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<br />I. <br /> <br />. <br /> <br />, <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Appendix A - CCMPARISON OF METHODS <br />FOR DETERMIlfINO STONE SIZE <br /> <br />The procedure tor determining stone size given in section 2.1.1 of <br />this circular is referred to in this appendix as the Bureau ot Public <br />Roads method for identification purposes only. It is essentially the pro- <br />cedure given in reference 4 with emphasis on gradation of stone as learned <br />from the experiments described in reference 5. EDInons and Meyer, in their <br />discussion of the ASCE paper (4) OIl slope protection methods, stated that <br />TVA had used the procedures described since 1940. <br /> <br />To show the variability in riprap sizes as determined from several <br />procedures in CClalOn use, figure 9 has been plotted. Figure 9 shows the <br />size of stone required to resist displacement for various velocities as <br />determined by (1) the California Division of Highways method (6, p. 112); <br />(2) the Bureau ot Public Roads method (described in this circular); <br />(3) the Bureau of Rec1_tion method (20, p. 207-217); (4) and (5) the <br />Corps of Engineers method (21, p. 72).-A research report (22) by the <br />Waterways Experiment StaUoo presents a rational approach for the hydraulic <br />design of riprap and presents curves that range frClll about one grid to the <br />left of curve 1 (in figure 9) for channels with quarrystone to about one <br />grid to the right of curve 4 for small turbulent stilling basins. <br /> <br />The curves of figure 9 are not directly comparable to each other <br />because the size of stone given refers to a different "percentage finer <br />tIIan" on the gradatiOll curve. The curves for the California method and <br />the BPR method have been cOlllPl1ted for a 2: 1 slope, but the slope is not <br />given as a factor in the Corps of Engineers curves or in the Bureau of <br />Rec1amaticm curve. <br /> <br />The Bureau of Reclamation stone sizes are for use downstream trom <br />stillill8 basins. The Corps of Engineers (21) has two curves, No.4 .for <br />direct attack and for use downstreu trom hydraulic structures where tur- <br />bulence is high and 50. 5 tor protecting straight channels. In the <br />California method, protectiOll from direct attack is accomplished by <br />doubling the velocity used to select stone size tor straight channels. <br />This in effect moves the curve to the right of the "turbulent flow" curve <br />at the Corps ot Engineers. The Bureau of Public Roads method recommends <br />.w.tip1ying the velocity against the stone (Vs) by a tactor between 1 and <br />2 before selecting stone size for protection from direct impingeDlnt. It <br />also recOlllllenda using the mean velocity (Vm) rather tIIan the velocity <br />against the stone in dete1'lllining stone size to be used illlllediate1y down- <br />stream trom a culvert or an energy dissipator. <br /> <br />The thickness of the stone blanket is given as (1) suffie1ent tor two <br />layers of overlapping stone by California; (2) equal to the equivalent <br />diameter at the maximum size stone by the Bureau at Public Roads; (3) 1.5 <br />times the max1mulll stone size by the Bureau of Reclamation; (4) and (5) equal <br />to the longest dimension ot the me.x1mulll size stone required by the Corps of <br />Engineers. <br /> <br />All methods spee1fy a filter blanket when needed to prevent the bank <br />material tram filtering through the riprap cover, although the criteria for <br />designill8 the filter blanket differ. <br /> <br />11-31 <br />