Short-term effect of sea defense on shoreline and wave variability in Elmina Bay, Ghana

The geometry of many beaches could influence wave intensity and shoreline changes. To determine the response of embayed beaches to varied wave forcing is more challenging because of diverse flow patterns within the bays. This is even more complex when coastal defenses are constructed within the bay which affects the long-shore and cross-shore currents, maybe changing the direction of flow in line with the orientation of an installed structure. Beach surveys with Unmanned Aerial Vehicle flights and video camera systems were conducted from January, 2019 to April, 2021 to assess changes in beach morphology at the Elmina beach. The goal was to further evaluate the shoreline changes prior to April 2020 of the sea defense construction and the period of post-defense construction (May 2020 to April 2021). Our results reveal that the sandy part of the beach has become shorter while erosion has intensified during and after the construction of the sea defense. Waves have decreased heights and periods during the post-defense period although they remain important for high shoreline erosion. The beach became steeper as well as showing significant loss of sand as a consequence of the revetment sea defense construction activity. The sandy portion of the remaining beach will be rapidly eroded if the revetment defense is not extended to the rest of the beach.