Conduit enlargement in an eogenetic karst aquifer, , Moore Paul J. , Martin Jonathan B. , Screaton Elizabeth J. , Neuhoff Philip S.

Most concepts of conduit development have focused on telogenetic karst aquifers, where low matrix permeability focuses flow and dissolution along joints, fractures, and bedding planes. However, conduits also exist in eogenetic karst aquifers, despite high matrix permeability which accounts for a significant component of flow. This study investigates dissolution within a 6-km long conduit system in the eogenetic Upper Floridan aquifer of north-central Florida that begins with a continuous source of allogenic recharge at the Santa Fe River Sink and discharges from a first-magnitude spring at the Santa Fe River Rise. Three sources of water to the conduit include the allogenic recharge, diffuse recharge through epikarst, and mineralized water upwelling from depth. Results of sampling and inverse modeling using PHREEQC suggest that dissolution within the conduit is episodic, occurring only during 30% of 16 sampling times between March 2003 and April 2007. During low flow conditions, carbonate saturated water flows from the matrix to the conduit, restricting contact between undersaturated allogenic water with the conduit wall. When gradients reverse during high flow conditions, undersaturated allogenic recharge enters the matrix. During these limited periods, estimates of dissolution within the conduit suggest wall retreat averages about 4 × 10−6 m/day, in agreement with upper estimates of maximum wall retreat for telogenetic karst. Because dissolution is episodic, time-averaged dissolution rates in the sink-rise system results in a wall retreat rate of about 7 × 10−7 m/day, which is at the lower end of wall retreat for telogenetic karst. Because of the high permeability matrix, conduits in eogenetic karst thus enlarge not just at the walls of fractures or pre-existing conduits such as those in telogenetic karst, but also may produce a friable halo surrounding the conduits that may be removed by additional mechanical processes. These observations stress the importance of matrix permeability in eogenetic karst and suggest new concepts may be necessary to describe how conduits develop within these porous rocks.

Speleothems and paleoglaciers, , Spotl Christoph, Mangini Augusto,

Ice and speleothems are widely regarded as mutually exclusive as the presence of liquid water is a fundamental prerequisite for speleothem deposition. Here we show that speleothems may form in caves overlain by a glacier, as long as the temperature in the cave is above freezing and the conduits are not completely flooded by melt water. Carbonate dissolution is accomplished via sulfide oxidation and the resultant speleothems show high [delta]13C values approaching and locally exceeding those of the parent host rock (lack of soil-derived biogenic C). The [delta]18O values reflect the isotopic composition of the melt water percolating into the karst fissure network and carry an atmospheric (temperature) signal, which is distinctly lower than those of speleothems formed during periods when soil and vegetation were present above the cave. These `subglacial' speleothems provide a means of identifying and dating the former presence of warm-based paleoglaciers and allow us to place some constraints on paleotemperature changes

Predicting travel times and transport characterization in karst conduits by analyzing tracer-breakthrough curves, , Morales Tomas, De Valderrama Inigo, Uriarte Jesus A. , Antiguedad Inaki, Olazar Martin,

SummaryThis paper analyzes data obtained in 26 tracer tests carried out in 11 karstic connections following solutional conduits in karst aquifers in the Basque Country. These conduits are preferential drainage pathways in these aquifers and so they confer a marked anisotropy and high vulnerability to them. Consequently, their consideration in protection and management studies and projects is a priority.The connections studied cover a wide hydrogeological spectrum (a wide range of sizes, slopes, geomorphic and hydrologic types) and the tests have been carried out at different hydrodynamic states. It is noteworthy that they all follow a similar trend, which has allowed for the development of a statistical approximation for the treatment of the whole information.Relationships have been established involving velocity, solute time of arrival, attenuation of peak concentration and time of passage of tracer cloud. These relationships are a valuable tool for management and supporting decision-making and allow for making estimates in connections in which the information available was scarce. This information is especially useful, given that the complexity of transport in karst conduits gives way to important deviations between real data (empirical observations) and the data obtained by simple approaches based on the Fickian-type diffusion equation

