For 47 years, Deer Creek Reservoir has sat quietly in the southwest corner of Heber Valley a sleeping giant that belies the destructive power of thousands of acre-feet of water held at bay by a 150-foot-high earth-filled dam.
No one expects the structure to meet the fate of Idaho's Teton Dam, but officials are preparing for disaster just the same because the possibility of dam failure can't be ruled out.Officials say the most likely scenario is dam overflow. The dam, however, is designed to handle a flow of 12,000 cubic feet per second. Because the largest flow ever to be released has been only a fraction of that amount, officials believe an overflow is highly unlikely.
Bureau of Reclamation officials recently briefed Utah County commissioners on development of an emergency preparedness plan. The briefing gave information to authorities responsible for warning and evacuating residents. The plan is part of a nationwide effort for all federal dams where failure could endanger human life or cause property damage.
"We're doing this in a systematic order as we're required to do with all our federal dams and those administered by the bureau," said Laurel Pope, hydrologic technician with the bureau's Utah Projects Office. He said seven similar briefings have been presented across the state.
The study on Deer Creek Reservoir outlines potential hazards resulting from a variety of scenarios, including flooding caused by breaching of the dam or by the dam's failure.
County Commissioner Brent Morris said the county is organizing a countywide board to oversee emergency preparedness. The board to include representatives of law enforcement agencies, mayors, school districts, local churches, the Red Cross and other countywide organizations will include the Bureau of Reclamation study in developing a plan for dealing with all kinds of emergencies.
The study, including an inundation map that shows possible flood plains, reflects "conditions of an extreme nature with a very small probability of occurring and does not reflect in any way upon the integrity of Deer Creek Dam."
Nevertheless, local, state and federal governments have been instructed to formalize steps for emergency action.
"In the unlikely event of failure of Deer Creek Dam, the developed areas in Provo Canyon (Wildwood, Vivian Park, Canyon Glen and Olmsted) as well as other areas would be inundated by the flood wave and sustain heavy damage," the bureau study says.
"Study results indicate that flood flows caused by a dam failure would produce hazardous flooding along the entire reach in Provo Canyon. Flood depths and velocities along this reach would be severe, with depths ranging from 30 to 70 feet and velocities ranging from 15 to 25 mph."
U.S. 189 would be flooded if the dam failed, along with the Salt Lake and Olmsted aqueducts, Olmsted and Murdock diversion dams, pipelines, canals and bridges.
In addition, flooding would occur below the mouth of Provo Canyon.
"Flood flows along this reach would be contained in the large, natural channel extending from the mouth of Provo Canyon to the northern Provo City limits. Maximum flood depths would range from 15 to 20 feet, while velocities would be 10 to 15 mph."
Flood waters likely would fan out for several miles as they make their way to Utah Lake. Shoreline flooding also would occur as the lake level rises in the flood's wake.
As part of its plan, the Bureau of Reclamation is outlining its responsibilities in case of flooding as well as the responsibilities of local authorities and dam personnel.
"In most cases of potential failure, sufficient time is available for hydrologic or stability experts to evaluate the seriousness of the situation and to notify authorities of the possibility of evacuating people from the flood plain," the study says.
But, the study continues, "in the event of a sudden dam failure, the residents and authorities could have a complete lack of environmental cues, such as a rainstorm or earthquake, to use as a prediction of an impending hazard."