When he came to Poland than the Genoese Borisheavy rainfall caused more and more water in the rivers from hour to hour. After the flood of the millennium in 1997, many investments were made to protect against another disaster, including retention reservoirs, which quickly became the center of attention, and especially the dry Racibórz reservoir, which was decided to be put into operation. Unfortunately, many of the protection measures, including the embankments and some dams, did not withstand the pressure of the water and burst.
Is it possible to design hydrotechnical devices that effectively protect people from floods? Prof. Artur Magnuszewski from the Department of Hydrology at the University of Warsaw does not have good news. There is little we can do in the case of extreme phenomena.
Levees, dams, bridges. These are all structures related to water. Their construction is not just a schematic “tapping out” of the project, they must take into account many factors, such as average flow and possible floods.
– When building flood embankments, we take into account the so-called 100-year water, i.e. a flow in a river that has a repeat period of once every 100 yearsand also how much the size of such flow can be exceeded – explains Prof. Magnuszewski in an interview with the Polish Press Agency. The scientist also explained that larger bridges or dams are built taking into account 1000-year-old wateri.e. a flow that has a repeat period of once every 1,000 years, i.e. with an even larger safety margin.
So why do some solutions turn out to be insufficient? The expert cited the catastrophic flood on the Oder in 1903. It turns out that subsequent protection measures for Wrocław were made according to the pattern, which was precisely the situation at the beginning of the 20th century. The level to which the water reached and the amount that flowed in the riverbed were taken into account. Therefore, hydrotechnical solutions were designed so that Wrocław was prepared for a flow in the Oder of 2.1 thousand cubic meters of water per second.
– The year 1997 came, when 3.6 thousand cubic meters of water flowed down the Oder per second, so this shows what we are dealing with. Our ideas and calculations may often not correspond to what may happen in the conditions of an extreme, catastrophic phenomenon. When asked if we can do anything to prevent such floods from recurring, the answer is unfortunately negative – the geographer noted.
In Poland, we have many water reservoirs with a capacity of millions of cubic meters. These include, among others, the Pilchowice reservoir on the Bóbr River with a capacity of 50 million cubic meters, the dry reservoir (polder) Racibórz on the Oder with a designed capacity of 180 million cubic meters, and the largest reservoir – Lake Solina on the San – 400 million cubic meters. But how do these volumes relate to the flood wave?
– It is worth comparing the capacity of such a reservoir with the volume of a flood wave. If thousands of meters flow down a river per second and it lasts for a day or two, then if we multiply these thousand cubic meters by the number of seconds during the flood, we have the volume of the peak wave. And here we are talking about billions of cubic meters, which is much more than the retention capacity of the reservoirs – pointed out Prof. Magnuszewski. He also added that even if we build more reservoirs, we will not be able to capture the entire volume of the flood wave in the event of extreme rainfall – he added.
Moreover, the operation of reservoirs is not just about closing the culverts to stop the water. Their operation must be planned based on accurate hydrological forecasts, they must be controlled so as not only to reduce the amount of water in the river, but also to protect against the meeting of several flood waves in one place, e.g. culmination on the main river and its tributaries.
The Warsaw hydrologist also referred to planting a forest in an interview with PAP. He pointed out that it is important for water resources, but will not solve the flood problem, especially when several dozen hours of rain exceed the monthly rainfall total. – The Kłodzko Valley has a characteristic shape. There we have the mighty Śnieżnik massif, from which all rivers flow into Nysa Kłodzka. Additionally the mountains intensify the effect of precipitationbecause they force the air masses to rise and the water vapour to condense – noted Magnuszewski.
According to the scientist from the University of Warsaw, retention reservoirs should be built and the existing ones modernized – The problem is that all the locations that were suitable for this have already been used – he noted. There are still some possibilities in the lower reaches of the Oder, where polders such as Racibórz can be built. They will be able to collect the water that has not been captured in the mountains.
Civil protection is not only about embankments and reservoirs, but also effective procedures that allow for a quick response and then help those who have lost their homes or need to renovate their homes. The problem is very complex and solving it requires intensive and long-term work by an interdisciplinary team of experts whose work will be professional, objective and will take place above politics. Polish hydrologists will certainly include the flood of 2024 in scientific studies that will be taken into account in the design of subsequent hydrotechnical facilities.
Source: naukawpolsce.pl
Source: geekweek.interia.pl
