The Government of Manitoba immediately assessed the need to protect Grande Pointe from similar floods in the future. Acres was awarded the contract to provide design and construction administration services for the community’s flood protection infrastructure.
The Design
Since Grande Pointe was vulnerable to flooding from both the Seine and Red rivers, any flood protection system clearly required a design to protect the community from both.
Observations made in 1997 indicated that the two floods could be physically separated by extending the dyke far enough south to higher ground. As a result, it was determined that the crest elevation of the Seine River’s protection dyke could be lowered, realizing significant construction cost savings.
Therefore, the design involved dykes to the east (at a lower elevation for the Seine River), south and west.
A north dyke was not required, since the existing Floodway’s south embankment formed the northern protection.
Early in the Acres design process, the Manitoba Department of Transportation decided to twin PTH 59 (which runs north-south along the town’s eastern boundary) from the Red River Floodway bridge to just south of Grande Pointe. This coincidence provided a unique opportunity to merge the flood protection project with the PTH 59 twinning and significantly reduce the total combined cost.
 Bridge and diversion channel |
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Protection from the Seine (east dyke) The innovative solution involved a self-regulating gated culvert control at the northbound lane of PTH 59. It could be left open for small flood events, then partially or completely closed for larger flood |
events. Flood waters would then flow through a diversion channel ("mini-floodway") to a drop structure at the Red River Floodway.
A drop structure is required in order to pass water from the diversion channel into the Floodway. While most of the Floodway’s existing drop structures are culvert based, Acres proposed an innovative baffled apron design for the new one. This design will provide increased energy dissipation and will operate with equal efficiency whether the Floodway is in operation (high tailwater level) or dry (no tailwater). The new drop structure, which also reduces construction and maintenance costs, is the only large baffled apron drop structure in Manitoba and one of the largest in Canada. |
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 Baffled apron drop structure in operation, spring 2004 |
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Protection from the Red River
Grande Pointe is protected from Red River overland flow by a 15-km earthen dyke that runs from the Floodway embankment south to Mondor Road, then east along Mondor Road to PTH 59.
Acres performed an analysis to determine an acceptable freeboard allowance for the dyke. The result is a
3-foot freeboard allowance from the Floodway embankment to the CP Rail tracks and a 2-foot allowance for the remaining dyke. The clay fill that was used to construct the dyke was obtained from three sources: a ditch adjacent to the dyke, a drainage swale, and the Floodway embankment as part of the Floodway Embankment Removal project. Constructing a drainage swale from the dyke to the Seine River eliminated the need for a pumping station, which offered a significant capital and maintenance cost advantage. All internal drainage within the dyke area flows into the Seine River. The additional drainage ditches provide an added benefit for farmers, allowing them to improve drainage of their fields.
Management Challenges
Significant cost savings were achieved by combining the Grande Pointe flood protection system with the PTH 59 twinning and the Floodway Embankment Removal project. However, the overlap complicated the scheduling of various construction activities due to the interdependence of the various tasks – including a requirement for 10 separate construction tenders.
Strict project management procedures were implemented, and frequent meetings were held to ensure timely completion of designs, tender documents and construction activities. Critical path tasks were identified early in the design stage and measures implemented to avoid potential scheduling conflicts which would have had significant implications, particularly during some of the more seasonal construction activities.
The cooperation and information sharing between Manitoba Water Stewardship, Manitoba Transportation and Government Services and Acres was paramount in the successful completion of this project – on budget and on schedule.
For further information, please contact:
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Warren Gendzelevich Acres Manitoba, Winnipeg, MB 204-786-8751 wgendzelevich@acres.com
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