Province of Manitoba – The Hydrologic Forecast Centre of Manitoba Infrastructure and Transportation advises that outflows from the Shellmouth Reservoir will be increased today by an additional 500 cubic feet per second (cfs) down the Assiniboine River to better manage reservoir water levels.
Outflow from the dam was increased last week from approximately 1,900 cfs in two stages up to 3,000 cfs. An additional increase in discharge will result in a 3,500 cfs flow.
Water level increases as a result of these two flow increases will be between two to three feet from the Shellmouth Dam to St. Lazare. This may be affected by other streams that flow into the Assiniboine River downstream of the dam. The higher outflows will result in some overbank flooding along the upper Assiniboine River and will result in some flooding of low-lying agricultural land between the reservoir and St. Lazare.
Based on current forecasted weather conditions, the highest water level between the dam and Brandon is expected in the first week of May.
Without the dam, flows on the Assiniboine River in the vicinity of the dam would be significantly higher at approximately 10,600 cfs.
The operating guidelines for Shellmouth Dam and Reservoir call for outflows to be increased to keep water levels from exceeding the top of the reservoir spillway. Higher outflows now will slow the rate at which the reservoir water level is rising and preserve storage space on the reservoir for the growing season. The additional space also allows the dam and reservoir to be used to capture run-off from summer storms and to prevent potential flooding later in the year during the growing season.
The Shellmouth Dam and Reservoir are operated in consultation with the Shellmouth Reservoir Regulation Liaison Committee. The committee has been meeting on a regular basis to discuss and advise on operations.