The De Hoop Dam is a gravity dam on the Steelpoort River near Burgersfort, Limpopo. The dam is 81 metres in height and 1000 metres in length, with a total capacity of 347 million cubic metres and a surface area of 1690 hectares. It is operated by the Department of Water and Sanitation. The De Hoop Dam project, worth R3,4 billion, is the largest dam built in South Africa since the 1970s. Its purpose is to enable the extraction of rich mineral deposits in the eastern Limpopo province and to improve the supply of water to towns, industries and communities in the Sekhukhune district. The dam opened in 2014.
Challenge
There have been large earthquakes in South Africa in the past, notably a 6.3 magnitude earthquake north of Cape Town in 1969. Experts report that the East African Rift tectonic plate faultlines are spreading to southern Africa. Cognisant of the fact that major earthquakes can lead to large scale loss of life and property, the government wanted a system that would effectively monitor the dam. The remote location of the dam made the installation a substantial challenge because all the necessary equipment and consumables had to be brought in from outside.
Solution
The goal of the project was to supply a modern, state-of-the-art seismic monitoring system as well as an Ambient Vibration Monitoring (AVM) system. GeoSIG offers a wide range of seismic sensors, recorders and software for projects of this nature. With more than 25 years experience in providing earthquake, seismic, structural, dynamic and static monitoring and measuring solutions, GeoSIG’s partner, Tilt-Tech proposed a winning solution with the expert help of engineers at GeoSIG. In this case two GMSplus recorders and six AC-73D digital force balance accelerometers were utilised. Communication to the outside world was achieved with industrial GSM modems connected to an LPDA high gain antenna.
The six sensors required 900 metres of industrial cable to be installed, including about 370 metres of the outside cable into galvanised pipes for protection against the elements. Even the pipes had to be installed using saddles and anchor nails. The main equipment, such as the two GMSplus units, battery and battery charger, was installed into a specially manufactured stainless steel enclosure, which also housed the modems, network switches, inverter and laptop. The battery enclosure and charger were installed just below the main enclosure. The system is currently being monitored remotely and is set up to send system error messages, log files and event triggers. The customer also concentrates on ambient vibration monitoring in order to ascertain the health of the structure over the years to come. Site inspections, as well as collection of raw data, are done on a monthly basis.
This is another example of a solution using GeoSIG instruments together with a capable partner, effectively showing that quality and reliability can also be cost-effective.
For more information contact Jan Hanekom, Tilt-Tech, +27 (0)83 370 2125, [email protected], www.tilt-tech.co.za
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