A first integrated modelling of a river-lagoon large-scale hydrological system for forecasting purposes

Hydrological-hydrodynamic modelling of basins, rivers and large bodies of water, such as lakes and lagoons, is usually performed by external coupling of hydrological-hydraulic models and 2D or 3D hydrodynamic models. Therefore, the river discharges into the lake are calculated by using the hydrologic model. The data is used then as an input to the hydrodynamic model. This approach allows for a detailed simulation of lake or lagoon hydrodynamics and circulation. However, when the objective is solely to simulate water levels and flooded areas, this approach may become too costly, making it difficult to establish operational systems such as those for flood forecasting. Therefore, in the present study, we propose a first integrated approach using one single hydrologic hydraulic model, the MGB-IPH model, to simulate complex systems such as wind shear influence. This model was applied to simulate the Patos Lagoon (PL) basin located in Brazil and Uruguay countries. Results showed that it was possible to use the single model to simulate hydrographs, flooded areas and water levels in the PL basin. Results of performance indicators in the lakes and lagoons were within the range of results available in the literature. Improvements of model performance metrics were verified with the inclusion of wind effect in the flow routing algorithm, thus encouraging the use of the proposed model for the establishment of flood forecasting systems or for the simulation of other similar hydrological systems.