An Attempt Towards an Assessment of the Cerknica Polje Water Balance

Abstract

Izvleček UDK 556.3(497.4 Cerknica) Gregor Kovačič: Poskus ocene vodne bilance Cerkniškega polja V članku je predstavljena vodna bilanca Cerkniškega polja. Rezultati predhodnih raziskav so primerjani z izračuni dotokov in odtokov s polja v hidrološkem letu 1975 (411 dni). Izračun vodne bilance Cerkniškega polja je narejen na osnovi dnevnih sprememb prostornin Cerkniškega jezera, izračunanih s pomočjo podatkov o vodostajih Stržena na vodomerni postaji Dolenje Jezero in digitalnega modela višin Cerkniškega polja (velikost celic 25 x 25 m). Za preučevano leto je skupen odtok s hidrološkega zaledja Cerkniškega polja (475 km 2) ocenjen na 620 milijonov m 3 vode oziroma 17 m 3 /s. V hidrološkem letu 1975 je največje naraščanje prostornine jezera, preračunano v pretok, znašalo 135 m 3 /s, medtem ko je največje zmanjšanje prostornine jezera znašalo 60 m 3 /s. Največji možni dotok na Cerkniško polje je izračunan na 232 m 3 /s. V hidrološkem letu 1975 je povprečni odtok s Cerkniškega polja skozi ponorne jame in talne ponore znašal 23,69 m 3 /s, izračunani največji pa 91,7 m 3 /s. Ključne besede: Cerkniško polje, kraška hidrologija, vodna bilanca, kraški odtok, Cerkniško jezero.

Extreme hydrological events in karst areas of Slovenia, the case of the Unica River basin

“…The mean annual precipitation of the studied area ) is estimated at 1,776 mm, and the mean annual evapotranspiration at 720 mm . The mean annual runoff is estimated at 1,055 mm, with the runoff coefficient being around 60 % [5]. In the 1971-2000 period, the discharge of the Unica River varied between 1.08 m 3 /s and 100 m 3 /s, and the mean discharge was 20.95 m 3 /s [6].…”

“…It drains the Javorniki (1,273 m) and Snežnik karst plateaus, the Loško polje, the Bloke plateau, and Mount Slivnica (1,114 m). The inflow (~210 to 240 m 3 /s) to the polje often exceeds the runoff (~40 to 92 m 3 /s), causing flooding or the intermittent occurrence of Cerknica Lake, which can cover an area of 30 km 2 [5,7]. The lake appears when the water in the Stržen River starts to overflow, i.e,.…”

“…3). On average the lake lasts for eight months, but once in a 10-year return period the lake does not drain completely [5,7]. At the maximum recorded lake level of 552.096 m asl (observation period 1955-2008), the volume of water in the lake can reach around 82 million m 3 ( Fig.…”

“…At the maximum recorded lake level of 552.096 m asl (observation period 1955-2008), the volume of water in the lake can reach around 82 million m 3 ( Fig. 9) and the speed of lake level increase can be more than 75 cm/day [5].…”

Surface Karst Landforms of the Notranjska region (south-western Slovenia)

“…The main swallow holes are situated in the north-western part of the landform (Cucchi et al, 1997;Kovačič, 2010) (Figs 9, 10). Depending on the season and the level of water in the polje, tourists can experience completely different landscapes.…”