High water probable
The risk of minor flooding at various points along the Souris River this spring is considered “slightly above normal.” That was the primary message contained in a National Weather Service Flood Potential Outlook issued for the Souris River Basin on Thursday.
Hydrologist Allen Schlag of the Bismarck office of the NWS is the person who compiles information from various sources to produce Flood Potential Outlooks for the Souris. Well aware that many persons will use the rampant flooding that occurred in 2011 as a guideline from which to evaluate water level projections, Schlag included the following statement in Thursday’s outlook: “Importantly, no indicators exist that suggest a repeat of the very wet spring of 2011.”
When asked about his evaluation of the initial flood outlook of the season, Schlag replied, “It isn’t the kind of stuff that will create flooding and mayhem in Minot, but it will get some attention. There is going to be a lot of water moving through the system. Still, it is one-twentieth of the amount of water that came through Minot in 2011.”
Thursday’s outlook comes with at least six weeks of winter remaining before any snowmelt can be expected to get under way. Additional snowfall in the coming weeks has the potential to significantly alter future outlooks. As always, spring rainfall is another factor that can make a substantial and instant impact on runoff.
“We are a long way out, too far to be really firm with an understanding of what spring rains will be like,” said Schlag. “The spring flood risk is highly dependent upon rain storms this year, as it often is, but right now there is not enough snow to create problematic flooding.”
Surveys show that the heaviest snowpack in the Souris River drainage lies above two key capture points in Saskatchewan Rafferty Reservoir near Estevan and Alameda Reservoir near Oxbow. Moisture estimates in the Canadian snowpack range as high as 200 percent of normal. However, most of that snowpack is situated over drainages that do not reach the Souris. Additionally, Rafferty and Alameda Dams are believed to have enough storage currently available to adequately handle expected runoff.
“Most of the heaviest snowpack is above the dams,” explained Schlag, “but not so much as to create an unnecessarily high amount of concern to exert control over the river. There is notably less snow on the plains above Lake Darling.”
Lake Darling is the last of the reservoirs on the Souris above Minot. The level of that reservoir, like the Canadian reservoirs, is slightly below the Feb. 1 target level as assigned by the International Souris River Board.
Thursday’s outlook raises the possibility of flows coming out of Lake Darling that could reach minor flood stage at Baker’s Bridge above Burlington. However, notes Schlag, the amount of water currently projected is little cause for alarm.
“That’s not real problematic. There’s a very small probability to create flood stage in the Minot area,” said Schlag. “Once you get downstream from Minot, say the Towner area, the snowpack starts to pick up again. Towner, Bantry and Westhope could reach minor flooding.”
According to Thursday’s outlook, the chances of reaching flood stage at Minot’s Broadway Bridge is less than 10 percent. Flood stage is 1,549 feet. Farther downstream on the Souris the chances of flooding increases. For instance, Velva is given a 30 percent chance of reaching flood stage. Flood stage is used for projection purposes and does not always equate to flood protection that may be in place at various points along the river.
Of greatest concern along the Souris in the most recent outlook is Willow Creek and its contribution to runoff into the Souris. Willow Creek drains approximately 1,160 square miles. It flows primarily south out of the Turtle Mountains and joins the Souris on the lower reach of river at the Upper Souris National Wildlife Refuge. The combined flows then turn north toward Westhope. Willow Creek is given a 70 percent chance of reaching minor flood stage.
“There’s not a lot of potential for damage in North Dakota at this time,” emphasized Schlag. “Some points along the river could reach minor flooding. It will be kind of a timing issue.”
Timing includes weather conditions during the runoff, namely temperatures and rainfall, two items that are impossible to predict with the runoff season more than one month away.
“There is a bit of a wild card, too,” added Schlag. “Soil moisture content across the state was much drier than normal last fall. However, we did see a little bit of moisture in November that didn’t end up in any rivers. That tells me it is still in the soil.”
Soil moisture content can play an important role during spring runoff. Generally, the amount of snowmelt and rainfall that reaches a river basin increases if soil moisture is high and decreases if soil moisture is low.
The next Flood Potential Outlook for the Souris River Basin is scheduled to be released March 7.