Channel and 

Hillslope Processes 

in a Semiarid Area 

New Mexico

GEOLOGICAL SURVEY PROFESSIONAL PAPER 352-G
Channel and 

Hillslope Processes 

in a Semiarid Area 

New Mexico

By LUNA B. LEOPOLD, WILLIAM W. EMMETT, and ROBERT M. MYRICK 

EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

GEOLOGICAL SURVEY PROFESSIONAL PAPER 3S2-G

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

First printing 1966 

Second printing 1967

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 50 cents (paper cover)
CONTENTS

Abstract.-_________________________________________

Acknowledgments__ _ __------__-___________________

Alluvial fills in western valleys.______________________

Geographic setting._________________________________

Valley alluvium.___________________________________

The local bedrock___--------_-_-__________________

Relation of valley alluvium and colluvium to headwater 

areas..-.-_______________________________________

Study areas._----_-_-_--___________________________

Methods of study_______________.___________________

Magnitude and frequency of rainfall and streamflow, 

1958-64.________________________________________

Channel form and bed materials._____________________

Spacing of gravel bars_____________________._________

Movement of coarse particles_______________________

Scour and fill.____________________________________

Hillslope erosion.___________________________________

Erosion plot on Slopewash Tributary____________

Slope-retreat pins on Slopewash Tributary__.______

Other measurements of slope erosion on Slopewash 

Tributary_ _ -_--_--_--______________________

Erosion nails on Coyote C. Arroyo___-____________

Tracing of fluorescent sand_____________________

Channel enlargement on Slopewash Tributary__________

Soil creep or mass movement_________________________

Slopewash Tributary.___________________________

Coyote C. Arroyo_____________________________

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Headcut enlargement_______ __ ____- ---- 

Fence Line Headcut_______------__--------------

Coyote C. Arroyo Headcut ___ _ _- _ 

Movement of large particles in headwater rills._-__--___

Slopewash Tributary________________----_--_----

Gunshot Arroyo___________________--_----__----

Morning Walk Wash._______________-___-_-_--_-

Sedimentation in channels and reservoirs. _ ____________

Analysis of sediment budget __ ___ ___-_---_----

Climatological observations during aggradation... ______

References. _ ___-__ ___ - - --- ---

Summary of data:

A, Nonrecorded rain-gage data, Arroyo de los Frijoles, 

159-63-.---.--------------------------------

B, Recorded rain-gage data at Main Project Reach, 

1959-62___-__-______--.___________ ._

C, Erosion-pin plot in Slopewash Tributary, 1959-64.

D, Slope-retreat pins in Slopewash Tributary,

1959-64. __-----------_--_____-- - -

E, Iron-pin lines in Slopewash Tributary, 1958-64. _

F, Erosion nail lines in Coyote C. Arroyo, 1961-64. _

G, Nail sections A-J in Slopewash Tributary,

1959-64- _________-_.--__-__ ___-_-_-.

H, Mass-movement line in Slopewash Tributary, 

1959-64__.____ --

I, Mass-movement line in Coyote C. Arroyo, 1961-64.

J, Movement of coarse particles in Morning Walk

Wash, 1961-64_------------------------------

ILLUSTRATIONS

FIGURE 138. Location map______________________________________________________________________

139. Detailed area map______.___._._____________________________________________________

140. Photographs showing typical aspects of valleys and terraces-_____________-_-_--_-___-----

141. Diagrammatic cross section of alluvial valley ___ _____ __-_ _ _ -

142. Stratigraphic cross sections of minor tributaries__________ _ - - 

143. Topographic map of Arroyo de los Frijoles__________________________-___--------------_

144. Topographic map of Slopewash Tributary.____________________________________________

145. Sketch map of Coyote C. Arroyo________-________________.______-________-_--_----_--

146. Photographs of several study areas__-________._________________________-_-_-_-------

147-150. Graphs showing:

147. Magnitude and frequency of streamflows, Arroyo de los Frijoles-_______________

148. Relation of channel width and drainage area to channel length_________________

149. Bed-material grain-size analyses____________________________________________

150. Distribution of coarsest particles along length of channel ___________------___--

151. Sections showing spacing and composition of gravel bars_______________________________

152. Photographs of painted rock experiments__-______-_______________-----_--__-----------

153-156. Graphs showing:

153. Effect of spacing and particle size on ability of flows to move rocks_____----------

154. Summary of data relating discharge, size, and spacing for painted rock experiments.

155. Transport distance of rocks as function of particle weight.__________----__------

156. Transport distance of rocks as function of discharge_________-______----_-------

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m
IV CONTENTS

	Page 

FIGURE 157. Photograph of scour chain__.__________________________________________________________________ 220

158-161. Graphs showing:

158. Downstream pattern of scour and fill for different time periods._________-_-__-__--___-____ 221

159. Depth of scour as function of discharge------------------------------------------------- 222

160. Scour and fill, Main Project Reach_____-__._-_______.___._______._-_____._.____._ 223

161. Accumulative net changes in bed elevation, Arroyo de los Frijoles_-_______--______-________ 224

162. Photographs of erosion pin8-___-_________-___________--_---_-__--_--_---_-----_--_-_----------- 225

163. Sketch map showing slope-retreat pins, Slopewash Tributary.___-___-__--___--_-__-_____-__--______ 226

164. Graph showing 6-year net erosion, Slopewash Tributary.________-__-______-___-____-_-_-_-__..-_--_ 227

165. Photograph of Fence Line Headcut------------------------------------------------------------- 229

166. Photographs of headcuts and valley alluvium.___________________________________________________ 230

167. Topographic map and profile, Coyote C. Arroyo headcut._________________________________________ 231

168. Photograph of Green Rock Gulch_____-__.______-.__._._______._____-____-___-___.---____-.__ 232

169. Profile of Gunshot Arroyo showing movement of coarse particles ________________________________ 233

170. Topographic map of dam and reservoir, Coyote C. Arroyo-_-__-________-_-__---__---_-_--____----_ 235

171-174. Graphs of:

