Vízügyi Közlemények, 1999 (81. évfolyam)
4. füzet - Szlávik Lajos-Galbáts Zoltán-Kiss Attila-Kisházi Péter-Rátky István: A Fehér-, Fekete- és Kettős-Körös árvizei, árvízvédelmi rendszere és a Kisdelta szükségtározó
A Fehér-, Fekete- és Kettős-Körös árvizei, árvízvédelmi rendszere... 607 Peak water levels of the floods of the Fehér- and Fekete-Körös rivers were rising, in the 20 th Century, at such a rate which has never been experienced before in Hungarian rivers. The trend of this rise has not changed in the recent years, either (Table V, Figure 9.). The slope of flood water levels has also changed (Table VI.). Substantial number of discharge measurements has been made in the past decades, in order to determine the flood water discharges and volumes with the possible highest accuracy. (Table VII. ). These data allowed the reliable estimation of the loops (hysteresis) of the flood discharge rating curves (Figure 10.). Peak water discharges and flood volumes also show rising trends (Figure 11., Table V). These is likely due to anthropogenic impacts on the catchment areas of the rivers. Analysing the parameters of the most significant flood of the 20 l h Century (14 pes in the Fehér-Körös at Gvula. 13 ones in the Fekete-Körös at Remete) it turns out that the highest values correspond to the floods of the past 2—3 decades, while the frequency of occurrence of such floods is also rising. (Table V.). Features of the passing of the floods of the rivers Fekete- and Fehér-Körös were similar in the past decades and stem from the shape of the catchment area, the type of the river network and from the effects of the flood control works. Flood conditions of the system were defined by the River Fekete-Körös. During the flood of the Christmas of 1995 the timing of the passing flood waves of the two rivers have changed and this has altered the slope conditions, creating a situation that was never experienced before: The flood waves were governed by the flood of the Fehér-Körös. Hydrological and flood-defence conditions of the Körös rivers can be considered extreme ones, without any exaggeration. Since 1966 there were two levee ruptures in the Hungarian reach of the rivers and practically all larger floods had to be stored, as the results of the successful defence actions. It is of special importance that the flood-defence problems of the Körös river system have been shifted towards downstream, to Hungarian territory, in the past two decades. While in the period 1925-1970 there were no levee ruptures or emergency flood storage necessitated in the Hungarian area, there were 13 such events in the period 1974—1995 (Figure 8.. Table VIII.). The eventual reason is that levees have been and are being gradually constructed even in the valleys of the tributary rivers of the mountainous areas. The consequence and dynamics of this process cannot even be estimated. It is apparent and needs consideration that ever more critical flood conditions occur in Hungarian territory, in spite of the continuous development of the flood control system. It is expectable that even more unfavourable floods will occur in the future in the Hungarian part of the Körös river system. It became evident in the past three decades, that the "traditional" means of flood control, the rising of the level of flood levees and the expansion of flood-channel cross-sections, cannot be followed anymore, and active flood control actions, the emergency storage of flood volumes, is needed. Upon the development of the flood control system of the Fekete Körös, after the flood of 1974, it was felt that the flood defence situation was stabilised with the construction of the emergency storage reservoirs of Mályvád, Tamásda, Kis-Zerind and Tôz-polder. (Figure I.). However, the flood of December, 1995, indicated that the elements of the flood defence system are not effective enough for the safe releasing of the increasing floods of the River Fehér-Körös, within the flood levees. After the flood of December 1995 it became evident, that flood defence problems of the area can only be effectively solved by emergency storage. Several emergency flood storage development alternatives were considered (Figure 12.) and the construction of the emergency reservoir Kis-delta (Little-delta) was decided. On the basis of the analysis of data it was unambiguously found that the emergency reservoir Kis-delta (Figures 13—14) represents a realistic alternative of the development of the flood levees of the right bank of the River Fehér-Körös and of the rising of the levels of the bridges of the river. The flood control facilities, which have been constructed at the Kis-delta emergency storage system are as follows (Figure 13): — A fixed sill opening in the right-bank levee of the River Fehér-Körös, between river kilometres (r.km) 2.530 and 2.600; — A stand-by deposit of materials for filling the opening; — Earthen dikes and their structures around the storage area (Figures 21-23)
