HS8.2.4

Karst groundwater dependent ecosystems (KGDEs) represent an important asset worldwide due to their ecological and socioeconomic values. Although they are increasingly recognized as such, they have not been adequately documented and studied. The present contribution aims at characterizing the main KGDEs of the Dinaric karst in Slovenia. Their classification is based on their position within the hydrological system, geomorphology and ecological settings The main hydrological processes (i.e., extent, duration and frequency of groundwater inflow), the main biota and indicator communities, and the factors limiting the evolution of species (e.g., darkness) were identified. An overview of rare, endemic and charismatic species was also shown including Proteus anguinus, Marifugia cavatica, Monolistra racovitzae racovitzae and others. Due to its location in an area of very high geographical diversity and between different climate types, the Slovenian Dinaric karst is one of the hotspots of subterranean biodiversity on a global scale. The interaction between orographic, climatic, hydrological and edaphic conditions, as well as the fact that the area served as a hub for different species and as a refuge during the ice ages, are crucial for the very high biodiversity in this area. Due to deforestation in prehistoric times, man has even contributed to the diversification of the flora by creating space for the appearance or spread of habitats that are now considered natural (e.g., dry grasslands). An important factor in maintaining a particularly rich diversity of karst flora and fauna is also the low human impact and the very well preserved landscape in its natural state. KGDE sites in Slovenia with the greatest known species diversity are the Postojna-Planina and Škocjanske Jame cave systems, Cerkniško and Planinsko Polje, and the intermittent lakes of Pivka. Characterization of KGDEs is a prerequisite for a better understanding of the processes that control them, their biological function, and their vulnerability. Based on knowledge of how they will change and adapt under current pressures and global challenges from climate, land use, and societal changes, appropriate protection can be built. The ecohydrological characterization of KGDEs of Slovenian Dinaric karst presented here can serve as a pilot study for other karst regions with high biodiversity.

How to cite: Ravbar, N. and Pipan, T.: Ecohydrological characterization of the karst groundwater dependent ecosystems of the Dinaric karst in Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3675, https://doi.org/10.5194/egusphere-egu22-3675, 2022.

Groundwater recharge of mountain aquifer requires detailed knowledge of the hydrologic system and adequate monitoring and modeling methods to determine water amount and water quality evolution. Mountain aquifers are well known of their highly complex lithologic structure and surface morphology. These become more significant in dry climate regions (<300 mm rainfall/year) which are characterized by erratic rain pattern and extreme deep thickness unsaturated zone.

In this study we monitor the isotopic and geo-chemical evolution affecting the composition of the unsaturated porewater during deep infiltration, from surface to depth that is not affected from evaporation. The geo-chemical processes were characterized related to land surface morphology and climate conditions.

The research setup includes instrumentation of first-order stream which is characterized by two main typical geomorphologic setting: rocky terrain and deep soil along the stream channel. Each plot was instrumented with a monitoring setup that include a meteorological station and Vadose Zone Monitoring System (VMS) that enables continuous water content measurement and collection of unsaturated porewater from the vadose zone.

Fast increases in water content and arrival of depleted δ¹⁸O (VSMOW) reveal quick and deep infiltration of rainwater during storm events, while enriched δ¹⁸O arrival indicates slower infiltration of water that is exposed to evaporation. In addition, the geo-chemical processes exhibited depletion in δ¹³C (PDB) of rainwater during the infiltration (-19 to -11 ‰) which indicates on dominant of biogenic activities and relatively low rock-water interactions. Major elements correlation network expresses the contribution of dust and rain to the rock evolution across the water flow path.

The study results clearly exhibited different infiltration rates in each site. Fast infiltration at the rocky terrain due to rock outcrops on the surface create funnels for collecting the local runoff and delivering it into high permeability fractured zones where the water penetrates directly to the deep sections. In contrast, the bare soil areas such as hilltops or man-made terraces in streams with highly developed soil cross-section, reveal limited infiltration. Also, the annual rainfall pattern impacts the geochemical process and finally impacts the groundwater quantity and quality.

How to cite: Letz, O., Siebner, H., Avrahamov, N., Egozi, R., and Dahan, O.: Isotopic and geochemical evolution of rainwater percolating through the rocky outcrops: Judaea mountain case study.  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3926, https://doi.org/10.5194/egusphere-egu22-3926, 2022.

A hydrological model is a simplified representation of the water cycle. A model helps people to understand, predict, and manage water resources. The scope and complexity of the model depend on the modelling goal, availability of required inputs, and computational resources. A wide variety of different hydrologic models exist, which are from simplistic to complex.  Complex models are often computationally very expensive, hampering robust calibration, sensitivity evaluation, and uncertainty analysis. The purpose of this study was to develop a parsimonious distributed land surface-subsurface hydrological model.

The parsimonious model we are developing is a combination of the land surface model V2Karst and a groundwater model that adopts a two-dimensional representation of groundwater flow. V2Karst is a large-scale model for simulating land surface hydrological processes. . The coupled hydrological model can make the simulation steps clearer and meet the simplifying assumptions in some specific demand situations. The model will be useful for robust model calibration, sensitivity tests, and uncertainty analysis.

How to cite: Liu, H. and Rahman, M.: Developing a parsimonious distributed land surface-subsurface hydrological model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5759, https://doi.org/10.5194/egusphere-egu22-5759, 2022.

Starting from previous experiences in karst settings of southern Italy, and following the same procedure for the identification of dolines and endorheic basins (Zumpano et al., 2019; Pisano et al., 2020), we focus here our attention on several dolines characterizing the landscape of the Salento peninsula, in the southernmost part of Apulia. This region shows a typical low-topography karst, with elevations reaching maximum values of about 120 m a.s.l.. Thus, very often the main karst landforms, such as dolines and endorheic basins, are not clear to identify and present subdue connections with the adjoining land. Only at those sites where the doline was produced by collapse of the carbonate bedrock, or of the overburden above it, and where an active swallow hole is present, recognition appear more direct and straightforward.

Nevertheless, it is exactly this difficulty in identification of the karst landforms which makes particularly intriguing the research in the central sector of Salento. Further, in this area one of the two Apulian caves where speleologists are able to directly reach the water table, at depth of -60 m below the ground surface, is located: Vora Bosco opens within a narrow, W-E oriented, fissure in the topographic surface, and develops through the overall stratigraphic succession of Salento, from Quaternary deposits, to Plio-Pleistocene and Miocene calcarenites, down to the Cretaceous limestones, with these latter hosting the water table.