171. Precipitation parameters, 1853-1962, for station at Santa Fe, N. Mex.______-_-_--____--__- 241

172. Individual summer rains._____________________________________________________________ 241

173. Individual nonsummer rainS-________________-__------_---------__-------_----__------- 242

174. Average annual intensity of rainfall-.-------.------------------------------------------ 243

TABLES

	Page 

TABLE 1. Characteristics of locations studied._______________________________-___-_-------_----------------------- 201

2. Summary of flows at three locations along Arroyo de los Frijoles, 1958-63.___,___-__________--____i._-------- 203

3. Relation of transport distance to flow discharge___________________________--___-_--_--_-_---------------- 218

4. Mean depth of scour as a function of discharge_____.____-_______________-__---_---------_-------------- 220

5. Summary of particle movement, Morning Walk Wash, 1961-62_______-__---_------------------------------ 234

6. Observed sedimentation in reservoir behind dam on Coyote C. Arroyo, 1961-64_______________-_-_--_-------- 232

7. Observed rates of channel changes in Coyote C. Arroyo, 1961-64_____-______-____-__-___------------------- 236

8. Data on measured rates of erosion and deposition__________________________________--__--_-_----_-------- 237

9. Average rates of erosion and deposition.______________._______________________-__--___------------------ 238
EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

CHANNEL AND HILLSLOPE PROCESSES IN A SEMIARID AREA, NEW MEXICO 

By LUNA B. LEOPOLD, WILLIAM W. EMMETT, and EGBERT M. MTRICK

ABSTRACT

Ephemeral washes having drainage areas from a few acres 

to 5 square miles are shown by actual measurement to be accumulating sediment on the streambed. This aggradation is not 

apparent to the eye but is clearly shown in 7 years of annual 

remeasurement.

A similar aggradation was in progress in the same area some 

3000 years ago as evidenced by an alluvial terrace later dissected by the present channel system. At that time as well as 

at present, aggradation occurred even in tributary areas draining a few acres. Colluvial accumulations merge with channel 

deposits and blanket the valleys and tributary basins even up 

to a few hundred feet of the drainage divides.

The present study concerned the amounts of sediment produced by different erosion processes in various physiographic 

positions in the drainage basins. Measurements show that by 

far the largest sediment source is sheet erosion operating on 

the small percentage of basin area near the basin divides.

Mass movement, gully head extension, and channel enlargement are presently small contributors of sediment compared 

with sheet erosion on unrilled slopes. As in previous studies, 

not all of the erosion products could be accounted for by accumulations on colluvial slopes and on beds of channels. The 

discrepancies are attributed primarily to sediment carried completely out of the basins studied and presumably deposited 

somewhere downstream.

Aggradation of alluvial valleys of 5 square miles area and 

smaller both in the present epicycle, and in prehistorical but 

post-glacial times in this locality, cannot be attributed to gullying or rill extension in the headwater tributaries but to sheet 

erosion of the most upstream margins of the basins.

Studies of rainfall characteristics of the 7 years of measurement compared with previous years in the 100-year record do 

not provide a clear-out difference which would account for the 

presently observed aggradation of channels. Longer period of 

measurement of erosion and sedimentation will be necessary 

to identify what precipitation parameters govern whether the 

channels aggrade or degrade.

ACKNOWLEDGMENTS

This study was conceived and initiated by Dr. John 

P. Miller and the senior author in the summer of 1958, 

and fieldwork was continued during each succesive summer for periods of 1-3 weeks. Immediately following 

the field season of 1961 Dr. Miller died from bubonic 

plague contracted during that fieldwork. We resolved 

to prosecute the work thereafter with especial diligence.

An important part of the observations made during 

the first 5 years consisted of the data on the movement 

of the hundreds of individual cobbles which had been 

painted for identification. Emphasis was gradually 

shifted to the observations on rates of erosion and sediment movement which had been begun as only an auxiliary part of the original investigation. It is with 

these observations that the present paper is primarily 

concerned.

For permission to work on the property known as 

Las Dos and for many other courtesies we are grateful 

to the late Mrs. Adelina Otero-Warren. Dr. Bergere 

Kenney has kindly encouraged the work to continue 

on that property.

The slope-area measurements of discharge and many 

other observations when we were not in the area were 

made under the direction of Wilbur L. Heckler, district 

engineer for the U.S. Geological Survey in Santa Fe. 

Louis J. Eeiland, Leo G. Stearns, Charlie E. Sieber, 

Leon A. Wiard, and others of the Santa Fe office contributed materially to these observations.

Field assistants and technical associates during various seasons included Brandis Marsh, Peter Sparks, 

Macklin Smith, Olav Slaymaker, Thomas Detwyler, 

Garnett Williams, and Lehn Franke.

The C14 analysis of the charcoal sample was run by 

Dr. Meyer Eubin in the laboratory of the Geological 

Survey in Washington, D.C.

For their review, comments, and suggestions, we are 

indebted to Stafford C. Happ, Asher P. Schick, George 

H. Dury, S. A. Schumm, E. F. Hadley, M. E. Collings, 

W. L. Heckler, and L. J. Eeiland.

ALLUVIAL FILLS IN WESTERN VALLEYS

To cross any valley in the foothills of a large part of 

the western conterminous United States is to traverse a 

flat floor of stream-deposited alluvium. Many such 

floors, once smooth and undissected, are now trenched 

by arroyos or troughlike gullies. Abandoned flood 

plains or alluvial terraces can be seen in many such valleys, representing the surfaces of previous valley fills.

193
194 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

A large literature describes the local sequences of alluviation and erosion in such valleys, and there appears 

to be considerable contemporaneity in the timing of 

these alterations in post-Pleistocene time over an area 

that stretches from Wyoming to Texas. When grazing 

by cattle reached peak intensity about 1880, the most 

recent epicycle of valley trenching began in what is 

now believed to be a coincidence of climatic conditions 

conducive to erosion and degradation of the vegetative 

cover by overuse.

