engleski

Hidraulic Limitation of Exploitation Vrana Lake for Water Supply (Croatia)

The cryptodepression of the Vrana Lake on the island Cres (Croatia) is a specific natural phenomenon of 220 million m3 of fresh water on the island's karst in the immediate nearness of the sea. The average water level of the Lake for analyzed 1929-1999 period is 13, 13 ma.s.l. (Meters above sea level) and the deepest bottom are 61.3 m bellow mean sea level. The Lake is the only source of water supply of the islands Cres and Lošinj. The noticed trend of declining of the water level at the end of eighties caused certain worries about further pumping and keeping the balance of the Lake's system. Because recharge and run off happen through not localized subterraneous karst ways their direct measurements and balancing are not possible. Therefore the elements of water balance and the pattern in the behavior of the lake's system have been established by hydrological methods through the monitoring of dynamic changes in the water level of the lake in different hydrological conditions. The significant influence of basic water balance parameters was determined as well as the influence of pumping on the lowering of the water level of the lake for approximately 2 m. An average annual inflow of 0, 588 m3s-1 was determined according to measured average annual rainfall of 1064 mm and average annual evaporation quantity of 1161 mm. This paper discusses the hydrological and hydrulical aspect of functioning of the lake system as a part of the island karst aquifer, and the related problems of protection of the Vrana Lake from excessive water consumption and pollution, i.e. disturbing of its highly sensitive ecosystem.

islands' aquifer; Vrana Lake; karst hydrology and hydraulic

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