Quail Creek Dam - the main structure at Quail Creek Reservoir and the one that did not fail on Jan. 1 - is designed to withstand only one-half of the probable maximum flood, says a special review team.
"The risk associated with this deficiency needs to be reviewed and, if necessary, remedial actions can be considered in the future reconstruction," members of the four-member team wrote to Gov. Norm Bangerter on May 24. By reconstruction, the group means the possible rebuilding of the reservoir.The governor's office has just released a copy of the letter from the Quail Creek Review Team, outside consultants appointed by Bangerter after the smaller dike at the reservoir collapsed Jan. 1.
The team concludes that the main dam is safe and performing well but apparently doubts its ability to hold back "the maximum probable flood."
Members of the four-man team told Bangerter that they undertook a comprehensive review of the dam, which is the larger structure at the reservoir, located nine miles from St. George. The dam did not fail when a chunk of the associated berm blew out on Jan. 1, releasing water that caused $12 million in damage.
The failure was not the result of a maximum probable flood, or any kind of flood at all. The simple accumulation of water in the reservoir, some of which worked its way beneath the earth-fill dike, caused the failure.
Earlier, the team concluded that the dike's design was flawed because planners did not expect the amount of seepage that actually occurred along joints in the rocks. In addition, grouting to control leaks in the dike may actually have contributed to its failure, according to the report.
The latest finding is that the main dam is performing properly.
"Based on our study, it is evident that there are distinct differences between the dike and dam, and that the dike failure should not prejudice a reasonable evaluation of the dam's safety," the four team members wrote to Bangerter.
"The team's principal conclusion is that, in its current state, Quail Creek Dam is safe; the dam is performing as intended by the design and, at this time, there are no indications of serious changes or threatening trends."