WSP00684

• File Number: 8220.101.16
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 1/1/2000
• Author: Webb et al.
• Title: Sediment Delivery by Ungaged Tributaries of the Colorado River in Grand Canyon Arizona
• Water Supply Pro - Doc Type: Report/Study

Table 13. Reach-averaged particle-size distribution 01 sand delivered by streamflow Irom ungaged tributaries
01 the Colorado River In Grand Canyon, Arizona.

Sediment
.yleld Mean D20 Mean Dso Mean DaD n
reach River miles (mm t 1 SD) (mm t 1 SD) (mm t 1 SD)
A -15.5 to 0.9 0.15 t 0.03 0.24 t 0.06 0.33 t 0.09 6
B 0.91061.5 O.IHO.03 0.20 t 0.06 0.29t 0.09 71
C 61.5 to 87.8 0.10 t 0.02 0.15 to.04 0.24tO.10 6
D 87.8 to 143.5 0.09 t 0.03 0.14 t 0.05 0.21 t 0.09 3
E 143.5 to 156.8 nd nd nd 0
F 156.8 to 225.8 0.07 t 0.01 0.11 t 0.09 0.13 t 0.01 3
G 225.8 to 276.0 nd nd nd
TOTAL 0.IHO.03 0.19 t 0.06 0.28 t 0.09 0

nd, no data

evidence of changes to rapids (Webb and Metis,
1996). Beginning with the first recorded trip in
1869, river trips typically encountered altered
rapids, destroyed campsites, or obvious changes in
the river channel after a debris flow. In some cases
(e.g., the 1993 Tanner Canyon debris flow), eye-
witnesses described the floods (Melis and others,
1994). In this report, we update information
contained in Melis and others (1994) and Webb and
others (I 999b). For the period of 1984-1998, we
present a history of all debris flows in Grand
Canyon that reached the Colorado River.

Photography

Repeat photography has been used successfully
in Grand Canyon to document long-term changes in
terrestrial ecology and geomorphology (Turner and
Karpiscak, 1980; Stephens and Shoemaker, 1987;
Webb, 1996; Webb and others, 1989, 1991, 1999b).
Most of our frequency information for historical
debris flows (1871 to 1998) used during this study
was obtained from systematic, repeat photography
and interpretation of historical photographs
(appendix 2). Abundant historical photographs of
the Colorado River corridor, dating to the Wheeler
Expedition of 1871, allowed us to study many
different debris fans for changes caused by debris
flows, river-reworking associated with mainstem
floods, and other geomorphic processes such as
rockfall. Examples of repeat photography that
document debris flows and the criteria used to
identify them are given in Metis and others (1994),

Webb (1996), Griffiths and others (1996), and
Webb and others (1999b).
During our study, we matched and interpreted
1,297 historic photographs of the river corridor to
determine significant canyon-wide changes to
tributary channels, debris fans, and rapids. The
years with the most abundant widespread coverage
are 1890 and 1923, the years of well documented
river expeditions. By using time series of historical
photographs of specific debris fans, we were able to
bracket when debris flows occurred in selected
tributaries. For example, at Prospect Canyon (mile
179.3-L), 121 of 232 historical photographs were
matched to provide detailed reconstruction of
debris-flow occurrence and changes to the Lava
Falls Rapid (Webb and others, 1999b). For some
tributaries, the dates of debris flows could be
determined to within I year. Detailed descriptions
of the repeat photography collection are given in
Melis and others (1994), Webb (1996), and Webb
and others (I 999b ).
We also analyzed several sets of low-altitude
aerial photographs taken between 1935 and 1999
for evidence of debris flows. In 1935, the Soil
Conservation Service took black and white aerial
photographs of Marble Canyon (river miles 0 to 61)
and Diamond Creek to the Snap Canyon (river
miles 225 to 280) at a scale of 1:31,800; these
photographs are stored at the National Archives in
College Park, Maryland. Another set of
photographs, taken in November 1935 under the
direction of John Maxon of the California Institute
of Technology, recorded par1s of the Inner Gorge
from the vicinity of Bright Angel Creek to Specter

22 Sediment Delivery by Ungaged Tributaries of the Colorado River In Grand Canyon