Exploratory Analysis of Water-Level Associations in a Disconnected Floodplain Oxbow Lake: Evidence from the Váh River, Slovakia

This study assesses the primary hydrological controls on water-level variability in the Dolnostredske oxbow lake (hereafter the oxbow), a disconnected waterbody in the Váh River floodplain, Slovakia. The oxbow is separated from the river by a cutoff embankment upstream of the Kráľová reservoir. Water levels were monitored approximately weekly on 31 dates from June 2025 to January 2026 and compared with regional groundwater level, the Váh River stage, precipitation, and actual evaporation. Cross-correlation, Granger causality tests and multiple linear regression were used to assess the relationships among these variables. Oxbow water level was most strongly associated with regional groundwater level (Pearson r = 0.657; Spearman ρ = 0.612; and p < 0.001). This finding demonstrates synchronous statistical dependence at the approximately weekly sampling scale, but it does not identify the direction, magnitude, or precise pathway of groundwater exchange. No candidate driver showed statistically significant lagged Granger predictability (p > 0.05). The regression model explained 67% of the in-sample variation in oxbow water level (cross-validated R2 = 0.612; RMSE = 0.063 m), with groundwater level as the strongest standardized predictor. The results support groundwater-related control of short-term water-level variability in the disconnected oxbow, while confirmation of groundwater-flow pathways requires hydraulic-gradient measurements, hydrochemical or tracer evidence, and more detailed characterization of alluvial heterogeneity.