Analysis on morphodynamics and evolution of bed forms in the Orinoco River

The Orinoco River is the third largest flow-discharge river in the world with an average water flow of 37,600 m3s-1. Due to the presence of the Guyana shield on the right bank, the lower reach of the Orinoco presents a plan form characterized by alternance of contraction and expansion zones (Laraque et al., 2013). Typical 1-1.5 km width narrow reaches are followed by 7-8 km wide reaches (Figure 1). A complex pattern of bed aggradation and degradation processes takes place during the hydrological cycle. The relationship between flow velocity and morphodynamic of sand waves and bars in an expansion/contraction channel is very important to understand the processes that control the evolution of rivers. Considerable research efforts has recently been directed towards the understanding of fluvial processes associated with geomorphology and hydrologic conditions with the river width, which are explained through the mechanics of formation and evolution of sand waves and bars

Morphodynamic change analysis of bedforms in the Lower Orinoco River, Venezuela

The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37 600m3 s1 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 ( 20 m) and under variable flow conditions

Carte géologique des terrasses alluviales de Garonne

Cette carte géologique constitue une synthèse des publications existantes et une harmonisation des contours des différentes feuilles à 1/50 000 publiées par le BRG

Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

International audienceThe Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin

Reconnaissance des placers alluviaux exploités en mines antiques : difficultés et méthodes

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