HS8.2.8

EDI
Field and modelling approaches to assess natural processes and engineering problems in the complex karst environment

Karst environments are characterized by distinctive landforms and unique hydrological behaviors. Karst systems are commonly extremely complex, heterogeneous and very difficult to manage, because their formation and evolution are controlled by a wide range of geological, hydrological, geochemical and biological processes. Furthermore, karst systems are extremely vulnerable due to the direct connection between the surface and subsurface through the complex networks of conduits and caves.

The great variability and unique connectivity may result in serious engineering problems: on one hand, karst groundwater resources are easily contaminated by pollution because of the rapidity of conduit flow; on the other hand, the presence of karst conduits that weakens the strength of the rock mass may lead to serious natural and human-induced hazards. The design and development of engineering projects in karst environments thus should necessarily require: 1) an enhanced understanding of the natural processes governing the initiation and evolution of karst systems through both field and modelling approaches, and 2) specific interdisciplinary approaches aimed at mitigating the detrimental effects of hazardous processes and environmental problems.

This session calls for abstracts on research related to geomorphology, hydrogeology, engineering geology, hazard mitigation in karst environments in the context of climate change and increasing human disturbance.

Public information:
As established by the International Union of Speleology and UNESCO, 2021 has been declared the International Year of Caves and Karst.
Our session "Field and modelling approaches for the assessment of hydrogeological and engineering problems in the complex karst environment" aims at contributing to the activity of this celebration. It will address 3 themes:
• Characterization and modelling of karst hydrodynamics
• Groundwater chemistry and transport processes in karst
• Characterization, mapping and modelling karst features and processes
Convener: Hervé Jourde | Co-conveners: Joanna Doummar, Mario Parise, Natasa Ravbar, Xiaoguang WangECSECS, Georg Kaufmann
vPICO presentations
| Thu, 29 Apr, 14:15–17:00 (CEST)
Public information:
As established by the International Union of Speleology and UNESCO, 2021 has been declared the International Year of Caves and Karst.
Our session "Field and modelling approaches for the assessment of hydrogeological and engineering problems in the complex karst environment" aims at contributing to the activity of this celebration. It will address 3 themes:
• Characterization and modelling of karst hydrodynamics
• Groundwater chemistry and transport processes in karst
• Characterization, mapping and modelling karst features and processes

vPICO presentations: Thu, 29 Apr

Chairpersons: Hervé Jourde, Joanna Doummar, Georg Kaufmann
14:15–14:20
Part I - Characterization and modelling of karst hydrodynamics
14:20–14:25
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EGU21-15209
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solicited
Fulvio Boano, Alberto Viglione, and Bartolomeo Vigna

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.

14:25–14:27
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EGU21-8672
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ECS
Jannick Strüven and Stefan Hergarten

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.

14:27–14:29
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EGU21-8818
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ECS
Adrijana Vrsalović, Ivo Andrić, and Ognjen Bonacci

Red Lake is an example of a karst phenomenon near the town of Imotski (Croatia), in the central part of Dinaric Karst. It is considered the deepest submerged karst feature in the world, located in an inaccessible area with large slopes of the lakeshore, which makes the research difficult and resource intensive. For this reason, to better understand the hydrogeological functioning of the lake, data on the water level in the lake, collected over a period of five years, were analyzed. The morphometric model of Red Lake was used to determine a relationship between lake volume and depth, furthermore to define integral water inflow and outflow quantities. Recession curves were extracted from the graphical representation of the water influx data series. The calculated recession coefficients were used to identify the dominant hydrogeologic mechanism respective to the water level in the lake and the ratio between recharge components of groundwater and direct runoff. The approach provides a tool for identifying the hydrogeological regime of karst lakes and the stratification of different porosity levels of the surrounding karst massif.

How to cite: Vrsalović, A., Andrić, I., and Bonacci, O.: Recession curve analysis in function of karst lake hydrogeological regime identification: case study Red Lake, Croatia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8818, https://doi.org/10.5194/egusphere-egu21-8818, 2021.

