What is a Floodplain Map?
A floodplain map delineates the area that can be expected to flood, on average, once every 200 years. This is called the 200-year flood. A 200-year flood can occur at any time in any given year; the indicated flood level may be exceeded; and portions of the floodplain can flood more frequently.
Floodplain maps show the location of the normal channel of a water course, surrounding features or developments, ground elevation contours, flood levels and floodplain limits (the elevation and horizontal extent of the high water marks of a 200-year flood).
Within the floodplain, flood level isograms show the water elevation during a 200-year flood. (The maps may also include the 20-year flood level, which is used in applying Health Act requirements for septic tanks.) A flood level isogram is a line which spans the floodplain, plotting the location at which the floodwater is expected to reach the indicated elevation. The elevation of floodwater between each isogram can be interpolated.