HS8.2.8

In karst catchments, aquifer recharge occurs through a composite mosaic of subsurface flow paths. Precipitation infiltrates in the subsurface and flows along a complex network of fractures – that are characterized by different sizes and degrees of saturation –  before eventually reaching the catchment outlet. The discharge of a karst spring is the result of the contributions of these flow paths, that may differ widely in terms of lengths, velocities, and travel times. Monitoring the spring discharge can thus provide information about flow within the aquifer. In particular, the spring discharge signal can be interpreted as the lagged response of the aquifer to precipitation inputs over the catchment, with the aquifer being characterized by a distribution of response times that relates input (precipitation) to output (discharge). Identifying these response times is not a trivial task as the input-output problem is often mathematically ill-posed, which leads to amplification of the errors and may prevent finding a physically meaningful solution.

In this work we propose a method to evaluate the distribution of response times of a karst aquifer. The method, that was originally developed to deal with ill-posed problems in geostatistical applications, relies on a probabilistic description of precipitation inputs and discharge outputs, and it provides an estimate of the response time distribution and of its uncertainty. The method is here tested through the application to two datasets collected in two cave systems in Northern Italy (the Bossea system and the Vene/Fuse system) with different hydrogeological properties. The results demonstrate that the method successfully identifies different response time distributions that reflect the differences in aquifer characteristics of the two systems. Furthermore, differences among response time distributions relative to different precipitation events in each system provide valuable insights on seasonal variations in aquifer recharge and fracture saturation. The method can hence be applied as a tool for the indirect investigation of karst systems.

How to cite: Boano, F., Viglione, A., and Vigna, B.: Identifying distributions of response times in karst aquifers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15209, https://doi.org/10.5194/egusphere-egu21-15209, 2021.

Spring discharge curves can be seen as the fingerprint of an aquifer. In particular, the recession of flow after strong recharge events has been widely used for aquifer characterization. Several conceptual models for recession curve analysis were proposed. They either provide a mathematical fit to empirical relations or approximate a solution to the diffusion equation.

This study investigates the flow recession behavior of aquifers with preferential flow paths with a structure according to the concept of minimum energy dissipation.
Assuming a power-law relationship between hydraulic conductivity and porosity, the subsurface flow patterns used in our model are organized towards an optimal spatial distribution of these two parameters in a way that the total energy dissipation of the flow is minimized. This leads to two-dimensional dendritic network structures similar to river networks. Starting from a steady-state initial condition with a constant recharge rate we model the decrease of discharge over time, under the assumption of a linear storage behavior.

Our model produces recession curves that follow an exponential function at large time scales, which is a behavior often observed in nature and corresponds to many previous studies. The recession coefficient of this exponential decay shows a power law relation to the catchment size of each individual spring. This relation however is significantly less prevalent than for corresponding linear flow in 1 or 2D. 
Projecting the exponential portion of flow over the complete recession time period shows that the majority of available water is drained in this baseflow component. The overall share ranges from 85-100% but is independent from spring catchment sizes.

How to cite: Strüven, J. and Hergarten, S.: Flow recession behavior of dendritic subsurface flow patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8672, https://doi.org/10.5194/egusphere-egu21-8672, 2021.

The Mediterranean region is identified as a climate change hotspot, where future scenarios indicate an increase of temperature associated with a decrease of precipitation. Providing future scenarios of water resource availability considering both climate and anthropogenic changes on karst catchments remains a major challenge for hydrological sciences. The study concerns the Oeillal spring, which is one outlet of the karst catchment associated with the Fonfroide-Monredon massif (southern France), mainly composed by Jurassic limestones. We assess the relative effects of climate changes and anthropogenic forcing on the karst spring discharge by coupling 12 climate model simulations (GCM/RCM) under two emission scenarios (RCP 4.5 and RCP 8.5) with 3 hydrological models and considering 4 scenarios of groundwater abstraction for drinking water supply (no abstraction, present-day abstraction, +50 % abstraction and +100 % abstraction at horizon 2100).  We find that climate change has a major effect on the future evolution of the Oeillal spring’s discharge and that groundwater abstraction constitutes a secondary but non-negligible factor, which increases the occurrence of dry up of the Oeillal spring.

