Tidal connectivity modelling in wetlands associated with coastal lagoon of Punta Rasa natural reserve, Argentina

Tidal flows play a crucial role in connecting coastal lagoons to the sea through channels, in this way determining the hydrological dynamics of these environments. The Punta Rasa Natural Reserve (Ramsar site) is located in a transitional zone between the outer limit of the estuary of the Río de la Plata and the open sea. In this work, we study the northernmost lagoon at the end of the spit, which is connected to the sea by a narrow tidal channel. Wetlands are developing at the edges of the lagoon and in lower lying sectors. The aim of this study is to develop a conceptual model that explains the tidal connectivity of the coastal lagoon and to assess how it affects the marsh environments. Detailed topographic surveys were performed using Structure from Motion Multi-View Stereo from a UAV, while sea level data was analyzed using recordings at 20-min intervals over a five-year period. This dataset facilitated an analysis of the frequency of exceedances for threshold values of 0.8, 1.0, 1.2 and 1.4 m. The frequency analysis reveals that the highest exceedances of these thresholds occur during the summer months. When the water level reaches 1 m, the lagoon is fully connected to the sea via the tidal channel, resulting in complete inundation of the low marshland and the margins of the high marshland. At a tidal level of 1.4 m, the high marsh connected to the tidal channel and the coastal lagoon experience flooding. The results obtained in this study provides insights into modelling hydrological connectivity between marshes and the sea, as well as determining the frequency of tidal inundation in each wetland.