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<br />Procedures for rip rap and channel design have been developed using <br />theoretical concepts to define the magnitude of hydraulic stress (force) in the <br />boundary zone at which movement of individual stones becomes imminent. These <br />procedures were then empirically confirmed or extended to prototype conditions <br />on the basis of laboratory flume study data. REC-lS swmnarizes the status of <br />some of these procedures and indicates that very few actual data points are <br />available for the study of flow at bends. Although the lack of actual data was <br />noted in reference to estimation of stresses at channel bends, it applies to <br />many of the other procedures for designing bank protection, A similar observa- <br />tion was also made in a report, "Practical Riprap Design," by Maynord (1978). <br /> <br /> <br />It was determined that the best approach for evaluating the various rip rap <br />design procedures would be to utilize prototype data. Three sources of data <br />were used: (1) Field surveys made specifically for this project, (2) the ongoing <br />U.S. Geological Survey stream-gaging program, and (3) reports that include <br />detailed tabulations of hydraulic and channel data, Field surveys for this <br />project were made at 26 sites in Washington, Arizona, Oregon, California, and <br />Nevada. Many of the sites, referred to as pilot study sites, were selected <br />because rock riprap had been installed. Data obtained as part of the stream- <br />gaging program generally were from sites without riprap but were selected to <br />provide flow and channel data. <br /> <br />REVIEW OF RIPRAP DESIGN TECHNOLOGY <br /> <br />A number of approaches have been developed to relate the magnitude and <br />direction of forces acting on the boundary of a channel with the passive forces <br />that tend to prevent erosion of the boundary material. These approaches can be <br />categorized as follows: <br /> <br />o Relationship of permissible velocity to particle size for cohesive and <br />noncohesive soils lining the channel (REC-ll, Cal-B&SP, EM-1601, Man-54, <br />USBR-EM-2S) . <br /> <br />o Relationship of permissible velocity to grasses or other channel linings <br />(REC-IS) . <br /> <br />o Relationship of boundary shear to the size of particles that comprise the <br />channel boundary (REC-IS, EM-1601, Simons-STT). <br /> <br />All of these approaches assume uniform and subcritical flow conditions in <br />the reach, although the procedures in EM-1601 consider supercritical flow also. <br />The channel shape is usually assumed to be trapezoidal with a constant cross <br />section and bed slope. <br /> <br />4 <br />