LIFE TRŠCA: Water level of Lake Cerknica

Karst Research Institute ZRC SAZU (IZRK) is involved in the LIFE TRŠCA project for the monitoring of the water level dynamics during various project activities. Research of the water level dynamics at different karst field has been one of the main topics of the institute for many decades.

At the beginning of the LIFE project, the research group of IZRK published a scientific paper, which is dedicated to the analysis of water level dynamics in the past 70 years and also to determine the impact of climate change and human interventions. The research was made on the basis of hydrological and meteorological measurements, which were carried out in several places in the recharge area of the Cerknica field by the Slovenian Environment Agency (ARSO). Here is the list of the main findings of the analysis:

• Increase in the mean water level before 1970s and gradual decrease after 1970s
• Increasing intensity and frequency of extreme hydrological events, represented by longer duration and higher extent of flood periods and longer duration of dry periods.
• Seasonal dynamics with the highest water levels in autumns and springs and the lowest in summers. The floods in springs seem to be smaller in extent now than in the past.
• Local deviations in water levels. During high waters the surface of the lake is almost flat, but as the water level drops, the water level difference between the upstream and downstream locations is increasing.
• Correlation between hydrological and climatological data indicates a decreasing impact of such human infrastructure over time, which matches with the gradual removal of some structures.

The quantification of human activities indicated that interventions in the 1970s caused the increase of the water level for 0.5–1.0 m under comparable hydrological conditions in comparison to the period 1961–1970. Gradual removal of the infrastructure after the 1970s resulted in an approximate 0.3 m drop of the water level under comparable hydrological conditions.

The impact of climate change and human activities on the Cerknica Field was also presented on national television in the TV show “Na Lepše”, which was broadcast on September 29, 2023 (6:09-12:27 min). The contribution was made in cooperation with the Notranjska Regional Park: https://365.rtvslo.si/arhiv/na-lepse-oddaja-o-turizmu/174990122

In the spring of 2024, the IZRK team devoted most of its activities to the establishment of additional water level observation points in order to determine more precisely the local deviations in the water level. In cooperation with the Notranjska Regional Park, 8 priority areas (lake windows) were selected. These are the locations where the water is present for the longest time in a year. Water level monitoring instruments will be installed at the first opportunity when the lake dries up to the extent that the measuring points are accessible.

Article was prepared by the IZRK.