TWENTIETH CENTURY ARROYO CHANGES

IN CHACO CULTURE NATIONAL HISTORICAL

PARK

Prepared in cooperation with the

NATIONAL PARK SERVICE

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4251
U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4251

TWENTIETH CENTURY ARROYO CHANGES

IN CHACO CULTURE NATIONAL HISTORICAL

PARK

Prepared in cooperation with the

NATIONAL PARK SERVICE

By Allen C. Gellis

Albuquerque, New Mexico

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Denver, CO 80225-0286

District Chief

U.S. Geological Survey

Water Resources Division

5338 Montgomery Blvd. NE, Suite 400

Albuquerque, NM 87109-1311

from:

Information regarding research and data-collection programs of the U.S. Geological Survey is available

on the Internet via the World Wide Web. You may connect to the home page for the New Mexico District

Office using the URL http://nm.water.usgs.gov.
iii

CONTENTS

Page

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

Introduction ........................................................................................................................................................................... 1

Purpose and scope ....................................................................................................................................................... 2

Description of study area............................................................................................................................................. 2

Climate and runoff....................................................................................................................................................... 2

Geomorphic description of arroyos at Chaco Canyon................................................................................................. 2

Previous studies ........................................................................................................................................................... 7

Methods for analysis of arroyo changes ................................................................................................................................ 7

Analysis of photogrammetric cross sections ............................................................................................................... 8

Delineation of arroyo geometry................................................................................................................................... 11

Results ................................................................................................................................................................................... 12

Analysis of errors in field surveys and photogrammetric data interpretation.............................................................. 12

Comparison of photogrammetric techniques to field surveys ..................................................................................... 12

Arroyo geometry changes............................................................................................................................................ 17

Arroyo top width ............................................................................................................................................... 25

Arroyo width at 50-percent depth...................................................................................................................... 25

Arroyo top depth................................................................................................................................................ 25

Arroyo cross-sectional area ............................................................................................................................... 28

Volumetric changes in Chaco Wash................................................................................................................... 28

Inner-channel changes ....................................................................................................................................... 28

Longitudinal and planform changes ............................................................................................................................ 32

Changes near Pueblo del Arroyo ................................................................................................................................. 32

Summary................................................................................................................................................................................ 40

References ............................................................................................................................................................................. 41

FIGURES

1. Map showing location of study area and cross sections measured along Chaco Wash and selected tributaries

in Chaco Canyon, New Mexico.......................................................................................................................... 3

2. Graphs showing precipitation at Chaco Culture National Historical Park Headquarters, 1934-99.

(A) Annual precipitation and (B) average monthly precipitation....................................................................... 4

3. Graphs showing (A) mean monthly runoff at streamflow-gaging station Chaco Wash near Chaco Canyon

National Monument, May 1976 to April 1990, (B) number of days in a month with discharge,

(C) mean monthly runoff, and (D) instantaneous peak flow, 1976-90 ............................................................... 5

4. Model of arroyo evolution depicting changes at a cross section over time following channel incision.................. 6

5. Map showing reaches used to measure volumetric changes over time in Chaco Wash........................................... 10

6. Schematic of channel width and depth features in a typical arroyo channel ........................................................... 11

7-10. Graphs showing:

7. Channel cross-sectional measurements along Chaco Wash and selected tributaries in Chaco Culture

National Historical Park, 1934-2000 ............................................................................................................. 13

8. Comparison of surveyed channel cross sections to photogrammetric interpretations at Chaco Wash

cross sections CW3, CW8, and CW10 .......................................................................................................... 18

9. (A) Chaco Wash top width measurements from 2000 field surveys and photogrammetry and (B) top

depth measurements from 2000 data ............................................................................................................. 24

10. Changes in arroyo top geometry at selected cross sections along Chaco Wash and selected tributaries.

(A) Top width, (B) top width at 50 percent of arroyo depth, (C) arroyo top depth, and (D) top crosssectional area ................................................................................................................................................. 26
iv

Page

11-13. Graphs showing:

11. Average rates of (A) arroyo widening, (B) arroyo top depth, and (C) top cross-sectional area at selected

cross sections along Chaco Wash and selected tributaries............................................................................ 27

12. Changes in bankfull along Chaco Wash and selected tributaries. (A) Width, (B) depth, and

(C) cross-sectional area................................................................................................................................. 33

13. Rates of change in bankfull width from 1934 to 1973 and from the 1970’s to 2000........................................ 34

14. Maps showing topographic contours in relation to selected cross sections along Chaco Wash in Chaco

Culture National Historical Park. (A) 1934 National Park Service 1:480 contour map,

(B) 1:6,000 1973 aerial photography, and (C) 2000 aerial photography ........................................................... 35

15. Map and graph showing (A) longitudinal profile of Chaco Wash, 1934, 1973, and 2000 and (B) average

elevation changes over 250-meter increments ................................................................................................... 38

16. Map showing top width cross-sectional measurements along Chaco Wash in 1934, 1973, and 2000.................... 39

17. Map showing bankfull width cross-sectional measurements along Chaco Wash in 1934, 1973, and 2000............ 39

TABLES

1. 19th and 20th century Chaco Wash channel dimensions......................................................................................... 8

2. Vertical adjustments made to register cross sections to the same datum................................................................. 12

3. Comparison of channel geometry using 2000 surveys and 2000 photogrammetric

analysis for cross sections CW3, CW8, and CW10........................................................................................... 17

4. Arroyo geometry of Chaco Wash and selected tributaries: (A) 1934, (B) 1970’s, and (C) 2000............................ 19

5. Arroyo cross-sectional geometry at 50-percent depth............................................................................................. 21

6. Change in sediment volume, area, and depth of the arroyo channel at selected reaches in Chaco Wash ............... 29

7. Bankfull geometry of Chaco Wash and selected tributaries: (A) 1934, (B) 1970’s, and (C) 2000 ......................... 30

CONVERSION FACTORS AND DATUMS

Historical data collected and stored as National Geodetic Vertical Datum of 1929 have been

converted to North American Vertical Datum of 1988 (NAVD 88) for this publication.

Vertical coordinate information is referenced to the North American Vertical Datum of 1988

(NAVD 88).

Horizontal coordinate information is referenced to the North American Vertical Datum of 1983

(NAD 83).

Multiply By To obtain

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.06102 inch (in.)

centimeter per year (cm/yr) 0.06102 inch per year (in./yr)

meter (m) 3.281 foot (ft)

meter per year (m/yr) 3.281 foot per year (ft/yr)

kilometer (km) 0.6214 mile (mi)

square meter (m2) 10.76 square foot (ft2

)

square kilometer (km2

) 0.3861 square mile (mi2)

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3

/s)

foot (ft) 0.3048 meter (m)

acre 4,047 square meter (m2

)
1

ABSTRACT

Chaco Wash arroyo channel changes in the 20th

century have become a major concern of the National

Park Service. Several archeologic and cultural sites are

located in the Chaco Wash corridor; thus, increased

erosional activity of Chaco Wash, such as channel

incision and increased meandering, may affect these

sites.

Through field surveys, photogrammetric

analyses, and reviews of existing reports and maps,

arroyo changes at Chaco Culture National Historic

Park were documented. Arroyo changes were

documented for the inner active channel and the entire

arroyo cross section. The inner channel of Chaco Wash

evolved from a wide, braided channel in the 1930’s to

a narrower channel with a well-developed flood plain

by the 1970’s. From 1934 to 1973 the active channel

narrowed an average of 26 meters, and from the 1970’s

to 2000 the channel narrowed an average of 9 meters.

Overall from 1934 to 2000, the inner channel narrowed

an average of 30 meters.

From 1934 to 2000, the top of Chaco Wash

widened at four cross sections, narrowed at one, and

remained the same at another. The top of Chaco Wash

widened at a rate of 0.4 meter per year from the 1970’s

to 2000 compared with 0.2 meter per year from 1934 to

1973. At 50-percent depth or halfway down the arroyo

channel, four cross sections widened and two cross

sections narrowed from 1934 to 2000. Rates of

widening at 50-percent depth decreased from 0.2 meter

per year from 1934 to 1973 to 0.1 meter per year from

the 1970’s to 2000. From 1934 to 2000, arroyo depth

decreased at five of six cross sections and increased at

one cross section. Arroyo depth between 1934 and

1973 decreased an average 1.4 meters from

aggradation and between the 1970’s and 2000

increased an average 0.4 meter from channel scour.

From 1934 to 2000, arroyo cross-sectional area

decreased at all six cross sections. Cross-sectional

areas in Chaco Wash decreased from 1934 to 1973 as a

result of sediment deposition and both decreased and

increased from the 1970’s to 2000. The cross-sectional

area decreased by the 1970’s due to channel narrowing

and flood-plain formation. Increases in cross-sectional

area are from channel scour and channel widening.

Photogrammetric analyses of volumetric changes for a

1.7-kilometer reach of Chaco Wash showed sediment

deposition from 1934 to 1973 of 64 square meters per

unit length of channel over 1.7 kilometers to erosion

from 1973 to 2000 of 7 square meters per unit length of

channel.

Chaco Wash evolved from a braided channel in

the 1930’s to a narrow, sinuous inner channel by the

1970’s. Chaco Wash was widening in the 1930’s,

leading to sediment deposition and formation of an

inner flood plain. Channel narrowing resulted from

increased sediment deposition on the flood plain.

Sediment deposition may be related to a decrease in

peak flows, an increase in flood-plain vegetation, or an

increase in the transport of fine-grained sediment.

Increases in bankfull depth of Chaco Wash between the

1970’s and 2000 were due to aggradation of the flood

plain and channel scour. Thus, rates of aggradation and

cross-sectional filling were greater from 1934 to the

1970’s than from the 1970’s to 2000.

INTRODUCTION

Chaco Wash channel changes in the 20th century

have become a major concern of the National Park

Service (NPS). Many of the cultural sites at Chaco

Culture National Historical Park (CCNHP) are situated

on the alluvial valley floor near Chaco Wash. The

alluvial valley floor can erode from changes in the

geometry of Chaco Wash and sheetwash erosion, soil

piping, and gullying on the alluvial valley. Changes in

the geometry of Chaco Wash from channel incision,

widening, and sinuosity can lead to bank collapse and

erosion of the alluvial valley floor. Erosion of the

alluvial valley floor from any of these processes may

affect cultural sites. To address the concern of 20th

century arroyo changes in Chaco Wash and their effect

on archeologic sites, the U.S. Geological Survey

(USGS), in cooperation with the NPS, conducted a

study to examine 20th century channel changes in

Chaco Wash near the CCNHP. This report was

prepared in cooperation with the NPS.

TWENTIETH CENTURY ARROYO CHANGES IN

CHACO CULTURE NATIONAL HISTORICAL PARK

By Allen C. Gellis
2

Purpose and Scope

This report summarizes the changes in Chaco

Wash from 1935 to 2000. Changes in arroyo channel

geometry for the entire arroyo and for the inner channel

were compared from 1934 to 1973 and for selected

years from the 1970’s to 2000. Channel geometry in

1934 was quantified from 1931 and 1934 1-ft contour

maps and in 1973 was quantified from aerial

photography. Channel geometry in the 1970’s was

determined from an average of channel dimensions

from 1972, 1974, 1976, and 1977 field surveys

conducted by Malde (1977) or from interpretations

from the 1973 aerial photographs. Channel geometry in

2000 was determined from either field surveys or aerial

photographs.

Description of Study Area

The 33,989-acre CCNHP (fig. 1) in northwestern

New Mexico, formerly known as Chaco Canyon

National Monument, is a renowned site for archeology

and is listed by the United Nations Educational

Scientific and Cultural Organization as a World

Heritage site. Chaco Canyon begins 1 km west of

Cañada Alemita Junction and extends for 32 km to the

junction with Escavada Wash (DeAngelis, 1972).

Chaco Wash drains 11,500 km2 at its confluence with

the San Juan River and is 220 km long (Love, 1980).

Chaco Wash is sinuous and incised and in places is as

much as 10 m below the alluvial valley floor. After its

junction with Escavada Wash, Chaco Wash takes on the

appearance of Escavada Wash: unincised and braided.

Bedrock in Chaco Canyon is mostly sandstone and

shale; grain-size distribution of sediment in the innerchannel Chaco Wash is predominantly fine sand (Love,

1980).

Climate and Runoff

Climate in the CCNHP is semiarid. Average

annual precipitation recorded at the NPS Headquarters

from 1934 to 1999 is 226 mm (U.S. Department of

Commerce, 1934-99) (fig. 2A). Annual precipitation

appears to have increased 21 percent from 1934 to 1999

(fig. 2A). About half the average annual precipitation

results from convective storms from July through

October (fig. 2B).

Monthly runoff measured at the USGS

streamflow-gaging station Chaco Wash at Chaco

Canyon National Monument from March 1976 to April

1990 is highly variable (fig. 3A). From 1976 through

1990, all months recorded some flow (fig. 3B). Mean

monthly runoff was largest in February and July

through September (fig. 3C). The highest monthly

runoff was recorded in February 1979 (8.88 x106

 m3)

and August 1988 (5.38 x 106 m3). Instantaneous peak

flows from 1976 to 1990 ranged from 0.5 to 54.4 m3

/s

(fig. 3D). Average monthly precipitation (fig. 2) shows

a similar pattern to mean monthly runoff for summer to

fall (June to November) but not for the winter and

spring months (December to May). This difference

may be due to the influence of snowmelt on runoff.

Geomorphic Description of Arroyos at

Chaco Canyon

Arroyos are stream channels incised into valley

alluvium and colluvium (Elliott and others, 1999).

Geologic evidence exists for past episodes of arroyo

incision in the American Southwest during the

Holocene (Webb and Hereford, 2001) and recently in

the late 19th century (Cooke and Reeves, 1976). The

causes for arroyo incision in the late 19th century can

be separated into three arguments: (1) arroyos were

incised following a change in precipitation intensity

(Leopold, 1951; Balling and Wells, 1990), (2) arroyos

were incised as a result of overgrazing (Cooke and

Reeves, 1976; Aby, 1997), and (3) arroyos were incised

because of internal adjustments of slope, sediment

transport, and hydrology. In argument 3, climate and

grazing are triggers for arroyo development (Schumm

and Hadley, 1957; Gellis and Elliott, 2001). Whatever

the causes of arroyo incision in the Southwest, the

result is that valley floors, which formerly supported

small, unincised channels or discontinuous channels,

were incised, in some places more than 10 m.

The stratigraphic record exposed along the walls

of arroyos shows numerous paleoarroyos, indicating

that arroyos have incised and filled during the late

Quaternary. The cycle of incision and filling is called

arroyo evolution (Schumm and others, 1984; Gellis and

others, 1991; Elliott and others, 1999). A generalized

model of arroyo evolution, depicting the stages that an

arroyo goes through following incision, is shown in

figure 4. These changes in arroyo cross section are

observed through time at one selected location in the

arroyo (fig. 4A). Generally, the arroyo changes through

time from a narrow, V-shaped gully (stage B) with low

width-to-depth ratios to a wide, U-shaped gully with
0

0 0.5

0.5

1 MILE

1 KILOMETER

Fajada Wash

Base from 7 1/2-minute quadrangle

 Pueblo Bonito NW, Sargent Ranch,

 and Kin Klizhin Ruins

CW13

CW12 CW11

U.S. Geological Survey

stream-gaging 

station

CW10

CW9

CW8

CW7

CW6

CW5

CW4

CW3

CW2

CW1

Area shown in

 figures 5, 14,

 16, and 17

CROSS S

EXPLANATION

#

#

X

Figure 1.Location of study area and cross sections measured along Chaco Wash and selected tributaries in Cha

35°

05’

108°01’ 107°55’ 

107°57’ 107°59’

35°

03’

35°

01’

R. 11 W. R. 10 W.

Pueblo 

Bonito 

bridge

Pueblo Bonito 

Ruins

Chetro Ketl

Ruins

Hungo Pavi

Ruins

Kin Kletso

Ruins

Pueblo del Arroyo

Ruins

Chaco Wash

Escavada

 Wash

Chaco Wash

Gallo Wash

Clys Canyon

Weritos 

Rincon

Canyon

Mockingbird 

CHACO CULTURE

NATIONAL HISTORICAL PARK

Chaco Canyon

Chaco Canyon

F1

F1

CW

G1

National Park Service

Headquarters, 

Museum, and

Visitors Center

57

STUDY AREA

NEW

MEXICO

3
1934-59

average = 197 mm

1960-99

average = 238 mm

P

R

E

CIPITATIO

N, IN

MILLIM

E

T

E

R

S (m

m) P

R

E

CIPITATIO

N, IN

MILLIM

E

T

E

R

S (m

m)

Figure 2. Precipitation at Chaco Culture National Historical Park Headquarters, 1934-99.

(A) Annual precipitation and (B) average monthly precipitation.

1930 1940 1950 1960 1970 1980 1990 2000

0

100

200

300

400

500

(A)

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

0

10

20

30

40

(B)

Average for period = 226 mm

4
77 78 79 80 81 82 83 84 85 

JAN FEB MAR APR MAY JUNE JULY AUG 

8

6

4

2

0

10

12

14

1976

(B)

0

10

20

30

40

50

60

(D)

Figure 3. (A) Mean monthly runoff at streamflow-gaging station Chaco Wash near Chaco Canyon Nation

 May 1976 to April 1990, (B) number of days in a month with discharge, (C) mean monthly ru

 (D) instantaneous peak flow, 1976-90.

, FF ONUR YL HT NOM NAE M

SRETE M CI BUC NI

, FF ONUR YL HT NOM NAE M

DNOCES REP SRETE M CI BUC NI

, W

OLF KAEP SUOENAT NATSNI

DNOCES REP SRETE M CI BUC NI

E GRAHCSI D GNI VAH SYAD F O REB MUN

1976 77 78 79 80 81 82 83 84 85 86 87 88 89 1990

0

2e+6

4e+6

6e+6

8e+6

1e+7

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

0

2e+5

4e+5

6e+5

8e+5

1e+6

(A)

(C) 5
Incision

Widening

Incipient

flood plain

Complete filling

G2

F1 F2

G1

E

D

C

B

A

CHANGES AT A CROSS SECTION OVER TIME

Figure 4. Model of arroyo evolution depicting changes at a cross section over time

 following channel incision (from Gellis, 1992).

6
7

high width-to-depth ratios (stages B and C). Arroyo

widening decreases flow depth, which decreases

streampower, thereby promoting sediment deposition

and formation of an incipient flood plain (stage D)

(Elliott and others, 1999). Decreases in runoff during

this stage may promote vegetation colonization

because seedlings are not removed by higher flows

(Hereford, 1984). Vegetation that becomes established

on the flood plain increases hydraulic roughness and

promotes increased sediment deposition (stage E). At

stage E, the inner channel narrows as a result of floodplain formation. Eventually the channel may aggrade

and completely fill the cross section (stage F1) or

become reincised from narrowing of the channel,

which decreases the channel width-to-depth ratio,

increases streampower, and causes reincision.

Previous Studies

Many geologists, geographers, and engineers

have documented channel width and depth in Chaco

Wash since the 1800’s (table 1). Bryan (1954)

estimated 1860 as the date of channel incision in Chaco

Wash. Love (1980) suggested an earlier date of incision

in the 1830’s to 1840’s, formation of a flood plain

between 1877 and the early 1890’s, and renewed

incision in the 1890’s. In the 1920’s to 1930’s, Chaco

Wash was flat floored, braided, and devoid of

vegetation (DeAngelis, 1972; Simons, Li, and

Associates, 1982); by 1965, Chaco Wash had changed

dramatically, having a sharply defined inner channel

with dense vegetation (Lagasse and Eggert, 1983).

Love (1980) attributed increases in the width of Chaco

Wash to a wet period from 1900 to 1934 and to

overgrazing. The increase in width led to a decrease in

slope, resulting in sediment deposition and

development of an incipient inner channel. From the

1930’s to the 1950’s, precipitation decreased, discharge

decreased, and sediment was deposited next to the

inner channel. Erosion-control structures built during

this time helped stabilize sediment (Love, 1980).

Aerial photographs taken in 1971 show

continued stabilization of the inner channel and more

frequent channel cutoffs from 1965 to 1971 (Simons,

Li, and Associates, 1982). From 1934 to 1972, Chaco

Wash widened from 4 to 35 percent of its 1934 width at

an average rate of 5 to 15 cm/yr, whereas between 1924

and 1972, the depth of the channel changed little

(DeAngelis, 1972). Leopold (1976) reported

aggradation of the Chaco Wash flood plain from 1961

to 1974, about 1.0 km upstream from the visitors center

at CCNHP. Aggradation of Chaco Wash from the

1930’s to the 1970’s was followed by incision of the

inner channel (DeAngelis, 1972; Love, 1980; Simons,

Li, and Associates, 1982). In 1979, many tributary

arroyos along Chaco Wash were actively eroding

headward (Love, 1980).

Channel erosion is a major problem affecting the

cultural resources of the CCNHP. Pueblo del Arroyo

was threatened by lateral erosion of Chaco Wash in the

early 1920’s (Simons, Li, and Associates, 1982).

Chauvenet (1935) examined channel erosion, its

possible effect on archeologic sites, and erosion

protection; he reported that several structures, Kin

Kletso, Pueblo del Arroyo, Wijiji, Hungo Pavi, and

Chetro Ketl (fig. 1), were affected by a variety of

erosion processes, including undermining by lateral

erosion of Chaco Wash, sheetwash action on the

exposed banks, gullying, and tributary erosion. In

1981, Simons, Li, and Associates (1982) reported that

gullies and soil piping were affecting Pueblo del

Arroyo and Wijiji and that channel erosion was

affecting Kin Kletso.

Chauvenet (1935) also described some erosion

structures built of wood, rock, and wire to control

channel erosion. Love (1980) reported that the Civilian

Conservation Corps, Soil Conservation Service, and

the NPS planted more than 1 million trees and shrubs

for erosion control in the CCNHP in the 1930’s. Other

erosion-control strategies since the 1930's include

jetties, earth dams, and contour furrowing (Simons, Li,

and Associates, 1982). For flood-control purposes, the

NPS straightened some sections of Chaco Wash in the

1960’s (Love, 1980).

METHODS FOR ANALYSIS OF ARROYO

CHANGES

Sixteen arroyo cross sections in the CCNHP

were used to measure arroyo and inner-channel

geometry and to describe changes in Chaco Wash and

selected tributaries (fig. 1). Five of these cross sections

were established in 1972 and resurveyed in 1974, 1976,

and 1977 using a survey level (Malde, 1972, 1977);

three of the cross sections (CW3, CW13, and CW14)

were on Chaco Wash, and two of the cross sections (F1

and C1) were on the tributaries Fajada Wash and Gallo

Wash (fig. 1). Original field notes of Malde’s five cross
8

sections were obtained from USGS archives. The five

cross sections were resurveyed in August 2000, in

conjunction with this study, with a total station survey

and survey level. Two new cross sections (CW1 and

CW7) also were surveyed in August 2000 using a total

station survey. An additional nine cross sections (CW2,

CW4, CW5, CW6, CW8, CW9, CW10, CW11, and

CW12) (fig. 1) were analyzed using aerial photographs.

Photogrammetric cross sections CW4, CW5, CW6,

CW8, CW10, and CW11 were selected for analysis

because of their proximity to Pueblo del Arroyo

(fig. 1).

One-foot contour maps of the CCNHP (1:480

scale) were surveyed by the NPS in 1931 and 1934. The

contour maps were digitized into a geographical

information system (GIS). The accuracy of the NPS

contour maps to the true surface of the Earth is

dependent on the amount of data collected and the

experience of the survey crew. Black and white aerial

photographs of the CCNHP were obtained for 1973

(1:6,000 scale) and 2000 (1:3,000 scale). By using a

GIS, 0.3-m contour maps were generated from the

1973 and 2000 aerial photographs.

Analysis of Photogrammetric Cross

Sections

The 1973 photogrammetric analysis was

modeled with software using discrete stereo pairs,

meaning that the stereo model (georeferencing and

exterior camera orientationQ—or the position of the

Table 1. 19th and 20th century Chaco Wash channel dimensions

[--, no data]

Date Location

Arroyo

depth

(meters)

Arroyo

width

(meters) Observer Reference

1849 Una Vida 0.46 2.4 Lt. Simpson Bryan, 1954

1849 Wijiji 0.5 2.4 Lt. Simpson Chauvenet, 1935

1860 Pueblo Bonito 1.5 -- Local Navajo Bryan, 1954

1877 Pueblo Pintado 3.0-3.6 -- William H.

Jackson

Bryan, 1954

1877 Pueblo del Arroyo 4.9 12.2-18.3 William H.

Jackson

Bryan, 1954

1925 Escavada Wash 3.0 46-91 Bryan Bryan, 1954

1925 Pueblo Bonito 9.1 -- Bryan Bryan, 1954

1925 Pueblo del Arroyo 9.1 46-91 Bryan Bryan, 1954

1925 Wijiji 6.1 -- Bryan Bryan, 1954

1934 Entire Chaco Canyon 3.6-7.6 15-76 Chauvenet Chauvenet, 1935

1934 Kin Kletso 6.7 76 Chauvenet Chauvenet, 1935

1965 Pueblo del Arroyo 5.2 -- Tuan Simons, Li, and

Associates, 1982

1972 Entire Chaco Canyon 3.8-9.6 28-126 DeAngelis DeAngelis, 1972

1972 Pueblo Pintado 5.5-6.4 -- DeAngelis DeAngelis, 1972

1972 Pueblo del Arroyo 7.3 -- DeAngelis DeAngelis, 1972

1974 1.0 kilometer

upstream from

museum at Chaco

Canyon National

Historical Park

About 9 About 47 Leopold Leopold, 1976

1979 Entire Chaco Canyon 3-12 -- Love Love, 1980

1979 Entire Chaco Canyon

(inner channel)

1-3 m 10-30 Love Love, 1980
9

camera relative to a horizontal plane and in real x, y, z

space) is set up on the basis of individual stereo pairs.

The orientation of the camera lens relative to the plane

on which the photographic file sits and the camera

metrics (except for calibrated focal length) were set

automatically by the software using the location of the

camera fiducial marks. Centimeter Global Position

System (GPS) data were used for georeferencing.

Some error is associated with the georeferencing

because the exact point location on a photo taken 27

years earlier is difficult to identify. Maximum

estimated vertical errors for the 1973 1:6,000 aerial

photograph interpretations average less than +0.75 m

with a maximum error of +2.0 to +2.5 m (Rich

Friedman, McKinley County GIS, written commun.,

2001). Maximum estimated horizontal errors average

+0.66 m with a maximum error of +2.0 m (Rich

Friedman, written commun., 2001).

The 2000 photogrammetric analysis was

modeled using software (http://erdas.com) that

allowed for the creation of stereo models across

multiple stereo pairs, used block-bundle adjustment,

and allowed for importation of exterior orientation data

from flight-recording systems. In block-bundle

adjustment, all tie points and georeference information

for each photo in the flight line(s) are used to calculate

the orientation parameters for the entire block of

photos instead of two at a time; this achieves superior

consistency and accuracy. The images were

georeferenced using the same data that were used to

georeference the 1973 images. Maximum estimated

vertical errors for the 2000 1:3,000 aerial photograph

interpretations average less than +0.5 m with a

maximum error of +1.5 to +2.0 m (Rich Friedman,

written commun., 2001). Maximum estimated

horizontal errors average less than +0.5 m with a

maximum error of +1.5 to +2.0 m (Rich Friedman,

written commun., 2001).

For the georeference points collected for image

registration, the High Accuracy Reference Network

station established by the National Geodetic Survey

just south of Pueblo Bonito, Chaco Canyon, was used

as the base location; rapid, static data-collection

procedures were used to acquire the position readings

for the point locations. The expected errors with these

data should be less than 10 cm vertical (z) and from 2

to 5 cm horizontal (x,y).

Errors reported in this study’s photogrammetric

analysis are similar to errors reported for other

geomorphic studies on erosion and deposition.

Dymond and Hicks (1986) used 1950 aerial

photographs at a scale of 1:17,500 and 1981 aerial

photographs at a scale of 1:12,000 to obtain volumetric

measurements of erosion and deposition in

mountainous areas of New Zealand. Accuracy of

elevation using their photogrammetric technique

ranged from +0.5 to +4.0 m. Coe and others (1997)

used Digital Elevation Models (DEM’s) derived from

1982 pre-debris-flow aerial photography (scale

1:8,000) and 1991 post-debris-flow aerial photography

(scale 1:3,000) to volumetrically calculate net erosion

and deposition from a modern debris flow near Yucca

Mountain, Nevada. Based on their photogrammetric

mapping configuration, the vertical accuracy derived

between the two sets of photos was +0.14 m. Fryer and

others (1994) reported that the accuracy of vertical

measurements using aerial photographs is +1 to +3

parts per 10,000 m of flying height. For a flying height

of 1,500 m the vertical precision is +0.15 m. Miller

(1986) analyzed channel changes using aerial

photographs between 1971 (scale 1:20,000) and 1983

(scale 1:24,000) for Smoky Creek, Tennessee, and

found horizontal displacement errors of +1 to +5 m.

Volumetric changes in Chaco Wash also were

quantified through photogrammetric techniques.

Chaco Wash was divided into six reaches covering

approximately 1.7 km of channel (fig. 5). The area of

the reaches ranged from 15,600 to 30,300 m3. The

volume in each reach was calculated to the same

elevation for 1934, 1973, and 2000. The areas for the

volume calculations overlapped to ensure that

orientations of the plane in three-dimensional space

were placed in locations that had not changed from

1934 to 2000 for each data set. Four points defined the

orientation of each plane in three-dimensional space

and were placed in locations that had not changed from

1934 to 2000. Because the elevations were not the same

across all three data sets, greater accuracy for volume

comparisons was achieved by defining unique

elevation planes for each of the three elevation sets

rather than trying to adjust the data sets to the same

elevation. The change of volume in each reach is

related to sediment deposition and erosion. Deposition

decreases the volume, and erosion increases the

volume. The planimetric area or the area of the reach at

the top of the arroyo was calculated over time.

Increases in planimetric area over time indicate arroyo

widening. The average arroyo depth for a reach was

calculated as the volume of the reach divided by the

planimetric area.
Figure 5. Reaches used to measure volumetric changes over time in Chaco Wash.

 

35°

04’

35°

03’

30”

107° 58’ 107° 57’ 30”

0

0 0.5 MILE

0.5 KILOMETER

Pueblo del

Arroyo

Reach 6

Reach 3

Reach 4

Reach 2

Reach 1

Reach 5

Pueblo

Bonito

Bridge

10
11

Delineation of Arroyo Geometry

To present a coherent description of channel

geometry, features along the arroyo cross section are

defined. Arroyos at Chaco Canyon are typically

characterized by two distinct geomorphic features

(fig. 6): (1) the entire arroyo channel confined by the

arroyo walls and the top height of the alluvial valley

floor and (2) a sinuous, active inner channel

characterized by levees, flood plains, and point bars

(Love, 1983). In this report the term "channel" signifies

the inner channel within the arroyo.

Changes in the entire arroyo were evaluated by

analyzing the top width and the width at 50-percent

depth (fig. 6). The top edge of the arroyo, where width

and depth are measured, is the abrupt break in slope of

the alluvial valley floor and arroyo wall. The alluvial

valley floor is the highest elevation of the arroyo. Top

depth was measured as the distance from the top edge

of the arroyo to the lowest part of the channel or

thalweg (fig. 6). If the alluvial valley floor had different

elevations on either side of the arroyo, the lowest

elevation was used. Selecting the top edge of the arroyo

can be subjective, but the first abrupt break in slope of

the arroyo wall and the alluvial valley floor was usually

selected. Fifty-percent arroyo depth is measured from

half of the top-depth elevation to the thalweg (fig. 6).

Width, depth, and cross-sectional area were quantified

for these two elevations in the entire arroyo channel. To

compare width changes over time, the elevation in the

channel used to define width was kept constant for each

year. The cross-sectional area is defined as the area

under a line drawn across the top of the entire arroyo

from the left bank to the right bank.

For the inner channel, channel top width and

depth and cross-sectional area were quantified. The

width and depth of the channel are synonymous with

bankfull. Bankfull is a morphologic feature in the

channel that generally is the top of the levee or the

break in slope of a point bar as it flattens (fig. 6).

Channel changes that were analyzed included bankfull

width and depth.

