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Wednesday, October 4, 2023

Floods – and what now?

Dr. Andrej Umek

The floods that hit Slovenia at the beginning of this August represent a significant disaster, at least for a part of the country. The raging waters destroyed homes and workplaces for many residents. The bright, positive point in this disaster is the significant solidarity shown by Slovenians with those affected. However, I am far less satisfied with the response of the government and its institutions to this disaster, even though they talk about recovery and promise all possible help. But the mere restoration of the situation to pre-flood conditions should not be our only goal. This column is dedicated to addressing the issue of why and how we should define the goals of post-flood recovery.

When considering how to begin post-flood recovery efforts, I was troubled by the fact that authorities talk about five-hundred-year floods, which occur every five hundred years. Data on the precipitation that caused these floods, their total amount and intensity, as well as their return period, remain hidden from the public eye. To the best of my knowledge, the return period for both the quantity and intensity of precipitation was significantly, significantly less than five hundred years. This fact clearly shows that in past decades, Slovenia has not adequately managed its watercourses, neither rivers nor torrents. In areas where watercourses were properly managed, the damage was significantly less or even non-existent. Watercourses did not change their course in such places. The essential element of watercourse management is slowing down the water flow. This is achieved through the construction of cascades and ensuring a sufficiently wide wetted perimeter. A great example of correct management of torrential watercourses is the Pišnica in Kranjska Gora. Despite increased flow throughout the entire golf course, it did not cause any damage. A bad example of watercourse management is the “regulation” of the Gradaščica in the Dobrova-Polhov Gradec municipality. With these regulations in this municipality, they accelerated the drainage of risen waters, saving a few meadows. However, by speeding up the water flow, they raised the flood wave and, in the past, flooded Vrhovci, Vič, and Kozarje. Extensive work carried out on the Gradaščica and Mali graben this year saved southwestern Ljubljana from flooding. From what has been said, it follows that meaningful recovery is only possible based on a decision on to what extent watercourses will be restored.

The second question that significantly affects the sense of recovery is how to deal with structures that were built in the past on floodplains or without considering high waters. This group includes road sections located in riverbeds. This situation occurred more frequently, especially in the Upper Savinja Valley and in Carinthia. These were bridges with too small a span, insufficient clearance height, and with supports in the riverbed. There were also residential buildings constructed on floodplains. A clear example of irresponsible residential construction on a floodplain is Sneberje in Ljubljana. The same can be observed for numerous constructions in the most affected parts of Slovenia.

Before starting the recovery, the government and its related institutions should, in accordance with the rules of project management, establish clear objectives and priorities for the recovery. Defining these objectives is a challenging issue due to past mistakes over the decades. The first task should be defining the planned recovery of Slovenian watercourses and determining the relationship between the quantity and intensity of rainfall and flows. Based on this, a new map of flood-prone areas should be created. The second critical decision before floods is how we want to protect our infrastructure and residential buildings in terms of return period. In this regard, we could take a cue from the old Austro-Hungarian Empire, which clearly defined, before the construction of the Southern Railway, that this railway connection must be safe from five-hundred-year floods. Only based on this can rational decisions be made regarding which structures need to be repaired and which, unfortunately, need to be demolished.

In conclusion, many mistakes were made in the management of watercourses in the past. These need to be corrected. We need to repair watercourses and those structures that will not be threatened by future high waters, and abandon those that are located in flood-prone areas. This column was written with the belief that Slovenians deserve greater flood protection, and that this can be achieved.


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