WILLMAR - There is one underlying fact about Willmar and its continued fight to alleviate flooding following major rain events: the city's elevation.
"We are still low," Willmar Public Works Director Sean Christensen said. No matter how many detention ponds are built or how big the storm pipes are, Willmar's own elevation will continue to play a major role in how quickly stormwater is able to leave the city and eventually find its way to the Minnesota River, approximately 40 miles away.
If several inches of rain falls in a few hours, and the water level rises in Lake Wakanda or Hawk Creek, where the city's stormwater flows on its way to the river, there will the possibility of standing water in low areas around Willmar.
"You would still have localized flooding. The location of Willmar is low," Christensen said. "You can't change the elevation."
When the Lake Wakanda rises to a certain level, Willmar's stormwater will back up until the lake level reduces enough to take more water. That is one of the reasons why Willmar had such major flooding in August 2016 when more than 8 inches of rain fell.
"There was nowhere else for the water to go," Christensen said.
The goal of the stormwater system is not to drain the water out of Willmar faster. Instead it is to detain the water until it can be drained into Lake Wakanda or Hawk Creek as nature allows. If Willmar did try to flush all of its stormwater out at once, it could mean serious issues downstream, affecting everyone on the way to the Minnesota River.
"We'd be pushing the water out quicker to others," who also don't have a stormwater system built to handle that amount of water at once, Christensen said. "It is bad news for those downstream."
The stormwater system in Willmar takes stormwater away from yards, homes and businesses and drains it into the system, which includes city streets, curbs and gutters.
"We don't want to use people's basements as stormwater retention," Christensen said.
Sometimes low-lying street intersections in Willmar will flood as water drains into the pipes. That is supposed to happen, Christensen said, though it might take some intersections longer than others to drain depending on elevation, the amount of rain and whether the catch basins are clear of debris.
"The intent of the storm system is to keep it in the right of ways," Christensen said. "In a typical rain event, the water doesn't stay in the intersections very long."
The city system is designed to service a 10-year rain event. Christensen said the cost of building a system to handle a larger storm event, such as the storm in 2016, would be astronomical. However, Christensen said parts of the current system could be updated.
"Some of the system is too small," he said.
City staff have been looking at ways to help reduce the risk of flooding in Willmar. Projects are in the planning stages, including larger, regional detention ponds on the south side of town and near the Kennedy Elementary School area. The potential local option sales tax, which city voters will decide in November, has $7 million set aside for stormwater projects.
This year the city is working on the Western Interceptor project on the west side of town, which will increase the size of the pipe draining water to Hawk Creek. There is also the Cambridge housing addition project, which will add an outlet out of the stormwater detention pond just off U.S. Highway 12 on the east side of town, helping the pond drain more efficiently.
Most new development in Willmar is required to take care of its own stormwater detention with ponds and other measures. City ordinances require the stormwater runoff from new development to be at the pre-construction level when construction is complete.
Residents can help as well, by keeping the gutters and catch basins on the streets free of things like leaves and grass clippings. Christensen said the city also advises new developers to add elevation to a building site or not put in basements.
"We are trying to get the education out there. It all works together," Christensen said.
While there are things that can be done to help Willmar's stormwater system work more efficiently, overall it is working and doing what is was designed to do.
"It is getting better, when big storms come," Christensen said.