<br />
<br />respect[vely. The flood may occur In any year.
<br />stat[stlcal analyses of streamflow records and
<br />fall and runoff characterlst[cs In the general
<br />watershed.
<br />
<br />It Is based on
<br />analyses of raln-
<br />region of the
<br />
<br />Sheet Flow
<br />The water,whlch Is diverted from the,ma[n floodflow by
<br />obstructions and variances In topography. This water flows at
<br />shallow depths and normally at elevations different from the water
<br />flowing In the adjacent channel or on the adjacent flood pla[n.
<br />Due to the shallow depths and Irregular flow patterns associated
<br />with this type of flow, computations to predict flow depth are
<br />considered Impractical.
<br />
<br />,
<br />
<br />Standard Project Flood <S.P.F.)
<br />The flood that may be expected from the mqst severe com-
<br />b[natlon of meteorolog[cal and hydrological conditions that are
<br />considered reasonably characteristic of the geographical area In
<br />which the drainage basin [s located, excluding extremely rare com-
<br />binations. Peak discharges for these floods are generally about
<br />40 percent to 60 percent of the Probable Maximum Floods for the
<br />same basins. Such floods, as used by the Corps of Engineers, are
<br />Intended as practicable expressions of the degree of protection
<br />that should be sought In the design of flood control works, the
<br />failure of which might be disastrous.
<br />
<br />Top of Waterway
<br />This Is the roof of the opening [n a stream crossing
<br />through which water flows under normal conditions. It Is the
<br />underside of the deck span - sometimes called "low steel", the
<br />roof of a box culvert, or the crown of an arched or circular
<br />culvert.
<br />
<br />28
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