As the nation’s principal conservation agency, the Department of the Interior has the
responsibility for most of our nationally owned public lands and natural and cultural
resources. This includes fostering wise use of our land and water resources, protecting
our fish and wildlife, preserving the environmental an cultural values of our national
parks and historical places, and providing for enjoyment of life through outdoor
recreation, The department assesses our energy and mineral resources and works to
ensure that their development is in the best interests of all our people. The department
also promotes the goals of the Take Pride in America campaign by encouraging
stewardship and citizen responsibility for the public lands and promoting citizen
participation in their care. The department also has a major responsibility for
American Indian reservation communities and for people who live in island territories
under U.S. administration.

NPS D-191 May 1993


OBJECTIVE

The objective of this analysis is to demonstrate an approach to sand balance analysis
in the Grand Canyon. We will determine how annual variations in sand input
from the Paria River affect the balance of river-stored sand in the Colorado River
between the Paria and Little Colorado Rivers under alternative conditions of annual
sand transport capacity in the Colorado River. It will be shown that flow
fluctuations and corresponding sand transport in the Colorado River can be
managed to achieve a balance with long-term average annual sand inputs from the
Paria River. However, it will further be shown that the variability in annual
tributary sand inputs means that even under conditions of long-term sediment
balance, there will inevitably be periods of fairly substantial deficits in river-stored
sand. The implications of this analysis for dam operations are discussed.
Specifically, the implications of six hypothetical flow release patterns from Glen
Canyon Dam on annual sand transport are evaluated. The reach between Paria
River and Little Colorado River is the focus of this analysis, because this reach is
most susceptible to management-induced reductions in sand storage.

Objectives for sediment management along the Colorado River in the Grand
Canyon were developed by the Grand Canyon National Park as part of its river
management planning process. Those objectives are: 1) to maintain a positive sand .
balance, and 2) to maintain the range of morphologic features associated the
temporary storage of sand in the river system (e.g., sandbar deposits, high-flow
terrace deposits, return channels, etc.).

BACKGROUND

Flow Fluctuations and Sand Transport

Andrews has determined elsewhere that sand transport, Qs (in tons/day), by the
Colorado River in the Grand Canyon can be estimated by the relationship

Qs = 2.84 x 10% Qw** (1)

where Qw is stream discharge in cubic feet per second (cfs) (E. Andrews, U.S.
Geological Survey, pers. com., 1992). This power function relationship means that
sand transport through the Grand Canyon can be minimized for any given annual
release by releasing water at a constant rate. As flow fluctuations are introduced to
the system (both the range of fluctuation and the period of time during which flows
are higher than the annual mean) annual sand transport rates increase. If annual
sand transport is increased by highly fluctuating flows above a certain amount, a
long-term reduction of stored sand will result in the subject river reach.



7b.
6 :
H Oulput m Hedign input!
° ti
e
=
2
D
Q and
2
a =
uv wi
5
& Bolonce
o
3
é
=
i

-s ii iii iii
1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975

Year

Figure 4. Sand budget for the Colorado River: sand storage cumulative
surplus/deficit.


35

3.0

2.0 ferebeersnerafrnereenfsensenfeneeeendneten

Annual Sand Delivery (MT)

EN sus
WII Medien

Vere

0.0
1948 1950 1952 1954 1986 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976

Lo

ey
a a

i

—

0.5 }-

Yeor

Figure 2. Sand delivery from the Paria River into the Colorado River (1948-1975).

5



When the amount of stored river sand is decreased, there is less sand available for
deposition in backwaters and eddies, less sand available to "nourish" beaches during
periods of high flow (flows in excess of normal operations), and a greater likelihood
that the bases of margin deposits (including beaches) will be eroded. Because
tributary sand inputs are highly variable on an annual basis, simply managing main
channel sand transport to achieve a balance with long-term (mean) sand inputs will
not avoid reoccurring (and sometimes fairly large) periods of deficit in river-stored
sand, This situation will be further described and quantified in the analysis which
follows.

