Secretariat

Conditions across the Winnipeg River basin remain dry. High winds over the last week have made it difficult to accurately estimate average lake levels and inflows. The wind is also causing increased water loss through evaporation for the large lakes, and this loss is not being offset by rainfall. Lake of the Woods outflow reductions are therefore needed to slow the lake level decline.

How Wind Affects Water Levels on Large Lakes

We often think of a lake’s surface as flat and still—aside from waves. But on large lakes like Lake of the Woods, wind can cause noticeable changes in water levels from one location to another. This phenomenon is called wind setup. When sustained winds blow across the lake from one direction, they push water toward the far shore, raising the water level there while lowering it on the windward side. This creates a temporary tilt in the water surface. As wind speed, direction, and duration change, so does the distribution of water across the lake.

In early September, strong winds swept across Lake of the Woods, causing noticeable shifts in water levels at different locations around the lake. At first, winds blew from the west, pushing water away from the western shore—where the Cyclone gauge is located—and piling it up along the eastern shore, near the Hanson gauge. Later, as the wind shifted and strengthened from the north, the effects became more visible along the north and south shores. Water levels dropped at gauges on the north shore (Clearwater and Keewatin) and rose at gauges on the south shore (Warroad and Springsteel).

During windy periods, the average lake level computed from the measurements around the lake may change from day to day, even though the amount of water in the lake has changed little. And because lake inflow is computed using the change in lake level over time, this instability also causes inflow values to fluctuate from day to day.

The current level of Lake of the Woods 322.69 m (1058.7 ft) a 15^th percentile level for this time of year. The average lake level declined by 3.5 cm (1.4 in) over the past week and is expected to remain stable or decrease by up to 1 cm (0.5 in) over the next week. Lake of the Woods authorized outflow will decrease from 200 to 150 m³/s on Thursday, September 11^th.

This outflow change will cause levels along to Winnipeg River to decrease by 8 cm (3 in) below the Norman Dam, by 5 cm (2 in) above Kimberley Rapids and by 2 cm (0.8 in) at the Dalles. This outflow reduction will have no impact on levels at Minaki.

Notice: on Wednesday, September 17^th, the Kenora Powerhouse will be shut down for regular station maintenance and Lake of the Woods authorized outflow will be fully transferred to the Norman Dam. Temporary water level fluctuations on the Winnipeg River are expected directly below the dams that day.

The current level of Lac Seul is 356.23 m (1168.7 ft), a 30^th percentile level, within the normal range for this time of year. The lake level remained stable over the last week and is expected to increase by 1 to 2 cm (0.5 to 1 in) over the next week. Lac Seul authorized outflow is 125 m³/s with no changes scheduled at this time.

The current level of Lake of the Woods is 322.72 m (1058.8 ft) a 15^th percentile level, below the normal range for this time of year. The average lake level declined by 3.8 cm (1.5 in) over the past week and is expected to decrease by 1 to 2 cm (0.5 in) over the next week. Lake of the Woods authorized outflow is 200 m³/s with no changes scheduled at this time.

The current level of Lac Seul is 356.22 m (1168.7 ft), a 25^th percentile level, within the normal range for this time of year. The lake level increased 1.5 cm (0.6 in) over the last week and is expected to increase by 2.5 to 4 cm (1 to 1.6 in) over the next week. Lac Seul authorized outflow is 125 m³/s with no changes scheduled at this time.

Although some portions of the Winnipeg River basin have received normal precipitation amounts over the last few weeks, inflow to Lake of the Woods remains in the low-normal range. As per the LWCB Regulation Strategy, the objective heading into the fall will be to maintain stable water levels. With water loss through evaporation expected to increase over the next month, this may require outflow reductions. An initial outflow reduction is scheduled for Tuesday, September 2^nd.

Why is lake evaporation typically higher in the fall?

There are three main drivers for evaporation: (1) warm water temperatures coupled with cold air temperatures, (2) low relative humidity and (3) high wind speeds. In summer, the air temperature is higher than the water temperature and humidity also tends to be high. But by September, these conditions reverse. The water has warmed and its temperature can be higher than the air temperature. Humidity drops and wind speeds can increase. At Lake of the Woods, it is common in September for evaporation to remove more water from the lake than it receives from rainfall and tributaries. This means water levels would drop even if no water was flowing out to the Winnipeg River.

