High-frequency water level oscillations in a coastal shallow lake

Vilibić, Ivica; Bubalo, Maja; Zemunik Selak, Petra; Pranić, Petra; Radovan, Ana; Mihanović, Hrvoje; Dominović, Iva (2025) High-frequency water level oscillations in a coastal shallow lake. Natural Hazards, 121 (20). pp. 23951-23975. ISSN 0921-030X

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Official URL: http://doi.org/10.1007/s11069-025-07506-7

Abstract

Unusually strong water level oscillations (up to half a meter) associated mostly with lake seiches were observed in Vrana Lake near Biograd, Croatia. This shallow lake (up to 4 m deep) has limited water exchange with the adjacent sea through an artificial channel and karst formations. Based on the largest variances estimated from 1-min water level series measured between September 2021 and March 2024 under different mean water level conditions, the eight strongest episodes were analysed. Most episodes were observed during the colder part of the year, particularly between November and January. A decrease in the periods of spectral peaks by approximately 25% was documented between episodes occurring during maximum and minimum mean water level conditions. Most episodes were associated with a strong mid-troposphere jet, with its core located southwest or west of the lake, and a cyclone centered west or northwest of the lake. A strong episode observed during the summer months—on 5 September 2024—resembled synoptic conditions typically seen during Mediterranean meteotsunamis. All investigated water level oscillations were linked to travelling mesoscale convective systems. Modelling exercises indicate that the strongest lake oscillations correspond to the fundamental seiches of the lake, driven mostly by along-lake winds, while air pressure forcing contributes primarily to higher-frequency seiche modes. Modelled strong currents, reaching up to 50 cm/s, are associated with the most intense water level oscillations, presumably resulting in strong mixing of the lake, sediment resuspension, and the transport of salt and chemical compounds along the lake. This is particularly important as the lake is a protected Nature Park due to its ornithological reserve in the northwest, which is endangered by ongoing climate change. Rising sea levels and decreased precipitation in the lake’s drainage area could lead to a substantial increase in salinity, threatening the lake’s ecosystem.

Item Type:

Article

Uncontrolled Keywords:

coastal lake; meteotsunamis; convective storms

Subjects:

NATURAL SCIENCES > Geophysics

Divisions:

Division for Marine and Enviromental Research

Projects: