This is an output of NANO Regional Project North-West Africa

NANO Alumni Abdelfattah Atoui, Houssem SmetiSana Ben Ismail and colleague published the following article in the Estuarine, Coastal and Shelf Science Journal:

Water renewal in the Boughrara lagoon (Tunisia, central Mediterranean Sea) under tidal forcing

Atoui et al. (2020) Estuarine, Coastal and Shelf Science, DOI 10.1016/j.ecss.2020.106680

Abstract

The aim of this study is to estimate the water renewal time in the Boughrara lagoon. This is a key parameter for ecological studies of the lagoon. The method used consists of the injection of a soluble tracer which has a concentration of zero at the open boundaries of the domain (C0 = 0) and is equal to one inside the lagoon (C1 = 1). In this study, we use numerical simulation modules developed by Deltares: the hydrodynamic Delft-Flow module and the Horizontal Large Eddy Simulation (HELS) module. We compute the horizontal advection and dispersion and get estimates, at every mesh of the computational grid, of the time needed for the tracer’s concentration inside the lagoon to drop from 1 (C1) to 0.38. This time is known as the Local Renewal Time (LRT).

A spatial distribution analysis of the LRTs enables a subdivision of the domain based on the similarity of values near the LRT (at every mesh of the domain) and on the physical configuration of the domain (e.g. bay, deep/shallow zone, harbor). Then it becomes simple to compute a renewal time for each region in the domain, which is the Integral Renewal Time (IRT). If we want to take into account the whole domain, we consider the maximum value of the IRT.

The numerical simulations were run taking into account the effect of the predicted tide. The computational grid has a horizontal mesh size of 150 m × 150m. The LRT under only the effect of the tidal forcing at the zone where an aquaculture farm is located is estimated at one week. Moreover, in the region of the mini-gulf of Guellala, this LRT is estimated to be one month.

The encounter between the waters coming from the two channels of the lagoon occurs after a period of four months in the zone bounded to the south by the island of Djilij and to the north by the mini-gulf of Guellala. South of the fishing port of Boughrara and Djilij Island, the local water renewal time varies between 5.5 and 6.5 months.

Keywords

  • Boughrara lagoon
  • Ecological studies
  • Delft-Flow
  • Renewal time

Link for the publication here

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