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00(137 Modelling of sand deposition in Colo,ado River 387 . '00000 80 000 Discharge (m'lo). sand supply , . . . . 1270. low - - 1270, intermediate - 1270. high .....2830. W -.. 2830, intermediate -2830. high - Zero line ~ .s. ~ 60 000 g i ~ '" ~ 40 000 .--- .- ---- - .- --.. .......... ....- ...... - .. , ... ... ... ... r ..- I .. .. .. , ------------- --- ....................... ...... 20 000 o 38 Time (hool1) Fjgu~ 14.76 Modelled change in sand volume as a function of rime in rhe Lower Tanner reach. o 12 24 48 60 72 . the high sand supply, the maximum value was reached after about I day. In contrast to the smoothly increasing deposit volume at 1270mJ/s, sand deposits above the 708mJjs stage at 2830mJ/s accumulated in irregular temporal patterns. The initial deposition rate was highest with the high sand supply, but dropped off after about 6 hours to match the sand volume aCCUJDulated with the intermediate sand supply. With the low sand supply, an initial scouring was followed by a rapid increase in volume until about 12 hours, followed by a steady increase in sand volume over the rest of the simulation. A sand deposit on river left near the reach inlet was inundated at 2830mJjs and eroded at that discharge with all sand supplies. With the low sand supply, deposition elsewhere was initially insufficient to offset erosion at this location. Sand volume at 2830mJ/s with the low sand supply exceeded all the sand deposited at 1270 mJ Is after about 36 hours. The volume of deposits above the 708 mJ Is stage, which have the most potential ror preservation, is only about a third of the sand volume stored in the recirculation zone in the Above Lava Chuar reach (zone C) and the recirculation zone in the Palisades reach (zone 0). This relatively small volume reflects the absence of significant recirculation zones in this reach. The volume of sand with preservation POtential in this reach is small compared to that in the two upstream reaches, but there is some compensation in that these deposits are above typical dam-release stages. The recirculation deposits in the upstream reaches, although removed from . the main channel, are subject to {low-induced erosion, albeit at a rate much lower :...... than thar for main channel deposits. ,'. :;" .>;:t~ ;<~}: L" 1. r.'. ... . ( .