Vízügyi Közlemények, 1970 (52. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
tated by the ferromagnetic coating, permitting automatic devices to be used. Particles down to 0,1 mm diameter can be coated in a reliable manner. The hydraulic properties of the particles remain essentially unchanged if the coating is applied at the rate of 1—2 g of Fe 20 3 per 100 g of sand material. The main field of application for the ingenious device and method appears to be in the study of littoral drift, where at times of low tide, the container including the tracer material and the probes can be installed by simple digging work, while in shallow water frogmen could do the job efficiently. Unfortunately, in the case of rivers the task appears to be very cumbersome, or even impossible, even if the river bed consists of sandy material. In Hungary the method could be tested for studying the movement of silt in Lake Balaton. A largely unexplored and almost completely uncleared field of sediment transportation phenomena is dealt with by Egiazaroff, in his paper [6]. In the introductory part the classification of torrential watercourses is given as accepted in the Soviet Union: 1. Cohesionless. turbulent Newtonian fluid, non-torrential sediment flow; 2. Cohesionless, turbulent Newtonian fluid, torrential sediment flow (mud-flow); 3. Cohesive, rheological (non-Newtonian) fluid, structured flow. The two lastmentioned types occur but infrequently and in very few locations, even under the wide range of geological conditions of the Soviet Union. In structured mud flows the concentration of solid particles may be as high as 85%, but mudflow having solid concentrations of 60%, or less are already turbulent and obey the laws of Newtonian fluids. In describing the conditions under which a turbulent highwater flow turns into a torrential sediment flow, the author starts from earlier relationships established in previous papers [22] on the movement and self-lining of non-uniform bed materials and demonstrates that once the self-established lining of the watercourse is disrupted and its protective influence is destroyed, the general moving effect is extended to all particles, there is a sudden drop in the resistance coefficient of the bed and the same time sediment concentration increases, the sediment flow becomes torrential and avalanche-like. The transition to torrential conditions could not be described by a fixed numerical value (e. g. limit concentration), since depending on the strong, or weak nature of the selfestablished lining in the antecedent condition, transition may occur already at concentrations lower than 60%. For model tests on torrential sediment flows the fundamental formula relating concentration modulus to relative excess energy of flow is recommended by the author, whereafter a few practical remarks on the composition of model sediment material are given. In conclusion the present state of scientific research on turbulent torrential sediment flows in Soviet Union is summarized in a brief review. It will be perceived 55
