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• Anoka County Multi- Jurisdictional All Hazards Mitigation Plan Flooding tends to occur in Minnesota during anomalous years of prolonged, regional rainfall (such as an El -Nino year) and excessive snowfall, and is typified by increased humidity and high spring /summer temperatures. Flash flooding is a critical natural hazard caused by too much rain falling and /or snow melt in a short time, often a result of thunderstorms or the remnants of a tropical storm. Several factors contribute to flash flooding: rainfall intensity and duration, topography, soil conditions, and ground cover. Most flash flooding is caused by slow - moving thunderstorms, repeatedly moving over the same area, or by multiple storm cells colliding. Flash flooding can occur within a few minutes of excessive rainfall or from a quick release from a dam or levee failure. Thunderstorms produce flash flooding, often far from the actual storm, and water may rise at night when natural warnings may not be noticed. Normal Annual Precipitation (1961 - 1990) 34 32 30 28 26 24 22 20 18 16 (inches) The 1997 spring flooding along the upper Minnesota River, Red River, Mississippi River and Rum River broke most existing flood records in Minnesota. The Federal Emergency Management Agency's (FEMA) estimate of public infrastructure damage in Minnesota from the flood was approximately $300 million. Before the water receded, 58 of Minnesota's 87 counties were declared federal disaster areas. The American Red Cross reported that the massive floods affected 23,263 families. Total flood damages and associated economic impacts were estimated to be as high as $2 billion. The City of Anoka, which is located along the lower Rum River and Mississippi River was impacted to the extent that residents were evacuated, city streets closed, and septic and drain fields failed. Clean up was extensive in removing sandbags and debris. For Ramsey, Fridley and Anoka the likelihood of occurrence is moderate but the impact is considered high. Columbia Heights also experienced flooding citywide in 1997, with street flooding and flooding of structures in low areas. The likelihood of occurrence is considered moderate. Loss impact of future occurrence is less likely due to mitigation projects to correct flooding problems although the impact will continue to be moderate. In April of 2001 heavy snowfall during winter remained on the ground through the end of March and then rapidly melted, resulting in river stages close to record levels. Numerous roads and bridges were closed and thousands of sandbags used. Coon Rapids located along the east bank of the Mississippi River experienced flooding from the Mississippi River in April of 1965, 1997 and 2001. All three years were the result of heavy spring rains combined with heavy winter snowfall amounts in the Mississippi River drainage areas. The southwest corner of the city requires sandbagging for approximately 25 homes. Additional sandbagging is necessary for an additional 12 properties in the northwest corner of the city. The river overflowing its banks threatens homes and property, utilities, and back - flooding of sanitary