Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

These observations must be performed at low-, medium- and high stages alike, samples must be taken further from the bed material and the river bed must be surveyed topographically at least once each year. From the observation data the changes in bed conditions can be estimated, which is a prerequisite for designing regulation structures. Similar estimations have been performed repeatedly and in some cases even the results could be made available for purposes of comparison after the regulation was completed. These comparisons have shown that the changes could be predicted in advance with a fair degree of accuracy, provided the factors taken into consideration were truly typical for a particular river and were determined by field observations. Valuable information has always been gained from observations aiming at the determination of changes over backwater reaches created by river barrages. Similar field surveys have been performed over the reach upstream of the Tiszalök Barrage and these yielded data on the annual rates of sedimentation and permitted moreover the determination of degradation over the reach downstream of the barrage. For the determination of bed changes valuable information can be gained in many instances from model tests. Although the similarity criteria of watercourses having a movable bed are highly complex, the test results are in many cases useful for predicting the effect of contemplated regulation measures. From among the field observations those on sediment transportation are perhaps the most important ones. Permanent sediment observation stations have recently been established on several rivers. In many instances these stations are combined with, or incorporated in the barrages, they are automated, so that the retrieval and analysis of water samples is performed automatically. The observation results are filed in a punched-card system and can be processed with the help of computers. Sediment observations using tracer techniques have already been mentioned. It is felt advisable, however, if the priciples underlying these tracer observations are also reviewed. In this method samples are taken from the sediment material under consideration and these are labelled with a material having physical properties other than those of the sediment. For labelling sediment particles coating with a luminescent dye, the incorporation of radioactive isotopes, or sometimes the activation of a sediment sample may be applied. In principle the most simple solution consists of determining the average travelling velocity of bed-load with the help of tracers. If the average travelling velocity is v

s, the width in which movement occurs is m, the dry density of bed-load is W, then the rate of bed-load transportation in the channel is obtained from the expression q, = v

smW (14) The observation proper is performed by introducing the tracer material at one or several points, occasionally over the entire width into the channel and detecting after a certain period by periodical or continuous scanning. 2* 19