Ramping Rates, Stage Fluctuations and Beach Erosion

While flow fluctuations influence sediment conditions in the Grand Canyon
through their effect on sand balances in the Colorado River, stage fluctuations and
ramping rates also influence sediment conditions through their effect on the stability
and morphology of sediment margin deposits, including beaches (Bhudu 1992;
Werrell et al. 1992). This analysis deals only with the effects of flow fluctuations on
sand balances, and is not concerned with sandbar deposition and erosion induced by
fluctuating flows.

METHODS

Mean daily flow and suspended sediment transport data are available for the Paria
River at Lees Ferry streamgage for the 1949-1976 period. Daily sediment loads were
summed to determine annual sediment yields for each year of record (Figure 2).
Sand loads were approximated by assuming that 20 percent of the total suspended
sediment load was sand and that 20 percent of the total sand load occurred as
unmeasured bedload (Randle et al. 1991). The derived values for Paria River sand
transport used to plot annual sand inputs to the Colorado River were plotted over
time, and summary statistics were generated (annual means, annual medians, and
sand-flux duration curves).

To describe the effects of annual variations in sand input on the balance of stored
sand in the Colorado River, three alternative annual sand transport rates were
assumed for the Colorado River (565,000 tons/yr, 790,000 tons/yr, and

1,000,000 tons/yr) and tributary sand inputs which corresponded to the measured
inputs for the 28-year period of record on the Paria River. All changes in stored
river sand were expressed as deviations from 1948 amounts (where the 1948
deviation was defined as zero). The low Colorado River transport rate equates to
the median annual sand input from the Paria River; the medium transport rate
corresponds to the mean annual sand input from the Paria River; and the high sand
transport rate corresponds to approximately the 30 percent transport rate on the
Paria River sand flux duration curve (Figure 3).

4


Annual Sand Delivery (MT)

Mean

Medion

0.0
° 10 20 30 40 50 60 70 80 90 100

Percent of Time Delivery was Greater or Equal to the Indicated Value

Figure 3. Paria River sand-flux duration curve.



COLORADO RIVER SAND BUDGET:
LEES FERRY TO LITTLE COLORADO RIVER

Gary M. Smillie
William L. Jackson
and

Dean Tucker

Technical Report NPS/NRWRD/NRTR-92/12

May 1993

United States Department of the Interior
National Park Service
Washington, D.C.



Release Pattern Tons of Sand/year*

Steady, year-round flows 204,000

Daily Fluctuations:

8,000-13,000 cfs 218,000
5,000 - 20,000 470,000
5,000-25,000 821,000
3,000-30,000 1,470,000
5,000 - 20,000 (11.5 months) 716,000

31,500 (2-weeks; to build sandbars)

* Mean Annual Sand Input (Paria River): 790,000 tons/year

Qs = 2.84 x 10°? Qw*
All daily peaks were held for four hours.

Table 1. Sand transport examples.

10


Of course, if main channel transport capacities are less than the long-term mean
sand inputs, there will be less chance for short-term periods of sand-storage deficits
and there will be a long-term trend towards sand accumulation. Conversely, if sand
transport rates in the Colorado River are greater than the mean sand inputs from
tributaries, there will be a long-term trend of sand depletion from storage.

Effects of Alternative Dam Operations on Main Channel
Sand Transport

To illustrate how alternative dam release regimes affect main channel sand transport,
and thus the long-term balance of sand in the subject river reach, six different
hypothetical release regimes were modelled, including the two cases previously
mentioned (Table 1). In all cases, the maximum discharge was maintained for four
hours daily. Discharges were distributed over the rest of the period to minimize
daily ramping rates and to achieve the required water delivery volume on a monthly
and annual (11,200 cfs) basis. The results suggest that when fluctuations exceed
roughly 18,000 to 20,000 cfs daily, long-term sand deficits will occur in the subject
river reach.

DISCUSSION AND RECOMMENDATIONS

This analysis does not enable us to predict whether any particular operating regime
for Glen Canyon Dam will cause significant short-term deficits in Colorado River
sand storage in the Paria River to Little Colorado River reach. Furthermore, a
longer simulation period would have produced a much wider range in the amount
and duration of fluctuations in sand storage. However, it does suggest that if
Colorado River sand transport is managed to achieve a balance with long-term
average annual sand inputs, periods of sand storage deficit of some magnitude and
duration, as well as periods of surplus, are likely to occur. We recommend that
specific alternatives developed as part of the EIS process be analyzed for sand
balance implications using methods similar to those presented in this paper. This
action, of course, will require detailed information on the effects of various
alternatives on the actual long-term operation of Glen Canyon Dam.

