Floodplain Management in Minnesota: Past, Present, and Future

^{City of Roseau, 2002 with permission}

River Diversion in Roseau

Located ten miles south of the Canadian border, the City of Roseau is bisected by the Roseau River. Roseau is home to Polaris Industries, a major regional employer and maker of snowmobiles and off-road vehicles. Since its founding, the city had experienced frequent flooding, despite a series of emergency levees and other flood protection measures. Record flooding in 2002 resulted in damage to 90% of commercial buildings, 90% of public buildings, and 80% of the town's 1,200 homes, totaling close to $100 million in flood damage. Following this devastating flood of record, the city asked the US Army Corps of Engineers (COE) to conduct a feasibility study for a flood control project in Roseau. The COE completed the study and subsequently partnered with the city and state to construct a flood risk reduction project. In 2015, construction of a 4.5 mile Roseau River diversion channel and nine mile long levee were completed. The $44 million project effectively removed all of the city from the mapped 100-year floodplain.

"Our city's various flood mitigation projects have transformed our community from one that was under constant threat from flooding, from as far back as the city's founding, to a community that does not even think about flooding anymore. The projects have also lifted a significant regulatory and financial burden off the community in terms of building restrictions and flood insurance premiums. Implementing our flood mitigation projects was not easy financially, logistically and politically at times, but residents and business owners have responded very favorably to the outcome of virtually all of the city being removed from the 100-year floodplain." Todd Peterson, City of Roseau Community Development Director

^{One last home remains behind Newport’s old emergency levee}

Open Space Preservation in Newport

Newport is a town 3,400 on the Mississippi River downstream of St. Paul. As with many communities, an emergency earthen levee was quickly constructed in response to forecasted flooding in 1965. The levee was constructed on private property, without much in the way of engineering, design, and construction, and were expected to be removed when flood waters receded. This “temporary” levee has remained in place for decades, subjecting about 15 homes to risk of catastrophic flooding should it fail. In 2004, the US Army Corps of Engineers determined the levee was in poor shape. Tree growth, structural encroachments, and other construction deficiencies rendered the levee unsafe. It was estimated that a compliant replacement levee would cost nearly $20 million. That was not a cost-beneficial solution, or one the city could afford. Instead, Newport has partnered with FEMA and the DNR to acquire and remove structures and other improvements from willing sellers. As of 2019, that emergency levee remains in place, but the risk to people and property has been significantly reduced. A single home remains behind the levee. Ultimately, Newport hopes to acquire the remaining property, breach the levee, and create a public space with direct access to the Mississippi River.

"The mitigation of the six homes with aid from FEMA and the DNR has been a blessing for the City of Newport. Not only did it help mitigate a dangerous situation, it drastically cut the cost to the city and reduced the time in flood planning efforts." Deb Hill Newport City Administrator

^{Aerial overview of the city, detailing the extensive levee network and riparian open spaces along the Red River. With permission by Vern Whitten Photography, 2015}

Aggressive Flood Fighting in Moorhead

Few areas of the state have a more storied flooding past than the Red River basin in northwestern Minnesota. The City of Moorhead is the most populated city in the watershed at over 43,000 and has long been plagued by flooding from the Red River of the North. The frequency and severity of floods since 1997 have increased considerably.  Major flooding in 2009 (flood of record) compelled the city to develop a comprehensive long-term flood risk reduction plan.  Flooding in consecutive years of 2010 and 2011 reinforced the city’s commitment to action.

Since 2009, the city has embarked upon a comprehensive and phased flood risk reduction initiative with nearly $100 million in state Flood Hazard Mitigation grant assistance. This includes voluntary acquisition of over 250 properties that have been converted to public open space, 12 miles of levee and floodwall, and 19 sanitary and stormwater pump stations. These mitigation efforts result in flood protection three feet above the flood of record and significant reduction in costs associated with emergency flood preparation and response.  For example, the record flood of 2009 required 2.5 million sandbags and 3 miles of temporary clay levees. Today that would be reduced to 150,000 sand bags and only a mile of emergency levee.

"Following three consecutive years of major flooding (2009-2011), including the 2009 flood of record, the City of Moorhead initiated an aggressive flood mitigation program. These improvements have dramatically decreased the need for emergency measures used during previous floods. Overall, the improvements have reduced flood risk to nearly 4,000 properties within the City. As a result of this work, the City is better positioned to avoid costly flood fights, temporary closure of businesses, and evacuation of vulnerable citizens and homes." Bob Zimmerman, City of Moorhead City Engineer

^{The city of Delano deployed their fully-engineered temporary flood wall in 2019. Used by permission.}

Acquisitions and Flood Control Projects in Delano

Delano is a small community west of the Twin Cities. Its historic downtown and several homes along the river were susceptible to flooding from the South Fork of the Crow River that meanders through town. Until recently, the city frequently employed time and labor-intensive emergency measures to hold floodwaters at bay. These measures included sandbagging and temporary clay levees on local streets paralleling the river. For nearly 15 years, the city has invested in a host of flood risk reduction measures to minimize flood threat and disruption to downtown businesses. With funding through the DNR’s Flood Hazard Mitigation grant assistance program, the city acquired and removed a number of at-risk homes from the floodplain. In addition, the city constructed permanent earthen levees and temporary floodwalls to reduce flood risk. The time, stress, and financial burden that flooding brings has been reduced in Delano through phased sound and methodic flood mitigation efforts.

