Quantification of exchange processes between a bay and a river using a two-dimensional high-resolution flow and transport model

Hydrodynamics and transport simulations were conducted with the modeling software TELEMAC-2D (Hervouet, 2007) on Icó-Mandantes Bay, a branch of the Itaparica Reservoir, within the INNOVATE project. The bay has a seasonal water level variation of around 5 m and is suffering for eutrophication and algae bloom. Therefore, we investigated low and high water level scenarios with two different high resolution meshes, with the purpose to deeper understand their impact on transport of substances and to improve the watershed management. In particular, nutrient emissions from a hypothetical net cage aquaculture system located in the bay were investigated on half-year cycles. We observed a relevant impact on water quality for a tilapia production of 130 to y-1, i.e. after 6 months simulation we obtained around 8 μg P L-1 and 6 μg P L-1 at the source of emissions, for low and high water scenario, respectively. Additionally, uniform distribution of a mass-conservative passive tracer in the whole bay was imposed as initial condition to quantify water retention times of the bay, which resulted higher for the high water level scenario compared to the low, and even higher when we took evaporation into account (around 725 days).