The LWCB held a public webinar on May 10 to review the high flow conditions across the Winnipeg River drainage basin. A recording of the presentation will be posted for limited period on YouTube.
Key points from the Webinar are as follows:
1. A moderately high snowpack by end March in the Rainy-Namakan sub-basin and most of the Lake of the Woods sub-basin, with higher amounts near Kenora. Snowpack for this region was similar to 2019, and much less than 2014, the last year with high water in spring.
2. Precipitation in April set new records for all regions of the Winnipeg River basin except Lac La Croix (3rd highest) and Rainy-Namakan (tied with 2001 for record). April 1-May 9 precipitation was near double the total precipitation from December 1-March 31 for Lac Seul, Rainy-Namakan and Lake of the Woods sub-basins, and 300-500% of normal for April, with the highest amounts to the northwest.
3. Much of the precipitation in early April added to the water in the snowpack and temperatures mid-month fell well below normal. The spring melt was delayed, as three consecutive weeks saw large Colorado Lows pass through. As temperatures warmed at the end of the month, rain on snow caused a rapid rise in flows in the Lake of the Woods-Rainy River basin. This rise started in early May in the English River basin.
4. The rain-on-snow occurred while the ground was still frozen, resulting in rapid runoff to tributaries and eventually to the major rivers and lakes. Record flows for early May developed in all regions, with some rivers seeing all-time records broken (e.g. Wabigoon River, Vermilion River). Record inflows for this time of year are occurring in each of the major lakes (Lac Seul, Namakan Lake, Rainy Lake and Lake of the Woods). In many areas the major tributaries continue to rise, exceptions being the Big Fork and Little Fork Rivers that feed into Rainy River, and Vermilion River that flows to Namakan Lake. Dams at Namakan Lake and Rainy Lake have been fully opened and will not be closed until these lakes return to the regulated level ranges set by the International Joint Commission, which will likely take weeks. Outflow from Rainy Lake will, therefore, provide high flow input to the Rainy River and Lake of the Woods for weeks.
5. Compared to spring high water events in recent memory (2001, 2002, 2014) which peaked in June or July, this event is occurring earlier. This is cause for concern because May and June are typically the wettest months of the year, and there is little removal of water through evaporation or plant take-up compared with June or July.
6. The LWCB expects that weeks of high water will be ahead for all regions of the Winnipeg River watershed. How long this lasts depends on how much rain falls in the coming weeks. There are no additional actions that can be taken at dams to limit water level rise in the Lake of the Woods-Winnipeg River system now that the dams in Kenora are fully opened. Along the Winnipeg River in Ontario, Whitedog Generating Station operations are not able lower the level of the river due to hydraulic constrictions below Roughrock Lake. Whitedog is passing the water that is received and is not backing up the river.
Because rainfall cannot be accurately forecast beyond 5-7 days, it is not possible for the LWCB to provide an estimate as to when any region of the basin will see water levels stop rising or return to normal. Both Lake of the Woods and the Winnipeg River will continue to rise as long as the flow into Lake of the Woods is greater than the flow going out of the fully opened dams in Kenora. The Winnipeg River in Manitoba is likely to reach extremely high levels with high flows from both the English River and Winnipeg River in Ontario flowing into the Whiteshell.
7. Water levels across the region could reach 2014 peaks or higher. There is no upper limit for flows, which are entirely dependent on rainfall across the basin in the coming weeks. Residents and communities in areas that experienced high water impacts in 2014 should make preparations accordingly.
The LWCB will post 7-day lake level forecasts for Lake of the Woods and Lac Seul on Mondays, Wednesdays and Fridays through the high water period. Forecasts will be posted on this Notice Board.