The article of Blatnik et al. (2019) “Groundwater dynamics between Planinsko Polje and springs of the Ljubljanica River, Slovenia” published in Acta Carsologica, 48/2 focused on describing the ...hydrogeological behaviour of the aquifer between Planinsko Polje and the springs of the Ljubljanica River. The authors analysed the effect of different high water events that occurred between January 2015 and May 2018. Interpretations were based on hydrographs obtained by continuous measurements of water level, temperature and specific electric conductivity in selected ponors, springs and water active caves located in the area between Planinsko Polje and the springs of the Ljubljanica River. Through these interpretations, different conceptual hydrological models about the dynamics and directions of the flow in the aquifer have been proposed and tested. A flow connection was proposed between the Hrušica Plateau, estavelles located at the NW border of Planinsko Polje, and caves Gradišnica (W2) and Gašpinova Jama (W3) close to town Logatec. In this supplement, we provide new data recorded during an unusual hydrological event in August 2018. These further support and stress the importance of the connection between the Hrušica Plateau and Logatec region (W2 and W3).
Various multivariate statistical techniques (MST) can provide valuable insights into water quality variability. Despite numerous studies in which these methods have been used, their potential has not ...been fully exploited. This paper presents an improved approach to better understand the hydrodynamics of karst systems. The integrated application of hierarchical cluster and principal component analysis in combination with factor analysis allowed the construction of an advanced multivariate chemograph. The analytical procedure was applied in a binary karst aquifer known for its complex hydrodynamics and mixing of water with similar hydrochemical composition. In addition, the study area provides access to an integral groundwater flow system (ponor‐cave‐spring) and offers extensive prior hydrogeological knowledge. The approach allowed reduction and discrimination of the main parameters affecting water quality characteristics. Their identification enabled recognition of three predominant recharge components: (a) stored water impact with Cl and electrical conductivity, (b) sinking stream impact with turbidity and bacteria composition and (c) karst aquifer impact with Ca/Mg ratio as principal parameters. The results supported innovative characterization of the dominant processes and isolation of temporal hydrodynamic phases of individual monitoring points within the aquifer system. On this basis, a spatio‐temporal conceptual model was developed and the hydrodynamic behavior of the main springs was revealed. The applied methodology demonstrated to be useful in ascertaining functioning of a complex karst system under flood event conditions.
Plain Language Summary
Karst aquifer systems contain important water resources. The quality of karst springs can deteriorate significantly after rain events, but it is difficult to distinguish how water flows and mixes in the subsurface, especially in large and complex systems. Statistical methods are powerful tools for studying these issues, but most common approaches are inadequate in some cases to reveal the origin of the water and its fate. In this paper, we present an approach in which we combined different statistical methods to explain the dynamics of water flow based on the physicochemical and microbiological properties of water. The application of these methods led to the discrimination of parameters most useful for a reliable interpretation of statistical results, such as turbidity, bacteria, Cl, EC, and Ca/Mg, and to the construction of an advanced diagram that we called a multivariate chemograph. This diagram allowed us to see where the water was coming from at any given time to our monitoring points, which allowed us to construct a detailed explanation of water flow dynamics in space and time. Our contribution is important to better predict the fate of contaminants in karst underground and to develop an early warning system for better water supply management.
Key Points
A new approach to study and explain hydrodynamics of karst aquifers was developed
It offers an innovative solution to distinguish influential monitoring parameters
Multivariate chemographs allowed spatio‐temporal detection of recharge phases
Caves reaching the (epi)phreatic zone may provide the only access to groundwater in the internal parts of karst aquifers. Modern instruments enable unattended high frequency measurements of ...groundwater parameters in such caves. A network of distributed observation points may give new information on temporal and spatial pattern of groundwater flow. Such network, recording water level, temperature and specific electrical conductivity was established in all major ponors and active water caves of the karst aquifer between Planinsko Polje and springs of the Ljubljanica River, Slovenia. Up to three and a half years long records were analysed in view of available and relevant geological, speleological, meteorological and hydrological information, and basic hydraulic principles of the epiphreatic flow. The result of the interpretation were models of possible conduit networks of the three main flow subsystems draining Planinsko Polje. For each subsystem a hydraulic model comprising the main features of the inferred conduit network and inputs was made. The models were adjusted until their response to the typical flood situations gave a good qualitative fit to the response of the observation network. The results provide new insights into the mechanism of flood propagation through the system and its relation to the known conduit geometry. The hydraulic role of known cave passages is assessed and new flow pathways are proposed. Back-flooding within the aquifer causes an increase of head in the polje, followed by the activation of higher located ponor zones and flow pathways related to them. Hydrographs recorded in two caves located northwest from Planinsko Polje revealed possible high transmissivity zone of the Idrija Fault Zone and the mechanism of estavelles located at the polje's north-western border. The approach taken in this work offers new insights into the relation between the conduit network geometry and flood mechanism. It can be used elsewhere in conduit-dominated systems with multiple accesses to groundwater flow and well constrained recharge.
