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A floodplain or flood plain or bottomlands [1] is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high discharge. [2] The soils usually consist of clays, silts, sands, and gravels deposited during floods. [3]
For example, a 10-year flood has a 1/10 = 0.1 or 10% chance of being exceeded in any one year and a 50-year flood has a 0.02 or 2% chance of being exceeded in any one year. This does not mean that a 100-year flood will happen regularly every 100 years, or only once in 100 years. Despite the connotations of the name "return period".
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 years. [ 2 ] Such maps are used in town planning , in the insurance industry, and by individuals who want to avoid moving into a home at risk of flooding or to know how to protect their property.
The county is currently using 500-year flood maps to indicate areas where residents should be ready to evacuate. "We are using the 500-year flood plain maps as kind-of a guide.
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]
Ten-year floods have a 10% chance of occurring in any given year (P e =0.10); 500-year have a 0.2% chance of occurring in any given year (P e =0.002); etc. The percent chance of an X-year flood occurring in a single year is 100/X. A similar analysis is commonly applied to coastal flooding or rainfall data.
A day after Hurricane Ian made landfall in southwest Florida as a Category 4 storm, Florida Gov. Ron DeSantis said Thursday that the storm surge that came with it was “basically a 500-year flood ...
The map to the right shows a flood map for the City of York, including the floodplain for a 1 in 100-year flood (dark blue), the predicted floodplain for a 1 in 1000 year flood (light blue) and low-lying areas in need of flood defence (purple). The most sustainable way of reducing risk is to prevent further development in flood-prone areas and ...