We caution that the analysis presented in this study does not consider that over the
long term, spills from Glen Canyon Dam will occur resulting in potentially large-
scale depletions of sand from the Paria River to Little Colorado River reach.
Therefore, periodic or even modest long-term sand accumulations in storage are of
less concern than periodic depletions from storage. In fact, given both the
unpredictability of spills, and the need for periodic sandbar nourishment above the
normal flow zone, it may be wise policy to manage for modest long-term accumu-
lations of sand in river storage. In this case, there would be some rationale for

9



Finally, to evaluate the effects of alternative dam operations on main-channel sand
transport, a computer program was developed which calculated annual flow-duration
curves for alternative operations and applied the sand transport function in
Equation 1, to calculate annual sand transport for alternative daily flow patterns
(this program has a user-interface which permits alternative sand-transport functions
to be evaluated).

RESULTS

The distribution of annual sand inputs from the Paria River to the Colorado River
is positively skewed. Thus, the mean annual sand input (790,000 tons) is con-
siderably larger than the median annual sand input (565,000 tons) (Figure 2). A
constant year-around release of 11,200 cfs from Glen Canyon Dam would result in
approximately 200,000 tons/year of sand transport in the Colorado River. This
mean flow release corresponds to a "minimum" release volume from Glen Canyon
Dam as permitted by a compact between the upper and lower Colorado River Basin
states. This value is far less than the mean annual supply from the Paria River and
corresponds to approximately the 87 percent rate on the sand flux duration curve
(Le, 87 percent of the time, annual sand input equals or exceeds 200,000 tons).

At the other end of the spectrum, nearly 1.5 millions tons/year of sand is predicted
to be transported with a daily fluctuating flow of 3000 to 30,000 cfs (this regime
also averages 11,200 cfs). This magnitude of transport is far in excess of the mean
annual supply from the Paria. These results are very significant because they
strongly suggests that given a long term mean flow in the Colorado River of
11,200 cfs, it is possible to operate the Glen Canyon Dam in a manner that will
result in surplus, deficit, or balance of sediment transport relative to supply.

In examining the effects of annual sand input variations on the balance of river-
stored sediment in the Colorado River, several interesting points can be observed
(Figure 4). First, if the sand transport capacity of the Colorado River is set to
equate exactly to the long term average annual input of sand from the Paria River,
fluctuations in river-stored sand occur, even though a long-term balance is achieved.
In fact, for the simulated period of record, there was an 11-year period (1949-1960)
of deficit in stored river sand. The maximum deficit during this period was about
2.1 million tons of sand. This deficit equates to approximately three times the
annual mean input from the Paria River, or approximately four times the median
sand input from the Paria River. Following this period of sand deficit, there was
approximately a 15-year period of stored sand surplus. Over a longer period of
record, continued periods of deficit and surplus would continue to occur. Over any
relatively short time period (several years) there is a fairly high probability that
managing for a balance with mean sediment inputs might result in a substantial sand
deficit in the reach between the Paria and Little Colorado Rivers.

6


NEVADA
T
|

MILES
2 25 50

KILOMETERS

Loke Powell

Glen
Canyon
Dam

AREA
@ Flogstatt

ARIZONA

Phoenix

Tucson

Figure 1, Location map and study reach.



INTRODUCTION

Historically, the pre-dam Colorado River in the Grand Canyon was characterized
by enormous sediment-laden spring floods, and low flows during most of the
remaining year. During periods of low discharge and low sediment transport,
sediments were stored on the river bed and as sandbars along the river margins.
Sandbars were deposited, principally in eddy zones, during periods of high
discharge, and subsequently eroded as spring floods receded. Over periods of years
a “dynamic mass balance" existed between the delivery of sediments to the Grand
Canyon, the storage of sediments within the canyon, and the export of sediments
out of the canyon.

