Some oceanographic and hydrographic characteristics of the lake Vransko jezero and southwestern coastal part of the island of Cres (Hydrographic survey in Vransko jezero)

U radu se razmatraju oceanografska obilježja i rezultati hidrografskog premjera Vranskog jezera na otoku Cresu. Naime, izmjeren je znatan pad razine vode u jezeru, pa se razmatraju razlozi toj pojavi. Javlja se povremeno (Riđanović 1994.) . Nije poznato da li postoji fizička komunikacija jezero-more na zapadanoj obali Cresa, ili dubokopodzemna veza između jezera i ponornica u Liki (Pomorska enciklopedija, 1975.), što ne potvrđuju rezultati jednokratnog istraživanja u jesen, 1990. Također nema ni tragova slatke vode u morskoj, u području zapadno od Cresa, osim možda u tankom površinskom sloju. Budući da su mjerenja obavljena jednokratno, sigurno je da bi višegodišnja sezonska/mjesečna dala pouzdanije rezultate. U jugozapadnom dijelu Vranskog jezera postoji subdepresija, vjerojatno zatrpana recentim sedimentom i ne predstavlja aktivni odvodni kanal. Rad predstavlja smjernice za buduća istraživanja. Daljnja sustavna istraživanja trebala bi objasniti drastične promjene vodostaja u jezeru, glede ukupnog dotoka slatke vode (oborina i kapacitativno ograničeni izvori u sjevernom dijelu), kao i utjecaj isparavanja i drugih značajnih čimbenika.The paper deals with some oceanographic characteristics and result of the hydrographic survey in Vransko jezero on the island of Cres. A significant falling of the water level in the lake been recorded, therefore it was necessary to investigate the reasons for such phenomenom. It occurs occasionally (Riđanović 1994.). There is no evidence of existence of a physical communication between the lake and the sea near the western coast of Cres, nor of a deep underground connection between the lake and the underground streams of Lika ( Pomorska enciklopedia 1975). Such attitudes were not confirmed by the results obtained from the survey carried out in autumn 1990. The sea water in the area west of island of Cres does not contain any traces of fresh water, exept in its thin surface layer. As these measurements were performed only, it is likely that season/monthly measurements of several years would give better results. In the southwestern part of Vransko jezero there is a subdepresion, probably covered up with recent sediments, not representing an active draining canal. This paper provides fundamental lines for future systematic researches, the principal objective of which wil be to explain drastic changes of the water level in the lake, with regard to the total inflow of the fresh water (precipitation and springs with limited capacity in the northern part) as well as to the influence of evaporation and other significant factors