 2002, Zhou Wanfang, Beck Barry, Adams Angela,

Identification of karst features using seismic P-wave tomography and resistivity anisotropy measurements, 2004, Karaman Abdullah, Lar Turhan,

Inversion strategy in crosshole radar tomography using information of data subsets, 2004, Becht A, Tronicke J, Appel E, Dietrich P,

Detecting discrete anomalies, such as cavities or tunnels, is an important application of crosshole radar tomography. However, crosshole tomographic inversion results are frequently ambiguous, showing smearing effects and inversion artifacts. These ambiguities lead to uncertainties in interpretation; hence, the size and position of anomalies can only be interpreted with limited accuracy and reliability. We present an inversion strategy for investigating discrete anomalies with crosshole radar tomography. In addition to the full traveltime data set, we use subsets of specified ray-angle intervals for tomographic inversion. By analyzing inversion results from different ray-angle intervals, a more accurate interpretation of anomalies is possible. The second step of our strategy is to develop a good inhomogeneous starting model from joint interpretation of the inversion results from different subsets. The third step is to invert the full data set using this new starting model and to evaluate the inversion results by analyzing the distributions of mean square traveltime residuals with respect to the ray angles. We use a synthetic model with two discrete anomalies located roughly at the same depth to demonstrate and evaluate our approach. This inversion strategy is also applied to a field data set collected to investigate karst cavities in limestone. From the inversion results of both examples, we show that horizontal smearing of anomalies can be reduced by eliminating near-horizontal rays. A good starting model can be obtained based on the joint interpretation of the inversion results of the different subsets; it leads to a high-resolution final image of the full data set

maging subsurface cavities using geoelectric tomography and ground-penetrating radar., 2005, Elqady G. , Hafez M. , Abdalla M. A. , Ushijima K.

In the past few years, construction extended extraordinarily to the southeast of Cairo, Egypt, where limestone caves occur. The existence of caves and sinkholes represents a hazard for such new urban areas. Therefore, it is important to know the size, position, and depth of natural voids and cavities before building or reconstruction. Recently, cavity imaging using geophysical surveys has become common. In this paper, both geoelectric-resistivity tomography using a dipole-dipole array and ground-penetrating radar (GPR) have been applied to the east of Kattamya at Al-Amal Town, Cairo, to image shallow subsurface cavities. The state is planning to construct a new housing development there. The resistivity survey was conducted along three profiles over an exposed cave with unknown extensions. The radar survey was conducted over an area of 1040 m², and both sets of data were processed and interpreted integrally to image the cave as well as the shallow subsurface structure of the site. As a result, the cave at a depth of about 2 m and a width of about 4 m was detected using the geophysical data, which correlates with the -known cave system. Moreover, an extension of the detected cave has been inferred. The survey revealed that the area is also affected by vertical and nearly vertical linear fractures. Additionally, zones of marl and fractured limestone and some karstic features were mapped.

Improved karst exploration by VLF-EM-gradient survey: comparison with other geophysical methods, 2005, Bosch Fp, Muller I,

The knowledge of size, density and both orientation and vertical distribution of fractures as well as their opening and filling material or overburden thickness is a valuable contribution to estimating hydraulic conductivity and to evaluating the vulnerability and protection strategy of karst aquifers. To obtain some of these parameters and to ascertain high-permeability zones, the Very Low Frequency-Electromagnetic Gradient (VLF-EM GRAD) method was applied, together with Radio Frequency-Electromagnetics (RF-EM), Radioinagnetotellurics (RMT), Geoelectrical Tomography and refraction seismics, over a karstic terrain in the Swiss Jura Mountains. In this area, karst springs infiltrate a porous aquifer. This survey investigated the highly permeable karst structures, which provide fast water-infiltration pathways into the karstic flow network. A dye tracer test validated the geophysical results. The results show the efficiency and reliability particularly of the VLF-EM GRAD method, for high-resolution investigation at shallow depths and for its potential for fast data acquisition over large surfaces at catchment area scale without ground contact

Sinkholes and the Engineering and Environmental Impacts of Karst, 2005, Beck B. F.

