Case Study: Harmony Gold Mine No. 4 Tailings Dam (South Africa, 1994)

Construction of the Harmony Gold Mine No. 4 tailings dam began in 1978 and was sited 300 m (1,000 feet) away from the suburban town of Merriespruit in South Africa.  The dam was built using the upstream semi-dry paddock method of construction, reaching a height of 31 m (102 feet).  After 16 years of construction and operation, the dam failed on February 22, 1994, resulting in a 630,000 m3 (500 acre-feet) liquefied outflow which swept 4 km (2 miles) through the town, causing 17 fatalities, destruction of 80 properties, and widespread environmental damage.

A few hours before the failure, a storm produced approximately 50 mm (2 inches) of rain over the dam in just 30 minutes.  Due to very low freeboard in the dam, this rainfall resulted in overtopping of the dam, and the resulting overflow runoff was observed in the town for at least 2 hours before the failure.  The overtopping caused erosion of the downstream face of the dam, which is believed to have resulted in progressive slope failures, which then triggered a static liquefaction flow failure of the metastable tailings.

This catastrophic failure was not due to an extreme natural event nor ‘bad luck’. Rather, the failure was preventable and was ultimately attributable to human factors, specifically a series of poorly judged managerial and operational decisions which spanned years prior to the failure and stemmed from a poor economic climate and cost-cutting pressures.  Evidencing this, a Ministry of Justice inquiry found the dam owner, the operator, and six of their employees guilty of negligence and fines were imposed. An array of physical and human factors contributed to the failure of Harmony Gold Mine No. 4 tailings dam, and warning signs which were not heeded. As a result, post-failure reforms in regulation and mining industry practices which were implemented in South Africa.