In a 240km²-wide area around Vora Bosco, a systematic survey was carried out aimed at identifying all dolines. The work started from analysis of historical sources, integrated by periodic field surveys, and by detailed analysis of multi-temporal sets of aerial photographs. Several tens of dolines and endorheic basins of variable size were mapped, and distinguished on the basis of the mechanism at the origin of their formation, according to the most widespread international classification (Gutierrez et al., 2014).

In addition to the genetic and morphometric characterization of the identified dolines and endorheic basins, these were also discriminated as concerns the role they play for hydraulic functioning: based upon the local situation, with particular regard to presence and thickness of residual deposits, and to the discontinuity networks in the rock mass, these sites may act as absorption point to recharge the karst aquifer, or as impervious areas which retard the downward infiltration of water.

References

Gutierrez F., Parise M., De Waele J. & Jourde H., 2014, A review on natural and human-induced geohazards and impacts in karst. Earth Science Reviews, vol. 138, p. 61-88.

Parise M., 2019, Sinkholes. In: White W.B., Culver D.C. & Pipan T. (Eds.), Encyclopedia of Caves. Academic Press, Elsevier, 3^rd edition, ISBN 978-0-12-814124-3, p. 934-942.

Pisano L., Zumpano V., Liso I.S. & Parise M., 2020, Geomorphological and structural characterization of the “Canale di Pirro” polje, Apulia (Southern Italy). Journal of Maps, vol. 16 (2), p. 479-487.

Zumpano V., Pisano L. & Parise M., 2019, An integrated framework to identify and analyze karst sinkholes. Geomorphology, vol. 332, p. 213-225.

How to cite: Pisano, L., Francesca, L., Liso, I. S., and Parise, M.: Geomorphological analysis of dolines in a low-topography karst, and considerations about their hydraulic functioning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2372, https://doi.org/10.5194/egusphere-egu22-2372, 2022.

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. Furthermore the matrix and conduits compartments respond to different flow physics that can be approached by considering Darcy flow and pipe flow, respectively. Thus, one needs to employ a multi-physics model, an inversion method able to capture the properties contrast, and also to 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 250 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 11 wells and incorporating a periodic response due to a daily pumping at the aquifers spring were thus considered to identify the location of the conduit network. The periodic responses can provide connectivity information between wells in the inversion process, while non-periodic responses permit to better assess the large-scale property values of the whole aquifer. 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 solving Darcy flows. However, pressure data alone remain limited to characterize the fast flows that can occur in the conduits network. Thus, the flow velocities in the preferential flow paths located with the pressure data are then reconstituted by inverting a set of different tracer tests responses at the Lez spring, considering this time a pipe flow physics in the model.

How to cite: Fischer, P., Jourde, H., and Leonardi, V.: Large-scale spatial reconstitution of pressure and tracer tests responses in a karst aquifer (Lez aquifer, France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2628, https://doi.org/10.5194/egusphere-egu22-2628, 2022.

Poljes are flat closed depressions in karst terrains that are prone to regular flooding. The strongest floods can be several meters high and persist for months, making significant damages in infrastructures. To predict how climate change might affect the occurrence, amplitude and duration of the flood, a better understanding of the flooding dynamics is necessary. Among others, the computation of the water balance is a prerequisite. This method allows assessing when the polje will begin to flood, and gives information on the maximum water level potentially reached. However, this technique encounters the difficulty that a notable part of the inflow entering in poljes is generally ungauged, while it is challenging to quantify the outflow. This is because numerous springs and ponors activate only temporary with the rise of the water level. Moreover, many poljes are generally poorly monitored due to financial reasons. This work aims to see whether these drawbacks can be overcome. To this end, a typical Dinaric polje recharged by a combination of allogenic inflow and a rise of the regional groundwater level is equipped with a network of several measuring stations installed over its surface and in the nearby water-active caves. Combining an accurate Lidar of the surface with recorded water levels and inflow of the main two springs made possible to evaluate the polje flooding dynamics and to characterize its water balance. The method is able to quantify the polje total inflow, while an estimation of the outflow is presented. Then, the main ungauged signals affecting flooding are identified and separated. These values are used as input and calibration data in a numerical model aiming to reproduce the flood dynamics of the polje and its surrounding aquifer. Modelling results validate both water balance and conceptual hydrogeological model, and justify the significance of installing a network of several hydrological stations to monitor the poljes. The method can be applied to other poljes flooding in a complex way of superimposed input and output signals.

How to cite: Mayaud, C., Kogovšek, B., Gabrovšek, F., Blatnik, M., Petrič, M., and Ravbar, N.: Assessment of the water balance of a Dinaric karst polje (Planinsko Polje, Slovenia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4866, https://doi.org/10.5194/egusphere-egu22-4866, 2022.

The Nadìa spring is the second largest tapped spring in the Emilia Romagna Region (northern Italy), representing a strategic local source of drinking water, also in the perspective of future global changes. The spring flowrate ranges between 65 l/s in the recharge season and 45 l/s at the end of the low-flow season, when most of the other tapped springs in the region have flowrates lower than 5 l/s. Geological, geomorphological, hydrological and geochemical investigations were carried out in the spring watershed to unravel the factors causing this peculiarly high discharge. The spring arises at the base of a calcarenitic fractured aquifer (Pantano Formation, upper Burdigalian-lower Langhian) underlain by lower permeability units. Karst dissolution along structural discontinuities in the Pantano Formation has been suggested in the past as a possibility to account for the aquifer high permeability resulting in the high spring discharge. A continuous monitoring of the spring flowrate, temperature, electric conductivity and pH was conducted during the 2020-2021 hydrologic year. Hydrographs and chemographs indicated atypical karst flow dynamics. The time to halve the peak-discharge of the spring is between 20 and 50 days, lower than that of most springs of the Northern Apennines (> 50 days). This implies a higher average aquifer flow rate (around 10 m/day) compared to that typical of arenitic or turbiditic aquifers (around 1 m/day). Spring water samples collected once to twice a year since 2011 for the analysis of major ions revealed an obvious calcium-bicarbonate hydrochemistry that is consistent with the hypothesis of karst dissolution. However, the chemical variability over time expected in a karst system due to the drainage of different groundwater fractions (newly infiltrated vs. older groundwater) was not observed. Instead, the water chemical composition was exceptionally constant over time, suggesting that drainage occurs from a large, homogeneous reservoir. Water stable isotopes have been analyzed in 2021 revealing a composition close to that of the local winter precipitations and suggesting exceptional stability of the spring water composition over different seasons. An 80 m deep borehole has been drilled in the Pantano Formation 7 km away from the spring, documenting the occurrence of fractures with decimetric apertures as deep as 60-70 m below ground surface, which may be interpreted as the result of karst dissolution. In addition to the debatable karst aquifer hypothesis, geomorphological observations indicate the occurrence of depressed areas, of likely tectonic origin, in the aquifer overlying the spring, which may provide a favorable setting for concentrated infiltration and groundwater recharge. However, the hypothesis of concentrated recharge is in apparent contrast to the abovementioned stability of spring water chemical composition over time. A volume of the aquifer representing a reasonable reservoir for the spring has been identified based on spring flow recession analysis and a geo-structural model of the Pantano outcrop up-gradient to the spring. The structural-stratigraphic setting of the hypothesized reservoir includes the occurrence of fault-related fractures that cross-cut the low-dipping bedding of the calcarenites, possibly enhancing the local permeability and the drainage towards the Nadìa spring.