14:29–14:31
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EGU21-4009
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ECS
Guillaume Cinkus, Naomi Mazzilli, and Hervé Jourde

10% of the world’s population is dependent on karst water resources for drinking water. Understanding the functioning of these complex and heterogeneous systems is therefore a major challenge for long term water resource management. Over the past century, different methods have been developed to analyse hydrological series, and subsequently characterize the functioning of karst systems. These methods can be considered as a preliminary step in the development and design of hydrological models of karst functioning for sustainable water resource management. Recent progress in analytical tools, as well as the emergence of data bases of discharge time series (e.g. the French SNO KARST database and the WoKaS database at global scale) allow reconsidering former typology of karst system hydrodynamic responses. Ten karst systems and associated spring discharge time series were considered for developing the typology. The systems are well-known with a high-quality monitoring and they cover a wide range of hydrological functioning, which ensure the relevance of the analyses. The methodology for the assessment and the development of the typology consisted in (i) the analysis of springs discharge time series according to four different methods, (ii) the selection or proposal of the most relevant indicators of karst systems hydrodynamics, and (iii) the interpretation of the information from these indicators based on principal component analysis and clustering techniques. A typology of karst systems accounting for 6 different classes is finally proposed, based on 3 aspects of functioning: the capacity of dynamic storage, the draining dynamic of the capacitive function and the variability of the hydrological functioning. The typology was applied to a wider dataset composed of spring discharge of 78 karst systems. The results show a relevant distribution of the systems among the different classes.

How to cite: Cinkus, G., Mazzilli, N., and Jourde, H.: Proposal of a typology of karst systems functioning based on relevant indicators of karst springs hydrodynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4009, https://doi.org/10.5194/egusphere-egu21-4009, 2021.

14:31–14:33
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EGU21-9987
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ECS
Giorgia Lucianetti, Zhao Chen, Andreas Hartmann, and Roberto Mazza

Water resources from high-alpine karst aquifers are used for drinking, hydropower generation and artificial snowmaking. Therefore, understanding of their storage and flow dynamics is crucial for a sustainable water management. However, high-alpine karst areas are characterized by a great geological complexity due to the presence of mountain block fractured and karst aquifers interdigitating with the heterogeneous valley floor porous aquifers. For that reason, hydrogeological characterization and model prediction remains a big challenge. In this work, we investigated a geologically complex alpine catchment in the Dolomites (Italian Alps) by using experimental data and a reservoir numerical model to simulate three years of stream discharge. The structure of the model is based on experimental knowledge of the catchment and on previous studies and investigations. It (1) includes snow dynamics and accounts for hydrogeological heterogeneities, (2) separately considers karstic conduit and matrix flow in a dolomitic aquifer and flow through the porous deposits accumulating on the slopes and at the valley floor in an unconsolidated aquifer (non-karst), and (3) takes into account the groundwater transfer between the two aquifers. In the frame of a multi-step model evaluation, we used a Regional Sensitivity Analysis with three performance measures including observations of catchment discharge, karst spring discharge and unconsolidated aquifer spring discharge to assess the realism of model simulations. We show that the newly developed model reliably reproduces the hydrogeological variability of the catchment, even during strongly different hydroclimatic conditions. Analyzing its simulated storage dynamics, we can show that despite its moderate storage, the porous aquifer contributes most to catchment discharge, while the largest storage of the system is the matrix of the dolomite aquifer that recharges the unconsolidated aquifer together with discharge from the karstic conduits. A clear seasonality of groundwater storage in the karst matrix and of unconsolidated aquifer discharge indicates a strong sensitivity of this complex aquifer system to climatic variability.

How to cite: Lucianetti, G., Chen, Z., Hartmann, A., and Mazza, R.: Understanding storage and discharge behavior of a high-elevated and geologically complex karst catchment using numerical approach, Dolomites (Alps), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9987, https://doi.org/10.5194/egusphere-egu21-9987, 2021.

