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 and early May. Forecasts indicate that inflows to all major lakes will continue to be exceptionally high, but falling, for the 7-day forecast period. Many natural tributaries across the region have crested with some now falling, but it is unlikely that they will return to normal flows this month. Water levels will remain high for at least several weeks across most areas of the basin as a result. Wet weather will prolong the duration of high water levels.
Rainfall over the past several days has been greatest in the northern portion of the watershed, along the English River.
The current level of Lake of the Woods is 323.71 m (1062.0 ft), over 95th percentile level for this time of year. The average lake level rose by 23 cm (9 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 is working 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.
The flow of the Rainy River at Manitou Rapids, approximately halfway between Rainy Lake and Lake of the Woods, is over 1500 m³/s and falling. Total inflow to Lake of the Woods, including the flow out of the Rainy River and all other sources is estimated at over 2400 m³/s, while Lake of the Woods outflow from the fully opened dams in Kenora is estimated at 1292 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 13-15 cm (5-6 in) over the next 7 days, likely reaching the 2014 peak early next week. Continued rise at a slower rate is expected into June. However, 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 7-10 cm (3-4 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 356.28 m (1168.9 ft), over 95th percentile level for this time of year. Lac Seul inflow is extremely high, resulting in a rise of 56 cm (1.8 ft) over the past week. The lake is nearing the Flood Reserve, a range of water levels above the normal operating range defined by federal Order-in-Council that corresponds to a key level for dam safety concern for the Ear Falls dam. To avoid exceeding this range , additional outflow increases are scheduled. Outflow is scheduled to be gradually increased from the current authorized flow of 565 m³/s to 800 m³/s by the end of the weekend. This is a very high outflow, last reached in 2008. Further outflow increases will be evaluated on Monday.
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 the 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 has provided the following forecast for Winnipeg River levels through the Whiteshell: