Flood protection offers win-win for irrigators

New reservoir could protect both Calgary from catastrophic flood while increasing supply for irrigation

The 2013 “super flood” that hit southern Alberta was the country’s costliest natural disaster — with the bill for damages and recovery measures topping $6 billion.

Now, a new report says there are ways to both prevent a similar disaster and also help mitigate the impact of drought.

The Bow River Working Group — composed of officials from the province, Calgary, and rural municipalities as well as reps from irrigation districts, First Nations communities, TransAlta, and others — has recently submitted a report to the province on infrastructure options.

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“The appropriate studies need to be done so they can determine what can be implemented for infrastructure,” said Richard Phillips, general manager of the Bow River Irrigation District. “If something isn’t done, sooner or later Calgary will be hit by a Bow River flood that will be an absolute disaster there.”

The Elbow River was the primary cause of flooding in Calgary in 2013 and there’s already a plan to deal with that waterway — the Springbank Off-Stream Reservoir, which will be able to temporarily store 70 million cubic metres of surge run-off.

But the Bow River and its upper tributaries are also a major flood threat. The working group used computer modelling and other information to examine three possible options to protect Calgary: expand the Ghost Reservoir (located in the foothills west of the city); build a new dam just upstream from that reservoir near Morley; or build a new dam between the reservoir and Calgary at Glenbow Provincial Park.

From an irrigation perspective, the Glenbow option is the least beneficial, said Phillips.

“(The reservoir) would be so small as to offer no benefit whatsoever to the irrigation districts,” he said. “An expansion of Ghost could be more beneficial for overall water management, and the Morley reservoir could be very beneficial because that can operate both as a meaningful water management reservoir as well as providing significant flood protection.”

Drought protection

The old saying, ‘it never rains but it pours,’ applies to this sort of project — but the former is more frequent than the latter.

“Droughts happen much more frequently than floods,” said Phillips. “Both 2015 and 2017 were dry years and we did OK with them, but we sure drew hard on the river both those years.”

One solution recommended for drought mitigation is off-stream reservoirs. Two options are the Delacour Reservoir in the Western Irrigation District, and Deadhorse Coulee Reservoir in the Bow River Irrigation District. Preliminary engineering on these projects looks promising and it’s important to recognize that what benefits one irrigation district benefits all, said Phillips.

“Any time any one of us has better storage, it can help everybody because if you’ve got water in storage you don’t need to be pulling it out of the river as much,” he said. “So there’s more in the river for others.”

The group also determined that a dam at Eyremore could flood back to the Bassano Dam and provide a backup for release into the lower Bow River if the river levels are very low. That would give the Eastern Irrigation District valuable water security while providing excellent flood protection for Medicine Hat, the working group concluded.

“This is a project that was first looked at back in the ’60s by what was then known as Calgary Power, for a new hydro dam,” said Phillips. “(Eyremore) is in a sparsely populated area and there’s a good site to build a dam there.

“The modelling showed excellent results. It would also provide benefit to the Oldman basin because right now when things are tight, the only provincial storage they can really draw on is the Oldman reservoir.”

Balancing the system

Many of the projects suggested by the working group address more than one area of water management.

The Carseland Bow River headworks system offers relatively straightforward solutions to balancing the system. If the province and Bow River Irrigation District fill reservoirs at McGregor, Travers, and Little Bow earlier when flows are higher (or even hold more water over the winter some years), it would provide water security for irrigators and the Siksika Nation irrigation project.

Other potential solutions for balancing the system include increasing the size of the Glenmore Reservoir (for Calgary’s use, not for irrigation); using the Kananaskis reservoirs for drought mitigation (currently being done on a trial basis); and increasing the ability to draw the Ghost Reservoir down rapidly.

The working group also recommended continuing the practice of keeping water levels lower at the Ghost Reservoir until late June in case there’s a large rainfall and quick snowmelt (which caused the 2013 flood).

“The options for balancing the system are obviously good pro­jects,” said Phillips. “They’re easily implemented at a very reasonable cost and in some cases at no cost.”

The group’s report has been submitted, and now it’s in the hands of officials at Alberta Environment and Parks. Improving water management will benefit water users, communities along the river, and the river itself, said Phillips.

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