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TOPPING ET AL: COLORADO RIVER SEDlMENI' TRANSPORT, 2 _1200 -!! 1. 1100 wl000 Cl !;:: 900 i3 800 !!l 700 c ffi 600 !;( 500 ;: 400 C) _1200 ;e 11100 wl000 If 900 < 5 800 (fJ 13 700 ffi 600 !;( 500 ;: 400 d) 'i;'200 11100 wl000 Cl ~ 900 ~ 800 is 700 ffi 600 !;( 500 ;: 400 e) ___ LEES FERRY -0- lOWEA MARBlE CANYON ............- GRAND CANYON ---<>-- ABOVE DlAMONO CREEK DAY 1 DAY 2 ___ LOWER MARBLE CANYON --0- ABOVE DIAMOND CREEK DAY 1 DAY 2 ___ LOWER MAABLE CANYON -G- ABOVE DlAMONO CREEK DAY 1 DAY 2 Figure 7, (continued) sediment data collected at the Grand Canyon, National Can- yon, and Above Diamond Creek gages during and after a large flood on the Little Colorado River in September-October 1983, (2) suspended- and bed-sediment data collected at the Lower Marble Canyon gage during a period of large Paria River and ungaged tributary floods in August-Seplember 1997, (3) bed-sediment data collected along the 100-km length of Marble Canyon 6 months before, immediately after, and 9 months after two large Paria River floods in September 1998. 5.1. Metbods: Collection and Processing of tbe 1983 Data As pan of the Bureau of Reclamation's "Glen Canyon En- vironmental Studies," the USGS Arizona District conducted an intensive sediment data collection program on the Colorado River and its major tributaries during July-December 1983 (Carrett el al., 1993J. This 1983 data collection period included a 300-m'/s (10,600 cfs) flood on the little Colorado River; high flows on the little Colorado River associated with this flood lasted from late September through early October (Figure lOa). These high flows were measured to have transponed approximately 1.0 ;: 0.2 million t of sand into Ihe Colorado River over 10 days. Following this event, no high flows oc- 55! 0.18 (fJ 0.17 Zi 0.16 ;R 0.15 l5 0.14 m 0.13 ~ 0.12 )> 0.11 15 0.10 0 " 0.09 0.06 3 0.07 .2. 0.6 o 8 0.5 0 ~ Z'" tllZ mm 0.4 0", '3gJ 3 - 0.3 - Iii z --I 0.2 ~ ~~ 6 mJl 5 ~~ 4 0'" 3 ~eJ ~~ 2 ..m 1 p~ o ~g -1 3 tll -2 3~ corred in the little Colorado River, and thus no substantial inputs of sand to the Colorado River occurred through the end of the December sampling period. During mid-September through December, flows in the Colorado River were quasi- steady, with dam releases decreasing over this period from 770 to 670 m'/s. The September-October high flows in the Little Colorado River had minimal impact on the flows in the Col- orado River and increased the discharge of water at the Grand Canyon gage for several days by about 12%. Prior to intelJlTeting suspended-sediment data, it is impor- tant to check the data for possible bed-sediment contamina- tion. Bed contamination of suspended-sediment samples (oc- curring when the nozzle of the sampler is dipped into the bed) is one of the largest sources of error in measuring suspended- sediment concentration !Allen and Peterson, 1981; D. J. Top- ping and R. S. Parker, unpublished data from the Colorado River near Cisco, Utah, 1995]. Contamination of suspended- sand samples with sand from the bed results in higher apparent suspended-sand concentrations and in a suspended-sand grain- size distribution that approaches that of the bed sand (D. J. Topping and R. S. Parker, unpublished data from the Colo- rado River near Cisco, Utah, 1995). Both suspended-sediment