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

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Table 2. Drainage areas 01 ungaged tributaries 01 the Colorado River between Glen Canyon Dam and Upper
Lake Mead reservoir, Arizona.

TOlal
Trlbulary dralnaga Extra drainage area drainage area
Sedlmenl-yleld reach River mll"s area (km2) (km2) (km2)
A -15.5100.9 291 31 321
8 0.9 to 61.5 2,833 120 2.953
C 61.5 to 87.8 458 36 494
0 87.8 to 143.5 1,540 100 1,640
E 143.5 to 156.8 234 42 276
F 156.8 to 225.8 3,820 138 3,958
G 225.8 to 276.0 3,[87 48 3,236
TOTAL 12,363 515 12,878

albeit in a complex manner (Webb and others,
1999b). Several studies have analyzed various
aspects of rainfall variability in the Grand Canyon
region (Hereford and Webb, ] 992; Hereford and
others, 1993; Melis and others, 1994, 1996; Webb
and others, 1999b). To update these analyses, and to
add more data, we used 14 weather stations from
around Grand Canyon (fig. I, table 3), Few of these
weather stations are between the North and South
Rims. Stations in the Grand Canyon region have
mean annual precipitation that ranges from 148 to
655 mm; the average of the 14 stations is 316 mrn.
About 37 percent of precipitation in the Grand
Canyon region occurs in winter (November-March)
and 35 percent occurs in summer (July-September).

Seasonal precipitation by water year was
standardized following an established technique
(Hereford and Webb, 1992) to examine the effects

3.
A.
3.
! 25
~ 2.
15
~ 15
g ,.
~
.
0
~ ~ C> "1 ~ :iI ~ '"
'" '"
.. .. .. :;;; '" ~ ~
:g 6
;; ., '" ~
., "
Range In Drainage Area (km1

of antecedent soil moisture on debris-flow
initiation, For each weather station (table 3), we
calculated the standardized seasonal precipitation,
Ps, by

p = L{L[(Xij-u)/cr;llk}
s '
n

(2)

where XjJ = monthly precipitation for weather sta-
tion i in monthj (mm); J.lj = the mean and IJj = the
standard deviation of monthly precipitation for
weather station i (mm); k = the number of months
in the season; and n = the number of weather sta-
tions with data.
Annual and seasonal precipitation in the Grand
Canyon region has varied considerably in the 20th
century (figs. 3,4). In the period from 1980 through
1998, 15 years had above-average annual

4.000
1:
~ 3.000
I
~
I 2,000
0 I,aoo
t

.

Reach A Resch BReach CReach 0 Reactl E Reach F Reach G

Figure 2, Drainage areas of ungaged Grand Canyon tributaries. A. Histogram of drainage areas. B. Comparison of
total ungaged drainage area by sediment-Yield reach.

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