Residence Time Modelling in the Nador Lagoon, Morocco

A hydrodynamical model has been applied to the Nador lagoon, Morocco. The model is a semi-implicit finite element model that solves the hydrodynamic and transport-diffusion equations. Both the lagoon and the shelf sea in front of the coastal zone are modeled. Simulations have been set up to compute the residence time under various settings and forcings. The residence time has been defined through the decay of a tracer released in the lagoon. Results show that the most important factor that controls the residence time is the wind action on the lagoon surface. The residence time is ranging from 590 days under a situation without wind down to less than 30 days under the action of moderate to strong winds. Other factors that influence the residence time are the presence of a coastal current and the return flow, which is the phenomenon of water returning to the lagoon from the open sea.