Flooding is defined as the accumulation of water within a water body and the overflow of excess water onto adjacent floodplain lands. The floodplain is the land adjoining the channel, river, stream, lake, or other water body that is susceptible to flooding. The majority of areas of flooding have been identified by FEMA and mapped for floodplain management. River flooding occurs when the water over tops the stream banks and encroaches into the floodplain. Flooding in rivers and streams generally result from a combination of deep, late-winter snow pack, frozen soil that prevents infiltration, rapid snow melt, and heavy widespread precipitation.
Flash flood is a term widely used by flood experts and the general population. However, there is no single definition or method to distinguish flash flooding for river and other floods. For the purpose of this plan, we will define flash flooding as flooding that occurs due to localized drainage and is outside the boundaries of the Flood Insurance Rate Maps (FIRM) floodplain. Flash floods result form powerful, concentrated, slow-moving thunderstorms. The effect of a flash flood is often greater in areas with inadequate storm sewers and storm drainage systems.
The 100 year floodplain is a misleading term. It identifies areas that have a 1 % chance of occurring annually. These areas may be flooded more than once every 100 years. These Special Flood Hazard Areas (SFHA) are mapped by FEMA and the Minnesota Department of Resources through the National Flood Insurance Program (NFIP). FIRM are used to determine what areas need flood insurance and are on file with the Wadena County Emergency Management Director.
Slow Rising Lakes
A type of flood that is less frequent in Wadena County but has the potential to cause significant localized damage, is slow rising lake levels. Above average precipitation over a long term period will increase the risk of potential lake flooding, especially in land locked basins with poor lake outlet.
The list of Federally declared disasters, input form the Planning Committee, and the Storm Events Database were utilized to profile the history of flood events in Wadena County. Flooding and heavy rain have both been know to cause road damage. Floodwaters that cover the surface of the road often cause the base of the road to wash away and the surface asphalt to crack and fail. This failure to roads can lead to utility damage.
Major flooding in Minnesota took place in 1950, 1965, 1968, 1972, 1987, 1993, and 1997. These floods are considered among the most severe in Minnesota's history in terms of stream flow magnitude, extent of lands inundated, loss of life, and property damage.
Though Wadena County has several rivers, the history of flooding in the county is minimal. Due to river characteristics, soil type, land use, etc. overland flooding in Wadena County has little damage effect on property. The following is a synopsis of potential impacts on the communities of Wadena County:
Aldrich – The Partridge runs through the city. Due to the high banks only one business, a restaurant/bar, in the city face the risks potential of flooding. This business has flooded in the past.
Menahga – The Blueberry River flows through the North part of the city. Table 3-5 identifies a 1905 Menahga flood. In 1997 the river was over its banks but did no damage.
Nimrod – The Crow Wing River flows through the center of the city. A potential exists in spring if ice backs up. No history can be found of this occurring.
Sebeka – The Red Eye River that flows through the city caused concern in 1997 when it spilled over its banks and into the city park.
Staples – No part of the Wadena County portion of Staples is near a river. No history can be found of any flooding in this area of the city.
Verndale – The Wing River flows about three miles northwest of the city. Verndale sits on high ground and has little flood threat.
Wadena – The Leaf River that flows on the North edge of the city has gone over its banks and over Trunk Highway 71 in the past. There is a remote chance of flooding on the city’s fringes.
The area known as Wahoo Valley in Bullard Township has had a history of flooding. A restaurant/bar located on the low banks of the Crow Wing River has flooded in the past due to ice backing up behind the bridge downstream. Thomastown Township has numerous isolated homes that are right along the river. These homes have been threatened in the past.