Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

Since river regulation was called upon to meet higher objectives of water management and these objectives called for more accurate results, even the methods of computation were affected. For predicting changes in flow and sediment regime, as well as in bed development and their influence on the objectives of water management, increasing use is made of computers. Economic co-ordination of the great variety of water management objectives can be solved reasonably by mechanical data processing and computing only and this entailed the revision of the mathematical expressions hitherto used [13]. Attempts have recently been made to use theoretical methods developed for sediment transportation in describing ice transportation as well. In connecting the two phenomena bed-load is replaced by ice running on the surface, while the counterpart of suspended sediment is the frazil ice carried in water. These special types of sediment are subjected to a buoyant force. In this approach consideration must be given to the fact that bed-load on the bottom moves at a velocity lower than that of the surrounding flow, whereas the velocity of ice floating on the surface is higher than that of water layers in contact with it, as long as the effect of the sloping water surface is not overcome by bank friction [16]. As far as the devices serving for the observation of sediment transportation are concerned, development seems to have been restricted to bed-load traps [4]. The measurement and observation of suspended sediment seems to have been solved in a satisfactory way. An improvement over the conventional traps or collecting boxes is presented by a device consisting of a funnel installed on the bottom which collects bed-load continuously and from which it is removed again continuously by a pump. For improving bed-load observations at the laboratory a periodical feeding and observing device has been described [10]. An interesting and promising new approach to the study of sediment transportation and bed development is based on biological methods [8], the first favourable results of which must be verified by further experience. From the analysis of plankton retrieved from the bank- and bottom material of the bed, conclusions may be arrived at on sediment movement and bed changes which occurred in the past at the sampling point and further on the length of the period during which no movement occurred. This method offers the opportunity for checking the theoretical conclusions on sediment movement in bands, on the periodicity of sediment movement and from this information the total annual sediment volume can be estimated more accurately than with the help of the conventional sampling methods. The experience gained so far is promising and the data published appear to be reliable. From the foregoing it will be perceived that in the development of theory and practice in river regulation the emphasis has shifted to the study of problems related to suspended sediment, but it should be remembered that the role of bed-load remains predominant. Moreover it has become necessary to refine the bed-load relationships, since the earlier formulae derived on the basis of physical processes, and the most signi39