Summary:

The paper describes geometric internal granulometric structure of lowland river bed forms called sand river dunes. Dunes are typical features associated with sand river bed and studies of processes connected with their formation are essential in understanding fluvial processes within the catchment. Also the knowledge of sedimentary structure and morphology of dunes are important for geologists and paleogeologists to interpret how sedimentary rocks were deposited. Also, in the time of changes of global and local climates, frequent changes of water regime in river could be noted when the development or not-development of river bed-forms can have an important influence on quantity of sediment moving in rivers and water reservoirs built on such rivers. The work was set up on the Rhine River in Germany close to Niderwalluf. The research conducted on the Rhine River involved many of research equipment and river vessels is very rare and unique in the world as far as fieldwork is concerned. Within a paper it is show, that the Rhine River Dunes do not reach the height H which would be expected by the water depth which is responsible for their formation. There could be a couple of reasons for such situation. One of those is the fact that along the research reach there was not noticed a forming channel discharge which would last long enough to supply a sediment discharge for building up the dunes. Also the density of the Rhine river sediment differs from those found along other sand bed rivers. The density which was found was 1,5–1,69 g*cm^-3. This low value of the density is due to the fact that the Rhine river dunes are under the continuous process of formation. Such detailed sediment research was possible since the diving bell was employed. It was found that for the research reach the function between the steepness and the length of dunes is described by following functions (respectively for 1991 and 1992): H/L = 0,082 L^-0,55 and H/L = 0,104 L^-0,63. The work described in the paper was set up clone to Mainz in Germany, and was possible because of the cooperation of the Institute of Freshwater Ecology from Great Britain and Hydrological Institute from Koblenz in Germany. Also thanks to support of the British Council.