Analysis of the morphological behaviour along the Luanda coast

Deltares is currently involved with multiple Angolan companies to advice on several coastal projects along the Angolan coast, especially in the Luanda area. Luanda is expanding rapidly trying to keep up with its economic growth as such coastal projects like land reclamation occur often these days. Still there is little understanding of the coastal systems along the coast of Luanda, whereas the demand for information and knowledge is rising. To increase efficiency of coastal projects, information about the Luanda coastal area is highly preferable. Main features of the Luanda coastal area are the Kwanza River, the Bay of Mussulo, the Island of Mussulo, the submerged shoal, the Luanda bay and the Island of Luanda. The objective of this research is to increase the insight of the Luanda coastal area by analysing the longshore sediment transport. In particular, the sediment transport between the Island of Mussulo and the Island of Luanda. Relevant information will be bundled and used to set-up relevant models which are used to describe the sediment transports. Analysis With the help of old charts an analysis is made of the long scale changes along the Luanda coast. It is shown that the coast undergoes some major changes between 1870 till 1950. The Island of Mussulo is reformed as the inlet existing nowadays was shifted south (or this inlet was filled and the nowadays opening in the Bay of Mussulo happened due to a breach). During the last 60 years no major changes were observed. With the help of the software packages UNIBEST-CL+ and Delft3D multiple model simulations were made to get an insight in the sediment transport rates at the Luanda coastal area. The simulations were validated with the help of observation. To qualitatively increase the insight in the Luanda area conceptual models were made which indicates the range within the real LST has to be in. This was first done for each area separate. By combining these models the sediment transport between the Island of Mussulo and the Island of Luanda via the shoal could be investigated. Conclusions and recommendations The following conclusions were drawn from the research. The sediment transport along the coast is mainly driven to the north by waves approaching from the south-west. The Kwanza River is not seen as a main sediment supplier for the present Luanda area. Sediment supply at the south is mainly expected to be from the coastal area south of the Kwanza River. Part of the sediment transported along the tip of the Island of Mussulo will be transported to the shoal and partly to the tip of the Island of Mussulo where it will settle. The tide has a relatively small influence on the interaction between the shoal and the Bay of Mussulo. The dredged channel in the shoal will act as a sand trap and reduce sediment to be transported to the north. This will not have a large effect and a short time scale but can have a major impact on the long term. The LST by the sandbars via the shoal supplies the Island of Luanda with sediment as well as sediment transport from the coast south of the Island of Luanda. The Island of Luanda suffers from structural erosion as the supplied sediment is not enough in order to keep up with the LST. The erosion is nowadays compensated with beach nourishment and coastal structures such as groynes.