Another diversion option should be considered

Hey there, time traveller!
This article was published 06/01/2022 (1550 days ago), so information in it may no longer be current.

THE government of Manitoba is proceeding with measures to address major flooding in Lake Manitoba and Lake St. Martin. Flooding issues came to the forefront in 2011 and 2014, when the drastically swollen Assiniboine River necessitated much beyond maximum-design usage of the Portage Diversion.

This valuable public-works infrastructure diverts excess water from the Assiniboine River, during emergencies, northward into Lake Manitoba, avoiding costly flood damage in the Red River Valley.

The current proposal involves digging two significant outlet channels, the first from Lake Manitoba to Lake St. Martin, and the second, larger channel, on to Lake Winnipeg. Yet the proposal is complex and expensive: at least 46 kilometres of constructed channels; two bridge and control structures; three roadway bridges; multiple dropping structures to accommodate elevation decline into Lake Winnipeg; additional roadways; construction camps; quarries; and a new transmission line to power one control structure.

A capital cost of roughly $540 million has been noted in media. Indigenous groups have also raised important concerns.

Could there be a better way? Reviews so far did consider options, but only land use, other types of channels and control structures (i.e. ditching). The problems for Lake Manitoba and Lake St. Martin arise from overwhelming volumes of water, in particular from the Portage Diversion. This raises the possibility of other ways to deal with excess water.

The Portage Diversion is not the sole, or original, inlet into Lake Manitoba. The natural inflow comes south from Lake Winnipegosis, via the Waterhen River. Rather than trying to address the Portage Diversion directly, it could be possible to reduce inflow from the Waterhen River to achieve the same net result of reduced water volumes. This is an interesting and, perhaps, vital option that appears not to have been considered.

Reducing corresponding flows from Lake Winnipegosis relates to a novel twist on a renewable energy technology seeing increased significance across North America, namely pumped hydroelectric water storage. This option also brings skills and resources of Manitoba Hydro into play.

Lake Winnipegosis is only separated from Cedar Lake by a narrow isthmus, and Cedar Lake happens to be the inlet supply for the Grand Rapids generating station.

Just as in the case of the diversion channels, peak flow from the Portage Diversion need not be matched exactly, especially if well-planned water removals start in advance. A project to pump water across from Lake Winnipegosis to Cedar Lake at a nominal rate of 3,500 to 5,000 cubic feet per second would require pumping energy in the range of 10 to 20 megawatts (MW). Once into Cedar Lake, however, given flow rate and rough head of 120 feet at the Grand Rapids generating station, this could produce as much as 46 MW of output power.

This could be readily accommodated given the Grand Rapids station is running at less than 60 per cent capacity, due to chronic flow decline of the Saskatchewan River these past 50 years.

Next door in Ontario, TC Energy is seriously pursuing a massive pumped-storage proposal. Using its project for rough guidance, capital costs here could range from $150 million to $300 million. Although still a rough estimate, this is lower than for diversion channels from Lake Manitoba, and Manitoba Hydro also ends up earning revenue when the system is active.

Lower costs for pumped storage make sense, too. The head difference between Lake Winnipegosis and Cedar Lake is relatively small at 10 feet, and the distance involved is much shorter than the proposed channels (five kilometres versus 50 kilometres). There also already happens to be a major interregional transmission line (230 kV) through the isthmus, making it simple and cost effective to supply electricity for the water pumps.

As a starting point, this option looks promising, although it comes relatively late in the overall process. There are uncertainties, notably clarifying the dynamic behaviour of hydraulic equilibrium in Lake Winnipegosis, and the resulting extent of water removal needed to ensure flows are sufficiently reduced from the Waterhen River. On the other hand, there are more than 50 years of hydrographic data available.

Environmental review obviously is needed, but should note: the lakes are in immediate proximity, part of the same watershed; only limited water transfer is required; and Cedar Lake is already subjected to profound changes in quantity and quality, owing to upstream irrigation and industrial activities in Alberta and Saskatchewan.

Concerted consultation with Indigenous groups would be helpful and important for any new option. In this case, there is potential for revenue sharing, helping to address problematic concerns at the level of the five to six communities in proximity.

The idea is worth considering. And more importantly, this exercise shows that we should never give up considering new alternatives, nor cease using our ingenuity to think outside of the box to come up with innovative and multi-benefit solutions.

Edward Schreyer served as Manitoba’s 16th premier, from 1969 through 1977, and Canada’s 22nd Governor General, from 1979 through 1984. Robert Parsons teaches sustainability economics and basic quantitative methods at the I.H. Asper School of Business, University of Manitoba, and helped clarify the economics.