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GLOSSARY OF TERMS Flood St~qe. The stage or elevation at which overflow of the natural banks of a stream o~ body of wate~ begins in the reach or area in whiCh the elevation is measured. Low Steel Or Underclearance. The lowest point of a bridge or other structure over or aCrOsS a river, stream, or watercourse that limits the opening through which water flows. lO-year Flood. A flood having a ten percent chance of being equaled or ~ceeded in anyone year period at a designated location. 50-year Flood. A flood having a two peZ'(:ent chance of being equaled or exceeded in anyone year period at a designated location. lOa-year Flood. A flood having a one percent chance of being equaled or exceeded in anyone year at a designated location. It has an average frequency of occurrence in the order of once in 100 years, although the flood may occur in any year and possibly in successive years. In the past, this flood was r..ferred to as the Intermediate Regional FlOOd. SOO-year Flood. A flood having a 0.2 percent chance of being equaled or exceeded in anyone year at a designated location. It may be expected tooccw: f:rom the most severe oombination of meteor- ologio"l and hydrologic~l conditiono that is con~idered reasonably characteristic of the g~r"vhical area in which the draina9~ ba~in i~ located. It represents the reasonable upper limits of expected flooding. Flood. An overflow of lands not normally covered by ~ater, that are used or usable by man. Floods have two essential characteristics: the inundation of land is temporaryt and the land is adjacent to and inundated by overflo~ trom a river or stream, or an ocean, lake, or other body of standing ~ater. Normally. a "flood" is considered as any temporary rise in streamflow or stage. but not the pending of surface water, that results in significant adverse effects in the vicinity. Adverse "ffects may include damages from overflow of land areas, temporary backwater effects in sewers and local drainage channels, creation of unsanitary conditions or other unfavorable situations by deposi- tion of materials in stream channels during flood recessions, rise of ground water coincident with increaaed streamflow. and other probleme. Flood Crest. The maximum etage or elevation reachod by th~ water" of a flood at a given location. Flood Peak. The maximum instantaneous discharge of a flood at a given location. It usually QCcur$ et ~r near the timP. of the flood crest. Flood plain. The relatively flat area or lowlands adjoining the channel of a river, stream or watercourse, Or ocean, lake, or other body of standing water, whiCh has been or m.ay be covered by floodwater. Flood Profile. A graph showing the relationship of water surface elevation to location, the latter generally expressed as distance above mouth for a etraarn of water flowing in an open channel. It io generally drawn to ahow aurtace elevation for the erout of a apecifie flood, but may b. prepared for eo,~itionH Bt " given tim~ orstaqe. " "