Manitoba Water Stewardship is issuing a flood warning for areas of western Manitoba including the Assiniboine River watershed from Shellmouth to Brandon, the area from Dauphin to Swan River and portions of the Souris and Pembina river watersheds. The warning also includes some portions of the Interlake.
. Western Manitoba and adjacent areas of Saskatchewan were drenched by 30 to 50 millimetres (1.2 to two inches) of rain from yesterday afternoon to this morning. The heavy rain fell in the area from Swan River southward into North Dakota. Some areas east of Estevan, Sask., received at least 100 mm (3.9 in.) of rain. A portion of the Pembina River watershed near Pelican Lake received at least 75 mm (three in.) and some areas of the Interlake received 35 mm (1.4 in.). The Red River Valley received much less rain with five to 15 mm (0.2-0.6 in.) in most areas.
. Run-off from the additional rain is heavy due to previously saturated soil conditions. Extensive overland flooding is underway in the flood-warning area and streams are rising rapidly. Some streams will overflow their banks and road washouts have occurred in some areas.
. The area east and just north of the Duck Mountains is experiencing the worst summer flooding in memory with many streams overflowing.
Duck Mountain Area
. The area from Dauphin to Swan River is experiencing extensive flooding. Areas just east and north of the Duck Mountains have the worst flooding with streams overtopping their banks and washing out roads and some bridges. The North Duck River is one of hardest hit.
. Larger streams will rise further, while smaller streams will crest today. It is possible that some homes will be flooded.
. Some areas near Riding Mountain and west of Lake Manitoba are also experiencing some flooding due to heavy downpours.
Shellmouth Reservoir Operation:
. The Shellmouth Reservoir water level has risen 0.26 m (0.85 ft.) since yesterday morning and stood at 429.3 m (1,408.4 ft.) this morning. Part of this rise was due to wind. The computed inflow has risen to 8,000 cfs and the outflow remains at 2,200 cfs. The spillway will be overtopped later today and the reservoir level is expected to rise to 430.2 m (1,411.5 ft.) by June 26 to 27 even without additional rain. The spillway elevation is 429.3 m (1,408.5 ft.). Calculations show that the minimum total reservoir outflow is 4,000 cfs based on surcharging of the reservoir (reducing controlled conduit flows to minimize total outflows). However such an operation is not planned since it would require an immediate increase in outflow which would aggravate flooding in areas from St. Lazare to Brandon. The present outflow of 2,200 cfs will therefore be maintained. A maximum spillway flow of 3,550 cubic feet per second is expected June 26 to 27.
. All tributaries of the Assiniboine River will rise significantly due to the rain, resulting in over-bank conditions and flooding of valley lands from Shellmouth to Brandon over the next few weeks. Without further rain, the crest is expected at Millwood on June 28, St. Lazare on June 29, Virden on July 2 and Brandon on July 5.
. Minor flooding could develop in low-lying areas of the city of Brandon and from Brandon to Portage la Prairie. The Portage Diversion will be used if necessary to prevent flooding downstream to Headingley.
. The floodway control structure will continue to be operated to reduce levels at the floodway inlet by about 0.3 m (one ft.) per day. The flow at the floodway inlet this morning was 17,350 cfs. Only minimal rises are expected on the Red River since precipitation was of a scattered nature.
. The river level in downtown Winnipeg changed little and stood at 2.78 m (9.15 ft.) this morning. The natural level without operation of major flood control works was three m (9.95 ft.) this morning.
. The level of Red Deer Lake remains near 263.37 m (864 ft.). The record crest in 2006 was 264.56 m (868 ft.). The Red Deer River watershed received relatively little precipitation from this storm and as a result little further rise in the lake is expected.
. Some portions of the Interlake and areas west of Lake Manitoba to the escarpment will experience overland flooding due to heavy downpours.
. Some flooding is underway in the portions of the Souris River watershed. The Souris River will rise up to 1.2 m (4 ft.) by the middle of next week but will remain within its banks.
. Flooding is underway in the Pelican Lake area due to 75 mm (three in.) of rain. The Pelican Lake outlet control works have been activated to reduce rises of the lake. The Pembina River from Rock Lake to Windygates is expected to remain well below flood stage.
. Manitoba’s Emergency Measures Organization is in contact with affected municipalities to ensure they have the tools and resources needed to respond to the immediate affects of the flooding.
. Provincial staff will be working through the weekend to remove culvert blockages to reduce overland flooding from the provincial drainage system.