Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

given in the paper by Hartke and Mauersberger [5]. According to their method the particles of the natural sediment are labelled, instead of an isotope or luminescent coating, by an extremely fine-grained ferromagnetic material fixed using a suitable cementing agent at the surface. The tracer material thus prepared is placed in a cylindrical vessel and is submerged in this condition into the river bed. Two detector probes are installed below the vessel (Fig. 3.). A secondary field of forces of a magnitude depending on the volume of the tracer material is induced in the latter by the magnetic field of the Earth. If material is removed from the vessel either by river flow, or by wave action, the height of the tracer filling and consequently the intensity of the secondary field of forces is reduced. With the help of the probes and the instruments connected thereto and accomodated in the majority of cases on a launch, these changes of filed intensity can be measured with an accuracy high enough to indicate changes of mm order of magnitude in the height of the cylinder filling. Fig. 3. Diagrammatical sketch of the observation device 1. Retrievable mantle of the tracer container, 2. Bottom plate of the container, 3. Protecting tube for the probes 4. and 5., 6. Connecting cable, 7. Instrument with amplifier, 8. Recording device, 9. Spirit level, 10. Channel bottom, 11. Cylindrical labelled sediment sample, 12. Unlabelled bed material This new principle is combined with the familiar tracer techniques in the method, inasmuch as samples are retrieved in the surroundings of the vessel from the bottom and the number of ferro-magnetic-labelled particles is determined. In this manner conclusions on the direction and rate of bed-load movement can be arrived at. Counting is greatly facili54