Substantial change to Souris River flows
The water content in the snow in the Souris River drainages in Saskatchewan doubled in the month of March. Consequently, water being released into the Souris from two Canadian reservoirs and Lake Darling Dam is being dramatically increased.
A decision to open the release gates at Lake Darling Dam from 800 cubic feet per second to 1,100 cfs was made Tuesday afternoon by the U.S. Army Corps of Engineers in St. Paul, Minn. The release rate was scheduled to be increased to 1,500 cfs late Tuesday. According to the Corps, the amount of water being released from Lake Darling will be stepped up to 2,300 cfs later today. The amount will mirror the combined 2,300 cfs being released from Rafferty Reservoir near Estevan and Alameda Reservoir near Oxbow, Sask.
Aerial gamma ray surveys were conducted over the Souris River Basin in Saskatchewan this past Sunday. The flights had been delayed previously by fog and rain. Information obtained from the flights revealed that the amount of snow moisture on the ground in the Souris and Moose Mountain Creek drainages increased from three to six inches during March.
The substantial increase in releases from the three dams is a reaction to the latest data accumulated by the National Weather Service and the Saskatchewan Water Security Agency. Flows of 2,300 cfs are normally easily contained by the Souris. However, because of ice remaining in the river from Burlington through Minot and beyond, how the river will behave is an unknown.
“Ice was dissipating from Baker’s Bridge and going downstream,” said Allen Schlag, NWS hydrologist in Bismarck. “However, such as at the Boy Scout Bridge four miles northwest of Minot, we don’t have any expectations that the ice is degraded. I suspect, especially at 2,300 cfs, we’ll be running the risk of ice jams.”
The Souris has risen more than 10 feet recently at Sherwood, reversing the moderate drawdown of Lake Darling to the point where the lake had begun to increase in elevation. The level of Lake Darling was inches over 1,595 feet Tuesday. The goal now, according to the Corps, is to lower Lake Darling to 1,593 feet in the coming days. The lake’s summer operating goal is 1,596 feet.
Other goals, say the Corps, are to maintain a flow of 3,200 cfs at the Sherwood crossing of the Souris and flows of 5,000 cfs at the Boy Scout Bridge the same target levels that were in place in the historic flood year of 2011.
“We are maintaining a Flood Warning for Foxholm, Baker’s Bridge, and are working possible effects at the Boy Scout Bridge,” explained Schlag. “If it was open water we would be below flood stage but we are not working with open water conditions.”
According to a news release issued Tuesday by Minot Public Works Director Dan Jonasson, the Souris through Minot is expected to rise approximately two feet when the flow of 2,300 cfs reaches the city. Ice in the river slows flows, meaning the full effect of 2,300 cfs may not be felt within Minot until late Thursday or sometime Friday.
The possibility of ice jams and subsequent rapid rises in the Souris remains an immediate concern. There is no way to accurately predict where such jams may occur, if at all, or what their effect will be. An ice jam within the city could result in a sudden change of river elevations.
Of greater concern is the amount of snow remaining on the ground throughout the Souris River drainage in both North Dakota and Saskatchewan and the amount of moisture contained in the snowpack. March temperature averaged an astounding 14.5 degrees below normal in Minot, erasing any chance for an early melt.
“That is an amazingly negative value,” noted Schlag. “At two and one-half degrees difference the lay person notices it. This is amazingly chilly weather for you guys.”
The result is the lack of any significant melting to date and the ever increasing possibility that a return to normal temperatures could trigger a rapid melt.
“What is reasonable to say, given the current status of winter, given the amount of snow already on the ground, is that there is a fair amount of risk for flooding along lowlands,” said Schlag. “Runoff forecasts are most likely to go up as opposed to down in the short term.”
Flood Potential Outlooks issued by the NWS are based on scheduled releases from all dams along the Souris, the amount of water content in the snowpack, the rate of melt and additional factors. Current outlooks have the Souris generally remaining below flood stage at most reporting points along the river, including Minot.
The NWS plans to release updated Flood Potential Outlooks for the Souris as conditions warrant, such as changes to the amount of water being released from dams and the progress of the snowmelt.