Conference Proceedings

Sinkholes and the Engineering and Environmental Impacts of Karst Contains over 70 papers addressing karst topography which impacts water resources, waste disposal, foundation stability, and a multitude of other geotechnical and environmental issues. These papers were presented at the 10th Multidisciplinary Conference held September 24-28, 2005 in San Antonio, Texas and Sponsored by the Geo-Institute of ASCE, P. E. LaMoreaux & Associates, Inc. and Edwards Aquifer Authority. The goal of this conference was to share knowledge and experience among disciplines by emphasizing practical applications and case studies. This proceedings will benefit environmental and geotechnical engineers, and others involved in water resources, water disposal, and foundation stability issues.

Contents:

 Application of Geophysical Logging Techniques for Multi-Channel Well Design and Installation in a Karst Aquifer (by Frank Bogle, ...)

 Case Studies of Massive Flow Conduits in Karst Limestone (by Jim L. Lolcama)
 
 A Case Study of the Samanalawewa Reservoir on the Walawe River in an Area of Karst in Sri Lanka (by K. Laksiri, ...)

 Characterization and Water Balance of Internal Drainage Sinkholes (by Nico M. Hauwert, ...) 

 Characterization of Desert Karst Terrain in Kuwait and the Eastern Coastline of the Arabian Penninsula (by Waleed Abdullah, ...)

 Characterization of a Sinkhole Prone Retention Pond Using Multiple Geophysical Surveys and Closely Spaced Borings (by Nick Hudyma, ...)
 
 Combining Surface and Downhole Geophysical Methods to Identify Karst Conditions in North-Central Iowa (by J. E. Wedekind, ...)

 Complexities of Flood Mapping in a Sinkhole Area (by C. Warren Campbell, P.E.)
 
 Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas (by R. J. Lindgren, ...)

 Database Development and GIS Modeling to Develop a Karst Vulnerability Rating for I-66, Somerset to London, KY (by Michael A. Krokonko, ...)

 Design and Construction of the Foundations for the Watauga Raw Water Intake Facility in Karstic Limestone near the City of Johnson City, TN (by Tony D. Canale, P.E., ...)

 Detection of Three-Dimensional Voids in Karstic Ground (by Derek V. Morris, P.E., ...)

 Development and Evolution of Epikarst in Mid-Continent US Carbonates (by Tony L. Cooley, P.E.)

 Dye Tracing Sewage Lagoon Discharge in a Sandstone Karst, Askov, Minnesota (by Emmit Calvin Alexander, Jr., ...)

 The Effectiveness of GPR in Sinkhole Investigations (by E. D. Zisman, P.E., ...)

 Effects of Anthropogenic Modification of Karst Soil Texture on the Water Balance of ?Alta Murgia? (Apulia, Italy) (by F. Canora, ...)

 Environmental Isotope Study on Recharge and Groundwater Residence Time in a covered Ordovician Carbonate Rock (by Zhiyuan Ma, ...)

 Error and Technique in Fluorescent dye Tracing (by Chris Smart)
 
 Essential Elements of Estimating Engineering Properties of Karst for Foundation Design (by Ramanuja Chari Kannan, P.E., Fellow, ASCE)

 Estimating Grout Quantities for Residential Repairs in Central Florida Karst (by Larry D. Madrid, P.E., ...)

 Evaluation of Groundwater Residence Time in a Karstic Aquifer Using Environmental Tracers: Roswell Artesian Basin, New Mexico (by Lewis Land)

 Experience of Regional Karst Hazard and Risk Assessment in Russia (by A. L. Ragozin, ...)

 Experimental Study of Physical Models for Sinkhole Collapses in Wuhan, China (by Mingtang Lei, ...)

 Fractal Scaling of Secondary Porosity in Karstic Exposures of the Edwards Aquifer (by Robert E. Mace, ...)

 The Geological Characteristics of Buried Karst and Its Impact on Foundations in Hong Kong, China (by Steve H. M. Chan, ...)

 Geophysical Identification of Evaporite Dissolution Structures Beneath a Highway Alignment (by M. L. Rucker, ...)

 Geotechnical Analysis in Karst: The Interaction between Engineers and Hydrogeologists (by R. C. Bachus, P.E.)

