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e <br />1. Divided Flow Problems: Braided streams with three or more <br />channels; island complex in larger streams. <br />2. Channels with unstable or rapidly changing channel geometry. <br />Fluid bed streams; irregular and rapidly varied cross sec- <br />tional configuration. <br />3. Large bed.element streams: Channels with large, irregularly <br />spaced roughness elements.. <br />Limitations-to hydraulic simulations are related either to the <br />number of cross sections needed to describe the reach, or to problems <br />with calibrating the modeT to fieTd data.. The latter problem is <br />associated primarily with the use of the Manning equation, while the <br />former affects both types of simulations discussed in this paper. <br />Aside from the problem of a rapidly growing population of tran- <br />sects simulation of complex channels by the rating curve approach is <br />not difficult and results are quite reliable. However, due to the <br />types of computations involved with Manning equation simulations, <br />coupled with the channel segmentation process used to describe the <br />velocity distributions, complex channels are difficult tQ model by this <br />method. <br />In complex channels, hydraulic controls may be difficult to identify <br />or be so numerous.that the field team spends most of its time surveying <br />` controls. A stream reach with a complex of hydraulic control's is shown <br />in Figure 20. <br />Figure 20. Strum reach with complex hydraulic controls. Controls <br />marked in white. Photo courtesy of Don Kelly, aquatic <br />biologist, Sacramento, CA. <br />? v