Hydrodynamic characterization of Baía de Todos os Santos-BA using numerical modeling

Daniel Salles, Cristina Horita, Tobias Bleninger, João L. Carvalho

Wednesday 1 july 2015

12:15 - 12:30h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine outfall system

Parallel session: 9D. Special Session: Marine Outfall System

Baía de Todos os Santos (BTS) is the second largest bay at Brazilian coast, being surrounded by 12 cities, among those Salvador, the capital of the state of Bahia. BTS presents environmental problems caused by disorderly occupation and an accelerated industrialization process. To better understand the BTS’s circulation, a 2DH hydrodynamic model was generated using DELFT3D. Bathymetry and wind time series used as input to the model in this project as well as the measured data in situ (water level and depth average velocity) were collected by the program Bahia Azul and shared by professor Paulo C. C. Rosman (COPPE / UFRJ). Sea boundaries used astronomic constituents calculated for Salvador’s Harbour were used. The model was validated through statistical methods R2 and Mean Absolute Error (MAE) for water level, depth average velocity and total energy spectrum. Results showed that BTS has small influence of sub-inertial frequencies and river discharge, being mainly influenced by astronomical tide. Higher values of depth average velocity were found at BTS’s outlet. At neap tide high peak velocity for depth average velocity is 1.0 m/s for both inflow and outflow and at spring tide depth average velocity reaches 1.6 m/s and 1.9 m/s for outflow and inflow, respectively. Inside the bay the water level varies between -0.5 m and 0.65 m at neap tide and -1.5 m and 1.5 m at spring tide. In total, 9 observation points were compared with measured data. Better results were found inside the bay with R2 as high as 0.8994, 0.8411, 0.9236 and 0.9996 for water level, U and V depth average velocity component and total energy spectrum, respectively. Observation points in open sea, close to boundaries presented worst results, mostly in U and V depth average velocity components, showing results as low as 0.0060 and 0.0541, respectively. This can be explained by the proximity of the boundary and also because the presence of a sub-inertial frequency, not calculated in this model. The numerical results showed that the model could accurately predict the flow dynamics inside de BTS bay.