Due to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several ...orders of magnitude from local (borehole) to regional (catchment) scale because of the large contrast in hydraulic parameters between matrix and conduit, their heterogeneity and anisotropy. One approach to deal with the scale effect problem in the estimation of hydraulic parameters of karst aquifers is the application of large‐scale experiments such as long‐term high‐ion conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fractured matrix. The numerical discrete conduit‐continuum modeling approach MODFLOW‐2005 Conduit Flow Process Mode 1 (CFPM1) is employed to simulate laminar and nonlaminar conduit flow, induced by large‐scale experiments, in combination with Darcian matrix flow. Effects of large‐scale experiments were simulated for idealized settings. Subsequently, diagnostic plots and analyses of different fluxes are applied to interpret differences in the simulated conduit drawdown and general flow patterns. The main focus is set on the question to which extent different conduit flow regimes will affect the drawdown in conduit and matrix depending on the hydraulic properties of the conduit system, i.e., conduit diameter and relative roughness. In this context, CFPM1 is applied to investigate the importance of considering turbulent conditions for the simulation of karst conduit flow. This work quantifies the relative error that results from assuming laminar conduit flow for the interpretation of a synthetic large‐scale pumping test in karst.
Key Points
Flow simulation of karst systems with slightly enlarged flow features demands information about conduit flow conditions
For mature karst systems laminar conduit flow equations might be applicable even for fully turbulent conditions
Conduit roughness should be considered as a lumped parameter reflecting wall roughness as well as geometrical conduit properties
Groundwater from various shallow and deep reservoirs converges in interaction with marine waters into the limestone aquifer of the Balaruc peninsula (Thau lagoon, southern France). This aquifer faces ...temporary phenomena of marine water intrusion through the Vise submarine spring located at −29.5 m below the lagoon level. Since the 1960s, seven flow reversal phenomena have occurred, the last one occurring between 11/28/2020 and 03/14/2022. During these phenomena, which can last from a few weeks to several months, the salty water is absorbed from the lagoon to the conduit of the submarine spring, which leads to the salinization of the underlying karst aquifer. The monitoring of flow, water specific conductivity and water temperature data from the karst submarine spring is a key element of the research project to understand the hydrogeological functioning of the karst aquifer under normal conditions or during flow reversal periods. This monitoring allows the characterization of the (in- or out-) flows at the submarine spring, the evaluation of the volume or mass balances, the identification of the hydrogeological and physico-chemical responses (water temperature, specific conductivity) observed within the karstic aquifer. Here, we present the means implemented offshore to acquire data at the submarine spring over the 06/25/2019 - 12/31/2022 time period together with lagoon water's physico-chemical parameters and levels and onshore groundwater's physico-chemical parameters and levels acquired at springs and boreholes from the karst aquifer.
This study aims to assess surface water–karst groundwater interactions during floods in the Mediterranean karst watershed of the Coulazou River (southern France) using a conceptual semidistributed ...model at 5 min time steps. The kinematic wave routing approximation is used for the transfer of surface flow, while overflows from a linear underground reservoir account for karst flows along the riverbed. After calibration, values of parameters and simulated time series are compared to independent physical measurements. Results show that direct runoff can be neglected on the karst terrains. In addition, this study demonstrates that, in some cases, karst watersheds can be considered as relatively poor systems of regulation but strong systems of amplification or generation of floods and flash floods, depending on rainfall characteristics and also on groundwater level conditions prior to the flood event. Considering that the flood peak is the most important factor defining flash flood hazard, it is shown that the flood hazard regulation effect of the karst is relatively limited for low water table conditions prior to the flood, while the aggravating effect for high water table conditions may be higher than 80% with respect to expected values from surface runoff only. These results show that understanding groundwater–surface water interactions is crucial for describing the flash flood dynamics in karst terrains.
