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I 34 I Floodplain, An area in and adjacent to a stream, which area is subject to flooding as the result of the occurrence of a 100-year flood and which area thus is so adverse to past, current, or foreseeable con- struction or land use as to constitute a significant hazard to pub- lic health and safety or to property. I I Flood Profile. A graph showing the relationship of water surface eleva- tion to location, the latter generally expressed as distance above mouth for a stream of water flowing in an open channel, It is generally drawn to show surface elevation for the crest of a specific flood, but may be prepared for conditions at a given time or stage, I I Flood Stage, The stage or elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured, I Intermediate Regional Flood. A type of flood, including the water sur- face elevation and territorial occupation thereof, which can be expected to occur at any time in a given area based upon recorded historical precipitation and other valid data, but with an average statistical one percent change of being equalled or exceeded during anyone year, The term is used interchangeably with a one percent flood or 100-year flood (see definition for 100-year flood), II I I Left Bank. The bank on the left side of a river, stream or water course as the observer looks downstream. I Probability, The annual chance of occurrence of specific hydrologic events, such as rainfall over a specified area or peak discharge at a specified location expressed in percent, e.g., 5% representing one chance in 20 of the event occurring in any year or an average recurrence of once in 20 years. I Recurrence Interval. The average number of years within which a given flood event will be equalled or exceeded. I Reference Point. A numbered point identifying a specific location for correlating the data shown in various forms throughout the report, I Right Bank. The bank on the right side of a river, stream or water course, looking downstream. I Runoff, The quantity of rainfall which flows over the surface to enter the stream as discharge volume, The difference in quantity between rainfall and runoff represents losses to infiltration and intercep- tion, I I Stream, Any natural channel or depression through which water flows either continuously, intermittently or periodically, including any artificial modification of the natural channel or depression, I Watershed. The drainage area situated above a specified point on a stream including the area drained by tributary streams which enter the main stream above this point, I