Preliminary communication

Analysis of groundwater levels and Lake Vrana water levels on the Cres Island

Ognjen Bonacci orcid.org/0000-0002-7123-3421 ; Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia
Tanja Roje-Bonacci orcid.org/0000-0002-7123-3421 ; Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Split, Croatia

Abstract

The paper analyses the behaviour of groundwater levels recorded in three deep piezometers located in the Like Vrana basin on the Cres Island in the period from 10 September 1997 to 31 December 2000, i.e. a total of 1209 days. The behaviour of groundwater levels in all three piezometers was nearly identical, with the values of square coefficients of linear correlation among the piezometer pairs ranging from R2=0.955 and R2=0.998. The daily inflows and lake water losses were calculated as well. The maximum mean daily inflow into the lake in the analysed period equalled Q=8,9 m3/s, whereas the maximum mean daily loss from the lake was Q=-1,9 m3/s. The differences between simultaneously measured groundwater levels in each individual piezometer and the lake water level were analysed. It was determined that in the piezometer B1, 335 m away from the lake shore, the groundwater level was higher or equal to the lake water level for a period of only 56 dana (4.6 % of the analysed time period). In the piezometer B2, 540 m away from the lake shore, the groundwater level was higher or equal to the lake water level for a period of 262 dana (21.7 % of the analysed time period),whereas in the farthest piezometer B3, drilled 790 m away from the lake shore, the groundwater level was higher or equal to the lake water level 89.1 % of the analysed time period. This relation was unexpected and difficult to explain or correct without further measurements, which is necessary due to doubts as to the veracity of the measured groundwater levels. Lake Vrana on the Cress island, a unique water formed on a karst island mass in the world, deserves that the processes occurring in the lake itself and its environment should be reliably clarified, which is the primary objective of this paper.

Keywords

lake water level; water inflow into a lake; groundwater level; Lake Vrana; Cres Island; Croatia

Hrčak ID:

197082

URI

https://hrcak.srce.hr/197082

Publication date:

19.3.2018.

Article data in other languages: croatian

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