Channel Change and Sediment Transport 

in Two Desert Streams in Central Arizona, 

1991-92

By JOHN T.C. PARKER

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 95 4059

Prepared in cooperation with the 

FLOOD CONTROL DISTRICT 

OF MARICOPA COUNTY

Tucson, Arizona 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For additional information Copies of this report can be 

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Open-File Section

Water Resources Division Box 25286, MS 517

375 South Euclid Avenue Denver Federal Center

Tucson, AZ 85719-6644 Denver, CO 80225
CONTENTS

Page

Abstract ........................................................................................................................................................... 1

Introduction........................................................................................................................................................ 2

Scope of study and purpose of report........................................................................................................ 2

Description of study sites.......................................................................................................................... 4

Salt River........................................................................................................................................... 4

Hassayampa River............................................................................................................................. 6

Flows of 1992............................................................................................................................................ 8

Methods of sediment and channel-change data collection........................................................................ 9

Channel change.................................................................................................................................................. 12

Salt River................................................................................................................................................... 12

Hassayampa River..................................................................................................................................... 13

Sediment transport............................................................................................................................................. 26

Salt River.................................................................................................................................................. 26

Hassayampa River..................................................................................................................................... 30

Discussion.......................................................................................................................................................... 33

Summary and conclusions................................................................................................................................. 35

References cited................................................................................................................................................. 36

Survey data......................................................................................................................................................... 39

FIGURES

1. Map showing location of streamflow-gaging stations and study sites, Salt and Hassayampa

Rivers, central Arizona............................................................................................................... 3

2. Diagram showing cross-section and bed-material sampling locations on the Salt River

below 16th Street, Phoenix, Arizona.......................................................................................... 4

3. Photographs showing Salt River before winter flows of 1992, Phoenix, Arizona:

A. Looking upstream from the 24th Street bridge......................................................................... 5

B. Looking across the channel from the left bank downstream from the

16th Street bridge.................................................................................................................. 5

4. Diagram showing cross-section and bed-material sampling locations

on the Hassayampa River below the Southern Pacific Railroad bridge,

near ArUngton, Arizona.............................................................................................................. 6

5. Photographs showing Hassayampa River before winter flows of 1992

near ArUngton, Arizona: 

A. Looking downstream from the Southern Pacific Railroad bridge at

the head of the study reach................................................................................................... 7

B. Looking upstream from the old U.S. Highway 80 bridge ....................................................... 7

6. Cross section showing channel topography characteristic of study reach

in the Hassayampa River............................................................................................................ 8

7. Hydrographs of flows on the Salt River at 24th Street, Phoenix, Arizona:

A. January through April 1992...................................................................................................... 9

B. August 22-31,1992.................................................................................................................. 9

8. Graph showing peak discharges from floods on the Salt River, 1966-92....................................... 10

9. Hydrographs of flows on the Hassayampa River near ArUngton, Arizona:

A. January 6,1992 ...................................................................................................................... 10

B. February 7,1992 ...................................................................................................................... 10

C. February 14,1992..................................................................................................................... 10

D. August 22-23,1992.................................................................................................................. 10

E. Decembers, 1992..................................................................................................................... 10

Con'onts III
FIGURES Continued Page

10-11. Graphs showing:

10. Annual flood series on the Hassayampa River near Arlington, Arizona, 1961-92................. 11

11. Results of repeat surveys on the Salt River below 16th Street, Phoenix, Arizona.................. 14

12. Photographs showing effects of flows on the Salt River, Phoenix, Arizona, 1992:

A, Incised channel below 16th Street near cross section 1........................................................... 16

B. Erosion of boulder revetment and loss of structure at storm-drain outlet below

16th Street near cross section 2........................................................................................... 16

C. Gravel berms between cross sections 4 and 5 about 800 m below 16th Street bridge............ 16

13-15. Graphs showing:

13. Longitudinal profiles of elevation on the Salt River through the study reach

before and after winter flows of 1992: 

A. Thalweg elevation............................................................................................................. 17

B. Mean channel-bed elevation............................................................................................. 17

14. Discharge and gage-height relations at streamflow-gaguig stations on lower

Salt River on the basis of discharge measurements made during flows in 1992: 

A. Salt River at 24th Street, Phoenix, Arizona...................................................................... 18

B. Salt River at Alma School Road near Mesa, Arizona....................................................... 18

15. Results of repeat surveys of 11 cross sections on the Hassayampa River below

the Southern Pacific Railroad bridge, near Arlington, Arizona.......................................... 19

16. Photographs showing effects of flows on the Hassayampa River near Arlington,

Arizona, 1992: 

A. Looking downstream at streambank just below cross section 2

after the flow of January 6,1992.......................................................................................... 23

B. Bank erosion after the flow of February 7,1992...................................................................... 23

C. Looking upstream at low terrace near cross section 10 before

flow on February 7,1992...................................................................................................... 24

D. Low terrace along right side of channel after the flow on

February 7,1992................................................................................................................... 24

17-21. Graphs showing:

17. Longitudinal profiles of elevation on the Hassayampa River through the study

reach before and after winter flows of 1992: 

A. Thalweg elevation............................................................................................................. 25

B. Mean channel-bed elevation............................................................................................. 25

18. Relation of suspended-sediment concentration to time and discharge on the

Salt River, Phoenix, Arizona, winter 1992.......................................................................... 26

19. Sediment-transport data, Salt River and other rivers in Arizona

controlled by dams: 

A. Relation of suspended-sediment concentration to discharge............................................ 27

B. Comparison of suspended-sediment concentrations and discharge relations

on the Salt River with relations for other controlled rivers in Arizona......................... 27

20. Particle-size data, Salt River in Arizona:

A. Particle-size distribution of suspended-sediment and sand-sized bed-material

samples.......................................................................................................................... 29

B. Particle-size distribution of gravel-sized bed-material samples....................................... 29

21. Relation of suspended-sediment concentration to time and discharge,

Hassayampa River near Arlington, Arizona: 

A. February 7,1992............................................................................................................... 30

B. February 14,1992............................................................................................................. 30

C. August 23,1992................................................................................................................ 30

IV Contents
FIGURES Continued Page

22-23. Graphs showing:

22. Sediment-transport data on the Hassyampa River and other rivers in Arizona:

A. Relation of suspended-sediment concentration to discharge............................................ 31

B. Comparison of suspended-sediment concentrations and discharge relations 

on the Hassayampa River with relations for other uncontrolled rivers 

in Arizona...................................................................................................................... 31

23. Particle-size distribution of bed-material samples from the Hassayampa

River below the Southern Pacific Railroad bridge, near Arlington, Arizona...................... 32

TABLES

1. Characteristics of continuous winter flows and a summer flow event

on the Salt River at 24th Street, Phoenix, Arizona, 1992........................................................... 9

2. Characteristics of periods of runoff on the Hassayampa River below the Southern

Pacific Railroad bridge, near Arlington, Arizona, 1992............................................................. 11

CONVERSION FACTORS

Multiply

millimeter (mm)

meter (m)

kilometer (km)

square kilometer (km2)

cubic meter per second (m3/s)

By

0.3937

3.281

0.6214

0.3861

35.3107

To obtain

inch

foot

mile

square mile

cubic foot per secxnd

ABBREVIATED WATER-QUALITY UNITS

Chemical concentration and water temperature are given only in metric units. Chemical concentration in water is given 

in milligrams per liter (mg/L) or micrograms per liter (|J.g/L). Milligrams per liter is a unit expressing the so'ute mass 

per unit volume (liter) of water. One thousand micrograms per liter is equivalent to 1 milligram per liter. For 

concentrations less than 7,000 milligrams per liter, the numerical value is about the same as for concentrations in parts 

per million (ppm).

VERTICAL DATUM

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 A geodetic datun derived 

from a general adjustment of the first-order level nets of the United States and Canada, formerly called "5"ea Level 

Datum of 1929."

Consents V
Channel Change and Sediment Transport in Twc 

Desert Streams in Central Arizona, 1991-92

SyJohnT.C. Parker 

Abstract

Channel change and suspended-sediment transport were monitored in the Salt and 

Hassayampa Rivers in Maricopa County, Arizona, during the winter and summer rainy seasons of 

1991-92. Rows were moderate. Results illustrate the high instability of these channels and high 

variability of process and response.

A channelized, gravel-paved reach of the Salt River in an industrial part of Phoenix was 

incised 2 meters by sustained winter flows from upstream reservoir releases that had a peak 

discharge of 368 cubic meters per second. Similar amounts of channel incision occurred at bridge 

crossings at four other locations within 20 kilometers upstream from the study reach at 16th 

Street. Channel incision changed the stage-discharge relation at the streamflow-gaging station at 

24th Street. Bank erosion below 16th Street undermined bank revetment and caused a large 

concrete-drop structure at the mouth of a storm drain to fall into the channel. About 23 kilometers 

upstream from the study area, bank erosion on the Salt River exhumed a landfill that resulted in 

entrainment and transport of refuse. The flows, which lasted 5 months beginning in early January, 

produced the highest peak discharge in 9 years on the normally dry lower Salt River. Tl n. flows 

were minor, however, compared to peak discharges that occurred during a series of floois from 

1966 to 1980. The flood of 1980 that had a peak discharge of 5,100 cubic meters per second was 

the largest since 1905. In August 1992, several days of flows from reservoir releases produced a 

higher peak discharge of 493 cubic meters per second that resulted in little or no channel change.

On a sandy, ephemeral reach of the Hassayampa River in rural Maricopa County west of 

Phoenix, as much as 20 meters of bank erosion resulted from three flows of short duration and 

low-to-moderate peak discharge. Most bank erosion resulted from a winter flow that lasted about 

7 hours, had a peak discharge of 127 cubic meters per second, and an estimated recurrence 

interval of less than 5 years. A summer flow that lasted 3 hours had a peak discharge of 173 cubic 

meters per second and caused some bank erosion and possibly some dissection of terraces. The 

magnitude of change, however, was far less than that of the winter flow.

Suspended-sediment concentration on the Salt River during the winter flows was typical 

of those for other regulated streams in Arizona and ranged from 2 to 617 milligrams per liter at 

discharges from 6.7 to 343 cubic meters per second. Fine-grained sediments in the channel 

bottom probably were the main source of sediment transported in suspension. During periods of 

prolonged, steady flows, suspended-sediment concentration tended to decline, which ind: cated a 

probable depletion of sediment supply.

On the Hassayampa River, suspended-sediment concentrations ranged from 12,800 to 

132,000 milligrams per liter at discharges of 13 to 128 cubic meters per second. The relation of 

sediment concentration to discharge was poor for the entire set of samples, but a clear pattern was 

evident for each period of storm runoff. In two of three periods of runoff sampled, maximum 

suspended-sediment concentration occurred just before peak discharge and declined rapidly.

Abstract 1
INTRODUCTION Scope of Study and Purpose of Report

Desert streams commonly are characterized by 

unstable channels, high sediment loads, and long 

periods of low or no flow punctuated by brief 

floods that increase discharge several orders of 

magnitude within minutes. Unstable desert streams 

near urban areas or transportation networks present 

special problems to flood-plain managers and 

engineers who must delineate flood-hazard zones, 

regulate flood-plain activities, and design and 

protect structures such as bridges and culverts. 

Effective management is hampered by the limited 

knowledge of stream processes in arid regions 

compared with stream processes in humid regions.

A major obstacle to understanding stream 

processes in arid and semiarid regions is the 

meager data base that exists in most areas. Flow 

records are often fragmentary and short; sedimenttransport data are scarce, and data on channel 

change, such as aerial photographs, generally are 

historical and of low resolution. The Salt and 

Hassayampa Rivers in Maricopa County, Arizona 

(fig. 1), are typical in those respects. Although the 

lower Salt River passes through the heavily 

urbanized Phoenix metropolitan area, flow records 

before 1989 consist only of miscellaneous direct or 

indirect discharge measurements of the river's few 

large floods. Sediment-transport data apparently 

were not collected before 1992. Graf (1983) conducted a study of channel change on the lower Salt 

River that resulted from floods of 1966-80, but 

until 1992, no program of systematic measurements of channel morphology for the purpose of 

monitoring channel change had been undertaken. 

Stream flow records exist for several sites on the 

Hassayampa River, beginning as early as 1938, but 

no sediment-transport or channel-change data are 

known to have been collected before 1992.

The U.S. Geological Survey (USGS) in cooperation with the Flood Control District of Maricopa 

County began a monitoring program to investigate 

channel change and sediment transport on the Salt 

and Hassayampa Rivers at the start of the 1991-92 

flood season. Characterization of channel properties, measurements of suspended-sediment transport during floods, and repeated measurements of 

channel morphology were the main components of 

the program.

A study site was established on the Sa't River 

in Phoenix because of the urban location and the 

stream's economic significance to the Phoenix 

metropolitan area. During the 1980 flood, which 

was the largest of six floods during 1966-80, all 

but two of about 25 bridges and grade crossings on 

the Salt were closed by flood damage, which 

caused extreme disruption of the area's transportation network (Chin and others, 1990). 

Extensive commercial development adjacent to the 

channel, sand- and gravel-mining in the channel, 

and many costly channel modifications, such as 

bank revetment and grade structures, make an 

understanding of processes in the Salt River 

especially critical. For decades at a time, the Salt 

River has had no significant flow in its channel 

(Graf, 1983). Modification of the dam at Roosevelt 

Lake, which is the largest upstream reservoir, 

reduced reservoir capacity beginning in 1991 and 

increased the probability that at least moderate 

floods would occur and would provide an 

opportunity for obtaining data from a monitoring 

program.

The Hassayampa River was chosen for study 

because it is the last large, uncontrolled, generally 

unmodified desert stream in central Arizona. The 

ephemeral stream, characterized by a shifting, 

braided to meandering sand channel, is typical of 

many alluvial streams in arid to semiarid regions. 

Except for streamflow records, data are scarce for 

such streams because flows are of highly variable 

frequency and magnitude, which makes data 

collection difficult. Streamflow data are of low 

accuracy because the unstable channels produce 

frequent changes in stage-discharge relations. 

Records at the two active USGS strennflowgaging stations on the Hassayampa River a"? rated 

poor, which means that published discharges may 

be more than 15 percent above or below the true 

value (Smith and others, 1993). Althor^h the 

Hassayampa crossed generally undeveloped desert 

lands from Wickenburg to the Gila River at the 

time of this study, the area probably will be 

subjected to development pressures in the coming 

decades because of its proximity to the Phoenix 

metropolitan area. Identification and understanding of processes on the Hassayampa Rive" would 

aid flood-plain managers and engineers in

2 Channel Change and Sediment Transport in Two Desert Streams in Central Arizona, 1991-92
112°45' 112°30'

^95165000

\ \3Monristown

33°15' 

Base from U.S. Geological Surey digital data, 1:100,000, 1983

Lambert Conformal Conic projection

Standard parallels 33° and 45°. central meridian -90°00'

10 15 MILES

095170000<

10 15 KILOMETERS

EXPLANATION

STREAMFLOW-GAGING

STATION Number is 

site identifier

Site number Site location

095120600 Salt River at Alma School near Mesa

095121900 Salt River at 24th Street at Phoenix

095165000 Hassayampa River near Morristown

095170000 Hassayampa River near Arlington

Figure 1. Location of the streamflow-gaging stations and study sites, Salt and Hassayampa Rivers, central Arizona.

Introduction 3
developing strategies for coping with the unstable 

channel before residential and commercial development force government agencies to use expensive structural methods of flood and erosion 

control.

The monitoring program at both sites originally was to continue for several years, but budgetary considerations forced cancellation of the 

program after the first year of operation. 

Fortunately, prolonged flow on the Salt River in 

winter 1992 and the occurrence of several moderate flows in the winter and summer of 1992 on 

the Hassayampa River permitted collection of 

sediment-transport and channel-change data that 

allow some insight into processes on those streams. 

This report presents the data collected during the 

1-year monitoring program and presents tentative 

hypotheses and conclusions about processes on the 

Salt and Hassayampa Rivers and the significance 

of those conclusions for management issues.

Description of Study Sites

Location of study sites was influenced by the 

presence of stream flow-gaging stations and by the

degree to which a reach was characteristic of the 

larger system. In both cases, the reach on which the 

gaging stations were located was not suitable 

for monitoring channel change, and monumented 

cross sections were installed nearby. Both streams 

studied in this investigation vary in morphology 

and hydraulic characteristics throughout their 

length, but the reaches studied are representative of 

most of the respective channels.

Salt River

On the Salt River, sediment was sampled at 

24th Street in Phoenix. Drainage area at the gaging 

station is 34,683 km2. Monumented cross sections 

were established 1.6 km downstream between 16th 

Street and 7th Street to avoid channel disruptions 

from active sand-and-gravel mining (fig. 2). The 

channel at 24th Street is typical of urban reaches on 

the lower Salt River (fig. 3A). Various in-iustrial 

facilities, including an auto-wrecking yrrd and 

sand-and-gravel operations, occupy the terrace on 

either side of the river. The 280-meter wide 

channel was entrenched 6 to 8 meters be^ow the 

bank crests, primarily as a result of floods from 

1966 to 1980 (Graf, 1983). Most of the channel

DIRECTION 

FLOW

D

O 

V

EXPLANATION

- LINE OF CROSS SECTION Number 

is cross-section identifier

APPROXIMATE BED-MATERIAL 

SAMPLING LOCATIONS

Gravel-bed channel 

Channel mud 

Terrace

100 

I

200 300 METERS 

_I

Figure 2. Cross-section and bed-material sampling locations on the Salt River below 16th Street, Phoenix, Arizona.

4 Channel Change and Sediment Transport In Two Deaert Streams In Central Arizona, 1991-92
A, Looking upstream from the 

24th Street bridge. Much of the 

channel bottom has been scraped, 

and gravel was pushed into piles 

shown at the left edge of the 

photograph.

6, Looking across the channel from 

the left bank downstream from the 

16th Street bridge.

Figure 3. Salt River before winter flows of 1992, Phoenix, Arizona.

was gravel paved; however, upstream from the 

bridge, much of the bottom had been scraped and 

consisted of hardpacked fine sand and silt 

embedded with gravel that had been redistributed 

by heavy machinery. In late 1991, flow 

approaching the 24th Street bridge was obstructed 

by a 15- by 60-meter gravel pile about 3 m high 

that was formed from material that had been 

scraped from the channel bottom (fig. 3A). In 

December 1991, a low-flow channel was barely 

incised into the cobble-paved bottom near the left 

side of the stream. Banks near 24th Street were

composed of a variety of materials including fill, 

gravel-mining spoils, boulder riprap, and natural 

deposits of sand and gravel.

The reach below 16th Street (fig. 3fi) is similar 

to that at 24th Street; however, there were no signs 

of active channel manipulation by mining activities. The reach was channelized with boulder 

revetment covering each bank from 16th Street to 

7th Street. The left bank was armored with angular 

boulders that are 0.5 to 0.75 m in diameter. The 

right bank was armored with bed material, 

apparently derived from the adjacent channel

Introduction
bottom, consisting of rounded cobbles and 

boulders 0.1 to 0.3 m in diameter that were 

anchored with a heavy wire mesh. The channel 

bottom was paved with gravel for about 400 m 

downstream from the 16th Street bridge. Farther 

downstream, most of the channel bottom had been 

scraped, and bed composition was highly variable. 

Bed material in the scraped areas included fine 

sand and silt with little or no gravel, pebble-, 

cobble-, and boulder-sized gravel in a fine-grained 

matrix, and hard-packed gravel pavement. Most of 

the bed material in the middle to lower part of the 

study reach appeared to have been redistributed by 

heavy machinery. Thickets of saltcedar grew on 

deposits of fine-grained sediments from about the 

middle of the reach to the 7th Street bridge. 

Tributary flow carrying local runoff enters the Salt 

River between 16th and 24th Streets, but such flow 

was a negligible contribution to total flow through 

the study reach.

Hassayampa River

On the lower Hassayampa River near 

Arlington, a 730-meter-long reach below the 

Southern Pacific Railroad bridge about 2.1 km 

upstream from the Old U.S. Highway 80 bridge 

(fig. 1) was chosen for monitoring channel change 

(fig. 4). The reach, which has a wide, sandy, 

ephemeral channel (fig. 5A), was selected for 

studying channel change because it was 

representative of the Hassayampa River between 

Wickenburg and the Gila River. Immediately 

downstream from the study reach is a channelized 

reach that receives irrigation-return flow and 

contains a base flow of 0.5 to 3.5 m3/s (fig. 5B). 

The channelized reach extends from about 975 m 

upstream to about 1,220 m downstream from the 

Old U.S. Highway 80 bridge on which the 

streamflow-gaging station was located. Drainage 

area at the gaging station is 3,810 km2. The baseflow channel, lined by dense vegetation through 

most of the reach, is shallowly incised into a wider 

channel enclosed by levees. Sediment-transport 

data were collected in this reach because the 

highway bridge provided the only suitable 

structure on which the pumping sampler could be 

installed; however, the reach is atypical of the 

Hassayampa River in general, which is mainly 

ephemeral and largely unchannelized. Flow at the

 Survey 

station 2

EXPLANATION

9 LINE OF CROSS SECTIpN Number 

Is cross-section identifier

APPROXIMATE BED-MATER'AL 

SAMPLING LOCATIONS

CD Unvegetated channel

A Vegetated channel

O Sandy terrace

Figure 4. Cross-section and bed-malarial sampling 

locations on the Hassayampa Riv^r below the 

Southern Pacific Railroad bridge near Arlington, 

Arizona.

gaging station includes irrigation-ret irn flow that 

enters between the study reach and the gaging 

station. During periods of runoff, retirn flow may 

contribute discharges of more ttan 6 m3/s. 

Therefore, actual discharges through the study

6 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
A, Looking downstream from the 

Southern Pacific Railroad bridge at 

the head of the study reach.

Figure 5. Hassayampa River before winter flows of 

1992, Arlington, Arizona.

reach are somewhat lower than those recorded at 

tiie gaging station.

In the upper part of the study reach, the channel 

was a 45-meter-wide main channel barely incised

B, Looking upstream from the 

Old U.S. Highway 80 bridge.

into a wider flood channel (fig. 6) that formed a 

compound channel as denned by Graf (1988a). The 

main channel was a sandy, unvegetated zone that 

included the thalweg (the deepest part of the 

channel) and a sparsely vegetated zone along the 

channel margins. The high-flow channel consisted 

of a low, sandy, unvegetated terrace that stood 

above the left edge of the main channel. Above the 

low terrace, a vegetated terrace had abundant 

evidence of recent inundation including woody 

flood debris and overflow channels. The distinct 

high-flow channel terminated at about the lower 

third of the reach where the channel consisted only 

of tiie vegetated and unvegetated zones. Maximum 

relief across the compound channel in the upper 

reach was about 1.2 m; maximum relief across the 

channel in the lower reach was about 0.6 m. The 

right bank of the study reach abutted the remnants 

of a levee and consisted of 1 to 3 stepped terraces 

that were 0.5 to 1.5 m high and 15 to 75 m wide. 

Bank material consisted of beds of weakly 

cohesive medium to fine sand and silt with some 

gravel. The material was sufficiently cohesive to 

maintain a vertical bank, but the banks failed 

readily when subjected to slight stress. The left 

bank was a gently sloping earthen levee that had a 

crest that was 2.4-3.4 m above the channel bottom. 

Bank material consisted of weakly cemented fineto-medium sand overlain by 0.15 to 0.5 m of 

sandy-gravelly fill.

Introduction
cr

tw 

mcr 

cc w

p5° 2

111111111

I I I I I I I

240 220 200 180 160 140 120 100 80 60

HORIZONTAL DISTANCE ACROSS CHANNEL, IN METERS

Figure 6. Channel topography characteristic of study reach in the Hassayampa River.

40 20

Flows Of 1992

Flows on the lower Salt River from reservoir 

releases began January 6,1992, (fig. 7, table 1) and 

continued with a few brief interruptions until 

June 12, 1992. Mean daily discharge at 24th Street 

during that period was 54.2 m3/s; peak discharge 

reached 368 m3/s on February 15. A second peak 

of 241 m3/s was reached on March 10, and a third 

peak of 306 m3/s was reached on March 27. The 

flows of 1992 at the gaging station at 24th Street 

were the highest and most prolonged in the short 

history of the streamflow-gaging station, and the 

peak discharge was the highest since 1983. Flows 

within 15 percent of the peak discharge were 

sustained for about 40 hours from February 14 to 

February 16. Flows near the peak discharge were 

sustained for almost 100 hours, March 9-14, and 

for about 20 hours, March 27-28. Reservoir 

releases in August 1992 produced an even higher 

peak discharge of 493m3/s; however, flow 

duration was only for a few days, and flows 

within 15 percent of the peak were sustained for 

only 6.5 hours on August 24. Peak discharges 

on February 15 and August 24 were minor 

compared with some flood peaks of 1966-80 

(fig. 8), particularly the flood of 1980 the highest 

flood since 1905 that had a peak discharge of 

5,100 m3/s. Total volume for the flows of 1992, 

from January 6 to June 12, was 725,600,000 m3 .

The gaging station on the Hassayampa River 

near Arlington recorded five periods of storm 

runoff during water year 1992 (fig. 9, table 2) that 

were characterized by a rapid rise and fall of stage. 

In terms of peak discharge, all of the flows of 1992 

were moderate events (fig. 10). The flows of 

January 6, February 14, and Decenber 8 have 

recurrence intervals of less than 2 y^ars, and the 

flows of February 7 and August 22 have recurrence 

intervals of less than 5 years (Garrett and 

Gellenbeck, 1991). All flows, except possibly that 

of August 22, were confined to the nain channel 

and did not top the vegetated ternce (fig. 6). 

Abundant flood debris, noted at the time of the 

initial survey of the study site, was s mattered over 

the terrace. The debris probably was deposited by 

the flood of March 2, 1991, that had a peak 

discharge of 199 m3/s (Smith and others, 1993).

Flows on the Hassayampa River are subject to 

substantial attentuation of peak discharge and of 

flow volume because of transmission losses to the 

permeable sandy channel bottom. Gating stations 

were operated simultaneously on the lower 

Hassayampa near Arlington and 57 km upstream 

near Morristown for all but 2 of the 30 years 

from 1961 through 1992. In that period, only nine 

of the annual floods (the highest discharge of the 

year) occurred at both stations as a result of the 

same event In all but two of those cases, peak 

discharge of the annual flood was less at the

8 Channel Change and Sediment Tranaport In Two Desert Streams In Central Arizona, 1991-92
500

22 23 24 25 26 27 28 29 30 31 

JANUARY FEBRUARY MARCH APRIL AUGUST

Rgure 7. Flows on the Salt River at 24th Street, Phoenix, Arizona. A, January through April 1992. B, August 22-31,1992.

downstream station (Garrett and Gellenbeck, 1991; 

Boner and others, 1991, 1992; Smith and others, 

1993). All of the peak discharges of the annual 

floods that occurred at both stations from the same 

event were in response to dissipating tropical 

cyclones in the fall months or frontal storms in the 

winter months rather than summer monsoonal 

thunderstorms (Smith, 1986). Dissipating tropical 

cyclones and frontal storms typically are more 

likely to be regional in extent than monsoonal 

storms (Hirschboeck, 1985; Webb and Betancourt, 

1992).

Methods of Sediment and ChannelChange Data Collection

Suspended-sediment data were collected 

manually on the Salt River at 24th Street in 

Phoenix near the streamflow-gaging station using 

the equal-width-increment method (Edwards and 

Glysson, 1988). A total of 21 composite samples 

were collected from January 9 to March 26, 1992, 

at discharges that ranged from 6.7 to 343 m3/s from

Table 1 . Characteristics of flows on the S?tt River at 24th 

Street, Phoenix, Arizona, 1992

Discharge, In cubic 

maters per second1

Date

01-15-92

02-15-92

03-27-92

04-06-922

08-24-92

Instantaneous

pesk

59.8

368

306

104

493

Mean

dally

23.6

81.7

133

46.5

28.9

discharge, 

In cubic

meters

63,000,000

205,000,000

356,000,000

120,000,000

77,400,000

Flows from winter reservoir releases continued until 

June 12, 1992.

2Highest discharge occurred April 1,1992, during waning stages 

of flood that peaked on March 27,1992.

reservoir releases. Sediment concentration was 

determined for all samples, and particle-size 

distribution of the sand fraction was determined for 

four samples.

Introduction 9
6,000

O 

O 

LU 

W 

QC 

LU 

Q.

W

oc

LU

5,000

4,000

3,000

? 2,000

LU 

O 

QC

<

O 1,000

January | February | 

1966 1973

March December! January March 

1978 1979

February | October | 

1980 1983

March | February August 

1991 1992

DATE OF FLOOD PEAK

Figured. Peak discharges from floods on the Salt River, 1966-92. (Source: Flood peaks for 19f6 to 1980 are 

published in Graf, 1983. Flood peak of 1983 is based on miscellaneous-discharge measurement at Alma School 

Road and is published in White and Garrett, 1987. Flood peaks of 1991 and 1992 are based on ccntinuous-gage 

record at 24th Street and are published in Boner and others, 1992, and Smith and others, 1993.)

180

160

8 140

LU

w

£120

w 

cc

H100 

LU 

5 

O 

m 80

O

r 60

40

20

10 15 20 0

. c D

10 15 200 5 10 15 20 0 5 10 15 20 0 

DURATION, IN HOURS

10 15 20

Figure 9. Flows on the Hassayampa River near Arlington, Arizona. A, January 6, 1992. B, February 7, 1992. 

C, February 14, 1992. D, August 22-23, 1992. E, December 8, 1992.

10 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
1,200 I I I I I I I T I I I II I T I I I I I I I I \ I I

1,000

LU 

O)

£ 800

Q600

LU

O 

CO

O

§

0 200 h

1960 1970 1960 1990

WATER YEAR 

Figure 10. Annual flood series on the Hassayampa River near Arlington, Arizona, 1961-92.

On the Hassayampa River, an automated 

pumping sampler was programmed to collect 

suspended-sediment samples at ±0.152-meter 

changes in stage or at 1-hour intervals when stage 

was between 1.07 and 1.52 m. When the stage was 

above 1.52 m, samples were to be collected at 

10.152-meter changes in stage or at 4-hour 

intervals. During two winter flows, 15 samples 

were collected, and 5 more samples were collected 

during a flow in August. All samples were 

analyzed for sediment concentration. Because of 

the brief duration of flows on the Hassayampa, it 

was not possible to collect sediment-transport data 

manually to calibrate the point samples collected 

automatically.

Bedload-transport sampling was not practical 

on either stream in the study. Bed material on the 

Salt River was sampled across two cross sections 

below 16th Street using a grid system to sample 

gravel greater than 11 mm in diameter. Gravel 

diameter was measured along the intermediate axis 

using calipers. Grab samples of finer-grained 

material were taken from representative deposiTabie 2. Characteristics of periods of runoff on the 

Hassayampa River below the Southern Pacific Railroad 

bridge, near Arlington, Arizona, 1992

Date

01-06-92

02-07-92

02-14-92

08-22-92

12-08-921

Duration of 

flow, In 

hours

4.25

7.25

5.50

3.25

14.00

Discharge, In 

cubic meters per 

second1

Instantaneous 

peak

43.9

136

29.5

173

26.4

Mean 

of flow 

period

23.3

59.2

14.7

67.4

91.18

Total flood 

discharge, 

In cubic 

meters

378,000

16,000,000

291,000

789,000

429,000

'Flow for December 8,1992, was in water year 1993.

tional environments for laboratory-si^ve analysis. 

On the Hassayampa River, bed material was 

sampled across four cross sections below the 

railroad bridge by taking grab sample? at intervals 

of about 5 m. The sampling populations were

Introduction 11
classified according to sedimentation units that 

were identified (unvegetated main channel, 

vegetated main channel, sandy terrace) and the 

samples from each unit were composited for sieve 

analysis.

To monitor channel change, eight monumented 

cross sections were established on the Salt River 

below the 16th Street bridge. The cross sections 

and the surveying station were monumented with 

1-meter lengths of iron rebar that were driven into 

the ground on the crests of the river banks. About 

0.15 m of rebar is exposed at each cross section 

end point. Survey data were collected as xyz coordinates referenced to an arbitrary horizontal and 

vertical datum that was established at Station 1 

(fig. 2). The initial survey was completed in 

December 1991 immediately before sustained 

winter flows began. Plans to survey a ninth cross 

section were abandoned because of the onset of 

flows. Eleven cross sections and two survey 

stations were monumented on the Hassayampa 

River, xyz coordinates were referenced to an arbitrary horizontal and vertical datum established at 

Station 1 (fig. 4). The initial survey was completed 

in November. Both streams were resurveyed in 

June and July 1992. All values were converted to 

metric units for this report except the xyz 

coordinates in the section entitled "Survey Data" at 

the back of this report.

CHANNEL CHANGE

Both streams in this study showed a variable 

relation between channel response, sediment 

transport, and magnitude of discharge. Relations 

for the Hassayampa River are particularly variable. 

A 1-year monitoring program clearly is not 

adequate to fully describe the variability in 

processes, but the data collected exhibit certain 

patterns that reflect the processes occurring on 

desert channels of central Arizona and that suggest 

potential areas for further study.

Salt River

The monumented cross sections below 16th 

Street (fig. 2) were resurveyed after the 1992 flows. 

The most pronounced channel change is evident on

cross sections 1 and 2 (figs. 11-12). In 

mid-December 1991, at the time of tl <; first survey 

of cross section 1, which is about 8 IT downstream 

from the 16th Street bridge, low-flow zones were 

weakly denned by two gentle swales one near the 

midchannel and one along the left side of the 

channel (fig. 11). When the cross1 section was 

resurveyed in June 1992, a chanrel had been 

incised 2 m into the gravel bottom along the left 

side of the main channel (fig. 12A). The incised 

channel began about 90 m upstream from the 16th 

Street bridge and continued as far as cross 

section 3 about 450 m downstream from the 

bridge.

During the winter flows, the former low-flow 

channel near the middle of cross s^-ction 2 was 

buried by a gravelly fan that was as rruch as 1.2 m 

thick and 90 m wide. The fresh g-avel deposit 

forced flows against the left side of the channel. 

This diversion of flow caused incision and lateral 

erosion that led to failure of riprap on the main 

channel banks and the loss of a concrete-drop 

structure at the mouth of a storm-drain outlet 

(fig. 125). The only other location where lateral 

erosion was known to have sigr'ficant consequences was upstream from the city of Mesa 

where a landfill was exposed by tank erosioa 

Refuse from the landfill was entrained by 

streamflow and transported downstream through 

the Phoenix area (Yozwiak, 1992).

At the remaining cross sections, channel 

change was minor. At cross section 3, the low-flow 

channel that formed during the winter is shallow 

but still distinct. Instead of incising into the pre1992 channel bottom, however, fre low-flow 

channel formed in alluvium deposited earlier 

during the 1992 flows (fig. 11). S^nd deposits 

blanketed much of cross sections 3 and 4. As much 

as 1 m of fine sand and silt was deposited in a 

saltcedar thicket between the middle of the channel 

and the right bank. Some of the sand deposits were 

eroded following deposition. The significance of 

the deposits for long-term channel change is not 

clear. Deposition of the sediments may be the 

beginning of a trend of long-term aggradation or 

may be only short-term storage of sediment that 

soon will be transported from the reach. Almost 

no measurable change occurred at c~oss sections 

5-8 (fig. 12Q.

12 Channel Change and Sediment Tranaport In Two Desert Streams In Central Arizona, 1991-92
The dependence of the location of channel 

incision and deposition on channel gradient is seen 

in longitudinal profiles (fig. 13). The gravel pavement of the channel bottom was removed from 

most of the reach and used to armor the right bank. 

As a result, an anomalously steep gradient existed 

at the downstream edge of gravel removal between 

cross sections 1 and 3. Incision of the thalweg 

flattened the oversteepened channel gradient 

upstream from cross section 2, and deposition 

below cross section 3 steepened the thalweg where 

channel gradient had been flat and even negative 

because of gravel extraction. Although the oversteepened channel gradient below 16th Street could 

be the primary cause of channel incision, similar 

incision occurred beneath at least four other 

bridges as much as 20 km upstream including 24th 

Street, Rural Road, Alma School Road, and 

Country Club Drive (fig. 1). The pattern was 

similar at each location beginning upstream from 

the bridge and continuing downstream from the 

bridge for three to six times the length of the 

upstream segment. None of the other locations had 

an oversteepened channel gradient, which suggests 

that incision generally was associated with flow 

contraction beneath the bridges.

At 24th Street, channel incision produced a 

substantial change in the stage-discharge relation at 

the gaging station (fig. \4A). By April 2, a stage 

of -0.45 m (relative to the original datum for the 

station) reflected a discharge of 63 m3/s compared 

to a stage reading of 0.84 m for a discharge of 

58 m3/s on January 15. The trend of stagedischarge relations suggests that the incision may 

have occurred in two stages that lowered the 

channel bed after the flood peak of February 14 and 

possibly again after the flood peak of March 7. The 

data, however, are too limited to conclusively 

determine the timing of incision. At Alma School 

Road about 16.25 km upstream from 24th Street, 

channel incision did not produce a significant 

change in the stage-discharge relation, or the data 

are too limited to reflect a change in the relation 

(fig. 14J8).

No obvious channel changes were observed at 

bridge crossings downstream from the study area 

between 7th Street and the Gila River during a 

reconnaissance on July 1-2, 1992. The Salt River 

below 7th Street appears to be characterized 

primarily by channel deposition rather than

erosion, and the apparent lack cf substantial 

channel change may reflect the low sediment load 

of the previous winter's flows.

On August 25, upstream reservoir releases 

produced a peak discharge of 493 m3/s at 24th 

Street (fig. IB). Although higher than the discharge 

of February 14, the flows did not cave significant 

channel change at 24th Street or at 16th Street. The 

short duration of the flows in August may be the 

reason for the absence of channel change. 

Another possible reason for the lack of significant 

change during the period of runoff in August may 

be that the channel had been adjusted to 

accommodate higher discharges by the flows of the 

previous winter.

Hassayampa River

Channel adjustments within the study reach on 

the Hassayampa River were prirrarily lateral. 

More than 15 m of bank erosion occurred at cross 

sections, and banks eroded more than 20 m 

between cross sections (figs. 15-16). Most erosion 

was along the outside of a channel bend impinging 

on the right bank of the study reach at cross 

sections 1-3 and on the left bank at cross section 

11 where the thalweg crosses over to the opposite 

side of the channel. Erosion of sediments stored in 

the high-flow channel, such as fre vegetated 

terrace and the sandy terrace, accounted for 

additional widening of the main channel. Vertical 

channel changes consisted of minor increases in 

bed elevation (fig. 17) mainly from filling of the 

channel thalweg. Vertical changes m?y have been 

the result of locally heavy sediment deposition in 

association with rapid bank erosion. Local 

adjustment of the longitudinal channel profile 

occurred as a result of the vertical changes. 

Channel segments that had a less-than-average 

gradient before the flows of winter 1992 tended to 

have a steeper gradient at the time of the second 

channel survey, and those that had a steeper 

gradient before the flows tended to have a 

shallower gradient after the flows. The gradient 

between most cross sections, however, did not 

change despite some increase in bed elevation. 

Through the entire 720-meter study reach, gradient 

of the channel thalweg was reduced from 0.0042 to 

0.0038. The gradient of the channel-bed surface,

Channel Change 13
20

15

10

o> 

a:

TI1I|11II|11II|1III|IIII|IIII|-

CROSS SECTION 1

Survey of December 12,1991

 ^Survey of June 26, 1992 EXPLANATION

ill DEPOSITION 

I I EROSION

I I I I I I L

- 350

Q 15 -

a:

< 

a:

m

tr

o

m

O

< 

> 

LU

300

i i i i I i i i i I i i i i 

CROSS SECTION 2

Survey of December 12, 1991

_ EXPLANATION 

DEPOSITION Survey of June 26, 1992

I i i i i I 

L CROSS SECTION 3

15

10

5 -

EXPLANATION

DEPOSITION 

I I EROSION

_| | | | | | L

Survey of December 12, 1991-

Survey of June 26, 1992/

I I I _L

350 300 250 200 150 100 50 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

Figure 11. Results of repeat surveys of the Salt River below 16th Street bridge, Phoenix, Arizona. 

14 Channel Change and Sediment Transport In Two Desert Streams in Central Arizona, 1991-92
20

15

10

CROSS SECTION 4

- EXPLANATION

iH DEPOSITION 

I I EROSION

, i , : I i

Survey of December 12, 1991

350 300 250 200 150 100 50

20

15

10

m 

DC

O 

m

CROSS SECTION 6

|- EXPLANATION

Hi DEPOSITION 

I I EROSION Survey of December 12, 1991'

i , , . , i . , , , i

350 300 250 200 150 100 50 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

Figure 11. Continued.

which is the mean elevation of the channel bottom 

at each cross section, was unchanged.

Almost all of the channel change measured by 

resurveying the study reach was caused by the flow 

of February 7, which was the largest of the three 

flows recorded between the surveys of November 

1991 and June 1992. At the time of bed-material 

sampling on January 31, evidence of minor bank 

erosion was observed from the flow of January 6. 

Blocks of bank material in the channel at that time 

(fig. 16A) were the result of the flow of January 6. 

The presence of bank material in the channel 

indicates that bank failure was caused by low 

flows that were incapable of disaggregating and

transporting the material from the reach. When the 

site was inspected on March 12, the channel had 

been greatly altered, primarily by migration of the 

channel and erosion of the right bmk. Several 

small terraces were obliterated by erosion or buried 

by deposition, and several mature pal? verde trees 

had been washed away. In contrast to conditions 

after the flow of January 6, almost no sloughed 

bank material was observed in the channel in 

March. The absence of failure blocks indicates 

either that no bank failure occurred during waning 

flows on February 7 or that any material left in the 

channel was subsequently removed b;' the flow of 

February 14. Except for possible removal of failure

Channel Change 15
A, Incised channel below 16th 

Street near cross section 1; preflow 

gravel-paved channel bottom was 

0.3 to 0.4 meters below vegetated 

surface (Top right of photograph).

B, Erosion of boulder revetment and 

loss of structure at storm-drain 

outlet below 16th Street near cross 

section 2.

C, Gravel berms between cross 

sections 4 and 5 about 800 meters 

below 16th Street bridge showing 

little or no disturbance from winter 

flows.

Figure 12. Effects of flows on the 

Salt River, Phoenix, Arizona, 1992.

16 Channel Change and Sediment Transport in Two Desert Streams in Central Arizona, 1991-92
if 4

EXPLANATION 

[Number Is cross-section location 

identifier]

SURVEY OF DECEMBER 1991 

SURVEY OF JUNE^JULY 1992

6'

-50 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800

8

HI i.

< rr 

z uj 6

Om

II

LU .

Oil

QH 4 

CD Q

LUCC

Z<

S5

EXPLANATION 

[Number Is cross-section location 

identifier]

SURVEY OF DECEMBER 1991 

SURVEY OF JUNE^JULY 1992

6'

-O 8' 

-o

B

-50 0 200 400 600 800 1,000

LONGITUDINAL DISTANCE, IN METERS

1,200 1,400 1,600

Figure 13. Longitudinal profiles of elevation on the Salt River through the study reach before and afte* winter flows 

of 1992. A, Thalweg elevation. S, Mean channel-bed elevation.

material from the channel, little if any of the 

channel change observed in March is likely to have 

been caused by the flow of February 14, which was 

smaller than the flow of January 6.

The cross sections were not resurveyed after 

the August 22 flow, which had the highest 

discharge in water year 1992. A cursory inspection

of the channel was conducted on December 23, 

1992, to assess the effects of flows occurring after 

the resurvey in June. The right bank ha-1 undergone 

additional erosion although much less erosion 

occurred than after the flow of February 7. The 

distance from the right end points to tl <*. bank edge 

was measured at cross sections 2 and1 3; no bank

Channel Change 17
CO

cc

LU

X

o

LU

o

< 

o

1.5

1.0

0.5

- + BEFORE FEBRUARY 15, 1992

O FEBRUARY 15 THROUGH 

MARCH 17,1992

- A AFTER MARCH 17,1992

-0.5

-1.0

0.1

2.0

1.B

1.6

1.4

1.2

0.1

10 100 1,000

B

+ BEFORE FEBRUARY 15,1992 

O FEBRUARY 15,1992 AND AFTER

1 

DISCHARGE,

10 100 

IN CUBIC METERS PER SECOND

1,000

Figure 14. Discharge and gage-height relations at streamflow-gaging stations on lower Salt River on the basis of 

discharge measurements made during flows in 1992. A, Salt River at 24th Street, Phoenix, Arizona. Change in 

relation between discharge and gage height at 24th Street reflect incision of channel. B, Salt River at Alma School 

Road near Mesa, Arizona. Although incision occurred at Alma School Road, change is not evident in the discharge 

and gage-height relation.

retreat had occurred at cross section 2, but about 

5 m of retreat was measured at cross section 3 

(fig. 15). Low terraces at the base of the right bank 

in cross sections 4 and 5 had been eroded somewhat. The left bank also had retreated at cross 

sections 10 and 11. In addition to the rather minor 

amounts of bank retreat, the channel may have 

been downcut somewhat although the generally

low magnitudes of fluctuations in channel-bed 

elevation on the Hassayampa River make such a 

determination difficult without su-vey measurements.

Additional erosion of gullies aid overflow 

channels in the vegetated terrace on the left of the 

channel took place between late June and 

December 23, 1992. Headcut erosion extended the

18 Channel Change and Sediment Tranaport In Two Desert Streams In Central Arizona, 1991-92
CO

cc

I 'I ' I ' T 

CROSS SECTION 1

Survey of Novembers, 1991

- EXPLANATION 

DEPOSITION 

I I EROSION

I , I i I I

- 260 240 220 200 180 160 140 120 100 80 60 40

8

I ' I ' I ' I ' T 

CROSS SECTION 2

r

Survey of November 6, 1991 

Survey of June 24, 1992s

m

EC

o

m

O

_ EXPLANATION 

iii DEPOSITION 

I I EROSION

i I i I ,

260

8

240 220 200 180 160 140 120 100 80 60 40

n i r \ 'i ' r 

CROSS SECTION 3

Survey of November 6, 1991

_ EXPLANATION 

ill DEPOSITION 

I I EROSION

_j__L _L _L _L J_ _L _L _L _L J_

260 240 220 200 180 160 140 120 100 80 60 40 20 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

Figure 15. Results of repeat surveys of 11 cross sections on the Hassayampa River below the Southern 

Pacific Railroad bridge, Arlington, Arizona.

Channel Change 19
CO 

DC

1 i ' i ' i ' r

CROSS SECTION 4

Survey of November 7, 1991 

_ EXPLANATION

iJi DEPOSITION 

I I EROSION

I . I i I J_ I I

260 

81 

240 220 200 180 160 140 120 100 80 60 40 20

1 i ' r ^ i ^

CROSS SECTION 5

r T

Q

> 

DC 

< 

DC

H

CD 

DC

O

CD

Survey of November 7, 1991.

Survey of June 24, 1992-^

i_ EXPLANATION

ill DEPOSITION 

I I EROSION

i I i I i i i _i_ I i I

260 240 220 200 180 160 140 120 100 80 60

O 8

40 20

l|I]i^ -r

CROSS SECTION 6

Survey of November 8, 1991

_ EXPLANATION 

DEPOSITION 

I I EROSION

I i I i I

Survey of June 24, 1992

I I I

260 240 220 200 180 160 140 120 100 80 60 40 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

20

Figure 15. Continued.

20 Channel Change and Sediment Transport In Two Desert Streams in Central Arizona, 1991-92
CO

tr

CROSS SECTION 7

_ EXPLANATION

ill DEPOSITION 

I I EROSION

Survey of November 13, 1991

I

260

8

240 220 200 180 160 140 120 100 80 60 40 2")

1 I r 1 ' I ' I

CROSS SECTION 8

O 6

rr

m 

tr

O

m

_ EXPLANATION

ill DEPOSITION 

I I EROSION

i I , I i

Survey of June 25, 1992

Survey of November 13, 1991

_|_

z 260 

O 8

LLJ

LJJ

240 220 200 180 160 140 120 100 80 60 40

CROSS SECTION 9

U EXPLANATION 

 DEPOSITION 

I I EROSION

i I , I

Survey of November 13, 1991

I

Survey of June 25, 1992

I , I i I i I I

260 240 220 200 180 160 140 120 100 80 60 40 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

Figure 15. Continued.

Channel Change 21
2

3 

IQ

>-

cr

<

CO

cr

o

m

i- 

< 

>

1 1 ' 1 ' I ' T 

CROSS SECTION 10

_ EXPLANATION 

M DEPOSITION 

I I EROSION

I i I i

Survey of November 14,1991

I i I i I , I

260 240

8

220 200 180 160 140 120 100 80 60 40 20

1 i ' i ' i ' r 

CROSS SECTION 11

\

- EXPLANATION 

DEPOSITION 

I I EROSION

I i I i

Survey of 

November 14,1991X

Survey of June 25,1992

I I

260 240 220 200 180 160 140 120 100 80 60 40 

DISTANCE ACROSS CHANNEL FROM RIGHT BANK, IN METERS

20

Figure 15. Continued.

length of the small channel by about 10 m 

upstream at the base of the levee on the left bank at 

cross section 5 (fig. 15). Although overflow 

occurred on the vegetated terrace during the 

August flow, the amount of overflow was small, 

perhaps confined to rivulets no more than a few 

inches wide that flowed toward headcutting gullies 

and overflow channels. Headcut erosion seems too 

great to have been caused entirely by the small 

amount of overflow that occurred. Sapping of the 

headcut wall by seepage of subsurface water may 

have contributed to headcut retreat (Higgins, 

1990). Most of the channel changes noted on

December 23 probably were caused by the flow of 

August 22; however, the flow of December 8 was 

the longest of the 1992 events and could have 

caused some localized erosion.

Although the peak discharge on August 22 was 

15 percent greater than the peak of February 7, the 

flow of February 7 apparently cause 1 more bank 

erosion than the flow in August. Pe*k discharge 

generally does not correlate directly with rates of 

bank erosion because of other factors such as 

cohesiveness of bank material and pre-existing 

conditions (Knighton, 1984). Most streambanks 

have some degree of cohesion so that erosion does

22 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
A, Looking downstream at streambank just below cross section 2 

after the flow on January 6, 1992. 

Failure material at base of bank 

indicates some erosion occurred 

from the flow in January. (Photograph was taken on January 30, 

1992.)

B, Bank erosion after the flow on 

February 7, 1992. (Photograph 16B 

is the same location as photograph 16A Photograph was taken 

on April 10, 1992.)

Figure 16. Effects of flows on the Hassayampa River, near Arlington, 

Arizona, 1992.

not occur immediately upon application of the 

minimum shear stress necessary for movement of 

the sediment particles comprising the bank 

material. Cohesive forces are weakened by 

increased soil moisture (Wolman, 1959; Hooke, 

1979); therefore, flows must not only be of 

sufficient magnitude to provide the necessary shear 

stress for bank erosion to occur, they also must last 

long enough to infiltrate banks and break down 

cohesive forces. The event on February 7 lasted 

twice as long as the event in August; however,

mean discharge during both events was comparable. Consequently, during the February flow, 

infiltration of flow into streambanks and associated 

weakening of cohesive forces occurred over a 

longer period of time, and the threshold at which 

bank erosion takes place was exceeded for a 

greater period of time. Nonetheless, the magnitude 

of bank erosion from the first event seems disproportionate to that of the flow in August solely as a 

result of a few hours flow duration. The close 

succession of two flows of comparable peak

Channel Change 23
C, Looking upstream at low terrace 

near cross section 10 before flow 

on February 7, 1992. (Photograph 

was taken on January 30, 1992.)

D, Low terrace along right side 

of channel after the flow on 

February 7, 1992. Deposition in 

channel nearly buried the terrace. 

(Photograph 16D is the same 

location as photograph 16C. 

Photograph was taken on April 10, 

1992.)

Figure 16. Continued.

discharge may account for much of the discrepancy 

in erosion rates. The event in February adjusted the 

channel to accommodate a peak discharge of about 

136 m3/s; the single intervening flow before the 

event on August 22 did not modify the channel 

significantly, so only moderate changes in channel 

geometry were necessary to accommodate the peak 

discharge of 173 m3/s.

Long-term channel instability is difficult to 

assess on the basis of a single season of channel 

monitoring. The amount of bank erosion occurring

on the Hassayampa River as a result of a single, 

moderate event seems quite high but may not be 

atypical of alluvial channels in the Southwest. Data 

on erosion rates for single events on other streams 

are few. On an entrenched reach of the Santa Cruz 

River south of Tucson, Arizona, peak discharge of 

1,492 m3/s during the flood of October 1983 

caused as much as 250 m of bank erosion. During 

the same flood, about 365 m of bank erosion 

occurred on an unentrenched reach of the Santa 

Cruz River near the Pima-Santa Cruz County line

24 Channel Change and Sediment Transport in Two Desert Streams in Central Arizona, 1991-92
EXPLANATION 

[Number is cross-section location 

identifier]

SURVEY OF NOVEMBER 1991

1' 2'

O O SURVEY OF JUNE 19?2

900

CQ Q

II

1 2

EXPLANATION

[Number Is cross-section location

identifier] 

1 2 

O O SURVEY OF NOVEMBER 1991

1' 2'

O O SURVEY OF JUNE 19S2

B

I I I I

-250 100 200 300 400 500 600

LONGITUDINAL DISTANCE, IN METERS

700 800 900

Figure 17. Longitudinal profiles of elevation on the Hassayampa River through the study reach before and after 

winter flows of 1992. A, Thalweg elevation. B, Mean channel-bed elevation.

where peak discharge reached 1,274 m3/s (Parker, 

1993). The 1983 flood on the Santa Cruz River, 

however, lasted for 9 days compared to a duration 

of 7.25 hours for the event on February 7 on the 

Hassayampa River. Depending on the method used 

to estimate flood frequency, the Santa Cruz River 

flood had a recurrence interval from less than 50 to 

more than 100 years (Roeske and others, 1989; 

Webb and Betancourt, 1992). Hays (1984) reported

as much as 60 m of bank erosion on the lower 

Santa Cruz River in response to a 6-day flow with a 

peak discharge of 234 m3/s and a recurrence 

interval of about 2 years.

In reaches of maximum bank erosion on the 

Santa Cruz River, hourly bank-erosion rates 

averaged over the entire period of runoff for the 

flood of 1983, were about 0.6-2 m/hr. The maximum bank-erosion rate on the study reach of the

Channel Change 25
Hassayampa River, averaged over the entire period 

of runoff for the flow of February 7, was about 

2.1 m/hr. Comparison of erosion rates on the 

Hassayampa River with other published rates 

worldwide is difficult because of differences in 

methods of determining and reporting erosion rates 

(Hooke, 1980).

SEDIMENT TRANSPORT

Salt River

Suspended-sediment concentration on the Salt 

River generally increased with flow peaks during 

the 5-month sampling period (figs. 18 and 19/4, B)\ 

however, during prolonged periods of steady flow, 

such as from January 15 through January 29, 

sediment concentration decreased. Although the 

sampling density was too low to completely 

characterize the temporal variability of suspendedsediment transport during the winter flows, a 

general trend seems to have been toward 

decreasing sediment concentration with discharge 

over the entire season, which would suggest

depletion of sediment availability. Seliment concentration generally increased and decreased more 

rapidly than discharge.

Suspended-sediment concentration, which 

ranged from 2 to 617 mg/L, is low but is 

comparable to that of other Arizona streams that 

are controlled by dams (fig. 195). Because most 

sediment is trapped in the upstrearr reservoirs, 

most suspended sediment in transport on the lower 

Salt River must be supplied by local runoff, bank 

erosion, and entrainment of sediments stored in the 

channel. J_x>cal runoff was a negligible component 

of winter flows. J_x>cal bank erosion occurred but 

was of low magnitude. Almost all suspended 

sediment transported through the lower Salt River, 

therefore, must have come from the channel 

bottom.

Systematic mapping of channel segments was 

beyond the scope of this project; however, 

qualitatively, most of the channel upstream from 

the sampling site at 24th Street seems to be gravel 

paved. Fine sand, silt, and clay that constitute the 

suspended-sediment load is in scattered patches 

along channel margins, in channel bar? and sheets, 

and in the interstices among gravel clasts. In at 

least some locations, gravel pavement is only

500

O 400

LLJ 

«

EC 

LLJ 

QC/> 30°

O

m

o 20°

C3 

EC

I 100 

O

EXPLANATION 

 DISCHARGE 

+ SEDIMENT CONCENTRATION

700

600

500

cc

LLJ 

O.

I

400

300

200

O

o

100

Q 

LLJ

JANUARY FEBRUARY MARCH APRIL

Figure 18. Relation of suspended-sediment concentration to time and discharge on the Salt River, Phoenix, 

Arizona, winter 1992.

26 Channel Change and Sediment Tranaport In Two Desert Streams In Central Arizona, 1991-92
100

DC 

LU

I]

DC 

LU 

Q.

DC 

O

O

Z

o 

o

iz

LU

Q 

LU

10

10 100 

DISCHARGE, IN CUBIC METERS PER SECOND

1,000

1,000

500 -

EXPLANATION

+ SALT RIVER, PHOENIX

A AGUA FRIA RIVER BELOW WADDELL DAM

D COLORADO RIVER, 

LEES FERRY

O VERDE RIVER BELOW 

BARTLETT DAM

10

UNIT DISCHARGE, IN THOUSANDTHS OF CUBIC METERS 

PER SECOND PER SQUARE KILOMETER

50

Figure 19. Sediment-transport data, Salt River and other rivers in Arizona controlled by dams. A, Relation 

of suspended-sediment concentration to discharge. 6, Comparison of suspended-sediment concentrations 

and discharge relations on the Salt River with relations for other controlled rivers in Arizona.

Sediment Transport 27
1-2 particles thick and is underlain by beds of fine 

sand and silt. The underlying fine-grained material 

provides a source for suspended-sediment transport 

whenever the gravel pavement is disrupted by 

streamflow or human activity, such as 

channelization or sand-and-gravel mining (fig. 3A).

Particle-size analysis of the sand fraction of 

suspended-sediment and bed-material samples 

shows sediment transported in suspension 

generally to be finer than deposited material 

(fig. 20A). Channel sands collected from the predominantly gravel-paved channel bottom, and 

terrace sands collected from the channel margin 

(fig. 2) are composed of 30-55 percent material 

finer than 0.25 mm in diameter. Suspended 

sediment is composed of 80-99 percent of material finer than 0.25 mm in diameter. Bed material 

collected from channel bottom that had been 

scraped of gravel has a particle-size distribution 

similar to that for suspended-sediment samples. 

Such material appears to be primarily alluvium 

exposed by gravel-removal operations rather than 

recent sediments deposited after gravel removal. 

The alluvium appears to be the most volumetrically significant suspended-sediment source immediately upstream from the sampling site; however, 

the relative importance of this sediment source 

through the entire lower Salt River was not 

determined.

Variability in the relation of discharge to 

sediment concentration (fig. 19B) probably is 

related to the fluctuations in the availability of sediment for transport. Variability is particularly great 

at discharges lower than 160 m3/s. At many 

locations, sediment is not entrained across the 

entire width of the channel during lower discharges, and heterogeneity of sediment availability 

may affect suspended-sediment concentration 

more than at higher discharges. At higher discharges, all sediment in the channel bottom 

available for suspended transport is likely to be 

entrained.

Bedload transport was not measured in this 

study, but some qualitative statements about 

bedload entrainment, transport, and deposition can 

be inferred from the spatial patterns of channel 

change. Bed material available for transport as 

bedload is predominantly coarse gravel (fig. 20B). 

At cross section 1 below 16th Street, median 

diameter of gravel-sized bed material (>11 mm) is

27 mm, and maximum particle size was 355 mm. 

The particle-size distribution of gravel across cross 

section 8 was slightly lower.

Channel incision that occurred at 16th Street 

and at other bridges upstream from the study area, 

where particle size of bed material p-obably was 

greater, generally occurred in the gravel-paved 

channel bottom. Apparent lack of channel change 

before the flood peak of February 15 suggests that 

little movement of coarse-grained t?4 material 

occurred before that date. At flows of about 

30 m3/s, during which wading-dischane measurements were made and the channel bottom was 

observed, neither entrainment, traTSport, nor 

deposition of bedload could be seen.

The flows of February 14-16, which caused 

the initial incision at 16th Street, w^re the first 

flows of sufficient magnitude to entrain the coarser 

gravel on the channel bottom. The channel bottom 

at 16th Street was not resampled following the 

winter flow; however, on inspection, no obvious 

change in particle-size distribution of bed material 

was observed. Transport distance of coarse gravel 

was apparently short, and most material from the 

incised channel beneath the 16th Stree* bridge was 

deposited in the gravel lobe at crops section 2 

(fig. 11). No evidence of significant deposition of 

gravel is seen as far downstream as cress section 3, 

about 430 m downstream from the 16th Street 

bridge. Indeed, a sheet of sand deposited throughout much of cross sections 3 and A terminated 

abruptly about 500 m downstream from 16th 

Street, which indicates that transport distance of 

sand-sized bedload also was short.

Entrainment of coarse gravels may have 

occurred only in association with contracted flow 

at bridge sites on the lower Salt River. The short 

transport distance of such gravels witl in the study 

reach may have been a function of the flattening of 

channel gradient caused by removaf of bottom 

material downstream from cross sectio^ 2 (fig. 13). 

The low channel gradient results in a low-energy 

reach below cross section 4 in wh'oh bedload 

transport was apparently negligible. Gravel berms 

left on the channel bottom by grading equipment 

generally were undisturbed by the vdnter flows 

(fig. 12Q, and pebbles as small as 20 mm in 

diameter appeared to have remained in place.

28 Channel Change and Sediment Tranaport In Two Desert Streams In Central Arizona, 1991-92
99.999

99.99

99.9

LU 

N

LU

_l

o

99 

98 -

95 

90 -

80 - 

70 - 

60 i50 L 

40 - 

30 -

20 i10

0.01

~ 99.999

toc

LU

z

z

LU 

O

cr

99.99 L99.9 EEXPLANATION

A-A SUSPENDED-SEDIMENT 

SAMPLES

O-O CHANNEL MUD SAMPLE 

FROM SCRAPED 

SURFACE

D-D GRAVEL-BED CHANNEL 

SAMPLES AT CROSS 

SECTIONS 1 AND 8

V-V TERRACE SAMP'.E FROM : 

EDGE OF CHANNEL AT - 

CROSS SECTION 1

I

0.1 10

EXPLANATION -=

D-D CROSS SECTION 1 -E

CROSS SECTION 8 -

100 

PARTICLE DIAMETER, IN MILLIMETERS

1,000

Figure 20. Particle-size data, Salt River in Arizona. A, Particle-size distribution of suspended-sediment and 

sand-sized bed-material samples. B, Particle-size distribution gravel-sized bed-material samples.

Sediment Transport 29
Hassayampa River

For the three events sampled, suspendedsediment concentrations on the Hassayampa 

River were high and ranged from 12,800 to 

132,000 mg/L (fig. 21, 22A). Variability also is 

high, and the number of samples are few; therefore, 

any generalizations about sediment transport on the 

Hassayampa must be tentative. The high sediment 

concentrations were typical of concentrations on 

other unregulated alluvial streams in Arizona 

(fig. 22B).

The entire Hassayampa data set shows a poor 

relation between sediment concentration and 

discharge; however, distinct patterns are evident 

within and among individual events. On the basis 

of two flows sampled during the rising limb of the 

hydrograph, maximum sediment concentration is 

reached before peak discharge and then falls off 

rapidly (fig. 21). The lowest sediment concentrations were recorded for the flow of August 22, 

which had the highest peak discharge of the year. 

The highest sediment concentrations were attained 

during the flow of February 14, which was the 

smallest of the sampled flows. Variability of 

sediment concentration to flood magnitude may 

reflect (1) a system-wide limited sediment supply 

so that increasing discharge dilutes sediment 

concentration; (2) spatial and temporal variability 

in sediment supply resulting from episodic bank 

and channel erosion, or (3) differences in flow 

characteristics among events. The relation of 

sediment concentration to flood discharge with 

time forms a clockwise loop for the floods on 

August 22 and February 7 (fig. 22A); a similar 

pattern probably would have been seen for the 

flood on February 14 if the flow had been sampled 

before the flood peak. Williams (1989) suggests 

that such a pattern may be the result of a limited 

sediment supply or an intense flood that forms an 

armored layer before the discharge peak.

The nature of the Hassayampa River drainage 

basin, which consists mainly of low-elevation alluvial basins filled with unconsolidated sediments, 

suggests that the sediment supply probably is not 

limited. Some data indicate that spatial and 

temporal variability in sediment supply is at least a 

partial factor in determining the discharge and 

suspended-sediment concentration relations for 

the events in this study. The flow on February 7

140

120

100

80

60

Q 40

z

0 20

O

LU

co o 

DC 140

LU

°-120

CO

tr ujlOO

LU

80

_ 60 

m

O 40

Z 

- 20

LU

O °

tr 140

o 120

CO

Q 100

80

60

40

20

B

140

120

100

80

60

40

20

0

140

120

100

80

60

40

20

0

140

120

100

80

60

40

tr 

LU 

a.

CO

tr 

o

2468 

DURATION, IN HOURS

EXPLANATION

DISCHARGE + SEDIMENT CONCENTRATION

CO

Q

Z

<

CO

3

o

X

LU

2

o

LU

20 »

Figure 21. Relation of suspended-sediment concentration to time and discharge on the Hassayampa River 

near Arlington, Arizona. A, February 7, 1992. B, February 14,1992. C, August 23,1992.

30 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
200

100

70

50 

CC 

in 

t 40

CC

UJ

a.

co 

Q

co 

O

UJ

o

z 

O

O

Q 

UJ

co

30

co

CC

<5 20

10

i i r i

10

500

100

10

EXPLANATION

DATE OF SAMPLES 

WERE COLLECTED

O February?, 1992

n February 14,1992

A August 22,1992

 < DIRECTION OF TIME 

FOR INDIVIDUAL 

FLOODS Arrow 

indicates end of 

sampling period

50 100 

DISCHARGE, IN CUBIC METERS PER SECOND

0.1

0.0001 0.001 0.01 0.1 1 10

UNIT DISCHARGE, IN THOUSANDTHS OF CUBIC METERS 

PER SECOND PER SQUARE KILOMETER

100

500

-

-

-

: +

_ A 

V

To

- n

" \X

B 0

v ®Q Q §+

v o v O °A <DH 

V v v + 3^ SP* D

v v O V (y<y><3g+++ + D D

EXPLANATION v Q ^ <> r-,

HASSAYAMPA RIVER, <j~i7 r-rn 

ARLINGTON vv rj D-J

BLACK RIVER, HOUCK _

LITTLE COLORADO P] 

RIVER, CAMERON

PUERCO RIVER, V 

CHAMBERS

RILLITO RIVER, 

TUCSON A

> SANTA CRUZ RIVER, 

TUCSON

I I 1 Mill I I I 1 mil 1 1 1 1 Mill I I I 1 I nil 1 1 1 1 1 ml I ,111ml

1 1 1

-

-

-

!

-

~

500

Figure 22. Sediment-transport data on the Hassayampa River and other rivers in Arizona. A, Relat'on of 

suspended-sediment concentration to discharge. B, Comparison of suspended-sediment concentrations 

and discharge relations on the Hassayampa River with relations for other uncontrolled rivers in Arizona.

Sediment Transport 31
resulted in significant bank erosion. The high rate 

of bank erosion may have caused sediment concentration to locally exceed transport capacity 

resulting in deposition in the channel. Channelbottom material is primarily sand (fig. 23); 

however, most bank material, especially in the 

upper part of the banks, appears to have a higher 

silt-clay content. If such material were deposited 

on the channel bottom during the waning stage of 

the February 7 event, it would provide a source of 

readily available fine-grained material for 

suspended-sediment transport during the next 

event. Such an explanation also is consistent with 

Williams' (1989) suggestion that clockwise loop 

relations in sediment concentration and flood 

discharge with time may be the result of intense 

floods that flush sediment from a reach before 

forming an armored channel bottom at the peak of 

the flood. Whether an armored layer is actually

formed within the study reach of the Hassayampa 

River is unknown, but isolated boulders and large 

cobbles scattered over the channel borom indicate 

that such a layer might be formed at high 

discharges.

Differences in flow characteristics also have 

been cited as a cause of variability in d' 'charge and 

sediment-transport relations. In the Southwest, in 

particular, less intense winter frontal storms are 

believed to cause flows that have generally lower 

sediment concentrations than flows caused by 

summer monsoonal storms (Matbck, 1965; 

Burkham, 1972). In some cases, this assumption 

has been demonstrated (Graf and otters, 1991); 

however, supporting data generally are meager 

and sometimes contradictory (Parlor, 1993). 

Obviously, the seasonality of flow cannot explain 

the variability among the three Hassayampa River 

samples because the one summer flow has the

99.999

N

55

O

<

H

tr

o

IT

99.99

99.9

99

98

90

80

70

60

50

40

30

20

10

EXPLANATION

H CH SAMPLES FROM UNVEGETATED 

CHANNEL

A A SAMPLES FROM VEGETATED 

CHANNEL

O-O SAMPLES FROM SANDY 

TERRACE

0.01

I

0.1 1 

PARTICLE DIAMETER, IN MILLIMETERS

10

Figure 23. Particle-size distribution of bed-material samples from the Hassayampa River below the Southern 

Pacific Railroad bridge, near Arlington, Arizona.

32 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
lowest sediment concentration to discharge 

relation. The variability might be explained, 

however, by differences in the origin of flow for 

the three events. Because of high transmission 

losses to the streambed, flows on the Hassayampa 

River that originate well upstream from the 

sampling site can be expected to have higher 

sediment concentrations than flows originating 

closer to the sampling site. Higher stream 

velocities are required to entrain fine-grained 

sediment than are needed to transport it (Statham, 

1979, p. 120); therefore, as discharge (and velocity) decreases from transmission losses, most of 

the fine-grained sediment can be expected to 

remain in suspension and produce a downstream 

increase in suspended-sediment concentration. The 

sediment-ladened flow of February 14 apparently 

originated well upstream from the sampling site 

near Arlington. The flow produced a peak discharge of 95.7 m3/s on February 13 at the 

streamflow-gaging station near Morristown about 

57 km upstream from the Arlington station. At 

Arlington, the flood peak, which occurred early on 

the morning of February 14, was only 29.5 m3/s. 

Total streamflow for the period of storm runoff 

declined even more substantially between the two 

stations. At Arlington, where the period of runoff 

lasted less than 1 day, total streamflow was only 9 

percent of the total at Morristown where the period 

of runoff lasted 6 days (Smith and others, 1993). 

Such a depletion of streamflow would have 

significantly increased sediment concentration as 

the floodwave moved downstream. All the other 

flows at Arlington during the study period 

apparently resulted from runoff that originated 

primarily downstream from the gaging station at 

Morristown.

DISCUSSION

Geomorphic and hydrologic processes in 

dryland fluvial systems are fundamentally different 

from processes on streams in humid regions (Graf, 

1988b). One fundamental difference between dry 

and humid regions that has been suggested is the 

nature of the event that is most significant in 

determining the morphology and hydraulics of 

stream channels. In humid, temperate regions, 

streams generally are perennial; flow approaches

uniform, steady conditions for extended periods of 

time, and the range of discharge is net. great. The 

main hydrologic control on such systems is 

considered by some investigators to be a moderate, 

frequent flow event, such as the bank-fill discharge 

that has a recurrence interval of less than 2 years 

(Wolman and Miller, 1960). In drier ngions, such 

as the semiarid to arid western United States, many 

streams are ephemeral; extended periods of 

uniform, steady flow are exceptional, and the range 

of discharge can cover six orders of rragnitude on 

large streams. Rare, high-magnitude events may be 

the dominant hydrologic control on dryland 

streams, especially where channel resistance to 

erosion is high (Baker, 1977; Patton and Baker, 

1977). Where channel resistance is low, however, 

major channel changes can occur over a wide range 

of discharges although the rate of chmge and the 

mechanisms causing change will vary according to 

the magnitude of a flow event (Palter, 1990a, 

1990b, and 1993).

The moderate discharges that occ irred on the 

Salt River in 1992 could be expected to have 

limited effect on channel morphology. Both banks 

of the channel are armored with revetment, the 

channel bottom was paved with coarse gravel, and 

channel morphology at the beginning of 1992 had 

been shaped by flows of more than 10 times greater 

magnitude than flows that occurred in 1992. In 

fact, the channel changes measured in the study 

reach and those observed elsewhere on the lower 

Salt River probably were of little geomorphic significance but were of some importance from a 

stream-management standpoint Channel incision 

caused a change in stage-discharge relations and 

changed the hydraulic characteristics of the lowflow channel at bridge crossings. In the study 

reach, excavation of material by charnel incision 

underneath the 16th Street bridge and i*s deposition 

immediately downstream forced flow against the 

left bank, resulting in lateral erosion ard ultimately 

led to failure of bank revetment an-1 loss of a 

structure. Lateral erosion also led to bank failure 

and exposure of a landfill upstream fnm Country 

Club Drive in Mesa. The subsequent stream 

transport of refuse became a matter of public 

consternation (Arizona Republic, 1992).

Most channel change associated w;fh moderate 

flows on the lower Salt River in the winter of 1992 

was channel incision beneath bridge? suggesting

D'scussion 33
that the constriction of flow caused by bridge piers 

in the channel was the major factor controlling the 

occurrence of channel change. Changes in bedmaterial composition, channel gradient, channel 

morphology, and possibly of sediment availability 

as a result of gravel mining also may have played a 

role in channel change during the 1992 flows. At 

least within the study reach, flattening of channelbed gradient by removal of bed material and 

grading of the channel bottom could have been a 

factor in the rapid deposition of gravel immediately 

downstream from the incised channel. Formation 

of an anomalously steep channel profile upstream 

from where gravel had been removed may have 

increased the degree of channel incision at the head 

of the study reach. The degree of channel change 

occurring on the lower Salt River was 

unanticipated as shown by the failure of bank 

revetment in the study reach. The failure at 

moderate flow demonstrates that peak discharges 

associated with high-magnitude, low-frequency 

flows are not the only important design criteria on 

highly disturbed urban channels. A major issue to 

be addressed on the Salt River and other urban 

desert streams is the extent to which human 

alteration of the channel affects hydrologic and 

geomorphic processes.

Channel instability on the lower Hassayampa 

River is to be expected because of the easily 

credible fine to medium sand that forms the banks 

and channel bottom and the lack of stabilizing bank 

vegetation; however, the magnitude of bank 

erosion in response to the flows in 1992 was 

greater than had been expected. As more data on 

channel instability in desert streams becomes 

available, the Hassayampa River channel may not 

prove to be unusually unstable for a southwestern 

alluvial stream. The degree of channel response 

does not increase linearly with flood magnitude. 

The apparently greater magnitude of bank erosion 

resulting from the flow of February 7 compared to 

the flow of August 22, indicates that factors other 

than peak discharge control the amount of bank 

erosion. Although duration of flow has been cited 

as a possible cause of variability in bank-erosion 

rates for cohesive streambanks, the banks of the 

Hassayampa River exhibit little if any cohesion, 

and both of the largest flows of 1992 were of such 

short duration that additional explanation seems 

necessary. The sequence of events in this case,

the occurrence of flows of similar magnitude about 

6 months apart is a likely cause for the different 

effects of the two events. Stream channels retain 

the imprint of previous geomorohologically 

effective events until they are modified by subsequent flows. Ephemeral channels in dry environments may reflect the morphology ar«i hydraulic 

conditions imposed by the last effect:ve flow for 

months, years, or even decades depending on the 

magnitude of the effective event and the magnitude 

and frequency of subsequent channel-modifying 

events (Wolman and Gerson, 1978; Kochel, 1988; 

Parker, 1993).

At the time of this study, channel instability on 

the Hassayampa River below Wickent iirg was not 

a major stream-management issue. Other than 

railroad tracks and several major hi-ihways that 

crossed the channel, the lower drainage basin 

generally was undeveloped, and hurmn activities 

were minimally affected by the shifting, migrating 

channel. Future development near the Hassayampa 

River and similar streams, however, will increase 

the probability of problems related to channel 

instability. Furthermore, the high suspendedsediment load of such streams means that any 

activity that contaminates sediments o~ that causes 

an increase or decrease in sediment availability can 

have significant downstream consequences.

The findings of this study rnse several 

questions concerning processes on alluvial desert 

channels that may need further investigation to 

improve the ability of managers to effectively cope 

with potential problems:

1. What is the variability in bank erosion, 

channel deposition and channel erosion, 

and sediment transport fron event to 

event?

2. How are processes related from one reach 

to the next? What are the upstream and 

downstream effects of channel change in a 

reach?

3. What are the limits of lateral channel 

instability? What is the maxirr-'jm amount 

of bank erosion and channel migration that 

can be expected under current climatic 

conditions?

4. What is the depth of the active channel bed 

in sandy, ephemeral channels?

34 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-92
5. How does sediment move through the 

system? What is the source of fine-grained 

sediment; where is it stored; and, on 

an engineering time scale, what is its 

destination?

6. Do mechanisms of channel change vary 

according to flood magnitude and vary 

over longer periods of time such as years 

or decades?

7. How do hydraulic conditions, such as 

roughness, channel geometry, and gradient change over time; and what is the 

mechanism of such change?

8. How long do arid-region, ephemeral 

channels retain the imprint of previous 

floods, and what are the mechanisms that 

remove the imprint?

9. How does human alteration of the 

channels affect hydrologic and geomorphic processes on urban desert 

streams?

SUMMARY AND CONCLUSIONS

Sediment transport and channel change were 

monitored on the Salt and Hassayampa Rivers in 

Maricopa County, Arizona, during water year 

1992. Although the monitoring program did not 

continue long enough to sample the variability in 

stream processes, data that were collected provide 

some insight into the response of two desert rivers 

to moderate flows. Channel change was monitored 

by establishing monumented cross sections across 

the study reaches on each river. Channel 

morphology was surveyed along the cross sections 

before the onset of the winter rainy season, and 

each cross section was resurveyed in early summer 

before the summer rainy season. Suspendedsediment samples were collected manually on the 

Salt River and were collected by automatic sampler 

on the Hassayampa River. Bed material was 

sampled on both rivers to characterize channelbottom sediments.

The Salt River, a large, gravel-paved river in 

which streamflow occurs in response to releases 

from upstream reservoirs, was selected for 

monitoring because of the river's urban location 

and its potential for disrupting economic activity 

during floods in the Phoenix area. During sustained

flows from early January to early June 1992, 

flood peaks of 368, 241, and 306 m3/s occurred. 

Although the winter flows were the highest in 

9 years, they were minor compared to those 

occurring during a series of floods from 1966 to 

1980. In the study area between 16th and 7th 

Streets, the flows incised the channel 2 m and 

caused local bank erosion that undermined the 

boulder revetment and led to failure of a large 

concrete-drop structure. In August 1992, a short 

period of flow produced a peak discharge of 

493 m3/s; however, the flow had little or no effect 

on channel morphology. A total of 19 suspendedsediment samples were collected durir"? the winter 

flows. At discharges from 6.7 to 343 m3/s, sediment concentrations ranged from 2 to 617 mg/L, 

which are typical concentrations for large, 

controlled streams in Arizona.

The Hassayampa River near Arlington, 

Arizona, was selected for study because it is 

the last, large, unregulated, ephemeral stream in 

central Arizona. Furthermore, it is in an area that 

can be expected to be subjected to development 

pressures in coming decades because of its 

proximity to the Phoenix metropolitan area. An 

understanding of processes in the unstable, shifting 

river may enable flood-plain managers and 

engineers to plan urban development in a way that 

minimizes the need for expensive structural 

methods of flood-hazard control.

During 1992, five periods of flow occurred on 

the Hassayampa River. A flow on February 7 that 

produced a peak discharge of 127 m3/s caused 

considerable bank erosion through the study area. 

A flow on August 22 produced a peak discharge 

of 173 m3/s but apparently caused less erosion than 

the earlier, smaller flow. Both flows had a recurrence interval of less than 5 years. Suspendedsediment samples were collected during three 

periods of flow. Sediment concentrations ranged 

from 12,800 to 132,000 mg/L for discharges 

ranging from 13 to 128 m3/s. "Tie relation 

between sediment concentration and d^charge was 

complex.

Results of the monitoring program during 

flows of 1992 on the Salt and Hassayampa Rivers 

support the following tentative conclusions.

1. Moderate flows on the Salt River can cause 

channel changes of engineering significance. Channel hydraulics that control

Summary and Conclusions 35
the velocity and shear-stress distribution of 

moderate flows have been affected by 

human activity including bridge construction and gravel mining. On the lower 

Hassayampa River, the channel is highly 

unstable, and 15-20 m of bank erosion can 

occur from a flow with a recurrence 

interval of less than 5 years. The rate of 

bank erosion occurring in the flow of 

February 7, 1992, was comparable to 

bank-erosion rates for single events on the 

Santa Cruz River in southern Arizona.

2. Channel incision on the Salt River and 

bank erosion on the Hassayampa River do 

not increase linearly in relation to peak 

discharge. Both streams had summer flows 

with peak discharges higher than the peak 

discharges that occurred during the winter, 

yet channel change was much less from the 

summer flows. Summer flows were shorter 

in duration than winter flows especially on 

the Salt River, which partly may explain 

the variability in channel response. The 

sequence of events also appears to have 

been important in controlling the 

magnitude of channel response to flow 

especially on the Hassayampa River where 

the sequence of events probably was the 

dominant control

3. Suspended-sediment concentration is low 

on the Salt River, shows some relation to 

discharge, and tends to decrease during 

extended periods of steady flow. The 

channel bottom is the probable source for 

almost all suspended sediment. On the 

Hassayampa River, the relation of 

sediment concentration to discharge is 

extremely variable; however, maximum 

sediment concentration seems to occur 

immediately before peak discharge and 

then decreases steadily with the decreasing 

discharge. High rates of bank erosion may 

be related to high sediment concentrations. 

Sediment concentration also may depend 

on the distance upstream from the 

sampling site in which flow originates; 

high streamflow transmission losses may 

cause increased sediment concentration in 

flows originating well upstream from the 

sampling site.

4. The gravel bottom of the Salt River 

channel is a mobile pavement that can be 

moved at flows well below maximum 

flood levels at least within areas of 

contracted flow rather than an armor that 

can be entrained only by exfr?me floods. 

At the discharges occurring in 1992, coarse 

gravel within the study reach was 

transported only a short distance from its 

location at the time of entrainnent

REFERENCES CITED

Arizona Republic, 1992, Trashing our river Editorial: 

Phoenix, Arizona, The Arizona Republic, 

January 15,1992, p. A18.

Baker, V.R., 1977, Stream-channel response to floods, 

with examples from central Texas: Geological 

Society of America Bulletin, v. 88, p. 1057-1071.

Boner, F.C., Konieczki, A.D., and Davis R.G., 1991, 

Water resources data, Arizona, water year 1990: 

U.S. Geological Survey Water-Data Report 

AZ-90-l,381p.

Boner, F.C., Davis, R.G., and Duet, N.R., 1992, Water 

resources data, Arizona, water yea- 1991: U.S. 

Geological Survey Water-Data Report AZ-91-1, 

411 p.

Burkham, DJE., 1972, Channel changes of the Gila River 

in Safford Valley, Arizona, 1846-1970: U.S. 

Geological Survey Professional Paper 655-G, 24 p.

Chin, E.H., Aldridge, B.N., and Longfieli, RJ., 1990, 

Floods of February 1980 in southern California and 

central Arizona: U.S. Geological Survey 

Professional Paper 1494,126 p.

Edwards, T.K., and Glysson, G.D., 1988, Field methods 

for measurement of fluvial sediment U.S. 

Geological Survey Open-File Report 8 '-531,118 p.

Garrett, J.M., and Gellenbeck, D.J., 1991, Basin 

characteristics and streamflow statistics in Arizona 

as of 1989: U.S. Geological Survey WaterResources Investigations Report 91-4041,612 p.

Graf, J.B., Webb, R.H., and Hereford, Richard, 1991, 

Relation of sediment load and flood-plain formation 

to climatic variability, Paria River drainage basin, 

Utah and Arizona: Geological Society of America 

Bulletin, v. 103, p. 1405-1415.

Graf, W.L., 1983, Flood-related channel change in an 

arid-region river: Earth Surface Processes and 

Landforms, v. 8, p. 125-139.

___1988a, Definition of flood plains along arid-region 

rivers, in Baker, V.R., Kochel, R.C, and Patton,

36 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-82
P.C., eds., Flood geomorphology: New York, John 

Wiley and Sons, p. 231-241. 

_1988b, Fluvial processes in dryland rivers: Berlin,

Springer-Verlag, 346 p.

Hays, ME., 1984, Analysis of historic channel change as 

a method for evaluating flood hazard in the semiarid 

Southwest: Tucson, Arizona, University of Arizona, 

master's thesis, 41 p.

Higgins, C.G., 1990, Gully development, with a case 

study by Hill, B.R., and Lehre, A.K., in Higgins, 

C.G., and Coates, D.R., eds., Groundwater 

geomorphology The role of subsurface water in 

Earth-surface processes and landforms: Boulder, 

Colorado, Geological Society of America Special 

Paper 252, p. 139-155.

Hirschboeck, K.K., 1985, Hydroclimatology of flow 

events in the Gila River basin, central and southern 

Arizona: Tucson, University of Arizona, doctoral 

dissertation, 335 p.

Hooke, J.M., 1979, An analysis of the processes of river 

bank erosion: Journal of Hydrology, v. 42, p. 39-62.

___1980, Magnitude and distribution of rates of river 

bank erosion: Earth Surface Processes, v. 5, 

p. 143-157.

Knighton, D., 1984, Fluvial forms and processes: 

London, Edward Arnold, Ltd., 218 p.

Kochel, R.C., 1988, Geomorphic impact of large 

floods Review and new perspectives on 

magnitude and frequency, in Baker, V.R., Kochel, 

R.C., and Patton, P.C., eds., Flood geomorphology: 

New York, John Wiley and Sons, p. 169-187.

Matlock, W.G., 1965, The effect of silt-laden water on 

infiltration in alluvial channels: Tucson, Arizona, 

University of Arizona, doctoral dissertation, 102 p.

Parker, J.T.C., 1990a, Channel changing processes on 

the Santa Cruz River, Pima County, Arizona, 

1936-1986, in French, R.H., ed., Hydraulics/ 

Hydrology of Arid Lands Proceedings of the 

International Symposium: New York, American 

Society of Civil Engineers, p. 441-446.

___1990b, Temporal variability of lateral channel 

change on the Santa Cruz River, Pima County, 

Arizona: American Geophysical Union, EOS 

Transactions, v. 71, no. 43, October 23, 1990, 

p. 1322.

___1993, Channel change on the Santa Cruz River, 

Pima County, Arizona, 1936-86: U.S. Geological 

Survey Open-File Report 93-41,65 p

Patton, P.C., and Baker, V.R., 1977, Geomorphic 

response of central Texas stream channels to 

catastrophic rainfall and runoff, in Dc"hring, D.O., 

ed., Geomorphology in Arid Regions: Binghamton, 

New York State University, Publications in 

Geomorphology, p. 189-217.

Roeske, R.H., Garrett, J.M., and Eychane-r, J.H., 1989, 

Roods of October 1983 in southeas*ern Arizona: 

U.S. Geological Survey Water-Resorirces Investigations Report 85-4225-C, 77 p.

Smith, C.F., Boner, F.C., Davis, R.G., Dret, N.R., and 

Rigas, P.D., 1993, Water resources data, Arizona, 

water year 1992: U.S. Geological Survey WaterData Report AZ-92-1, 360 p.

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tropical cyclones on the southwestern United States: 

National Oceanic and Atmospheric Administration 

Technical Memorandum NWS WE-197,229 p.

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Oxford, Clarendon Press, 184 p.

Webb, R.H., and Betancourt, J.L., 1992, Climatic 

variability and flood frequency of the Santa Cruz 

River, Pima County, Arizona: U.S. Geological 

Survey Water-Supply Paper 2379,40 p.

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data, Arizona, water year 1984: U.S. Geological 

Survey Water-Data Report AZ-84-1,440 p.

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water discharge during single hydrologic events in 

rivers: Journal of Hydrology, v. 111, j\ 89-106.

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cohesive river bank: American Journal of Science, 

v. 257, p. 204-216.

Wolman, M.G., and Gerson, R., 1978, Relative scales of 

time and effectiveness of climate in watershed 

geomorphology: Earth Surface Processes, v. 3, 

p. 189-208.

Wolman, M.G., and Miller, JP., 1960, Magnitude and 

frequency of forces in geomorplrc processes: 

Journal of Geology, v. 68, p. 54-74.

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to valley: Phoenix, Arizona, The Arizona Republic, 

January 8,1992, p. A16.

References Cited 37
SURVEY DATA

The following data are published to facilitate 

future inoccupation of the cross sections established 

in this study for investigating channel change. 

Coordinate values shown in the tables are based on 

an arbitrary datum. The surveying instrument, a

Nikon Total Station DTM-1, recorded x 

coordinates from right to left values increased as 

the instrument was turned to the left. The values in 

the tables are the same as recorded by the 

instrument. In order to plot the data in plan view, 

the X values must be negative to orient the plot 

properly.

Coordinates for cross-section end points and other reference points, Salt River between 16th and 7th Streets, 

Phoenix, Arizona

[Dashes indicate no data]

Reference

Station 1

Coordinate, in feet

X

5,000

Y

5,000

Z

500

Degrees

Azimuth

Minutes

 Comments

Seconds

Station coordinates referenced 

to topofrebar.

Cross-section end points

1 right 

Heft

2 right

2 left

3 right

3 left

4 right

4 left

5 right

5 left

6 right

6 left

7 right

7 left

Bright

7,230.44 

7,485.36

6,606.42

6,736.14

5,894.80

6,036.71

5,226.89

5,365.10

4,572.53

4,623.23

3,901.00

3,986.03

3,245.51

3,373.50

2,646.67

4,970.26 

6,059.00

5,002.90

5,800.78

4,994.62

5,965.82

4,999.96

5,998.44

5,004.56

5,748.71

5,05238

5,777.04

5,137.80

5,860.79

5,284.83

507.09 

506.01

508.98 

508.40

502.11 

501.36

500.04 

499.27

502.02 

501.11

498.10 

500.16

500.16 

499.22

495.51 

494.87

499.13 

498.34

498.93 

498.19

497.77 

496.98

498.39 

497.62

496.56 

495.11

495.34 

494.46

495.11 

494.32

359

23

000

359

...

359

69

179

116

177

142

175

152

173

14 

4

6

39

59

54

23

42

16

32

30

6

5

4 End points momimented with 

rebar driven into ground with 

about 0.5 foot exposed.

43 Do.

12 Do.

Do.

20 Do.

Do.

22 Do.

51 Do.

19 Do.

46 Do.

17 Do.

10 Do.

32 Do.

40 Do.

54 Do.

Survey Data 39
Coordinates for cross-section end points and other reference points, Sah River between 16th and 7th St-^ets, 

Phoenix, Arizona Continued

Reference

Coordinate, in feet Azimuth

Degrees Minutes Seconds

Comments

Cross-section end points Continued

8 left

9 right

9 left

2,787.73

2,121.46

2,298.47

5,860.63

5,441.98

6,102.36

488.82

488.13

495.41

494.71

495.17

494.68

158

171

157

44

16

48

56

15

7

Do.

Only end points of cross section

9 were surveyed.

End points rmnrimented with

rebar driven intc ground with

about 0.5 feet exposed.

Other reference points

RM-1

RM-2

RM-3

RM-4

4.987.89

7,628.00

5,025.36

6,055.18

7,460.09 5,416.19

7,269.78 4,967.94

494.80 115 31 00 Chiseled "X" on vertical

concrete pipe in banks below 

Station 1.

513.17 358 28 00 Top of southwest anchor bolt in

handrail support on southwest 

end of 16th Street bridge, 

painted orange.

518.56 267 45 00 Middle of chiseled cross in

center of white painted cross 

(aerial photograph point) in 

middle of 16th Street, about 

460 feet south of RM-3 and 

620 feet north of RM-2, 

painted orange.

511.74 258 49 24 Top of northwest anchor bolt in

handrail support on northwest 

end of 16th Street bridge, 

painted orange.

40 Channel Change and Sediment Transport in Two Desert Strasms in Central Arizona, 1991-92
Coordinates for cross-section end points and other reference points, Hassayampa River bebw Southe*n Pacific 

Railroad bridge, near Arlington, Arizona

[Dashes indicate no data]

Reference

Station 1

BS-1

Coordinate, In feet

X

5,000.00

5,029.62

Y

5,000.00

5,000.00

Z

500.00

499.87

Degree*

000

Azimuth

Minute*

00

Seconds

00

 ComrranU

Rebar in ground on low terrace 

between cross sections 4 and 5 

on right side of channel.

Rebar in ground.

Cross-section end points

1 right

lleft

2 right

2 left

3 right

3 left

4 right

4 left

5 right

5 left

6 right

6 left

Station 2

7 right

7 left

8 right

8 left

5,569.88

5,326.57

5,446.72

5,300.90

5,332.73

5.179.22

5,049.69

4,948.50

4,764.28

4,795.67

4,585.64

4,574.62

3,890.59

4,314.83

4,378.35

3,941.11

4,101.87

4,988.67

5,771.20

4990.58

5,761.77

4,964.14

5,730.67

4,945.65

5,701.31

4,963.49

5,682.92

4,941.95

5,686.47

5,698.45

4,935.41

5,708.51

4,991.55

5,728.27

504.52 

504.11

508.79 

508.13

506.60 

506.36

509.07 

508.35

503.64 

503.09

506.85 

506.30

504.29 

503.74

503.83 

503.35

501.45 

500.69

504.26 

503.77

500.68 

499.89

503.21 

502.80

500.85

499.02 

498.45

503.66 

503.18

500.47 

499.97

501.40 

500.72

358

67

358

68

353

76

312

94

188

106

187

121

147

299

1

274

8

51

1

50

26

50

11

25

11

48

38

59

47

48

4

9

4

1

12

23

15

50

36

47

17

46

49

43

23

24

24

6

38

22

50

End points monumented with 

rebar driven into ground with 

about 0.5 feet exposed.

DC.

DC.

DC.

DC.

DC.

DC.

DC.

DC.

Do.

Do.

Do.

Rebar on left side of channel 

below levee crest about onequarter of distance between crest 

and base of levee.

Azimuth reading? for cross sections 7-11 taken from station 2.

Do

Do

Do

Survey Data 41
Coordinates for cross-section end points and other reference points, Hassayampa River below Southern Pacific 

Railroad bridge, near Arlington, Arizona Continued

Coordinate, In feet

Reference

X Y Z

Azimuth

Degrees Minutes Seconds

Comnrwts

Cross-section end points Continued

9 right

9 left

10 right

10 left

11 right

11 left

3,517.98

3,826.94

3,283.52

3,488.99

3,153.33

3,316.62

5,127.48

5,771.88

5,317.52

5,858.49

5,356.66

5,899.66

498.54

497.92

505.22

504.52

496.81

503.15

502.64

496.18

495.59

502.71

502.12

236

130

212

158

204

160

51 38

55 55

6 58

17 20

52 26

40 55

Do

Do

Do

Do

Do

Do

Other reference point

RM-1 6,102.48 5,516.19 496.22 . Bolt emplaced on seventh railroad bridge pier from right bank

about 5 feet above ground.

42 Channel Change and Sediment Transport In Two Desert Streams In Central Arizona, 1991-82