Study of sediment transport modeling in Vitória-ES Bay and potential changes in the hydro-sedimentological dynamics through the deepening of the estuarine channel

Name: Kaio Calmon Lacerda
Type: PhD thesis
Publication date: 21/12/2022

Name Rolesort descending
Julio Tomás Aquije Chacaltana Advisor *

Examining board:

Name Rolesort descending
Julio Tomás Aquije Chacaltana Advisor *
Marcos Nicolás Gallo External Examiner *
José Antônio Tosta dos Reis Internal Examiner *
Bruno Furieri Internal Examiner *

Summary: Several studies have been carried out on the possible impacts of natural changes or anthropic
interventions in coastal systems, such as the relative rise in sea level, landfills and dredging. In
this context, numerical modeling stands out as a key method for allowing hypotheses to be
tested in addition to providing assertive results with high spatial and temporal resolution.
However, simulating the spatial and temporal variation of Suspended Sediment Concentration
(SSC) in estuaries is a challenge, with additional difficulties due to the frequent presence of
cohesive sediments, with spatially and temporally variable parameters. In modeling this type of
sediment, the formulations used for the erosion and deposition processes, as used in most
numerical models, are defined as a function of the erosion parameter, the shear stress due to
currents and waves and the critical shear stress for erosion (TCE), which are often used
effectively by authors who consider them to be constant and uniform throughout the
simulations. Potential impacts of the deepening of the Vitória Port channel, completed in 2017,
are investigated using the numerical hydrodynamic and sediment transport model Delft3D,
three-dimensional (3D), forced by tide, wind, atmospheric pressure and thermohaline gradients.
The numerical model reproduced well the observed elevation, velocity, temperature, salinity
and CSS data in Vitória Bay. In addition, the importance of using a 3D model for the present
study was pointed out by the gradients of variables identified in the water column, with greater
emphasis on velocity and, consequently, on the shear stress at the bottom. In the sediment
transport model, among the bottom composition approaches evaluated, the surface composition
based on the percentages of cohesive and non-cohesive sediment was the one with the most
satisfactory results. Furthermore, the experiments in which the temporal variation of the model
parameters over the spring and neap cycles was considered, allowed to obtain better results,
which was indicated by the smaller values of the errors obtained in relation to the available
measured data, but without significantly overestimating the average and maximum
concentration values indicated by the measured data reported in the literature for area. For the
experiment that presented the most satisfactory results, a 3D model was considered in which
the erosion parameter (kg/m2
/s) varied from 5x10-6
(spring) to 30x10-6
(neap) with an TCE of
0.2 N /m2
. Regarding the deepening considered, from the velocity series it was possible to
observe that the impact on the velocities varies throughout the neap-spring tidal cycle, in
addition to presenting distinct patterns along the water column. So, despite the statistical
parameters pointing to trends in the average impact that deepening has on hydrodynamic
patterns throughout the study area, the results indicate that this pattern varies over time and
along the water column. Therefore, considering the analysis of the hydrodynamic results, it was
not possible to establish an expected pattern of impact on the transport of sediments in the
region. However, based on the sediment transport simulations carried out, it can be concluded
that, for the simulated conditions and the considered deepening, in general, there is a reduction
in resuspension fluxes along the bay, with a consequent reduction in CSS and eroded volume
along the study area. The results indicate a reduction of 4.3% in the total volume of material
eroded as a result of the deepening and a percentage reduction in the average CSS of up to 20%
in the evaluated stations.

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