Portage Diversion
Encyclopedia
The Portage Diversion (49°56′48"N 98°20′06"W) (also known as the Assiniboine River Floodway) is a water control structure on the Assiniboine River
in Portage la Prairie, Manitoba
, Canada
. The project was made as part of a larger attempt to prevent flooding in the Red River Valley
. The Portage Diversion consists of two separate gates which divert some of the flow of water in the Assiniboine River to a 29 km long diversion channel that empties into Lake Manitoba
near Delta Beach. This helps prevent flooding on the Assinboine down river from the diversion, including in Winnipeg
, where the Assiniboine River meets the Red River
.
During flood years such as spring 2011, inlet flows to the Portage Diversion control structure were measured at over 54000 cuft/s. This amount of water would have disastrous effects if left to flood southern Manitoba. During the flood of spring 2011 the Portage Diversion handled roughly half the flow of Niagara Falls.
The Assiniboine River can handle flows up to approx 19000 cuft/s before spilling over its banks. During years when the Assiniboine River Watershed achieves flows greater than 19,000cfs into the Assiniboine River the diversion gates are opened to allow the excess water to spill into lake Manitoba, at the same time the gates that feed the Assiniboine river can be closed to restrict the flow.
The diversion was originally designed to carry a volume of 25000 cuft/s. Under a state of emergency in early May 2011, Manitoba authorities did extensive work by raising the dikes and were preparing to send up to 34000 cuft/s down the diversion channel with bridges downstream being the determining factor in flow rate.http://www.winnipegfreepress.com/breakingnews/breach-best-of-bad-choices-121551129.html,http://news.gov.mb.ca/news/index.html?archive=&item=11454
The diversion was built at a cost of $20.5 million dollars in 1970. The diversion control dam is 35 feet (11 m) high and 1,400 feet (430 m) long and allows 14600 acre.foot storage.
, a freshwater lake, into the slightly saline Lake Manitoba. This has a dramatic effect on Lake Manitoba water quality. In 2009 alone, when the Portage Diversion was open for just 27 days, the Portage Diversion itself contributed 99 percent of the suspended sediments, 60 percent of the nitrogen, and most importantly 93 percent of the phosphorus that flowed into Lake Manitoba that year. The result of the excess nutrients sent into Lake Manitoba is that eutrophication
of the lake occurs. The result of eutrophication is that microorganisms such as cyanobacteria, a nitrogen fixing microbe can utilize the abudent supply of phosphorus to propagate itself. The end result is algal blooms which can result in the release of cyanotoxins in the case of cyanobacteria that are harmful to both humans, animals, and other marine life. The end result of all this leads to the deterioration of water quality, loss of aquatic life, disrutption of the ecosystem, and the real chance that the body of water could become a "dead lake" like Lake Erie
in the 1960s.
The Portage Diversion has also contributed enough water at times to Lake Manitoba to cause the lake to rise significantly. The first major occurrence of this was during the 1976 flood on the Assiniboine River when 1420000 acre.ft of water was diverted to Lake Manitoba, resulting in a 1.22 foot (0.371856 m) direct rise in water levels) The flooding on Lake Manitoba in 2011 has been more severe as a result of the operation of the Portage Diversion. As of June 13, 2011 at least 3000000 acre.ft (2.6 foot (0.79248 m) rise) of water has been directed toward Lake Manitoba rather than Winnipeg and the Red River, this number already being more than double the volume of the 1976 flood. After considering the fact that without the existence of the Portage Diversion, some water would flow into Lake Manitoba near Delta Beach through oxbow lakes and channels which were at one time the original channels of the Assiniboine River when it flowed to Lake Manitoba naturally around 2000 years ago, it is estimated that the Portage Diversion contributed to about 2 foot (0.6096 m) of a rise in water levels on Lake Manitoba, accounting for roughly two-thirds of the rise of the lake since the spring thaw.
Assiniboine River
The Assiniboine River is a river that runs through the prairies of Western Canada in Saskatchewan and Manitoba. It is a tributary of the Red River. The Assiniboine is a typical meandering river with a single main channel embanked within a flat, shallow valley in some places and a steep valley in...
in Portage la Prairie, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The project was made as part of a larger attempt to prevent flooding in the Red River Valley
Red River Valley
The Red River Valley is a region in central North America that is drained by the Red River of the North. It is significant in the geography of North Dakota, Minnesota, and Manitoba for its relatively fertile lands and the population centers of Fargo, Moorhead, Grand Forks, and Winnipeg...
