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Do rivers play a significant role in the ocean and marginal seas circulation and dynamics?
Do we need a fine representation of river release into regional ocean models?
Rivers are found to affect the coastal and the basin wide overturning circulation and dynamics. The regional ocean models cannot solve the estuarine dynamics and they parameterize the river release in an oversimplified way. Doing this the water exchange into the estuaries, owing to the ocean water entrainment, is not represented.

Researcher Giorgia Verri, ocean modeler at the CMCC Foundation – OPA Division, realized a study aiming at (i) a realistic representation of the riverine freshwater release into coarse resolution ocean models by taking into account the estuarine water exchange and (ii) a proper reconstruction of the resulting dynamics in the ROFIs (i.e. Regions Of Freshwater Influence), the shelf areas adjacent to the estuaries. The main aim of the study was therefore to develop an interface between estuaries and regional ocean models in order to get a reasonable representation of river release in terms of runoff as well as to show the impacts on the ROFI dynamics.

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Three approaches (the three following models: the Knudsen’s relation, the UCONN-NCAR Estuary Box Model and the CMCC Estuary Box Model developed by researcher G. Verri)  to represent the estuarine dynamics are tested and compared.
All the approaches are able to solve estuarine processes such as river freshwater inflow, ocean water inflow and estuarine water outflow, but only two of them (the UCONN-NCAR and the CMCC Estuary Box Models) are capable to represent tidal pumping and mixing. More in detail, the approach developed by the CMCC is able to explicitly solve all the described estuarine processes with no parameterizations.

Two case studies were considered: the highly stratified estuary of the Ofanto River and the partially mixed delta of the Po river.
The second phase of the study was the development of the interface between the estuary and regional ocean models. The coupling with a regional ocean model over the Central Mediterranean Sea based on NEMO code has been investigated,
The coupled systems are capable to reconstruct well defined river plumes and outperform the climatological approach which neglects the estuarine water exchange. The validation of the numerical results shows a promising high statistics of the coupled system by using the CMCC estuary box model.

For more information, read the integral version of the following papers: