Use of long-term hydrological measurements for mapping of susceptibility to floods within selected karst areas in Slovenia

Country: Slovenia

eLTER site: Postojna-Planina Cave System

Karst areas are characterized by solubility of carbonate rocks, resulting in predominantly underground drainage. Due to rapid flow and quick transmission of any substances, these areas are very vulnerable to pollution. Some areas, like large enclosed depressions called poljes, are also susceptible to flooding. This happens when groundwater level rises above surface or when inflow into poljes is larger than outflow through swallow holes.

These floods are regular and usually don’t cause problems, but sometimes they are extremely high and cause substantial damage to infrastructure. Therefore, detailed studies for better understanding of their behaviour are necessary.

The goal of the present study was to determine the inundation of karst poljes and intermittent lakes occurrence for purposes of ephemeral flood mapping. The pilot area was Planinsko Polje, which receives most of its water directly from the Postojna-Planina Cave system.

There are almost 100 years of continuous hydrological measurements on Planinsko Polje, showing that the polje is usually flooded for three months per year. Detailed analysis of these long-term data, additional use of other sources (satellite images, land use) resulted in a proposal for a process of data analysis and the definition of intermittently flooded karst areas. Such an approach was tested on two additional poljes and 15 intermittent lakes.

The results provide spatial information that is important for the preparation of national plans for protecting sources of drinking water, for the protection of groundwater dependent ecosystems, identifying the effects of environmental changes on groundwater, etc.

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