Seismic assessment of sediment siltation in a tropical run-of-river hydroelectric reservoir

The Madeira River presents higher sediment flux in relation to others Amazonian rivers, contributing approximately 45 % of the sediment load to the entire Amazon Basin, that is also the region with the largest untapped hydroelectric potential. The implementation of Jirau and Santo Antonio Dams on Madeira River in Brazil created large run-of-the-river hydroelectric complex, and assessment of silting became an important issue to estimate the actual impact on sediment connectivity and on operation of the reservoir. This paper presents data of the morphology and stratigraphy of a portion of Jirau Reservoir, between the Jirau Rapids and the levees close to the Jirau Dam, in the period of February 8th to February 15th, 2022. The data were obtained by Multibeam Echo Sounder and High-Resolution Seismic Reflection. The results obtained by analysing reservoir bed morphology helped identify regions prone to siltation. The run-of-the-river Jirau Reservoir seems to have had minimal sediment retention since start of operations, as observed in seismic profiles. The suspended sediment concentration map of the study area collected for the year 2021, obtained within a parallel study based on satellite images, showed that the distribution on the surface of the reservoir correlates with the geophysical results, supporting our findings and suggesting the need for joint utilization of geophysical and remote sensing techniques.