Vízügyi Közlemények, 1970 (52. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
of bed-load transportation may be important for a wide variety of purposes (design of regulating structures, construction and maintenance thereof, determination of probable yields from gravel dredging operations, etc.). Urged by these demands investigators search for new and more reliable methods. A new approach consists of labelling bed-load particles with materials having other physical properties than those of other particles. Relying on examples and data published abroad, this method has been introduced in Hungary by L. Rákóczi [1] for studying the bedload on the upper Danube and the sediment in Lake Balaton. He used different luminescent dyes for labelling the bed-load particles. Coating gravels belonging to different size fractions with differently coloured dyes he succeeded in tracing the path of bed-load particles. The same method was used by him for measurements and observation also on the Elbow river in Canada. His objective there was not the mere tracing of particles, but the determination of the rate of bed-load transportation. The same objective was followed by J. Bransky and J. Skibinsky [3], who developed a new bed-load trap. From the results of observations carried out with the new device and by theoretical considerations they arrived at the following conclusions: a) The volume of bed-load may frequently form a significant proportion of the total sediment load transported by the watercourse. b) The opinion common in Poland in the years 1960 to 1968, according to which the volume of bed-load transportation is negligible in comparison with the total sediment load is incorrect. The ratio of bed-load transportation to total sediment load is obtained from the expression — ^ = 0,074 A 011 5. (1) G a + U a ' G a is the volume of bed-load in the annual average total sediment load (kg/cu.m), U a is the volume of suspended sediment in the annual average total sediment load (kg/cu.m), A the area of the cathcment area pertaining to the particular gaging section under consideration (sq.km). On the lower and medium reaches of the Wistula river the above ratio was 23,6 to 30%, increasing upstream. c) Considering a particular gaging section the ratio of the volume of bed-load transportation and total sediment load varies together with the ratio QIQ a • The relationship is expressed by the formula: G G a Í _Q_i<VB0 G + U G a + U a 1 Q a ! G is the rate of bed-load transportation at a particular discharge (kg/sec), (2> 62
