Abstract

The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37 600m(3) s(-1) at its outlet to the Atlantic Ocean. Due to the presence of the Guiana Shield on the right bank, the lower reach of the Orinoco has a plan form characterized by contraction and expansion zones. Typical 1-1.5 km wide narrow reaches are followed by 7-8 km wide reaches. A complex pattern of bed aggradation and degradation processes takes place during the annual hydrological regime. A series of Acoustic Doppler Current Profiler (ADCP) transects were collected on an expansion channel in the Orinoco River, specifically over a fluvial island, representative of the lower Orinoco. In this study, temporal series of bathymetric cartography obtained by ADCP profiles combined with Differential Global Position System (DGPS) measurements (with dual-frequency), were used to recover the local displacement of bed forms in this island. The principal aims of this analysis were: (1) to understand the dynamics and evolution of sand waves and bars at this section and (2) to quantify the volume (erosion vs. accretion) of a mid-channel bar with dunes by applying DEM of Difference (DoD) maps on time series of bathymetric data. This required sampling with ADCP transects during the months of: May 2016; November 2016 and April 2017. Each bathymetric transect was measured twice, 1 day apart and on the same trajectory obtained by a GPS receptor. The spatial analysis of these ADCP transects is presented as a novel tool in the acquisition of time series of bathymetry for a relatively deep section (similar to 20 m) and under variable flow conditions.