Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

4. Laboratory studies on the process of sedimentation As far as the settling process of bed-load material transported by rivers is concerned, the reservoir may be regarded to behave essentially as a settling basin with special operating conditions, so that it appears perfectly logical to attempt a laboratory study of the relevant phenomena. A number of reports on similar efforts have been published in the literature, although the restraint exercised by the authors in generalizing the results obtained is in most cases fully justified. In fact, owing to the generally recognized restrictions imposed on model techniques, no more than the demonstration of the main tendencies may be expected and the direct transfer of results to" the prototype may not always be feasible. Noteworthy suggestions for improving model techniques have been presented by S. Boursali [1], who succeeded in creating in the entrance section turbulence conditions resulting in a settling process closely approaching the actual situation. Owing to the difficulties encountered when using hydraulic models, I. Kalis [6] used an air-operated model for studying the sedimentation process of reservoirs. Pneumatic models have the advantage of permitting the use of appreciably higher degrees of distortion. Although the method is not expected to yield more than moderately accurate results, it should permit the study of large areas at a relatively low cost. 5. Other influences of the settling process Original sediment balance conditions of a river are greatly modified by the construction of reservoirs, the primary immediate consequence of which is the silting process considered previously. This is in accordance with the natural tendency of the watercourse for establishing dynamic equilibrium corresponding to the changed conditions. Beyond this primary effect a number of further consequences of silting may be observed, of which no more than two namely the sealing effect of silting, and the scouring, eroding capacity of overflow water (deprieved of its sediment) will be mentioned here. The material settling in reservoirs may differ in composition and seepage properties appreciably for the original bottom material (especially if the latter consists of gravelly, or sandy soils), and thus seepage losses may be reduced substantially by a process known as colmation. As indicated by the studies Ö. Starosolszky [10], the extent of silting depends, besides flow velocity and concentration, also on the granulometric composition of the original bottom material, and on the surface activity of the sediment. The relative decrease of seepage discharge has been found by laboratory measurements to follow fairly well the familiar formula by Kamenskyi, and thus a possibility is offered for estimating the yield of wells sunk into the permeable layer. In connection with the other problem, the uptake of sediment downstream of plain-land reservoirs, additional data are given by N. Hansel [5] 77