The risk of flooding this spring is low in most areas of the province as run-off from melting snow has ended or is low, but a major rain or snowstorm could still produce late spring or early summer localized flooding according to the Hydrologic Forecast Centre of Manitoba Infrastructure and Transportation’s second 2015 flood outlook.
The spring snowmelt is over in most of the southern, southwest and Interlake regions of Manitoba, peak flows have already passed and rivers have generally remained within banks.
Above-freezing temperatures and a gradual rise in temperatures in early March across southern and central Manitoba resulted in a slow, early spring melt.
Peak spring run-off has already passed for the Red River and its tributaries, the Souris River and its tributaries, the Qu’Appelle River and Manitoba portions of the Assiniboine River and its tributaries.
The run-off phase also passed for the Pembina River and tributaries, the Fisher, Icelandic, Roseau and Whitemouth rivers. All rivers and creeks in the western part of the province, including the Duck Mountain and Riding Mountain areas, have also peaked.
Most lakes are expected to be below the flood stage after the spring run-off.
The risk of ice jam-related flooding is mostly low, with the exception of the Saskatchewan River at The Pas and Carrot River as the spring melt is just underway.
If the current conditions continue, the risk of major ice jams will remain low. However, the possibility of ice jams cannot be ruled out until all ice has melted or moved.
The Fairford River control structure has run at full or near full capacity for most of the year drawing down Lake Manitoba. Flows were recently reduced to help reduce threat of ice jam flooding downstream on the Dauphin River. It will return to full capacity once the threat of ice jams has passed.
The Shellmouth Dam release has been reduced to 50 cubic feet per second into the upper Assiniboine River. The outflow on the Shellmouth Dam was reduced to help maintain summer target levels on Lake of the Prairies.
The Portage Diversion will continue to draw down the Assiniboine River to reduce the risk of
ice jam flooding around communities downstream from Portage la Prairie. It is anticipated to be a short duration operation and will have negligible impact on lake levels.
Red River basin flows through North Dakota are low enough that at this time it is unlikely the Red River Floodway gates will be activated this spring.
Northern Areas
Spring run-off has not yet started in the northern and northwest regions as temperatures continue below freezing. The outlook suggests the risk of flooding will be minor to moderate.
The Saskatchewan and Carrot rivers and the Saskatchewan portion of the Assiniboine River watersheds have substantial snow on the ground that has not melted.
However, winter precipitation records and soil moisture before freeze-up were near normal and the run-off potential is near normal.
The flood risk is minor to moderate.
Lakes
Most of the major lakes including Lakes Manitoba, Winnipegosis and St. Martin have not started to see the effect of the spring run-off.
Most of the lakes are expected to be below the flood stage after the spring run-off except Whitewater Lake which is already well above the long-term normal level.
Lake Manitoba is expected to peak between 813.08 to 813.18 feet. This is below the flood stage of 814 ft. but above its upper operating range of 812.5 ft.
Lake Winnipegosis is expected to peak between 833.01 to 833.40 ft.
Lake St. Martin is currently at 801.6 ft. The flood stage is 801 ft. Vulnerable communities are adequately protected at this level. However, there could be flooding of low-lying agricultural lands between now and mid-July. By the end of the spring run-off, the lake is expected to peak between 801.29 to 801.44 ft.
Dauphin Lake is expected to peak between 855.6 to 856.3 ft, which is below the flood stage of 858 ft.
Whitewater Lake is near peak level of 1,633 ft., which is five ft. above the long-term average level.
Whiteshell lakes are expected to see minimal rise due to the spring run-off as the potential was normal to below normal.
Most of the lakes are still frozen and the effect of wind and ice pileup is currently very low. This could change once lake ice reduces by 30 per cent and high winds develop.
Recent Snow and Rain
The March 23 and 24 snow and rain will have almost no impact.
A major snow storm in southern Manitoba and southeast Saskatchewan between March 23 and 24 resulted in about four to six inches of snow or 10 to 15 mm of water.
This will not have a major impact on flows and levels as almost all rivers and creeks in this region will have adequate capacity to handle the run-off.
Ice Jam-related Flooding
Thick ice remains on most rivers and lakes. Ice jams on the north Red River similar to 2009 are unlikely due to the ice jam mitigation program and the low spring peak flow.
Heavy ice is still present on the lower Assiniboine River. The Portage Diversion has been activated to reduce the effect of ice jam on communities downstream of Portage la Prairie.
Ice along the Icelandic River remains in place but is deteriorating. The Amphibex completed icebreaking at Riverton by March 20. Conditions are the same on the Fisher River where the winter snow mostly melted but left the ice in place.
The icebreaking work that has been done by the North Red Community Water Maintenance Corporation on the north Red River and the Icelandic and Brokenhead rivers has greatly reduced the potential of ice jams.
There is still a chance of localized ice-jam flooding on the Saskatchewan River at The Pas and Carrot River when melting starts. Major ice jams are difficult to predict as to location and magnitude. The possibility of ice jams on these areas cannot be ruled out.
Weather
At this time, there are no major storms predicted with temperatures normal to below normal.
The short-term forecast calls for a small amount of precipitation over the next seven to 10 days in most areas across the province.
Mean daily temperatures are predicted to be above 0 C starting March 28 for most of central and southern Manitoba.
Long-term weather forecasts are of minimal use in flood forecasting.
