{"id":12578,"date":"2025-09-02T13:31:54","date_gmt":"2025-09-02T11:31:54","guid":{"rendered":"https:\/\/www.npkrka.hr\/?p=12578"},"modified":"2025-12-02T13:01:32","modified_gmt":"2025-12-02T12:01:32","slug":"analiza-izmjene-vode-u-visovackom-jezeru-i-utjecaj-jezerskog-sustava-na-transformaciju-otjecanja","status":"publish","type":"post","link":"https:\/\/npkrka.hr\/hr\/2025\/09\/02\/analiza-izmjene-vode-u-visovackom-jezeru-i-utjecaj-jezerskog-sustava-na-transformaciju-otjecanja\/","title":{"rendered":"Analiza izmjene vode u Visova\u010dkom jezeru i utjecaj jezerskog sustava na transformaciju otjecanja"},"content":{"rendered":"

[hr]Rijeku Krku karakterizira nagla\u0161ena izmjena rije\u010dnog i ujezerenog toka, \u0161to je posljedica rasta sedrenih barijera. <\/strong><\/p>\n

Najzna\u010dajniji slatkovodni jezerski sustav na Krki Visova\u010dko je jezero, koje je tipi\u010dno kanjonsko jezero, ujedno i kriptodepresija. Po dubini spada u duboka (dublje je od 15 m), a po povr\u0161ini u srednja jezera (povr\u0161ina mu se kre\u0107e unutar klase 1 \u2013 10 km\u00b2).<\/p>\n

S obzirom na utjecaj izmjene voda u Visova\u010dkom jezeru na jezerski ekosustav, u sklopu ovog projekta razmatrana je hidrolo\u0161ka komponenta tih izmjena. Komponenta protjecanja vode kroz jezero vrlo je izra\u017eena: prora\u010dunato je da teoretsko vrijeme izmjene voda u njemu iznosi 28 dana, odnosno da se ona u njemu izmijeni prosje\u010dno trinaest puta godi\u0161nje. No tijekom su\u0161nijih godina, kakva je bila 1989., teoretsko vrijeme izmjene voda produlji se za vi\u0161e nego dvostruko (na 64,5 dana), \u0161to zna\u010di da se izmijeni prosje\u010dno 5,7 puta godi\u0161nje. S druge strane, za pojave velikih vodenih valova na rijeci Krki, proces izmjene voda u Visova\u010dkom jezeru dinamizira se, tako da je, na primjer, prora\u010dunato vrijeme izmjene u svibnju 2023. bilo puno kra\u0107e \u2013 iznosilo je svega 12,6 dana.<\/p>\n

Donesene su i prognoze utjecaja klimatskih promjena na dinamiku izmjene vode u jezeru. Kao \u0161to to prognoziraju kori\u0161teni klimatski i hidrolo\u0161ki modeli, utvr\u0111eno je da se, ako se srednji godi\u0161nji protoci smanje za 10 %, vrijeme izmjene vode pove\u0107a na 31,4 dana, ako se smanje za 20 %, pove\u0107a se na 35,4 dana, a ako se smanje za 30 %, pove\u0107a se na 40,4 dana. U takvim slu\u010dajevima mogu\u0107a su pove\u0107anja izmjene voda na gotovo dvostruko ve\u0107e vrijednosti od recentnih.<\/p>\n

Stvarno vrijeme izmjene voda u velikoj mjeri ovisi ne samo o morfologiji korita i hidrolo\u0161koj bilanci istjecanja vode iz njega, nego i o jezerskoj termici i hidrodinamici strujanja voda koja je povezana s periodi\u010dkom stratifikacijom jezerskih masa. U sezonskim uvjetima ja\u010de izra\u017eene vertikalne termi\u010dke izdiferenciranosti vodenih masa longitudinalno kretanje voda dominantno se odvija epilimnijem, \u0161to ote\u017eava i usporava izmjenu voda cijelog jezerskog sustava. Upravo zbog relativno kratkog vremena izmjene voda i nagla\u0161enog protjecanja voda kroz njega, sloj epilimnija relativno je plitak (2 \u2013 5 m), a sloj termokline ispod njega jako razvu\u010den, \u0161to dinamizira izmjenu voda u jezeru. Na temelju provedenog monitoringa potvr\u0111eno je da Visova\u010dko jezero spada u topla monomikti\u010dka jezera s potpunim mije\u0161anjem cjelokupne vodene mase jednom godi\u0161nje. U zimskom razdoblju javlja se izotermija \u2013 vode na povr\u0161ini jezera ohlade se na temperature voda u donjim slojevima pa se u tim uvjetima voda u jezeru redovito mije\u0161a s povr\u0161ine prema dolje i tako osvje\u017eava. Radi se o vrlo dinami\u010dnom sustavu kod kojeg je utvr\u0111eno relativno kratko teoretsko vrijeme izmjene voda, \u0161to pozitivno utje\u010de na promjene niza drugih abioti\u010dkih i bioti\u010dkih faktora toga iznimno vrijednog za\u0161ti\u0107enog vodnog resursa.<\/p>\n

