Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

terized according to sediment transportation. This approach is obviously founded on the recognition of the fact that the volume, particle size and granulometry of the sediment are closely related to the morphological properties of particular river stretches. 5. Sedimentation of watercourses, lakes and ponds Sediment once entered into the watercourse or scoured from the bed will settle in the channel or in the estuary thereof, regardless whether it is transported continuously, or by periodical movement. In the case of diversions along the watercourse, settling will take place at the point of utilization, for instance in the area irrigated. In the case of reservoir storage, practically all of the sediment transported by the river, whereas in the case of channel storage an appreciable part thereof will cause sedimentation in the storage area. In view of the fact that with the advent of complex water resources management the storage of water and the canalization of entire watercourses became inevitable, the problem of sedimentation assumed fundamental importance. Storage reservoirs created by dams built across river valleys and storage volumes created in the bed itself are gradually filled by sediment transported by the watercourse into the storage space. For this reason no estimation of reservoir silting is possible unless the sediment transporting capacity of the watercourse is known. In particular cases the actual sediment volume transported by the watercourse must be known. Sedimentation itself is a consequence of changed hydraulic conditions since flow in the reservoir — which may be regarded as a lake — yet even in the blocked channel occurs at an appreciably flatter slope, lower velocity and turbulence than in the original channel. Reservoir silting and the process of sedimentation has been studied by many field observations. Nevertheless, practically no attempt has been made at the theoretical analysis of the sedimentation process itself. The first step in the theoretical study of reservoir silting consists necessarily of determining the sediment transporting capacity of the watercourse. As already mentioned, the sediment transporting capacity of a watercourse is extremely difficult to determine. Equations describing the movement of sediment-carrying water as a two-phase fluid have been applied recently in a promising attempt towards the determination of sediment transportation. Once sediment transportation has been determined, the next step in the theoretical analysis of the silting process consists of describing the process of settling which presents an at least as complex a problem. In principle the process of settling can be approached by applying continuity conditions determined for the solid and fluid phases alike. 21