Lessons From the Gillespie Dam Failure

Gillespie Dam on the Gila River about 40 miles downstream of Phoenix, Arizona, failed during unprecedented flooding on 9 January 1993. The breach of the 20-foot high concrete diversion dam did not result in a dam breach flood wave, however, 14 million cubic yards of sediment were released from the reservoir sediment deposit upstream of the dam during the sustained flooding after the dam breach. Ten days after the dam breach, two large, high pressure natural gas pipelines failed about ¼ mile downstream from the dam. The failure of the dam and the pipeline resulted in claims for damages by the owner of the dam, the insurer of the pipeline and some farmers downstream of the dam. Those claims resulted in two civil trials in Arizona. The dam owner and the farmers claimed that a vegetation clearing project in the river by the Flood Control District of Maricopa County was the cause of the dam failure and the damage to downstream farm land. Extensive engineering analyses were conducted of the flood, the dam and the Gila River by consultants. The extent of those engineering investigations by consultants for the Flood Control District of Maricopa County are briefly described. The dam failure and resulting lawsuits suggest lessons to be learned by dam owners, regulatory agencies, private land owners and public agencies that undertake projects in rivers. 12 pp., 7 figures, 4 references.