Impact of a port and its structures on the morphodynamics of a tidal basin and its adjacent coast

Abstract

To improve the socioeconomic situation in the Republic of Nicaragua, the government has decided to strengthen the country’s transport infrastructure by building a port on the Caribbean coast. The future port will be in Bluefields Bay, which can be characterised as a lagoon-shaped estuary. The inner basin is connected to the sea by two tidal inlets, located north and south of a barrier island. This study assesses the hydrodynamics and morphodynamics of the area; in addition, it analyses the influence of the port structures on these natural processes. A qualitative analysis of the hydrodynamics and sediment transport in the area is conducted, and sedimentation rates in the navigation channel and the erosion rates of the coast are calculated. The area is analysed with the help of a conceptual model that is supported by the process-based model Delft3D. Large parts of the area consist of shallow depths of around 1.5 m below mean sea level (MSL). The bed of these shallow parts consists mainly of mud. In those areas with a depth of more than 5 m below MSL, which are the river channel and the tidal channels at the inlets, the flow velocity increases, and a more substantial fraction of sand can be observed. In the data analysis, distinct wet and dry seasons can be observed; these seasons change the hydrodynamic influences over the course of the year. The river discharge increases by a factor of 10 during the wet season. In addition, the river delivers large quantities of mud, particularly during the wet period. When the tidal flow enters the lagoon, it influences sediment transport. As the dominant hydrodynamics change throughout the year, the sediment fluxes change with them. Beyond the hydrodynamics within the lagoon, the adjacent coast is under the influence of a swell wave climate. As the waves mainly come from the east-northeast at a height of 1 m, a moderate southward longshore transport is initiated year-round. The Delft3D model is used to analyse the hydrodynamics and sediment transport of the area in more detail. The model is used to analyse the flow magnitudes and directions. This approach allows the dominant hydrodynamic components to be identified. The most relevant hydrodynamic components are considered in the Delft3D model. These include tide, river discharge, waves, and wind. The 2D mode is sufficient to model these hydraulic components. Because of the hydrodynamic climate changes that occur throughout the year due to changes in the meteorological climate, the simulation period is one representative year. The model is calibrated and validated by means of phenomenological calibration and expert judgement, as field data is scarce.