How to cite: Sivelle, V., Jourde, H., Bittner, D., Mazzilli, N., and Tramblay, Y.: Relative impacts of climate change and anthropogenic forcing on karst spring discharge forecasting of a Mediterranean catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4150, https://doi.org/10.5194/egusphere-egu21-4150, 2021.

Karst systems are challenging to model due to their heterogeneous hydraulic properties resulting in highly variable discharge behavior. Distributed models can be applied to karst aquifers but require detailed system knowledge and extensive hydraulic parameter datasets; lumped-parameter models are less complex, but still require parametrization. In this work, we demonstrate the application of a data-driven approach to model the discharge behavior of the Aubach spring in the Gottesacker karst system in the northern Alps, a well-investigated study site for which previous models are available for comparison (Chen et al. 2018; Fandel et al. 2020). Our approach is based on convolutional neural networks (CNN), which have proved to be well suited for time series forecasting in water-related contexts like runoff modelling or groundwater level prediction (Wunsch et al.). The approach is comparably simple in terms of data requirements as we rely mainly on widely available and easy-to-measure parameters such as precipitation and temperature. By implementing Bayesian techniques (Monte-Carlo dropout) we are able to report the predictive uncertainty of the CNN based forecasts. Our results challenge existing modelling results based on lumped-parameter models in terms of common error measures such as Nash-Sutcliffe efficiency. Furthermore, we explore the important role of snow accumulation and melting by coupling our model with a snow-routine to better represent their influence on spring discharge and further improve model performance. Our results demonstrate that the presented machine-learning approach can be applied to simulate karst spring discharge and has certain advantages in comparison with conventional karst modelling approaches, which require hydraulic parameters that are often not available.

Chen, Z.; Hartmann, A.; Wagener, T.; Goldscheider, N. (2018) Dynamics of water fluxes and storages in an Alpine karst catchment under current and potential future climate conditions. Hydrology and earth system sciences, 22 (7), 3807–3823.

Fandel, C.; Ferré, T.; Chen, Z.; Renard, P.; Goldscheider, N. (2020) A model ensemble generator to explore structural uncertainty in karst systems with unmapped conduits. Hydrogeology journal, published online.

Wunsch, A.; Liesch, T.; Broda, S. (2020) Groundwater Level Forecasting with Artificial Neural Networks: A Comparison of LSTM, CNN and NARX. Hydrology and Earth System Sciences Discussions 2020:1–23. https://doi.org/10/ghtcz3

How to cite: Liesch, T., Wunsch, A., Chen, Z., and Goldscheider, N.: Modeling the discharge behavior of an alpine karst spring influenced by seasonal snow accumulation and melting based on a deep-learning approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12181, https://doi.org/10.5194/egusphere-egu21-12181, 2021.

Vis, a small remote island in the Adriatic Sea, inhabited since the time of ancient Greeks and Romans, exhibits a unique historical and natural environment. With an area of 89.7 km², the island is mostly composed of karstified carbonate rocks and belongs to Dinaric karst region, locus typicus for karst landforms. Its distance from the mainland is around 50 km from the city of Split, 147 km from the Italian coastline and 18 km from neighbouring Hvar island. The climate on the island is Mediterranean with dry and hot summer and mild, rainy and humid winter (Csa). Vis island, due to its remote location, is not connected to the mainland by submarine water pipeline so it has autonomous water supply due to favourable geological and hydrological conditions which enabled the formation of excellent karst aquifers. The majority of water is abstracted from drilled wells in the central part of the island (Korita extraction site), around 40 l/s, while additional quantities are obtained from coastal spring of Pizdica. Although predominantly of good quality, existing groundwater quantities on Vis are extremely vulnerable to the effects of climate change, namely increase in temperature, quantitative and temporal variability in precipitation trends as well as seawater intrusion. Moreover, Vis island is an attractive location for summer bathing tourism which causes the highest pressure on drinking water resources precisely during the hydrological minimum. An idea to apply artificial recharge of karst aquifer on Vis emerged during the 1970s, however, only on the theoretical level.