Widening of the entire arroyo top width is caused

by processes on the alluvial valley floor, such as

sheetwash, gullying, and soil piping, that may lead to

erosion and bank failures. Increased in-channel

sinuosity also may result in an increase in arroyo width

as the active channel undercuts the arroyo walls,

leading to bank failures. Changes to bankfull width and

depth are affected by in-channel flows and sediment

deposition.

0 10 20 30 40 50 60 70 80 90 100 110 120

20

22

24

26

28

30

32

Arroyo top width

Arroyo width at 50-percent depth

Active inner-channel width or bankfull

Arroyo top

depth

Active inner-channel depth

Arroyo

50-percent

depth

Alluvial valley

floor

Bottom of

thalweg

STATIONING FROM LEFT BANK, IN METERS

ELEVATION, IN METERS

Figure 6. Schematic of channel width and depth features in a typical arroyo channel.

FLOOD PLAIN
12

Aggradation is an increase in the thalweg

elevation over time, and degradation is a decrease in the

thalweg elevation over time. Longitudinal profiles of

the channel thalweg were created from the 1934

topographic maps and 1973 and 2000 aerial

photogrammetry.

RESULTS

This section describes the results of arroyo

changes at CCNHP from 1934, 1973, and 2000. Errors

encountered in the field surveys and photogrammetric

interpretations are presented. Changes in width and

depth are discussed for select arroyos and the inner

channel. Longitudinal and planform changes of Chaco

Wash in 1934, 1973, and 2000 are also discussed.

Analysis of Errors in Field Surveys and

Photogrammetric Data Interpretation

Analyses of 16 arroyo cross sections through

time were used to quantify arroyo geometry and

changes in Chaco Canyon (fig. 7). Accuracy of the field

resurveys was determined as the error in closing the

survey and the difference between elevation of the

cross-sectional end points in 2000 and Malde’s 1972-

77 surveys. Accuracy in closing the 2000 resurveys

ranged from 0.3 to 2.4 cm. Accuracy in elevation of the

cross-sectional end points in 2000 compared to

Malde’s surveys ranged from 0.7 to 5.9 cm. Because

CW3 had an end-point steel bar bent on the left bank

and CW13 had one end point missing on the left bank,

accuracy in elevation between the cross-sectional end

points in the 2000 resurvey of CW3 and CW13 and

Malde’s 1972-77 surveys could not be determined.

Difficulty was encountered when trying to

register the three cross sections (CW4, CW5, and

CW6) generated from the 1934 topographic maps and

1973 and 2000 aerial photographs to the same vertical

datum. Differences in elevation among the 3 different

years were due to differences in the data source and

photogrammetric techniques. The 1973 data are closest

to the actual elevation based on the North American

Vertical Datum of 1988. The 2000 photography was

acquired at a nominal scale of 1:3,000 with a digital

camera. The primary source of differences in elevation

between the 1973 and 2000 data sets may be the

exterior orientation parameters (GPS location data and

camera and (or) plane orientation information) from

the in-flight recording system, which is assumed to be

at the centimeter level. The higher elevation in the 2000

data was in part due to the exterior orientation of the

2000 data, which seemed to carry a heavier weight in

the elevation solutions than the georeference points do

(12 georeference points were used compared to more

than 50 elevations generated from the exterior

orientation data).

To correct for this error in elevation for the 1934,

1973, and 2000 coverages, the surface of the alluvial

valley floor at a distance of at least 3 m from the edge

was used as the datum for all 3 years. Processes that

may affect the elevation of the alluvial valley floor over

time are erosion and deposition associated with

sheetwash and eolian activity. The rates of elevation

change on the alluvial valley floor associated with

sheetwash and eolian activity are relatively small

compared with elevation changes in the channel. The

vertical adjustments made to register CW4, CW5, and

CW6 to the same datum are listed in table 2. Some

difficulty was encountered when interpreting

elevations of the inner channel during

photogrammetric analysis. Elevation data are difficult

to determine in photographs that show featureless areas

and dark shadows. This problem is especially true

where the elevation suddenly changes. One area where

this was a constant problem was the active inner

channel, which appears as a homogeneous area that is

almost white. This source of error was encountered in

both the 1973 and 2000 data.

Table 2. Vertical adjustments made to register cross

sections to the same datum

Comparison of Photogrammetric

Techniques to Field Surveys

The geometry of three cross sections (CW3,

CW8, and CW10) was generated using the 2000 field

surveys and the 2000 aerial photogrammetric

interpretations and, therefore, can be used to compare

the accuracy of photogrammetric techniques to field

Cross

section

(fig. 1) Year

Vertical

adjustment

(meters)

CW4 1934 1.43

CW4 2000 1.15

CW5 1934 0.68

CW5 1973 1.62

CW6 1934 1.02

CW6 2000 1.45
1,854

1,852

1,856

1,858

1,860

1,862

1,864

24

26

28

30

32

34

36

1,852

1,854

1,856

1,858

1,860

1,862

1,864

S

R

E

T

E

M

NI , N

OI TA

V

ELE

Y

R

A

R

TI B

R

A

Figure 7. Channel cross-sectional measurements along Chaco Wash and selected tributaries in Chaco Cu

 Historical Park, 1934-2000. Locations of cross sections shown in figure 1. 

STATIONING FROM LEFT BANK, IN METERS

1,854

1,852

1,856

1,858

1,860

1,862

1,864

2000

CW1

CW2

0 10 20 30 40 50 60 70 80 90 1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

CW3

CW4

May 30, June 3, 1974

July 21, 1972

August 2, 2000

13
CW5 CW6

CW7

CW8

S

R

E

T

E

M

NI , N

OI TA

V

ELE

Y

R

A

R

TI B

R

A

STATIONING FROM LEFT BANK, IN METERS

1,854

1,856

1,858

1,860

1,862

1,864

1,866

1,854

1,856

1,858

1,860

1,862

1,864

1,866

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

20

22

24

26

28

30

32

2000

0 10 20 30 40 50 60 70 80 90 

1,854

1,856

1,858

1,860

1,862

1,864

1,866

Figure 7. Channel cross-sectional measurements along Chaco Wash and selected tributaries in Chac

 Historical Park, 1934-2000. Locations of cross sections shown in figure 1--Continued. 

1973

2000

1934

14
S

R

E

T

E

M

NI , N

OI TA

V

ELE

Y

R

A

R

TI B

R

A

STATIONING FROM LEFT BANK, IN METERS

20

22

24

26

28

30

32

34

36

2000

1,856

1,858

1,860

1,862

1,864

1,866

1,868

1,870

1,872

1,856

1,858

1,860

1,862

1,864

1,866

1,868

1,870

1,872

1,856

1,858

1,860

1,862

1,864

1,866

1,868

1,870

1,872

0 10 20 30 40 50 60 70 80 90 1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

CW9 CW10

CW11

CW12

Figure 7. Channel cross-sectional measurements along Chaco Wash and selected tributaries in Chaco 

 Historical Park, 1934-2000. Locations of cross sections shown in figure 1--Continued. 

1973

2000

1934

15
CW13

CW14

FW1 GW1

0 10 20 30 40 50 60 70 80 90 1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

S

R

E

T

E

M

NI , N

OI TA

V

ELE

Y

R

A

R

TI B

R

A

STATIONING FROM LEFT BANK, IN METERS

August 1, 2000

July 18, 1972

20

22

24

26

28

30

32

34

August 1, 2000

June 7, 1976

July 20, 1972

June 5, 17, 1974

88

90

92

94

96

98

100

102

20

22

24

26

28

30

32

34

August 1, 2000

June 4, 1976

July 13, 1972

20

22

24

26

28

30

32

34

Figure 7. Channel cross-sectional measurements along Chaco Wash and selected tributaries in Chaco 

 Historical Park, 1934-2000. Locations of cross sections shown in figure 1--Concluded. 

16
17

surveys. The latitude and longitude of the crosssectional end points at CW3, CW8, and CW10 were

obtained from a GPS. The accuracy of the latitude and

longitude measurements ranged from +4 to +8 m.

The cross sections obtained from the

photogrammetric interpretations had a different

vertical datum than the surveyed cross sections. To

correct for this difference in elevation, the field survey

and photogrammetric cross sections were registered to

a common surface, either the alluvial valley floor or the

flood plain. Because of error in the GPS readings, the

horizontal stationing had to be adjusted to the break in

slope of the alluvial valley floor and the arroyo wall or

edge of bankfull.

Comparisons of photogrammetric techniques to

field surveys illustrate some similarities and

differences in the methods. In general, the channel

shape obtained from photogrammetric techniques

(fig. 8) is similar to that obtained from the surveyed

cross sections. Differences exist in arroyo widths and

depths (table 3). The arroyo top widths derived from

the two methods were within 10 and 18 m at CW3 and

CW8, respectively. At CW10 the arroyo top widths

differed by 40 m (close to 100 percent). At CW8 and

CW10, bankfull width was less than 2 m but at CW3

differed by 7 m (60 percent). For all three cross

sections, arroyo top depths differed by as much as 2.9

m and bankfull depth differed by as much as 0.9 m

(table 3).

Differences in channel geometry between the

photogrammetric techniques and field surveys may be

due to differences in the precise location of cross

sections and scale. Channel geometry may change

within a few meters upstream or downstream from the

cross section. Changes may be greater in more sinuous

reaches where channels alternate from impinging on

the arroyo walls to being in a broad flood plain.

Differences also are due to inherent errors in the

photogrammetric techniques used to generate the

elevations. Scale is an important consideration in the

difference between the photogrammetric techniques

and field surveys. Field surveys are done on a scale of

1:1, which allows for great detail and very little error.

In contrast, the measurements from the

photogrammetric sources were done from scales of

either 1:6,000 (1973) or 1:3,000 (2000). Although

measurements can be very good at these scales,

achieving the same detail or accuracy that can be

achieved at a 1:1 scale is extremely difficult.

For interpretive purposes, the 2000 field surveys

were not compared to earlier photogrammetric

interpretations of the same cross section. However, the

relative changes in channel geometry at the same cross

section in 1934, 1973, and 2000 using

photogrammetric techniques and the contour map are

acceptable.

Arroyo Geometry Changes

Arroyo geometry in 1934 at CW4, CW5, CW6,

CW8, CW10, and CW11 was quantified from GIS

interpretations of the 1931 and 1934 NPS contour maps

(tables 4 and 5). Arroyo geometry in 1973 at CW4,

CW5, CW6, CW8, CW10, and CW11 was quantified

from photogrammetric interpretations. Field surveys at

CW3, CW13, CW14, F1, and G1 were conducted

between 1972 and 1977 (tables 4 and 5). Arroyo

geometry in the 1970’s was based on an average of all

measurements in the 1970’s. In the 2000 survey at cross

section CW1, the survey was not completed far enough

along the left bank to accurately define the arroyo top

width and top depth. Changes of channel geometry in

Chaco Wash for the 2000 survey upstream from

Escavada Wash are shown in figure 9. No trend is

evident in arroyo top width or area in an upstream

direction. Top depth increases slightly upstream from

Escavada Wash (fig. 9).

