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<br />flow just upstream of the pier by including the Froude Number in <br />the equation. Chang (30) pointed out that Laursen's (8) 1960 <br />equation is essentially a special case of the CSU equation with <br />the Fr = 0,4 (see Figure 4,6), <br /> <br />The equations illustrated in Figures 4.4, 4.5 and 4.6 do not take <br />into account the possibility that larger sizes in the bed <br />material could armor the scour hole. That is, the large sizes in <br />the bed material will at some depth of scour limit the scour <br />depth. Raudkivi and others (8,9,10,11,12) developed equations <br />which take into consideration large particles in the bed. The <br />significance of armoring the scour hole over a long time frame <br />and over many floods is not known. THEREFORE, THESE EQUATIONS <br />ARE NOT RECOMMENDED FOR USE AT THIS TIME. <br /> <br />FOR THE DETERMINATION OF PIER SCOUR, THE CSU EQUATION IS <br />RECOMMENDED FOR BOTH LIVE-BED AND CLEAR-WATER SCOUR. The equation <br />predicts equilibrium scour depths. In the unusual situation <br />where a dune bed configuration exists at a site during flood <br />flow, the maximum scour will be 30 percent greater than the <br />predicted equation value, For the plane bed configuration, which <br />is typical of most bridge sites for the flood frequencies <br />employed with scour, the maximum scour way be 10 percent greater <br />than computed with CSU's equation. <br /> <br />With a dune bed configuration the equation predicts equilibrium <br />scour depths and maximum scour will be 30 percent greater. For <br />flow with a plane bed configuration or antidunes, depths computed <br />with CSU's equation should be increased by 10 percent, <br /> <br />49 <br />