Assessing Geomorphological Changes in Coastal lagoon using Geospatial Tools: a case study Moulay Bousselham Lagoon, Moroccan Atlantic Coast

Abstract

Abstract This study aims to assess the morphodynamic changes undergone by an inlet, sandpits, and adjacent beaches of Moulay Bousselham lagoon (Morocco Atlantic coast), considered as a RAMSAR site of significant biodiversity. Firstly, a Digital Shoreline Analysis System (DSAS) is applied to monitor shoreline evolution for 72 years between 1949 and 2021, based on the EPR and LRR models, with the study area divided into south and north sides. Secondly, we mapped sandpit areas in the lagoon using recent satellite images and historical aerial photos within a GIS (Geographic Information System) environment. As a result, the average annual accretion rates on the north side, comprising 276 transects, are + 0.63 m/year (EPR) and + 0.55 m/year (LRR). Accretion is observed in 239 transects, while erosion is recorded in 37 transects. The south side, comprising 2211 transects, shows average annual erosion rates of -0.67 m/year (EPR) and − 0.82 m/year (LRR), with 1359 transects showing accretion and 872 transects indicating erosion. We show significant changes in the sandpit areas at the entrance and inside the lagoon, with the area of accumulation increasing from around 155662 m² in 1949 to 983823 m² in 2021. Accordingly, a Morphodynamical model is developed Based on the obtained results, which explains the main factors controlling the inlet evolution taking into account the dominant swell direction and energy. This article will help us to understand the relationship between the evolution of the coastline and its immediate influence on sediment supply to the lagoon.