How to cite: Filippini, M., Segadelli, S., Failoni, M., Stendardi, F., Vignaroli, G., Viola, G., Stumpp, C., Dinelli, E., and Gargini, A.: Hydrogeological, geochemical and structural features of the aquifer feeding the Nadìa spring: an "oasis in the desert" of the Northern Apennines (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2297, https://doi.org/10.5194/egusphere-egu22-2297, 2022.

In karst catchments, groundwater is generally drained from recharge zones towards main outlets (springs). Karst systems develop mainly in limestone and have three different porosities which are the result of sedimentation, diagenesis, tectonics but also dissolution that generate the conduits.  Continuous monitoring at high temporal resolutions is largely used to characterize the hydrodynamic behavior and variability of karst systems hydrological functioning Hydrologic models are used in order to better asses the functioning of karst systems but can also help identifying the impact of global change on water resources. Though these models require an adequate representation of main heterogeneities and processes, the heterogeneity of karst systems is often poorly characterized by available data. For these reasons, most of hydrological models considered for the understanding of karst systems hydrodynamic are lumped parameters models. In this study, we simulate precipitation-discharge relationship as a function of different karst geometries and topologies using two dimensional distributed models. We then investigate the relationship between the hydrodynamic response (e.g. flow rate at discharge point) and topology of the karst conduit network. Lumped approaches are later on compared to distributed models in term of predicting hydrodynamic response to precipitation.

How to cite: Aliouache, M., Jiang, C., and Jourde, H.: Relationship between the hydrodynamic response and the geometrical and topological properties of the karst conduit network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2785, https://doi.org/10.5194/egusphere-egu22-2785, 2022.

The Mediterranean coastline presents a high number of marine caves of different types. Marine caves are protected by the EU Habitats Directive (92/43/EEC - code 8330). Semi-dark and dark cave communities have been included in two Action Plans by UNEP-MAP-RAC/SPA (2008 and 2015 respectively) and are considered as sensitive reservoirs of biodiversity requiring protection. However, the scientific community still has scarce information about these important habitats, that are listed as Data Deficient.

The main reason for the lack of knowledge about marine caves is that they are very difficult to access and study. Lack of a breathable source, lack of light and a physical ceiling are the hazards characterising any underwater cave; specific locations can force cave divers to deal with limited visibility, restricted passages or high water flow. The number of individuals with the skills required to safely navigate such caves while carrying out research or scientific work is extremely limited.  

Our project aims at closing this information gap, by providing a methodology for surveying underwater caves. Our main study area is the Gulf of Orosei, Sardinia Italy. We count essentially on two important elements: 

• citizen science - over the years, we gained a lot of experience in coordinating groups of volunteers, working with professional scientists to achieve common goals. All our projects and missions are carried out with the precious involvement of skilled individuals that perform specific tasks.
• advanced technology - technology is essential to gather information about underwater environments in general, and caves in particular. Photogrammetry is the most detailed methodology to create a multidimensional cave model. Thanks to the precision and the very realistic representation of the environment, these models are ideal for both scientific and dissemination purposes. Photogrammetry relies on the connection between polygon line survey and photographic data. We can split the procedure in three parts: data collection (survey and media), software processing and model refinement. Once the model is finished, there are many useful applications that can be considered. For scientific purpose, the model can be geo-referenced and can be scaled and calibrated by a variety of methods to allow measurements and further analysis of the cave environment and surrounding landscape. For publication purposes to the wider public, the model can be exported to graphical design or ‘animated’ with VR and gaming softwares. Annotating the model and any artifact inside it with information can entertain and educate the visitors in virtual reality.

Possibilities are endless and to fully master the flow from data capture inside the cave down to an interactive virtual representation or a scientific survey, a lot of expertise and knowledge is required and a strong cooperation between cave divers and researchers.

References:
Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000;
Directive 2006/118/EC of the European Parliament and of the Council of 12 December 2006;
Global Wetland Outlook: State of the World’s Wetlands and their Services to People. Gland, Switzerland: Ramsar Convention Secretariat (2018);
European Red List of Habitats (ISBN 978-92-79-61586-3; ISBN 978-92-79-61588-7).

How to cite: Marroni, L., Brandt, P., Gaertner, P., and Marassich, A.: Citizen science and 3D modeling to study and protect Mediterranean marine caves: a real application in the caves of the Gulf of Orosei (Sardinia, Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3817, https://doi.org/10.5194/egusphere-egu22-3817, 2022.

In coastal karst lands, due to difference in permeability among contiguous strata, emergence of springs may occur inland or as submarine springs, as in the Gulf of Taranto (Italy), marking the S limit of Murge, the largest karst sub-region in Apulia. Groundwater from N-NW feed some inland springs, sometimes originating small rivers, with Tara as the main significant. In addition to surface waters, submarine springs are present within the gulf, namely in Mar Piccolo of Taranto, an over 20 km² wide basin (10-14m depth) consisting of two bays with elliptical shape, connected through a channel. In the N sectors of the bays 34 submarine springs have been identified. Locally called citri, a word of Greek origin, deriving from history of Taranto (founded as a Greek colony), they work as thermal regulators for the water temperature, allowing extensive development of mussel farming. The groundwater emission sites are characterized by funnel-shaped morphology with a circular profile at the sea surface. In the past, attempts were done to tap these waters (Cotecchia et al., 1990), but technical and engineering problems, brought to abandon such activities.

