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Flooding is a natural occurrence of a river’s riparian zone and provides many benefits including groundwater recharge, settling out sediment and supporting valuable wildlife habitat. A flood occurs when a waterbody like the Minnesota River receives a greater volume of water than it can handle, either at spring snowmelt or during a heavy rainstorm. Flooding only becomes a concern to humans when they impact the river’s floodplain either by adding structures or planting crops. Humans have added to flooding problems primarily by intruding on the natural floodplain, but also by increasing the amount of impervious surface on the terrain and by displacing other natural storage on the landscape.
What Increases the Flooding Risk?
• Removal of stabilizing vegetation around stream banks and rivers
• Erecting structures that deflect or inhibit the flow of floodwaters
• Constructing bridges, culverts, buildings, and other structures that encroach on the floodplain.
• Drainage systems that funnel stormwater quickly into a receiving body of water like the MN River.
• Straightening meandering watercourses to hasten drainage.
• Filling and dumping of debris in floodplains.
Situated on a convex alluvial fan of the Little Minnesota River that drops rapidly some 780 vertical feet as it flows out of the Coteau des Prairies, the city of Browns Valley has dealt with major flooding issues since it was established in 1866. Most recently on March 4, 2007, the town was overwhelmed by intense and disasterous flooding when rapidly melting snow and ice jams forced the evacuation of about 100 people. The Little Minnesota River alluvial fan has partially filled the Glacial River Warren spillway in which it is located to form a very unique and dynamic quasi Continental Divide between the Red River and the Minnesota River basins.
The convex form of the still actively forming alluvial fan and subsequent continental divide may distribute discharge from the Little Minnesota River north, east and south as different times or at the same time depending on the amount of discharge and the distributary nature of the stream channel at a particular point in time.
One of two cities with development on both sides of the Minnesota River, Granite Falls has been hit hard by flooding including 1997 (11.3 feet above flood stage) and 2001 (7.3 feet) with considerable damage to both residential and commercial buildings. To mitigate some of the flooding problems, the city has built a retaining wall and incorporated it with buildings located along the river, relocated other businesses and homes and put in additional flood prevention measures. In the near future, city officials hope to improve the levee, relocate City Hall and build a new water treatment plant out of the floodplain.
Major Floods 1881-2009: Historical Crests at Minnesota River USGS Gaging Site at Mankato
Mankato & North Mankato
Construction of a Flood Control System by the U.S. Corps of Engineers after the devastating 1965 flood has spared Mankato and North Mankato from any serious flooding since that time. Mankato is located at the confluence of the Blue Earth and Minnesota rivers. A doubling of water flow caused wide-spread flooding in 1881, 1908, 1916 and 1951 before the final major flood event in 1965. Today, both cities are protected by a flood wall levee system started in 1959 and finished thirty years later on each side of the Minnesota River along with sluice gates, additional gates and values, large pumps and pumping stations. Mankato and North Mankato have begun to make strides to make the Minnesota River a community asset. See historic flood photos in the Mankato region.
One of the historically significant towns along the Minnesota River, Henderson has been able to protect itself from flooding problems and still maintain some of its connection to the river. The 1965 flood hit this small community hard with a crest of 31.4 feet (highest in history). Approximately 285 people were evacuated from 95 homes. A $2.4 million levee system was completed by the U.S. Corps of Engineers in 1990 surrounding the city on three sides. This 1.5 mile permanent levee protected Henderson during the 1993, 1997, and 2001 floods along the Minnesota River. Today, residents enjoy a walking trail on top of the levee providing a close-up view of the Minnesota River floodplain.
Learn more about River Trends: Minnesota River Basin Trends Report