Vízügyi Közlemények, 1954 (36. évfolyam)
2. szám - XV. Szilágyi József: Az Erzsébet-híd roncsainak hatása a mederalakulásra
(26)development of methods and equipment that may be regarded as most up-to-date from all points of view. After initial measurements of suspended load the determination of the variation of the suspended matter according to depths and water stages has been successfully introduced. Even the determination of the relation between concentration and suspended load on the one hand, and of the water stage on the other hand, has been solved. Since Hungarian rivers generally carry fine silt, the sampler is a very simple device. (Fig. 1.) In measuring the bed load the design of a suitable trap was the principal task. The bed load trap of latest Hungarian design is shown in Fig. 2. (Cf. : Mesures se rapportant au débit solide du Haut Danube, by Z. Károlyi, IAHSR, Third Meeting, Grenoble 1945. Rapport 11 — 12.) Of course, the difficulties presenting themselves in measuring bed load call for still more solutions ; the most important of these is the calibration of bed load traps. For the lack of adequate calibrations our data on bed load movement may be considered as initial and approximative results only. The bed material was initially examined on sporadic samples only. Great differences in bed material indicated that cross-sectional survey had to be made by taking profiles one close upon another. Extensive bed sediment measurements have hitherto been carried out on the Danube River only. The bed material sampler used in Hungary is pictured in Fig. 3. 2. Evaluàtion of sediment measurements In general one sediment measurement extending to a full cross section is made per week at each sediment station. At selected verticals the transported bed load is measured, from several depths a total of 10 lit. of water sample, and material samples from the bed are taken, the velocity being metered at the same time. (Cf. the author's paper in Vol. 3 — 4, 1949, of this Review, with English and Russian summaries.) Of course, at the time of the measurement the water stage (h) is observed, the wetted cross-sectional area, the width of the water surface, mean velocity, discharge and mean depth are computed. With the aid of the mean concentrations of the verticals and with consideration of discharges the total suspended load (G x kg/sec), and with discharge Q the mean concentration representative of the section С * (g/m 3) = G^Q- are calculated. Of each sediment and bed material sample mechanical analysis is made ; the mean diameter and other characteristics of the transported sediment are determined. The critical bottom velocity corresponding to the mean of the bed material, as well as the theoretical suspension velocity of the mèan diameter of the suspended material are also computed. From results of several characteristic measurements are computed the so-called saturation concentrations and velocities. Similarly for some representative measurements, with the aid of the mean diameter of the bed material d g, velocity head h v = v 2/2g, as well as hydraulic radius R and slope J. factor a = d g/h as well as value b = d gjRJ representative of the stability of the river bed are calculated.. Mean concentration Ck determined at each measurement as well as suspended load Gi and bed load G g are in general expressed in terms of the river stage, exceptionally as functions of the velocity or of the discharge. With consideration of the relationships C* = f(h), G g = f(h ) and Gi = f(h) and of the water stage frequencies, mean concentrations and mean sediment loads are calculated. The extrapolation of relationships yields extreme values. Rasides these, special studies are made in particular cases such as those in context with problems of sediment transportation in river canalization and industrial water supply. 3. Sediment transportation of the Hungarian rivers The Research Institute for Water Resources has executed or is carrying out sediment measurements on 10 rivers, at 10 gauging stations (See fig. 4.) Besides the two major Hungarian rivers, the Danube and the Tisza, conditions of sediment transportation by 4 minor rivers can be characterized already. Table I. lists characteristic mean diameters, concentrations and sediment load for each of the measuring stations on these rivers. The sediment transportation of the Hungarian rivers, in comparison with foreign rivers, cannot be called extreme.
