The karst periodical lakes of Upper Pivka, Slovenia
Nataša Ravbar, Stanka Šebela - (33/1,2004)
At dry season the Pivka river appears between Prestranek and Rakitnik while near Zagorje the underground karst waters are about ten meters below the valley bottom of periodical Pivka river. High waters pour over the surface and fill stream valley of the Pivka river, which runs continually from Zagorje to the ponor of Postojnska jama. When the level of the underground water increases, also shallow karst hollows - uvalas are flooded and changed into more than 15 periodical karst lakes.