The current level of Lake of the Woods 322.76 m (1058.9 ft) a 15^th percentile level for this time of year. The average lake level declined by 3 cm (1 in) over the past week and is expected to remain stable over the next week. Lake of the Woods authorized outflow will decrease to 200 m³/s on Tuesday, September 2^nd.

This outflow change will cause levels along to Winnipeg River to decrease by 9 cm (3.5 in) below the Norman Dam, by 6 cm (2.5 in) above Kimberley Rapids and by 3 cm (1 in) at the Dalles. This outflow reduction will have no impact on levels at Minaki.

The current level of Lac Seul is 356.24 m (1168.8 ft), a 25^th percentile level, within the normal range for this time of year. The lake level increased 3 cm (1 in) over the last week and is expected to increase by 2 to 5 cm (0.75 to 2 in) over the next week. Lac Seul authorized outflow is 125 m³/s with no changes scheduled at this time.

The current level of Lake of the Woods 322.78 m (1059.0 ft) a 15^th percentile level for this time of year. The average lake level declined by 2 cm (0.75 in) over the past week and is expected to decrease up to 1.5 cm (0.5 in) over the next week. Lake of the Woods authorized outflow is 250 m³/s with no changes scheduled at this time.

The current level of Lac Seul is 356.21 m (1168.6 ft), a 25^th percentile level, within the normal range for this time of year. The lake level increased 5 cm (2 in) over the last week and is expected to increase by 4 to 7 cm (1.5 to 3 in) over the next week depending on precipitation. Lac Seul authorized outflow will increase to 125 m³/s on Friday, August 22^nd.

The current level of Lake of the Woods 322.79 m (1059.02 ft) a 15th percentile level for this time of year. The average lake level decreased 2 cm (0.75 in) over the past week and is expected to remain stable or decrease 2.5 cm (1 in) over the next week. Inflows have temporarily increased as a result of recent precipitation but are expected to continue declining over the next week. As such an outflow reduction to 250 m³/s is scheduled for Tuesday August 19^th.

This outflow change will cause levels along to Winnipeg River to decrease by 5 cm (2 in) below the Norman Dam and by 2 cm (0.75 in) at the Dalles. This outflow reduction will have no impact on levels at Minaki.

The current level of Lac Seul is 356.19 m (1168.6 ft), a 25th percentile level, within the normal range for this time of year. The lake level increased 5 cm (2 in) over the last week and is expected to increase 5 to 9 cm (2 to 3.5 in) this week depending on precipitation. Lac Seul authorized outflow is 100 m³/s with no changes scheduled.

The current level of Lake of the Woods is 322.81 m (1059.1 ft), a 15^th percentile level, below the normal range for this time of year. The average lake level is unchanged from a week ago.

Most weather forecast models from Canadian, American, and European weather agencies indicate relatively dry conditions over the next week. A few forecast runs indicate the potential for heavy rainfall from Lake of the Woods to Rainy Lake from Sunday to Tuesday.

Based on the majority of forecasts, the level of Lake of the Woods is expected to change little over the next week with further declining inflows. A reduction in outflow, from 300 m³/s to 275 m³/s is scheduled for Friday, August 15. The level of the Winnipeg River below Norman Dam will decline by 5 cm (2 in) as a result of this flow change, while the river level at Minaki will not be affected. A second 25 m³/s cut in outflow is tentatively scheduled for Tuesday, August 19 and will be reassessed on Monday based on rainfall conditions.

The current level of Lac Seul is 356.17 m (1168.5 ft), a 20^th percentile level, below the normal range for this time of year. The lake level increased by 5 cm (2 in) over the last week and is expected to increase by 4 to 7 cm (1.6 to 2.7 in) over the next week. Lac Seul authorized outflow is 100 m³/s with no changes scheduled.

Severe thunderstorms moved through the basin yesterday, with more expected this weekend. These storms may produce heavy rainfall, leading to localized increases in river flows and lake inflows. Currently, no changes to outflows from Lake of the Woods or Lac Seul are scheduled. However, adjustments may be necessary in the coming days. Please check the Noticeboard regularly for updates on any scheduled flow changes.

The current level of Lake of the Woods is 322.82 m (1059.1 ft), a 15^th percentile level, below the normal range for this time of year. The average lake level changed little over the last week and is expected to increase by up to 4 cm (1.6 in) over the next week. Lake of the Woods authorized outflow is 300 m³/s with no changes scheduled.

