Introduction
Analysis of the time series of annual maximal, mean and minimal water stages of the past century at the Szolnok gauging station shows a trend of increasing high water levels, slightly decreasing mean water levels and decreasing low water levels. The decrease in the mean and low water levels is the result of the deepening and narrowing of the mean river bed as it will be seen on the evaluation of the changes of the cross sections. The reason of the increasing maxima is also partly connectable to the above changes but is more complex and will be explained by the evaluation of the discharge measurements.
Flood conveyance of the Middle-Tisza reach can be best and most accurate demonstrated by analysis of the flood discharge measurements of different floods. We may declare this despite the fact, that due to the slight bed and water surface slopes, the backwater effects of the Hármas-Körös, the Maros and, to a certain extent, also the Danube river have impact on the passing down of flood waves and on the shape of flood loop curves.
An important question of analyses of flood discharge measurements was whether to accept or involve into the survey the historical measurement results (from 1895 and 1932). We will see below, that these measurements must not be disregarded by all means. Only by the processing and analyses of these measurement results is possible to find an explanation and to understand the phenomena have been taking place in the regulated bed for 100 years.
Results of flood discharge measurements performed at the Szolnok section of the Tisza river during significant and extreme floods in the years 1895, 1932, 1970, 1979, 1999 and 2000 are shown in figure below.
An important factor that gives explanation on the high conveyance capacities measured in those years, that no summer dikes existed yet in 1895 and only a few in 1932 with significantly lower dike crests than in the period of 1950-1980.
The fundamental aim of the regulation of the floodway is to restore the flood conveyance capacity of the River Tisza to the level of prior to the year 1970. Possible scenarios for improvement were tested using a HEC-RAS model of the river for the study area.
The tested scenarios were:
