The Council for Scientific and Industrial Research (CSIR) has recorded record-height waves during the storm that battered the Western Cape on Wednesday, 7 June 2017. The unusually large and violent storm resulted in wind speeds exceeding 120 km/h, with significant wave heights of up to 11 metres. The wave heights were recorded using the CSIR Datawell Waverider MK-III buoy deployed south-west of Kommetjie, Cape Town.

CSIR coastal technologist, Sarel Haasbroek, says that there is only a 2.5 – 3% probability per year of a similar wave event occurring.

“The number of these wave events occurring in the next 30 to 40 years is one,” says Haasbroek.

Using the CSIR-TRANSNET Integrated Port Operation Support System tool to record wave conditions, CSIR engineers have confirmed that this was the largest wave event recorded since 1978 when  a single wave reached a height of 20.5 metres, the approximate height of a seven-storey building. This record was captured west of the Cape Peninsula.

Haasbroek adds that another astonishing feat was that the CSIR Waverider Buoy survived the massive storm wave onslaught. “It did not break free from its mooring and to this day, it has kept on recording,” he says, adding that the CSIR technical team has to be acknowledged for their integral part in maintaining these systems, not only at Cape Point, but all around the South African coast line. “They ensure that quality data reaches our shores.”

The CSIR recorded similar but slightly lower wave events in 2001 and 2002. Haasbroek says that the storm that occurred on 7 June 2017 was an extraordinarily large storm produced by exceptional conditions. During storms, engineers often record so-called freak or rogue waves. In the case of the recent storm, there was no indication that the wave heights were not in line with standard distributions.

The recording of these wave conditions is essential as continuous monitoring of the wave conditions allows the determination of the wave steepness and the groupness of large waves in a storm. This data is useful for the design of offshore structures, both floating and fixed installations. These data also provide a relationship between wave conditions offshore and long-wave conditions in a port. Comparing the measured data with the forecast conditions will also allow for the improvement of future forecasts.

The CSIR, in partnership with TRANSNET, monitors the wave conditions near the main ports - Saldanha, Cape Town, Ngqura, East London, Durban and Richards Bay – while it also monitors long waves inside the ports of Ngqura, Cape Town and Saldanha Bay.

During the recent storm, an extreme long-wave height of 0.7 m was recorded at the Container Terminal in Schoeman Dock, in the Port of Cape Town, and although this may not seem to be a very high wave, it was the biggest long-wave condition recorded in the Port of Cape Town to date. Such long waves may lead to water resonance and in turn cause ships to part from their moorings.

Wave data are crucial for maritime and marine operations around the South African coast. The international meteorological community uses these data to calibrate numerical models for weather and sea state forecasting.

The output of the weather and sea state forecasting models are used to warn the maritime and marine industry of imminent adverse conditions. The wave data is also analysed and archived by the CSIR for future characterisation and statistics.

The CSIR operates a number of numerical models for the computation of wave, shipping and mooring conditions in the ports. The wave data are used to calibrate or verify these models to improve and quantify their accuracy and reliability.

The local fishing communities, surfers, tourism and recreation industries also make use of wave information displayed on the website. The wave information is freely available at wavenet.csir.co.za

ENDS

For more information, please contact:
Tendani Tsedu
Group Manager: CSIR Strategic and Stakeholder Communication
Tel: +2712 841 3417
Cell: +2782 945 1980
Email: mtsedu@csir.co.za

About the CSIR:

The CSIR is one of the leading scientific and technology research, development and implementation organisations in Africa. Constituted by an Act of Parliament in 1945 as a science council, the CSIR undertakes directed and multidisciplinary research, technological innovation, as well as industrial and scientific development to improve the quality of life of all South Africans. For more info visit www.csir.co.za