Spring Runoff Update – April 6, 2016
Well above seasonal temperatures in January and March resulted in an early spring melt across southern Saskatchewan. As shown in the satellite image in Figure 1, for areas south of Highway 16 snowmelt runoff is generally complete or nearing completion. Runoff is generally in early stages within the northern portion of the grain belt with the exception of the Prince Albert area where runoff is nearing completion. Limited melt has occurred in the northern boreal forest.
Spring runoff so far has been below normal and generally lower than what was forecasted in the March 1 Spring Runoff Forecast. The runoff potential for areas where runoff is ongoing or yet to occur has not changed significantly from the March 1 forecast.
Figure 1: April 2, 2016 Satellite Image
Snowmelt runoff in the southwest occurred in the second half of February and early March. Although runoff was below normal, it was enough to fill many of the irrigation reservoirs in the area.
Runoff occurred in the Souris River Basin in late February and early March. Both Boundary and Rafferty reservoirs saw minimal inflows. Inflows to Alameda Reservoir were more significant and are still ongoing, but are also well below normal. Consequently, we do not expect to fill the Souris Basin reservoirs in 2016 unless rainfall is well above normal. Reservoir releases will likely only occur if required for international apportionment obligations.
Runoff began in the Qu’Appelle Basin in mid-March and is nearing completion. With the tributaries located to the south of the Qu’Appelle Valley seeing little to no runoff, including the Moose Jaw River and Wascana Creek which are the two largest tributaries to the system, runoff was well below normal within the system.
Stop logs were installed in the Echo and Crooked Lake structures in early March to capture what little runoff occurred above these lakes. While runoff from Pearl and Pheasant Creeks was sufficient to bring Crooked Lake to near the top of its summer operating range, Jumping Deer and Loon Creeks did not produce the runoff expected so Pasqua-Echo Lake is still about 0.5 m below the top of its summer operating range. The Craven Control Structure was also closed in early March to store runoff in Last Mountain Lake. While Last Mountain Lake is still rising, it is about 0.15 m below the top of the summer operating range. The Water Security Agency is monitoring conditions in the Qu’Appelle System.
Saskatchewan River System
The early melt resulted in prairie inflow occurring in March rather than the usual April, and as a result the Lake Diefenbaker is currently at an above normal level for March, 1.0 m above median for this time of year. Since the prairie melt occurred early, April inflows to Lake Diefenbaker are expected to be well below normal. This will allow the reservoir to be at its median level on May 15 prior to the month of June when the flood risk is highest on the system.
Outflows will be staged down in April to reduce flows on the Saskatchewan River while the ice is coming off the North Saskatchewan River. The mountain snowpack is currently below normal and with only a few weeks left in the snow accumulation season; however, a significant summer rain over the mountain headwaters event could still result in a flood event on the system in 2016. Snowmelt alone is unlikely to fill Lake Diefenbaker in 2016.
Ice on the North Saskatchewan River has been breaking up in Alberta over the past week and is expected to breakup through the Saskatchewan portion in the coming days. Flows on the North Saskatchewan River are currently high in response to this early breakup. Following the breakup of ice, below normal flows are expected on the North Saskatchewan River and downstream on the Saskatchewan River.
The Quill Lakes are at an elevation of 520.60 m and increasing at a rate of about 1 cm per day. With some snow remaining in northern tributaries, it is likely that the peak elevation of 520.65 m observed in May of 2015 will be exceeded in 2016. The forecast for the Quills will be refined this week.
Northern Grain Belt
Runoff is still ongoing or yet to begin in many areas north of Highway 16. Runoff is nearing completion in the Prince Albert area, underway in areas north of the Battlefords, and in early stages for areas north of Yorkton. Above normal snowfall through this area in March has increased the runoff potential, particularly north of Lloydminster, the Battlefords, and Yorkton. Near normal runoff is now expected from the Battlefords up to Meadow Lake and above normal runoff is now expected from Yorkton up to Hudson Bay. Significant flooding is not expected in these areas unless a rapid melt occurs or above normal precipitation occurs between now and the melt.
A low pressure system tracked through the province yesterday bringing precipitation to much of the southern half of the province. As shown in Figure 2, accumulations as high as 20 mm were observed north and east of Swift Current with more general accumulations in the 5-10 mm range.
Figure 2: April 5, 2016 Precipitation Map
A clipper system is forecasted to move across the province today bringing additional mixed precipitation. A swath of 5-10 cm of snow, extending from Buffalo Narrows down to Hudson Bay is expected from this system. As shown in Figure 3, up to 20 mm of precipitation is expected in east central areas of the province from this system.
Figure 3: Precipitation Accumulation Forecast (12:00 AM Wednesday to 6:00 AM Thursday)
Over areas of southern Saskatchewan much of this precipitation is expected to infiltrate, as soils have thawed, with very little runoff expected from these events. These events will have an impact on the runoff in east central areas, adding to the recession in areas where runoff is more advanced and adding to peaks where runoff is in early stages
With snowmelt runoff well underway, a complete Spring Runoff Forecast based on conditions as of April will not be issued. Updates on current conditions will however be issued when warranted. Beginning in early May, the Water Security Agency will resume issuing our monthly Current Conditions and Water Supply reports.
The Water Security Agency will post the next update on April 13, 2016 or before if conditions warrant it.