PRAIRIE FARM REHABILITATION Administration (PFRA), a Canadian federal government agency,
is changing the operation of the Shellmouth dam to store more water.
The operational changes to be carried out over a period of three years are expected to cost US$6.1M. The reservoir, located on the Assiniboine river near the Manitoba-Saskatchewan border, controls the flow of water in the Assiniboine, Portage La Prairie’s main source of drinking water. Among the main goals of the joint federal-provincial proposal is to enhance flood control and provide additional water storage for downstream users including the city and Rural Municipality of Portage la Prairie.
The PFRA, which will oversee the improvement project, is studying the best method to increase water capacity at the 35-year-old dam. Completed in 1969, the Shellmouth dam created a reservoir, known as Lake of the Prairies, with a capacity of 4.8Mm3. The dam is about 21m high and 1270m 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.