In the Murge district the Cretaceous limestone aquifer is covered by Plio-Pleistocene calcarenites, clays and terraced marine deposits, with secondary porous aquifers flowing within these latter. Origin of the citri is related to surface dismantling and erosion of the cover, and to emergence of the confined water hosted in the limestones. In most of the cases, it comes out in wide areas, without a clear karst conduit. Among the few caves explorable by man, there is Citro Galeso, at the W bay: with a diameter of 20 m, and 18m depth, it has discharge of 0,750 m³/s.

Inventoried since the first half of the XX century (Cerruti, 1938), only recently the distribution of citri was studied in detail (Valenzano et al., 2018). The largest spring (Saint Cataldo’s eyes) is located just outside the two bays, in Mar Grande: 200x300 m-wide, it consists of two cavities, reaching depth of 48 and 52 m, respectively, below sea level, and deepening for 20 additional meters.

To improve the hydrogeological knowledge of the area, we are carrying out a variety of scientific activities, starting from exploration and surveying of accessible springs. A significant role is being attributed to the study of the cave systems, as regard their distribution and pattern network. As outflow yield and flow velocity data are not yet available for all citri, some measurements will be done at this aim. In addition, water samplings will be taken for characterizing the chemical constituents, and for assessing the presence and nature of pollutants.

References

Cerruti A., 1938, Le sorgenti sottomarine (Citri) del Mar Grande e Mar Piccolo di Taranto. Ann. Ist. Sup. Navale, Napoli, 7.

Cotecchia et al., 1990, Hydrogeological conditions and field monitoring of Galeso submarine spring in the Mar Piccolo of Taranto (southern Italy). Proc. 11^th SWIM, 171-208.

Valenzano et al., 2018, Holocene Morpho-sedimentary evolution of Mar Piccolo basin (Taranto, Southern Italy). Geogr. Fis. Dinam. Quat., 41, 119-135.

How to cite: Marassich, A., Bertelmann, S., D'Onghia, F. M., Liso, I. S., and Parise, M.: Submarine springs in the Gulf of Taranto (Italy): geology, hydrogeology and cave diving explorations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4232, https://doi.org/10.5194/egusphere-egu22-4232, 2022.

Grotta delle Corvine is a submarine cave which opens along the Ionian coast of Apulia (southern Italy), in the spectacular landscape of the Natural Reserve of Porto Selvaggio. The cave takes its name from a species of fish (corvine = Sciaena umbra), which accompanied the cave divers during the first phases of exploration. As concerns its origin, Grotta delle Corvine represents the remaining part of an original karst conduit which development was controlled by the fault systems that shaped the Ionian coastline in the time span from Miocene to Pliocene, and that was later invaded by the sea due to the Mediterranean eustatic movements during the Quaternary. It is definitely the largest among the many submarine caves in the area: with a 8mt-wide and 4mt-high access, opening at -12 m below the sea level, it is widely decorated by speleothems, reaches a total development of some 50 meters, and is characterized by two aerated rooms in its final sector. These latter are two large air sacks, with the widest being over 8mt-large and about 12mt-high, without communication with the outside. The cave hosts a remarkable biodiversity, as testified by a variety of biological studies which documented the presence of 195 species, including 2 new ones. In addition to biology, several other issues are of scientific interest in the cave: these include the “fog effect” related to the wave action and to condensation of the water vapor due to pressure changes, and the presence of cold and hot springs in different sectors of the karst system, among the others.

Recently, research activities have been started by a group of multi-disciplinary scientists and cavers, aimed at exploring some aspects of scientific interest at Grotta delle Corvine, and at documenting them. In detail, an experiment for measuring the amount of radon in the innermost room of the system has been performed by leaving for 15 days in the cave a measure station with plastic nuclear track detectors (CR39 and Makrofol) in a diffusion chamber. The sensors were dislocated at different heights (from the sea level to 6 mt). Analysis of the CR39 detectors showed uniform radon values over 4000 bequerel/m³ for all sensors, regardless of the height position. Analysis of the Makrofol sheets, on the other hand, is still ongoing.

The activities performed so far highlighted the importance of Grotta delle Corvine for many aspects of science: beside the marine biology, already extensively studied but still with a high potential to explore, further geological, hydrogeological and physical investigations are worth to be undertaken at the site. For these reasons, in the next future we plan to continue these experiments aimed at collecting data about the physics of the underground climate, and to add observations and water samplings to define the main hydrogeological characters of the karst system, and to check the main variations in temperature and salinity of the waters, in particular at the two identified springs.

How to cite: Parise, M., Chiarusi, T., Esposito, M., Onorato, M., Onorato, R., Orsini, S., Palmisano, G., and Poto, M.: Experimental studies at a coastal cave in the Apulian karst, southern Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1906, https://doi.org/10.5194/egusphere-egu22-1906, 2022.

Karst landscapes are perceived as sensible environments due to soluble rocks (limestone, marble, dolomite, etc.) being the predominant features. The dissolution process in karstic structures poses serious multiple hazards to the communities on which they are built. Sinkholes and ground subsidence are the main geological hazards from these areas causing damage to lives and livelihoods. Meteorological events such as heavy rainfall leading to flooding play an important aggravating factor for these areas which often can collide with the special geological situation resulting in a cascade of hazards (flooding and sinkhole collapse). Consequently, such multi-hazard-forming environments like karst regions present a need to better understand the complex interrelationship of water in the form of flooding and underground cavity collapses. Yet, till the present, our approaches to these hazardous events have been often fragmented and inadequate. Moreover, with climate change having a significant impact on Earth, a change in hydrological processes followed by increasing dissolution of limestone, which may lead to more flooding and sinkhole occurrences, can be predicted in the immediate future. Therefore, research on interrelated hazards will be imperative in order to set priorities for complex natural events. While numerous research works have made attempts to study sinkholes and their contributing factors, to date if not any, few studies have perceived and assessed flooding and sinkhole as a multi-hazard event. Since globally, a shift from single to multi-hazard assessment is being encouraged by international risk communities, the present study is to provide new insight towards flooding and sinkholes assessment emphasising multi-hazard approaches. This critical review aims at understanding the current state of sinkhole-related researches, reviewing grey- and peer-review literature. Afterwards, the studies are classified into seven research themes (Morphology, Flood impacts on karst, Monitoring and prediction, Hazard & risk assessment, Multi-hazard-mapping modelling, Mitigation measure, and Others), demonstrating the more favourite research directions and research gap in the field of sinkhole hazard assessment. The results highlight the importance of the integrated multi-hazard assessment in the areas affected by both flooding and karst hazards and show that so far sinkhole risk assessment (70 articles – 35%) followed by sinkhole morphology (63 articles – 31,5%) have been the most popular research subject within the discipline. This research aids future research to bridge the existing gap towards improving mitigation planning and helping policy and decision-makers in their inclusion of multi-hazard interactions in municipal policies and approaches.

