Wave Modeling and Coastal Erosion in Upstream Dams

Abstract

A surface wave modeling was applied on the right margin of Sergio Motta Dam Reservoir (Porto Primavera Dam), Brazil, to investigate the behavior of breakwaters against impact of incoming waves. The Simulating WAves Nearshore (SWAN) spectral wave model was applied to simulate waves generated by wind in the reservoir. Between 2009 and 2012 researchers from the Brazilian Institute of Technological Research (IPT) conducted several studies and developed an experimental project to protect reservoir banks from erosion caused by waves. Three different kinds of submerged breakwaters were installed in 2009, 1.0 km along the shoreline, in five stretches of 100 m length each, with an interval of 100 m between them. Two breakwaters were made of concrete (with an innovative arrangement) and the third one was made from geotextile tubes. The objective of the study was to compare and validate the modeling results with those observed in situ. Different simulations were done: 1—for the same arrangements of breakwaters installed on a segment in the reservoir, 2—for each structure, with a single side-by-side arrangement. The results indicate that the structures reduce wave heights by 35–40% compared to no breakwater. The single side-by-side structure arrangement showed better performance results when compared to the original in situ configuration installed. Wave height attenuation was found to be highly dependent on the incident wave direction relative to breakwater orientation, and even considering a single structure configuration, the differences in performance depends on the wind direction and speed relative to the structure position.