WSP00054

• File Number: 8220.101.17
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 3/7/2001
• Title: Sediment Delivery by Ungaged Tributaries of the Colorado River in Grand Canyon - Summary
• Water Supply Pro - Doc Type: Report/Study

Prepared In cooperation with the Grand Canyon Monitoring and Research Center

Sediment Delivery by Ungaged Tributaries of
the Colorado River in Grand Canyon

Introduction

Sediment supply and transpon in
Grand Canyon IS an imponant
management issue because of the presence
and operation of Glen Canyon Dam on thc
Colorado River (U.S. Depanmcnt of lhe
Interior, 1995). Most of Ihe fine-grained
sedimcntlhat fonnerly cnlcred lhe canyon
from upstream is trapped in Lake Powell:
this sc.diment once replenished bcaches
and pm\'ided substrate for lhe riverine
ecosystem in Grand Canyon. Wilh lhe
closure of the dam in 1963, sources of
fine-grained sediment have been limited to
major tributaries, such as the Paria and
Litlle Colorado Rivers and Kanab and
Havasu Creeks, and numerous small
tributaries. Small tributaries are also the
source of coarse-grained sediment
(cobbles and boulders), which fonns
debris fans and rapids, defines pools and
eddies that Irap and store fine sediment,
and provides substrate for aquatic and
terrestrial habilals throughoul Ihe river
channel. Between Glen Canyon Dam and
the Grand Wash Cliffs (fig. 1) 768 small
tributarit.~ were designatcd, moSt of which
,
range from Ilhrough 5 km. in area. At] of
these tribUlaries produce streamflow. but
only the 736 tribularies t;lelween Lee's
Ferry and the Grand Wash Cliffs produce
debris flows (fig. 2). \I.'ith the exceplion of
Bright Angel Creek and Ihc major
tributaries, lhese small tributaries between
Glen Canyon Dam and the Grand Wash
Cliffs werc ungaged bcfore 1999.
A combination of fluvial and hillslopc
processes occurs in small tributaries in
Grand Canyon, making eSlimates of
sediment yield complicated. Sediment-
yield eSlimatcs mU.~t consider the
contributions of both sU"eamflow. which

'D.~j

.,Creek.,

Figure 1. 768 ungaged tributaries 01 the Colorado River between Glen Canyon Dam
and lake Mead. Sediment-yield reaches are indicated by letter.

n .

~,.~

I

L~.__..

n

-=-:=-
~~

j

.1

1000g-lenn sediment yields for both coarse
and fine panicles from all 768 tributaries
bul panicu]arly from tributaries in
Reaches A and B (fig. I), where sand bar
resources arc moSI threalened. Because
the si/.e of panicles transported by the
river vary with discharge, data on !he
particle-siu distribution of sediment
delivered by both debris flow and
streamflo..... are also needed. Increased
knowledge of debris flow' and mainstem
processes in Grand Canyon will
contribute 10 efforts 10 operate G]en
Canyon Dam in ways thai minimize
downstream impacts. This Fact Sheel
summarizes a repon (\\'ehb and others.
2000) that presents the IOla] sediment
yield and sand delivery rates for the
ungaged tributaries.

U,S Departmet1torl1'8lnteroo<
u.sGoologIcaJ~

uSGS Fad Snoot 018-(H
February2QOl

occurs annually in aU tributaries, and
debris flow, which occurs rarely. Debris
flows arc slurries of c1ay- to bou]der-
sized sediment wilh sedimenl
concentrations of 70 to 90 percent by
volume. In contrast, streamflow
Iypically has a sediment concentration
by weighl of less than 40 percent. A
IOlal of 12,072 km2 in 736 tributaries
produces debris flow, and 12,900 kJn2
produce streamflo...... The tributaries
were organized inlO seven sedim...'nt-
yield reaches thai correspond to river
segments between major tributaries
with gaging re...'Ords or other estimates
of sediment input (fig. I).
Dc\'e]opment of a sediment budget
for the Co]omdo Ri\"Cr through Grand
Canyon requires an eSlimate of the