Nature · Karst phenomenon
Duvalo Estavela
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A reverse ponor near Grančarevo that seasonally expels water instead of swallowing it — one of the more unusual karst phenomena of the region.
Estavelas are karst features that behave in two ways — for part of the year they swallow water like ordinary ponors, while for the rest of the year they do the opposite, expelling it to the surface. The "Duvalo" estavela, near the Grančarevo dam, is one of the most striking examples of this phenomenon around Bileća.
What makes Duvalo special is that it sometimes discharges water even during the summer drought, when it would be least expected. Phenomena like this bear witness to the complex underground hydrological system that connects the Trebišnjica, the karst fields and Bileća Lake.
