Sediment delivery by ungaged tributaries of the Colorado River in Grand Canyon, Arizona

Sediment input to the Colorado River in Grand Canyon, Arizona, is a valuable resource required to sustain both terrestrial and aquatic ecosystems.  A total of 768 ungaged tributaries deliver sediment to the river between Glen Canyon Dan and the Grand Wash Cliffs (river miles - 15 to 276).  The 32 tributaries between the dam and Lee's Ferry produce only streamflow floods, whereas 736 tributaries in Grand Canyon produce streamflow floods and debris flows.  We used three techniques to estimate annual streamflow sediment yield from ungaged tributaries to the Colorado River.  For the Glen Canyon and Marble Canyon reaches (river miles -15 to 61.5), respectively, these techniques indicate that 0.065^.10⁶ and 0.610^.10⁶ Mg/yr (0.68^.10⁶ Mg/yr of total sediment) enters the river.  This amount is 20 percent of the sediment yield of the Paria River, the only gaged tributary in this reach and a major sediment contributor to the Colorado River.  The amout of sand delivered ranges from 0.10^.10⁶ to 0.51^.10⁶ Mg/yr, depending on the sand content of streamflow sediment.  Sand delivered in Glen Canyon is notably coarser (D₅₀ = 0.24 mm) than sand in other reaches (D₅₀ = 0.15 mm).  A relation is given for possible variation of this sediment delivery with climate.