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Table 4. Measured sediment loads at gaging stations on Black Mesa, tributaries of the Colorado River, and for the Colorado River at Lee's Ferry and Grand Canyon, Arizona. Gaging station name 'Moenkopi Wash #\ 'Yellow Water Wash # 1 .Coal Mine Wash #1 'Red Peak Valley Wash .Coal Mine Wash #2 'Yellow Water Wash #2 'Moenkopi Wash #2 .Coal Mine Wash #3 tKanab Creek near Fredonia tparia River at Lees Ferry tMoenkopi Wash near Tuba City tLittle Colorado River near Cameron tColorOOo River at Lee's Ferry tColorado River near Grand Canyon Years of data (Water years) 1985-1997 1985-1997 1985-1997 1986-1997 1987-1997 1985-1997 \986-1997 1986,1997 1968,1973 1949-1976 1977-1979 1957-1970 1948-1962 1948-1962 Drainage area (km2) 29.2 52.2 77.\ 80.9 94.3 100 131 293 2,810 3,650 4,219 68,600 290,000 366,000 Sediment load (10. Mglyr) 0.0081 0.030 0.018 0.042 0.0099 0.015 0.052 0.172 0.809 3.0 0.65 9.2 65 84 Sediment yield' (Mg km-2y..-') 277 575 233 519 105 150 396 587 288 820 155 130 220 230 .Sediment data are unpublished ...alues from Peabody Coal Company. tSediment data are annual means for the waler years shown from the USGS ADAPS database. These values differ slightly from Andrews (1991). who used different years of record. #Sedimenl-yield calculation assumes no change in storage along the Colorado River. na, not applicable independent variables (fig. 7). The Flaxman (1972) equation overpredicts sediment yields for drainage areas < 10 krn2 and underpredicts substantially for larger drainages in comparison to the data regression equation and the Renard (1972) equation (fig. 7) 10' ~ ~ ,. .. > i E i '" 1 01 -0." 193 A '001, R2" 0.86 -----R.nard (1972) equetlon 108 . Flaxman (1972) ~u8110n 10' 10' 10' 10' 10' , O' 001 01 10 100 1,000 10,000 100,0 Dr811'18g8 Ar.. (kl'l"f) Figure 7. Estimates of streamflow sediment yield from the empirical equations of Renard (1972) and Flaxman (1972) and the data regression equation. The data regression equation and the Renard (1972) equation produce similar sediment yields when ungaged tributaries in Grand Canyon are grouped by sediment-yield reach (table 6). Using these equations (eqs. 3 and 4), we estimate that ungaged tributaries in Grand Canyon bring 2.65'106 Mg/yr of sediment to the Colorado River by streamflow (table 6). Reach A, from Glen Canyon Dam to Lee's Ferry, receives an estimated sediment input of 64,800 to 76,400 Mg/yr, and Reach B (Marble Canyon, from Lee's Ferry to the Little Colorado River), receives about 600,000 Mglyr (table 6). This combined annual sediment input by streamflow from reaches A and B is 20 percent of the annual sediment load delivered by the Paria River (table 4). Most of the sediment input by ungaged tributaries is in western Grand Canyon (Reaches F and G; table 6). We rejected other sediment-yield approaches, such as the Universal Soil Loss Equation (USLE; Wischmeier and Smith, 1978; Peterson and Swan, 1979), the CREAMS and WEPP models of the Agricultural Research Service (Knisel, 1980; Gilley and others, 1988), and the procedure STREAMFLOW SEDIMENT YIELD 13