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<br />... <br /> <br />182 Computational Fluid Dynamics <br /> <br /> 25000 <br /> 20 000 <br />~ <br />E. <br />~ 15000 <br />~ <br />~ <br />'" <br />8. 10000 <br />~ <br />"0 <br />~ 5000 <br /> 0 <br /> -5000 <br /> 0 <br /> <br />Discharge (m3/s). sand supply <br /> <br />1270, low <br />- - 1270, intermediate <br />- 1270.high <br />.....2830, low <br />- - 2830, intermediate <br />- 2830. high <br />- Zero line <br /> <br />. <br />I <br />I <br />I <br />I <br />i <br /> <br />30000 <br /> <br />36 <br />Time (hours) <br /> <br />Figu... 14.17 Modelled change in Sand deposit volume above the 708m"/s stage in the <br />Lower Tanner reach. <br /> <br /> <br />_._------~------- <br /> <br />...... <br />........ <br /> <br /> <br />....... - - - - - - - - - - - - <br />"Ua: - - - - . . . . . . .. . . . . . . . . . . . . <br />~~.................. <br />." <br /> <br />12 <br /> <br />24 <br /> <br />48 <br /> <br />60 <br /> <br />72 <br /> <br />. <br /> <br />14.6.4 Upper Unkar reach <br /> <br />14.6.4.1 l"iliai co"ditio". <br /> <br />The Upper Unkar reach (Figures 14.18a and 14.19a) is about 1.6-km long down the <br />channel centreline. A small recirculation zone is on river left near the reach inlet, and <br />a deep hole in the main channel typically associated with recirculation zones in the <br />upstream reaches is present here as well. The reach bends to the left and maintains a <br />more consistent channel width at higher flow than the other study reaches. The most <br />striking feature of this reach is the mid-channel bar that is inundated at higher flows. <br />but forms an island at most typical dam releases (below about 500mJis). This bar <br />was formed by a debris flow that spilled gravels into the reach that have been <br />reworked into the present configuration. At low flow, when the bar is an island, <br />most of the discharge occupies the left channel. <br />A -No Visitation" label in river guides of Grand Canyon (e.g. Stevens. 1990) <br />dramatically marks this reach as one of the most sensitive in Grand Canyon. The <br />part of the reach labelled' r on Figures 14.18 and 14.19 has been declared off limits <br />to the public by the National Park Service because of the abundance of artefacts at <br />that location. The gullies mapped by Hereford ,/01. (1991. 1993) also are located in <br />this area (Figures 14.18 and 14.19). <br /> <br />. <br />