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<br />Table 8. Sediment rating curves lor Bright Angel Creek and at live gaging stations on Black Mesa, Arizona. <br /> <br /> Drainage <br /> Veers 01 dete area Maximum <br />Trlbutery (Weter y..rs) (km2) Coefficient a Exponent b R2 dlscherge (m3/s) <br />Bright Angel Creek 01991-1993 260.3 1.83 2.32 0.42 11.8 <br />Moenkopi Wash #1 11985-1997 29.2 2,540 1.52 0.80 65.1 <br />Yellow Water Wash #1 11985-1997 52.2 9,500 1.16 0.79 42.5 <br />Coal Mine Wash # I 11985-1997 77.1 5,730 1.28 0.84 93.5 <br />Yellow Water Wash #2 11985-1997 80.9 6,410 1.24 0.89 42.4 <br />Coal Mine Wash #2 11985-1997 112.7 4,050 1.28 0.89 24.9 <br /> <br />The coefficient Bnd exponent are for the equation Sy = a' (I, where Sy = sediment yield (Mglday) and Q = instantaneous discharge (m3ts). Minimum <br />discharge for the rating curves is 0.1 m3ts. <br />o DalO from ROle and others (1997). <br />t Unpublished data from Peabody Coal Company. <br /> <br />Table 9. Linear regression between peak discharge and sedimenl yield for 42 floods In Bright Angel Creek, <br />Arizona. <br /> <br />Coefficient (a) <br /> <br />Exponent (b) <br />R2 <br /> <br />Bright Ange.1 <br />Creek <br />0.18 <br />2.23 <br />0.90 <br /> <br />VellowWeter <br />Wesh #1' <br />1987 <br /> <br />1.09 <br />0.76 <br /> <br />SEDIMENT RATING CURVE <br />Vellow Weter eoe' Mine <br />Wesh #2' Wesh ,f <br />1258 1088 <br />1.17 1.21 <br /> <br />0.77 0.78 <br /> <br />Coe' Mine <br />Wesh #2' <br />773 <br />1.21 <br />0.78 <br /> <br />MoenkoplWesh <br />#1' <br />404 <br />1.45 <br />0.82 <br /> <br />The coefficient and exponent are for the equation QJ = a Q/ where QJ = sediment yield (Mg/event) and Qp = instantaneous peak discharge (m3/s). <br />The Bright Angel Creek gage record runs from 1924 to 1973. <br />. Gaging stations on Black Mesa. Arizona (table 4). <br /> <br />than those of other rating curves from the region <br />(table 8). This likely results in par1 from an over- <br />representation of spring snow-melt floods in the <br />small Bright Angel data set; over 70 percent of the <br />data points were measured in the spring and snow- <br />melt floods are typically less sediment-rich than <br />floods at other times of the year. During the period <br />of record (1924 - 1973), 55 percent of flood events <br />in Bright Angel Creek occurred in summer (mean <br />peak discharge of 13 m3 Is) while only 25 percent <br />occurred in spring (mean peak discharge of9 m3/s). <br />Given the small data set from Bright Angel Creek, <br />removal of the spring floods would leave <br />insufficient data points for effective modeling. <br />Rating curves were developed for 8 gaging <br />stations operated by Peabody Coal Company on <br />Black Mesa. These gaging stations (table 4) are on <br />Coal Mine Wash (3 gaging stations), Yellow Water <br />Wash (2 gaging stations), Moenkopi Wash (2 <br />gaging stations), and Red Peak Valley Wash (I <br />gaging station). Although Black Mesa is about 100 <br />kilometers east of Grand Canyon (fig. I) and is <br />underlain by different geologic formations, the <br /> <br />paucity of data for smaller drainages from Grand <br />Canyon compelled us to look elsewhere for suitable <br />proxy data. The climate at Black Mesa is similar to <br />that of Grand Canyon and both areas are underlain <br />by primarily sedimentary bedrock. In general, the <br />Cretaceous strata of Black Mesa are notably less <br />competent than the Paleozoic strata of Grand <br />Canyon and include none of the well-indurated <br />carbonates typical of Grand Canyon (e.g., the <br />Redwall Limestone). Consequently, the drainages <br />on Black Mesa likely yield a higher proportion of <br />sediment per unit area than most of the ungaged <br />tributaries of Grand Canyon. (The one exception <br />may be upper Marble Canyon, where significant <br />exposures of Mesozoic shales and sandstones are <br />still present.) Any sediment-yield estimates based <br />on these data are likely to overestimate Grand <br />Canyon sediment yield and should be considered <br />maximum values at best. <br />Using the 42 flood hydrographs from Bright <br />Angel Creek, we applied five rating curves from <br />Black Mesa to calculate total sediment yield :Er <br />event. We separated base flow (0.4 to 1.0 m Is) <br /> <br />STREAMFLOW SEDIMENT VIELD 17 <br />