Morphologic Changes at the Guaraíras Lagoon Mouth, RN/Brazil

In the south coast of the state of Rio Grande do Norte, northeast of Brazil is situated the Guaraíras Lagoon. This lagoon has shown significant changes in its morphodynamic and hydrodynamic behavior in the last decades. Factors such as changes in superficial runoff, silting and erosion of embankment margins are already evident and compromise the whole functioning system. Added to these factors, there is a strong presence of shrimp farming in the area around the lagoon, representing 9% of national production, thus generating great relevance for the local and regional economy. In this context, the present study aims to analyze the morphodynamic behavior of the mouth of the Guaraíras Lagoon, based on the application of geoprocessing techniques to quantify the rate of erosion and deposition of the study area. For the methodological procedures the work counted on the multitemporal analysis of variations of beach line, using satellite images of the Landsat series, between 1984 and 2018, and the application of geostatistical analyzes (End Point Rate - EPR, Linear Regression Rate - LRR e Net Shoreline Movement - NSM) for quantification of the erosion/deposition rate of the changes that occurred during this period of analysis (1984 - 2018). Based on the results obtained by the EPR, an intense erosion rate of 6.4 m/year and 0.34 m/year of deposition of the left embankment margins of Guaraíras Lagoon occurred. The margin to the right of the embouchure presented a variation of 1 m/year of erosion and a rate of 1.34 m/year of deposition. In the beach strip south of the embouchure there was 1.5 m/year of erosion and 1 m/year of deposition and in the northern portion of the mouth a rate of 3 m/year of erosion with 1.57 m/year of deposition. Considering the results obtained, there was a morphological instability at the mouth of the Guaraíras Lagoon, with a strong erosive tendency in the left margin, resulting a decrease of -217.82 m in relation to 11.67 m of deposition; and on the right bank the trend was depositional, corresponding to 45.6 m increase in relation to -31 m of erosion. Thus, through the geoprocessing techniques applied, it was possible to quantify the rate of erosion/deposition at the mouth of the Guaraíras Lagoon during the period studied (1984 - 2018).