Civil Engineering May 2022 | Vol 30 No 4

W ithout warning, storms in August and September 2017, co- inciding with spring high tides, caused rapid deterioration by substantially scouring the seawall founding material (see Figures 2 and 4), affecting Erf 234 owned by the Hartwig Trust and the neighbouring Erf 636 owned by the Craig Jarvis Trust, and leaving them in a vulnerable condition. The damage to these walls placed the houses on both properties and the City of Cape Town’s (CoCT) foul sewer gravity pipeline located directly behind the sea- walls at risk of undermining, necessitating urgent repairs. This article describes some of the design and construction challenges associated with reconstructing these walls in difficult conditions. BACKGROUND Both properties are located on Small Bay beach (see Figure 1) between the mu- nicipal Small Bay Play Park and the res- taurant Ons Huisie. Small Bay is a popular beach used by the public for recreational purposes all year round. In low tide condi- tions there is a sandy beach in front of the walls, while in high tide conditions the sea reaches the wall. The purpose of the seawalls is to pro- tect these properties from erosion by the Big challenges at Small Bay Francois de Roubaix Associate Transport and Infrastructure: Maritime WSP Group Africa (Pty) Ltd francois.deroubaix@wsp.com Small Bay, also known as Kleinbaai (see Figure 1), to the south of Big Bay in Bloubergstrand, is a bay protected from the offshore westerly swells hitting the shores of Cape Town. A storm on 7 June 2017 caused extreme inshore conditions (see Figure 3) and damage to the seawall scour protection of the seafront properties in Small Bay. During this storm, the waverider buoy at Cape Point/Slangkop measured significant wave heights (average of the highest one third) of up to 11.5 m, which is the highest ever recorded at this location. 22 May 2022  Civil Engineering Figure 1 Small Bay in Bloubergstrand Play Park Ons Huisie Erven 234 & 636