Vízügyi Közlemények, 1970 (52. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
therefrom that since the first conference was held in 1962 the development in this field has been a significant one, and the achievements of this research are worthy of interest even in countries, where the phenomenon of torrential sediment flow does not cause immediate problems. To conclude the present report two papers will be introduced, which although not concerned with the boundary conditions of bed-load movement, offer valuable help in the field study of this phenomenon. According to the paper of Bozinovic [2] in the course of preliminary studies related to a proposed hydroelectric development the author performed his observations on a straight, regulated section of the river, using a modified Károlyi-type bed-load sampler. Samples were retrieved first in five, later in a single vertical in each of the cross-sections, at the point of most intensive movement. Hydraulic parameters of the watercourse were observed simultaneously and the constants of the Meyer —Peter formula were calculated from the rates of trasportation determined with the help of the sampler. The original constant 0,047 of the equation was found to vary from 0,0248 to 0,0525. It is demonstrated that no detectable relationship existed between this variation and the rate of bed-load transportation. It is suggested that it would be interesting to relate the computed values to changes of relative roughness. Drawing on the experiences gained it is suggested by the author to observe simultaneously with bed-load measurements the hydraulic parameters of the watercourse as well, and further sampling in a single, carefully selected vertical should be sufficient. The latter conclusion does not appear as fully convincing, as it is widely recognized that rate of sediment transportation is subject to both quantitative and qualitative changes even at the same stage and discharge. Consequently the reliability of conclusions arrived at on sediment transportation from a single observation seems to be questionable. The same problem was studied in Hungary by J. Csoma [27] on the Upper Danube, where he performed a series of observations. In each of seven verticals in a single cross section 30 samples were taken using the Károlyi-type bed-load sampler, under approximately steady flow conditions. Mean values and standard deviation were computed, from which the statistical distribution of observation data was determined for each vertical (Fig. 4). Appreciable differences were found to exist between the distribution curves obtained for individual verticals. As revealed by the test of homogeneity, the data originated from different populations. The values obtained for the rate of sediment transportation through a cross-section may thus vary widely depending on the location and frequency of sampling. The second paper on techniques of field observations is that by RomanovsJcyi [7]. This method is used since 1961 by the State Hydrological Institute, Leningrad. The bed-load material is photographed in the field, in situ, together with a 10 by 10 cm wire mesh, permitting the determination of the photographic scale. Sets of standard discs have been 56
