Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

THEORY OF BOUNDARY CONDITIONS OF SEDIMENT MOVEMENT By DR. L. RÁKÓCZI

1 From among the different observable forms of sediment transpor. tation the boundary conditions of the phenomenon attracted first and most ontensively the attention of both theoretical and practical experts engaged in sediment studies. The beginning and termination of movement, the conditions of the limit state between movement and no-movement and — in recent decades — the transition from one developed stage of sediment movement into another, were the main points of interest, which urged many theoretical and experimental investigators to devote their attention to this field of problems, of considerable importance also to hydraulic engineering practice. Since the formula for critical bottom velocity was published first in 1753 by Brahms, many other expressions have been published from time to time in the literature, with the objective of establishing a relationship between incipient sediment movement and the hydraulic characteristics of the watercourse. Since the relationship can hardly or not at all, be observed under natural conditions, since the turn of the century innumerable laboratory experiments were and are conducted on sediment movement in almost every hydraulic laboratory of the World. As a result of this extensive experimental research work, the formulae derived by a ' purely theoretical approach have been completed by an increasing number of purely empirical, or semi-empirical expressions. Different authors used different approaches to solve the problem, investigations were performed under widely differing conditions, different stages of movement were frequently considered critical, or significant and this may be offered as an explanation for the deplorable situation that different formulae yield frequently contradictory results. Before attempting to review the basic methods of approach to the problem, it is considered necessary to consider the beginning of bed-load movement as a physical phenomenon. Bed-load movement will be under1 Research Institute for Water Resources Development, Budapest, Hungary 43