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00631 . . Modelling of sand deposilion in Colorado River 373 . 100000 i 80 000 ~ ~ ~ 80 000 I ~ 40 000 ) 20000 Discharge (m3Ia), sand supply .. .. . 1270, low - - 1270, intermediate - 1270, high .....2830,low - - 2830, intermediate - 2830, high ...... .......... .." .,--~... "........... ---------.. , "" , .. ." ~~------------------- 00 t2 24 36 48 Time (hours) 80 72 Figure 14.9 Modelled change in sand volume as a function of time allocation C in lhe Above Lava Chuar reach. . bars migrated downstream, the sand deposits in A were restored slightly as sand was redeposited along the bank. Deposition occurred in all cases within C (Figures 14.5, 14.6 and 14.9), the most critical area for archaeological resources. The sand volume within C increased with higher sand concentration in the flow at 2830mJ/s during the first day (Figure 14.9). There was a rapid initial increase in sand volume, followed by a steady decline after about 12-14 hours. This pattern is related to the increase in sand flux that resulted from the erosion of the sand deposit in A, followed by partial erosion of the deposit in C after most of the sand in A had been evacuated. A similar pattern, but with a smaller amplitude, occurs for the intermediate sand supply. At 1270mJ/s, model results show volumes similar to the low and intermediate sand supplies, and the largest sand volume coincided with the high sand supply. At 2830mJjs, more sand was deposited within the embayment and to a higher elevation, although backwaters i remained in the emhayment. i , 14.6,2 Palisades reacb 14.6,2.1 1lfitiQ/ COllllilioll The Palisades reach has a simpler form than the Above Lava Chuar reach, with a recirculation zone (G) on river lell downstream from the rapid that forms the reach inlet (Figures 14.IOa and 14.lla). The channel expands (H) downstream from the recirculation zone. A cobble bar is located midway in the channel adjacent to H . it 't: "'Y ~~ -~ l