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Table 14. Debris flows that have had significantly changed debris fans and rapids during the last century in Grand Canyon. [A full list of debris flows observed or recorded in repeat photography in Grand Canyon is in appendix 2.] Tributary name Year(s) or year range 01 Name of rapid River mile Side debris flow(s) Method used Jackass Canyon tBadger Creek 7.9 L 1994 I Badger Canyon Badger Creek 7.9 R 1897 to 1909 2 Soap Creek Soap Creek 11.2 R 1923 to 1934 2 House Rock Canyon House Rock 16.8 R 1966 I Unnamed canyon #New riffle 18.0 L 1987 I Unnamed canyon Unnamed riffle 21.5 L 1890 to 1990 2 Unnamed canyon t24-Mile 24.2 L 1989 I Tiger Wash Tiger Wash 26.6 L 1890 to 1990 2 Unnamed canyon No rapid 30.2 R 1989 2 South Canyon Unnamed riffle 31.6 R 1940 to 1965 2 Unnamed canyon Unnamed riffle 42.9 L 1983 2,3 Tatahoysa Wash "Boulder" 43.2 L 1983 2.3 Unnamed canyon #New rapid 62.5 R 1990 I Palisades Creek fLaw Canyon 65.5 L 1966,1984,1987,1990 1,2 Comanche Creek Unnamed riffle 67.2 L 1999 I Tanner Canyon tTanner 68.5 L 1993 1,3 Basalt Canyon Unnamed riffle 69.6 R 1999 I Unnamed canyon #Newriffle 72.1 R 1984 1,3 75-Mile Creek Nevills 75.5 L 1959 2 75-Mile Creek tNevills 75.5 L 1987,1990 I Hance Creek Sockdolager 78.7 L 1890 to 1990 2 complications, we did not find a useful relation between climate and debris-flow initiation that can be extrapolated to all tributaries, despite indications that debris-flow activity is related to variation in long-term precipitation (fig.5). DEBRIS-FLOW SEDIMENT YIELD Our model of debris-flow sediment yield in Grand Canyon involves four distinct elements: (I) frequency model for all 736 tributaries in Grand Canyon that produce debris flows, (2) a model of the expected volumes of debris flows reaching the Colorado River, (3) the particle-size distribution of debris flows, and (4) a depiction of river reworking that accounts for storage of debris-flow deposits on debris fans because of operations of Glen Canyon Dam. Debris-Flow Frequency Griffiths and others (1996) developed a logistic-regression model of debris-flow frequency in Grand Canyon between Lee's Ferry and Diamond Creek (river miles 0 to 225.8). For this report, that model was extended to the Grand Wash Cliffs (mile 276). Logistic regression predicts the probability of a binomial outcome from continuous, discrete, and (or) binomial independent variables, x. In the case of Grand Canyon debris flows, the outcome is whether or not debris flows have occurred during the last one-hundred years in each tributary (yes or no). The independent variables were 22 drainage-basin parameters related to morphometric, climatic, and lithologic character- istics (Griffiths and others, 1996). A total of 160 tributaries had debris-flow frequency information. 24 Sediment Delivery by Ungaged Tributaries of the Colorado River In Grand Canyon