Abstract. - The floodwaves of 1998-2001 and the year 2006 reached never before measured heights on the river Tisza. The peak heights of the upper and middle reaches of the river exceeded the maximum values by 130-150 cm. Such an intense growth has never been experienced (the peak heights measured at the Tivadar gauging station exceeded the values of 1970 by 149 cm and at the Szolnok gauging station by 132 cm), not even after the river regulations in the XIX. century. The new, critical maximum water levels urged the reconsideration of the flood protection system’s development strategy alongside the river Tisza. Taking the present flood-conveyance capacity with its declining tendency and the possible reoccurrence of the latest (1998-2001) or earlier (1970, 1947/48, 1940, 1941, 1932, 1919, 1895, 1888) hydro-meteorological phenomena into consideration, the success of a flood protection procedure can only be guarantied by the improvement of the riverbed’s flood conveyance capacity and the concerted operation of several reservoirs. The concerted and effective operation of the reservoirs (6 to be built in the I. development phase and others to be constructed later) have to be based on a complex and steering high-water operational model, a constantly updated data-base and a well functioning organization. The river Tisza demonstrated its power this year as well. The river exceeded the highest water levels on a 270 km long reach from Tiszaug (Tiszainoka) down to the Danube influx. Experiencing the flood of spring 2006, the floodwave of 2000, called to be the floodwave of the millennium, is not exceptional anymore. It seems, that we have to prepare for water levels 100-150 cm higher than the maximum levels of the last, hydro-meteorologicaly similar period of 1960-1970. This statement is based on the following: considering the data of the period 1901-2006, the 1% water level calculated by traditional probability theory is 1059 cm, calculated by intercept method is 1058 cm. For the accuracy of our forecasts, during the flood in spring 2006 we combined the hydrodynamic model with our forecasts prepared for the boundary cross-sections. In this study we present the hydrodynamic model prepared for a 740 km long reach of the river Tisza and the combination of the model with the forecast system.

Key words: maximum discharge, Water discharge curves, 1D hydrodynamic modelling, hydraulic engineering structures, calibration of the model