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9 --- Existing Construction - For the purposes of flood plain management regulations requirements, existing construction means those structures in existence or on which con- struction or substantial improvement was started prior to the effective date of a flood plain management regulation adopted by a COn1munity. "Existing construction" may also be referred to as "existing structures." Equal Degree of Encroachment - A rule, used in determining permissible flood plain encroachments, that the flood plain on each side of a stream must be capable of conveying a proportionate share of the design flood flow, Flash Flood - A flood that reaches its peak flow in a short length of time (hours or minutes) after the storm or other event causing it. Often characterized by high velocity flows, First Floor - The floor which is level with of immediately above the main point of entry into the building. For residences, it is addition"lly that floor which comprises the main living area of the dwelling. Flood or Flooding - Temporary inundation of normally dry land areas from the overflow from the unusual and rapid accumulation or runoff of surface waters from any source. The rise in water may be caused by excessive rainfall, snowmelt, natural stream blockages, wind storms over a lake or any combination of such conditions, Flood Control - Keeping flood waters away from specific developments and/or populated areas by the construction of flood storage reservoirs, channel alterations, dikes and levees, bypass channels, or other engineering works. Flood Crest - The maximum stage or elevation reached or expected to be reached by the waters of a specific flood at a given location. Flood Duration - The length of time a stream is above flood stage or overflowing its banks, Flood Fighting - Actions taken immediately before or during a flood to protect human life and to reduce flood damages such as evacuation, emergency sandbagging and diking, and provision of assistance to flood victims, Flood Forecasting - The process of predicting thE' occurrence, magnitude and duration of an imminent flood through meteorological and hydrological observations and analysis. Flood Frequency - A statistical expression of the average time period between floods equaling or exceeding a given magnitude. For example, a 1 DO-year flood has a magnitude expected to be equaled or exceeded on the average of once every hundred years; such a flood has a one-percent chance of being equaled or exceeded in any given year. Often used interchangeably with "recurrence interval." Flood Fringe - The portion of the flood plain outside of the floodway but still subject to flooding. Sometimes referred to as "floodway fringe". Also used to refer to areas subject to flooding by water with velocities less than the floodway area. Flood Hazard Areas - The lands adjoining the channel of a river, stream or watercourse which would be covered by flood water during the regulatory flood. These areas embrace those lands frequently designated as floodway and flood fringe or flood plain districts on the offi- cial zoning map of the municipality. Flood Hazard Boundary Map - An official map of a community issued by the Federal Insurance Administration on which the boundaries of the flood plain (I.e" subject to the 1 DO-year flood), mudslide and/or flood- related emsion areas having special hazards have been drawn.