Through the scope of the DEEPWATER-CE project, funded by Interreg Central Europe Programme, the aim is to develop implementation frame for managed aquifer recharge (MAR) solutions. Simplified, MAR is a process by which excess surface water is directed into the ground — either by spreading on the surface, by using recharge wells, or by altering natural conditions to increase infiltration to replenish an aquifer (DILLON et al., 2019). Globally, various designs of MAR schemes have successfully been implemented in unconsolidated aquifers, but there is little experience with artificially recharging karst aquifers (ROLF, 2017). A particular challenge for the technical implementation and operation of MAR is posed by strong hydraulic anisotropy and heterogeneity of karst aquifers and by their high vulnerability to contamination (XANKE, 2017). To investigate whether a MAR operation is feasible and suitable for karst aquifer on Vis, a detailed field and laboratory investigations were carried out. Field investigations included in-situ measurements of physicochemical parameters on water samples from springs and boreholes, groundwater monitoring (conductivity, temperature and water levels), geophysical methods (ERT, magnetotellurics, and seismic refraction) and structural measurements. Laboratory analyses included measurements of stabile water isotopes, and principal cations and anions. Hence, by conducting extensive investigations, coupled with historical data and previous research, a foundation for implementing efficient and sustainable management of karst aquifer through MAR on Vis island will be provided. 

How to cite: Borović, S., Patekar, M., Terzić, J., Pola, M., Filipović, M., Briški, M., Kosović, I., and Novosel, T.: Options for managed aquifer recharge of karst aquifer of Vis island (Croatia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12195, https://doi.org/10.5194/egusphere-egu21-12195, 2021.

The hydraulic phenomenon of upwelling, affecting several karst springs of Apennines, has been investigated through water level monitored in several boreholes of different depth, and chemical-physical data of springs water. Three different springs in Campania region, southern Italy, were analyzed (Serino, Grassano and Caposele springs), characterized by different ground­water hydraulic schemes, but with the same upwelling phenomenon at the springs.

Even if the ascending groundwater flow is expected from the hydraulic features connected to the local and regional groundwater flow theory, these observations are original in areas analyzed.    

Some data (spring discharge and piezometric levels) have been acquired mainly from aqueduct companies, other data (physical-chemical param­eters and Radon values (²²²Rn)) have been collected ad hoc in spring waters.

All data pointed out that karst springs considered are fed by ground­water flux that locally is vertical; in some cases, CO₂ and H₂S dissolved gas in the deep groundwater are transported in surface by the ascendent flow, which can cause typical collapse sinkholes near the karst springs. All these features, common to others springs of Apennines, can be relevant in the realization of the tapping work, in their maintenance and for the definition of the protection area of the springs.

How to cite: Fiorillo, F., Leone, G., Pagnozzi, M., Catani, V., Testa, G., and Esposito, L.: The phenomenon of ascendant flow which characterizes karst springs, southern Apennines, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10142, https://doi.org/10.5194/egusphere-egu21-10142, 2021.

Climate change and pollution are posing additional unprecedented threats to existing water resources, especially to water supply from karst aquifers in Mediterranean and semi-arid regions. A numerical model considering the most important key hydraulic parameters can forecast the impact of any given input on model quality and quantity output. In this work, we propose to model flow and transport using Comsol multiphysics in a synthetic model and to apply it to a simplified real case study (Jeita spring in Lebanon supplying water to 1.5 million inhabitants). The model geometry consists of a 5300 m long variably saturated horizontal conduit portrayed as 1) 2-D continuum and/or 2) a channel draining a porous equivalent matrix (400 m thick). Flow is simulated using the Richards Equation in both saturated and unsaturated medium. Recharge is applied vertically as both diffuse and point source in a shaft linked to the conduit. Percentages of fast infiltration rates are obtained from the analysis of event time series recorded at the spring (electrical conductivity and discharge). Flow rates at the outlet are used for transient model calibration. Mean velocities, dispersivities, and phreatic conduit diameters obtained from tracer experiments under various flow periods are used for transport validation in the channel. The aim is to test the validity of a functional simplified flow model on a complex real case and to identify based on a sensitivity analysis the key parameters that allow an optimal calibration of such a model. 

