A new report indicates soil moisture levels in the province are normal to drier than normal.
“We have several months before the spring flood season begins, but this report provides us with an idea of moisture levels in the soil now, plus water levels in rivers and lakes as the deep freeze begins,” said Infrastructure Minister Ron Schuler. “Floods are caused by a combination of unique circumstances and there is a risk of over-estimating or under-estimating the flood potential too far in advance.”
The 2017 Fall Conditions Report covers three key potential flood factors: soil moisture at the time of freeze-up, base flows on rivers and water levels on lakes prior to spring run-off, and long-term forecast winter precipitation.
While the flood risk this coming spring is very dependent on weather conditions in the coming months, current conditions indicate there is a chance of moderate flooding at some locations. The flood risk in some watersheds will be determined by river flows from Saskatchewan and North Dakota.
One major factor that affects spring run-off potential is the soil moisture at the time of freeze-up. All river basins in Manitoba received normal to below-normal precipitation between May and October. Consequently, soil moisture levels are normal to below normal for the watersheds of most Manitoba rivers. Soil moisture in most Manitoba river basins is generally drier than the soil moisture observed in the past three years.
Generally, higher winter flows on rivers and lake levels indicate a higher risk of spring flooding, as there is more water already in the system before run-off occurs. At this time, flows on many rivers are near normal for this time of year including the Assiniboine, Souris, Qu’Appelle and Red rivers. The exceptions are the Saskatchewan, Carrot, Waterhen, Dauphin and Fairford rivers, which are above normal.
Most major lake levels, with the exception of Lake Winnipeg, are above normal for this time of year. Lake Winnipegosis, Dauphin Lake and Lake Manitoba are high for this time of the year. Lake Manitoba is at the upper end of its operating range and the outflows from the lake are at maximum levels. Flows are above normal on the Waterhen River, Fairford and Dauphin rivers due to the above-normal lake levels flowing into these rivers. The water level in the Shellmouth Reservoir is being lowered to create storage space for spring run-off waters. Lake Winnipeg is at near-normal level and within the operating range. Lake St. Martin is below flood stage.
Lake Manitoba is expected to remain near 812 feet throughout the winter, which is within the normal operating range. Lake Winnipegosis will remain near 832.4 ft. throughout the winter, two ft. above normal. Lake St Martin is expected to reach near 801.5 ft. before the spring run-off, three ft. above the normal level but slightly below flood stage.
Snowfall is also another indicator of the potential for spring flooding. Environment and Climate Change Canada’s precipitation forecast issued early in November for November-December-January indicates precipitation will be above normal for most of Manitoba and Saskatchewan. There is no clear trend in its precipitation forecast for the months after January. The U.S. National Weather Service Climate Prediction Center forecasts above-normal precipitation for the Red River and Souris River basins for January to April.
“Manitoba’s Hydrologic Forecast Centre works in collaboration with weather services and flood forecasters in neighbouring states and provinces to monitor regularly the winter precipitation patterns throughout these watersheds,” said Schuler. “We always have to be ready for a higher spring flooding risk if heavy winter precipitation occurs, or if a fast melt rate or heavy spring rainfall were to occur.”