The Red Lake River’s crest earlier this month may have seemed mild, provisionally cresting at 6:30 p.m. on April 8 at 24.74 feet. That’s just outside a top 10 river crest. It was, however, a 10-year flood according to the flow of water, said Blake Carlson, the City of Crookston’s engineer with Widseth Smith Nolting.
The max flow of water, this year at around 20,000 cubic feet per second, generally coincides with the river’s crest point explained Carlson. “We rank floods based on how often they occur, so a 10-year flood means that in the last 100 years there would’ve been 10 floods with that amount of flow going through town,” said Carlson. “A 10-year flood for Crookston is about 18,000 cubic feet per second. The peak flow Crookston got this year was about 20,000 cubic feet. In 1997 we were at about 28,000 cubic feet per second.”
In 1997 the ice jammed on the river, causing the water level to rapidly rise. During the work to install Crookston’s levee system after 1997, two cutoffs were added down the river that Carlson says have a pretty significant effect on the river level during high water events. “There are two channel cutoffs downstream from Crookston,” said Carlson. “One is just downstream from the Highway 75 bypass and then another one about another half a mile west of that. The effect on the level of the water those cutoffs create is about the same on a 10-year and 100-year flood. The effect on the water level at the Highway 75 bypass is about two feet lower and diminishes as you move upstream. At the Robert St Bridge, the effect is about one and a half feet and about a half foot back by Riverside dike. Once you get upstream much more than that the water level is not affected by those downstream cutoffs, but it does make a big difference going through town.”
A levee system in Crookston has been around a long time, but the levee system upgrades after 1997 also certified many of the dikes throughout Crookston to 31 feet limiting the amount of sandbagging the City of Crookston needs to do for even a 10-year flood event like this year. Had Crookston still the 1997 levee system, the City probably would’ve estimated a higher river crest and put in a lot more work sandbagging because the 1997 system would’ve required thousands of feet of sandbags rather than a couple of hundred feet. “We had an advantage this year in that we have a lot of certified dikes in town to 31 feet,” said Carlson. “We didn’t really have to worry about those. Early on we looked at the predicted levels for the river and picked a level that was probably lower than we would’ve picked back in 1997. The level we sandbagged to this year would’ve taken thousands of feet of dikes to raise in ’97 taking a significant amount of time. This year we could take a sit back and see attitude and if it appeared the water was going to go higher than we had assumed based on forecast there was such a limited length of dikes that needed to be raised that could be done in a relatively short amount of time. If today, we had the dikes that were in place in ’97 we probably would’ve picked a potentially higher level to protect to then when did which would’ve meant a lot of work and as it turned out part or a lot of that wouldn’t have been needed.”
This year Crookston was also aided by an atypical thaw with almost no precipitation, and gentle, cool temperatures limited flow tributaries upstream from Red Lake Falls and Thief River Falls explains Gregory Gust with the National Weather Service in Grand Forks. “In a typical year you would’ve seen a little bit more contribution coming in out of the Clearwater River and Thief River contributing to the crest in Crookston,” said Gust. “After the big winter storm and rain events that came through, we had bumped the crest prediction up to 26.9 feet looking at the additional amount of moisture into the basin. That would’ve been more what we would’ve expected under normal thaw conditions. But we didn’t have a normal thaw cycle, we had a period of three weeks or better with very little or any precipitation. We’re talking a few hundredths of an inch, and a very even thaw cycle with above freezing temperature during the day and freezing again at night.”
The levee system in Crookston, not only saves the City and its residents from a stressful spring flood season, but it also saves hundreds of hours of sandbagging for employees, residents, and volunteers.