"Well, we’re on day 4 at major flood stage levels. Reached 19.7 this morning and holding steady for the better part of a week. Been pretty lucky there hasn’t been any rain or any forecasted this week. All of the infrastructure we put in place is holding up and functioning great! It’s such a relief so far... I think back to my first flood event in 2001 and the level of effort compared to now. The public is protected better, our employees are functioning in a far safer environment, and there are definitely fewer impacts." Phil Kern, Delano City Administrator

 

Restrictive Ordinances in Dodge, Fillmore, and Nicollet Counties

A number of communities have chosen to restrict the development of new buildings in floodplains. This simple and highly effective approach to floodplain management is common in cities that don’t contain much mapped floodplain, as well as well as rural areas with parcels large enough to accommodate more suitable building locations. Some communities have experienced too many losses and extraordinary public expenditures with flooding. Dodge and Fillmore Counties have both adopted ordinances that prohibit the construction of new dwellings in the 100-year floodplain (1% annual chance). Nicollet County prohibits new dwellings in the 100- and 500- year (.02% annual chance) floodplains. These communities still allow certain developments in floodplains such as streets, culverts, boat launches, public waters work, or the construction of accessory structures, yet protects valuable building stock from larger flood events and meandering rivers. Preserving our flood prone areas as open space helps to utilize the beneficial functions of floodplains to stabilize a river and minimize infrastructure damage to bridges, culverts and other infrastructure.

FEMA’s Community Rating System program incentivizes strong protections in return for cheaper premiums for residents that carry flood insurance policy. Enforcement of a restrictive ordinance of this type carries a heavy reward for participating communities.

^{The city promotes open disclosure of flood risk – with maps that detail 100 year flood zones with strict insurance implications, as well as localized flood risk where protective development standards are promoted.}

Communicating Unmapped Risk in Edina

The City of Edina is facing dramatic increases in flooding tied largely to a significant trend in redevelopment, primarily the conversion of small residential homes into larger homes. This redevelopment is adding impervious surfaces, leading to increases in runoff and localized stormwater issues. Local flooding has become more of a problem, and the city is pursuing a variety of corrective mitigation actions. Recognizing that no single mitigation action will remove all flood risk and that flooding cannot simply be “engineered away,” the city has mapped those areas vulnerable to localized flooding in an effort to better inform decision making. The city assigned probabilities that a home will experience any of three risk categories (direct, indirect, and sanitary), and communicate this risk through the city’s website, newsletters, direct mailings, and other outlets. Identifying and sharing this risk helps to minimize losses through effective design standards and the promotion of flood insurance coverage to affected property owners.

There are many ways that a community can utilize a similar approach. Identifying localized urban flooding areas can lead to a conversation about how to protect these areas.

^{The image above details areas where the city has modeled and regulates development for flood risk beyond the FEMA 100 year flood elevation – both through updated precipitation data (in blue) and dam breach areas (in gray).}

Regulating for Expanding Risk in Rochester

The City of Rochester, in coordination with Olmsted County, has implemented a multi-faceted approach to floodplain administration. The city has a history of flood risk going back to the late 1800’s, and they’ve been active to control these events since 1962 – long before their historic 1978 flood. Higher flows continue pose serious concerns to the city. To protect against this, the city has implemented a number of projects to protect its businesses and residents, and has also adopted zoning standards designed to reduce future risk. These efforts are guided by a two pronged approach to reducing future risk: 1) preserve storage, and 2) accurately show risk to ensure protection of all development.

To preserve storage, the city completed a comprehensive flood control project in 1995 – paid through a local sales tax to match funding through USACE and NRCS. In addition to levee work, the project was responsible for the construction of seven upstream reservoirs to control flood flows. These efforts have proven successful. In 2007, the city withstood a 500-year rainfall event, and remained largely protected from surface flooding. The city recognizes there is still risk from sustained events, and has concerns of about increased flows. To combat this, they’ve worked with the county to restrict floodplain fill within the watershed. Any fill that is brought into the floodplain to accommodate new development is required to be offset by removal at a 1:1 ratio. Additionally, they’ve limited the disturbances allowed on alluvial soils outside of the mapped floodplain areas to preserve storage elsewhere in the watershed.

The city also recognizes that the official FEMA floodplain maps do not accurately identify flood risk because they are based on old data. The city created its own maps using updated to data to accurately show risk and ensure protection of future development. Engineers and hydrologists map a floodplain using hydrologic models that are based off of a 100-year storm event. In 2013, the National Oceanic and Atmospheric Administration (NOAA) updated a 1960 study of precipitation data that essentially redefined what is considered a 100-year storm event. In the Olmsted County area, a 100-year, 24-hour rain event increased from approximately 6 inches over a 24-hour period to 7 to 8 inches. The city ran models that simulated this updated 100-year storm event and mapped it. Additionally, the city ran models that simulated dam breaches for its reservoirs, and mapped those as well. This new flood elevation data is used for permitting to determine the minimum elevations that a structure must be protected to. By utilizing data that promotes sound development decisions and establishing strong zoning standards in high-risk areas, Rochester is protecting itself from expanded risk.

