Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

tracers permitted the observation of bed-load particles moving in the watercourse itself, the determination of the sorting and rate of abrasion of sediment materials of different mineralogical composition, and it is to be hoped that in the near future even the rate of sediment transportation can be measured. Investigations are under way for labelling natural sediment materials with the help of magnetism and for tracing its movement in this manner. No conclusive evidence is as yet available on the development of ripples, dunes and antidunes, as well as on their influence on sediment transportation. The first steps have already been undertaken in this direction, but the number of measurement data is too scarce to derive general relationships therefrom. 4. Influence of sediment conditions on river-bed morphology The objective of river regulation is always to effect certain changes in the stream channel. Consequently, it would be of paramount importance if the changes in bed configuration resulting from the regulation measures could be predicted in advance. Similar forecasts on bed changes would justify in advance the soundness of the contemplated regulation measures. The prediction of bed changes to be expected after regulation presents an extremely complex problem. Experiences gained on river sections regulated earlier are very valuable in this respect. The theoretical determination of silting and watersurface profiles over the backwater reach created by the Iron Gate power project on the Danube, is an illustrative example for the estimation of potential bed changes. For estimating future sediment concentrations the expression KœH v = — (13; V

s has been used, where К is sediment concentration (kp/m

3), v the average velocity (m/sec), œ the fall velocity of the suspended sediment (m/sec) and Я the mean depth of the channel (m). By plotting the values of r; in terms of the shear velocity U

X

). a relationship has been obtained which was found suitable for determining the limit values of sediment concentration, which varies from cross-section to cross-section. In these computations the rate of bed-load transportation has been ignored as being substantially smaller than that of suspended sediment and the original particle sizes have been determined from samples retrieved from the bed material. From the estimated values of silting the potential rise of stages could be predicted. If it is desired to determine bed changes on the basis of field studies, data on stream flow, local slope and sediment transportation must be available for several cross-sections, the granulometry of suspended sediment must be determined, bed-load transportation must be measured using either a bed-load trap, or radioactive tracers and finally the flow pattern must be known for the entire stretch affected. 18