On the following subject:
"Study of the natural and anthropogenic terrigenous impact on a tropical lagoon system using a 3D hydro-sedimentary modelling approach linked to a measurement network".
Thesis supervisor: Christel Pinazo, Senior Lecturer
Co-director: Pascal Douillet , Research Fellow
The overall objective of this thesis is to use a hydro-sedimentary model (coupled model of sediment circulation and dynamics) to simulate the impact of natural and anthropogenic inputs on an oligotrophic lagoon environment. The results of this work, centred on the south of New Caledonia (Figure 1), will then be transposable to other coasts of the territory or region influenced by terrigenous sources.
The main objectives are :
- Quantify and characterise inputs ;
- Characterise the transport of dissolved and suspended particulate elements carried by rivers;
- To develop and validate a hydro-sedimentary model taking into account circulation forcing (tide, wind, rivers, regional circulation, stratification), inputs, resuspension, then deposition and flocculation (the latter phenomena not being integrated into the existing models implemented to date in New Caledonia);
- To develop the first decision-making tools for assessing the impact of particulate inputs generated by mining projects on the lagoon environment, such as early siltation areas (for sustainable management).
This work is based on theoretical modelling experiments carried out jointly by the Institut pour la Recherche et le Développement (IRD) and the Mediterranean Institute of Oceanography (MIO) in the south-western lagoon, as well as on research into algorithms adapted to tropical coastal waters for use with satellite data as part of an ACI (Action Concernée Initiative) "Earth Observation" research project and the PNEC Chantier Nouvelle-Calédonie.From a scientific point of view, these results will represent a significant advance in terms of predicting the impact on lagoon ecosystems of climatic and anthropogenic factors. The model will have to account for the impact of these conditions by drawing on the knowledge acquired since 1997 by the IRD at the Noumea centre and the PNEC "New Caledonia" projects.
From the point of view of its applicability, this modelling should outline the future of Kwé Bay and propose scenarios for the dynamics of silting according to the values of the source term. In this way, it will be possible to show whether controlling terrigenous inputs from the River Kwé could be a natural solution for de-silting the bay. In other words, is the reduction in the source term sufficient, and on what timescale, to allow the phenomena of resuspension and export of sedimented particulate material to the Havannah Channel to take precedence over the inputs?
Another important question to which the model can provide answers by estimating particle transport concerns the dredging operations planned in the bed or on the beaches of the Kwé. On what time and space scales would such operations resuspend fine particles have an impact on the environment? What size should the anti-silt dams be and how effective will they be?
This study will also be applied to the modelling of Prony Bay and, in particular, the transport of solid and liquid inputs from the Creek de la Rade Nord.
Thesis keywords: hydrodynamics,sedimentation,modelling,