Table 3. Comparison of channel geometry using 2000 surveys and 2000 photogrammetric analysis for

cross sections CW3, CW8, and CW10

[m, meter; m2, square meter]

Method

Cross

section

(fig. 1)

Arroyo

top

width

(m)

Arroyo

top

depth

(m)

Arroyo

top

area

(m2

)

50-

percent

width (m)

Bankfull

width

(m)

Bankfull

depth

(m)

Bankfull

area

(m2

)

Survey CW3 115 6.0 435 104 10 1.6 11

Photogrammetry CW3 125 5.0 416 98 17 1 9

Survey CW8 91 7.5 457 85 8.3 1.9 8

Photogrammetry CW8 73 4.6 182 7 1 5

Survey CW10 83 7.7 309 47 7.1 1.7 7

Photogrammetry CW10 43 6.1 177 37 8.8 1 8
Figure 8. Comparison of surveyed channel cross sections to photogrammetric

interpretations at Chaco Wash cross sections CW3, CW8, and CW10. 

Location of cross sections shown in figure 1. 

A

R

BIT

R

A

R

Y

ELE

V

ATIO

N, IN

M

E

T

E

R

S

STATIONING FROM LEFT BANK, IN METERS

2000 FIELD SURVEY

2000 AERIAL PHOTOGRAPHY

CW3

CW8

CW10

1,852

1,854

1,856

1,858

1,860

1,862

1,864

22

24

26

28

30

32

22

24

26

28

30

32

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

18

EXPLANATION
19

Table 4. Arroyo geometry of Chaco Wash and selected tributaries: (A) 1934, (B) 1970’s,

and (C) 2000

[GIS, Geographical Information System; --, no data]

 (A) 1934

 (B) 1970’s

Cross

section

(fig. 1)

Method used to

quantify arroyo

geometry

Arroyo top

width, in

meters

Arroyo top

depth, in

meters

Arroyo top crosssectional area, in

square meters

CW4 GIS 76 7.2 519

CW5 GIS 59 7.1 362

CW6 GIS 52 7.4 344

CW8 GIS 68 5.5 279

CW10 GIS 43 7.2 272

CW11 GIS 95 6.4 600

Arroyo top width, in meters

Cross

section

(fig. 1)

Method used to

quantify arroyo

geometry 1972 1973 1974 1976 1977

CW3 Survey 104 -- 104 -- --

CW4 Photogrammetry -- 87 -- -- --

CW5 Photogrammetry -- 79 -- -- --

CW6 Photogrammetry -- 56 -- -- --

CW8 Photogrammetry -- 78 -- -- --

CW10 Photogrammetry -- 45 -- -- --

CW11 Photogrammetry -- 94 -- -- --

CW13 Survey 102 -- -- -- --

CW14 Survey -- -- 90 96 --

F1 Survey 61.6 -- -- 61.3 --

G1 Survey 17.0 16.7 -- 16.7 15.3
20

Table 4. Arroyo geometry of Chaco Wash and selected tributaries: (A) 1934, (B) 1970’s,

and (C) 2000--Concluded

(B) 1970’s--Concluded

(C) 2000

Arroyo top depth, in meters

Arroyo top cross-sectional area, in

square miles

Cross

section

(fig. 1) 1972 1973 1974 1976 1977 1972 1973 1974 1976 1977

CW3 5.5 -- 6.1 -- -- 428 -- 440 --

CW4 -- 5.3 -- -- -- -- 414 -- -- --

CW5 -- 5.8 -- -- -- -- 355 -- -- --

CW6 -- 5.8 -- -- -- -- 244 -- -- --

CW8 -- 3.8 -- -- -- -- 136 -- -- --

CW10 -- 6.0 -- -- -- -- 204 -- -- --

CW11 -- 6.1 -- -- -- -- 477 -- -- --

CW13 10.6 -- -- -- -- 672 -- -- --

CW14 -- -- 9.0 9.1 -- -- -- 587 595 --

F1 7.6 -- -- 7.5 -- 345 -- -- 330

G1 3.3 -- -- 3.2 3.6 36.8 -- -- 40.4 35.6

Cross

section

(fig. 1)

Method used to

quantify channel

geometry

Arroyo top

width, in

meters

Arroyo top

depth, in

meters

Arroyo top crosssectional area, in

square meters

CW1 Survey Not surveyed Not surveyed Not surveyed

CW2 Photogrammetry 38 4.9 143

CW3 Survey 115 6.0 435

CW4 Photogrammetry 82 5.3 391

CW5 Photogrammetry 179 6.8 338

CW6 Photogrammetry 62 6.1 273

CW7 Survey 62.3 7.4 324

CW8 Photogrammetry 73 4.6 182

CW9 Survey 102 7.5 383

CW10 Photogrammetry 43 6.1 177

CW11 Photogrammetry 94 6.6 476

CW12 Photogrammetry 33 6.5 147

CW13 Survey 127 10.5 765

CW14 Survey 99.2 9.1 624

F1 Survey 61.5 7.6 308

G1 Survey 17.1 3.4 39.7
21

Table 5. Arroyo cross-sectional geometry at 50-percent depth

[--, no data]

 (A) 1934

 (B) Selected years during the 1970’s

Cross

section

(fig. 1)

Width at 50-

percent

depth, in

meters

Depth at 50-

percent

depth, in

meters

Cross-sectional

area at 50-

percent depth, in

square meters

CW4 75 5.0 319

CW5 55 4.8 210

CW6 47 5.1 220

CW8 55 3.8 147

CW9 -- -- --

CW10 38 4.9 147

CW11 83 4.2 284

Width at 50-percent depth, in meters

Cross

section

(fig. 1) 1977 1976 1974 1973

CW3 -- -- 101 --

CW4 -- -- -- 77

CW5 -- -- -- 68

CW6 -- -- -- 53

CW8 -- -- -- 53

CW10 -- -- -- 35

CW11 -- -- -- 86

CW13 -- -- -- --

CW14 -- 86.3 87.6 --

F1 -- 54.7 -- --

G1 14.6 14.5 -- --
22

Table 5. Arroyo cross-sectional geometry at 50-percent depth--Continued

(B) Selected years during the 1970’s--Concluded

Width at 50-percent depth, in meters

Cross

section

(fig. 1) 1977 1976 1974 1973 1972

CW3 -- -- 3.9 -- 3.3

CW4 -- -- -- 3.0 --

CW5 -- -- -- 3.5 --

CW6 -- -- -- 3.4 --

CW8 -- -- -- 2.1 --

CW10 -- -- -- 3.6 --

CW11 -- -- -- 3.9 --

CW13 -- -- -- -- 6.0

CW14 -- 5.6 5.4 -- --

F1 -- 4.7 -- -- 4.9

G1 2.4 2.0 -- -- 2.1

Cross-sectional area at 50-percent depth, in meters

Cross

section

(fig. 1) 1977 1976 1974 1973 1972

CW3 -- -- 229 -- 209

CW4 -- -- -- 163 --

CW5 -- -- -- 162 --

CW6 -- -- -- 128 --

CW8 -- -- -- 52 --

CW10 -- -- -- 85 --

CW11 -- -- -- 214 --

CW13 -- -- -- -- 281

CW14 -- 301 321 -- --

F1 -- 160 -- -- 169

G1 22 21 -- -- 15
23

Table 5. Arroyo cross-sectional geometry at 50-percent depth--Concluded

 (C) 2000

Cross

section

(fig. 1)

Width at 50-percent

depth, in meters

50-percent depth,

in meters

Crosssectional

area at 50-

percent

depth, in

square

meters

CW1 45.8 2.7 21

CW2 29.7 2.4 49

CW3 104 3.8 204

CW4 72 3.0 192

CW5 69 4.5 161

CW6 55 3.8 112

CW7 60 3.7 91

CW8 58 2.9 61

CW9 50 3.7 74

CW10 37 3.8 80

CW11 87 4.4 166

CW12 23.2 3.2 52

CW13 86.7 5.9 263

CW14 90.9 5.6 291

F1 54.7 4.8 146

G1 14.8 2.2 21
DISTANCE UPSTREAM FROM ESCAVADA WASH, IN KILOMETERS

DISTANCE UPSTREAM FROM ESCAVADA WASH, IN KILOMETERS

A

R

R

O

Y

O T

OP DEPT

H, IN METER

S

A

R

R

O

Y

O T

OP WID

T

H, IN METER

S

0 2 4 6 8 10 12 14 16

0

50

100

150

200

(A)

0 2 4 6 8 10 12 14 16

0

2

4

6

8

10

(B)

Figure 9. (A) Chaco Wash top width measurements from 2000 field surveys and

 photogrammetry and (B) top depth measurements from 2000 data.

 Location of cross sections shown in figure 1.

CW2

CW2

CW3

CW3

CW4

CW4

CW9

CW9

CW11

CW11

CW12

CW12

CW13

CW13

CW14

CW14

24
25

Arroyo Top Width

From 1934 to 1973, Chaco Wash arroyo top

width increased at five of six cross sections (CW4,

CW5, CW6, CW8, and CW10) (fig. 10A) and

decreased 1 m at CW11. Widening at the five cross

sections ranged from 2 to 20 m and averaged about 9 m.

From the 1970’s to 2000, changes in Chaco Wash top

width were more variable, with increases at four of nine

cross sections (CW3, CW6, CW13, and CW14),

narrowing at three cross sections (CW4, CW8, and

CW10), and no change in arroyo top width at CW5 and

CW11 (fig. 10A). Widening at the four cross sections

ranged from about 6 to 24 m and averaged 12 m.

Narrowing of the channel ranged from 2 to 5 m. The

largest increase in arroyo top width for any resurvey

was 24 m at CW13 measured from the 1970’s to 2000.

Tributary arroyos F1 and G1 showed a small amount of

widening from the 1970’s to 2000, 0.1 and 0.8 m,

respectively (fig. 10A). Overall, from 1934 to 2000

Chaco Wash widened at four of six cross sections on

Chaco Wash (CW4, CW5, CW6, and CW8), narrowed

at CW11, and remained the same at CW10. Widening

at the four cross sections ranged from 5 to 20 m and

averaged about 10 m.

An arroyo can narrow if sediment such as talus is

deposited along arroyo walls. A decrease in arroyo top

width is not expected because deposition is not possible

on a vertical or near-vertical arroyo wall; the channel

can narrow, however, if it is modified by human activity

such as adding fill material to the channel. The

narrowing of channel top widths at cross sections

CW4, CW8, CW10, and CW11 was interpreted from

aerial photography and may be due to inherent errors in

photogrammetric examination of the data.

Arroyo Width at 50-Percent Depth

From 1934 to 1973, arroyo width at 50-percent

depth increased at four of six cross sections (CW4,

CW5, CW6, and CW11) (fig. 10B; table 5) and

narrowed at two cross sections (CW8 and CW10).