How to cite: Soltanpour, H., Serrhini, K., Serrano, J., and Noury, G.: A Critical Research Gap Study of Sinkhole Hazard Assessments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6036, https://doi.org/10.5194/egusphere-egu22-6036, 2022.

The Grotte della Poesia karst system is a complex of caves, sinkholes and submerged galleries, located along the Adriatic side of southern Apulia (Italy). In detail, the system consists of two main collapse sinkholes (Grotta della Poesia Grande and Piccola), connected through sumps with an intervening cave, and linked to the sea on two sides. Sinkhole development was strongly favoured by hyperkarst processes due to intermixing between fresh and salt water, and by the resulting increased aggressivity on carbonate rocks. The overall system is within the remarkable archaeological site of Roca, which incorporates remains from late Bronze to Medieval age (Scarano 2010). In particular, Grotta della Poesia Piccola hosts along its walls thousands of Messapian inscriptions dating back to IV-II centuries B.C., which are still the object of study by archaeologists.

Local stratigraphy in the area consists of weak, laminated calcilutites and fine calcarenites alternated to coarser macro-fossiliferous and bioturbated calcarenites (Middle-Upp. Pliocene). Differences in permeability among the layers originate a multi-layered water table. To this, name of the caves has probably to be related, since the word poesiacomes from the local dialect (in turn, from ancient Greek), to indicate a spring or water emergence (Parise et al. 2003). A spring would therefore have been present within Grotta della Poesia Piccola, but at present is not visible anymore, probably due to lowering of the water table.

Tectonically, wide folds with N 150 E axes (about parallel to the coast) characterize the area. They determine the presence inland of a wide marshland (Tamari), that has been interpreted as the inner and protected harbour for the ancient town of Roca.

The Adriatic coastal landscape is characterized by a number of marine terraces resulting from the combined action of regional uplift and glacio-eustatic sea level changes. The coastline is very articulated, with 10-15m high cliffs, intensely affected by slope instabilities (Delle Rose and Parise 2004; Lollino et al. 2021). Within this geological setting, we are carrying out detailed speleological and diving explorations aimed at fully surveying the intricate system of caves (in both aerated and flooded conditions), as a mandatory step in order to identify the sites most susceptible to rock instabilities. Since the site is highly touristic, it is crucial to recognize the likely hazards, and to properly delimit the most dangerous areas. The surveys are also going to be used to better understand the hydrogeological situation, and to verify the possibility of presence of submarine springs in the coastal area and its surroundings.

References

Delle Rose M. & Parise M., 2004, Slope instability along the Adriatic coast of Salento, southern Italy. Proc. IX Int. Symp. Landslides, 1, 399-404.

Lollino et al., 2021, Multi-scale approach to analyse the evolution of soft rock coastal cliffs and role of controlling factors: a case study in South-Eastern Italy. Geomatics 12 (1), 1058-1081,

Parise et al., 2003, Karst terminology in Apulia (southern Italy). Acta Carsologica 32, 65-82.

Scarano T., 2010, Roca. Le fortificazioni della media età del Bronzo. Ann. Scuola Normale Sup. Pisa, s. 5, 2 (2), 151-204.

How to cite: Bertelmann, S., Marassich, A., Liso, I. S., and Parise, M.: Morphology and hydrogeology of a complex sinkhole system in a remarkable archaeological site along the Adriatic coastline (Apulia, S Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4715, https://doi.org/10.5194/egusphere-egu22-4715, 2022.

The South Franconian Alb is a well known karst area in Southern Germany. It comprises mainly of a slightly inclined plateau intersected by a few rivers and numberless dry valleys. Main rocks are limestones and dolomites of Jurassic Age.

Numerous sinkholes occur within the area. Unfortunately, till now the data collection is fragmentary done for the whole area. Consequently, the sinkhole distribution is incomplete and very heterogenously spread. Nevertheless, to gain insights into the background of sinkhole distribution and the associated geologic, geomorphic and land use conditions the available data were compiled. Different local archives, the available geologic and topographic maps of the South Franconian Alb were searched for sinkhole informations, on the other hand digital elevation models from selected areas were detected for hollow shapes or depressions to estimate the maximum quantity of possible dolines. For all detected objects both verified sinkholes and unclassified depressions the geomorphological environment, cover deposit, host rock, rock facies, stratigraphy and land use were listed.

First results show great discrepancies for the sinkhole distribution related to land use. More than 90% of the detected objects are located within forests although forested areas cover only 30-50% of the South Franconian Alb. Thus, most of former sinkholes were destroyed by agricultural or other activities. Furthermore, historic mining activities (stone-age chert mining, historic mining pit areas for iron mining, small local quarries) have also changed the sinkhole distribution. Due to such anthropogenic overprinting of the landscape an automatic detection of dolines from digital elevation models requires a very critical assessment.

Geologically, sinkhole occurrences are closely related to the host rock distribution or rock facies. About 60% of sinkholes are hosted by dolomites, massive reefal or thick-bedded limestones whereas dolines within platy or thin-bedded rocks occur more rare.

How to cite: Trappe, M. and Hein, M.: Relations between geomorphic and geologic framework and sinkhole distribution of the South Franconian Alb, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6384, https://doi.org/10.5194/egusphere-egu22-6384, 2022.

Studies of karst denudation rates are great approach to provide an insight to karst landscape development. Traditionally, dissolution of carbonate rocks is considered to be the main process governing carbonate weathering, other processes should not be overlooked. Here we present research done in the North Dalmatian Plain, a carbonate erosive surface located in the Dinaric karst region. Although study site is composed of two different carbonate lithologies having different weathering style, there is no evident lithological impact on the topography of erosive surface. Analyses of ³⁶Cl were performed in ten proximal samples from both lithologies resulted in denudation rates from 14.7 to 22.7 m/Ma. Since no statistical significance was found between samples from different lithologies (all samples belong to a single normal population) having same geomorphological context and climate features, variable denudation rates are attributed to local differences in denudation.  

