50 years ago, there was an extraordinary flood of the Fehér- and Fekete-Körös rivers

Abstract

Between 1895 and 2006, 17 significant water waves descended on the Körösök, and the peak water levels of quite a few of them exceeded the previous highest water levels. Many embankment breaks occurred in Hungarian or Romanian territory, so that they spread and caused flooding in Hungarian territory as well. In the seven decades between 1925-1995, 31 such events are recorded here. The hydrological experience of these embankment breaks, and embankment crossings had a significant impact on the development of the emergency flood storage method. The low-precipitation weather of the end of 1973 - beginning of 1974 changed radically in May, in three months the number of rainy days in the Fehér and Fekete-Körös mountain watersheds exceeded 60, and the amount of rain that fell in some places was 500-700 mm. Five tidal waves formed on the two rivers in a few weeks, the second of which, on June 14-15, caused extraordinary water levels. In the upper and middle sections of the Körösök, 104 km of embankment had to be raised in a few hours in order for the tidal wave to be channeled between the embankments. A decision was made that the so-called delta area between the two Körös should be filled up and used as an emergency reservoir in order to prevent major economic damage. On the afternoon of June 15, the embankment on the right bank of the Fehér-Körös was opened by blasting, and in the Fekete-Körös, the water breached the embankment in the two pre-weakened places. The flooded agricultural area is 7 100 ha, with scattered farms. Based on the calculations, the stored water mass was 118 million m3. The 1974 emergency reservoir was of extraordinary importance from a hydrological point of view. As a result of the levee openings, the regularity of the order of peaks (fall, velocity, water flow) was overturned and what we call the "inverted loop curve" developed in the Remet Remete and Gyula section. The relationship Δh=f(W) obtained for the emergency reservoir in 1974 clearly proves that even with the release of a relatively small amount of water, a significant flood peak reduction effect can be achieved, and that lowland flood reservoirs can also be an effective flood protection method. This was confirmed by the floods of the following decades, also on the Körösök and other rivers. During the catastrophic flood in Körös 50 years ago in 1974, emergency reservoirs used as planned for the first time by cutting the embankments. Based on the experiences of this flood, 3 emergency reservoirs were built in a few years, and this served as the methodological basis for the design of the Tisza reservoirs (now 7).