HYDRODYNAMIC, SEDIMENTOLOGICAL AND MORPHOLOGICAL ASPECTS OF A SAO FRANCISCO RIVER STRETCH, BRAZIL

摘要

This paper presents the main sedimentological and morphological characteristics observed during a field visit, in a stretch of the Sao Francisco River of approximately 10 km, in the border of the States of Minas Gerais and Bahia, downstream from the junction of the Verde Grande River, Brazil. The purpose of the visit was to provide technical input to the selection of alternatives for water intake from the river for an Irrigation Project named Iuiu. They are the outcomes of a thorough field analysis that is part of a methodology adopted in Brazil for the study of sediments in open-water flow. Among other observations, measurements of the water discharge were made and sediments from the riverbed and in suspension were collected. Longitudinal and transversal bathymetric measurements were taken, as well as topographic profiles of the water level and of historical flood marks were made. The hydrodynamic measurements characterized a period of minimum flow. During this period, the cliffs, beaches, sand banks, inlets and islands are exposed and accessible, allowing the tracking of the sediment trajectories and the understanding of the morphological formation and evolution of their deposits. The HEC-RAS -Hydrologic Engineering Center - River Analysis System - software was used. Its application had double objective: firstly, the reproduction of the values of the hydraulic variables measured in the field. Secondly, with the adjusted values of these variables, additional hydrodynamic simulations were made, varying the water discharge, the slope of the longitudinal water line and the roughness of the riverbed. For the entry of the extreme values of the hydrological variables, the following two stations were considered: Manga, situated 20 km upstream, and Carinhanha, 20 km downstream. The results from the calibration and the simulations obtained were presented in this text. In addition, the adopted methodology, the equipment, the region, and particularities of the sediment deposits, are described and thoroughly illustrated.