The Aggitis karst system, Eastern Macedonia, Greece: Hydrologic functioning and development of the karst structure, , Novel Jean Paul, Dimadi Agoro, Zervopoulou Anna, Bakalowicz Michel,

SummaryThe Aggitis karst system developed in the marbles of the Rhodope massif. The conditions of the development of its karst drainage network are determined from the geological and geomorphologic settings by means of a microstructural analysis, following Eraso's method. This analysis shows that the karst conduit network intensely developed in the western part of the mountain Falakro where the majority of the open fractures oriented in the same direction as the hydraulic gradient, while the two directions are perpendicular in its eastern part drained by the spring of Drama.The behaviour of the system was analysed by means of hydrodynamic and water geochemical techniques. Despite the extension of the cave system and of the favourable development conditions of conduits, the functioning appears complex, with a significant storage, and a slow infiltration as well as an easy drainage. On the contrary the Drama karst system, characterised by a low variability in its hydrological and geochemical characteristics does not show any karst functioning.In the Aggitis karst system the initial groundwater flow conditions in combination with the aperture planes of which the directions are in agreement with the hydraulic gradient, favoured the rapid development of a drainage network system. The recharge from a large surface catchment area on non-karstic rocks, through swallow holes in a wide polje contributed to increase the groundwater flow through the karst part of the system, facilitating the development of the conduits

Assessing the importance of conduit geometry and physical parameters in karst systems using the storm water management model (SWMM), , Peterson Eric W. , Wicks Carol M. ,

SummaryQuestions about the importance of conduit geometry and about the values of hydraulic parameters in controlling ground-water flow and solute transport through karstic aquifers have remained largely speculative. One goal of this project was to assess the role that the conduit geometry and the hydraulic parameters have on controlling transport dynamics within karstic aquifers. The storm water management model (SWMM) was applied to the Devil's Icebox-Connor's Cave System in central Missouri, USA. Simulations with incremental changes to conduit geometry or hydraulic parameters were performed with the output compared to a calibrated baseline model. Ten percent changes in the length or width of a conduit produced statistically significant different fluid flow responses. The model exhibited minimal sensitivity to slope and infiltration rates; however, slight changes in Manning's roughness coefficient can highly alter the simulated output.Traditionally, the difference in flow dynamics between karstified aquifers and porous media aquifers has led to the idea that modeling of karst aquifers is more difficult and less precise than modeling of porous media aquifers. When evaluated against models for porous media aquifers, SWMM produced results that were as accurate (10% error compared to basecase). In addition, SWMM has the advantage of providing data about local flow. While SWMM may be an appropriate modeling technique for some karstic aquifers, SWMM should not be viewed as a universal solution to modeling karst systems

Anomalous behaviour of specific electrical conductivity at a karst spring induced by variable catchment boundaries: the case of the Podstenjšek spring, Slovenia, , Ravbar, N. , Engelhardt, I. , Goldscheider, N.

Anomalous behaviour of specific electrical conductivity (SEC) was observed at a karst spring in Slovenia during 26 high-flow events in an 18-month monitoring period. A conceptual model explaining this anomalous SEC variability is presented and reproduced by numerical modelling, and the practical relevance for source protection zoning is discussed. After storm rainfall, discharge increases rapidly, which is typical for karst springs. SEC displays a first maximum during the rising limb of the spring hydrograph, followed by a minimum indicating the arrival of freshly infiltrated water, often confirmed by increased levels of total organic carbon (TOC). The anomalous behaviour starts after this SEC minimum, when SEC rises again and remains elevated during the entire high-flow period, typically 20–40 µS/cm above the baseflow value. This is explained by variable catchment boundaries: When the water level in the aquifer rises, the catchment expands, incorporating zones of groundwater with higher SEC, caused by higher unsaturated zone thickness and subtle lithologic changes. This conceptual model has been checked by numerical investigations. A generalized finite-difference model including high-conductivity cells representing the conduit network (“discrete-continuum approach”) was set up to simulate the observed behaviour of the karst system. The model reproduces the shifting groundwater divide and the nearly simultaneous increase of discharge and SEC during high-flow periods. The observed behaviour is relevant for groundwater source protection zoning, which requires reliable delineation of catchment areas. Anomalous behaviour of SEC can point to variable catchment boundaries that can be checked by tracer tests during different hydrologic conditions.

