CS30A - Concurrent Session 30A: Unmitigated Disaster, Val di Stava Dam Failure

Abstract Description: Located in northern Italy, the Val di Stava dam was originally constructed as a tailings storage facility for mining waste from the extraction of fluorite. Over the years, the dam grew from a small decanter pond to two dams totaling nearly 60 meters in height with slopes ranging from 32 degrees to 40 degrees. Construction of the dams reused the processed tailing sands and placed them using hydrocyclones without compaction. During the construction of the dams the safety regulators did not inspect the embankments of either dam. The Municipality of Tesoro, downstream of the dam, raised concerns over the dams in 1974 and the report stated that the dam’s stability was marginal. Unfortunately, the recommendations of the report were ignored and the dam continued to grow, and the construction methods went unchanged.

Operations of the dams continued unchanged until the dams collapsed on the morning of July 19, 1985. Just after 12pm the dams collapsed releasing the entire 180,000 cubic meters of waste stored. The failure initiated with the collapse of the upper dam and destroying the lower dam in a domino effect. Following the collapse a torrent of water, silt and mud came crashing down the valley floor at a speed of approximately 90 km/h destroying everything in its path. The damage included the loss of 268 lives, 53 houses, 3 hotels, 8 bridges, and 6 warehouses along the 4.2 km path of destruction.

Forty years later this disaster still stands as one of the most severe dam failures in Italian history. Following the disaster an investigation into the failures began immediately. The Italian Government investigated the failure to determine the underlying causes of the failure. In their conclusions the report stated “The plant collapsed essentially because it was designed, built and managed in such a way as not to offer those safety margins that civil society expects from works that can jeopardize the existence of entire human communities.”
Ten people, including directors of the mine, managers responsible for construction decisions and managers of the mining district that neglected to monitor the safety of the dams were convicted in June of 1992. Their crimes consisted of culpable disaster and multiple manslaughter for their respective roles in the collapse of the dam. None of the convicted served a prison sentence, however, they were sentenced to pay damages.