14:33–14:35
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EGU21-10846
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ECS
Cousquer Yohann and Jourde Hervé

A quantitative estimation of the sustainability of groundwater resources is a challenge for water supplies. This study focuses on karstic hydro systems, which provide water resources to a large part of the Mediterranean population. Here, we address the long-term changes in the functioning of the Lez karst aquifer, which has been providing water to the city of Montpellier since the XIXth century.  Before 1965, only the natural overflow of the spring was used, then pumping in the spring, down to -6.50 m below the overflow level of the spring, was performed until 1981. After this date, the management of the water resource consisted in pumping groundwater at a much greater flow rate (up to 2000 l/s) than the natural discharge during low flow (200 l/s), which seasonally generates important drawdowns (down to ~25 m) at regional scale.

The available time series consist in more than 70 years of discharge and water table (with some gaps) that encompass the three kinds of groundwater management, spanning from a passive management to the current active management. The change in water budget terms over time (before and after active management) highlights the modification of transfers and storage in the different karst compartments (epikarst, unsaturated zone, saturated zone), and the climatic variability of precipitation, evapotranspiration at inter-annual. A lumped parameter model was set up in order to simulate spring discharge, while accounting for surface water and grandwater level dynamics, and better assess the changes in the storage dynamics within the different compartments (matrix-conduits) of the karst. A robust parameter estimation, accounting for groundwater discharge and surface water discharge observations, has been conducted using a Monte-Carlo procedure. In order to obtaines a robust model, divers data type such as groundwater flow, surface flow and water level, have been used. [H1]  Once the model was calibrated over (1955-2020) reference period, several prospective management scenarios based on pumping discharge were simulated with an estimation of predictive uncertainty. This allowed evaluating the influence of pumping at large flow rate (active management) on the flux and storage on matrix-conduits exchanges of such karst hydrosystem. A modification on both the discharge rates and the direction of water exchanges between compartments, and especially between matrix and conduits, have been noted. The importance of climatic variability at inter-annual scale on water availability has been discussed as well.

How to cite: Yohann, C. and Hervé, J.: Long term changes in the functioning of a karst aquifer under anthropogenic forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10846, https://doi.org/10.5194/egusphere-egu21-10846, 2021.

14:35–14:37
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EGU21-5868
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ECS
Tamara Leins, Isabella Serena Liso, Mario Parise, and Andreas Hartmann

Vora Bosco Cave is located in the Salento karst peninsula (Apulia, S Italy), surrounded by the Ionian and Adriatic Seas. In this part of Apulia, due to climate change, the typical Mediterranean climate is moving towards arid and semi-arid, with scarce or absent surface runoff. The Salento groundwater is a freshwater lens fluctuating on seawater, entering inland because of intrusion phenomena. The freshwater volume stored in the lens is subjected to both sea level rise and an increasing pressure caused by the high water demand, especially in summer time, for touristic purposes. Therefore, developing an understanding of the hydrogeological dynamics of the karst aquifer can be a useful tool for planning better protection and management actions on Apulian groundwater resources.

Vora Bosco cave was instrumented with a multi-parameter probe for groundwater level measurements from November 2017 to July 2018. Thereby, the system behaviour within the cave recharge area can be explored. To characterise and quantify the natural recharge and discharge behaviour of the system, a simple reservoir model was developed and calibrated with the measured data. The model consists of 4 reservoirs, which are filled and emptied using simple discharge equations. The model considers evapotranspiration from the soil, slow flow in the unsaturated and saturated zone, as well as fast flow in the karstic conduits. Daily data of precipitation and potential evapotranspiration are used as model inputs. The model simulates the water level at Vora Bosco and is calibrated by comparison of simulated and measured water level, using the Kling-Gupta-Efficiency as an objective function. Our results reveal that the model simulations show acceptable performance in reflecting the dynamics of the observed water level data. The calibration achieves reasonable results for the model parameters. In addition to the water level simulations, quantifying predictions uncertainty by Monte Carlo approach, it is shown that there is still potential to produce more reliable estimates of future groundwater dynamics, in order to better manage the precious regional groundwater resources.