Widening at the four cross sections ranged from 3 to 13

m and averaged about 6 m. Narrowing was 2 m at CW8

and 3 m at CW10. From the 1970’s to 2000, arroyo

width at 50-percent depth increased at eight of nine

cross sections (CW3, CW5, CW6, CW8, CW10,

CW11, CW13, and CW14) and narrowed 6 m at CW4

(fig. 10B). Widening in these eight cross sections

ranged from about 1 to 9 m and averaged about 3 m.

The greatest increase in width at 50-percent depth was

13 m at CW5 from 1934 to 1973. Tributary arroyo F1

narrowed 0.7 m from the 1970’s to 2000, and G1

widened 0.9 m (fig. 10B). Overall, measured changes at

50 percent of arroyo depth from 1934 to 2000 indicate

widening in four of six cross sections (CW5, CW6,

CW8, and CW11) on Chaco Wash and narrowing in

two cross sections (CW4 and CW10). Widening in the

four cross sections ranged from 3 to 14 m and averaged

about 7 m. Narrowing was 3 m at CW4 and 1 m at

CW10.

Overall widening at 50-percent depth is

generally less than at the top of the arroyo, which may

be due to colluvial deposits (talus aprons) developing

along the arroyo walls from upslope bank failures. The

narrowing at CW4 and CW10 from 1934 to 2000 may

be due to talus deposits. Rates of widening at the top of

the channel doubled from 0.2 m/yr during 1934-73 to

0.4 m/yr during the 1970’s-2000 (fig. 11A). Rates of

widening at 50-percent depth decreased from 0.2 m/yr

(1934-73 cross sections) to 0.1 m/yr (1970’s-2000) (fig.

11A).

Arroyo Top Depth

Changes in arroyo top depth were measured at

selected cross sections from 1934 to 1973 and from the

1970’s to 2000 (table 4). From 1934 to 1973, all six

cross sections showed a decrease in depth, ranging

from 0.3 to 1.9 m and averaging 1.4 m. From the 1970’s

to 2000, arroyo top depth increased at seven of nine

cross sections (CW3, CW5, CW6, CW8, CW10,

CW11, and CW14), decreased 0.1 m at CW13, and

showed no change at CW4 (fig. 10C). The increase in

depth at the seven cross sections ranged from 0.1 to

1.0 m and averaged 0.4 m. Tributary arroyos F1 and G1

showed no appreciable change in depth from the 1970’s

to 2000 (fig. 10C). The average rate of decreasing

arroyo depth from 1934 to 1973 (0.04 m/yr) was higher

than that from 1934 to 2000 (0.02 m/yr) (fig. 11B).

Overall, from 1934 to 2000, arroyo top depth decreased

at five of six cross sections (CW4, CW5, CW6, CW8,

and CW10) and increased 0.2 m at cross section CW11

(fig. 10C; table 4). The decrease in depth ranged from

0.3 to 1.9 m and averaged 1.1 m.

Decreases in arroyo top depth are related to

changes in the channel thalweg. Changes of the arroyo

top surface are related to sheetwash and eolian activity

and generally are negligible. The major cause for the

decrease in depth is aggradation of the thalweg. In the

Rio Puerco channel, an arroyo draining central New

Mexico, the channel aggraded 2.55 m between 1936

and 1995 (Gellis and Elliott, 2001).
-1

0

0

10

20

30

Figure 10. Changes in arroyo top geometry at selected cross sections along Chaco Wash and selecte

(A) Top width, (B) top width at 50 percent of arroyo depth, (C) arroyo top depth, and (D) 

area. Location of cross sections shown in figure 1.

-1

0

0

10

20

30

(A) (B)

CW3

CW3

CW4

CW4

CW5

CW5CW6

CW6

CW8

CW8

CW10

CW10

CW11

CW

CW13

CW14

F1

G1

-2

-

2

1

0

1

0

-150

-100

-50

50

100

1934 TO 1973

1970's TO 2000

C (D)

S

RETE M

NI , H

T

DI WP O

T

NI E G

N

A

H

C

S

RETE M

NI , H

TPED P O

T

NI E G

N

A

H

C

, AER

A LA

N

OI T

CES- S

S

O

R

C P O

T

NI E G

N

A

H

C

S

RETE M

NI

F O

T

NEC

REP 05 TA

H

T

DI W

O

Y

O

R

R

A

NI E G

N

A

H

C

S

RETE M

NI , H

TPED

O

Y

O

R

R

A

gni nedi W gni worr a N

gni nedi W gni worr a N

gni nedi W gni worr a N

gni nedi W gni worr a N

CROSS SECTION CROSS SECTIO

EXPLANATION

( )

26
0.0

0.1

0.2

0.3

0.4

0.5

0.6

1934 to 1973

1970's to 2000

1934 to 2000

Top of

arroyo

50 percent of

arroyo depth

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

-3

-2

-1

0

1

2

1934 to 1973

1934 to 1973

1970's to 2000

1970's to 2000

1934 to 2000

1970's to 2000

1934 to 2000

(A)

(B)

C

Figure 11. Average rates of (A) arroyo widening, (B) arroyo top depth, and (C) top cross-sectional 

 area at selected cross sections along Chaco Wash and selected tributaries.

R

ATE OF C

H

A

N

GE IN

A

R

R

O

Y

O

WIDENIN

G,

IN

METER

S PER

YEA

R

R

ATE OF C

H

A

N

GE IN

A

R

R

O

Y

O

T

OP

DEPT

H, IN

METER

S PER

YEA

R

R

ATE OF C

H

A

N

GE IN

C

R

O

S

S-SEC

TIO

N

AL A

REA,

IN

S

Q

U

A

RE METER

S PER

YEA

R

EXPLANATION

Increase Increase Decrease Decrease

( )

6

5

4

6

6

8

6

5

4

4 4

8 4

6 NUMBER OF MEASUREMENTS

AVERAGE RATES

27
28

Arroyo Cross-Sectional Area

Changes in cross-sectional area are an

informative way to determine erosion and deposition

for the arroyo. From 1934 to the 1970’s, all six cross

sections showed a decrease in arroyo top crosssectional area, ranging from 7 to 143 m2 and averaging

91 m2

 (fig. 10D). Between the 1970’s and 2000,

changes in arroyo top cross-sectional area varied,

increasing at five cross sections (CW3, CW6, CW8,

CW13, and CW14) and decreasing at four cross

sections (CW4, CW5, CW10, and CW11) (fig. 10D).

Increases in area at the five cross sections ranged from

1 to 92 m2

 and averaged 40 m2. Decreases in area for

the four cross sections ranged from 1 to 28 m2

 and

averaged 17 m2. The greatest decrease in arroyo top

cross-sectional area was 143 m at CW8 from 1934 to

1973. The greatest increase in arroyo top crosssectional area was 92 m at CW13 from the 1970’s to

2000. Tributary arroyo F1 showed a decrease in arroyo

top cross-sectional area of 30 m2 from the 1970’s to

2000, and G1 showed no appreciable change in the

same period (fig. 10D). Overall, from 1934 to 2000,

arroyo top cross-sectional area decreased at six cross

sections (CW4, CW5, CW6, CW8, CW10, and CW11)

(fig. 10D). Decreases in arroyo top cross-sectional area

ranged from 24 to 128 m2

 and averaged 90 m2.

 The average rate of decrease in cross-sectional

area from 1934 to 1973 was 2.3 m2

/yr (fig. 11C). This

rate decreased to 0.6 m2/yr for the four cross sections

(CW4, CW5, CW10, and CW11) that continued to

decrease in cross-sectional area from the 1970’s to

2000 (fig. 11C). The average rate of increase in crosssectional area was 1.6 m2/yr at the five cross sections

where area increased from the 1970’s to 2000 (fig.

11C).

Volumetric Changes in Chaco Wash

Changes in the volume of the six reaches shown

in figure 5 were quantified over time. From 1934 to

1973, sediment was deposited in all six reaches and

ranged from 6,700 to 26,600 m3

. By dividing the

volume filled (109,200 m3) from 1934 to 1973 over the

length of channel (1.7 km), the cross-sectional area

filled per unit length of channel of 64 m2 or 1.65 m2

/yr

can be calculated. From 1973 to 2000, four of the six

reaches showed erosion or an increase in volume

(table 6) ranging from 3,300 to 4,500 m3 and two of the

reaches showed deposition of 400 and 1,800 m3. The

cross-sectional area eroded 7 m2

 per unit length of

channel or 0.27 m2/yr. Overall, volume calculations

along six reaches of Chaco Wash from 1934 to 2000

(table 6) showed sediment deposition in all reaches

ranging from 8,500 to 23,200 m3

. For the entire 1.7 km,

the arroyo filled about 96,900 m3

 or 57 m2 per unit

length of channel (0.87 m2

/yr). The volume decreased

at a rate of 130 to 350 m3/yr at all reaches.

Changes in planimetric area show widening of

the channel for all reaches from 1934 to 2000 (table 6).

Five of six reaches show greater rates of widening from

1973 to 2000 than from 1934 to 1973. Reaches 3 and 4,

near Pueblo del Arroyo (fig. 5), show greater increases

in planimetric area, 87 and 62 m2/yr, respectively, from

1973 to 2000 than the rates of 6 and 21 m2/yr from

1934 to 1973.

Inner-Channel Changes

In 1934, Chaco Wash channel was a broad,

braided channel without a well-defined inner channel

(DeAngelis, 1972). Because of this lack of a welldefined inner channel, determining bankfull geometry

is difficult. A well-defined inner channel is evident

from the 1970’s to 2000; thus, bankfull geometry is

easier to discern. Bankfull width in 1934 was generally

selected along the arroyo wall near the bottom of the

channel where a break in slope is observed. Bankfull

depth and cross-sectional area were not quantified.

Geometry for the bankfull channel for 1934,

selected years during the 1970’s, and 2000 is shown in

table 7. From 1934 to 1973 all six cross sections

showed a decrease in bankfull width, ranging from 0.4

to 45 m and averaging 26 m (fig. 12A). Narrowing

continued at seven of nine cross sections from the

1970’s to 2000, ranging from 1.9 to 19.3 m and

averaging 9 m (fig. 12A). From the 1970’s to 2000,

CW4 showed widening of 8 m and CW5 showed little

change (fig. 12A). Overall, from 1934 to 2000,

narrowing was the dominant form of change in

bankfull width and occurred in all six cross sections on

Chaco Wash (fig. 12A). Narrowing ranged from 13 to

55 m (table 7) and averaged 30 m. Rates of channel

narrowing from 1934 to 1973, averaging 0.7 m/yr, were

generally greater than rates from the 1970’s crosssectional survey to 2000, averaging 0.3 m/yr (fig. 13).

