Original scientific paper
https://doi.org/10.17794/rgn.2026.2.10
HYDRAULIC CONNECTIVITY BETWEEN THE SAVA RIVER AND LAKE JARUN DURING DROUGHT: A HIGH-RESOLUTION MONITORING AND TIME SERIES APPROACH
Jelena Parlov
orcid.org/0000-0002-2862-7222
; University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, HR10000 Zagreb, Croatia
*
Filip Šegović
orcid.org/0009-0006-3815-7582
; Croatian Geological Survey, Sachsova 2, 10000 Zagreb
Kristijan Posavec
orcid.org/0000-0002-5392-9329
; University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, HR10000 Zagreb, Croatia
Zoran Kovač
orcid.org/0000-0001-8091-7975
; University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, HR10000 Zagreb, Croatia
* Corresponding author.
Abstract
This study offers the first detailed insight into the hydraulic relationship between the Sava River and Lake Jarun, an urban lake formed from a former river meander in Zagreb, Croatia. The main objective was to quantify and understand the temporal variability of their hydraulic connectivity under drought conditions. Continuous, high-resolution (hourly) water level monitoring of Lake Jarun, established in April 2022, was combined with interpolated Sava River water level derived from national gauging stations. Using a suite of statistical tools – Pearson correlation, linear regression, crosscorrelation, and the sliding window correlation method – the study assessed the strength, direction, and timing of river– lake interactions. The results revealed a clear but dynamic subsurface connection, with the lake typically responding to river fluctuations after a delay of five to six days. During the exceptional drought in the summer of 2022, this response weakened significantly, and the time lag extended beyond 21 days, indicating reduced hydraulic connectivity. The sliding window approach further revealed temporal variability, with sharp declines in correlation during low-flow periods and rapid recovery during high-water events. These findings highlight the non-stationary nature of hydraulic connectivity in regulated floodplains and the sensitivity of such systems to hydrological extremes. In addition to providing the first highresolution dataset for Lake Jarun, this study introduces a time-adaptive analytical framework that enhances the understanding
of short-term river–lake interactions and supports future management of urban water systems under increasing climatic pressure.
Keywords
Hydraulic connectivity; River–lake interaction; Cross-correlation; Sliding window analysis; Drought impact
Hrčak ID:
345695
URI
Publication date:
13.3.2026.
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