How to cite: Doummar, J., Farran, N., Fahs, M., Belfort, B., and Graf, T.: Testing the validity of different synthetic scenarios for flow and transport simulation in karst systems using a real case study application., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8769, https://doi.org/10.5194/egusphere-egu21-8769, 2021.

The Transfer Function (TF) approach, applying the Laplace transform, is known to be effective in interpreting tracer BreakThrough Curves (BTCs) in karst systems. Although this approach has several advantages over the classical Advection Dispersion Equation (ADE), the parameters of the TF are difficult to interpret directly in terms of transport properties, e.g., flow velocity and dispersion coefficient.

We present two approaches to relate the TF parameters to those of the ADE parameters. The first uses a consistency analysis, the other uses an asymptotic analysis in the Laplace space. The TF parameters can be transformed into equivalent ADE parameter groups that have an apparent physical meaning about the transport process. We further provide guidelines for choosing the suitable fitting models for artificial tracer tests and offer some suggestions for utilizing the TF approach in BTCs interpretation.

How to cite: Wang, C., Wang, X., Sivelle, V., Majdalani, S., Guinot, V., and Jourde, H.: The physical meaning of transport properties evaluated from BTC in karst conduit networks using transfer functions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9488, https://doi.org/10.5194/egusphere-egu21-9488, 2021.

Lowland karst aquifers in Ireland are extremely complex to understand and are considered to be highly vulnerable to pollution (e.g. low-lying karst catchments exhibit a lot of surface water – groundwater interactions which makes them very susceptible to direct contamination). These aquifers are impacted by multiple contamination sources on land (in particular, rural sources from agriculture and on-site domestic wastewater effluent) which makes their protection and management challenging. Human wastewater effluent is identified as significant threat to groundwater quality in such lowland Irish karst environments, since approximately one-third of the population in Ireland is relying on decentralized wastewater treatment systems for the treatment of domestic wastewater. However, it is difficult to distinguish between human wastewater effluent and agricultural pollution impacts on karst aquifers using only traditional water quality parameters or any single environmental tracing method. Hence, the impact of microbial and chemical contaminants of human wastewater origin on groundwater quality must be assessed using a multiple-tracer approach, ideally targeting source-specific tracers. This paper presents an overview of the results obtained during the research conducted throughout the last several years at nine karst catchments in Ireland using a range of methodologies in order to determine and quantify domestic wastewater pollution impacts on karst springs. Microbial pollution was assessed using flow cytometric fingerprinting and faecal indicator bacteria, while chemical pollution impact assessment included the analysis of fluorescent whitening compounds (FWCs; well-known indicators of human contamination since their origin is mostly from laundry detergents), specific anion ratio signatures (Cl/Br), quantification and identification of microplastic particles using Fourier-transform infrared spectroscopy (FTIR), and faecal sterol and stanol profiles and ratios. A thorough analysis of the results obtained using a multiple-tracer approach has been conducted and methodologies have been evaluated in terms of applicability and sensitivity in a range of different karst catchments. The ability of these methodologies and techniques to determine and quantify human faecal pollution impacts on karst springs will be discussed. The results show a significant correlation between microplastic particle counts and detected FWCs signals at different springs, which helps to understand the contribution of household-derived contaminants to this environmental problem. Moreover, our results indicate that faecal sterols and stanols can be useful faecal source tracking method in karst aquifer systems despite the fact that concentrations of sterols and stanols of interest were usually low which makes the interpretation of results challenging.