How to cite: Leins, T., Liso, I. S., Parise, M., and Hartmann, A.: Understanding of reservoirs in karst: the case of Vora Bosco cave (Salento, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5868, https://doi.org/10.5194/egusphere-egu21-5868, 2021.

14:37–14:39
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EGU21-4150
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ECS
Vianney Sivelle, Hervé Jourde, Daniel Bittner, Naomi Mazzilli, and Yves Tramblay

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.

14:39–14:41
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EGU21-12181
Tanja Liesch, Andreas Wunsch, Zhao Chen, and Nico Goldscheider

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.

14:41–14:43
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EGU21-12195
Staša Borović, Matko Patekar, Josip Terzić, Marco Pola, Marina Filipović, Maja Briški, Ivan Kosović, and Tomislav Novosel

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.

14:43–15:00
Chairpersons: Mario Parise, Natasa Ravbar, Xiaoguang Wang
Part II - Groundwater chemistry and transport processes in karst
15:30–15:35
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EGU21-10142
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solicited
Francesco Fiorillo, Guido Leone, Mauro Pagnozzi, Vittorio Catani, Giovanni Testa, and Libera Esposito

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.

15:35–15:37
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EGU21-2021
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ECS
Ilenia M. D'Angeli, Jo De Waele, Adriano Fiorucci, Bartolomeo Vigna, Stefano M. Bernasconi, Lee Florea, Isabella S. Liso, and Mario Parise

Santa Cesarea Terme (SCT) karst system opens along the Adriatic coastline of Apulia (southern Italy) and is composed of four sub-horizontally caves Fetida, Sulfurea, Gattulla and Solfatara. Being influenced by rising sulphidic waters, it is used as thermal spa for human health treatments. The caves show interesting signs of hypogene sulphuric acid speleogenetic (SAS) activity such as peculiar morphologies and mineralogical by-products. From the geomorphological standpoint it is possible to observe ceiling cupolas, megacusps (former megascallops), rising channels, submerged feeders, weathered walls, replacement pockets, whereas for mineralogy sulphur, gypsum and jarosite deposits have been recorded. Despite the presence of extensive SAS features, SCT is also intensely influenced by marine water.

All these observations induced us to conduct a long-lasting (2015-2018) geochemical monitoring to understand intensity and tendency of the two main domains (rising acidic vs. marine).

Water sampling was done every 3-4 months at 4 sites in Fetida (2 in areas influenced by sea water movements, and 2 in the innermost zone, less but still influenced by sea), and 1 site in Gattulla. Moreover, 1 sampling site located along the coastline (sea water) was constantly monitoring for comparative reasons.

Collected groundwaters exhibit mean temperatures of 23 °C (7 °C higher than average annual air temperature) and circumneutral pH. All samples belong to the Na-Cl-SO4 type of waters. Sea waters display the highest pH (ranging between 8.15 and 8.20), [Na+], [K+], [Mg2+], [Cl-], [SO42-], and total dissolved solids (TDS), and on the other hands one of the innermost sampling site in Fetida Cave showed the highest values of temperature (29 °C), [HS-], [Ca2+] and the lowest pH (6.76). In addition, the Ba2+/Sr2+ ratio compared with Ca2+/HCO3- or Ca2+/SO42- clearly exhibit the presence of two main domains: rising acid and marine. In particular, the samples collected in the Adriatic Sea are always in the domain of marine influence, whilst all the others from Gattulla and Fetida, depending on sampling conditions (tides, waves, etc..), can fall in both domains.

Our investigations demonstrated rising sulphidic fluids to reach the surface through deep tectonic fractures and karst flowpaths, but seasonal effects due to modest water head variations (tides) and meteomarine conditions affect the geochemical variability, even in the innermost portion of the caves, inducing these slightly thermal acidic fluids to partially mix with marine waters.

