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<br />Head Loss. The effect of obstructions, such as narrow bridge <br /> <br />openings or buildings that limit the area through which water <br /> <br /> <br />must flow, raising the aurface of the water upstream from the <br /> <br /> <br />obstruction. <br /> <br /> <br />Intermediate ReDional Flood. A flood having an average frequency <br /> <br /> <br />of occurrence in the order of once in 100 years although the flood <br /> <br /> <br />may occur in any year. It is based on statistical analyses of <br /> <br />streamflow records available for the watershed and analyses of <br /> <br />rainfall and runoff characteristics in the "general regi.on of the <br /> <br /> <br />watershed.11 <br /> <br /> <br />Left or Rieht Bank. The bank on the left or right side of a river, <br /> <br /> <br />stream, or watercourse, looking downstream. <br /> <br />Standard Pro iect Flood. The flood that may be expected from the <br /> <br /> <br />most severe combination of meteorological and hydrological con- <br /> <br /> <br />ditions that is considered reasonably characteristic of the geograph- <br /> <br /> <br />ical area in which the drainage basin is located, excluding extremely <br /> <br /> <br />rare combinations. Peak discharges for these floods are generally <br /> <br /> <br />about 4(1}1: to 6(1}1: of the probable Maximum Floods for the same <br /> <br /> <br />basins. Such floods, as used by the Corps of Engineers, are <br /> <br /> <br />intended as practicable expressions of the degree of protection <br /> <br />that should be sought in the design of flood control works, the <br /> <br /> <br />failure of which might be disastrous. <br /> <br /> <br />Underclearance. The lowest point of a bridge or other structure <br /> <br /> <br />over or across a river, stream, or watercourse that limits the <br /> <br />opening through which water flows. This is referred to as "low <br /> <br /> <br />steel" in some regions. <br /> <br />44 <br />