Key Points
Quantitative estimate of karst contribution to surface flow
Conceptual modeling with parameters compared to measurements in the aquifer
Transport rates and residence time in the subsurface are critical parameters for understanding water‐rock interactions for efficient contaminant remediation. This paper presents a methodology for ...assessing flow and transit time of water through hydrological systems, with specific applications to karst systems and implication for hydraulics of a conduit system surrounded by a porous and permeable intergranular matrix. A time variant cross‐correlation function analysis is applied to bivariate time series that characterize mass transfer, assuming a stationary system using sliding windows of various sizes. We apply the method to 1 year long temperature records in the Santa Fe River (north central Florida) measured at (1) the River Sink, where all the incoming surface water drains into a sinkhole, (2) Sweetwater Lake, where the river resurges into a 500 m long karst window, and (3) the River Rise, where the water discharges from a first‐magnitude karst spring. Results are compared with those obtained using specific conductivity. Estimated residence time ranges from less than 1 day during floods to more than 15 days during base flow within the 8000 m flow path between the River Sink and the River Rise. Results are used to characterize geometric, hydraulic, and hydrodynamic properties of this sink‐rise system with strong matrix‐conduit interactions. These properties are critical to the chemical and physical behavior of surface water–groundwater mixing. Our results also have direct implications for sampling strategies and hydrograph separation of many karst systems with different degrees and types of matrix porosity and permeability.
Key Points
Development of a new method for residence time estimation in water
Geometry and hydraulics of a karst conduit surrounded by a porous matrix
Use of time series of natural tracer in water
The Lengguru fold-and-thrust belt in West Papua (Indonesia) has all the characteristics of a young orogen involved in a rapidly changing tectonic setting. The analysis of the young wedge shows ...however that its internal shortening has ceased recently, and that it is nowadays suffering severe extension. Recent topographic data, marine industrial seismic lines and drilling, were used with field observations and measurements to create detailed cross-sections and a new structural map. The study allows us to distinguish two superimposed prisms composed of stacked Mesozoic marine sediments of the Australian margin against a crustal buttress. The construction of these two wedges is younger than 11
Myr. The structures of the Lengguru belt external zones are sealed by an unconformable clastic series, indicating that the construction of the Lengguru prism had aborted suddenly due to a change in the way the Australian and Pacific plate convergence was accommodated. At that time, the internal zones probably started to exhume and the tectonic regime became extensional. Nowadays the internal part of the Lengguru fold-and-thrust belt is undergoing an active east–west extension. We believe that the extension observed in the Lengguru wedge is coeval with a transition from a compressive to a transtensional regime illustrated in the Central Range of Papua, and the onset of the Tarera-Aiduna and Paniai left-lateral faults. The structure of the Lengguru belt therefore results from events occurring over a very short time span; a previous Late Miocene northeast–southwest compression linked to the subduction process, a second from Middle Miocene to Early Pliocene and a Late Pliocene-Quaternary global extension in the whole range. The evolution is compared with that of the Seram wedge and the Misool–Onin–Kumawa continental ridge to the west; where deformation is accommodated at a localized zone which jumps as convergence between Australian and Pacific plate proceeds. This evolution of the belt reflects rapid changes in the accommodation oblique shortening, with the isolated orogenic wedge of Lengguru fold-and-thrust belt left to collapse.
This example illustrates the way a long-lasting subduction terminates. At the lithospheric scale, the deformation remains rooted at the suture zone. However at the surface, the shortening is suddenly widespread over a large area during a very short time span (formation of the Lengguru belt) prior to being transferred to another plate boundary.
The RAD6 and RAD18 genes of Saccharomyces cerevisiae are required for postreplicative bypass of ultraviolet (UV)-damaged DNA and for UV mutagenesis. The RAD6 encoded protein is a ubiquitin ...conjugating enzyme, and RAD18 encodes a protein containing a RING finger motif and a nucleotide binding motif. Rad18 can be co-immunoprecipitated with Rad6, indicating that the two proteins exist in a complex in vivo. Here, we co-overproduce the two proteins using a yeast multicopy plasmid, purify the Rad6-Rad18 complex to near homogeneity, and show that the complex is heterodimeric. The Rad6-Rad18 heterodimer has ubiquitin conjugating activity, binds single-stranded DNA, and possesses single-stranded DNA-dependent ATPase activity. The Rad6-Rad18 complex provides the first example wherein a ubiquitin conjugating activity is physically associated with DNA binding and ATPase activities provided by an associated protein factor. The co-existence of these activities should provide the complex with the ability to recognize single-stranded DNA resulting from stalling of the replication machinery at DNA damage sites and to recognize the components of the DNA replication machinery for ubiquitination by Rad6.