. The Portage Diversion consists of two separate gates which divert some of the flow of water in the Assiniboine River to a 29 km long diversion channel that empties into Lake Manitoba
Lake Manitoba
Lake Manitoba is Canada's thirteenth largest lake and the world's 33rd largest freshwater lake. It is in central North America, in the Canadian province of Manitoba, which is named after the lake...
near Delta Beach. This helps prevent flooding on the Assinboine down river from the diversion, including in Winnipeg
Winnipeg
Winnipeg is the capital and largest city of Manitoba, Canada, and is the primary municipality of the Winnipeg Capital Region, with more than half of Manitoba's population. It is located near the longitudinal centre of North America, at the confluence of the Red and Assiniboine Rivers .The name...
, where the Assiniboine River meets the Red River
Red River of the North
The Red River is a North American river. Originating at the confluence of the Bois de Sioux and Otter Tail rivers in the United States, it flows northward through the Red River Valley and forms the border between the U.S. states of Minnesota and North Dakota before continuing into Manitoba, Canada...
.
During flood years such as spring 2011, inlet flows to the Portage Diversion control structure were measured at over 54000 cuft/s. This amount of water would have disastrous effects if left to flood southern Manitoba. During the flood of spring 2011 the Portage Diversion handled roughly half the flow of Niagara Falls.
The Assiniboine River can handle flows up to approx 19000 cuft/s before spilling over its banks. During years when the Assiniboine River Watershed achieves flows greater than 19,000cfs into the Assiniboine River the diversion gates are opened to allow the excess water to spill into lake Manitoba, at the same time the gates that feed the Assiniboine river can be closed to restrict the flow.
The diversion was originally designed to carry a volume of 25000 cuft/s. Under a state of emergency in early May 2011, Manitoba authorities did extensive work by raising the dikes and were preparing to send up to 34000 cuft/s down the diversion channel with bridges downstream being the determining factor in flow rate.http://www.winnipegfreepress.com/breakingnews/breach-best-of-bad-choices-121551129.html,http://news.gov.mb.ca/news/index.html?archive=&item=11454
The diversion was built at a cost of $20.5 million dollars in 1970. The diversion control dam is 35 feet (11 m) high and 1,400 feet (430 m) long and allows 14600 acre.foot storage.
Effects on Lake Manitoba
When the Portage Diversion is opened, it sends water intended for Lake WinnipegLake Winnipeg
Lake Winnipeg is a large, lake in central North America, in the province of Manitoba, Canada, with its southern tip about north of the city of Winnipeg...
, a freshwater lake, into the slightly saline Lake Manitoba. This has a dramatic effect on Lake Manitoba water quality. In 2009 alone, when the Portage Diversion was open for just 27 days, the Portage Diversion itself contributed 99 percent of the suspended sediments, 60 percent of the nitrogen, and most importantly 93 percent of the phosphorus that flowed into Lake Manitoba that year. The result of the excess nutrients sent into Lake Manitoba is that eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
of the lake occurs. The result of eutrophication is that microorganisms such as cyanobacteria, a nitrogen fixing microbe can utilize the abudent supply of phosphorus to propagate itself. The end result is algal blooms which can result in the release of cyanotoxins in the case of cyanobacteria that are harmful to both humans, animals, and other marine life. The end result of all this leads to the deterioration of water quality, loss of aquatic life, disrutption of the ecosystem, and the real chance that the body of water could become a "dead lake" like Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
in the 1960s.
The Portage Diversion has also contributed enough water at times to Lake Manitoba to cause the lake to rise significantly. The first major occurrence of this was during the 1976 flood on the Assiniboine River when 1420000 acre.ft of water was diverted to Lake Manitoba, resulting in a 1.22 foot (0.371856 m) direct rise in water levels) The flooding on Lake Manitoba in 2011 has been more severe as a result of the operation of the Portage Diversion. As of June 13, 2011 at least 3000000 acre.ft (2.6 foot (0.79248 m) rise) of water has been directed toward Lake Manitoba rather than Winnipeg and the Red River, this number already being more than double the volume of the 1976 flood. After considering the fact that without the existence of the Portage Diversion, some water would flow into Lake Manitoba near Delta Beach through oxbow lakes and channels which were at one time the original channels of the Assiniboine River when it flowed to Lake Manitoba naturally around 2000 years ago, it is estimated that the Portage Diversion contributed to about 2 foot (0.6096 m) of a rise in water levels on Lake Manitoba, accounting for roughly two-thirds of the rise of the lake since the spring thaw.