How to cite: D'Angeli, I. M., De Waele, J., Fiorucci, A., Vigna, B., Bernasconi, S. M., Florea, L., Liso, I. S., and Parise, M.: Santa Cesarea Terme, a sulphuric acid speleogenetic system intensely influenced by marine waters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2021, https://doi.org/10.5194/egusphere-egu21-2021, 2021.

15:37–15:39
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EGU21-10811
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ECS
Iva Kůrková and Jiří Bruthans

Localities containing karst features were studied in the northwestern part of Bohemian Cretaceous Basin. Namely Turnov area in facies transition between coarse-delta sandstones and marlstones (Jizera Formation, Turonian) and Miskovice area in limestones and sandy limestones - sandstones (Peruc-Korycany Formation, Cenomanian). Evolution of karst conduits is discussed elsewhere (Kůrková et al. 2019).

In both localities, disappearing streams, caves and karst springs with maximum discharge up to 100 L/s were documented. Geology and hydrogeology of this area was studied from many points of view to describe formation of karst conduits and characterize groundwater flow. Tracer tests were performed using NaCl and Na-fluoresceine between sinkholes and springs under various flow rates to evaluate residence times of water in conduits and to describe geometry of conduits. Breatkthrough curves of tracer tests were evaluated by means of Qtracer2 program (Field 2002). Groundwater flow velocity in channels starts at 0.6 km/day during low water levels up to 15 km/day during maximum water levels, the velocity increases logarithmically as a function of discharge. Similar karst conduits probably occur in other parts of Bohemian Cretaceous Basin where lot of large springs can be found.

Mean residence time of difussed flow based on tritium, CFC and SF6 sampled at karst springs is 20 years for 75% of water and 100 years for remaining 25%, based on binary mixing dispersion model. This shows that most of the water drained by karst conduits is infiltrated through the soil and fractured environment with relatively high residence time. Residence times in different types of wells and springs were also measured in whole north-western part of Bohemian Cretaceous Basin. Results indicate long residence times in semi-stagnant zones represented by monitoring wells and short residence times in preferential zones represented by springs and water-supply wells.

 

Research was funded by the Czech Science Foundation (GA CR No. 19-14082S), Czech Geological Survey – internal project 310250

 

Field M. (2002): The QTRACER2 program for Tracer Breakthrough Curve Analysis for Tracer Tests in Karstic Aquifers and Other hydrologic Systems. – U.S. Environmental protection agency hypertext multimedia publication in the Internet at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=54930.

Kůrková I., Bruthans J., Balák F., Slavík M., Schweigstillová J., Bruthansová J., Mikuš P., Grundloch J. (2019): Factors controlling evolution of karst conduits in sandy limestone and calcareous sandstone (Turnov area, Czech Republic). Journal of Hydrology: 574: 1062-1073

How to cite: Kůrková, I. and Bruthans, J.: Flow pattern and residence time of conduit flow and diffuse flow in calcareous sandstones (Bohemian Cretaceous Basin, Czech Republic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10811, https://doi.org/10.5194/egusphere-egu21-10811, 2021.

15:39–15:41
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EGU21-8769
Joanna Doummar, Nidal Farran, Marwan Fahs, Benjamin Belfort, and Thomas Graf

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.

15:41–15:43
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EGU21-9488
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ECS
Chaoqi Wang, Xiaoguang Wang, Vianney Sivelle, Samer Majdalani, Vincent Guinot, and Hervé Jourde

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.