How to cite: Vucinic, L., O'Connell, D., Dubber, D., Behan, P., Crowley, Q., Coxon, C., and Gill, L.: A comparison of emerging contaminant fingerprinting techniques to assess the impact of human wastewater on karst groundwater quality, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7645, https://doi.org/10.5194/egusphere-egu21-7645, 2021.

Under special meteorological and hydrological circumstances, shallow karst areas and karst poljes may experience surface water overflow. As a result, surface- groundwater interaction occurs usually creating intermittent lakes. Although human settlements and activities have traditionally adapted to these natural conditions, extensive temporary floods are classified among the most common natural disasters in karst. On the other hand, intermittent lakes are considered as natural reservoirs of excess recharge and good flood regulators in the lower parts of river basins. Due to specific ecohydrological processes and environmental conditions, these areas host unique wetland ecosystems with high levels of biodiversity and provide various ecosystem services, such as ecological productivity, photosynthesis and carbon storage. Given the dynamic nature of hydrological processes in karst aquifers, a distinctive feature of the phenomena described is its high variability of occurrence and duration. Therefore, the identification, characterization as well as the determination of the spatial dimension of flood levels is a challenging task. Focusing on the Slovenian karst, a literature review and analysis of topographical and hydrological data of the selected study areas was conducted. The hydrological analyses were based on long-term monitoring data from Slovenian Environmental Agency and partly on the authors' own database of field measurements and knowledge of the areas concerned. Consequently, the conceptual framework and the key criterion for the determination and recording of areas subject to temporary flooding were developed. A systematic survey reveals the significance of the extent, duration and frequency of flooding. Evaluation results are useful to designers of various water policies and management mechanisms for flood mitigation and protection of special habitats. Observing trends in the spatial and temporal dynamics of flood levels is also valuable for understanding how and to what extent karst aquifers are vulnerable to environmental changes. Finally, the analyses also enable prediction of the effects of these changes on other parts of the environment (e.g., hydrophilic habitats).

How to cite: Ravbar, N., Mayaud, C., Blatnik, M., and Petrič, M.: Surface-groundwater interactions in karst: overview, concept and mapping, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4572, https://doi.org/10.5194/egusphere-egu21-4572, 2021.

Carbonate aquifers in karst systems are very important water reservoir and are recognized as the most difficult to characterize. The purpose of this article is to present a project aimed to understand the circulation of fluids in carbonate reservoirs through innovative hydrogeophysical methodologies both in the laboratory and in the field. The test site is located in the Castel di Lepre karst system, which is disposed in the Mezo-Cenozoic carbonate substratum of the Monti della Maddalena ridge (Southern Appenines). In the karst area are located several caves, but the presence of an artificial tunnel (disused railway tunnel) could give the opportunity to characterize the whole area and the fluid circulation by multisensors geophysical sensors installed inside the karst aquifer. This natural laboratory permits to define an Applied Geophysics strategy developing several main topics from an engineering to hydrogeological point of view. Firstly, the geophysical investigations conducted, without altering the structure and in a fast manner, obtains important information concerning the construction of the tunnel, and the interaction between the infrastructure and surrounding rock, in that area that we define infrastructural critical zone. The study conducted aims to highlight the potential and any limitations of the use of geophysical techniques applied to infrastructures, emphasizing the emerging role of urban geophysics for the importance and topicality of its contents as well as the important innovations that the use of these techniques they can contribute to the hazardous processes. Secondly, the geophysical methods are used as a tool to characterize the fluid circulation by hydrogeophysal sensors installed inside the karst aquifer. The hydrogeophysics arose as an interdisciplinary field that focuses on the improved understanding of hydrological processes through geophysical observation. These approaches aimed at mitigating the detrimental effects of environmental problems.

How to cite: Rizzo, E., Capozzoli, L., De Martino, G., Fornasari, G., and Giampaolo, V.: Geophysical measurements in an abandoned old railway tunnel located in a karst area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13518, https://doi.org/10.5194/egusphere-egu21-13518, 2021.