Because of the problems discussed earlier in

defining bankfull depth from the 1934 cross sections,

changes in bankfull depth and cross-sectional area are

shown only from the 1970’s to 2000 (fig. 12B,C). From

the 1970’s to 2000, bankfull depth increased at six of

nine cross sections on Chaco Wash (CW3, CW5, CW6,

CW8, CW11, and CW14), ranging from 0.2 to 1.2 m

and averaging 0.5 m (fig. 12B). From the 1970’s to

2000, CW4 showed no change in bankfull depth. Depth

in tributary arroyos F1 and G1 showed an increase of

0.1 m and a decrease of 0.1 m, respectively (fig. 12B).
29

Table 6. Change in sediment volume, area, and depth of the arroyo channel at selected reaches in Chaco Wash

[--, no data]

Change in volume, in cubic

meters/year

Difference in planimetric

area, in square meters/year

Location-year

(fig. 5)

Volume,

in cubic

meters

Planimetric

area, in

square

meters

1934-

73

1973-

2000

1934-

2000

1934-

73

1973-

2000

1934-

2000

Reach 1-2000 83,200 25,300 -450 160 -200 43 218 115

Reach 1-1973 78,700 19,500 -- -- -- -- -- --Reach 1-1934 96,400 17,800 -- -- -- -- -- --Reach 2-2000 103,600 30,300 -170 -70 -130 0 6 2

Reach 2-1973 105,400 30,100 -- -- -- -- -- --Reach 2-1934 112,100 30,100 -- -- -- -- -- --Reach 3-2000 70,900 18,600 -550 120 -270 6 87 39

Reach 3-1973 67,600 16,300 -- -- -- -- -- --Reach 3-1934 89,000 16,000 -- -- -- -- -- ---Reach 4-2000 70,000 18,100 -600 130 -300 21 62 38

Reach 4-1973 66,600 16,400 -- -- -- -- -- --Reach 4-1934 89,900 15,600 -- -- -- -- -- --Reach 5-2000 83,100 24,500 -350 -10 -210 68 88 76

Reach 5-1973 83,500 22,100 -- -- -- -- -- --Reach 5-1934 97,000 19,500 -- -- -- -- -- --Reach 6-2000 91,400 24,000 -680 120 -350 89 16 59

Reach 6-1973 88,000 23,500 -- -- -- -- -- --Reach 6-1934 114,600 20,000 -- -- -- -- -- ---Combined reaches 2000 502,200 140,800 -2,800 460 -1,470 227 478 330

Combined reaches 1973 489,800 127,900 -- -- -- -- -- --Combined reaches 1934 599,100 119,000 -- -- -- -- -- --
30

Table 7. Bankfull geometry of Chaco Wash and selected tributaries: (A) 1934,

(B) 1970’s, and (C) 2000

[--, no data]

(A) 1934

(B) 1970's

Cross

section

(fig. 1)

Bankfull width, in

meters Bankfull depth, in meters

Bankfull crosssectional area, in

square meters

CW4 59 1.7 86

CW5 36 0.6 16

CW6 44 1.1 41

CW8 38 1.5 51

CW10 22 0.9 17

CW11 64 1.5 67

Cross

section

(fig. 1)

Bankfull crosssectional area, in square meters

1977 1976 1974 1973 1972

CW3 -- -- 10.5 -- 7.2

CW4 -- -- -- 8 --

CW5 -- -- -- 11 --

CW6 -- -- -- 4 --

CW8 -- -- -- 14 --

CW9 -- -- -- --

CW10 -- -- -- 28 --

CW11 -- -- -- 19 --

CW13 -- -- -- -- 38.7

CW14 -- 9.9 8.9 -- --

F1 -- 29.5 -- -- 31.8

G1 5.1 3.7 -- -- 6.0
31

Table 7. Bankfull geometry of Chaco Wash and selected tributaries: (A) 1934,

(B) 1970’s, and (C) 2000--Concluded

 (C) 2000

Cross section

(fig. 1)

Bankfull width, in

meters

Bankfull depth, in

meters

Bankfull crosssectional area, in

square meters

CW1 8.5 2.0 10.8

CW2 21.3 1.6 24.9

CW3 10.4 1.6 11.1

CW4 28 0.8 17

CW5 13 2.2 13

CW6 8 1.4 6

CW7 10.4 2.5 12.9

CW8 7 1.2 5

CW9 6.5 1.8 6.1

CW10 9 1.4 8

CW11 9 2.1 8

CW12 11 0.8 5

CW13 6.3 1.4 5.1

CW14 6.9 2.0 7.3

F1 17.6 2.0 15.8

G1 8.8 1.0 5.1
32

From the 1970’s to 2000, bankfull crosssectional area changes were variable (fig. 12C); four

cross sections (CW3, CW4, CW5, and CW6) showed

increases in area ranging from 2 to 9 m2 and averaging

4 m2

. Cross-sectional area at five sites (CW8, CW10,

CW11, CW13, and CW14) showed decreases ranging

from 2 to 34 m2

 and averaging 15 m2 (fig. 12C).

Tributary arroyo F1 showed filling of 15 m2

, and G1

showed no appreciable change in area (fig. 12C).

Love (1979) documented the adjustment of

Chaco Wash from a braided channel in the 1930’s to a

channel with a well-defined flood plain by the 1970’s.

The braided form of the channel in the 1930’s may have

been a response to increased discharge (Love, 1980) or

to an increase in sediment supply (Schumm, 1977).

Love (1980) speculated that periods of less than

average rainfall were favorable for deposition and that

periods of greater than normal rainfall favored erosion.

Channel narrowing resulted from the development of

the modern flood plain, which began by 1939 (Love,

1979). Following incision, the arroyo channel widens

(fig. 4C). The arroyo channel may widen to a width at

which it can no longer transport sediment; thus,

sediment is deposited, the channel aggrades, and an

incipient flood plain is developed (fig. 4D). Vegetation

establishes itself on the flood plain, stabilizes the inner

channel, and increases roughness, which further

enhances sediment deposition on the flood plain.

Similar changes in arroyo geometry from a braided

channel to a well-developed inner channel have been

documented for the lower reaches of the Rio Puerco

(Elliott and others, 1999). The increase in bankfull

depth is from aggradation of the flood plain. Scour of

the channel also increases bankfull depth. Because

arroyo top depth increased at seven of nine cross

sections from the 1970’s to 2000 (fig. 10C), channel

scour or lowering of the thalweg elevation may also be

a factor in the increase in bankfull depth. Because a

decrease in cross-sectional area was observed in all

cross sections from 1934 to 2000 (fig. 10D), channel

scour alone cannot explain the increase in bankfull

depth.

Longitudinal and Planform Changes

Contour maps created from the 1934

topographic maps and 1973 and 2000 aerial

photographs (figs. 14A-C) were used to describe

longitudinal profile changes and planform changes of

the arroyo. Planform changes in the arroyo are viewed

from above. The longitudinal profile extends from

reach 1 to reach 6 (fig. 5). The longitudinal profile of

the channel (fig. 15A) shows net aggradation of the

channel for all reaches from 1934 to 1973. This

matches the results of the photogrammetric

interpretations (fig. 7). From 1973 to 2000, reaches

from 0 to 1,000 m upstream showed degradation of the

channel (fig. 15A). This includes cross sections CW3,

CW4, CW5, CW6, CW8, CW10, and CW11, which

showed decreases in channel depth (fig. 10C). From

1973 to 2000, reaches from 1,000 to more than 1,500 m

upstream (fig. 15A) showed no appreciable change in

channel elevation.

Elevations were averaged in 250-m increments

to determine elevation changes through the six reaches.

Average elevation increases (aggradation) of the

channel from 1934 to 1973 ranged from 0.2 to 1.4 m

(fig. 15B). Decreases in elevation from 0 to 1,000 m

upstream showed degradation of 0.4 to 0.8 m (fig.

15B).

Planform changes in Chaco Wash show arroyo

top width widening from 1934 to 1973 and little change

from 1973 to 2000 (fig. 16). The planform changes

closely match the interpretations of arroyo top width

changes from the field resurveys and photogrammetric

interpretations. Planform changes in Chaco Wash show

bankfull width narrowing from 1934 to 1973 and from

1973 to 2000 (fig. 17). Most of the narrowing was

between 1934 and 1973.

Changes near Pueblo del Arroyo

Three cross sections (CW6, CW8, and CW10)

were used to assess changes in Chaco Wash geometry

over time near Pueblo del Arroyo. From 1934 to 2000,

the arroyo top widened at CW6 (10 m) and CW8 (5 m)

and showed no change at CW10 (fig. 10A; table 4).

From 1934 to 2000, CW6 widened 9 m, CW8 widened

3 m, and CW10 narrowed 1 m (fig. 10B) at 50-percent

depth. From 1934 to 2000 near Pueblo del Arroyo,

three cross sections (CW6, CW8, and CW10) showed

decreasing arroyo depths close to 1 m (fig. 10C). From

1973 to 2000, these same three cross sections showed

an increase in depth from 0.2 to 0.8 m (fig. 10C). From

1934 to 2000, CW6, CW8, and CW10 showed

decreases in cross-sectional area of 71, 97, and 96 m2

,

respectively (fig. 10D). From the 1970’s to 2000, CW6

and CW8 showed increases in cross-sectional area of

29 and 46 m2

, respectively. CW10 decreased 27 m2 in

cross-sectional area from the 1970’s to 2000 (fig. 10D).

Chaco Wash geometry changes near Pueblo del Arroyo

are similar to changes elsewhere in the CCNHP.

Between 1934 and 2000, Chaco Wash widened and

aggraded. In the more recent time period, 1973-2000,

Chaco Wash near Pueblo del Arroyo incised and

increased in cross-sectional area.
-2

-

2

1

0

1

(B)

-40

-2

0

0

20

40 1970's to 2000

-40

-2

0

0

20

(A)

WC

3

WC

4

WC

5

WC

6

WC

8

WC

01

WC 11

WC

31

WC

41

1F

1 G

CROSS SECTION

WC

3

WC

4

WC

5

WC

6

WC

8

WC

01

WC 11

WC

CROSS SECTION

WC

3

WC

4

WC

5

WC

6

WC

8

WC

01

WC 11

WC

31

WC

41

1F

1 G

CROSS SECTION

SRETE M NI , HT DI WLL UFKNAB NI E GNAHC

LANOI T CES- SS ORCLL UFKNAB NI E GNAHC

SRETE MERAUQS NI , AERA

, HTPEDLL UFKNAB NI E GNAHC

RAEY REP SRETE M NI

Figure 12.Changes in bankfull along Chaco Wash and selected tributaries. (A) Width, (B) depth, and (C) c

 Location of cross sections shown in figure 1.

C

gni nedi W gni worr a N

noi sor E gnilli F

gni saer cnI gni saer ce D

1934 to 1973

1970's to 2000

( )

33
CW3 CW4 CW5 CW6 CW8 CW10 CW11 CW13 CW14 F1 G1

-2

-1

0

1

2

1934 to 1973

Figure 13. Rates of change in bankfull width from 1934 to 1973 and from the 1970’s to 2000.

