Tracing experiment at Lake Bohinj

Investigations of the lake water circulation

Boat with measuring equipment (Variosens)

The water circulation is one of the governing factors for the eutrophication state of a lake and therefore of major importance. Numerical water circulation models are tools to better understand the water circulation and particle transport in lakes. However, they can only provide reliable results when calibrated on experimental data. In the framework of a co-operation between the University of Ljubljana in Slovenia and the Institute of Hydrology, a tracer experiment was conducted at Lake Bohinj, to investigate the water circulation and provide calibration data for such a model. The lake is located in the Triglav National Park in the central part of the Eastern Julian Alps in Slovenia at an altitude of 525 m a.s.l.. It is dimictic, has a surface area of 4.3 km2, a mean depth of 30 m and is surrounded by steep, high mountains. In September 1997 the main inflow to the lake was traced with 30 kg of the fluorescence tracer uranine. During the following nine days the tracer distribution in the lake was recorded by a team of scientists. Two boats, equipped with in situ tracer measuring devices, shipped the lake during day times. Vertical profiles of the tracer distribution were recorded in different locations, while the boats' position was determined by GPS. The in situ measurements were supplemented by samples from the boats and at the lake outlet for laboratory analysis. Another method of observation was photography. Due to the clearness of the lake the horizontal tracer distribution during the first days with high tracer concentrations was visible. The field experiment resulted in differentiated insights into the water circulation pattern of the lake. The lake circulation was mainly induced by the main inflow, which forms different distinct vertical layers in different depth. These layers have very different dynamics, decreasing from the top to the bottom. The experimental results were an important basis to develop and calibrate a numerical lake circulation model.


  • Finanzierung: EU, Hydraulic Division of the Dept. of Civil Engeneering, University of Ljubljana, Slovenia
  • Projektleitung: Prof. Dr. Ch. Leibundgut
  • Projektbearbeitung: Dipl.-Hyd. V. Armbruster

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