A New Equation Solver for Modeling Turbulent Flow in Coupled Matrix‐Conduit Flow Models, ,

Karst aquifers represent dual flow systems consisting of a highly conductive conduit system embedded in a less permeable rock matrix. Hybrid models iteratively coupling both flow systems generally consume much time, especially because of the nonlinearity of turbulent conduit flow. To reduce calculation times compared to those of existing approaches, a new iterative equation solver for the conduit system is developed based on an approximated Newton–Raphson expression and a Gauß–Seidel or successive over-relaxation scheme with a single iteration step at the innermost level. It is implemented and tested in the research code CAVE but should be easily adaptable to similar models such as the Conduit Flow Process for MODFLOW-2005. It substantially reduces the computational effort as demonstrated by steady-state benchmark scenarios as well as by transient karst genesis simulations. Water balance errors are found to be acceptable in most of the test cases. However, the performance and accuracy may deteriorate under unfavorable conditions such as sudden, strong changes of the flow field at some stages of the karst genesis simulations.

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Conduits souterrains en relation avec les terrasses fluviales, 1961, Ek C.

Sinuosity in limestone solution conduits, 1969, Deike G. H. , White W. B.

Observations at the Blue Waterholes, March 1965 - April 1969, and Limestone Solution on Cooleman Plain, N.S.W., 1972, Jennings, J. N.

After brief descriptions of the geomorphology of the Cooleman Plain karst and in particular of the Blue Waterholes, the methods adopted to analyse the functioning of these major risings are detailed. The discharge regime of Cave Creek below them is oceanic pluvial in type perturbed by drought and snow. There is much annual variation both in seasonal incidence and total amount, with catchment efficiency correspondingly variable. Suspended sediment concentration is even more erratic and monthly determinations are inadequate for calculating corrasional denudation rates. Mean concentrations of suspended solids are about 1/18th of solute load. Total dissolved salts have a strong inverse relationship with discharge, and mean values are high compared with those for other catchments in eastern Australia but none of these determinations are from limestone catchments. Sodium, potassium, and chlorine contents are low compared with the same catchments but silica is relatively high. The ratio of alkaline earths to alkalis indicate that Cave Creek carries carbonate waters and there is an inverse regression of the ratio on discharge. There is inverse correlation of total hardness on discharge likewise due to concentration of surface waters by evaporation in dry periods, together with reduced underground solution rate at times of large, rapid flow. The spring waters remain aggressive. Close regressions of hardness on specific conductivity now permit the latter to be determined in the place of the former. Much evidence converges to indicate that all the springs at the Blue Waterholes are fed from the same conduit. The intermittent flow which comes down the North Branch on the surface to the Blue Waterholes differs significantly in many characters from the spring waters. Rates of Ca + M carbonate equivalent removal vary directly with discharge since hardness varies much less than does water volume. These gross rates have to be adjusted for (a) atmospheric salts entering the karst directly, (b) peripheral solute inputs from the non-karst two-thirds of the catchment and (c) subjacent karst solution before they can be taken as a measure of exposed karst denudation. The methods for achieving this are set out. The total corrections amount to about one third of the total hardness, though the correction for subjacent karst on its own lies within the experimental error of the investigation. The residual rate of limestone removal from the exposed karst also shows a winter/spring high rate and a summer/autumn low rate but the seasonal incidence and annual total varied very much from year to year. In comparison with results from karsts in broadly similar climate, the seasonal rhythm conforms and so does the high proportion (78%) of the solution taking place at or close to the surface. This reduces the importance of the impounded condition of this small karst but supports the use of karst denudation rate as a measure of surface lowering. Cave passage solution may however be more important in impounded karst than its absolute contribution might suggest, by promoting rapid development of underground circulation. The mean value of limestone removal is low for the climatic type and this is probably due to high evapotranspirational loss as well as to the process of eliminating atmospheric, peripheral non-karst and subjacent karst contributions. The difficulties of applying modern solution removal rate to the historical geomorphology of this karst are made evident; at the same time even crude extrapolations are shown to isolate problems valuably.

