These floods convinced County officials of the need for flood insurance to protect people living in flood prone areas and that managing the floodplain is an absolute necessity. Late fall and early spring floods caused by supercell thunderstorms are common in the Polk County area. Summer floods are uncommon events, except for those associated with hurricanes and tropical storms that may occur in summer and autumn. On the basis of present knowledge, the size, time and place of floods cannot be predicted more than a few hours in advance. Runoff from these intense rainfalls result in high flood waters that can destroy roads, bridges, homes, buildings and other community developments.
Discharges quickly reach a maximum and diminish almost as rapidly.
Flash floods are a potential source of destruction and a threat to public safety in areas where the terrain is steep or hilly, surface runoff rates are high, streams flow in narrow creek beds and gullies or severe thunderstorms stall over an area. Due to the rapid growth and development many areas in the county that have never experienced flooding and do not have a history of flooding are now experiencing flashflood problems. New housing projects, roads, commercial buildings and increased land usage, including clear cutting forestlands have substantially increased the potential for flooding. Few areas of the County are free from the effects of flashfloods, below is a listing of these areas. Riverine floods are caused by precipitation over large areas and differ from flash floods in their extent and duration.