Manitoba Water Stewardship advises recent heavy rains have caused sudden rises in river levels in southern Manitoba and are expected to affect levels of some lakes. The rain, while beneficial in most respects, has caused rising water levels in some areas.
The weather systems since April 28 in southern Manitoba produced more rain in one week than normally falls in April and May combined. The heavy rains followed an unusually dry period from mid-February to late April, when very little precipitation was recorded.
Most areas of southern Manitoba received between 25 and 40 millimetres (one to 1.6 inches) of rain, however, the area from Ethelbert to Mafeking in western Manitoba received 50 to 75 mm (two to three inches) from the first storm, with 100 to 135 mm (four to 5.3 in.) in the higher grounds of the Duck and Porcupine mountain areas. This rainfall was excessive and resulted in high river levels and overland flooding. The flooding has gradually subsided in recent days as river levels have begun to decline.
The most recent storm produced 25 to 40 mm (one to 1.6 in.) of rain over the western tributaries of the Red River from Emerson to Ste. Agathe. This caused overnight rises of up to one metre (3.3 feet) on many streams in the area with additional rises of between 0.5 and one metre (1.6 to 3.3 ft.) possible by today. Localized overland flooding due to excessive rain is underway in this region. Rainfall was only five to 15 mm (0.2 to 0.6 in.) east of the Red River, which mostly soaked into the ground. The Assiniboine, Whitemud and Dauphin Lake watersheds received 15 to 20 mm (0.6 to 0.8 in.) of rain from this second storm, causing rises on smaller streams with additional rises expected for the next few days.
Levels of the Red River have begun to rise slowly. Rises in the Manitoba portion will be generally less than one m. It is unlikely the river’s crest will exceed three m (10 ft.) unless significant, additional rain develops by next week. The level at James Avenue in downtown Winnipeg at noon yesterday was 2.4 m (eight ft.).
Levels of the Assiniboine River are rising gradually with minor crests expected at Brandon and Portage la Prairie late next week. However, no problems are expected.
Lakes have not yet been affected significantly as it takes time for most of the run-off to enter lakes. The rain will significantly raise the level of Dauphin Lake, where the outflow will be increased to the maximum possible to prevent excessive rises.
