PROVINCE ADVISES POTENTIAL FLOODING OF LOW-LYING AGRICULTURAL LANDS ALONG THE UPPER ASSINIBOINE RIVER
Manitoba Infrastructure and Transportation advises a flood warning has been issued for Assiniboine River Valley agricultural lands in an area just downstream of the Shellmouth Reservoir, up to the Shellmouth Bridge.
The Hydrologic Forecast Centre of Manitoba Infrastructure and Transportation reports river levels in the low-lying areas immediately downstream of the dam are exceeding flood stage. Further downstream, the river is expected to remain within its banks.
An unstable weather system has brought significant rain in parts of the upper Assiniboine River in Manitoba and Saskatchewan during the last 24 hours. Cumulative rainfall amounts up to 30 millimetres (mm), with localized amounts up to 48 mm have been reported.
Portions of the upper Assiniboine River are already experiencing wet conditions as a result of significant storms which produced double the normal precipitation in the months of April and May. More localized rains with amounts up to 40 mm are expected over the upper Assiniboine River in the next three days. For the lower Assiniboine River, forecasts are calling for up to 20 mm.
Additional rainfall will result in increased reservoir inflows and levels. Manitoba Infrastructure and Transportation is monitoring weather across Saskatchewan and southern Manitoba, and will provide updates as conditions evolve.
River Flow Conditions and Shellmouth Reservoir Operations
Shellmouth Reservoir level is 1,409.1 feet (ft.), a rise of one-third of a foot in the last 24 hours. This level is 0.6 ft. above the spillway elevation. The conduit outflow is 1,430 cubic feet per second (cfs) and spillway outflow is 320 cfs, totalling 1,750 cfs. Localized rainstorms over and around the reservoir have resulted in significant inflow of 4,200 cfs this morning, compared to 2,900 cfs yesterday.
The gate is operated to keep the combined spillway and conduit outflow to around 1,580 cfs. Outflows higher than 1,600 cfs will affect areas immediately downstream of the dam up to the Shellmouth Bridge. The flows of the Assiniboine River at Kamsack and the Shell River at Inglis are 2,610 cfs and 260 cfs respectively. The river is flowing near Miniota at 3,200 cfs and near Brandon at 3,600 cfs.
The operation strategy for the reservoir is continually reviewed with the Shellmouth Reservoir Regulation Liaison Committee, which has representation from municipalities and conservation districts on the reservoir and downstream of the Shellmouth Reservoir. Water level conditions of the dam are provided daily to the committee members.