The alluvium which now fills these valleys and which 

is being trenched is usually similar in texture to that 

representing the fills of previous epicycles, though in 

some places the recent fill material is somewhat coarser. 

This alluvium is predominantly silt, often fine sandy 

silt, sometimes silty fine sand. The amount of clay is 

generally not great. The fills may be only a few feet 

deep in ephemeral tributaries draining several acres, 

and can be at least 50-feet thick through long distances. 

The latter figure applies to the alluvial valley, 150 miles 

in length, of the Kio Puerco, a tributary to the Rio 

Grande.

Three periods of late Pleistocene and recent alluviation are recognized in many places in Western States. 

The most recent fills now being eroded are less deep 

than those of previous periods of aggradation represented by the terraces which stand above the present 

valley floors, so even larger amounts of alluvium were 

stored in valleys in the past than are now observed.

Thus an immense amount of silty and fine-sandy alluvium has been produced by ephemeral drainage basins 

in the five states Arizona, New Mexico, Utah, Colorado, and Wyoming and has been deposited in valleys. 

When a period of valley trenching occurred, much was 

eroded out, carried downstream, and the process repeated.

It is logical to suppose that the source of sediment 

which would contribute to such aggradation during the 

periods of alluviation would be rill and gully erosion 

in the headwater tributaries. Deposits in the valley 

must have been derived from the basin upstream. But 

alluviation, when it occurred in the main valleys or 

master streams, also affected minor tributaries as well. 

The ground surface seems to sweep from valley floor 

up to the adjacent hills and up tributary valleys in concave-to-the-sky profiles. The topography of the adjacent hills seems to have been drowned in a sea of alluvium, softening and smoothing the surface configuration of the whole landscape. This phenomenon occurs 

widely and is the general rule in Nebraska, Kansas, Missouri, and the driftless area as well as in New Mexico, 

Wyoming and other parts of the Rocky Mountain area.

So widespread has been the phenomenon of valley 

aggradation with silty alluvium and so large are the 

volumes of sediment involved that the geomorphologist 

may wish to see examples of present-day streams currently undergoing such alluviation, and to discern the 

areal sources of the material being deposited. But, interestingly, it is difficult to designate channels undergoing such a process at least any that are identifiable 

by visual or qualitative criteria. The processes which 

were so important even in the historic past cannot easily 

be observed at present.

Furthermore, if Leopold and Miller (1954) were correct in their assertion that the source of the valley 

alluvim was not in channel and gully erosion of the 

headwaters, then the processes of such sediment production must have been mass wasting and sheet erosion. 

The first of these is a process little studied and the second is a process studied far more on agricultural than 

on grazing or uncultivated areas. Little is known 

about rates of such processes on nonagricultural land, 

nor have the effects of relief, land slope, vegetation density, or other relevant factors been observed.

The present investigation was initiated to study both 

process and rate of aggradation and degradation in the 

channels, rills, and on the hillslopes of a drainage basin 

typical of many parts of the semiarid West, This 

paper is a progress report on that study.

Investigations of the kind described here involve the 

operation of field stations and specific experiments over 

a period of several years. Results can be obtained only 

at infrequent intervals because of the sporadic character of the precipitation. The general method, then, 

was to establish observation stations which could be 

visited for resurvey during a period of a few weeks in 

summer each year, and to maintain a more restricted 

number of observations after each important storm. 

The area chosen, Arroyo de los Frijoles near Santa Fe, 

N. Mex., was one in which previous work had been done 

by Leopold and Miller (1956), and for this reason it 

provided a familiar geographic and geologic background on which to base further investigations.

Our objective was to integrate several aspects of 

fluvial processes operating in the area: specifically, to 

study sheet, erosion on the divide and interstream areas, 

slope retreat adjacent to steep-walled gullies that prevail in the uplands, and in particular, the movement of 

coarse and fine sediment down the arroyos of various 

dimensions. To this end, various kinds of measuring 

devices were gradually developed and installed. The 

results reported here represent information collected 

during 7 years of observation, but some measurements 

have been made for only a part of the 7-year period.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 195

GEOGRAPHIC SETTING

Arroyo de los Frijoles and the other ephemeral channels discussed here are a few miles west-northwest of 

Santa Fe, N. Mex. (figs. 138 and 139). They are typical of many small arroyos or dry channels in the lowlands of the Bio Grande Depression at the base of the 

Sangre de Cristo Range. As one approaches Santa Fe 

from the west, the Sangre de Cristo Mountains appear 

to be abutted by a broad sloping surface underlain by 

poorly consolidated sand and gravel. There are actually several surfaces differing but slightly in elevation. 

However, the local relief is considerable, with rolling 

hills dissected by gullies, rills, and broad sandy-floored 

washes. As is typical of arid regions everywhere, these 

channels present almost endless variety. They range 

from tiny rills near the drainage divide to deep, wide 

arroyos incised in flat alluvial valleys. Vegetation is 

sparse, both adjacent to the channels and on the interfluves between them. In general the area is a woodland association, including juniper, piiion, sage, and a 

low-density understory of grasses.

Because of its geological character and climate, the 

area studied is characterized by huge amounts of both 

fine and coarse sediment readily available for transportation. During runoff sediment may be derived from 

the unconsolidated country rock or from recent alluvium 

adjacent to the channels.

An arroyo discharges water only when a moderately 

heavy rain falls on the drainage basin. This is a summer phenomenon because heavy rains fall only from 

thunderstorms. No flow occurs during the winter. 

Ordinarily during a summer there are about three rainstorms of sufficient magnitude to produce runoff. However, only exceptional rains affect an entire drainage

FIGURE 138. Area in New Mexico where detailed studies 

were made.

basin the size of the Arroyo de los Frijoles at Sand Plug 

Reach (drainage area 3.75 sq mi).

VALLEY ALLUVIUM

Many widely separated areas in southwestern United 

States have undergone three periods of alluviation followed by erosion, and there is evidence of approximate 

simultaneity of the respective events from one area to 

another. That some or all of these events should have 

occurred in the study area would be a logical supposition.

Arroyo de los Frijoles through most of its length is 

incised into an alluvial fill of silty sand which at present 

has a surface configuration characterized by two terraces, and paired remnants of each are common along 

the principal drainage ways. The higher terrace stands 

about 5 feet above the channel bed in upper tributaries 

and tends to remain about the same height downstream 

along the 7-mile reach which we have studied in detail. 

The terrace tread is uniform and flat, and vegetated, as 

are the hills, with pinon and juniper and an understory 

of grass. Along much of the stream length the terrace 

is bounded by a vertical wall, at least on one side of the 

channel, but elsewhere it slopes down to the lower terrace in a subdued S-shaped profile which may have a 

maximum slope of 1: 5. Such a rounded scrap is generally vegetated with bunch grasses of low density. The 

terrace tread grades in a smooth curve to the adjacent 

hills, and its whole width seldom is more than 300 feet.

The low terrace averages about 1-2 feet above the 

present streambed and is seldom bounded by vertical 

banks. Its surface tends also to be somewhat irregular 

and can usually be recognized by the occurrence of rabbit brush, locally called chamiso [Chrysotliamnus nauseosus (Pall.) Britt.], which occurs neither on the higher terrace nor on the presently active point bars.

Typical aspects of the valleys and the terraces are 

shown in figure 140.

The stratigraphic relation of the alluvium of the high 

terrace to the bedrock underlying the adjacent hills is 

commonly seen in the vertical banks. The valley fill was 

laid in a shallow U-shaped trough cut into the friable 

and poorly consolidated bedrock, and the bed of the 

present channel lies very near the bottom of this trough 

in the smaller valleys and probably close to it even in the 

main stream. That is to say, the present stream has cut 

nearly through the valley alluvium and most of the 

depth of alluvium can be seen in the cut banks or vertical 

walls.

The relation of the alluvium underlying the tread of 

the lower terrace to that of the upper terrace is difficult 

to decipher. So nearly the same is the alluvium under 

the two terrace treads that even when a vertical bank
196 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

cuts through both, no stratigraphic contact is obvious, 

though an inset relation is suggested by the contacts 

seen. The same difficulty is often observed in alluvial 

fills of western valleys. We have concluded after inspection of many sections, that the lower terrace represents the top of an inset fill and that Arroyo de los Frijoles is an example of a two-fill, two-terrace alluvial 

valley (see Leopold and Miller, 1954, p. 5, for a discussion of the classification of terraces and fills). A diagrammatic cross section is presented of this valley in 

figure 141. We here apply the name Coyote terrace deposits to the alluvial deposit under the higher terrace 

so prominent along streams in the vicinity which will 

be referred to as the Coyote terrace.

The type locality for the Coyote terrace deposits will 

be along the Arroyo de los Frijoles at what we will

106°O2'30" 106° 00' 105°57'30"

35°45' -

T. 18 N. 

T.17N.

35°42'30" -

R.8E. R.9E.

2000 0 2000 4000 6000 8000 FEET 

I__i I 1_____I_____I_____I

FIGURE 139. Drainage basins of Arroyo de Los Frijoles, Coyote C. Arroyo, and Morning Walk Wash. Named reaches are locations where 

detailed studies were made. Also included are principal stream channels and roadways within the area.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 197

"««*». j£*n»7**<! ' *£-!

describe here as our main-project reach, in the 

SEi/4 sec. 17, T. 17N., R. 9E., 4.2 miles from Santa Fe. 

The name is derived from Coyote C. Arroyo at Las 

Dos (see p. 205), where a sample of charcoal buried in 

this deposit gave a date of 2800 ±250 years B.P. (TJSGS 

sample W1328).

Coyote terrace deposit is alluvium consisting of redbrown, slightly indurated silty sand or fine sand, sometimes fine sandy silt, with occasional discontinuous lenses

B

FIGURE 140. Typical aspects of the valleys and the terraces. A, Drainage basin of Coyote C. Arroyo; the man Is standing on a flat surface 

of alluvium or colluvium. B, Two terrace levels along Arroyo de los 

Frijoles; the lower terrace, about 18 Inches above the channel bed, 

Is In the foreground; at the tree near the channel edge, the upper 

terrace stands 5 feet above the present bed and grades smoothly to 

adjacent hills. C, Arroyo de los Frijoles; the channel is cutting 

into the upper terrace material that here stands 8 feet above the 

present bed elevation ; the view is on the left bank just downstream 

from Fence Line Headcut; bedrock crops out in the channel bed at 

this place, dipping downstream.

of fine gravel. When dry, the cut banks stand vertica ly 

and are hard to dig with a shovel. The alluvium is 

5-10 feet thick and rests on bedrock, which here is nilconsolidated sand and gravel. The top several inches 

may contain more fine sand or silt than at greater 

depths. No soil zonation is apparent though the upper 

6 inches are slightly darker from the admixture of 

humus and incipient soil development.

The Coyote terrace forms a curving surface as it rises 

away from the valley floor and joins the hillslopes underlain by the Santa Fe Group. The alluvium interfingers with colluvium at the valley sides and extends 

upstream in minor tributary valleys, where the distinction between valley alluvium and colluvium at the base 

of the slope often cannot be made.

In the Tesuque Valley just 4 miles to the north, similar alluvial terraces have been studied by Miller and 

Wendorf (1958) at a location shown on figure 139. 

