Vízügyi Közlemények, 1934 (16. évfolyam)

4. szám - XI. Szakirodalom

I. RELATION OF THE REGIONAL CHARACTER OF RIVERS TO THEIR IMPROVEMENT AND TO IRRIGATION. BY DR. J. CHOLNOKY. The tractive force of rivers is dependent on their discharge, slope, and the frequency and range of variations in water levels. Rising water has greater tractive force, because increasing velocity sweeps off more detritus, while with decreasing velocity part of the material is left in the river bed and the transport gradually ceases. The comparison of the tractive force with the work needed for transporting detritus in river beds throws light upon the most important characteristics of the river, which have not as yet been sufficiently taken into consideration. Where the tractive force of the river is greater than the work to be done, the river has an upper-section character ; the abundant force of the water attacks the bed and deepens the valley. Such a river has a V-shaped valley. Where the tractive force equals the work to be done, the river has a middle-section character ; it meanders, and broadens its valley until, in the course of time, conditions become stable. Where the tractive force of the river is less than the work to be done, the river has a lower-section character, branching off and forming sandbanks and arms. These latter are always of middle-section character, because they are able to increase or decrease the material carried to a quantity proportionate to their tractive force. Rivers show their typical lower-section character in deltas. Here the main branch is full of banks, and the side branches meander greatly, as, for instance, the deltas of the Danube and the Ganges. Rivers in their upper-section need not, as a rule, be flood-controlled, because there is no plain valley exposed to danger of inundations. In the middle section, where the river forms many bends, the river improvement can be definitely planned by establishing the respective intervals between the levees according to the principle of P. Vásárhelyi, i. e. the proportion between the width and the depth of the flood bed should be the same as in a stable middle-water channel. In their lower section rivers cannot be definitely improved, because they are constantly filling up their bed and flood area (the Hoang-ho, the Tonking, the Po and many other Italian rivers, etc.). The lower sections of rivers are suitable to irrigation, because the regional character permits the water to be conveyed in all directions through irrigation canals. The water of the middle section of rivers, e. g. the Tisza, can hardly be used for irrigation, because of the character of their surrounding region, unless the water is hoisted by certain mechanical means. In the lowlands of the Ganges,