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<br />1 <br /> <br />NAU Sand Bar Studies <br /> <br />Final Report <br /> <br />1. <br /> <br />104 <br /> <br /> <br />/ <br />,I <br /> <br />102 <br /> <br />-100 <br />E <br /> <br />Reattachment Bar <br /> <br />--1274m3/s-----------------------= <br />I ..._____________; _ ____ <br />--878m3" -----/'-- ,,11iP' <br />/ dl:(l[W'/ <br />--s66m3/s---- . ..t <br /> <br /> <br />~ <br /> <br />c: <br />,!;! 98 <br />.. <br />> <br />.!!! <br />UJ 96 <br /> <br />94 <br /> <br /> <br />. Deposition <br />umm Erosion <br /> <br />02/16/96 <br />-------------" 0"/17/96 <br />------- 08/26/97 <br />................-.......... 11/08/97 <br />---------- 04/16/98 <br /> <br />>. <br />I:~ <br /> <br />92 <br />150 <br /> <br />140 <br /> <br />130 <br /> <br />120 <br /> <br />110 <br /> <br />100 <br /> <br />90 <br /> <br />, <br />Ii <br />" <br />.:'1 <br />f-I <br />'., <br /> <br />Distance From Right Bank (m) <br /> <br />I <br /> <br />. <br />t <br />., <br /> <br />Figure 8. Selected cross section of the high-elevation part of the sand bar at site #30 in upper Marble <br />Canyon, Elevation datum is arbitrary, Flow stage elevations for high-elevation (566 m3ts), the 1997 <br />Test Flow (878 m3ts), and the 1996 Controlled Flood (1,274 m3ts) are shown, Erosion and deposition <br />as a result of the 1996 Controlled Flood and the 1997 Test Flow are depicted, Location is shown in <br />Fig, 1. <br /> <br />H <br />. <br />:-. <br /> <br />~ <br />~~; <br />" <br />if <br />~~ <br />;~ <br /> <br />concentrations in the main channel at the lower Marble Canyon gage (discussed earlier), suggests that <br />the stage change during the 1997 Test Flow was not high enough to redistribute sand to areas where <br />depositional sites were open, Hazel et ai, (1999) show that the stage elevations reached during the <br />1996 Controlled Flood inundated areas where space was available for deposition, termed <br />"accommodation space," and differences in depositional thickness were directly correlated with the <br />magnitude of stage change in Marble Canyon, The stage change during the 1997 Test Flow was <br />roughly half that of the 1996 Controlled Flood in Marble Canyon (Fig, 9). <br />Sediment deposited during the 1997 Test Flow was sampled vertically in trenches at 11 of the <br />study sites (Fig, 10), The new deposits were less than I m thick above the 566 m3/s stage elevation <br />and were typically composed of fine-grained climbing ripple stratification, The deposits lacked the <br />coarser-grained cross bedding that characterized the top portion of the 1996 Controlled Flood deposits <br />described by Rubin et ai, (1998), However, the same upward-coarsening trend described by Rubin et <br />ai, (1998) was observed (Topping et ai" 2000b). With the exception of one out of 11 sites, the mean <br />grain size increased upward by the same factor of two, from 0,015-0,15 mm at the base to 0,065-0.24 <br />mm at the top of the deposits, <br /> <br />~ <br />"f <br /> <br />i <br /> <br />; <br />" <br /> <br />~ <br />~ <br /> <br />~ :.:. <br /> <br />.. <br />., <br />~ <br />~, <br />Ii <br />,:1 <br />;0:. <br />':';.,- <br /> <br />/1' <br />"0'1 <br /> <br />,I <br />I <br />1 <br /> <br />25 <br />