There, two terraces occur at 18-20 feet and 8-10 feet 

above the present channel ; the alluvium underlying the 

higher one contains dateable artifacts and charcoal. A 

C14 date of charcoal lying 130 inches below the surface 

of the upper terrace was 2230± 250 years. Between the
198 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FEET

10 -

o-1

Sand and gravel of 

present streambed

FEET

-5

Bedrock, Santa Fe Grou

25 50 FEET

FIGURE 141. Diagrammatic cross section, Coyote terrace deposits.

Tesuque area and Arroyo de los Frijoles, the agreement 

of dates, the similarity in form, the comparable character of the alluvial materials, and the geographic proximity of the areas suggest that the respective periods 

of deposition and erosion in the valleys of the whole 

area are correlative and may be considered Coyote terrace deposits.

Though the terrace heights and the depth of alluvium 

of the Coyote terrace deposits differ somewhat from 

valley to valley as indicated by the comparison between 

Arroyo de los Frijoles and Tesuque Creek, such a valley 

fill is ubiquitous in all the ephemeral valleys in the area. 

It typifies all the drainages rising in the foothills which 

lie west of the Sangre de Cristo Range and east of the 

escarpment of La Bajada, a distance of 11 miles or more 

in most places, and extending north-south at least from 

Cuyamungue, 12 miles north of Santa Fe, to San Cristobal, 25 miles south of the city. This area of more 

than 100 square miles has been seen, at least in reconnaissance, during this study, and our impression is that 

similar relations would be observed over a much larger 

area in central New Mexico. The Coyote terrace deposits correspond to Deposition 2 in the regional alluvial chronology of Kirk Bryan. (See Leopold and Miller, 1954, p. 58.)

THE LOCAL BEDROCK

The hills being drained by the network of ephemeral 

channels are composed of the upper beds of Santa Fe 

Group. The whole group is at least several thousands 

of feet thick, but that part with which we are concerned 

includes the upper zones only, principally the Tesuque 

and Ancha Formations (Miller, and others, 1963, especially p. 50-51 and pi. 1). The geologic map by these 

authors includes similar landscape 3 miles north of our 

study area which they mapped as Tesuque Formation 

described as follows (p. 50) :

The Tesuque Formation of the Santa Fe Group, as defined 

here, consists of poorly consolidated, water-laid silt, sand, and 

gravel, mostly tan in color. . . . Abrupt changes in texture, both

vertically and horizontally, are the rule. Bedding is locally distinct, but few beds can be traced more than a mile or two. Some 

of the sandstone beds are fairly well sorted and locally crossbedded. Their coherence is due to cementation by calcium carbonate. At most places, even in unconsolidated materials, the 

sediments are highly calcareous.

The Tesuque Formation was derived from Paleozoic and Precambrian rocks of the mountains. The presence of a considerable quantity of quartzite pebbles, for example near Tesuque, 

indicates drainage southward from Rio Santa Cruz or Rio de 

Truchas, which requires a radical difference from the present 

drainage pattern.

Miller, Montgomery, and Sutherland (1963) consider 

the Tesuque Formation to be Tertiary. They identify a 

Pleistocene or upper Pliocene Ancha Formation consisting of remnants of a once-continuous sheet of unconsolidated gravel which extended originally from the western part of the Sangre de Cristo range to the Rio 

Grande. The gravels were considered to be laid down 

as fan deposits derived from glacial action and carried 

out to cover the older Tesuque beds as glacial outwash 

deposits.

Those workers did not map as Ancha Formation any 

of the deposits in the area just to the north; the bedrock 

materials with which we deal are probably entirely 

Tesuque Formation. Because, as Miller, Montgomery, 

and Sutherland stated (1963, p. 51), 100-300 feet of dissection has occurred since deposition of the fan gravel 

comprising the Ancha Formation, the concentration of 

gravel on many hilltops which we observe in our study 

area may represent a lag concentrate of gravel derived 

from Ancha beds which now have been removed.

Other than the gravel concentrate on hilltops, the decription given by Miller and his associates fits the bedrock materials. Those authors, as well as we, observed 

many places where the upper surface of the Santa Fe 

beds is weathered. A zone of caliche, 2-3 feet thick locally, permeates the sandy, or elsewhere the gravelly, 

bedrock materials. This caliche where it crops out does 

not affect the alluvium or colluvium and indicates processes of soil formation and weathering related to events 

prior to the deposition of the Coyote alluvium.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 199

RELATION OF VALLEY ALLUVIUM AND COLLUVIUM TO 

HEADWATER AREAS

The surface of the Coyote terrace can be followed as 

remnants along the main valley of Arroyo de los Frijoles 

and other washes upstream to where the present channel 

is only a few feet wide. Similarly, the surface can be 

followed up lateral tributaries where it grades to the 

adjacent hills. Colluvium deposited by rills and unconcentrated wash merges and interfingers with alluvial 

deposits of the main valleys and tributaries. Excavation by shovel in the bed of any small, even any steep, 

tributary reveals alluvial-colluvial material within a few 

hundred feet of the watershed divide. The same relation of alluvium to headwater slopes was found in eastern Wyoming by Leopold and Miller (1954) who summarized their findings in these words (p. 83) :

The terraces of master streams can be traced directly into 

many tributaries of moderate size, indicating that erosion of 

alluvium in the master streams was accompanied by gully erosion in tributaries, even the ephemeral ones.

* * * likewise, aggradation in the main stream valleys was 

accompanied by deposition in tributary valleys and draws. 

Probably these deposits were derived by mass movement and 

sheet erosion on upland slopes.

It seems logical that the shift in relations between runoff 

and vegetation which caused erosion of all major streams would 

also affect the smallest tributary valleys in a'similar way at 

the same time. ... As the deposit in the main valley gradually increased . . ., the wash slopes that were graded to the 

main river accumulated material which blanketed all except the 

most prominent hills and uplands. The area of upland from 

which alluvial materials were being derived by erosion shrank, 

while the area of deposition increased.

The percentage of area of a small basin blanketed 

with alluvium-colluvium is exemplified in Coyote C. 

