Flooding has occurred throughout Willmar's history, city is topography challenged
WILLMAR -- The rains and flooding that swept through Willmar and the surrounding area this past August got a lot of people thinking about the city's stormwater system and whether enough is being done to reduce the possibility of such flooding in ...
WILLMAR - The rains and flooding that swept through Willmar and the surrounding area this past August got a lot of people thinking about the city's stormwater system and whether enough is being done to reduce the possibility of such flooding in the future. However, this storm was just the latest in a long line of rain events that have caused water to back up into Willmar's business and residential areas dating back to the 1950s and before.
"It is not new," said Sean Christensen, Willmar Public Works Director.
The main culprit in Willmar's ongoing flooding is not development or the speed at which water is flushed out of town, it is geography and topography.
"There is not enough grade difference between the city of Willmar through the drainage basin. We're built in a low area," Christensen said.
Willmar is less than a foot above Lake Wakanda, Christensen said, which is where the water from the southeast portion of the city drains. Lake Wakanda is located southeast of Willmar in both Whitefield and Fahlun townships.
According to a December 2013 memo written by then interim city engineer Jared Voge, the lack of fall can cause water from Lake Wakanda to flow back into Willmar when the levels in the lake are too high, called a tailwater effect. This water ends up causing flooding in Willmar's low areas until the water drops enough in Lake Wakanda to take the extra water back.
Willmar's stormwater system is designed to provide service in a 10-year storm event, based on measurements from the U.S. Department of Commerce, according to the City of Willmar Watershed Management Plan approved in August 2012.The system is also designed to provide protection from significant damage to structures or risk to public health and safety from a 100-year event. What it is not designed for is a 1,000-year event, or a storm which only has a 0.1 percent chance of happening in any given year: The kind of event which hit Willmar on Aug. 10 and 11.
"Nobody designs for that. It costs too much money, too much real estate. You can't design for those, you can't plan for those," Christensen said.
While Willmar's topography cannot be changed, there are ways to either store or remove more of the city's storm water and potentially reduce flooding occurrences.
"That means ponds, storage," Christensen said.
There are stormwater ponds throughout Willmar. Since the late 1990s, the city has required stormwater management for all new developments, Christensen said. This means a new development cannot release storm water drainage at a higher rate than what the property did before it was developed. Current projects such as the Hobby Lobby building on First Street and the new elementary school on Lakeland Drive Southeast will all include stormwater projects, including retention ponds.
The city has also created new ponds in areas where the need is greatest, including around 10th Street Southwest and Kandiyohi Avenue. The city also performs annual ditch cleanings and periodically cleans out stormwater ponds, such as the one near the MinnWest Technology Campus along Civic Center Drive.
"We try to manage what we can manage," Christensen said.
Another project that may help is the long planned Grass Lake project, which will restore a dry lake basin and include spillways, embankments and diversions to help with stormwater mitigation.
"I believe it will help," Christensen said.
The water management plan said the stormwater system in many areas is at or even above capacity and that some of the pipes are undersized. Lack of stormwater ponds or other retention schemes also add to the flooding risk and an interconnected system makes it difficult to address one problem without affecting another.
Voge said in his memos from 2013 that to completely combat the tailwater effect from Lake Wakanda, the city would need to spend approximately $20 million.
Funding can be a stumbling block for some projects, especially those with higher price tags, including pumps and ditch diversions.
"I think we're doing as much as we can with the resources available," Christensen said.
There are ways to have dedicated funding sources for projects, including a stormwater utility, which charges residents a monthly fee for stormwater service, like it does for sewer. But there doesn't seem to be much appetite for that, Christensen said.
Flood insurance could help those affected by floods when they do happen, but Willmar does not participate in the federal flood insurance program.
"It requires people in a floodplain to get insurance," Christensen said, even if they don't want it. On the flip side though, those who want flood insurance cannot get it without the city as a whole participating in the program.
When stormwater projects are undertaken, Christensen prefers projects which store more of Willmar's water, instead of those that try to get rid of the problem as fast as possible.
"What does that do downstream? It floods everyone downstream," Christensen said, who doesn't like pushing Willmar's problems on to its neighbors.
In Christensen's opinion, city staff and engineers are the best they can be in trying to minimize the causes and effects of Willmar's stormwater concerns, but it's hard to fight against Mother Nature and Willmar's natural state. The massive amount of rain that has fallen this year has been another test for Willmar, pushing the system beyond its designed capabilities.
"You build these things based on numbers, history and design. Until it happens you don't know if it will work. It's been one of those years," Christensen said.