The current level of Lac Seul is 356.12 m (1168.4 ft), a 20^th percentile level, below the normal range for this time of year. The lake level increased by 5 cm (2 in) over the last week and is expected to increase by 4 to 8 cm (1.6 to 3 in) over the next week. Lac Seul authorized outflow is 100 m³/s with no changes scheduled.

The current level of Lake of the Woods is 322.83 m (1059.1 ft), a 15^th percentile level, below the normal range for this time of year. The average lake level increased by 3 cm (1.2 in) over the last week and is expected to remain stable over the next week. Lake of the Woods authorized outflow is 300 m³/s with no changes scheduled.

The current level of Lac Seul is 356.08 m (1168.2 ft), a 20^th percentile level, below the normal range for this time of year. The lake level increased by 6 cm (2.4 in) over the last week and is expected to increase by 4 to 6 cm (2 to 2.4 in) over the next week. Lac Seul authorized outflow is 100 m³/s with no changes scheduled.

Inflow to Lake of the Woods remains in the normal range and the lake level is expected to continue rising over the next week. As per the Regulation Strategy, under normal inflow conditions, the Board is targeting a summer level between 322.8 and 323.1 m (1059 to 1060 ft) with an outflow between 300 and 700 m³/s.  Therefore, to balance lake levels and flows on the Winnipeg River, another small outflow increase is scheduled for tomorrow. This outflow increase is in line with the strategy, and will allow both the lake and river levels to gradually rise.

How does the level of Lake of the Woods compare to the levels on the Winnipeg River?

On July 28, the level of Lake of the Woods was 322.83 m (1059.1 ft), which is 20 cm (8 in) lower than the median level for the end of July. On the Winnipeg River, the level directly below the Norman Dam was 30 cm (12 in) lower than median, and the level at Nutimik Lake in Manitoba was 75 cm (30 in) lower than median.

How will the outflow increase affect levels of the lake and river?

This outflow increase will slow the rate of rise of Lake of the Woods by 0.4 cm (0.15 in) over the next 7 days.

The level of the Winnipeg River will increase by 5 cm (2 in) below the Norman Dam, 3.5 cm (1.4 in) above Kimberley Rapids and 2 cm (0.8 in) at the Dalles as a result of this flow change. Levels at Minaki will not be affected.

How much inflow is needed for levels on Lake of the Woods to rise?

Lake of the Woods will rise by approximately 1 cm (0.4 in) over the course of a week for every 64 m³/s of excess inflow —that is, if inflow exceeds outflow by that amount.

For example, on July 28, the 7-day average inflow to the lake was 460 m³/s, while the outflow was 275 m³/s, resulting in an excess inflow of 185 m³/s. Since 64 m³/s results in a 1 cm rise, an excess of 185 m³/s would lead to a rise of about 3 cm (1.2 in) over the week.

The current level of Lake of the Woods is 322.83 m (1059.1 ft), a 15^th percentile level, below the normal range for this time of year. The average lake level increased by 3.3 cm (1.3 in) over the last week and is expected to increase by up to 2 cm (0.8 in) over the next week. Lake of the Woods authorized outflow will increase from 275 to to 300 m³/s tomorrow, Wednesday July 30.

Scattered thunderstorms over the past week have brought localized rainfall to parts of the Winnipeg River basin. As a result, flows in the southern portion of the basin have returned to the normal range, providing a more consistent supply to Lake of the Woods. To help stabilize lake levels, a small increase in outflow is scheduled. The lake level is currently within the preferred range for recreational activities, and conditions have also supported healthy wild rice growth.

The current level of Lake of the Woods is 322.80 m (1059.0 ft), a 10^th percentile level, below the normal range for this time of year. The average lake level increased by 2.5 cm (1 in) over the last week and is expected to increase by up to 4 cm (1.6 in) over the next week. Lake of the Woods authorized outflow will increase to 275 m³/s tomorrow, Friday July 25^th.

This outflow increase will cause levels along the Winnipeg River to increase by 5 cm (2 in) below the Norman Dam, 3.5 cm (1.4 in) above Kimberley Rapids and 2 cm (0.8 in) at the Dalles. Levels at Minaki will not be affected by this flow change.

The current level of Lac Seul is 356.01 m (1168.0 ft), a 20^th percentile level, below the normal range for this time of year. The lake level increased by 4 cm (1.6 in) over the last week and is expected to increase by 4 to 5 cm (1.6 to 2 in) over the next week. Lac Seul authorized outflow is 100 m³/s with no changes scheduled.