Manitoba Water Stewardship has issued a flood watch for most areas of southern Manitoba. The watch includes the Red River Valley, the southern Interlake and much of the Westman region from Neepawa to Swan River. The watch is for the weekend and early next week and will be updated if conditions change significantly.
A storm system brought 50 to 70 millimetres (two to 2.8 inches) of rain to the La Salle and Seine River watersheds overnight and this morning and some flash flooding has occurred in these watersheds. Many other areas of Manitoba have received 20 to 30 mm (0.8 to 1.2 in.) of rain and an additional 25 to 40 mm (one to 1.6 in.) is expected over much of southern Manitoba tomorrow and Sunday with 50 to 70 mm (two to 2.8 in.) possible over the Red River valley from Emerson to Winnipeg and eastern Manitoba.
The rain is falling on soils already near saturation from heavy rain on the Victoria Day long weekend and a lot of run-off is occurring, which will increase as additional rain falls. This will result in overland flooding with overtopping of ditches and smaller streams and rapid river rises. Most tributaries of the Red, Assiniboine and Souris rivers are expected to remain within their banks. However some over-bank flooding of low-lying areas is possible on these tributaries as well as on streams in eastern Manitoba.
Levels of the Red River are already rising quite rapidly, mainly from heavy rain in the U.S. portion last weekend. The rate of rise will increase due to recent heavy downpours and the additional rain expected will cause the river to rise further. Total additional rises are expected to range from 2.1 to 2.4 metres (seven to eight feet) from Emerson to the floodway inlet and about one m (3 ft.) in the Selkirk area. The river will remain within its banks unless additional heavy rain develops in early June.
The river level in downtown Winnipeg was at 3.4 m (11 ft.) this morning and could crest at about 4.9 m (16 ft.) by June 5 if the additional rain falls as expected. Levels in this range pose the risk of sewer backup in Winnipeg in the event of a heavy downpour. In accordance with the Red River Floodway’s rules of operation, Manitoba Water Stewardship will complete an assessment of whether operation of the floodway is necessary to prevent widespread basement flooding in Winnipeg if the rain this weekend results in a river level forecast above 4.3 m (14 ft.). A decision on whether to operate the Portage Diversion to lower river levels in Winnipeg will also be made in the next few days.
Shellmouth Reservoir outflows have been increased to guard against excessive reservoir levels due to the expected rain. Flooding is not expected along the Assiniboine River.
The latest information on water levels and outlook reports is available at www.gov.mb.ca/waterstewardship.