Arroyo. (See fig. 139 for location.) This typical 

drainage basin has an area of 0.064 sq mi (40.8 acres) 

of which 0.022 sq mi (14.4 acres) is covered by alluvium-colluvium, the remainder being hillslope and hilltop area of Tesuque Formation. In this example, then, 

34 percent of the surface area was alluviated, and the 

average distance from the head of deposition in small 

swales to the watershed divide was 190 feet. The alluviation extends headward astonishingly close to the 

drainage divides. The proximity of the colluvialalluvial deposits to drainage divide can be seen in figure 140-4.

The relation of the small tributary draws to the headwater slopes may be typified by the two examples in 

figure 142. Profiles of the surface of the alluviumcolluvium merge smoothly into the unrilled hillslope 

underlain by bedrock. Cross profiles drawn nearly 

parallel to the contours of the side hills demonstrate, 

in conjunction with the stratigraphic evidence seen in 

the channel walls and in pits dug in the plane of the

profile, that alluvial and colluvial material fill a former 

channel system cut into the bedrock and that subsequently the present channels have reevacuated parts of 

the earlier system. The present channel network incised into the alluvium makes a present topography 

similar to that existing before the Coyote terrace 

deposition.

This conclusion is supported by observations of the 

extent of gravel which more or less covers many of the 

rounded hilltops of the area. In the Slopewash Tributary example in figure 142, section B-B' crosses from 

west to east a gravel-covered hilltop, a gravel-free area, 

and again a gravel-covered hilltop. At the base of the 

channel on the right bank the bedrock is permeated 

with a white cement, presumably CaCO3 .

Exposures elsewhere also indicate that hilltops covered with lag gravel are usually underlain by bedrock. 

Thus the deep layers of silt exposed in present channel 

walls were deposited in channels which dissected the 

bedrock. The alluvium lapped up against the gravelcovered slopes and in places covered the gravel.

Investigations of the relation of the alluvium to the 

bedrock topography showed that the underlying 

Tesuque Formation generally appears no more weathered at the contact than elsewhere. In some places, 

however, alluvium was deposited over a surface heavily 

cemented with caliche. The caliche appears as a hard 

cement where the Tesuque was gravel, and where the 

Tesuque was silty, as a whitish calcification of a zone 

extending 3-4 feet below the contact, and especially concentrated on fracture planes. Hard nodules of caliche 

in the silt are seldom seem, but amorphous soft masses 

without sharp boundaries are common.

These facts support the conclusion reached by Miller, 

Montgomery, and Sutherland (1963), that a long period 

of weathering under subhumid conditions was followed 

by a semiarid climate during which caliche permeated 

an undulating topographic surface. Our observations 

add the additional postulation that, subsequently, this 

topography was first alluviated and later erosion developed a drainage network similar to and about the 

same depth as the present one; the erosion removed part 

but not all of the materials which had undergone 

calichefication.

To summarize, alluviation during Coyote terrace time 

aggraded not only the main valleys but small tributary 

draws as well. Post-Coyote terrace erosion reexcavated 

much of the earlier topography. The problem posed by 

this sequence of events is the following:

If alluviation took place in all the headwater draws 

at the time the main valleys were being aggraded, where 

did all the debris come from, and by what processes?
fcOo 

o

ELEVATION, IN FEET, ARBITRARY DATUM

^ 8 £ to oo £ O O O O

ELEVATION, IN FEET, ARBITRARY DATUM

§ (O O >- PO CO 00000

ELEVATION, IN FEET

gs ^

8

8

8

North Frijoles Arroyo

C/)

05
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 201

Clearly, the sediment was derived from the hills above 

the areas of alluviation but not from rills or gullies on 

these hills, as evidenced by the absence of gullies or rills 

of any depth or importance outside of those which were 

being alluviated. Thus the sediment must have been 

derived from processes other than rill and gully erosion, 

specifically, sheet erosion or mass movement. This 

hypothesis attributes to the latter processes greater efficacy than we at least would have supposed. We were 

led, then, to devise methods of measurement which 

would allow the construction of a sediment budget, however approximate, to ascertain whether relative importance of present processes wTould shed light on these 

events of the past.

Another problem is highlighted by the postulates 

stated. It is usual to suppose that alluviation of a 

master stream would provide a rising base level for the 

tributaries which enter into it. Then the aggradation 

in the tributary would similarly provide a rising base 

level for its own subtributaries. Though this scheme is 

a simple one and would lead to field relations here observed, it also implies that the alluviation of the headwater tributaries would lag in time that of the main 

stem. But these inferences do not agree with field observations in the Arroyo Frijoles area.

It seems much more likely that in our study area the 

relation of runoff to vegetation which would lead a main 

stream to aggrade would similarly have the same result 

on the tributaries. We believe that control by base level 

is a relatively minor factor in alluviation of the valleys 

studied.

The remainder of this paper is organized around the 

measurement program instituted to investigate these 

questions. The sample areas studied will be described, 

the measurement methods outlined, and the results summarized. These measurements will then be discussed in 

terms of the problems outlined (see p. 236). We begin 

with a discussion of the study areas.

STUDY AREAS

The areas of special study shown in figure 139 include Arroyo de los Frijoles through its uppermost 7 

miles and some smaller basins of several acres in an area 

4 miles distant, near Las Dos. The principal basin, 

Arroyo de los Frijoles, has a channel width which 

ranges from the smallest recognizable rills a few inches 

wide to an arroyo 100-200 feet wide. All channels more 

than a foot wide have a flat predominantly sandy surface dotted in places with scattered gravel.

Larger scale maps, figures 143-45, show details of the 

areas of intensive study and will be referred to in later 

discussions.

Figure 146 illustrates the character of the country 

and the aspect presented by main and tributary channels. Figure 146, A and Z?, shows a small tributary 

within a few hundred feet of the headwater divide, a 

subbasin we called Slopewash Tributary.

