Red River Floodway

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Control gates at the inlet to the Floodway

Bridge over the control gates

The Red River Floodway is an artificial flood control waterway in Canada, first used in 1969. It is a 47 km (29 mile) long channel which, during flood periods, diverts part of the Red River's flow around the city of Winnipeg, Manitoba to the east and discharges it back into the Red River below the dam at Lockport. It can carry floodwater at a rate of up to 2,550 cubic metres (91,700 cubic feet) per second. It was built partly in response to the disastrous Red River flood, 1950.

The Floodway was pejoratively nicknamed "Duff's Ditch" by opponents of its construction, after Premier Duff Roblin, whose Progressive Conservative government initiated the project. It was completed in time and under budget. Subsequent events have vindicated the plan. Used over 20 times in the 37 years from its completion to 2006, the Floodway has saved an estimated $10 billion (CAD) in flood damages. The "Duff's Ditch" term is still used affectionately.

Construction of the Floodway started on October 6, 1962 and finished in March 1968, was a major undertaking with 76.5 million cubic metres (2.75 billion cubic feet) of earth excavated—more than what was moved for the Suez Canal.^{[citation needed]} At the time, this was the largest land moving project in the world.

The Floodway protection system includes more than just the channel to the east of the city, but also the dikes along the river through Winnipeg and the "Brunkild Z-dike" extending to the west from the south of the city. The Brunkild Dike was built in 1997 during the "Flood of the Century" when the volume of water exceeded the safe capacity of the Floodway and water lapped within inches of the city's dikes. Primarily as a result of the Floodway, the city suffered little flood damage.

The Brunkild dike is the limiting factor on the volume of water that can be diverted around the city, as a result of the extremely low grades in the area. In 2003, the province announced plans to expand the Floodway, increasing its flow capacity from 2,550 m³/s to 4,000 m³/s. It was decided to widen the Floodway as opposed to deepening it because of the soil and ground conditions in the area. There are many underground aquifers in the area that are used for drinking water for rural residents which could potentially be contaminated if the floodway were any deeper. There is also potential for pressures to increase in the aquifers, causing a "blowout" to occur, where water would flow from the aquifers in the ground to the surface and reduce the capacity of the Floodway. Thus, it was decided widening the floodway would be the best option despite the lower hydraulic capacity it would cause.

Since the 1997 Red River Flood resulted in water levels that took the existing floodway to the limits of its design. Various levels of government commissioned engineering studies for a major increase in flood protection for the City of Winnipeg. Work began in late 2005 under a provincial collective bargaining agreement and is slated to include modifications to rail and road crossings as well as transmission line spans, upgrades to inlet control structures and fire protection, increased elevation of existing dikes (include the Brunkild dike), and the widening of the entire floodway channel itself. Completion of the Red River Floodway Expansion is slated for late 2010 at a final cost of more then $665,000,000 CAD.