^{City of Rushford, 2007, with permission}

Overcoming Levee Issues in Rushford

Record flooding in the City of Rushford stands as a stark reminder that even with certified flood protection, catastrophic flooding can occur. Rainfall of historic proportion resulted in a 2007 flash flood event that exceeded the design parameters of the community’s federal flood control system. A flood that was estimated to approximate a 500-year (.02% chance) flood overtopped the Rushford levee, impacting nearly three quarters of the community of 1,700. Fewer than five flood insurance policies were in effect at the time. Since that time, the small idyllic community nestled in the bluff county of southeast Minnesota has methodically bolstered its existing flood control infrastructure and raised awareness about the residual risk of flooding, even with a sophisticated system in place to mitigate the effects of flooding. The city and state partnered to invest nearly $2 million for improvements to flood risk management. More property owners now carry flood insurance than before the 2007 flood.

"In 2007 the City experienced a traumatic flood event that affected every single one of the downtown businesses and approximately 75% of the residential properties in town. Receiving support from the DNR has allowed the City to rebuild and upgrade components of our levee system that has helped to restore a sense of security and safety for our community members. Seeing the benefits of the mitigation efforts funded by the DNR, the City also increased our financial commitment to plan for ongoing and future protective measures. These combined efforts have assured that both residential growth and business economic development will continue to improve and help insure the vitality of our community." Kathy Zacher, Rushford City Clerk

^{City of Austin floodwall incorporates landscape elements to promote the use of their protected open space.}

Acquisitions and Flood Control Projects in Austin

The City of Austin in southeast Minnesota has long struggled with repeated flash flooding from rivers and creeks that converge at the city. The Cedar River, along with Dobbins and Turtle Creeks have frequently overtopped their banks and caused extensive damage to homes, businesses, and public infrastructure. Eight of the highest 15 crests on the Cedar River have occurred since 2000. Since 2002, Austin has been implementing a community–wide flood risk reduction plan that includes acquisition and removal of at-risk structures, construction of levees and floodwalls, road raises, and installation of pumping stations. To date, nearly 275 homes and businesses have been acquired by the city and removed from the floodplain. Unlike most communities in the state, Austin uses a local option sales tax to generate a portion of its local share of flood mitigation projects. Its largest and most comprehensive flood risk reduction project to date, the $15 million North Main Flood Control project, was completed in 2018. The DNR’s Flood Hazard Mitigation Grant Assistance Program provided 50% cost share assistance to this important local project. With the state’s financial assistance, Austin continues to implement additional phases of its flood risk reduction plan in the Cedar River and Dobbins and Turtle Creek watersheds as funding allows. These efforts include the acquisition and removal of structures from voluntary sellers remaining in the floodplain.

"In the overnight of Wednesday September 21st and into the early morning of Thursday September 22nd the City of Austin received 5” of rain locally and greater amounts west and north of the city. Turtle Creek crested on Thursday afternoon at 13.6 ft, ranking 3rd among historical crests and the Cedar River crested on Friday at 19.8 ft ranking 7th among historical crests. We had only 5 properties that were impacted by floodwater, all of which have previously had discussions about acquisition, but were never able to come to an agreement. The limited impact to structures is an example of the success that we have seen as a result of our property acquisition efforts.

As part of our flood protection measures on North Main Street we installed stop logs at two locations where walkways pass through the floodwall. In addition we closed sluice gates, mobilized portable pumps and cycled the flood pump lift stations to evacuate water from the “dry side” of the levee/floodwall. The levee and floodwall functioned as designed. It provided a level of security for the businesses in the North Main area, eliminated the need to sand bag and allowed them to continue business operations. I would estimate an event of this magnitude in the past would have caused 6”-1’ of water to flow down Main Street, impacting traffic and adjacent businesses. Overall I think that we faired very well as a community considering the amount of rain that fell in SE Minnesota and NE Iowa. Our slogan for the past 10 years has been “BY SPENDING TIME AND ENERGY TOWARD FLOOD MITIGATION TODAY, WE CAN LESSEN THE COSTS OF DISASTERS TO OUR COMMUNITY TOMORROW." Steven Lang, Austin City Engineer

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Multi-Purpose Impoundment in the Middle-Snake-Tamarac River Watershed District

The Agassiz Valley Multi-Purpose Impoundment Project in Polk and Marshall Counties is a four-square mile flood risk reduction project that incorporated significant natural resource enhancement features in to its design and operation. This project provides peak flow reduction to the downstream community of Warren on the Snake River, as well as substantial habitat and water quality benefits for the surrounding area. The former agricultural property now includes wetland, prairie and woodland habitats that provide recreational, educational, and water quality benefits in addition to the flood risk reduction features. Because of the inclusion of these natural resource enhancements in the project design, the DNR’s Flood Hazard Mitigation Grant Assistance Program provided 75% of the $10.8 million project cost .