Vízügyi Közlemények, 1970 (52. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
results in the case of laboratory flumes, or other small canals, where the waterdepth is small and the flow is essentially two-dimensional. However, in wide channels and natural watercourses the flow, and in turn, the bed configurations are three-dimensional. Different bed-configurations may develop near to each other, or they may even merge together. This circumstance should be borne in mind regardless which of the formulae is used for computing the shape factor of bed-roughness. Dimensional analysis has been mentioned as one approach to the study of bed configurations. However, this method is even more widely used for the development of expressions for estimating the rate of bedload transportation. Its main advantage is that the parameters having the greatest influence on sediment transportation can be reduced to a practicable dimensionless form and their number reduced thereby. No information is obtained, however, on the functional relationships existing between various parameters. Laboratory and field observations are therefore required for determining which of the parameters are of decisive significance and in what manner are they interrelated. Analysing the experimental data obtained by himself and other investigators Liu realized that the scatter of data can be reduced by plotting the dimensionless parameter U./W, rather than the r, value of Shields, against R, [20]. The quantity W involved in the nominator of the „mobility parameter" is the fall velocity of the particle in standing water [cm/sec]. With the help of dimensional analysis most formulae on bed-load transportation can be reduced to the common form: The familiar formula of Meyer —Peter does not include the Reynolds number, so that its validity is not extended to cases where the role of viscosity is important. It is a difficult task to compare different bed-load formulae, since the development of critical conditions of movement are also influenced even by the dimensions of the laboratory flume [21], bed-load observations in the field are unreliable, so that very little information is available for checking the validity of relationship derived on the basis of laboratory experiments under the geometrical and flow conditions of natural watercourses. The difficulties mentioned in the concluding part of the introduction are dealt with in the paper presented to the Symposium by Burz [3], in which different empirical sediment-discharge formulae are reviewed critically. The structural and dimensional heterogenity of these formulae is attributed to the lack of uniform parameters. Reference is made to the Papers submitted to the Symposium 47