In the study site there are no large outstanding rock residuals, or deep soil patches, thus in order to maintain the levelled erosive surface local differential denudation rates have to vary with time. We hypothesize that lichens and pedogenic carbonates have a significant role in modulating local differences in denudation rates. Our study shows that even at outcrop scale, differences in local denudation rate can be significant and study of large set of samples is preferred to properly characterize the overall denudation rates of carbonate surfaces. Thus, the long-term denudation rate of the North Dalmatian Plain, including local variability, is 18.55 ±0.79 m/Ma. Despite classical studies on karst terrains assume that dissolution is the main process responsible for denudation of these landscapes, our research highlights the importance of physical weathering in combination with dissolution of carbonates as main controls on the denudation of karst landscapes.

Acknowledgements: This research is a part of the research project “Inter-comparison of karst denudation measurement methods” (KADEME) (IP-2018-01-7080) financed by Croatian Science Foundation.

How to cite: Krklec, K., Braucher, R., Perica, D., and Domínguez-Villar, D.: Variability of long-term denudation rates measured by 36Cl analyses on a karst levelled surface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2041, https://doi.org/10.5194/egusphere-egu22-2041, 2022.

Solution pipes are vertical or near-vertical cylindrical tubes occurring within the vadose zone of limestones during the eogenetic stage of their diagenesis, characterised by high permeability and matrix porosity (e.g., Quaternary calcarenites). The pipes vary in size and can be wider than 2 m and deeper than 100 m; depths between 1 m and 4 m and diameters between 20 cm and 80 cm are most common. The radius of a single pipe within a homogeneous rock is usually either constant or tapers slightly downwards. Some of the pipes, particularly the ones in coastal areas in the Mediterranean climate, have well cemented calcrete rims. These rims are usually less porous and more resistant to weathering than the host rock, and may consequently stand out after erosion of the surrounding material.

The unifying process responsible for their formation is a focused vertical flow of water, which depends primarily on sufficient water supply – e.g., rainfall. A detailed understanding of the formation of solution pipes can therefore provide us with a tool to estimate the climatic conditions prevailing at the time of their formation based on the density and shape of the pipes. The first important component here is the distribution of pipes. In addition to manual mapping and measuring, a combined photogrammetry and 3D laser scanning can be used to record their distribution on a larger scale. However, the machine learning algorithm needs to be developed to automatically detect their appearance and radius. This is challenging because pipes can appear in various shapes: as flat circles filled with sediment (with no relief on the surface), as holes, or as elevated cylindrical pinnacles due to erosion of the surrounding bedrock. In addition, their visibility is often limited due to sediment and vegetation cover. Cliff faces offer a glimpse of their interior, but their true spatial distribution is unknown. In contrast the eroded coastal platform shores provide a horizontal cross-section and distribution, but their vertical morphology and their depths are unknown. Similar situation appears in anthropogenic outcrops such as road cuttings and quarries. Promising methods for non-invasive mapping of the pipes are ground penetrating radar (GPR), magnetic gradiometer and electrical resistivity tomography (ERT), but with certain limitations, mainly related to unclear detection of the depths of the pipes, and the reliability of the mineralogy, geochemistry and texture of the fill of the pipes.

The second important component is the morphology of the pipes. In order to properly estimate their shapes, especially their depths, a denudation factor must be considered. This can be partially assessed with numerical modelling of reactive-infiltration instability, which incorporates the lowering of the landscape during the formation of the pipes. However, this remains limited to the accuracy of dating of solution pipe formation, and estimations of post-formation landscape denudation.

ACKNOWLEDGEMENT: We acknowledge the financial support of Slovenian Research Agency (P6-0101; I0-0031; N1-0162; J6-3142).

How to cite: Lipar, M., Szymczak, P., Ciglič, R., Prakash Sharma, R., Zorn, M., Stepišnik, U., and Ferk, M.: Challenges in characterisation and mapping of solution pipes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1619, https://doi.org/10.5194/egusphere-egu22-1619, 2022.

Carbonate rock formations are inherently extremely anisotropic rock masses, due to the simultaneous presence of well-defined stratabounds discontinuities and wide-spread fracturing. When karst processes occur, they can obliterate or widen the aperture of the original discontinuity networks, adding further complexity to the system. In karst territories the carbonate rock masses host important freshwater resources, which are often the only available water supply for local communities. In order to protect karst groundwater, it is imperative to properly evaluate the underground flow dynamics. To do so, we need to build detailed datasets of the three-dimensional (3D) spatial distribution of discontinuity networks, which serve as primary input for numerical simulation of fluid movement in the underground water reservoirs. Field structural-geological surveys are common means for obtaining the necessary information regarding the spatial distribution of the discontinuity networks. However, this approach is highly time-consuming and struggles to provide sufficient data to build robust statistics.

In recent years, the combination of new technologies for data acquisition (e.g. drones and high precision cameras) and new freely-available softwares, such as DigiFract (Hardebol and Bertotti, 2013), FracPaQ (Helay et al., 2017), and NetworkGT (Nyberg et al., 2018) are bridging the gap between fast and reliable fracture data acquisition and analyses. Through the use of these techniques, we are now able to directly work on digital images taken from the outcrops as input, and to produce outputs which provide robust statistics about the discontinuities within the analysed medium.

In this contribution, we present research aiming at full characterization of the rock mass discontinuities within a study area in Apulia Region (Southern Italy). Specifically, we studied the Canale di Pirro polje where the deepest Apulian cave, named Inghiottitoio di Masseria Rotolo, is located. The cave opens at 300 m a.s.l. and reaches the water table at about -260m depth below the topographic surface. By means of combining detailed photogrammetric survey and the use of the FracPaQ software toolbox, we were able to analyse in details the discontinuity network exposed at the outcrops, and consequently to use this information for evaluating how the network influences the underground flow direction and its velocity.  The statistical and spatial analysis of the discontinuity network, together with data derived from both the surface and underground, with specific surveys performed within the cave, allowed to present the first considerations about the groundwater flow in the surroundings of the karst system, useful to implement a numerical model heavily based upon direct observations from surface and underground karst areas.

REFERENCES

Hardebol, N. J., & Bertotti, G. (2013). DigiFract: A software and data model implementation for flexible acquisition and processing of fracture data from outcrops. Computers & Geosciences, 54, 326-336.

