Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

the maximum reservoir volume is expressed in terms of the ratio of reservoir volume and annual average streamflow. Relationships of this type can be improved considerably by including sediment concentration as a third variable. In Bulgaria, for example, a similar relationship has been derived on the basis of information gained by the study of 168 reservoirs. When considering the silting of a particular reservoir the properties of the catchment area should also be taken into account. In this respect average erosion conditions in the catchment should be related to the rate of reservoir silting. The empirical relationships derived in this manner cannot be generalized but their use is felt permissible for identical or comparable storage and catchment conditions. Valuable information on the silting of reservoirs can be gained from determining the density of the silt deposited. Besides changes in density, the determination of the grain size distribution of the sediment material is also of considerable interest. The settling of suspended sediment is obviously closely related to the hydraulic properties of the conveying flow. This circumstance offers the possibility for studying certain aspects of silting with the help of laboratory experiments. It should be clear that the process of silting and settling is considerably influenced by the intensity of turbulence. In this respect the results of laboratory experiments performed for determining the efficiency of common mechanical settling basins may also be utilized to advantage in studying the phenomena involved in reservoir silting. It should be obvious moreover that the qualitative aspects of reservoir silting can be studied in a scale model of the watercourse. Laboratory studies can be performed in air models as well, which are rather inexpensive and therefore attractive. Whereas silting and sedimentation has been studied widely, relatively little attention has been paid to the determination of degradation downstream of dams, although these are almost as important over river stretches below barrages, as the silting of reservoir space. Degradation affects not only the regime of flow but may necessitate also the regulation of the degrading river stretch. Besides modifying the regime of flow and reducing the storage space, silting and sedimentation affects other phenomena as well. Among these the sealing effect of silt should be mentioned by which the seepage losses from water-conveying canals may be reduced appreciably. 6. Recommendations for further research As mentioned in the introduction already, the very loose correlation between the practical methods of river regulation and the theoretical investigations should be regarded as a serious drawback. The reason for this lack of co-ordination between theory and practice in this field appears to stem from the fact that river regulation and the methods thereof 23