 The Gray Fossil Site: A Spectacular Example in Tennessee of Ancient Regolith Occurrences in Carbonate Terranes, Valley and Ridge Subpovince, South Appalachians U.S.A. (by G. Michael Clark, ...)

 Ground-Water Basin Catchment Delineation by Bye Tracing, Water Table Mapping, Cave Mapping, and Geophysical Techniques: Bowling Green Kentucky (by Nicholas C. Crawford)

 Groundwater Flow in the Edwards Aquifer: Comparison of Groundwater Modeling and Dye Trace Results (by Brian A. Smith, ...)

 Grouting Program to Stop Water Flow through Karstic Limestone: A Major Case History (by D. M. Maciolek)

 Highway Widening in Karst (by M. Zia Islam, P.E., ...)

 How Karst Features Affect Recharge? Implication for Estimating Recharge to the Edwards Aquifer (by Yun Huang, ...)

 Hydrogeologic Investigation of Leakage through Sinkholes in the Bed of Lake Seminole to Springs Located Downstream from Jim Woodruff Dam (by Nicholas C. Crawford, ...)

 The Hydrologic Function of the soil and Bedrock System at Upland Sinkholes in the Edwards Aquifer Recharge Zone of South-Central Texas (by A. L. Lindley)

 An Integrated Geophysical Approach for a Karst Characterization of the Marshall Space Flight Center (by Lynn Yuhr, ...)

 Integrated Geophysical Surveys Applied to Karstic Studies Over Transmission Lines in San Antonio, Texas (by Mustafa Saribudak, ...)

 Judge Dillon and Karst: Limitations on Local Regulation of Karst Hazards (by Jesse J. Richardson, Jr.)

 Karst Groundwater Resource and Advantages of its Utilization in the Shaanbei Energy Base in Shaanxi Province, China (by Yaoguo Wu, ...)

 Karst Hydrogeology and the Nature of Reality Revisited: Philosophical Musings of a Less Frustrated Curmudgeon (by Emmit Calvin Alexander, Jr.)

 Karst in Appalachia ? A Tangled Zone: Projects with Cave-Sized Voids and Sinkholes (by Clay Griffin, ...)

 Karstic Features of Gachsaran Evaporites in the Region of Ramhormoz, Khuzestan Province, in Southwest Iran (by Arash Barjasteh)

 Large Perennial Springs of Kentucky: Their Identification, Base Flow, Catchment, and Classification (by Joseph A. Ray, ...)

 Large Plot Tracing of Subsurface Flow in the Edwards Aquifer Epikarst (by P. I. Taucer, ...)
 Lithology as a Predictive Tool of Conduit Morphology and Hydrology in Environmental Impact Assessments (by George Veni)

 Metadata Development for a Multi-State Karst Feature Database (by Yongli Gao, ...)

 Micropiling in Karstic Rock: New CMFF Foundation Solution Applied at the Sanita Factory (by Marc Ballouz)

 Modeling Barton Springs Segment of the Edwards Aquifer Using MODFLOW-DCM (by Alexander Y. Sun, ...)

 Multi-Level Monitoring Well Completion Technologies and Their Applicability in Karst Dolomite (by Todd Kafka, ...)

 National-Scale Risk Assessment of sinkhole Hazard in China (by Xiaozhen Jiang, ...)

 New Applications of Differential Electrical Resistivity Tomography and Time Domain Reflectometry to Modeling Infiltration and Soil Moisture in Agricultural Sinkholes (by B. F. Schwartz, ...)

 Non-Regulatory Approaches to Development on Karst (by Jesse J. Richardson, Jr., ...)

 PA State Route 33 Over Bushkill Creek: Structure Failure and Replacement in an Active Sinkhole Environment (by Kerry W. Petrasic, P.E.)

 Quantifying Recharge via Fractures in an Ashe Juniper Dominated Karst Landscape (by Lucas Gregory, ...)

 Quantitative Groundwater Tracing and Effective Numerical Modeling in Karst: An Example from the Woodville Karst Plain of North Florida (by Todd R. Kincaid, ...)

 Radial Groundwater Flow at Landfills in Karst (by J. E. Smith)
 
 Residual Potential Mapping of Contaminant Transport Pathways in Karst Formations of Southern Texas (by D. Glaser, ...)

