The CSIR has completed the physical modelling studies of a proposed new tidal pool in Port St Johns, in the Eastern Cape, for the Department of Environment, Forestry and Fisheries. The studies were undertaken at the CSIR’s coastal and hydraulics laboratory, where some of the biggest and busiest ports in the world have been tested. 

Port St Johns was one of the most popular recreational swimming and surfing spots on the Wild Coast for many years, but has suffered a loss of visitors in recent years, following a number of shark attacks and drownings. Government considered various interventions, including the possibility of constructing a tidal pool to halt the decline in tourism and associated job losses, and more importantly, loss of lives. 

The CSIR constructed a small-scale replica of the tidal pool in the Stellenbosch-based laboratory. 

In constructing physical models, such as this one, engineers use the data from surveys to mimic the actual sea floor conditions, which contribute to how waves are formed. Data on local wave conditions were also used to simulate impacts on the tidal pool. 

Three aspects were tested. The first was the wave climate inside and outside the pool to ensure that the waves inside the pool are small enough for safe bathing. The second was overtopping, in which the water that is washed over the wall and into the pool is quantified; and thirdly, flushing – how different water currents that formed inside the pool behave and how the water is then evacuated out of the pool. Flushing is important to prevent the water in the tidal pool from stagnating. 

The testing was completed in November 2019 and the results were submitted to the consulting engineers.