Environmental reviews | Task force ponders diversion channel around High River
The Alberta government is studying the options for building a large dry dam upstream of Calgary to mitigate risk from future floods.
Premier Alison Redford announced Nov. 21 that environmental reviews are set to begin on the potential dam, as well as a diversion channel around the town of High River.
Roger Drury of TransAlta Utilities said a dam above Calgary would require 150,000 acre-feet of water capacity to prevent overland flooding within the city.
“The ugly part is you’ve got to leave it empty for it to work,” he told the Alberta Irrigation Projects Association conference in Lethbridge Nov. 26.
He thinks such a dam could mitigate flood damage but said it would be a complex undertaking. Its banks would have to be 20 to 50 metres high and be built to specific safety standards.
Such a dam would have to be about three times the size of the Ghost Reservoir, which is one of six reservoirs upstream of Calgary.
The others are Barrier, Minnewanka, Upper Kananaskis, Lower Kananaskis and Spray.
Drury said the reservoirs reduced water flow into Calgary during the June floods in southern Alberta, but maximum flows from uncontrolled sub-basins contributed to extensive flooding in the city’s downtown.
He said the 2013 flood on the Bow River wasn’t the largest ever experienced in the region in terms of water flow. That record was set in 1897.
Drury believes there is a correlation between Alberta floods and extended periods of cool weather created by the Pacific decadal oscillation, which was at work this year.
Heavy rain on already saturated ground and the remaining mountain snow pack resulted in high water flows and extensive flooding.
Provincial statistics indicate 14,500 homes, 80 schools and 10 health facilities were damaged in southern Alberta. Approximately 100,000 people were evacuated, 3,000 business affected and 985 kilometres of roads closed.
Andre Corbould, assistant deputy minister on the provincial flood recovery task force, said that kind of impact takes time to assess and repair.
“When the premier talks about a 10 year recovery, we believe that’s about right,” he said.
This year’s flooding is often referred to as a once-in-100-years flood, but Corbould said that’s inaccurate. In fact, there’s a one percent chance in any given year that a major flood will occur.
He said the task force also wants to avoid over-reaction to the flood because drought mitigation is also a concern for the future.
For more information, visit alberta.ca/Flood-Mitigation.cfm.