The construction and operation of Glen Canyon Dam located in northeastern
Arizona (Figure 1) has altered the natural flow and sediment transport of the
Colorado River in the Grand Canyon. The natural unimodal spring runoff peak
has been replaced by a series of lesser and more frequent peak discharges that are
intentionally sized and timed for the production of hydroelectric power.
Additionally, there have been dramatic reductions both in the amount of sediment
input to the Grand Canyon and in the capacity of the river to transport bed-sized
sediments (sand-size and larger sediments) through the canyon. Virtually all
sediment formerly delivered to the canyon by the Colorado River is now trapped
behind Glen Canyon Dam. The Paria River and the Little Colorado Rivers, located
approximately 15 and 80 miles downstream from the dam, respectively, are now the
primary sources of sediment to the Colorado River in Grand Canyon. Of
particular concern to river managers is the effect of dam operations on the balance
of sand-sized sediments stored along the river, especially as sandbars along the river
margins. This is because sandbars are critical to maintaining the river’s riparian and
near-shore aquatic habitats. They also are widely used by river recreationers as
camp sites.

The effects of alternative water release patterns from Glen Canyon Dam on
downstream natural, cultural and recreational resources, including sediment
resources, presently are the subject of an Environmental Impact Statement (EIS)
being prepared by the U.S. Bureau of Reclamation (BuRec) in cooperation with
other federal and state agencies and affected indian tribes. During the preparation of
the EIS, the Secretary of Interior has directed that "interim flow" operating criteria
be implemented at Glen Canyon Dam to minimize adverse effects of daily flow
fluctuations on downstream resources. The BuRec also is overseeing the Glen
Canyon Environmental Studies (GCES) Program, which is charged with conducting
research and monitoring in support of the information needs of the EIS process.
Numerous studies of sand transport and storage in the Grand Canyon are being
conducted as part of the GCES Program. This analysis was conducted as part of the
GCES Program in order to support the development of interim flow criteria.



TABLE OF CONTENTS

INTRODUCTION / 1
OBJECTIVE /| 3
BACKGROUND / 3

Flow Fluctuations and Sand Transport / 3
Ramping Rates, Stage Fluctuations and Beach Erosion / 4

METHODS / 4
RESULTS / 6

Effects of Alternative Dam Operations on Main Channel Sand
Transport / 9

DISCUSSION AND RECOMMENDATIONS / 9
ACKNOWLEDGEMENTS / 11
REFERENCES / 11

LIST OF FIGURES/TABLES

FIGURE 1. Location map and study reach. / 2

FIGURE 2. Sand delivery from the Paria River into the Colorado River. / 5
FIGURE 3. Paria River sand-flux duration curve. / 7

FIGURE 4. Sand budget for the Colorado River. / 8

TABLE 1. Sand transport examples. / 10

iv


managing flows to achieve sand transport capacities less than the long-term mean
annual sand input for this critical river reach, and using periods of sand surplus as
times to generate "sandbar building" flows (or to provide "insurance" against spills).

Finally, this analysis does not attempt to place significance on any particular level or
duration of stored-sand depletions, although additional work may permit such an
analysis to be made. This would further contribute to determining if temporary
sand depletions associated with managing flows to achieve a long-term sediment
balance should be a concern to resource management and protection agencies.

ACKNOWLEDGEMENTS

William Hansen and Marshall Flug of the National Park Service, and Jim Wilson of
the U.S. Geological Survey provided thorough and constructive reviews of an earlier
draft of this manuscript.

REFERENCES

Buddu, M. 1992. Mechanisms of erosion and a model to predict seepage-driven
erosion due to transient flow. University of Arizona, Department of Civil
Engineering and Engineering Mechanics. Tucson.

Randle, T.J., and E.L. Pemberton. 1987. Results and analysis of the STARS modeling
efforts of the Colorado River in Grand Canyon. Salt Lake City: USDI Bureau
of Reclamation, Glen Canyon Environmental Studies Technical Report.

Werrell, W., R. Inglis, and L. Martin. Geomorphic stability of sandbar 43.1L on the
Colorado River in the Grand Canyon in response to ground water seepage
during fluctuating flow releases from Glen Canyon Dam.. NPS Technical
Report. In press.

11