Record flow conditions are occurring across many areas of the Winnipeg River drainage basin in Ontario, Manitoba and Minnesota following record high precipitation since the start of April. Forecasts indicate that all areas will continue to see exceptionally high flows for the 7-day forecast period. A return to normal flows is unlikely in the coming weeks.
The current level of Lake of the Woods is 323.60 m (1061.7 ft), over 95th percentile level for this time of year. The average lake level rose by 30 cm (12 in) over past week. The lake has risen above the top of the Legislated Operating Range, 323.47 m (1061.25 ft). The International Lake of the Woods Control Board has been activated and will work with the Canadian Lake of the Woods Control Board to approve any actions taken with respect to Lake of the Woods. The dams in Kenora remain fully opened with no changes scheduled.
Inflow to Lake of the Woods remains more than double the maximum outflow that is being released through the fully opened dams in Kenora. Upstream, the dams at Namakan Lake and Rainy Lake continue to be fully opened, with gradually rising outflow. The level at Namakan Lake is higher than the 2014 peak and may exceed all-time records depending on precipitation this month. Rainy Lake is nearing the 2014 peak and continued rise is expected. Outflow reductions from these lakes, therefore, are likely weeks away. With Rainy Lake releasing over 1000 m³/s, inflow to Lake of the Woods will remain very high.
Adding to the flow from Rainy Lake, the tributaries to the Rainy River have peaked again and are slowly dropping. The flow of the Rainy River at Manitou Rapids, approximately halfway between Rainy Lake and Lake of the Woods, is over 1700 m³/s. Total inflow to Lake of the Woods, including the flow out of the Rainy River and all other sources is estimated at over 2500 m³/s, while Lake of the Woods outflow from the fully opened dams in Kenora is estimated at 1250 m³/s and slowly rising with the lake level. As long as outflow is less than inflow, the lake will continue to rise. The level of Lake of the Woods is expected to rise by approximately 15-20 cm (6-8 in) over the next 7 days. Inflow is expected to decrease over this period, but still remain well above the outflow. Continued rise beyond the 7-day forecast window is expected.
As the lake continues to rise, the level of the Winnipeg River between Kenora and Minaki will also rise. The level rise over the next 7 days below Norman Dam and down to Minaki is expected to be 12-16 cm (5-7 in). This estimate is approximate given uncertainty in the extremely high local flows entering the river from tributary areas below Kenora (e.g. Black Sturgeon). The river will continue to gradually rise as long as Lake of the Woods continues to rise.
The current level of Lac Seul is 355.99 m (1167.8 ft), a 90th percentile level for this time of year. Lac Seul inflow is extremely high, resulting in a rise of 68 cm (2.2 ft) over the past week. With the rapid rise in the level of the lake expected to continue, the LWCB has directed the closure of the Root River Diversion (which draws flow out of Lake St. Joseph into Lac Seul), on Thursday, May 19. This will reduce flow into Lac Seul by approximately 90 m³/s. The LWCB has also directed an increase in the outflow from Lac Seul from 415 m³/s to 465 m³/s on Tuesday, May 17, and to 565 m³/s on Thursday, May 19. Additional increases will be evaluated by the LWCB through the week.
The LWCB recognizes that downstream areas along the English River, including Pakwash Lake, Grassy Narrows, and the Winnipeg River in Manitoba are already experiencing extremely high and damaging water levels. However, should extreme inflows to Lac Seul continue through May, the level of Lac Seul will likely reach the top of the legislated flood reserve, requiring much higher outflows to prevent further lake level rise. High outflows from Lac Seul in the near term reduce the risk of extremely high flows in the medium term.
These flow increases from Lac Seul will take some time to work down the English River, with an estimate of about two weeks to reach Nutimik Lake. If there is limited precipitation in the English River basin over the next week, declining flows out of tributaries such as the Wabigoon River may balance the additional flow arriving from Lac Seul to some degree.