Vízügyi Közlemények, 1963 (45. évfolyam)

4. füzet - VIII. Könyvismertetés

"(67) The measured water content of the snow cover called attention as early as in February to the danger of large amounts of snowmelt water and pointed at the same time to the areas likely to become critical : the region around Lake Velence and the Bakony Range. Flood forecasts were prepared on a statistical basis, but with allowance to the storage reservoirs with the help of hydraulic calculations. These calculations rested on direct discharge measurements. The stage hydrograph of the reservoir created downstream from Lake Velence was described by a differential equation (Fig. 4.3) which was fully justified in practice. The forecasts issued during the floods proved correct in most instances. Discharges observed and the probability of occurrence of estimated, or measured peak discharges are shown in Figs. 4.4 and 4.8 Respectively, the frequency of floods which occurred over this area is illustrated in Fig. 4.8 with specific runoff values entered in Fig. 4.10. The correctness of forecasts issued in February is corroborated by these figures as well. The extraordinary meteorological conditions offered good opportunity for observing drainage conditions. A characteristic of catchments accessible to measurement is the runoff volume, although this value is fundamentally affected by human activity, by the density of the canal network, and the operation of sluices. Observation concerning the duration of inundation by snowmelt water and the percentage loss in different crops shown for one of the catchments (the Adony catchment) are seen summarized in Table 1. 5. Flood protection experience qaiiicd aloncf the Sió and Xádor Canals (Bij Z. Máthé, Civ. Eng.) The Sió and the Nádor Canals are the two main watercourses in the area mentioned in the proceeding section (for the map see Fig. 4.1 ). The stages observed on both watercourses in the spring 1963 were identical, or even slightly higher than the highest ones on record, the floods in 1940 and 1947. (A comparison for the Sió and Nádor Canals is given in Fig. 5.1, Table I and II, respectively.) The history of the floods and protective measures along the two watercourses are described, together with the experiences gained. Pictures illustrating flood fighting operations are shown in Fig's. 5.2 to 5.6. (i. Flood on the Marcal and Rába Rivers (Bg B. Sipos, Civ. Eng.) The other area suffering from flood damage was the western fringe of the part west from the Danube. The Marcal and Rába Rivers are tributaries of the Danube River and flow in this area from south to north. As pointed oui in the section describing meteorological conditions the extraordinarily long and severe weather in winter created exceptionally unfavourable conditions in this area, when the bare soil was first saturated, then frozen to 60 — 80 em depth and covered subsequently from midJanuary by a thick snow layer. At the beginning of March the melting of the snow layer of high water content created on lower reaches of Marcal River a flood wave which exceeded the highest stages on record. At the site indicated on the attached plan the left-bank levee of the Marcal River ruptured and about 4000 hectares were inundated by round 50 mil lion cu.m water. An ice-carrying flood developed this year for the first time on the Rába River. Major floods on this river occurred in the past in ice-free periods. The ice jam which developed on the lower reach created a critical situation, since the rupture of the leftbank would have entailed the inundation of 40 to 50 thousand hectares with numerous settlements. As a protective measure small tugboats were operated as ice breakers and ice blasting also produced good results. 7. Floods on the Zagyva and Tarna Rivers (By J. Dabolczy, Civ. Eng.) The third area of the country suffering flood damage was the valley of the Zagyva and Tarna Rivers north from the corner formed by the Danube and Tisza Rivers. The majority of the 5777 sq.km large basin is hilly and rolling country. Accordingly the floods are very violent and arrive in 12 to 16 hours to the plain region. The dangerous floods in this area were due to the thick snow cover and precipitation accompanying snowmelt.