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<br />The single channel analysis .ra.s supplemented with a multi- <br />channel method using normal flow depth calculations. To account <br />for multiple, braided channels 011 the lower portion of fans, <br />Edwards and Thielmann modified FEM.A' s procedure to incorporate a <br />normal depth calculation defined by J~anning's equation. Given the <br />correct choice of a Manning's n roughness value, this method more <br />closely predicts observed channel ,ddt:h CDMA, 1985). <br /> <br />Examples of the FEMA I s single channel and multi-channel <br />application to Hiko Springs Wash near Laughlin, Nevada are shown in <br />Figs. 3 and 4, respectively. As complicated as the single channel <br />procedure appears, only several dif;charges and their associated <br />return periods are required to predi,::t the flow depth and velocity <br />boundaries on the fan. After computing the fan arc widths, the <br />various depth and velocity boundaries can be located on a map <br />taking into consideration any topographical constraints which would <br />limit the fan arc width. In Figs. 3 and 4 the fan arc width <br />(indicated simply as 'width') is limited by the wash walls, <br />extending the depth and velocity boundaries farther downstream than <br />would be predicted if the flow was unconfined. <br /> <br />~1 ~LOV DIRECTION <br /> <br /> <br />20FT <br />~ 8 FPS <br />~ 8000 FT.I <br /> <br />'" <br /> <br />,0 <br /> <br /> <br />FIGURE 3 <br /> <br />FLOW HYDRAULICS COMPUTED BY <br />FE\IA SINGLE CHANNEL METHOD <br /> <br />HIKO SPRINGS WASH NEAR <br />LAGGHLIN, NV <br /> <br />,if> <br /> <br />DEPTH ~ 2.5 FT, <br />VEL ~ 9 FPS <br /> <br />WIDTH? <br /> <br />CONTOl'R INTERVAL 20 FT <br /> <br />V DEPTH ~ 3.5 FT I <br />VEL. = 10 FPS <br /> <br />~ <br />--- <br />"'" <br /> <br />GRAPHIC SCALE <br />1200 0 6001200 2400 <br />~ <br /> <br />4800 <br /> <br />- <br /> <br />( DI n:n) <br /> <br />11 <br />