Planinsko Polje is the westernmost active polje of Dinaric karst. It is a typical overflow-structural polje, with springs on the southern side feeding the superficial flow of Unica River. The river ...meanders over the polje towards the terminal outflow area on its northern side, where it sinks back into the aquifer through several ponors. Along the reach in proximity to the eastern border of the polje, the Unica River loses water through several outflow zones into distinct ponors and into a set of small openings and fracture zones. To estimate the outflow rate along these zones, the Unica discharge was measured upstream and downstream to the outflow zone. Seven velocity profiles were recorded with an Acoustic Doppler Current Profiler and the corresponding discharges were calculated. The measurements were taken within four hours during the flow recession following a partial flooding of the Planinsko Polje. Therefore, six outflow zones were evaluated with an outflow rate ranging between 1 m3/s and 5.6 m3/s. The total loss of water along the eastern border summed up to 18 m3/s under the given hydrological conditions. These results give new insight into the functioning of karst poljes and provide an important input for eventual future hydrological modelling of the area. Key words: polje, outflow, ponors, discharge, Acoustic Doppler Current Profiler, Planinsko Polje, Unica.
Karst ground water dynamics between the Planinsko polje and the springs of Ljubljanica (Slovenia) was studied based on the monitoring of stage and temperature of ground water in four caves. The Unica ...River, which flows over the Planinsko Polje, and sinks at its E and N rim, is considered as the main input to the observed system. At small flood events its role is none or questionable. At medium and large events, when the discharge of Unica exceeds 25 m super( 3)/s, it becomes an important and/or the dominant input to the system. When the capacity of the primary (eastern) ponors in the polje is exceeded, the stage in a cave, which is fed solely through these ponors, reaches the plateau followed by a very slow recession. The surplus flow goes towards northern ponors causing a fast rise of the stage in adjacent to them. In two of the northernmost caves, the stage response is almost identical, but the temperature variations are different. The uniform water level suggests a highly permeable region bounded by a low permeability barrier in the down-flow direction, while different temperature behavior indicates a different origin of the waters for each cave.
Hydrodynamic aspect of caves Prelovšek, Mitja; Turk, Janez; Gabrovšek, Franci
International journal of speleology,
01/2008, Volume:
37, Issue:
1
Journal Article
Peer reviewed
Open access
From a hydrological point of view, active caves are a series of connected conduits which drain water through an aquifer. Water tends to choose the easiest way through the system but different ...geological and morphological barriers act as flow restrictions. The number and characteristics of restrictions depends on the particular speleogenetic environment, which is a function of geological, geomorphological, climatological and hydrological settings. Such a variety and heterogeneity of underground systems has presented a challenge for human understanding for many centuries. Access to many underground passages, theoretical knowledge and recent methods (modeling, water pressure-resistant dataloggers, precise sensors etc.) give us the opportunity to get better insight into the hydrodynamic aspect of caves. In our work we tried to approach underground hydrodynamics from both theoretical and practical points of view. We present some theoretical background of open surface and pressurized flow in underground rivers and present results of some possible scenarios. Moreover, two case studies from the Ljubljanica river basin are presented in more detail. The approach and methodology in each case is somewhat different, as the aims were different at the beginning of exploration. However, they both deal with temporal and spatial hydrodynamics of underground waters.
Underground karst water is accessible only in two caves near Logatec town (30 km south of Ljubljana, central Slovenia); Gradišnica and Gašpinova jama caves. Water level and water temperature were ...continuously measured more than one year in both caves. Gradišnica and Gašpinova jama caves belong to the same karst aquifer, therefore fluctuations of water level are almost identical and simultaneous.According to our measurements,fluctuations are significant;they rach at least 50 m.Incontrast,water temperature is significantly different at both locations.Mean difference is 1-2 °C, the highest measured was 5 °C. Relatively high temperature differences are due to recharge characteristics of the aquifer. It is fed by waters which have different surface origin. Water temperature in Gradišnica Cave directly reflects temperatureof the surface Unica River at medium water condition. On the contrary, the Unica River influences on water temperature in Gašpinova jama Cave at the highest floods only.Ithappens when discharge of the surface Unica River at Haasberg exceeds 40 m3/s. Water temperature becomes similarin larger part of the aquifer between both discussed caves, at such high water conditions only. Temperature of underground water tells us much about the origin of the water, which feeds discussed caves.
For one year we have been measuring level and temperature of underground water in Vetrovna jama, to find outthe origin of underground water and hydraulic characteristics of the cave and karst aquifer ...north east of Planinsko polje (karst of Notranjska region, central Slovenia). Similar parameters as in Vetrovna jama were measured also at the Unica River and at the Cerknica Lake. Cave is located only 2.7 km north from the polje and is fed by the Unica River, according to measurements. But in contrast with our expectations, we did not directly detect undergroundwater flow, which drains from the Cerknica Lake. Hydrographs measured in Vetrovna jama were compared with those measured in some other caves within the aquifer. Hydrographs from Vetrovna jama are only partly comparablewith hydrographs obtained in other monitored caves, as comparison shows no statistical significant correlation.Final conclusion would be that drainage of water between “eastern” and “western” part of karst aquifer islimited. More over, out flow from Vetrovna jama strongly depends on local hydrogeological restriction, such as supposedrockfall under Laška kukava collapse doline.
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