Hydrodynamic modeling with scenario approach in the evaluation of dredging impacts on coastal erosion in Santos (Brazil)

Abstract

Coastal environments provide infrastructure and ecosystems that are key to modern human life and have long become a noticeably pleasant place to settle. Coastal zones are densely populated, and consequently one of the most urbanized areas around the world. However, coastlines are very dynamic and undergo constant changes that might be related to natural or anthropogenic sources. Hence, erosion has become one of the most alarming coastal hazards today, having caused serious damage to seaside infrastructure and properties. Santos is one of the most important cities in Brazilian Southeast region and home to the largest port of Latin America. Ponta da Praia, part of Santos' shoreline, has been suffering coastal erosion for the past few decades. The erosion became more severe after dredging activities were conducted to deepen and widen the port's navigation channel, having started in 2010 in order to expand the port activities. In this scenario, this study attempts to assess the dredging effects on the region hydromorphodynamics and analyze whether it represents a major cause for the rise of the erosion rate. To conduct the analyses, a hydrodynamic model and a spectral wave model with scenario approach were used, and three distinct scenarios were adopted: (1) before the dredging activities; (2) immediately after the dredging activities, but with an update of the port's channel bathymetry; (3) scenario 2 updating the bathymetry of beach profiles at Ponta da Praia and its surroundings. The resulting simulations and subsequent analyzes confirmed the hypothesis. The update of the bathymetric data of the port's channel allowed us to observe considerable changes on the hydrodynamic patterns. In addition, on the stretch where a recirculation zone was formed, the processed field data had already pointed to a more eroded area. Therefore, the beaches failed to achieve an equilibrium, which led to a continuous erosive process. Furthermore, the hydrodynamic modeling has proved effective to predict or detect changes and potential problems related to topobathymetric modifications.