Core Ideas
SNO KARST is dedicated to the study of karst functioning.
Hydrodynamics and geochemistry are measured at springs and in karst compartments.
Process sampling was set up at nine sites in ...various climatic contexts.
Continuous monitoring concerns timescales from 10 to >50 yr.
New tools and findings are due to the complementarity of gathered data.
Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface–groundwater interactions. Improving the understanding of karst functioning is thus a major issue for the efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems across a wide range of spatiotemporal scales under different geological, geomorphological, climatic, and soil cover settings. The objective of the French Karst National Observatory Service (SNO KARST) is to supply the international scientific community with appropriate data and tools, with the ambition of (i) facilitating the collection of long‐term observations of hydrogeochemical variables in karst, and (ii) promoting knowledge sharing and developing cross‐disciplinary research on karst. This paper provides an overview of the monitoring sites and collective achievements, such as the KarstMod modular modeling platform and the PaPRIKa toolbox, of SNO KARST. It also presents the research questions addressed within the framework of this network, along with major research results regarding (i) the hydrological response of karst to climate and anthropogenic changes, (ii) the influence of karst on geochemical balance of watersheds in the critical zone, and (iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds.
Karst aquifers are complex hydrogeological systems that require numerous in-situ measurements of hydrological and physico-chemical parameters to characterize transfer processes from the recharge area ...to the karst spring. Numerous graphical, statistical or signal processing methods have been developed for decades to interpret these measurements, but there is no simple and standardized tool that can be used for this purpose, which is necessary for a rigorous comparison of results between case studies. This Technical Note presents XLKarst, which has been developed to provide a simple and easy-to-use tool to process a selection of proven methods that characterize the functioning of karst systems. This tool allows (i) time series analysis based on correlation and spectral analysis and, for flow measurements, the use of other statistics and base flow separation, (ii) calculation of the cumulative distribution function to build a spring flow probability plot, and (iii) analysis of spring flow recession and expression of the results in a karst system classification scheme. These methods are first described by providing the key elements of their use and interpretation in the scientific literature. Then, an application to the Fontaine de Nîmes karst system (southern France) is used to highlight the complementarity of the methods proposed by XLKarst to describe the hydrodynamic behavior of a karst system based on daily data of rainfall and discharge over 22 years.
Over the last two decades, groundwater systems and surface water bodies are being more and more considered as a same entity which constitutes a single resource within the hydrologic system; ...understanding groundwater surface water (GW–SW) interactions is necessary to effectively manage the water resources. Concepts, methods of analysis and classifications of these hydrodynamic interactions have thus been developed, mostly in case of porous aquifer. Today, GW–SW interactions are still often poorly understood in many watersheds, particularly in the case of complex aquifers like karst aquifers.
This study focuses on the influence of groundwater on the genesis and propagation of surface floods in the case of a highly karstified watershed. GW–SW hydrodynamic interactions are analysed (i) at a local scale focussing on hydrodynamic interactions between the karst aquifer in the vicinity of the river and the river, and (ii) at a larger scale focussing on hydrodynamic interactions between a karst spring and sinkholes in the riverbed. Hydrodynamic time series are described using the karst watershed of the
Coulazou River (western
Montpellier, France) as a case study. Results are used to adapt GW–SW classifications that are usually devoted to porous media. In case of the studied karst aquifer, it is shown that the initial groundwater level may be used to forecast the type of hydraulic connection between the river and the saturated zone during flood. However, initial water level in the karst aquifer does not give any information about the flow direction (gaining or losing stream) during a flood. The latter is found to be also controlled by the limited discharge capacity of karst conduits. A conceptual model of karst/river interactions during flood is given, with concepts that are derived from the analysis of the
Coulazou watershed but that can be easily applied to most of the karst watersheds.
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