Variation of karstic permeability between unconfined and confined aquifers, Grand Canyon region, Arizona, 1999, Huntoon Pw. .

Most of the ground water in the Grand Canyon region circulates to springs in the canyon through the thick, deeply buried, karstified Cambrian through Mississippian carbonate sectionThese rocks are collectively called the lower Paleozoic carbonates and comprise the Redwall-Muav aquifer where saturatedThe morphologies of the caves are primarily a function of whether the carbonates are unconfined or confined, a distinction that has broad significance for groundwater exploration and which appears to be generally transferable to other carbonate regionsCaves in unconfined high-gradient environments tend to be highly localized, partially saturated, simple tubes, whereas those in confined low-gradient settings are saturated 2- or even 3-dimensional mazesThe highly heterogeneous distribution of the unconfined conduits makes for difficult drilling targets, whereas the more ubiquitously distributed confined mazes are far easier to targetThe distinctions between the storage characteristics within the two classes is probably even more importantThere is minimal groundwater storage in the unconfined systems because they are well drainedIn contrast, the saturated mazes exhibit maximal storageConsequently, system responses to major storm recharge events in the unconfined systems is often dominated by flow-through rather than the pulse-through hydraulics as found in the confined systemsSpring discharges from the unconfined systems tends to be both flashy and highly variable from season to season, but total dissolved solids are smallIn contrast, the pulse-through hydraulics in the artesian systems causes spring discharge responses to be highly moderated and, in the larger basins, remarkably steadyBoth total dissolved solids and temperatures in the waters from the confined aquifers tend to be elevated because most of the water is derived from storageKarst permeability is created by the flow system, consequently predicting where the permeability is best developed in a carbonate section involves determining how circulation should be ideally organized through an examination of the geometry of the flow systemThe areas where flow concentrates are the areas where karstification will maximize, provided enough time has elapsed to allow dissolution to adjust to the imposed boundary conditionsThe rate of adjustment in the Grand Canyon region appears to be related to the degree of saturationThe artesian systems are far better adjusted to hydraulic gradients than the unconfined systems, a finding that probably implies that there is greater contact between the solvent and rock in the saturated confined systems

Variability of karstic permeability between unconfined and confined aquifers, Grand Canyon region, Arizona, 2000, Huntoon P. W. ,

Most of the ground water in the Grand Canyon region circulates to springs in the canyon through the thick, deeply buried, karstified Cambrian-Mississippian carbonate section. These rocks are collectively called the lower Paleozoic carbonates and comprise the Redwall-Muav aquifer where saturated. The morphologies of the caves in the Grand Canyon are primarily a function of whether the carbonates are unconfined or confined, a distinction that has broad significance for ground-water exploration and which appears to be generally transferable to other carbonate regions. Caves in unconfined high-gradient environments tend to be highly localized, partially saturated, simple tubes, whereas those in confined low-gradient settings are saturated 2- or even 3-dimensional mazes. The highly heterogeneous, widely spaced conduits in the unconfined settings make for difficult drilling targets, whereas the more ubiquitously distributed mazes in confined settings are far easier to target. The distinctions between the storage characteristics within the two classes are more important. There is minimal ground-water storage in the unconfined systems because cave passages tend to be more widely spaced and are partially drained. In contrast, there is maximum storage in the saturated mazes in the confined systems. Consequently, system responses to major storm recharge events in the unconfined systems are characterized by flow-through hydraulics. Spring discharge from the unconfined systems tends to be both flashy and highly variable from season to season, but total dissolved solids are small. In contrast, the pulse-through hydraulics in the artesian systems cause fluctuations in spring discharge to be highly moderated and, in the larger basins, remarkably steady. Both total dissolved solids and temperatures in the waters from the confined aquifers tend to be elevated because most of the water is derived from storage. The large artesian systems that drain to the Grand Canyon derive water from areally extensive, deep basins where the water has been geothermally heated somewhat above mean ambient air temperatures. Karst permeability is created by the flow system, so dissolution permeability develops most rapidly in those volumes of carbonate aquifers where flow concentrates. Predicting where the permeability should be best developed in a carbonate section involves determining where flow has been concentrated in the geologic past by examining the geometry and hydraulic boundary conditions of the flow field. Karstification can be expected to maximize in those locations provided enough geologic time has elapsed to allow dissolution to adjust to the imposed boundary conditions. The rate of adjustment in the Grand Canyon region appears to be related to the degree of saturation. The artesian systems are far better adjusted to hydraulic gradients than the unconfined systems, a finding that probably implies that there is greater contact between the solvent and rock in the saturated systems. These findings are not arcane distinctions. Rather, successful exploration for ground water and management of the resource is materially improved by recognition of the differences between the types of karst present. For example, the unsaturated conduit karsts in the uplifts make for highly localized, high risk drilling targets and involve aquifers with very limited storage. The conduits have highly variable flow rates, but they carry good quality water largely derived from seasonal flow-through from the surface areas drained. In contrast, the saturated basin karsts, with more ubiquitous dissolutional permeability enhancement, provide areally extensive low risk drilling targets with large ground-water storage. The ground water in these settings is generally of lesser quality because it is derived mostly from long term storage

