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FIRMs display areas that fall within the 100-year flood boundary. Areas that fall within the boundary are called special flood hazard areas (SFHAs) and they are further divided into insurance risk zones. The term 100-year flood indicates that the area has a one-percent chance of flooding in any given year, not that a flood will occur every 100 ...
For river systems, a 100-year flood is generally expressed as a flowrate. Based on the expected 100-year flood flow rate, the flood water level can be mapped as an area of inundation. The resulting floodplain map is referred to as the 100-year floodplain. Estimates of the 100-year flood flowrate and other streamflow statistics for any stream in ...
U.S. Gazetteer, TIGER/Line shapefiles, census data. National Historical Geographic Information System: NHGIS provides free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2012. Atlas of Historical County Boundaries Project (AHCBP)
Theoretically a 100-year flood has a 1 percent chance (1/100 = 0.01 or 1 percent) of occurring in any given year and a 500-year flood has as a 0.2 percent chance (1/500 = 0.002 or 0.2 percent) of occurring in any given year. [12] However, these expected flood elevations actually occur more or less often than expected. [13]
The deluge in South Florida was the latest instance after 1-in-1000 year rains also struck in areas including Dallas, St. Louis, eastern Kentucky and Yellowstone.
From August 23–28, 2017, Potential Tropical Cyclone Ten's precursor stalled over Florida, causing the worst flooding the state had seen in at least 20 years. Fort Myers and other areas in southwestern Florida were the hardest-hit, forcing the evacuation of more than 200 people.
Peak discharges along the Flint and Ocmulgee rivers exceeded 100-year flood levels. [18] At least 100 dams and recreational watersheds suffered severe damage or were destroyed. Many roads were inundated, forcing the closure of 175 roads and 1,000 bridges. [18] [19] Damage to highway infrastructure exceeded $130 million. [18]
Milton, the third hurricane to hit Florida this year, dumped about 16 inches of rain on St. Petersburg, a more than a 1-in-1000 year rainfall event for the area, according to the National ...