Análise e estimativa do transporte de sedimentos em suspensão durante eventos chuvosos

Abstract

This work aims to monitor the transport of suspended sediments from the Taquarizinho River basin, throughout rainy events that occurred between 2005 and 2007. Using historic data, the evolution of water levels, flows and cross profiles during the last decades was evaluated. The settling rate curve for suspended sediments was determined, with which it was possible to estimate the annual sediment yield. The average sediment concentrations during events were analyzed. The results were shown to provide a useful alternative to estimate the sediment load. With regard to suspended sediments, the analysis of dimensionless cumulative curves of mass and volume, transported in flood waves, did not show any evidence of the occurrence of a “first flush” phenomenon. The particle size distribution of the bed material indicates predominant presence of medium and coarse sands. The determination of Manning’s coefficient, by means of a characteristic diameter for the river’s sandy bed, results in an average of 0.025, compatible with values found in scientific literature. It was verified that the majority of sediments was transported in approximately 25% of the annual time, concomitantly to the rainfall period. The solid contribution rates varied from 10 to 60t.km-2.year-1, which were below the average values of former researches in the region studied.