In some regions in Italy sinkholes are frequent and pose a serious threat to structures and infrastructures. Apulia region is largely affected by sinkholes of both natural and anthropogenic origin, due to the karst nature of large portions of the regional territory and to high diffusion of artificial cavities.

For this reasons, susceptibility, hazard and risk posed by sinkholes must be estimated in order to gain more insights into their spatial and temporal distribution, and to apply appropriate risk management and to take proper mitigation strategies.

In order to estimate the susceptibility to sinkholes in Apulia, the ensemble statistical modelling proposed by Rossi et al. (2010) and later refined by Rossi & Reichenbach (2016) is used. This allows assessing susceptibility using differentiated statistical approaches, quantifying accurately the modelling performances, and evaluating the associated uncertainty. In order to obtain accurate and reliable results thematic layers related to the sinkholes occurrence were carefully evauated and selected. This contribution shows the preliminary results of the analyses to evaluate the susceptibility to natural sinkholes, which used  as training dependent (i.e. grouping) set, data extracted from the regional inventory of natural caves, edited by the Apulian Speleological Federation (www.catasto.fspuglia.it), and as validation set the natural sinkholes occurred in Apulia, collected in the chronological catalogue of sinkholes in Italy (Parise & Vennari, 2013, 2017). Appropriate thematic layers, were selected heuristically on the base of the knowledge on the triggering mechanisms and the nature of the phenomenon gained previously in the study area.

Resulting regional-scale susceptibility map will be appropriately validated. The methodological procedure will be applied to the evaluation of susceptibility for anthropogenic sinkholes as well.

References

Parise M. & Vennari C. (2017) Distribution and features of natural and anthropogenic sinkholes in Apulia. In: Renard P. & Bertrand C. (Eds.), EuroKarst 2016, Neuchatel. Advances in the hydrogeology of karst and carbonate reservoirs. Springer, ISBN 978-3-319-45464-1, p. 27-34.

Parise M. & Vennari C. (2013) A chronological catalogue of sinkholes in Italy: the first step toward a real evaluation of the sinkhole hazard. Proceedings 8th Multidisciplinary Conference on Sinkholes & the Engineering and Environmental Impacts of Karst, Carlsbad, USA.

Rossi, M. & Reichenbach P. (2016) LAND-SE: a software for statistically based landslide susceptibility zonation, version 1.0. Geoscientific Model Development, 9(10).

Rossi M., Guzzetti F., Reichenbach P., Mondini A. C., Peruccacci S. (2010) Optimal landslide susceptibility zonation based on multiple forecasts, Geomorphology, 114, 129–142.

How to cite: Vennari, C., Rossi, M., Pisano, L., Zumpano, V., and Parise, M.: Sinkhole susceptibility evaluation in Apulia, southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2154, https://doi.org/10.5194/egusphere-egu21-2154, 2021.

In the last decades, climate changes are affecting the freshwater resources quality and quantity around the globe, reducing their availability. On Earth, glaciers and ice cap occupy 68,7%, but they are not easily usable for human purposes; groundwater stands for 30,1%, while surface waters represent the remaining 1,2%. Therefore, groundwater resource is by far the most important natural tank to be preserved.

In karst, scientists are still working on developing new methods to understand the true groundwater hydrological behavior, due to subsoil anisotropy in both space and time. This requires a deep knowledge about discontinuity systems in the carbonates, and to improve our comprehension of karst processes, as basic elements for modelling.

The possibility to collect data directly from the subsoil, thanks to speleological explorations, is a precious chance for hydrogeology, and in general, for the environmental sciences. In this contribution we take advantage from a variety of speleological data, plus traditional geological surveys, to study groundwater flow in the karst of Apulia. Many karst processes, indeed, affect the Cretaceous limestones belonging to the Apulia carbonate platform, where the deepest cave in the region opens in the Canale di Pirro polje (altitude 300m a.s.l.). This latter is a W-E elongated tectonic-karst valley, representing one of the most significant karst landforms in this sector of Apulia. The cave reaches groundwater at a depth of -260m from the ground surface, whilst additional 60m below the water table have been explored by diving the flooded channels (total depth of the cave 320m).

