Understanding the temporal variation of flow direction in a complex karst system (Planinska Jama, Slovenia)

Abstract

Karst aquifers are abundant, but vulnerable water resources. Therefore, a deeper understanding of possible mechanisms that determine the properties of karst springs is crucial. In this work, we present an example of Unica Spring and Malni Spring, the two main outlets of a large karst system in the Notranjska karst region, Slovenia. Although the two springs share same catchment area, the flow distribution between them shows an interesting behaviour: At low-flow conditions, Malni Spring is the main outlet, while Unica spring receives almost no water. During high water events, discharge of Malni Spring stays limited and Unica Spring becomes the main outlet. We relate these observations to the local geometry of the channels and breakdowns in the remote part of the Planinska Jama (Planina Cave), called Mysterious Lake. There, waters from Rakov Škocjan and Javorniki aquifer merge and further diverge to both springs. At low water conditions, the outflow towards the Unica Spring is restricted by the breakdown, so that most of the inflow is directed towards the Malni Spring. With increasing recharge, the level in Mysterious Lake rises until the water starts to flow over the breakdown along a system of large channels (Rak Branch of Planinska Jama) to the Unica Spring. The breakdown level keeps the hydraulic head and the flow towards Malni Spring limited. To verify this scenario, a hydraulic conduit model was made based on the known and predicted channels, and inflows calculated from the historical data of discharge measurements at related springs and ponors. An inversion procedure was used to obtain a satisfactory fit to the observed discharge data and to constrain the selected model parameters. The model accurately reproduced the observed discharge behaviour under low- andhigh-flow conditions.

The minnowPhoxinus lumaireul(Leuciscidae) shifts the Adriatic–Black Sea basin divide in the north‐western Dinaric Karst region

“…was shifted to the north-east (blue dotted line in Figure 5). and Ljubljana Basin (TOJN; Kaufman et al, 2020). There are few other studies on fishes with a dense sampling set in this area, though in the case of bullheads (Bravničar et al, 2021), the genetic structure follows the Adriatic-Black Sea basin divide, with one species populating the Adriatic and other the Black Sea basin.…”

“…However, even though shifted, the genetic divide between south‐western (mt‐1a, full GENELAND C3) and north‐eastern (mt‐1c, full GENELAND C5; Figure 5) LRS sampling sites still exists, despite numerous underground water connections between them (Figures 1b and 6). Further expansion of clade 1a to the north‐east into the Black Sea basin was possibly obstructed by hydrogeological barriers between LOGA, HOTE and the springs of Ljubljanica River (TOJN; Grabovšek & Turk, 2010; Blatnik, 2020), as well as the barrier to flow between the Idrija Fault Zone (sampling sites NANO, RAKU, MRZL, PRED, CERK, RAKO, MALI) and Ljubljana Basin (TOJN; Kaufman et al, 2020). There are few other studies on fishes with a dense sampling set in this area, though in the case of bullheads (Bravničar et al, 2021), the genetic structure follows the Adriatic–Black Sea basin divide, with one species populating the Adriatic and other the Black Sea basin.…”

“…In contrast, SDK-C3 seems to be permanently connected to farther distant LOGA (SDK-C2) sampling site through the Planina cave and Unica River but exhibits partial genetic isolation. The reason for this situation might be the temporary flow diversion along the Rak (RAKO) branch detected by Kaufman et al (2020) that maintains some, though incomplete, population connectivity. Meanwhile, within the northeast LRS (RASC, CERJ, BLOS, IZIC and TOJN, SDK-C4), the genetic structure is in line with the underground connections between RASC and CERJ.…”

Karst spring discharge modeling based on deep learning using spatially distributed input data

“…This makes a comparison of modeling results among these studies difficult. For the third spring (Slovenia), several earlier modeling studies are available (e.g., Kaufmann et al, 2016;Mayaud et al, 2019;Kaufmann et al, 2020;Kovačič et al, 2020), even including ANNs (Sezen et al, 2019), but none of these directly modeled Unica springs discharge but rather focused on other aspects like cave hydraulics or polje modeling. Besides existing studies, we compare the results of the 2D model with our own 1D CNN models using climate station input data to assess the usefulness and possible advantages of the direct use of spatially distributed input data.…”

Slovene Classical karst: Kras Plateau and the Recharge Area of Ljubljanica River / Klasični kras: planota Kras in kraško zaledje izvirov Ljubljanice

“…The cave is known to be the confluence of two important regional rivers (Figs 18,19): the Pivka River, which drains a large allogenic catchment through the Postojnska Jama (Gabrovšek et al 2010;Kaufmann et al 2016;Kogovšek 2022) and reaches the confluence with the cave via the Pivka Branch, and the Rak River, which carries water from Rakov Škocjan and Cerkniško Polje via the Rak Branch. Finally, a large amount of water also flows into the Rak Branch via the siphon of the Javornik Current, which is located the Mysterious Lake (Figure 21) (Kaufmann et al 2020). The water exits the cave under the common name Unica River with a discharge between 0.2 and 90 m 3 /s (Kogovšek 2022).…”