Flood control works
Immediately following the 1950 flood on the Red River, the federal government, together with the Province of Manitoba, set up a fact-finding commission to assess the damages and make recommendations. In 1958, the commission recommended the construction of the Red River Floodway, the Assiniboine (Portage) Diversion and the Shellmouth Reservoir.
The Red River Valley flood control works and related infrastructure in Manitoba performed very well in managing the flood of the century.
The floodway, which has been used 18 times since it was opened in 1969, has prevented over $2 billion dollars in damage to the City of Winnipeg alone. Although Winnipeg was spared major devastation during the 1997 flood, some areas south of the Winnipeg and in the U.S. were not. Many farms were flooded, resulting in property damage and interruptions to farm business operations. As well, significant groundwater contamination occurred south of the City of Winnipeg.
Although the Red River surface water quality didn't deteriorate to the extent expected, local impacts to on-farm surface water supplies did persist after the flood waters receded.
About the floodway
The floodway consists of four major components: the inlet structure, the floodway channel, the outlet structure and the east & west dikes.
The inlet structure is located in the Red River channel just a short distance downstream from the floodway inlet. The structure has two submersible gates, each 34.3 m wide, which, under non-flood conditions, remain at the level of the channel bottom. In times of flood, the gates are raised to control the division of flow through the City of Winnipeg and the floodway channel.
This channel provides a partial rerouting of the Red River and has a design capacity of 1,700 cubic metres per second (cms) and an emergency capacity of 2,830 cms. It is 46.7 km long with an average depth of 9.1 m and an average bottom width of 137.2 m.
The outlet structure is a concrete drop structure located just downstream of Lockport. At this location, under design discharge conditions, there is a drop in water surface from the floodway to the Red River of about 4.3 m. The outlet structure is required as an energy dissipater that prevents downstream scour and erosion as the floodway water re-enters the Red River.
Dikes are required to prevent flood water from passing downstream through the City of Winnipeg. On the east side of the Red River, the dike has been incorporated into the construction of the floodway channel. On the west side of the river, the dike extends a distance of about 34 km west from the inlet structure to tie into higher ground.
The Portage Diversion is a 29 km long channel designed to carry flows up to 708 cms from the Assiniboine River into Lake Manitoba. The major elements are the diversion dam in the Assiniboine River, the concrete spillway control structure, the inlet control structure in the diversion, the diversion channel itself, two gradient control structures and an outlet structure.
Shellmouth Dam and Reservoir
The Shellmouth Reservoir is located on the Assiniboine River at the Manitoba/Saskatchewan border. The reservoir's protection extends over the entire reach of the Assiniboine River between the Shellmouth Dam and its influence with the Red River at Winnipeg. Brandon and Portage la Prairie also benefit from flood reduction and low flow augmentation. The reservoir created by the Shellmouth Dam is approximately 56 km long and is capable of storing 863,398 cubic metres of water. The dam is about 21 m high and 1,270 m long with a reinforced concrete horseshoe-shaped conduit used to make reservoir releases. Flood flows in excess of conduit capacity are passed over a concrete chute spillway.
Red River Valley community dikes
After the 1966 flood, negotiations ultimately culminated in the federal government agreeing to share in the cost of permanent diking in the Red River Valley. Permanent diking consisted of both community diking in--Emerson, Letellier, Dominion City, St. Jean Baptiste, Morris, Rosenort, Brunkild and St. Adolphe--and, also protection of farmsteads in the valley by either constructing ring dikes or by raising the foundations of farm buildings.
Following the 1979 flood, the diking systems were upgraded to provide protection to the 100 year flood level.
City of Winnipeg primary diking system
Within the City of Winnipeg, primary dikes were put into place along the Red and Assiniboine Rivers. In some areas, riverbank residents were located in between the primary dikes and the river, and consequently these homes required diking during flood years.
Performance of flood protection works
The Red River Floodway diverted flows around the City of Winnipeg from April 21 to June 3, 1997. The floodway's peak discharge occurred on May 4, 1997 at 1,840 cms. The previous highest peak discharge was 1,127 cms on May 9, 1979.
The Portage Diversion operated from April 14 to May 29, 1997 with a peak discharge recorded on April 20, 1997 at 560 cms.
The Shellmouth Dam and Reservoir reduced the flows along the Assiniboine River by allowing only a peak outflow of 46 cms on May 20 and 21, 1997. The peak inflow to the reservoir was recorded at 283 cms on April 27 and 28, 1997. In the Red River Valley, the eight ring-diked communities became island fortresses at the height of the flood. These communities stayed dry through the flood of the century.
The west dike of the floodway inlet control structure, which prevents flood waters from bypassing the structure and entering the City of Winnipeg, had to be extended and raised to deal with this large flood event. More than 400 pieces of heavy equipment worked 24 hours a day for five days to construct 25 kilometres of new dike. Another 15 kilometres of the existing west dike was reinforced.
Steven D. Topping P. Eng. and John E. Towle P. Eng., Water Resources Branch, Manitoba Natural Resources; Rick M. Lemoine, P. Geol., Environmental Operations Division, Manitoba Environment; Dwight Williamson, Ed Sorba and Sharon Gurney, Water Quality Management Section, Manitoba Environment; and, Dr. Gus Wruck, Livestock Development and Diversification Section, Manitoba AgricultureTable 1: Comparison of major Red River flood flows in the 19th & 20 Centuries
It was how big?
The Red River's major flood history is summarized in the table above.
This spring's flood was the flood of this century. The unregulated discharge--the flow which would occur in the absence of the flood control works on the Red and Assiniboine rivers in Manitoba--estimated on the Red River downstream of the Assiniboine River was 4,586 cubic metres per second (cms) on May 4, 1997.
However, the largest recorded flood occured in 1826 at 6,370 cms.
The Great Flood of 1950 was small in comparison, at only 3,057 cms.