Vízügyi Közlemények, 1970 (52. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
transportation and the rate of streamflow, statistical methods must be resorted too, as it is impossible to trace the process of erosion caused by runoff passing along the catchment area and to observe the transportation of sediment caused by erosion. It is equally impossible to analyse the influence of the great number of parameters involved. On the other hand the rate of suspended sediment transportation can be expressed by a relationship [11] of the form: Q* = b-Q m where the magnitude of b and m is hardly affected by bed erosion while it is controlled almost exclusively by erosion in the catchment [3]. In the above formula Q s is the rate of suspended sediment transportation while Q is the rate of streamflow. For reason mentioned above the magnitude of b and m can be determined by regular observations. It will be readily appreciated that relationships derived on the basis of similar series of observations cannot be applied to other watercourses unless the catchment areas are similar in topography, vegetation and climatic as well as soil conditions. This probabilistic method has been extensively applied in river regulation and is still used for designing stream channels and canals in the former British colonies, deriving relationships of similar form by statistical methods between rate of streamflow, surface width, depth, slope and sediment volume. In the literature this method is referred to as „Regime theory", although essentially it is not a theory as it involves no more than the description by statistical methods of a great number of observation data. The advantage of the regime theory is that it offers a positive answer for the width, depth and slope of a particular river. The sediment formulae based on physical relationships between these three quantities are not unequivocal and thus the choice between depth and width is left to the designer. A considerable drawback of the method is, however, that experiences gained with one river can be transferred in a very restricted manner only to another watercourse. The applicability of the method is limited to river reaches with comparable flow regimes, with largely similar, usually low sediment transportation and even then only if these are straight, or of a mild curvature [12]. As mentioned before, in the case of more complex and involved phenomena the regime theory is suitable, in spite of its limitations, to describe the phenomenon correctly. The circumstance that it failed to receive a wider application in Europe may be attributed, at least partly, to the fact that the units figuring in the relationships derived are inches, cubic feet etc. and the coefficients have been determined for tropical rivers or watercourses in cohesive clay soils. As illustrated by the example of suspended sediment transportation, this method may be a welcome supplement to the familiar methods of fluvial hydraulics. It appears to be especially advantageous in the morphology of watercourses for determining radii of curvature, bend length and regulation width. Several attempts in this direction have been made recently abroad 37
