Abstract

In this paper, the bed form mechanisms are emphasized, with the following purposes: (1) to show that the bed migration is a result of the simple bed’s grain movements, (2) to distinguish between the flow energy losses due to the bed forms and to the bed’s grains roughness, (3) to determine the hydrodynamic forces responsible for the sediment movements, and (4) to apply the dunes equation to natural beds. Two cases are considered: the sediment banks formation in a stretch of the São Francisco River of approximately 10 km, and the second case which consists of hydraulic and sedimentological studies with the simultaneous use of classical methods and radioactive tracer technique performed in a representative stretch of the Horácio Creek, in the Paraná State, Brazil. The hydraulic and sedimentological studies performed in the São Francisco River (2700 km long, watershed area of 645000 km²) had the objective of providing technical support for the selection of the water intake cross section for an irrigation project. Among other field observations, longitudinal and transversal bathymetric measurements were taken, as well as topographic profiles of the water level and of historical flood marks were made. The Horácio Creek is 8.5 km long; its watershed area is only of 42 km² and its occupation, associated with its topographic and geological characteristics, created an intensive erosive process of the soil. The goal of this research is to measure the annual solid discharge through a transversal section of the flow. During the tracer measurements, longitudinal bed configurations, Lagrangean, were recorded, and temporal records in fixed transversal sections, Eulerian, were made. Four methods were used to calculate the bed load transport: (1) The Total Count-Rate Balance Method, (2) the Dunes Equation, (3) the Vukmirovic’ and Vukotic’ Method, and (4) the use of the Random Processes Theory. The results obtained were convergent. It is shown that the bed load can be precisely determined, using longitudinal and temporal bed forms registers. It is recommended that the transversal bands of same bed type form be considered during the in field registering.

Keywords: Sedimentological and morphological processes, fluvial morphology, São Francisco River, Horácio Creek, sediment movements