CROSS SECTION

R

ATE OF CHANGE IN BANKFULL WIDTH, IN METERS PER

YEA

R

Widening Narrowing

1970's to 2000

34
Figure 14A. Topographic contours in relation to selected cross sections along Chaco Wash in 

 Chaco Culture National Historical Park. Contours generated from 1934 National 

 Park Service 1:480 contour map. Location of this extent of Chaco Wash shown 

 in figure 1.

TOPOGRAPHIC CONTOUR-- 

 INTERVAL 0.3 METER (1 FOOT)

35°

04’

35°

03’

30”

107° 58’ 107° 57’ 30’

0

0

0.5 MILE

0.5 KILOMETER

CW4

CROSS SECTION

EXPLANATION

CW10

CW9

CW7

CW11

Pueblo del Arroyo

Pueblo 

Bonito 

Bridge

CW4

CW5

CW6

CW8

35
35°

04’

35°

03’

30”

107° 58’ 107° 57’ 30’

CW4

CW5

CW6

CW8

CW10

CW9

CW7

CW11

Pueblo 

del 

Arroyo

Figure 14B. Topographic contours in relation to selected cross sections along Chaco Wash in

 Chaco Culture National Historical Park. Contours generated from 1973 aerial

 photography. Location of this extent of Chaco Wash shown in figure 1.

Pueblo 

Bonito 

Bridge

TOPOGRAPHIC CONTOUR-- 

 INTERVAL 0.3 METER (1 FOOT)

CW4

CROSS SECTION

EXPLANATION

0

0 0.5 MILE

0.5 KILOMETER

36
35°

04’

35°

03’

30”

107° 58’ 107° 57’ 30’

Figure 14C. Topographic contours in relation to selected cross sections along Chaco Wash 

 in Chaco Culture National Historical Park. Contours generated from 2000

 aerial photography. Location of this extent of Chaco Wash shown in figure 1.

CW4

CW5

CW6

CW8 CW10

CW9

CW7

CW11

Pueblo del Arroyo

Pueblo 

Bonito 

Bridge

TOPOGRAPHIC CONTOUR--

 INTERVAL 0.3 METER (1 FOOT)

CW4

CROSS SECTION

EXPLANATION

0

0 0.5 MILE

0.5 KILOMETER

37
DISTANCE UPSTREAM FROM REACH 1, IN METERS

0 500 1,000 1,500 2,000

1,856

1,857

1,858

1,859

1,860

1,861

1,862

2000

1973

(A)

Figure 15. (A) Longitudinal profile of Chaco Wash, 1934, 1973, and 2000 and (B) average

elevation changes over 250-meter increments. Reaches shown in figure 5.

1934

A

R

BIT

R

A

R

Y

ELE

V

ATIO

N, IN

M

E

T

E

R

S

DISTANCE UPSTREAM FROM REACH 1, IN METERS

0-250

250-500

500-750

750-1,000

1,000-1,250

1,250-1,500

>1,500

C

H

A

N

G

E IN

ELE

V

ATIO

N, IN

M

E

T

E

R

S

DEG

R

A

D

ATIO

N

A

G

G

R

A

D

ATIO

N -1.0

-0.5

0.0

0.5

1.0

1.5

2.0

1934-73

1973-2000

No change 1973-2000

(B)

38
35°

04’

35°

03’

30”

107° 57’ 30’

0

0 0.5 MILE

0.5 KILOMETER

CW4

CW5

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Pueblo del Arroyo

Figure 16. Top width cross-sectional measurements along Chaco Wash in 1934, 1973, and 2000.

 Location of this extent of Chaco Wash shown in figure 1.

CW4 CROSS SECTION

107° 58’

Pueblo 

Bonito 

Bridge

35°

04’

35°

03’

30”

107° 58’ 107° 57’ 30’

0

0 0.5 MILE

0.5 KILOMETER

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Pueblo del Arroyo

Figure 17. Bankfull width cross-sectional measurements along Chaco Wash in 1934, 1973, and

 2000. Location of this extent of Chaco Wash shown in figure 1.

1973

1973

1934

1934

2000

2000

CW4 CROSS SECTION

39
40

SUMMARY

Trends in arroyo channel geometry for Chaco

Wash and selected tributaries were assessed through

photogrammetric techniques and field resurveys for

three time periods: 1934-2000, 1934-1973, and 1973-

2000. Maximum vertical errors associated with

photogrammetric techniques average less than +0.75 m

with a maximum error of +2.0 to +2.5 m. Maximum

horizontal errors average +0.66 m with a maximum

error of +2.0.

Five of the six photogrammetrically analyzed

cross sections in Chaco Wash show net aggradation

between 1934 and 2000 ranging from 0.4 to 1.9 m and

averaging 1.1 m, with most of the aggradation

occurring between 1934 and the 1970’s.

Photogrammetric analysis at cross sections and reaches

and field surveys indicate net widening from 1934 to

2000 at the top of Chaco Wash and at 50-percent depth.

The volume of the Chaco Wash arroyo decreased

from filling with sediment at all reaches from 1934 to

2000 and ranged from 130 to 350 m3

/yr. For the entire

1.7 km, the arroyo filled 96,900 m3

 or 57 m2 per unit

length of channel. Similar results for the channel filling

with sediment were obtained from the cross sections

where the cross-sectional area decreased from 1934 to

2000, ranging from 25 to 128 m2 and averaging 90 m2

.

A decrease in cross-sectional area is due to aggradation

on the channel bed and sediment deposition on the

flood plain.

Channel changes of width, depth, and crosssectional area are variable both in time and space. Five

of six cross sections widened between 1934 and 1973,

and four of nine cross sections widened between the

1970’s and 2000. At 50-percent depth, four of six cross

sections widened between 1934 and 1973 and widened

at eight of nine cross sections between the 1970’s and

2000. Rates of widening at the top of the channel

doubled from 0.2 m/yr (1934 to 1973 cross sections) to

0.4 m/yr (1970’s to 2000 cross sections). The top of the

channel widened from sheetwash, gullying, and soil

piping on the alluvial valley floor and from bank

collapse resulting from an increase in channel

sinuosity. Widening at the top of the channel has the

potential to affect cultural sites. Rates of arroyo

widening at 50-percent depth decreased from 0.2 m/yr

(1934 to 1973 cross sections) to 0.1 m/yr (1970’s to

2000 cross sections). Narrowing of the arroyo at 50-

percent depth may be due to talus deposits.

All cross sections on Chaco Wash showed

aggradation from 1934 to 1973 that ranged from 0.3 to

1.9 m and averaged 1.4 m. The aggradation trend

reversed between the 1970’s and 2000; most cross

sections (seven of nine) showed an increase in arroyo

depth or degradation ranging from 0.1 to 1.0 m and

averaging 0.4 m. Between 1934 and 1973, all six cross

sections filled with sediment and decreases in crosssectional area ranged from 7 to 143 m2

 and averaged

91 m2. From the 1970’s to 2000 changes in crosssectional area were variable, increasing at five cross

sections and decreasing at four cross sections. The

average rate of arroyo filling was greater between 1934

and 1973 (2.3 m2

/yr) than for cross sections that

continued to fill between the 1970’s and 2000 (0.6

m2/yr).

Bankfull depth increased over time as the flood

plain developed. Bankfull width continued to narrow at

six of nine cross sections between the 1970’s and 2000.

The inner channel may have stabilized through

colonization of vegetation, some of which was planted

as part of erosion-control strategies in the CCNHP.

After the 1970’s, channel depth increased at seven of

nine cross sections through bed scour or flood-plain

aggradation.

Changes in Chaco Wash since the 1930’s match

interpretations from previous investigations. The inner

channel of Chaco Wash evolved from a braided channel

in the 1930’s to a narrower, well-defined inner channel

by the 1970’s. Chaco Wash was widening in the 1930’s,

leading to sediment deposition and formation of an

inner flood plain. Bankfull width narrowed from 1934

to 2000, ranging from 13 to 55 m and averaging 30 m.

All cross sections showed narrowing of the inner

channel from 1934 to 1973, ranging from 0.4 to 45 m

and averaging 26 m. Channel narrowing continued

from the 1970’s to 2000, with six cross sections

decreasing in bankfull width. Average rates of bankfull

narrowing were greater from 1934 to 1973 (0.7 m/yr)

than from the 1970’s to 2000 (0.3 m/yr). Channel

narrowing resulted from increased sediment deposition

on the flood plain related to a decrease in peak flows;

an increase in flood-plain vegetation, some of which

was planted as part of erosion-control strategies; or an

increase in the transport of fine-grained sediment.

Bankfull depth increased in most cross sections

(seven of nine) on Chaco Wash from the 1970’s to

2000, ranging from 0.04 to 1.2 m and averaging 0.5 m.

The increase in bankfull depth may be due to formation

of a flood plain or channel scour. Changes in bankfull

area between the 1970’s and 2000 were variable, with
41

four cross sections increasing in area and five cross

sections decreasing in area.

Changes in arroyo and bankfull geometry of

width, depth, and cross-sectional area in tributary cross

sections F1 and G1 were minor compared with those in

Chaco Wash. A decrease in cross-sectional area from

the 1970’s to 2000 was noticeable at F1.

Changes in arroyo top width, arroyo depth, and

arroyo cross-sectional area near Pueblo del Arroyo are

similar to changes for all the study area. Arroyo top

width increased in two of three cross sections by 5 and

10 m, respectively. Arroyo width at 50-percent depth in

the channel increased at two of three cross sections by

9 and 3 m, respectively. Near Pueblo del Arroyo, arroyo

depths decreased between 1934 and 1973 and

increased between 1973 and 2000. From 1934 to 2000,

the arroyo depth near Pueblo del Arroyo had a net

decrease. The net change in cross sections between

1934 and 2000 around Pueblo del Arroyo was a

decrease in cross-sectional area. Cross-sectional area

decreased between 1934 and 1973 and increased in two

of three cross sections between the 1970’s and 2000.

The average rate of decrease in cross-sectional area

was greater between 1934 and 1973 (2.3 m2

/yr) than

between the 1970’s and 2000 (0.6 m2

/yr).

Precipitation has been increasing in Chaco

Canyon since records began in 1934. However, channel

erosion has not increased. Runoff is generally

correlated to rainfall, and runoff records exist only for

1976 to 1990. No discernible trend in runoff is apparent

during this short time span. If runoff increased during

this period when rainfall increased, the channel did not

return to the braided pattern of the 1930’s. The change

of Chaco Wash to a narrow, sinuous inner channel is

due to sediment deposition. Sediment deposition may

be from a number of factors, including a decrease in

peak flows, an increase of vegetation on the flood plain,

or an increase in the transport of fine-grained sediment.

A decrease in peak flows may be due to changes in

rainfall intensity, changes in infiltration characteristics

of the channel and watershed, or a response to changes

in channel geometry and hydraulic parameters (width,

depth, slope, and roughness). Increases in vegetation

may be a response to decreases in peak flows that favor

stable flood-plain sites for germination and growth or

to trees planted for erosion control. Increases in finegrained sediment may represent a change in sources.

As tributary headward erosion and streampower

decrease, more fine-grained sediment relative to sand is

transported.

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