Rainy River Watershed Conditions


International Falls, MN, Fort Frances, ON — Rainfall over the past week brought more than 2 in (50 mm) or rainfall to most of the Rainy River drainage basin, with many areas receiving higher amounts, up to 5 in (125 mm). Normal basin rainfall for the first week of June is about 1 in (25 mm). The rainfall occurred just after the tributary flows from the late, but strong, snowmelt had begun to decline. This has resulted in very high inflow conditions throughout the basin.

Dams at both Namakan Lake and Rainy Lake are operated to maintain the lake levels within an operating band, called the Rule Curve, specified by the International Joint Commission. The level of Namakan Lake is 18 cm (7 in) above the Upper Rule Curve (URC). The dams at the outlet to Namakan Lake have been fully opened since May 16th. Further upstream, particularly heavy rainfall near the Vermillion River has led to the level at Crane Lake rising by over 40 cm (16 in) since May 30th. Inflow to the Namakan chain of lakes is approximately 20 per cent higher than the outflow capacity of the dam.

Rainy Lake also rose above its URC, on May 29th, and is now 14 cm (6 in ) above the URC. Rainy Lake level has risen by 19 cm (8 in) over the past 7 days.

At Fort Frances-International Falls, the dam on the Rainy River has flow passing through all turbines and 13 of the 15 sluice gates. This configuration allows the dam to pass the flow at the rate received from the outlet of Rainy Lake. As the lake level rises, the rate of flow from the outlet of Rainy Lake increases. The last two gates will be opened as necessary to ensure maximum outflow from the dam.

Both Rainy Lake and Namakan Lake will continue to rise in the near term, and their ultimate peak levels will depend on the amount of rainfall received over the next few weeks.

The Rainy River is currently 2.2 m (7.2 ft) above its median level at this time of year below the Fort Frances- International Falls dam and is 2.7 m (8.9 ft) above the median level at Manitou Rapids. The level and flow at Manitou Rapids is rising quickly due to significant increases in flow from the Big Fork and Little Fork river basins which had some of the heaviest rainfall over the weekend.

The Board suggests that waterfront property owners and users of the system keep themselves updated on basin conditions. Up-to-date information can be found by following a link on the International Rainy-Lake of the Woods Watershed Board’s page to http://www.lwcb.ca/waterflowdata.html or calling 800-661-5922 ex. 3.