Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

There is no logical justification for considering the three parts of the phenomenon separately, unless it is assumed that within certain magnitude limits a particular quantity is of no consequence on the variations of the others. (E. g. within certain limits the velocity distribution in the channel is unaffected by the concentration of suspended sediment.) In general, the characteristics of fluid motion are obviously of great, although not exclusive, influence on the characteristics of sediment transportation and consequently on those of bed development — neglecting human interference and tectonic effects — while the characteristics of sediment transportation affect, within certain limits, flow conditions and naturally, bed development. And finally, bed characteristics affect flow and sediment transportation. Therefore, whichever part of the phenomenon is considered, the characteristics of the two other components must usually be taken into account. The problem is thus not one of interference among three different phenomena, but one of interrelationships between three different components of the same phenomenon. In the papers to be reviewed subsequently — with the exception of the paper by S. Doucet [7] devoted to chemical problems — considerations on sediment transportation are extended accordingly to the necessary extent to include also the characteristics of flow and bed development. 1. Determination of the characteristics of bed-load transportation Some of the quantities characterizing the movement of bed-load in watercourses — e. g. the particle diameter within certain limits — are readily accessible for determination, whereas others — to refer only to the pulsation of bed-load concentration — are difficult to explore, there being in many instances not even reliable methods available for determination and observation. The development of methods for determining the quantities characterizing bed-load transportation has been started essentially in the second half of the last century and has not been concluded yet. Many factors escape determination because of the lack of generally applicable, adequately developed methods of observation. One of these characteristics is the rate of bed-load transportation. By running bed surveys periodically, i. е., by determining the geometry of the bed, information can be obtained essentially only on the volume of sediment scoured from, or deposited over, a particular section of the bed during a certain period. (It is assumed of course that only bed-load is deposited and no suspended sediment.) Even this volume is related to a rather long interval of time, but no reliable data can be collected on the instantaneous rate (related to second, or minute units) of bed-load transportation. Sampling observations performed using one of the different bed-load trap devices yield results which may differ from the actual rate of bedload transportation by several hundred percents and the data may be useless even for rough estimates. Yet reliable information on the rate 61