At a point 1.1 miles from the furthest divide the 

North Frijoles Reach is typical, figure 146. One mile 

farther downstream the channel is larger, as shown at 

Locust Tree Reach (fig. 146Z>). Main Project Reach, 

4.9 miles from the headwater divide and at a place 

where the drainage area is 2.87 sq mi, is illustrated in 

figures 146# and F.

Some characteristics of each of the study areas are 

indicated in table 1.

TABLE 1. Characteristics of locations studied

Location

Arroyo de los Frijoles:

North Frijoles Arroyo:

Sand Plug Reach:

At Rockv Nose section

Morning Walk Wash:

Drainage area 

(sqmi)

0.05 

.5C

.70

1.36

1.49

1.61

2.87

3.75

.12 

.064

Elevation 

(ft above msl)

At 

headwater

7,280 

7,388

6,798 

6,800 

6,735

6,633 

6,615

At downstream 

point

7,200

7,159 

7,111 

7,048 

7,037 

6,987 

6,790

6,696 

6,672 

6,723 

6,620 

6,550

6,540 

6,540

Relief 

(ft)

80

229 

277 

340 

351 

401 

598

692 

716 

75 

180 

185

93

75

Length 

(ft)

1,200

5,800 

8,200 

11, 750 

12, 400 

15. 400 

28, 000

33, 600 

34,800 

1,150 

5,000 

3,600

700 

870

METHODS OF STUDY

Observations of nearly all the types described here 

began in the period 1958-61 and are continuing as this 

paper is written. Water stages of flow are measured by 

recorders at gaging stations installed on North Frijoles 

Arroyo and at Main Project. The duration of individual flows is generally two hours or less and current-meter 

measurements for the construction of stage-discharge 

rating curves are impracticable without a full-time resident hydrographer. Stage-time hydrographs are obtained from the stage recorders, but maximum discharge 

for each flow is computed using a survey profile of 

high-water marks. This, combined with cross-sectional 

areas of flow determined by scour chains (described below), permits the computation of discharge using an 

estimated value of flow resistance,

A network of 12 nonrecording rain gages is observed 

after each significant summer rain.

Depths of scour and fill in channels are measured by 

chains set vertically in a dug hole in the streambed. At 

maximum depth of scour the chain is bent over by the 

flow and is usually covered by fill on the receding stage 

(Emmett and Leopold, 1964).
202 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

EXPLANATION

6

Rain-gage location and number

1000

I I

1000I

3000

I

4OOO

I

60OO

I

CONTOUR INTERVAL 20 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 143. Arroyo de los Frijoles.

Erosion pins, consisting of a 10-inch nail put through 

a washer, driven flush with the ground surface, are used 

to record increments of surface erosion. Some of these 

pins are arranged in a grid over certain plots, but generally the nails are in a line as a transect from hilltop to 

base or across a channel as a cross-section.

Mass-movement pins are set on a line between immovable bench marks, and are surveyed for alignment by 

transit.

Many rocks have been painted for identification and 

observed for movement after each flow.

The individual plants on some 3 X 3-ft quadrats have 

been mapped and are to be remapped periodically to 

observe changes with time.

Although the methods are simple, the labor after each 

storm (about 3 per summer) and during the annual 

resurvey of all observation points is rather great.

MAGNITUDE AND FREQUENCY OF RAINFALL AND 

STREAMFLOW, 1958-64

Kainfall has been measured since 1959 at 12 locations 

within the drainage basin, as shown in figure 143. Summary of data A (p. 247) contains a partial summary of 

the data collected from these sites.

The gages were not read after each shower, but efforts 

were made to read them at least after every flow-producing storm. The sporadic nature of storms is indicated 

by the unequal distribution of rainfall among stations.

At the Main Project Keach a recording rain gage has 

been installed at the location of the water-stage recorder. Precipitation data (summary of data B) collected here allow a better indication of the rainfall characteristics. The record is too incomplete to show the 

mean annual precipitation which at that location must 

be about 12 inches per year.

The 1,300 cfs (cubic feet per second) flow of July 25, 

1962, the second highest flow recorded at the Main 

Project Keach, was caused by a storm which registered 

1.5 inches in 25 minutes at the Main Project gage.

Channel discharge is measured or estimated at three 

places in Arroyo de los Frijoles: Main Project, Locust 

Tree, and North Frijoles. Gaging stations are installed 

at the Main Proj ect and at North Frij oles reaches. During the period 1958-63, runoff occurred at the three
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 203

measuring stations on the dates indicated in table 2, in 

which are presented values of peak discharge. Spaces 

in the table usually refer to no flow; however, in a few 

instances some flow may have occurred but was of negligible magnitude. Flow data discussed in this report 

are all peak values.

TABLE 2. Summary of peak discharges, in cubic -feet per second, 

at three locations along Arroyo de los Frijoles, 1958-63

[(a) and (b) refer to separate flows or different peak flows occurring on the same day )

Date

1968

September 13 __ _. - .. . . .......

1959 

May 23.- _ . _ ... ____ .... _ ...

June 15 ___ _ _ _ __ ____ .

July 23. __ - . ____ ... _ ........

October 29 - ..... __ __ . _____ .

I960 

July 14... .-_ _ .

(b) .-.-.................-. .

(b) .-.... . .

October 17- _____ . _ _ . ______ 

1961 

June 26 __ __ ____ ._ .

July 8. . _ 

196$

July 5-.-- - - _ ... ... ... ... .

July 6---. ...... ... ... ..... ....... ... 

July 18--- ... . ... ... .... .... __ 

July 22..- .... ..... . ... ....... -- _. 

July 25.-. .. .

July 30-. .... ...... .....

1963 

July 20-. ... ..... - ..... __ ... ...

