UPGRADE OF COASTAL INFRASTRUCTURE AT SMALL BAY, BLOUBERGSTRAND
Bloubergstrand Beach node is an important recreational and tourism destination situated on the west coast of Cape Town. The existing concrete seawall and walkways, which extend from the play park in Small Bay to the De Mist parking area, had been undermined for a number of years. This had resulted in damage to the adjacent sewer system and undermining of road infrastructure. Popham Street had completely collapsed and was inaccessible by vehicle. The existing sea wall had not been constructed on bedrock and had been undermined over many years by wave action. Sections of sewer line and manholes had been located within the old sea wall, that consequently collapsed. There was therefore an elevated risk that the sewer line could fail, which would have created an environmental emergency.
The project entailed the upgrade of coastal infrastructure, including a new seawall, roadway, sewer line and associated infrastructure. HHO Consulting Engineers were appointed by the City of Cape Town to undertake this work and appointed PRDW Port and Coastal Consulting Engineers as sub- consultants to design the seawall. This project is a good example of excellent collaboration and synergy between consulting engineers and the successful completion of a challenging project, which was executed by a competent contractor for an exacting client.
Coastal Engineering Design
The structural solution for the seawall comprised a cast in-situ, reinforced concrete block wall founded on bedrock and also anchored to the bedrock with galvanised prestressed rock anchors. The construction methodology was adopted to suit the various site constraints such as site access, site storage, space availability, the proximity of residential properties and working in an exposed tidal zone with foundations below water level. The seawall has a design life of 50 years and was designed for a 100-year storm event. Due to the relatively low road and property levels behind the seawall, significant wave overtopping and flooding was encountered through the construction phase during storm and high-water conditions.
Civil Engineering Design
Popham Street had suffered complete structural failure and had been closed to traffic, while Pelegrini Street had experienced localised failures. A jointed concrete pavement road, with a minimum design life of 30 years, was designed for both roads. This pavement was best suited for this location due to its durability and low maintenance requirement. The amended vertical alignment of both roads allows for overland drainage of wave overtopping and all design rain storms.
The existing foul sewer pipe along Popham and Pelegrini Streets had been exposed by the undermining of the existing seawall and was at great risk of failure. This pipeline was realigned safely behind the new seawall, and was upgraded from DN150 to DN200. This work was done whilst accommodating sewer flows towards the Small Bay Sewer Pump Station, which was situated amidst the Works and required access at all times.
Completion of the Works took place in April 2025, with the upgraded coastal infrastructure providing a functional, durable and attractive environment that will be an asset to the Small Bay community for decades to come.