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

o 8
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0 . Summer (Jul-Sep)
~ 0.8
"- 0 Winter (Nav-Mar)
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~ 0.'
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.
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Figure 5. Standardized average decadal precipitation for
the Grand Canyon region from 1900 through 1998 and
the number of documented debris flows in each decade.

Empirical Sediment-Yield Relations

Previous estimates of streamflow sediment
yield from Grand Canyon tributaries have been
based solely on empirical approaches (Laursen and
others, 1976; Howard and Dolan, 1981; Randle and
Pemberton, 1987). Estimates derived from the
various approaches vary through two orders of
magnitude (table 5). Laursen and others (1976)
assumed that the ungaged tributaries contributed
insignificant amounts of sediment when compared
with the Paria and Little Colorado Rivers. Howard
and Dolan (1981) assumed that ungaged tributaries
yielded as much sediment per unit area as the gaged
tributaries and estimated a sediment yield of 780
Mg krn'2yr-t (table 6). Randle and Pemberton
(1987) based their estimate of?3] Mg km'2yr'1 on
a relation of sediment yield to drainage area derived
from reservoir sedimentation surveys ofthe western
United States and adjusted with data from the Paria
and Little Colorado Rivers, and Kanab and Havasu
Creeks.
We compared several empirical relations for
estimating streamflow sediment yield (table 5).
These relations calculate total sediment yield only,
with no discrimination of the particular par1icle
sizes that may be transported. An implicit
assumption in these approaches is that the percent
of exposed bedrock in the drainage basin is not a
factor in sediment yield. Most of the equations are

10'

. Smelll Reservoirs (Heins III 81 . 1952)
... Gaging StatIOns
-Q. ~ 193 A 'C14, R:z",O.B6
1 O'

10'

s
~ 10'
~
.
"
i
E
~
~

10'
10'
10'
10' 0
10'
0.01 01

. 0

10 100 1,000 10,000 100,00
Dreln8g8 Area (knf')

Figure 6. Sediment-yield data from small reservoirs
(Hains and others, 1952) and gaging stations on the
Colorado Plateau. Regional sediment-yield data is well
correlated using the data regression equation of Os =
193 . A1.04, with R2 = 0.86, where Os = streamflow
sediment yield in Mglyr and A = drainage area in km2.

in the form of power functions (table 5). Strand
(1975) based his method on reservoir surveys
throughout the western United States. Renard
(1972) and Renard and Laursen (1975) used both
reservoir sediment data and a stochastic runoff
model calibrated to southwestern watersheds to
calibrate their methods. Dendy and Bolton (1976)
related both drainage area and mean anriual runoff
to sediment yield. Flaxman (1972) developed a
more complicated empirical approach that relates
sediment yield to mean annual climate (a proxy for
vegetation), watershed slope, and soil
characteristics.
Sediment yields calculated from the empirical
sediment-yield equations range from 43 to 4,110
Mg km-2yr-t (table 5). Most of the empirically-
based estimates are significantly larger than
measurements at gaging stations (table 4). Of these
equations, Renard's (1972) method best
approximates the data from gaging stations and
reservoir surveys (fig. 6). The Renard (1972)
equation, converted to 51 units and assuming a
sediment density of 1.2 Mg/m3, is

Q,=351'Ao.88, (4)

where Q, = streamflow sediment yield (Mg/yr) and
A = drainage area (krn2). Flaxman's (1972)
approach produced the lowest sediment yield (43
Mg krn-2yr-l; table 5), although results from his
relation vary widely with small changes in the

12 sediment Delivery by Ungaged Trlbuterles 01 the Colorado River In Grand Canyon