15:43–15:45
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EGU21-12255
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ECS
Jannes Kordilla, Marco Dentz, and Alexandre M. Tartakovsky

Modeling of of infiltration and recharge dynamics in fractured-porous aquifers remain an extremely challenging task due to the formation of preferential pathways along fracture networks and hence deviation from classical diffuse Darcy-type percolation patterns. In contrast to soil systems the vadose zone of consolidated rock systems often reaches depths of several tens to hundreds of meters which limits the accessibility and complicates the application of moisture measurement techniques. Under partially-saturated conditions flow through percolating fracture networks contribute to the fastest spectrum of infiltration velocities. At fracture intersections flow is often fragmented into a vertical and horizontal component which controls the dispersive properties of the infiltrating fluid front. As hydraulic information in consolidated aquifers is often only available at boreholes or springs, we explore how internal fracture network geometries can potentially be reconstructed from external boundary information, e.g., the dispersive properties of discharge (groundwater level fluctuations). In order to relate boundary information, e.g. discharge measured at the water table within boreholes, to internal properties such as geometry of the fracture network and fluid-solid interaction properties we derive an approximate analytical solution for flow through a cascade of simple fracture intersections with the help of parallalized smoothed particle hydrodynamics simulations [1]. Via linear response theory we derive expressions for the non-dimensional bulk flow velocities and dispersion coefficient to characterize the fracture network in terms in the dimensionless time scales of the vertical and horizontal fracture components. We demonstrate that the dispersion coefficient converges towards a universal value for a realistic range of fluid and solid properties and recover a characteristics Washburn-type scaling for the dimensionless velocity.

[1] Kordilla, J., Tartakovsky, A. M. and Dentz, M. (2020): Numerical and analytical modeling of flow partitioning in partially saturated fracture networks, Earth and Space Science Open Archive, pp. 44, doi:10.1002/essoar.10504345.1

How to cite: Kordilla, J., Dentz, M., and Tartakovsky, A. M.: Flow partitioning in partially saturated fracture networks: Relation between dispersive properties and internal fracture geometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12255, https://doi.org/10.5194/egusphere-egu21-12255, 2021.

15:45–15:47
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EGU21-7645
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ECS
Luka Vucinic, David O'Connell, Donata Dubber, Patrice Behan, Quentin Crowley, Catherine Coxon, and Laurence Gill

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.

Part III - Characterization, mapping and modelling karst features and processes
15:47–15:49
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EGU21-4572
Natasa Ravbar, Cyril Mayaud, Matej Blatnik, and Metka Petrič

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.

15:49–15:51
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EGU21-13518
Enzo Rizzo, Luigi Capozzoli, Gregory De Martino, Giacomo Fornasari, and Valeria Giampaolo

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.

15:51–15:53
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EGU21-2366
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ECS
Gioacchino Francesco Andriani, Giuseppe Diprizio, Isabella Serena Liso, Lidia Loiotine, and Mario Parise

The Murge area extends for about 6000 km2 and is represented by a NW–SE karst plateau whose elevation decreases by means of fault-bounded displaced blocks toward NE, from about 680 m a.s.l. (High Murge) down to the Adriatic sea (Low Murge and Apulian Adriatic shelf). Geologically, it consists of a 3 km-thick Cretaceous carbonate succession of well-bedded limestones and dolomites, locally covered by thin Late Pliocene-Quaternary deposits, namely calcarenites and subordinate sands and clays. From the end of Cretaceous up to Pliocene, the Murge area experienced a long period of exposure which favored the development of karst processes responsible for the genesis of surface and underground features, like swallow holes, dolines, dry valleys, poljes and caves. In particular, the main cave and conduit systems develop in the first tens of metres from the ground, involving entirely the epikarst or subcutaneous zone. 

Many are the geoengineering problems in this area due to complexity of the karst landscape and of the underground drainage system. Some of them regard the hydrogeological and hydrological aspects, involving aquifer pollution and groundwater contamination, or flash floods related to clustered rainfall and the related sudden runoff; other problems result from rock or soil failure mechanisms through occurrence of collapse and suffosion sinkholes. In the Murge karst, collapse sinkholes occur both as natural phenomena, linked to karst caves, but they can be also induced by anthropogenic cavities, consisting of excavation by man for shelter, cultural proposes or where rocks were mined to be used as building material. In particular, the occurrence of sinkholes results typically from sudden collapses of the roof of underground voids, and have been at the origin of casualties and severe damage. Subtle and gradual suffosion sinkholes develop where seepage erosion occurs in sandy soils whose grains settle into voids in the underlying carbonate rocks. This mechanism induces differential settlements and rotations of foundations, leading to instability of buildings and other structures.

