There are so many numbers in the provincial flood study people are wondering how did you pick 1,850 m3/s and why are you referencing flows and not frequency? Let’s get the rumour stick and sort through the facts.
The study talks about a few things, like natural and regulated flow rates. Both are useful in different situations. The natural flow rate is how the river runs with no outside intervention like the Dickson Dam. From experience, we know the Dickson Dam mitigated risk during previous flooding events which makes the regulated flow rate of 1,850 m3/s the one to use. The Rosebud River and Willow Creek where there is no reservoir, the natural flow rate is more appropriate. We also use natural flow with Michichi since Michichi Dam is small and of a flow over design.
Flood frequencies are often confusing to understand. A frequency of 1:100 flood actually means in a given year there is a 1 in 100 (1%) chance of experiencing a certain level of flood. It is really the flow in the river, not flood frequency, that homeowners and the Town’s emergency managers are most interested in. The flow determines when the dikes will be overtopped, when conditions are threatening and when it is generally safe to enjoy the river.
The town is developing a simple way to communicate these flow rates with colour coded signage so everyone in Drumheller will understand the safety impact for people and property of different flow rates. Or, as I like to say, Know your Flow!