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 323.66 m (1061.9 ft), over 95th percentile level for this time of year. The average lake level rose by 26 cm (10 in) over past week. The lake is 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 is nearly 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 1100 m³/s, inflow to Lake of the Woods will remain very high for weeks.
Adding to the flow from Rainy Lake, the tributaries to the Rainy River are dropping. The flow of the Rainy River at Manitou Rapids, approximately halfway between Rainy Lake and Lake of the Woods, is over 1600 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 1283 m³/s and slowly rising with the lake level. Inflow is expected to decrease over this period, but still remain well above the outflow. 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, likely reaching the 2014 peak near the end of this period. Continued rise is expected into June, but the rate will depend on rainfall, particularly in the Rainy River and local Lake of the Woods area.
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 356.14 m (1168.4 ft), over 95th percentile level for this time of year. Lac Seul inflow is extremely high, resulting in a rise of 63 cm (2.1 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), which is occurring on May 18. 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 are being arranged, as soon as this weekend. More details will be provided on this Notice Board.
The LWCB recognizes that downstream areas along the English River, including Pakwash Lake, Grassy Narrows, Wabaseemoong, and the Winnipeg River in Manitoba are already experiencing extremely high and damaging water levels, with some areas well above previous records. The Board’s decision to increase flows out of Lac Seul is to address a significant risk of requiring much higher outflows towards the end of May and early June once Lac Seul reaches the top of its Flood Reserve. High outflows from Lac Seul in the near term reduce the risk of extremely high, possibly record-breaking outflows, 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. Manitoba Hydro will provide an updated forecast for the Winnipeg River in Manitoba on May 20.