Coastal evolution at Macaneta spit, Mozambique - an analysis of longshore and cross-shore processes

Abstract: Macaneta spit is located about 30km north of Maputo, Mozambique, with the Indian Ocean on the east side and Incomáti River on the west side of the spit, composing an interesting and vulnerable area from a hydrodynamic point of view. Few studies regarding coastal processes are done in the area and changes of the morphology could result in breaching of the spit and thereby affect both accessibility to the spit and the water supply for irrigation in the region. This master thesis was conducted as a minor field study in collaboration between Lund University, Sweden, and Eduardo Mondlane University, Mozambique. The study investigates the coastal evolution of the Macaneta spit, with hope to provide an understanding of the hydrodynamic conditions present at Macaneta and thereby assist policy makers in setting up priorities and taking preventive measures to for example avoid breaching of the spit. The investigation includes field studies at Macaneta together with modeling of cross-shore and longshore processes for the period 2005-2015. Modeling wave propagation from offshore in EBED generated a local nearshore wave condition used as input to the cross-shore and the longshore simulations. Result from the simulations was analyzed together with historical images of Macaneta to quantify the risk of overwashing and breaching of the spit at critical sections along the spit. The result obtained indicates that there is a stable condition in the northern part of the spit, although overwash events seem to occur often. In the southern part of the spit an eastern migration is observed. Moreover, ongoing erosion at the narrow isthmus in this region can be seen from satellite images. Further studies of the area are highly recommended, in particular for coastal sections evidently more prone to the risk of breaching.