Vízügyi Közlemények, 1997 (79. évfolyam)

1. füzet - Nagy Illés:A tiszai véderők árvízi terhelést csökkentő hatása

22 Nagy Illés Tompa K.-Briindl L.: A fiiz. Mg. Kiadó. 1964. Tóröcsik I.: Dendromassza hasznosítási lehetőségei a vízügyi szolgálatban. Kézirat. Szolnok, 1985. Vadas J.: Árvízvédelmi füzesek telepítése és müvelése. FM Во. 1888. Vásárhelyi P.: A Tisza folyó általános szabályozási terve. Királyi Építési Főigazgatóság. 1846. VITUKI: Kiskörei tározó áramlástani vizsgálata. Bp. 1979. VITUKI: Suhás véderdő hullámzáscsillapításának hidraulikai kisminta vizsgálata. Bp. 1983. Zitscher Z.: Analyse zur Bemessung von Aussenböschungen Scharliegender Seediche gegen Wellenbeanspruchung. Wasser und Boden. 1962/10. * * * Flood-reducing effect of the protection-forests of the River Tisza by Dr. Illés NAGY, С. E. The flood load on the levees of the River Tisza is increasing with the height of the wind driven waves which run up along the slopes of the dike (Figure I.). The magnitude of wave-runup on the slopes depends on: the wind velocity, the wind run-up the water depth, the steepnes of the slope of the levee, the lining/cover of the slope, the angle between the tangent of the levee and the wind direction, the wave-stilling effect of the protection forest, and the wind-setup (seiche) of the water level (Figure 2.). Having analyzed the extreme components of wave run-up of the levees of the River Tisza for the period 1960-1970s the following conclusions can be drawn: — In the light of the annual distribution of water levels higher than 75% of the maximum levels of the gauges of the River Tisza (since 1876) it can be concluded that it is sufficient to confine the analysis to the first half of the year (Table I.). — There is a trend in the occurrence of flood hydrographs of the River Tisza, which indicates that their period is being shifted from May—June to February—March (Figure 3.). — The frequency of the direction of winds of 5 m/s magnitude are, in the first half of the year, 24.3% to the west, 22.4% to the South and 16,5% to the NE (Table III). — The highest duration of the wind is 78 hours (NE). — The measured highest wind speed was 15 m/s. — The largest free wind run-up is 10 km in the floodplain of the River Tisza. — The possible largest water depth in front of the levee is 4.0 m. — Wind setup (seiche) can be neglected. Upon the effect of these extreme components, and assuming wind direction perpendicular to the levee, the largest calculated wave height is 1.32 m (Table IV.) and the distance of wave run-up on the slope of ratio 1:3 would be 1.85 m, without the stilling effect of the protection (shelter) forest. The shelter forest, planted in front of the levee, is to attenuate the effect of waves. As early as 1846 Pál Vásárhelyi and his Italian adviser Paleocapa called the attention to the importance of planting shelter forests (Figure 7.). Willow tree forests (Figure 8.) planted into the excavation pits and onto the earthen pathways among the pits (that served as access road to the pits earlier) were gradually formed. In order to keep the forests under flood level the trees were cut 1.0-1.5 m below the maximum water level H

max (Figure 9.). the new branches of 2—3 m length were regularly cut in every 3-4-th year, thus forming a broom-like canopy, wchich effectively attenuated the waves (Figure 10). This tiring manual work was abandoned starting with the seventies and the branches were growing freely. Consequently the