Healy D., Rizzo R.E., Cornwell D.G., Farrell N.J.C., Watkins H., Timms N.E, Gomez- Rivas E. and Smith M. (2017). FracPaQ: A MATLAB^TM toolbox for the quantification of fracture patterns. J. Structural Geology, 95, 1-16. http://dx.doi.org/10.1016/j.jsg.2016.12.003.

Nyberg, B., Nixon, C. W., & Sanderson, D. J. (2018). NetworkGT: A GIS tool for geometric and topological analysis of two-dimensional fracture networks. Geosphere, 14(4), 1618-1634.

How to cite: Liso, I. S., Cherubini, C., Parise, M., and Rizzo, R. E.: Improvement of structural data by means of FracPaQ software to implement groundwater flow model in karst settings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1913, https://doi.org/10.5194/egusphere-egu22-1913, 2022.

We develop methods for qualitative and quantitative assessment of the transformation of pore geometry of a rock as a result of karstification. We then apply these tools to characterize dissolution-induced changes in Miocene limestone samples collected from a quarry located near Smerdyna (Poland), where intense epikarst development is observed, with the formation of hundreds of solution pipes. Partially dissolved samples collected in the immediate vicinity of the pipes are compared with undissolved samples collected several meters away.

For both types of samples 26 micron resolution grayscale X-ray scans has been performed, and cubical regions of interest of size 506^3 voxels, which corresponds to (13,156 mm)^3, have been studied. Images have been segmented by tuning the grayscale threshold to match the experimentally measured porosity values of respective samples. Additionally, based on the segmented tomograph of undissolved sample another geometry was numerically created in order to mimic a uniform dissolution of the rock up to a porosity value equal to that of the dissolved sample.

The irregular geometry of the pore space, vast majority of which forms a single connected component, can be conveniently characterized by a local thickness function,  which corresponds to a diameter of the largest sphere that fits within the pore space and contains a given point. A similar measure can be introduced for the solid component (grains). We have compared thickness distributions  of undissolved and dissolved sample as well as numerically generated uniformly dissolved sample. Such a comparison allowed us to quantify the extent of homogeneity of the natural karstification process.

To further characterize pore geometry, we have calculated the ellipsoid factor, which – based on the axis lengths of the fitted ellipsoids – can be used to characterize how prolate or oblate the pore space locally is. Next, we have used (modified) Flinn diagram to quantify differences between undissolved, numerically eroded and naturally dissolved samples, especially those indicating pore merging and inhomogeneous dissolution.

The above analysis is complemented by calculation of connectivity density – a topological measure of the degree to which a structure is multiply connected. Values obtained for undissolved, numerically dissolved and naturally dissolved samples indicate on ‘excessive’ reduction of interconnections during natural dissolution, which may be understood on the basis of high degree of pore merging due to inhomogeneous dissolution.

Both methods: (generalized) thickness analysis and connectivity calculation emphasise the role of merging of pores and inhomogeneous dissolution in the process of natural dissolution for the analyzed  samples.

How to cite: Białecki, M., Sharma, R. P., Cooper, M. P., and Szymczak, P.: Comparative study of undissolved and karstified limestone based on microtomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5229, https://doi.org/10.5194/egusphere-egu22-5229, 2022.

We built 11 lab-scale dual-conduit structures by varying the apertures of the two conduits and we conduct solute transport experiments consisting of step tracing. We investigated how the transport process can be influenced by the following two factors: flow rate and aperture width of both conduits. We found that, as the flow rate increases, the dual-conduit structures more likely presents a breakthrough curve (BTC) with double-peak effect. When the shorter conduit has smaller aperture than the longer conduit, the dual-conduit structure may lead to either single-peaked BTCs or to dual-peaked BTCs with a much lower early peak. When the shorter conduit has larger aperture than the longer conduit, the dual-conduit structure may lead to double-peaked BTCs or to single-peaked BTCs with a bump on the falling limb.

We then compared the ability of three different numerical models in fitting the experimental BTCs: Weighted Sum Advection–Dispersion Equation (WSADE), Mobile Immobile Model (MIM), and Dual Region Mobile Immobile Model (DRMIM). MIM does not reproduce the double-peaked or bump-tailed BTCs, but it captures the overall shape of the experimental curves. The WSADE reproduces some of the double-peaked BTCs except the experiment of 4-6, 200 rpm. The DRMIM exhibits better performance than the other two models, and it captures the observed behaviors of all the experimental BTCs: the second peak, the bump, and the tailing. We finally showed that parameter estimation of the DRMIM model can be improved by restricting the contrast between the parameter pairs: u_m1 and u_m2, D_m1 and D_m2, k₁ and k₂, w_m1 and w_m2.

How to cite: Wang, C., Majdalani, S., Guinot, V., and Jourde, H.: Solute transport in dual conduit structure: effects of aperture and flow rate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5213, https://doi.org/10.5194/egusphere-egu22-5213, 2022.

Karst aquifers provide considerable groundwater resources and supplies in many countries of the world. Karst systems exhibit complex spatial distributions of conduits, caves and vugs, but speleogenesis modeling remains very limited at aquifer scale. Early stage of wormholes development generally controls the final pattern of karst due to the positive feedback loop. In this study, we analyze the incipient karst generation in 3D jointed carbonate rocks with multiple horizontal layers, on the basis of numerical simulations. First, the fracture networks are generated while considering pseudo-mechanical rules for the nucleation and propagation of joints. Then, we analyze the impact of aperture configurations and flow boundary conditions on the dissolution patterns in such a 3D joint layered rock based on a developed hydro-chemical model. Preliminary results show that, for uniform apertures and horizontal flow, similar dissolution patterns are obtained whatever the flow orientations; bedding planes control and favor the tree-shape conduit networks while the joints promote the vertical spread. Results also show that karstification processes are dominated by the joint network structure and are significantly confined in individual layers when the aperture of bedding plane is lower than that of the joints. Changing flow boundary conditions (i.e. recharge and discharge from localized points instead of domain borders) tends also to induce different dissolution patterns. Compared to dissolution in a 2D fracture networks, these 3D reactive transport simulations further reveal the interaction of joint networks among different layers. This study has an important implication on understanding the initiation of different types of incipient karst patterns observed in nature.

How to cite: Jiang, C., Wang, X., Jourde, H., and Aliouache, M.: Incipient karst generation in three-dimensional jointed layered rocks: influence of aperture configurations and flow boundary conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2789, https://doi.org/10.5194/egusphere-egu22-2789, 2022.

The hydraulic characterization of karst systems remains a high challenge given their heterogeneous nature and large range of hydrogeological properties. In this study, a methodological approach is presented that demonstrates to what extent the temporal variation of spring signals, such as discharge rate, dissolved constituents and water temperature can be employed to characterize the karst system and to differentiate the individual contributions of the different physical compartments, as well as to derive hydraulic properties of the individual compartments by integrated inverse modelling of the spring signals.

Each compartment – (i) surface zone, (ii) vadose zone, and (iii) phreatic zone – imposes a complex transformation of the input signals (e.g., flow rate, temperature, concentration) that are routed through the whole system. However, numerical approaches to reproduce flow and transport dynamics in karst systems often lack the physical representation of controlling processes (e.g., preferential flow dynamics in the vadose zone) and therefore struggle to provide unique solutions. Therefore, this study aims at the identification of parameter sensitivities and hence reduction of model uncertainty employing an integrated approach for the modeling of karst systems. In test scenarios artificial rain events deal as model input for the Precipitation Runoff Modeling System (PRMS) coupled to a dual-domain type vadose zone and discrete karst conduit network system embedded in a porous matrix within the phreatic zone in order to account for fast and slow flow components in each compartment. In the vadose zone diffuse flow through the porous matrix is modeled by standard bulk effective approaches (MODFLOW UZF or simple transfer functions) and rapid fluxes via preferential flow paths are represented by a source-responsive infiltration model governed by film flow dynamics. In the phreatic zone diffuse and conduit flow are represented by a discrete-continuum model (MODFLOW CFPv2). The model geometry is kept simple (i.e., one model layer and a single conduit connecting a single sinkhole with the spring) while vadose zone properties (e.g., overall thickness) and input signals are altered to focus on their impact on the flow signal and on the sensitivity of parameters.

How to cite: Noffz, T., Kordilla, J., Kavousi, A., Reimann, T., Liedl, R., and Sauter, M.: Integrated and process-based modeling of flow and transport in multi-compartment karst systems with thick vadose zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7502, https://doi.org/10.5194/egusphere-egu22-7502, 2022.

Performance criteria such as the mean squared error (MSE), the Nash-Sutcliffe efficiency (NSE) and the Kling-Glupta efficiency (KGE) are extensively used to calibrate hydrological models. In recent years, numerous authors have stressed the inherent limitations of squared-error based criteria such as MSE and NSE. As a result, KGE criterion is gaining in popularity and is being widely used for calibration and for assessment. KGE has been initially proposed to address the poor consideration of discharge variability by NSE, but it also helps to lower the impact of squared errors in highly variable time series. KGE is a combination of (i) the Pearson correlation coefficient (r), (ii) the ratio between simulated and observed means (β), and (iii) the ratio between simulated and observed variances (α). In this study, we used KGE to compare the performance of two karst hydrological models (ANN and LP) over different flow regimes (dry, intermediate, wet) of two karst springs. The considered karst systems exhibit high contrasts in geometrical and hydrodynamic properties, inducing a high variability of the discharge at the springs. The discharge time series were divided into three sub-time series (dry, intermediate, and wet flows) according to fixed thresholds of discharge values. KGE values were higher for LP model for each sub-time series of both karst systems, thus indicating a better performance of LP over ANN at dry, intermediate and wet flows. However, KGE of the whole discharge time series were higher for ANN model, thus indicating a better overall performance of ANN over LP. The analysis of the decomposition of KGE (r, β, α) alongside a visual assessment of the simulated discharges of both models revealed that a compensation bias may be induced by β and α parameters. Simultaneous and equal overestimations and underestimations of multiple parts of the discharge time series seem to favour β and α values, leading to an overall better KGE coefficient without being associated to an increased model relevance.

How to cite: Cinkus, G., Mazzilli, N., Jourde, H., Wunsch, A., Liesch, T., Goldscheider, N., Ravbar, N., Fernández-Ortega, J., Barberá, J. A., Andreo, B., and Chen, Z.: Possible bias in the assessment of karst hydrological model performance. Example of alpha and beta parameters compensation when using the KGE as performance criterion., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5149, https://doi.org/10.5194/egusphere-egu22-5149, 2022.

How to cite: Azimi, S., Massari, C., Formetta, G., Barbetta, S., Tazioli, A., Fronzi, D., Modanesi, S., Tarpanelli, A., and Rigon, R.: Assessing the ability GEOframe modeling system for water budget analysis of a challenging karst basin in the Apennines chains, Central Italy., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2878, https://doi.org/10.5194/egusphere-egu22-2878, 2022.

Snow recharge is an important dominant hydrological process in the high altitude mountainous karstic aquifer systems. In general, widely used karst hydrological models (e.g., KarstMod, Varkarst) do not include a snow routine in the model structure to avoid increasing the number of model parameters while representing the complex hydrological process. As a result, recharge process is not represented well, which questions the optimality of the results that can be obtained under available datasets. This study presents a novel pre-processing method –called SCA routine– to compensate for the missing snow routine in karst models. The proposed pre-processing method is driven by the temperature, precipitation, and satellite-based snow observation datasets while classifying the precipitation input into three physical phases (rain, snow, and mixed) based on the temperature datasets to distribute each phase over the catchment using satellite-driven Snow-Covered Area (SCA) products. By the proposed method, the spring discharge simulation result is regulated well in time and magnitude. To examine the added utility of the SCA routine, the SCA-included simulation results are compared to the model performances with no routine and the classical Degree-Day method as a benchmark. To test the efficiency of our proposed method we use a karst hydrological model (KarstMod) to simulate the karst spring discharge in a well-observed semi-arid snow-dominated karstic aquifer (Central Taurus, Turkey). Our results confirm that the KarstMod model coupled by SCA routine ensures better model performance with a value of NSE = 0.784 than those of the classical Degree-day method (NSE = 0.760) and the model with no routine (NSE = 0.306) while providing a physically more realistic parameter set.

Key Words: MODIS, Degree-Day, Hydrological model, Snowmelt, Mountainous karst

How to cite: Calli, S. S., Özdemir Calli, K., Yılmaz, M. T., and Çelik, M.: The contribution of Satellite-data driven snow routine to karst hydrological models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-725, https://doi.org/10.5194/egusphere-egu22-725, 2022.