Project context and challenge
The coastline of Água Grande, the district that includes the capital São Tomé, is the face of the country. The Marginal, the coastal road along Ana Chaves Bay, connects the airport, the city centre and the national road network, and runs past beaches, fish landing sites and historic buildings. Over the years, the ageing seawall and the road behind it have come under increasing pressure. During high seas, waves overtop the wall and flood the road, putting pedestrians and traffic at risk. Elsewhere, beaches are eroding, partly because sand is removed illegally for construction.
With sea levels rising, the Government of São Tomé and Príncipe recognised the need to invest in coastal protection. With funding from RVO, the Netherlands Enterprise Agency, the Ministry of Infrastructure, Natural Resources and Environment asked CDR to carry out a vulnerability analysis, feasibility study and preliminary environmental and social impact assessment. During the project, the rehabilitation of 8.8 km of coastal road from the airport to Pantufo was added to the scope.
The challenge was to protect the coast while creating a safe, attractive waterfront for residents, fishers and visitors on a small island with limited resources.
CDR’s approach and contribution
CDR led the project together with REBEL and IHE Delft. Site visits and stakeholder workshops in São Tomé helped the team understand local priorities, and surveys covered the condition of the road and traffic volumes.
Wave and flow models (SWAN and Delft3D) were used to analyse the marine conditions, erosion and overtopping along the coast. Combined with an analysis of exposure and vulnerability, this identified the hotspots where action was most needed, such as the northern and southern parts of Ana Chaves Bay and Lagarto beach.
Two alternatives were then developed, combining green, blue and grey infrastructure. Based on their strengths and weaknesses, a third, preferred alternative was formed that brings together the best of both. An urban zoning plan was prepared in parallel to align the design with the city’s development, and a cost benefit analysis and preliminary ESIA completed the assessment. A knowledge exchange and training programme ran throughout the project.
The integrated design rehabilitates the seawall in Ana Chaves Bay with a closed balustrade and rock berm to reduce overtopping, adds a rock revetment and wide seaside promenade at Lagarto, and improves the road profile with sidewalks, cycle lanes, drainage and safer junctions. Fish landing sites gain more space, beach access and sanitation facilities, and the characteristic old trees are preserved.
Result
The Ministry received a complete, integrated design for 8.8 km of coastline and coastal road that is technically and economically feasible. The design not only protects the road and the city against waves and erosion, but also turns the waterfront into a safer and more attractive public space for residents, fishers and tourists.
The study provides a ready basis for detailed design and tendering, and recommends a citywide mobility plan to guide future traffic and urban growth in São Tomé.