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[en]
\nThe analysis of water exchange in Visovac Lake and the influence of the lake system on the transformation of runoff<\/strong>
\n <\/p>\n

The Krka River is characterized by a marked change in its course between river and lakes, which is a consequence of the growth of tufa barriers<\/strong><\/p>\n

The most significant freshwater lake system on the Krka is Visovac Lake, which is a typical canyon lake and also a crypto-depression. In terms of depth, it belongs among deep lakes (deeper than 15 m), and in terms of surface area to medium lakes (with a surface area ranging from 1 to 10 km\u00b2).<\/p>\n

Given the impact of the exchange of water in Visovac Lake on the lake ecosystem, the hydrological component of these exchanges was considered in the context of this project. The component of water flow through the lake is very pronounced: it is calculated that the theoretical time of water exchange in it is 28 days, that is, that it is changed on an average of thirteen times a year. However, during drier years, such as 1989, the theoretical water exchange time is extended by more than twice (to 64.5 days), which means that it is exchanged an average of 5.7 times per year. On the other hand, during the occurrence of large water waves on the Krka River, the water exchange process in Visovac Lake becomes more dynamic, so that, for example, the calculated exchange time in May 2023 was much shorter \u2013 it measured only 12.6 days.<\/p>\n

Forecasts of the impact of climate change on the dynamics of water exchange in the lake have also been made. As predicted by the climatic and hydrological models used, it was established that if the mean annual flows decreased by 10%, the water exchange time would increase to 31.4 days, while if they decreased by 20%, it would increase to 35.4 days, and if they decreased by 30%, it would increase to 40.4 days. In such cases, it would be possible to increase the water exchange to almost double the recent values.<\/p>\n

The actual water exchange time depends to a great extent not only on the morphology of the riverbed and the hydrological balance of water outflow from it, but also on the lake thermals and the hydrodynamics of the water flow, which is associated with the periodic stratification of lake masses. In seasonal conditions of more pronounced vertical thermal differentiation of water masses, longitudinal water movement occurs predominantly through the epilimnion, which complicates and slows down the exchange of water throughout \u00a0the entire lake system. Precisely because of the relatively short water exchange time and the pronounced flow of water through it, the epilimnion layer is relatively shallow (2-5 m), and the thermocline layer below it is very extended, which dynamizes the water exchange in the lake. Based on the monitoring conducted, it was confirmed that Visovac Lake belongs to warm monomictic lakes with complete mixing of the entire water mass once a year. In the winter, an isothermal process occurs \u2013 the water on the surface of the lake cools to the temperature of the water in the lower layers, so under these conditions, the water in the lake is regularly mixed from the surface downwards, thus refreshing it. This is a very dynamic system with a relatively short theoretical water exchange time, which has a positive impact on changes to a number of other abiotic and biotic factors in this extremely valuable protected water resource.<\/p>\n

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 <\/p>
\n[\/en]<\/p>\n","protected":false},"excerpt":{"rendered":"

Rijeku Krku karakterizira nagla\u0161ena izmjena rije\u010dnog i ujezerenog toka, \u0161to je posljedica rasta sedrenih barijera.<\/p>\n","protected":false},"author":2,"featured_media":12580,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[44],"tags":[],"class_list":["post-12578","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/posts\/12578","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/comments?post=12578"}],"version-history":[{"count":4,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/posts\/12578\/revisions"}],"predecessor-version":[{"id":14151,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/posts\/12578\/revisions\/14151"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/media\/12580"}],"wp:attachment":[{"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/media?parent=12578"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/categories?post=12578"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/npkrka.hr\/hr\/wp-json\/wp\/v2\/tags?post=12578"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}