Condition Reports

River Conditions and Forecast for Manitoba

April 21, 2008

Weather:

Last weekend’s storm brought up to 35 mm of precipitation to much of Alberta and western Saskatchewan but precipitation in southeastern Saskatchewan and in southern Manitoba was generally less than 5 mm. Significant snow is still falling in northern portions of Saskatchewan and Manitoba (Saskatchewan River and Churchill River watersheds). A band of showers is crossing southeastern Manitoba today but is unlikely to produce more than 5 mm precipitation. Another storm is expected to bring rain to much of southern Manitoba and snow to portions of western Manitoba, mainly, south of a line through Miniota and Arborg on Thursday. Environment Canada weather maps suggest that amounts could be in the 10-20 mm range in southern portions of this region.

Red River:

Levels are declining at all points in Manitoba. The river level in downtown Winnipeg had decline to 7.4 feet this morning, about one foot below the walkway level. The normal summer level of 6.4 feet should be reached later this week unless Thursday’s precipitation will be heavier than presently expected. This will be the last report for the Red River this spring unless adverse weather causes significant river rises.

Assiniboine River:

The Assiniboine River crest is in the Portage la Prairie area. There is still a risk of ice jamming and minor flooding in the Long Plains area southwest of Portage la Prairie during the next few days. Flooding elsewhere on the Assiniboine River is very unlikely this spring despite Thursday’s expected storm. Ice moved out of the portion from Baie St. Paul to Lido Plage on the weekend and as a result levels from the coming flow crest will be lower than this of last week.

The Shellmouth Reservoir water level rose 2.4 feet over the weekend and was at 1399.3 feet this morning. Inflows to the reservoir have been declining since last Friday and should continue to decline unless significant precipitation develops. Updated forecasts based on little additional precipitation and on normal weather conditions indicate that the level will rise to the desired range of 1403-1404 feet before mid May based on the present outflow of 800 cubic feet per second. The outflow was increased to 800 cfs last Friday afternoon. No further increase in outflow may be required unless above average precipitation develops. Outflows may need to be decreased somewhat toward the end of this week if Thursday’s storm produces little precipitation upstream of the reservoir. The updated forecast will be provided to the Regulation Liaison Committee later today to facilitate further decisions on the outflow setting.

The Pas area:

Runoff is underway but crest will be delayed by anticipated very cool weather next week. The Saskatchewan Watershed Authority indicates that peak flows in the headwaters of the Red Deer River and the Carrot River are one-half to two thirds the magnitude of last years crests. Precipitation this past weekend was quite light and will have little effect on flows in these rivers, which are expected to remain within their banks

The effect of the heavy snow of the past few days on the flood potential of the Saskatchewan River is not yet known, but it is unlikely that there will be much change as plains runoff from winter snow was well advanced and cool weather will delay melt of the new snow.

Hydrologic Forecast Centre
Regulatory and Operational Services,
Manitoba Water Stewardship