Numerous remedial and preventive solutions dealing with geoengineering aspects in karst can be adopted due to the complex peculiarities and high variability of the Murge landscape. Thus, the selection of appropriate measures to predict and remediate future damage scenarios becomes very important and require i) the development of detailed geological and engineering geological models, and ii) careful understanding of the geological hazards, and of their likely effects.

The main difficulties for planning and monitoring actions are linked to the implementation of integrated methods capable of exploring and modeling carbonate rock masses and their structural uncertainty in the karst environment. Multi‐technique geophysical methods, integrated with geotechnical surveys (including borehole drillings) can be adopted for passing from a conceptual geological model to an observational engineering-geological model, constrained by data from site-specific ground investigation and laboratory tests. The next step is then constituted by assessing analytical and numerical models which usually require considerable simplifications of the engineering geological model and can be used as general guidelines for designing mitigation and remediation measures.

How to cite: Andriani, G. F., Diprizio, G., Liso, I. S., Loiotine, L., and Parise, M.: Geoengineering problems and solutions in the Murge karst (Apulia, SE Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2366, https://doi.org/10.5194/egusphere-egu21-2366, 2021.

15:53–15:55
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EGU21-2154
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ECS
Carmela Vennari, Mauro Rossi, Luca Pisano, Veronica Zumpano, and Mario Parise

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.

15:55–15:57
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EGU21-489
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ECS
Isabella Serena Liso, Costantino Masciopinto, and Mario Parise

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.

15:57–15:59
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EGU21-14290
Christos Filis, Emmanuel Skourtsos, Nikolaos Karalemas, Vasilios Giannopoulos, Ioannis Giannopoulos, Evangelia Kotsi, and Efthimios Lekkas

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.

15:59–16:01
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EGU21-3713
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ECS
Chuanyin Jiang and Xiaoguang Wang

We use numerical models to investigate the generation of incipient karst in layered geological systems, and specifically to investigate the effects of the structural and hydraulic properties of both joints and bedding planes on the distribution of the developed karst cavities. We develop a numerical model which couples the processes of fluid flow, mass transport and dissolution kinetics that govern the growth of fracture aperture, based on three-dimensional discrete fracture networks. The synthetic fracture networks made up of two jointed layers separated by a horizontal bedding plane are generated to represent the typical layered fracture systems often formed in carbonate rocks. We assume a relatively uniform aperture field with a small variance for each joint set and for the bedding plane, but different joint sets and the bedding plane can have non-identical mean apertures. Results show that the aperture ratio of the joint sets to the bedding plane is found to dominate the flow heterogeneity on the bedding plane, leading to various behaviors of karst development. We further suggest that the distinct flow regimes, i.e., joint-dominated, transitional and bedding plane-dominated, controlled by the magnitude of the aperture ratio, are responsible for the different types of incipient karst morphologies. Our investigations have an important application on the understanding of clustering behaviors of karst cavities in layered fractured carbonate rocks.

 

How to cite: Jiang, C. and Wang, X.: Karst generation in three-dimensional jointed layered rocks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3713, https://doi.org/10.5194/egusphere-egu21-3713, 2021.

16:01–16:03
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EGU21-10749
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ECS
Sandra Banusch, Márk Somogyvári, Martin Sauter, Philippe Renard, and Irina Engelhardt

Investigating the structure of conduit networks in karst aquifers is a common challenge when working in these complex hydrogeological environments. The network geometry plays an important role in karst flow dynamics, but highly karstified areas are often difficult to characterize by field measurements. Here, we present a methodology that generates karst conduit network geometries reasonably quick without solving complex flow or dissolution equations, and that uses only little input information. The stochastic approach also enables the investigation of the uncertainty of generated networks in the form of a karst probability map.