Deducing Flow Velocity in Cave Conduits from Scallops, 1974, Curl, Rane L.

Karst processes of the eastern upper Galilee, Northern Israel, 1974, Gerson R,

Karst processes dominate most of the geomorphic activity in the Upper Galilee, consisting mainly of dolomites and limestones. Study of the chemical evolution of water passing through the karst hydrologic cycle clearly shows that the major portion of its carbonate solute is gained subaerially and in the upper part of the vadose zone. Most cave and spring water is already saturated with respect to aragonite and calcite.The karst depressions typical to surface morphology are mostly associated with fault-line traces. Their evolution is possible mainly in areas sloping initially less that 5[deg].The absence of evolved caves, representing well-developed karst of an earlier period, is attributed mainly to the marginal climate throughout the past combined with tectonic, and hence hydrologic, instability of the region.The discharge of the karst prings shows clearly dependence on annual precipitation, with a lag of about 2 years of the response to drought or more humid periods. Long-term fluctuations are larger in the smaller T'eo Spring than in the affluent 'Enan Springs.Most of the denuded material is extracted from the region as dissolved load via underground conduits and only small amounts as clastics. Mean long-term denudation is approximately 20 mm/1000 years, averaged for the surface area contributing to the springs.In spite of the above, most topographic forms are shaped by runoff erosion, active during medium to high intensity rainstorms. Solution processes prevail during low to medium rainfall intensities, while different parts of the region are denuded at similar rates. Even in karst depressions, erosion becomes dominant after their bottoms are covered by almost impervious terra-rossa mantle

Paleohydrology and Streamflow Simulation of three Karst Basins in Southeastern West Virginia, U.S.A., PhD Thesis, 1975, Coward, Julian Michael Henry

This study was undertaken to gain a better understanding of karst hydrology. To do this, the present day hydrology and the paleohydrology were determined in three karst basins. The basins chosen were the Swago, Locust and Spring Creek basins in Pocahontas and Greenbrier Counties, West Virginia. A number of conventional field techniques were used successfully in this study, including the following: current meter and dye dilution gauging; dye and lycopodium stream tracing; geological and cave mapping; the setting up of stage recorders; geochemistry; and limestone erosion measurements. The climate of the region was investigated to obtain realistic precipitation, temperature and potential evaporation data over the study basins.
It was found that the mean precipitation over two of the basins was 30% higher than recorded data in the valleys. The karst development of the basins was found to take place in four major stages. These were: A) initial surficial flow, B) strike controlled drainage, C) major piracies from one sub-basin to another, and D) shortening of the flow routes. The major controls on the karst development were found to be: A) the Taggard shale, B) the strike direction, which controlled early basin development, and C) the hydraulic gradient from the sink to rising, which controlled later basin development.
To better assess the quantitative hydrology, and to assist in determining the type of unexplorable flow paths, a watershed model was developed. This modelled the streamflow from known climatic inputs using a number of measured or optimized parameters. The simulation model handled snowmelt, interception, infiltration, interflow, baseflow, overland flow, channel routing, and evaporation from the interception, soil water, ground water, snowpack and channel water. The modelled basin could be split up into 20 segments, each with different hydrological characteristics, but a maximum of 3 segments was used in this study.
A total of 29 parameters was used in the model although only 10 (other than those directly measurable) were found to be sensitive in the three basins. The simulated streamflow did not match the real flows very well due to errors in the data input and due to simplifications in the model. It was found, however, that as the proportion of the limestone in a segment increased the overland flow decreased, the interflow increased, the baseflow and interflow recessions were faster, the soil storages were smaller and the infiltration rate was higher, than in segments with a larger proportion of exposed clastics. The flow characteristics of the inaccessible conduits were inferred from the channel routing parameters and it was postulated that the majority of the underground flow in the karst basins was taking place under vadose conditions.

