Author(s): Maya Lambert; Sebastian Solari

Linked Author(s): ssolari

Keywords: Coastal lagoon; Hydrodynamic model; Coastal management; Heat and salinity transport; Climate change

Abstract: Intermittently Closed/Open Lakes and Lagoons (ICOLLs) are a particularly dynamic form of estuaries characterized by periodic entrance closure to the ocean (McSweeney et al., 2017). Laguna de Rocha is an ICOLL, located on the Atlantic coast of Uruguay. The lagoon closes almost every year and, usually, it is artificially opened at least once a year during the cold months to avoid floods and to facilitate the exchange of water, substances and organisms with the ocean. Recently a protocol was implemented in order to regulate artificial openings of the lagoon (Conde et al., 2019). However, in order to better understand how different protocols may affect the ecological evolution of the lagoon (in present as in future climate) it is necessary to model how they affect water and substance exchanges between the lagoon and the ocean and how these exchanges affect the spatial and temporal distribution of the physicochemical variables in the lagoon. A usual solution in this case would be to implement a hydrodynamic model with substance transport equation. However, some particularities should be considered when dealing with an ICOLL: (i) the time and spatial scales of variation of the inlet are much smaller than those of the lagoon or the ocean, being essential to consider its morphodynamic evolution, (ii) the characteristics of the water that enters the lagoon cannot always be assimilated to open ocean conditions, since they may be affected by the (large) discharge of the lagoon after an opening, which implies that both the lagoon and a stretch of the coast should be modeled after an opening, but not necessarily when the lagoon is closed. In this work a multiscale numerical model is developed for modeling exchanges between the lagoon and the ocean and the spatial and temporal distribution of the physicochemical variables in the lagoon. The inlet evolution and water and substances exchanges between the lagoon and the ocean are modeled following Hindwood et al. (2012) and Wu and Li (2017). This simplified morpho-hydrodynamic model has shown to reproduce reasonably well the opening and closing dynamics of the lagoon (Teixeira and Solari 2020). The simplified inlet model is coupled with two 2D hydrodynamic models, one for the lagoon and one for the ocean. This approach allows for modeling long term evolutions of the water quality variables in the lagoon without the need to resort to very high resolution models to solve the inlet, thus allowing to compare long term evolutions under several climate change scenarios and different opening protocols. Preliminary results show that the multiscale model is able to reproduce the spatial and temporal variation of the salinity in the lagoon under current climate.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022342

Year: 2022