Analysis of sub-bottom profile application to estimate sediment thickness over Itumbiara and Batalha HPP reservoirs, Brazil

Abstract

Reservoir’s construction on rivers interferes with natural hydro-sedimentary processes, disrupting sediment transport, and leading to reservoir siltation, thereby reducing its lifespan. Since the mid-1930s, sedimentation rates in reservoirs have been determined by calculating the multi-temporal volumetric differences of sediment infill. Low-resolution data from older surveys and the lack of pre-impoundment or long-term sediment accumulation data may hinder accurate estimations of sedimentation rates. A seismic system using a sub-bottom profiler Echoes 10 000 was used on the Itumbiara and Batalha large hydropower reservoirs, in central Brazil, to assess the post-impoundment infill and pre-reservoir morphology. The paper analyzed the applicability of the sub-bottom profiler with frequencies ranging from 5 to 15 kHz to supply missing pre-impoundment data. Fourteen sediment samples were recovered from the bed of Itumbiara Reservoir to validate the sediment layer defined as post-impoundment. It was established a correlation between the grain size of the deposits and the bathymetry of both Itumbiara and Batalha Reservoirs. The results demonstrated a positive correlation, revealing a low relative error for both reservoirs, under 4%, when excluding outliers. The sub-bottom profiler is a valuable tool for providing pre-impoundment bathymetry data and identifying thin sediment deposition in reservoirs even when operating at shallow water depths.