The “Stochastic Karst Simulator” (SKS) is a stochastic modeling approach developed by Borghi et al. (2012) to generate a 3D karst conduit network by computing a minimum effort path between the given inlet and outlet points. This study uses such a modeling approach to characterize the karst network geometry of the Western Mountain Aquifer (WMA), a highly karstified and exploited carbonate aquifer located in Israel and the West Bank. The SKS simulations are based on a conceptual model of the aquifer’s karst genesis, to identify the position of karst springs and recharge zones over past geological ages.

Three different phases of karst formation are identified for the WMA. Phase 1: a paleo-discharge zone exists, located close to the present-day coastline of Israel, phase 2: a period of extreme low sea levels during the Messinian salinity crisis, when paleo-canyons were reactivated along this coastline, and phase 3: the modern-day outlets of the aquifer. The iterative approach of the SKS algorithm accounts for these different phases and creates new conduit pathways by building on ones formed in earlier phases. The algorithm also uses the hydrological model of the study site as soft information, providing knowledge about the internal heterogeneities of the karst formations (e.g. statistical properties of fractures). The resulting karst probability map is compared to the location of the most productive pumping wells in the region, assuming a high yield in groundwater abstraction indicating major karst conduits near the pumped well. 

We demonstrate the method by showing a reconstruction of the karst conduit networks at the WMA model area, an otherwise not available spatial information. The simulations show that the changes in karst spring and recharge locations have a great impact on the geometry and connectivity of the conduit network. Overarching trends in the conduit orientation of the resulting probability map are in keeping with the proposed karst genesis model, resulting in the evolution of a hierarchical network. High karstification is indicated around modern-day springs, also in agreement with the location of numerous pumping wells in that region.

The SKS algorithm is a useful tool to test different hypotheses of karst genesis and to understand the evolution of karst network geometries. The methodology is numerically efficient, and its inputs can be easily adjusted. Soft information on karst development allows for the generation of a sound hydraulic parameter field, which can be implemented in hydrological models to better understand and manage these aquifer systems.

How to cite: Banusch, S., Somogyvári, M., Sauter, M., Renard, P., and Engelhardt, I.: A Karst Probability Map for the Western Mountain Aquifer (Israel & West Bank) using a stochastic modeling approach , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10749, https://doi.org/10.5194/egusphere-egu21-10749, 2021.

16:03–16:05
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EGU21-5597
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ECS
Pierre Fischer and Hervé Jourde

Spatial characterization of the hydraulic properties in the subsurface is an extensively studied problematic. Inverse problems allow to image those properties by interpreting the information from a dataset of field measurements with a chosen physical formulation of fluxes in a numerical distributed model. However, karst media characterization remains a complex task, due to the fact that the matrix and conduits entities generate a highly contrasted distribution of property values. Thus, one needs to employ an inversion method able to represent this contrast and also use data providing information on the localization of the conduits network and its connectivity.

We propose a large-scale 2-D application of characterization of the Lez aquifer in southern France, covering a surface of about 400 km². We take advantages of long-terms measurements within the framework of the MEDYCYSS observation site, part of the Karst observatory network (www.snokarst.org) initiated by the French institute INSU/CNRS. Drawdown signals measured in 14 wells incorporating a periodic response due to a daily pumping at the aquifers spring were thus considered for this study. The periodic responses can provide connectivity information between wells in the inversion process, while non-periodic responses will permit to better assess the large-scale property values of the whole hydrosystem. A Cellular Automata-based Deterministic Inversion (CADI) is used to generate a contrasted property field able to reproduce the measured signals in the 2-D distributed numerical model. This application is led with responses obtained at a high water-table level and also at a lower level in order to highlight the change in connectivity and flow paths mobilized at different depths.

How to cite: Fischer, P. and Jourde, H.: Large-scale spatial characterization of a karst aquifer by combination of periodic and non-periodic responses (Lez aquifer, France), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5597, https://doi.org/10.5194/egusphere-egu21-5597, 2021.

16:05–17:00