Karst Geomorphology of the Bruce Peninsula, Ontario, PhD Thesis, 1976, Cowell, Daryl William

This is the first detailed examination of the karst geomorphology of the Bruce Peninsula. It attempts to review all aspects including pavement phenomena and formation (microkarst features), surface and subsurface karst hydrology (meso to macro scale) and water chemistry. The latter is based on over 250 samples collected in 1973 and 1974.
The dolomite pavement is the best example of its kind that has been described in the literature. It covers much of the northern and eastern parts of the peninsula and can be differentiated into three types based on karren assemblages. Two of these are a product of lithology and the third reflects local environmental controls. The Amabel Formation produces characteristic karren such as rundkarren, hohlkarren, meanderkarren, clint and grike, kamentizas and rillenkarren on glacially abraded biohermal structures. The Guelph Formation develops into a very irregular, often cavernous surface with clint and grike and pitkarren as the only common recognizable karren. The third assemblage is characterized by pitkarren and is found only in the Lake Huron littoral zone. Biological factors are believed to have played a major role in the formation of the pavement. Vegetation supplies humic acids which help boost the solution process and helps to maintain a wet surface. This tends to prolong solution and permit the development of karren with rounded lips and bottoms.
Three types of drainage other than normal surface runoff are found on the Bruce. These are partial underground capture of surface streams, complete underground capture (fluvio-karst), and wholly vertical drainage without stream action (holokarst). Holokarst covers most of the northern and eastern edge of the peninsula along the top of the escarpment. Inland it is replaced by fluvial drainage, some of which has been, or is in the process of being captured. Four perennial streams and one lake disappear into sinkholes. These range from very simple channel capture and resurgence, as shown by a creek east of Wiarton, to more mature and complex cave development of the St. Edmunds cave near Tobermory. Partial underground capture represents the first stage of karst drainage. This was found to occur in one major river well inland of the fluvio-karst and probably occurs in other streams as well. This chapter also examines the possible future karst development of the Bruce and other karst feature such as isolated sinks and sea caves.
The water chemistry presented in Chapter 5 represents the most complete data set from southern Ontario. It is examined on a seasonal basis as well as grouped into classes representing water types (streams, Lake Huron and Georgian Bay, inland lakes, swamps, diffuse springs and conduit springs). The spring analyses are also fitted into climatic models of limestone solution based on data from other regions of North America. It was found that solution rates in southern Ontario are very substantial. Total hardness ranges from 150 to 250 ppm (expressed as CaCO3) in most lakes and streams and up to 326 ppm in springs. These rates compare with more southerly latitudes. The theoretical equilibrium partial pressure of CO2 was found to be the most significant chemical variable for comparing solution on different kinds of carbonates and between glaciated and non-glaciated regions. Expect for diffuse flow springs and Lake Huron, the Bruce data do not separate easily into water types using either graphical or statistical (i.e. Linear Discriminant Analysis) analyses. This is partly because of the seasonality of the data and because of the intimate contact all waters have with bedrock.

Diffuse flow and conduit flow in limestone terrain in the Mendip Hills, Somerset (Great Britain), 1977, Atkinson T. C.

The hydrogeology of the karstic Carboniferous Limestone is described. Water tracing has established recharge areas for fifteen major springs and water budgets confirm the size of the areas found. Groundwater flow occurs in two modes: turbulent conduit flow and diffuse Darcian flow in fine fractures. Recharge is 50% quickflow via caves and closed depressions and 50% slower percolation. Active storage in the diffuse component (S = 0.92%) is 30 times greater than in phreatic conduits. Diffuse hydraulic conductivity is 0.89 m day−1 and an average of 60?80% of groundwater is transmitted by conduits in this maturely karsted and steeply dipping aquifer.