 Resolving Sinkhole Issues: A State Government Perspective (by Sharon A. Hill)

 Shallow Groundwater and DNAPL Movement within Slightly Dipping Limestone, Southwestern Kentucky (by Ralph O. Ewers, ...)

 Sinkhole Case Study ? Is it or Isn?t it a Sinkhole? (by E. D. Zisman, P.E.)

 Sinkhole Occurrence and Changes in Stream Morphology: An Example from the Lehigh Valley Pennsylvania (by William E. Kochanov)

 Site Characterization and Geotechnical Roadway Design over Karst: Interstate 70, Frederick County, Maryland (by Walter G. Kutschke, P.E., ...)

 Soil Stabilization of the Valley Creek Trunk Sewer Relief Tunnel (by Jeffrey J. Bean, P.E., ...)

 Some New Approaches to Assessment of Collapse Risks in Covered Karsts (by Vladimir Tolmachev, ...)

 Spectral Deconvolution and Quantification of Natural Organic Material and Fluorescent Tracer Dyes (by Scott C. Alexander)

 Springshed Mapping in Support of Watershed Management (by Jeffrey A. Green, ...) 

 Sustainable Utilization of Karst Groundwater in Feicheng Basin, Shandong Province, China (by Yunfeng Li, ...)
 
 Transport of Colloidal and Solute Tracers in Three Different Types of Alpine Karst Aquifers ? Examples from Southern Germany and Slovenia (by N. Göppert, ...)

 Use of the Cone Penetration Test for Geotechnical Site Characterization in Clay-Mantled Karst (by T. C. Siegel, ...)

 The Utility of Synthetic Aperture Radar (SAR) Interferometry in Monitoring Sinkhole Subsidence: Subsidence of the Devil?s Throat Sinkhole Area (Nevada, USA) (by Rana A. Al-Fares)

 Void Evolution in Soluble Rocks Beneath Dams Under Limited Flow Condition (by Emmanuel S. Pepprah, ...)

Using 2D inversion of magnetic resonance soundings to locate a water-filled karst conduit, 2006, Boucher M, Girard Jf, Legchenko A, Baltassat Jm, Dorfliger N, Chalikakis K,

SummaryA new methodology for magnetic resonance sounding (MRS) data acquisition and interpretation was developed for locating water-filled karst cavities. This methodology was used to investigate the Ouysse karst system in the Poumeyssens shaft in the Causse de Gramat (France). A new 2D numerical MRS response model was designed for improved accuracy over the previous 1D MRS approach. A special survey performed by cave divers confirmed the accuracy of the MRS results. Field results demonstrated that in favourable conditions (a low EM noise environment and a relatively shallow, large target) the MRS method, used with a coincident transmitter/receiver loop, can be an effective tool for locating a water-filled karst conduit. It was shown numerically that because an a priori orientation of the MRS profile with the karst conduit is used in the inversion scheme (perpendicular for instance), any error in this assumption introduces an additional error in locating the karst. However, the resulting error is within acceptable limits when the deviation is less than 30[deg]. The MRS results were compared with an electrical resistivity tomography (ERT) survey. It was found that in Poumeyssens, ERT is not able to locate the water-filled karst. On the other hand, ERT provides additional information about heterogeneities in the limestone

Navier-Stokes flow and transport simulations using real fractures shows heavy tailing due to eddies, 2007, Cardenas M. B. , Slottke D. T. , Ketcham R. A. , Sharp Jr. J. M.

Two-dimensional Navier-Stokes flow and transport simulations are conducted for a 15-cm long fracture mapped via X-ray computed tomography. (1) The actual fracture with irregular aperture, (2) a truncated fracture where the largest aperture area is excluded from the domain, (3) the truncated fracture with further thinning of other large aperture areas, and (4) a fracture with uniform vertical aperture equal to the actual fracture’s mean aperture, are subjected to the same pressure gradient. Slight variations in fracture characteristics result in significantly different flow and transport behavior. Flux is much larger for the uniformaperture fracture compared to the actual fracture. A pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power-law tail absent in other cases. The uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1D analytical model. The analytical model fit to the other cases is not as robust as in the uniform aperture case