Karst groundwater: a challenge for new resources, 2005, Bakalowicz M,

Karst aquifers have complex and original characteristics which make them very different from other aquifers: high heterogeneity created and organised by groundwater flow; large voids, high flow velocities up to several hundreds of m/h, high flow rate springs up to some tens of in 3/S. Different conceptual models, known from the literature, attempt to take into account all these particularities. The study methods used in classical hydrogeology-bore hole, pumping test and distributed models-are generally invalid and unsuccessful in karst aquifers, because the results cannot be extended to the whole aquifer nor to some parts, as is done in non-karst aquifers. Presently, karst hydrogeologists use a specific investigation methodology (described here), which is comparable to that used in surface hydrology. important points remain unsolved. Some of them are related to fundamental aspects such as the void structure only a conduit network, or a conduit network plus a porous matrix -, the functioning - threshold effects and nonlinearities -, the modeling of the functioning - double or triple porosity, or viscous flow in conduits - and of karst genesis. Some other points deal with practical aspects, such as the assessment of aquifer storage capacity or vulnerability, or the prediction of the location of highly productive zones

Study of cavernous underground conduits in Nam La (Northwest Vietnam) by an integrative approach, 2005, Tam V. T. , De Smedt F. , Batelaan O. , Hung L. Q. , Dassargues A. ,

This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La catchment in the NW of Vietnam. The Nam La River disappears underground in several swallow holes near the outlet of the catchment. In the rainy season this results in flooding upstream of the sinkholes. A hypothesis is that the Nam La River resurges at a large cavern spring 4.5 km east of the catchment outlet. A multi-thematic study of the possible connections between the swallow holes and the resurgence was carried out to investigate the geological structure, tectonics, cave structure analysis and discharge time series. The existence of the underground conduits was also tested and proven by tracer experiments. On the basis of a lineament analysis the location of the underground conduits were predicted. A remote sensing derived lineament-length density map was used to track routes from the swallow holes to the resurgence, having the shortest length but highest lineament density. This resulted in a plan-view prediction of underground conduits that matches with the cave and fault development. The functioning of the conduits was further explained by analysing flooding records of a nearby doline, which turns out to act as a temporary storage reservoir mitigating flooding of the catchment outlet area

Processes of Speleogenesis: a Modeling Approach, 2005, Dreybrodt W. Gabrovsek F. , Romanov D.

 This book draws together the major recent advances in the modeling of karst systems. Based on the dissolution kinetics of limestone, and flow and transport processes in its fractures, it presents a hierarchy of cave genetic situations that range from the enlargement of a single fracture to the evolution of cavernous drainage patterns in confined and unconfined karst aquifers. These results are also applied to the evolution of leakage below dam sites in karst. The book offers a wealth of information that helps to understand the development of cave systems. It addresses geologists, hydrologists, geomorphologists, and geographers. It is also of interest to all scientists and engineers who have responsibilities for groundwater exploration and management in karst terrains.

?Processes of Speleogenesis: a Modeling Approach is an exciting book that brings together and displays the products of the first and second generations of karst cave and aquifer computer modeling in a succinct fashion, with excellent illustrations and stimulating contrasts of approach. It is a ?benchmark? publication that all who are interested in speleogenesis should read. It will be a very useful volume for teaching, not only in karst and hydrogeology, but for others who use computer modeling in the physical and spatial sciences.? (From the foreword by D.C. Ford)

?This book is an extraordinary achievement that warrants close attention by anyone interested in speleogenesis??This book is ideal for researchers in speleogenesis who have a solid grasp in technical aspects. Most of the necessary background information is outlined in the first chapter, but subtle aspects will be clear only to those who already have a good background in geochemistry and computer modeling especially when interpreting the figures. This book is not aimed at groundwater hydrologists, although the results would be eye-opening to anyone in that field who denies the importance of solution conduits in carbonate aquifers.? (From book review by A.N. Palmer, JCKS, Volume 67, No.3, 2005)

?To specialists the book is very helpful and and up-to-date, providing many ideas and answering many questions.? (From book review by P. Hauselmann, Die Hohle, Volume 56, 2005)

CONTENTS

1. Introduction
2. Equilibrium chemistry and dissolution kinetics of limestone in H2O-CO2 solutions
3. The evolution of a single fracture
4. Modeling karst evolution on two-dimensional networks: constant head boundary conditions
5. Unconfined aquifers under various boundary conditions
6. Karstification below dam sites
7. Conclusion and future perspectives
8. Bibliography

GUEST CHAPTER by Sebastian Bauer, Steffen Birk, Rudolf Liedl and Martin Sauter
Simulation of karst aquifer genesis using a double permeability approach investigation for confined and unconfined settings

GUEST CHAPTER by Georg Kaufmann
Structure and evolution of karst aquifers: a finite-element numerical modeling approach

Contribution of geophysical methods to karst-system exploration: an overview, 2011, Chalikakis Konstantinos, Plagnes Valerie, Guerin Roger, Valois Remi, Bosch Frank P.

The karst environment is one of the most challenging in terms of groundwater, engineering and environmental issues. Geophysical methods can provide useful subsurface information in karst regions concerning, for instance, hazard estimation or groundwater exploration and vulnerability assessment. However, a karst area remains a very difficult environment for any geophysical exploration; selection of the best-suited geophysical method is not always straightforward, due to the highly variable and unpredictable target characteristics. The state of the art is presented, in terms of the contributions made by geophysical methods to karst-system exploration, based on extensive analysis of the published scientific results. This report is an overview and should be used as a preliminary methodological approach, rather than a guideline.