Some folks have been wondering why Drumheller is using a regulated flow for flood mitigation strategies, and not a naturalized flow as seen in the province’s flood study materials. Let’s consult the old rumour stick and see what’s going on.
It turns out the provincial flood study evaluated and reported both naturalized and regulated flood flows for the Red Deer River. The naturalized scenario removes the effect of dams and reservoirs that regulate flows, which represents a worst-case scenario. The regulated scenario takes into consideration existing dams and reservoirs that may assist in reducing downstream flood flows.
Drumheller is using the regulated 1:100 flow of 1,850 m3/s for design of mitigation strategies because it takes the effects of the Dickson Dam into account and provides a level of protection exceeding the 2005 and 2013 floods.
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. For 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.
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!