A rockfall is the free falling of a rock from a cliff face or from the roof or walls of a mine or quarry. Mitigation techniques include passive drape nets, rockfall catchment fences, and diversion dams, as well as active rock bolts, shotcrete, and revegetation. Significant rockfalls in Colorado have occurred along interstate 70.

Avalanche debris in the runout zone taken from a helicopter on the morning after the avalanche occurred, 24 March, 2003. Photo credit: Xcel Energy.

Case Study: Avalanche – Silver Plume

On March 23, 2003, a large avalanche occurred about one mile west of the Town of Silver Plume. The avalanche brought trees, rock, soil and snow to the valley floor, knocked down overhead utility lines, blocked the I-70 frontage road, damaged the town’s water treatment plant (WTP), and dammed Clear Creek. The dam was breached using explosives before the plant’s electric pump motors were flooded. With damage to the WTP’s chlorine contact tank and building, Silver Plume residents had to boil their tap water for over a month.