We deal here with characterization of water flow direction into the fractured and karst aquifer, using a combined approach consisting of analysis of: i) primary and secondary discontinuities, ii) shape, size and orientation of karst conduits, and iii) geometry of the intersections between fractures and karst features.

The discontinuities have been analyzed with classical geological survey at the surface, and a semi-automatic extraction of their statistical properties, using the FracPaQ software. To characterize the water flow into the karst channels, we started from collection of available speleological maps of caves in the study area, in order to assess their main directions of development . From this analysis, some preliminary links were summarized: on the polje ridges, the prevailing discontinuity systems were well correlated with cave development, and, in turn, with the main regional tectonic directions (respectively, the SW-NE anti-Apennine, and the NW-SE Apennine systems). At the polje bottom, on the other hand, direction of cave segments and discontinuities are about similar, following the Canale di Pirro polje main elongation (W-E).

This first comparison among data from different sources eventually points out that water flows underground following the main structural lineations. These data, together with results of the groundwater flow model, confirm the key role of geo-structural control on karst development, and the possibility of variations at the local scale, as observed at the polje bottom. In karst, the integrated approach of geo-structural discontinuities and karst features and geometry is therefore a fundamental tool to gain insights into the understanding of the main groundwater flow directions.

How to cite: Liso, I. S., Masciopinto, C., and Parise, M.: Tectonic control on groundwater flow in a karst polje of southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-489, https://doi.org/10.5194/egusphere-egu21-489, 2021.

The most characteristic feature of carbonate rocks is that they are prone to dissolution due to the meteoric water circulation which is enriched in CO₂. One of the factors influencing this phenomenon is the existence of discontinuities within the mass of carbonate rocks. The Diros Vlychada show cave, on the peninsula of Mani in Peloponnese, Greece, has developed in marbles that belong to the Plattenkalk geotectonic unit. Most of the cave is flooded with water and its level changes depending on the external weather conditions and variations in sea level. The deformation of the marbles is represented by tectonic structures formed during the Lower Miocene metamorphism and their subsequent exhumation. The final uplift stage took place during the Pliocene-Quaternary and is still active. Five joints systems were distinguished:

A NW-SE joint system which is subdivided into a subsystem with low-angle dips, mainly towards to the NW, related to the main foliation of the marbles and a second subsystem characterized by stretching joints of the same strike (elongated joints), which have high-angle dips, also towards the NW. The latter system intersects the former but is confined between marble bedding and does not extend to more than three beds (the bedding is defined by the first subsystem).

A NW-SE striking joint system characterized by stretching joints with high-angle dips, which intersects diagonally the two previous. This system extends between more than three marble beds.

Two systems show E-W and N-S strike with the first one much better expressed. Those joints have developed diagonally to the previous ones. These are mainly shear joints that intersect the first system and are propagated within many marble beds.

The chambers of the cave have been developed along NW-SE and E-W directions. The first one is identified with the joint system that has been developed transversely to the strike of the marble foliation and the second in parallel with the main system of the shear joints. It is interesting that the bays forming the coastline of the Mani peninsula, have developed in an E-W direction, which coincides with both one of the growth directions of the cave and one of the joints systems, which correspond to shear joints developed during the folding of the marbles. Stalactites and stalagmites grow in a NE-SW direction that is identical to the elongated joints which form the system that is parallel to the foliation strike. Groundwater flow along these branches may be slower as these branches appear to be restricted between marble bedding.

How to cite: Filis, C., Skourtsos, E., Karalemas, N., Giannopoulos, V., Giannopoulos, I., Kotsi, E., and Lekkas, E.: The pattern of the tectonic joints and the development of the Vlychada karst show cave in Diros, Peloponnesus, Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14290, https://doi.org/10.5194/egusphere-egu21-14290, 2021.