Abstract

The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37600 m(3)/s at the outlet to the Atlantic Ocean. Several field studies were carried out within the HYBAM Program to characterize hydrodynamics and sediment transport in the reach of the Orinoco River close to the city of Ciudad Bolivar (Venezuela). The studies were performed in low, medium, and high flow conditions. During this field campaign, Acoustic Doppler Velocity Profiling (ADCP) was used as well as water sampling for the measurement of total suspended sediment (TSS). Surface sedimentary fluxes were ranging from 68 to 113 Mton/year for the bimodal sedimentological regime in the hydrological station at Ciudad Bolivar, marked by two TSS peaks respectively, before and after the maximum discharge peak. The ADCP measurements gained a comprehensive characterization of the basic hydrodynamics and sediment transport parameters in that reach as well as their variation in different flow conditions during the hydrological year. Large differences in discharge, flow velocities. Finally, bed shear stress distribution identified dominant transport mode and maximum suspended grain size, being in the range order of fine sands and very fine sands in medium/high flow and low flow conditions, respectively.