dam threatens Darby, Conner, Hamilton

Good management decisions use a probability/severity matrix. If the probability and severity of an event are both low, it is not worth much time and money planning for it. High probability events deserve some consideration, but when severity is inconsequential, not much.

Painted Rocks dam is earth-fill construction somewhat like the Teton Dam that spectacularly failed in the 1976 picture to the right.

In risk assessment, a large dam has 4,000 acre feet of water or more. Painted Rocks reservoir typically contains 14,000 acre feet at normal annual peak.

A High Hazard rating is not based on risk of failure, but if failure were to occur, the resulting consequences likely would be the direct loss of human life and extensive property damage. Painted Rocks dam is very definitely on the “High Hazard” lists.

Within an hour of a dam breach, Conner is under water. In 3 hours Darby is under a 25-foot churning mass of water and debris.

According to the Emergency Action Plan it would arrive in Hamilton, worst case, in 5 hours at a height of over 25 feet and would rise to 43 feet. In clear dry weather a breach would arrive at the North end of Hamilton in 8 hours at a height of 20 feet. According to the calculations an inundation would cover all of Hamilton to the East of the Fair Grounds.

Devastation from a dam failure would be catastrophic, wiping out all bridges, most roads and much of Ravalli County infrastructure. With no warning system or plan, such as is the case today, loss of life could easily exceed 10,000 of us.

“Gee, we didn’t think of that” will not be a good enough answer.

I can plan for my family’s escape and survival AS LONG AS we get some warning of the flood.

Automated, redundant warning systems are not expensive. Planning is cheap.

Painted Rocks should not be allowed to refill until there is some of both in place.

The County Commission Contact numbers are found at: http://ravalli.us/ and the main number listed here:

Commissioners
215 S 4th Street
Suite A
Hamilton, MT 59840

Phone: 406-375-6500