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Press Release from Intermountain Conservation District

Posted: July 12, 2019

Press Release from Intermountain Conservation District
Mitchell Flood Control Dam Grand Opening
 
The Mitchell Dam is the third flood control dam built by Intermountain Conservation District (IMCD). It was constructed in the fall of 2018 with the co-operation of landowner Merv Mitchell, as part of IMCD's long-term strategy to reduce flooding, erosion and infrastructure damages in the district. 
 
The dam is located on the Harper Creek south of Grandview, just 3 miles north of Riding Mountain National Park. From the Park Line to Hwy #366, the elevation drop is almost 100ft per mile. The Harper Creek is within the Wilson River, and the larger Dauphin Lake watershed. This steeply sloping watershed has undergone landscape changes that have caused water to flow rapidly and much quicker now than in previous generations.
 
The Mitchell Dam is designed as dry dam, so as to not hold water permanently. Rather, it has an undersized culvert pipe installed through it so it restricts water flow during spring runoff and large storms. It hold water back for a few days instead of a few hours, reducing the energy of the water and decreasing downstream flood damages. Then the dam reservoir will empty itself, ready and waiting for the next storm event. 
 
The Dauphin Lake watershed is a maze of creeks and streams that flow swiftly from the Riding and Duck Mountains towards Dauphin Lake. These natural waterways can be both a blessing and a curse....while beautiful most of the year, they possess tremendous power and potential to overrun their banks and erode and flood....previously there were more natural wetlands, more tree lined waterways, and more wooded lands and pasture, to help slow the water as it moved down the landscape. But under current land use, residents and municipalities face significant flood and erosion mitigation costs due to excess flows. Washed out roads and culverts every spring has become the norm.
 
Flood control dams such as Mitchell Dam help mitigate the tree removal and drainage that has taken place to accommodate modern farming practices. IMCD believes a network of flood control dams will provide a cumulative benefit to the watershed, and save the area money in the long-term. IMCD is reallocating funding from fixed erosion damages to proactively spending on this type of project.
 
We know land use has changed over the years, and water is moving down the watershed faster than ever before. And we know that market forces dictate that land use will continue to change, and that the water will come faster still. What can IMCD do to help mitigate this, even with a limited budget? The three IMCD flood control dams currently is use (at Merv Mitchell's, and two at Boris Michaleski's/Gilbert Plains Municipality) are in key headwaters of their watersheds, prevent erosion and flooding, be great demonstration projects, and hopefully will act as a springboard for many other flood control dams to be built in the district. 

Dam Construction Details:
 Height of dam: 2.5m (8ft)
Retention Capacity: 15ac/ft
Drainage area: 7800 ac (12.2sq.mi)
Culvert diameter: 900mm(3ft)
Culvert length: 36.5m (120ft)
Earth used in dam: 3500 cu.m.
Rock in spillway: 175cu.m.
Cost: $50,000
 
Financial Partners:
Merv Mitchell (land, donation of clay and rock for dam)
Intermountain Conservation District
Grandview Municipality
Lake Winnipeg Basin Program, Environment and Climate Change Canada
Ecological Goods & Services Program, Growing Forward 2