Floods should bring reckoning in siting and engineering, experts say

Ljubljana, 13 August - The recent floods, deemed the worst on record, have created a massive challenge for hydrology experts, who will have to prepare more effective flood safety measures. Experts believe these are relatively good, but no match for an event like last week's. Reconstruction will take a long time and autumn rains will come with additional risk this year.

The floods were not completely unexpected, the STA learnt from hydrology experts, as the Environment Agency has issued warnings about this kind of danger. But still, nobody was able to imagine a disaster of such proportions.

Hydrologist Jošt Sodnik, the director of Tempos, a company specialising in waterways, landslides and erosion, underlined reconstruction will not be possible before autumn rains.

Most urgent measures will be carried out, and beds of rivers and torrent streams will be cleared out, he said, adding that the most affected areas will take priority.

"We must not forget that autumn and winter rains are still coming. Critical locations will have to be identified where urgent works will be carried out in the event of strong rainfall. Autumn will not be easy due to a greater vulnerability of infrastructure."

Meanwhile, strong storms and rainfall are expected to become increasingly common, as the atmosphere continues to warm up, said Nejc Bezak, a hydrotechnology expert teaching at the Ljubljana Faculty of Civil and Geodetic Engineering.

A one-percent deviation in temperature increases the amount of water vapour in the atmosphere by 7% and increases the potential amount of rain by 15%, said Bezak, warning that preparations must be made for the future.

Bezak believes that flood safety in Slovenia is relatively good, but some infrastructure is inadequately maintained. Moreover, the majority of infrastructure is planned for an average period of 100 years between the occurrences of inundation events, he said.

"The recent flood event was truly extreme. Some analyses we conducted for certain precipitation stations and waterways have shown some return periods of over 1,000 years, which means that such an event may take place ten times in every 10,000 years."

"These estimates are rather uncertain," he added, "given that measurements have been made only for the past few decades. It is hard to be certain about water volumes with return periods of 20, 50 or 100 years, let alone 1,000 years."

What is more, climate change means that return periods for flood events are becoming shorter, Bezak said, adding that hydrology experts had been neglectful of climate change, especially in terms of infrastructure planning.

Relevant services should create guidelines for the determination of water volumes in engineering, which will take into account the potential effects of climate change, he said.

Sodnik said that virtually no building was designed for return periods attributed to the most recent floods, except maybe the Krško nuclear power plant. "Flood safety measures do not provide an adequate degree of flood safety in the face of such extreme events."

He believes the floods were all the more severe due to poor maintenance of some waterways over the course of the past 20, 30 years. "The monitoring of erosion in torrential streams was neglected. Now towns in the Upper Savinja Valley and Koroška, above all, are literally buried under grit from torrential streams."

No measure can ensure 100% flood safety, but a comprehensive approach in planning measures for entire river basins can significantly lower the risks, said Bezak.

First and foremost, torrential stream beds will have to be cleaned out, he said, adding that flood debris must be prevented from entering waterways.

Bezak also pointed to water reservoirs as being effective protection for densely populated areas, while green surfaces in cities are very good at absorbing precipitation.

Bezak and Sodnik believe Slovenia needs to change the approach to siting, so that building in flood zones is avoided.

"Despite the fact that good flood charts are available, flood zones are attractive to investors, perhaps because this land is somewhat cheaper than plots further away from waterways," said Bezak, expressing hope that the devastating floods will have served as a lesson.

Comparative analysis of areas that are flooded very rarely shows that over 50,000 buildings are located in such areas, he said. But in reality the number is higher still, because flood charts have not yet been created for all waterways in the country.