Vízügyi Közlemények, 1948 (30. évfolyam)

2. szám - VII. Szakirodalom

(41) Stage on the gauge in Szolnok cm Occurency of lower levels in the most unfavourable years days Number of years recording lower levels during Stage on the gauge in Szolnok cm Occurency of lower levels in the most unfavourable years days 0 30 60 90 days Stage on the gauge in Szolnok cm Occurency of lower levels in the most unfavourable years days in 30 years of investigation — 30 164 3 24 16 9 — 60 121 4 20 12 5 — 110 67 13 7 3 0 — 140 35 20 2 0 0 — 170 14 29 0 0 0 In consequence of the trifling low water discharge (minimum 65 cubic metres per second) and the great dimensions of the bed, the greatest depth achievable by regulation below Szolnok is 20 dm. The recorded readings of thirty years show that it is enough to secure this depth if the water stage is —140 cm. The occurence of a lower water level than the above mentioned one, is rare, and if we were to take these as a basis for regulation the achieved result would not be equal to additional costs. (The lowest recorded water stage of Szolnok is —180 cm, but during 30 years this occurred only once, lasting for 2 days.) The recently organized National Water Board has taken into consideration the canalization of the Tisza. The fundamental motive of this canalization is irrigation: to secure an elevated water level in order to facilitate water intake. (Besides: the possibility that a considerable part of the natural discharge of the canalized Tisza will be utilized for irrigation purposes.) By the erection of dams the possibilities of navigation will be of course further improved. Nevertheless, since previous to canalization the till nowunregulated river bed should be stabilified and as navigation on the river should continue (for instance the stone material for regulation purposes is obtainable at cheapest price from the quarries of Tokaj on the Tisza) the low water regulation must by all means continue. 2. Shape of the fords and discussion of the widenings of the river bed. The greatest obstacles to low water navigation are shallow folds. In the middle course of the Tisza (between Tokaj and Szeged) there are two kinds of fords: hard soiled clayey fords, where the bottom resists erosion and in consequence there is no sufficient depth of water, and fords of solid content, where in the widened river bed the deposition impedes navigation. The two causes are often found together. Fords are generally found at the passages of a river, and even occur in straight sections or in slight bends. They are mostly caused by widening of the river bed. This may be brought about by human interference, but can be caused by nature. In the case shown in Fig. No. 3 the widening of the channel below the bridge of Tiszafüred was caused by the construction of too short a dam, built to secure the right hand bank, in this way protecting the bridge head. Figure No. 4 shows a typical natural widening below a bend, caused by the fact that the thalweg, even after the cossing, remained near the hard concave shore. The classic masters of river regulation: Fargue and Girardon fixed the natural laws governing the formation of a river bed, stating the conditions of curves and the dimensions of width which ensure a favourable passage. There are experts who think that these geometrical data are of decisive importance; others try to state the characteristic distances of the passages of certain sections of the river. The author does not dey that in slack soil the river bed is formed in a regular way, according to the assertions of researchers, but the formation and bends of the river bed of the Tisza depend only on its soil. There are proper fords where the minor bed is wider than in the adjoining bends. There are no characteristic forms of bends, which guarantee a good ford. The distances