Author(s): Leonardo Zandonadi Moura; Sergio Koide; Jean-Michel Martinez; Henrique Llacer Roig; Alexandre Kepler Soares

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Keywords: Sediment budget; Reservoir sedimentation; Cohesive sediment; HEC-RAS; Amazo

Abstract: The Madeira River is the most significant tributary of the Amazon River, in terms of sediment load. A hydropower complex was built from 2008 to 2012 on a Brazilian stretch of the river with two large run of the river dams, which although do not have significant seasonal storage, inevitably changed the river sediment dynamics. A thorough sediment monitoring is conducted by the dam owners and operators since the beginning of construction works and is a valuable resource for understanding the consequences of the project. This work presents the phenomena that are perceivable through this monitoring data and how it can be used for calibration and validation of modelling studies. Through the fitting of simple rating curves, some preliminary conclusions are drawn. A sharp decline in suspended sand is observed on the reservoir, along with the development of a capacity to retain silts and flocculated clays. The first modelling exercises with a one-dimensional model (HEC-RAS) and a generalist sediment transport capacity formula (Laursen-Copeland) suggest that a specific treatment for cohesives is necessary. This work displays a sensitivity analysis where the sediment gradation was used as a calibration parameter, within the bounds of the monitoring data and applying considerations of flocculation of fines. A calibrated and credible model is an important resource for a better understanding of the sediment dynamics, interpolating in space and time the monitoring data. It will allow the simulation of long-range scenarios and impact evaluations for both upstream (changes in water levels) and downstream (sediment starvation).

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1275-cd

Year: 2023