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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />�,, Hazard Assessment: FLOODING, RIVER <br />4.2.2.1. Definition <br />River flooding occurs when river levels rise and overflow <br />their banks or the edges of their main channel and inundate <br />areas that are normally dry. River flooding can occur from <br />both high precipitation weather events and/or ice/snow <br />melt in the spring. The amount of flooding is usually a <br />function of the amount of precipitation in an area, the <br />amount of time it takes for rainfall to accumulate, previous <br />saturation of local soils, and the terrain around the river <br />system, dam failures, rapid snowmelt, and ice jams. Over <br />750 of Presidential Disaster Declarations result from <br />flooding. <br />River flooding is classified as Action, Minor, Moderate, or Major based on water height and impacts along <br />the river that have been coordinated with the National Weather Service. Action means the National <br />Weather Service, or a customer/partner, needs to take mitigation action in preparation for potential river <br />flooding. Minor river flooding means that low-lying areas adjacent to the stream or river, mainly rural <br />areas and farmland and secondary roadways near the river flood. Moderate flooding means water levels <br />rise high enough to impact homes and businesses near the river and some evacuations may be needed. <br />Larger roads and highways may also be impacted. Major flooding means that extensive rural and/or urban <br />flooding is expected. Towns may become isolated and major traffic routes may be flooded. <br />4.2.2.2. Range of Magnitude <br />• United States <br />o Most destructive flood: Mississippi River, 1927 (500 killed; 600,000 homeless) <br />o Costliest Flood: Great Mississippi & Missouri River Flood of 1993 ($30.2 billion) <br />• Minnesota <br />o Most destructive flood: 1997 Red River Flood (58 of 87 counties in Minnesota Federally <br />Declared Disasters) <br />o MN costliest flood: 1997 Red River Flood ($2 billion) <br />4.2.2.3. Spectrum of Consequences B2b <br />River flooding can affect both people and property. Losses in both wildlife and livestock can also occur, <br />which can drastically affect the economy. In addition, road washouts, power and water outages can also <br />be common with river flooding. <br />4.2.2.4. Potential for Cascading Effects <br />There is high potential for cascading consequences from river flooding. Depending on severity, there could <br />be public health sanitation problems, landslides, food spoilage and food production shortages from <br />farmland being underwater. <br />39 <br />