Manitoba flood warning update

FLOOD WARNING FOR WESTERN MANITOBA ENDED EXCEPT FOR ASSINIBOINE RIVER

 

Flood Warning/Weather

 

·         Manitoba Water Stewardship advises the flood warning ended for most areas of western Manitoba yesterday.  Overland flooding continues to subside and most streams have crested.

 

·         However, the flood warning continues for the Assiniboine River Valley from Shellmouth to Brandon.  Water levels in most areas of southern Manitoba will remain well above average and some overland flooding of low-lying areas will continue for several weeks, even with favourable weather.

 

·         The weather forecast calls for some showers today and tomorrow with 10 to 15 millimetres (0.4 to 0.6 inches) likely in most areas of Manitoba and eastern Saskatchewan, mainly in areas south of the Trans-Canada Highway, with lesser amounts north of the highway.

 

Duck Mountain and Eastern Riding Mountain Area 

 

·         All streams in the area have crested and are subsiding.

 

·         Overland flooding is decreasing, but low areas will continue to have standing water for one to two weeks, even with favourable weather.

 

·         Any additional rain during the next 10 days or so will sustain overland flooding in low-lying areas.  However, rivers are unlikely to rise significantly unless rainfall exceeds 20 mm (0.8 in.) per day.

 

Assiniboine River

 

Shellmouth Reservoir Operation

 

·         The Shellmouth Reservoir water level rose 0.15 metres (0.5 feet) since yesterday morning and was 429.76 m (1,410.0 ft.) this morning with 1,070 cubic feet per second flowing over the spillway.  The inflow crested Saturday at about 8,000 cfs and had declined to 7,100 cfs by this morning.  The controlled conduit outflow remains at 2,200 cfs and the total outflow this morning was 3,270 cfs.  An updated inflow forecast suggests that volume inflows will be somewhat less than recently anticipated.  The reservoir is now expected to crest at 430.1 m (1,411.1 ft.) on June 28.  The spillway elevation is 429.3 m (1,408.5 ft.) 

 

·         With the reduced inflow it now appears possible to keep the peak outflow from exceeding 3,500 cfs.  However, this will require peak shaving, which is a process where controlled conduit releases are gradually reduced to counter rising spillway flows and maintain a steady total outflow which will be 3,500 cfs in this case.  This forecast and operating plan is based on less than 10 mm (0.4 in.) additional precipitation during the next 10 days.  

 

·         Tributaries of the Assiniboine River from Shellmouth to Brandon have crested except for Birdtail Creek.  An updated flood routing based on the reservoir operating plan and updated tributary forecasts suggests that crests from Shellmouth to Portage la Prairie will be 0.15 to 0.3 m (0.5 to one ft.) lower than expected yesterday.

 

·         Flooding of valley lands from Shellmouth to Millwood is already occurring and will increase. However it now appears possible, with favourable weather for the next 10 days or so, that flooding in the portion from St. Lazare to Brandon will be limited to the lower-lying areas only.

 

·         Crests are expected at Shellmouth June 22 to 29, Millwood on June 26 to 27, at St. Lazare on June 27, Virden on June 28 to 29 and Brandon on July 2.  The Portage Diversion will be operated to prevent flooding downstream to Headingley and to prevent levels in Winnipeg from rising above 3.2 m (10.5 ft.).

 

Red River

 

·         The floodway control structure continues to be operated to reduce levels at the floodway inlet by no more than 0.3 m (one ft.) per day.  The flow at the floodway inlet this morning was 18,800 cfs.  Red River levels from Ste. Agathe to the floodway inlet will continue to decline due to operation of the control structure.  Levels from Emerson to Morris will change little over the next five to seven days as a small crest from recent rains approaches from the United States.

 

·         The river level in downtown Winnipeg changed little since yesterday and stood at 3.16 m (10.38 ft.) this morning.  The level is expected to be in the range between 2.7 m and 3.2 m (nine and 10.5 ft.) for the next 10 days.  The natural level without operation of major flood control works would have been 3.34 m (10.95 ft.) this morning.

 

Other Areas

 

·         Very wet conditions continue in a large portion of southern Manitoba from Swan River to Gypsumville south to the United States boundary, with overland flooding in low-lying areas.

 

·         The flooding is gradually receding in most areas, but additional rain will extend the flooding and could cause it to worsen.  Based on present rainfall forecasts, however, only minor rises in river levels would occur.