North 

Frijoles

15-20

194

140

50

.5

67

1

3-5

5-7

9-10

58

85 3-5

10

230

.3 6-8

.3

.5

85

90

1

10

5

Locust 

Tree

1,320

50-75

20-25

15

360

498

30(MOO 3-5

650

30

150

450

450

5

391

Main 

Project

20

10-15

3,060

3-5

2-4

10-15

20-25

1

35

152

10-20

10-15

10-15

10-15

1

98

80-90

.3

40

60

250

40

10

3

1300

300

15

316

Most storms are intense and so local that only a part 

of the drainage basin is affected by each. Only twice 

(September 13, 1958, and July 25, 1962) was there increasing discharge in the downstream direction due to 

heavy rainfall over the entire basin, and these two storms 

caused the greatest flows during the period of record.

For each of the three measurement locations, the peak 

flows experienced were arranged according to rank and 

recurrence intervals were computed. These are plotted 

against their corresponding discharge and are shown as 

dashed lines in figure 147. Recurrence intervals are 

determined by the U.S. Geological Survey method,

n+l 

T , where T=recurrence interval in years, n=

number of years of record, and m=magnitude or rank 

of flood, the highest being number one.

Excepting the two storms just mentioned, the spotty 

distribution of precipitation implies that data collected 

at each of the three reaches may be considered as independent flows. If this were in fact true, a type of 

station-year analysis might be attempted by combining 

5-years of record for each of three locations into a synthetic 15-year record. The solid line on figure 147 gives 

this average frequency of the three reaches. The solid 

circles on this graph represent all flows at the three stations, arranged in order of magnitude.

For small flows all moderate-size drainage areas are 

capable of receiving sufficient rainfall to produce a similarity in flow frequency. For drainage areas larger 

than some given size, further increases in area would 

not increase the size of flood of a given frequency. 

This feature is indicated by the fact that a flow of 2- 

year recurrence interval is about the same at Locust 

Tree and Main Project Reaches despite the fact that 

the drainage area of the latter is about twice that of 

the former.

The present data exceed by fivefold the values presented by Leopold and Miller (1956, fig. 21, p. 24) . The 

latter values should not be considered applicable to the 

foothill area of ephemeral streams though they were 

so considered in that report. It is now obvious that 

flow frequencies of the gaged streams emanating from 

the high mountains are not comparable with and are 

smaller than values for ephemeral washes in the foothills, despite the lower mean annual precipitation of 

the latter areas.

The problem of flow frequency is of paramount importance to evaluation of erosion and sediment transport processes. Though the method of determining 

frequency is still open to further study in ephemeral 

basins, figure 147 expresses the occurrence, of events in 

the studied basin during the period of observation.

CHANNEL FORM AND BED MATERIALS

A salient aspect of the change in channel characteristics downstream is the increase in width, shown in 

figure 148. As defined here, channel width refers only 

to the active channel which is swept free of vegetation 

except for annual plants. In some places the actual 

width between the steep banks is greater than indicated 

on figure 148. Such reaches usually include remnants 

of the lower terrace, which not only supports some vegetation but also stands 1-2 feet above the presently 

active bed.

The variability of channel width quite evident in figure 148 seems large, but one does not realize how large 

the variance is in the usual channel until he begins to 

make quantitative measurements. On a perennial eastern stream not much larger in drainage area than Arroyo de los Frijoles, the ratio of the standard deviation 

to mean channel width averages about 0.25 (data from 

Wolman, 1955, fig. 37), whereas lor a reach of Arroyo
204 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

Erosion-pin plot Nail section G

U\l

Nail section F 

P /Green Rock Guich

Nail section C

Nail section A 

Chain 2 and pins

721° 

Chain 3 and pinsr / J

50 100 150 200 FEET

CONTOUR INTERVAL 5 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 144. Slopewash Tributary

de los Frijoles below the junction of North and South 

Frijoles it is about 0.39. Also, the variability of width 

is not so great above that junction where the drainage 

area is less than 1 sq mi. In an ephemeral basin, it appears that when the drainage area exceeds the size of 

the usual summer thunderstorm, only parts of the basin

contribute runoff. Thus different reaches of channel 

experience different sequences of flows, and this probably tends to increase the variance of channel width.

The increase in drainage area with channel length is 

shown in the top part of figure 148. At three places, 

sudden increases in drainage area occur where relatively large tributaries enter the main channel. However, as mentioned above, it appears that these increases 

in drainage area affect channel width only incidentally, 

as the size of a given storm may or may not extend 

over the whole contributing area.

The bed of Arroyo de los Frijoles is predominantly 

sandy with scattered fine gravel and cobbles, but there 

are local concentrations of rocks. Considering first the 

nongravelly areas which predominate, sieve analyses 

are shown in figure 149,4. The median diameter for all 

surface samples are within the limits of medium to 

coarse sands.

Three samples from Arroyo de los Frijoles provide 

comparison of median grain diameter at points downstream in the same basin.

Location sampled

Slopewash Tributary. __ __

North Frijoles Reach _ _ Main Project Reach. _ _ _

Drainage

area

(sq mi)

0.05

.56

2.87

Median

grain size

(mm)

0.56

.78

.72

Though a larger number of samples may have yielded 

a more uniform set of values, at least it can be said that 

there is no progressive decrease of the size of sand downstream.

Figure 1495 illustrates the composition within the 

area of a gravel concentration or bar. Clearly, the 

majority of the larger particles are in the top 2 inches 

(discussed in more detail on p. 212) and the composition 

over the full depth of the concentration is more coarse 

than in a nonbar area. Downstream tips of gravel bars 

are characterized by material a little finer than in nonbar areas. This is an expected pattern and is observed 

in other depositional phenomena such as mudflows.

The largest particle occurring in each 100-foot segment of the channel of Arroyo de los Frijoles was measured, and the results are plotted in figure 150. The 

size of the material in the Slopewash Tributary is as 

large as that in North Frijoles and, indeed, almost as 

large as that anywhere in the whole length of the stream. 

Maximum particle size actually increases somewhat 

downstream, and local variations from section to section are commonly two to threefold.

In gravelly perennial streams the occurrence of pools 

and riffles is characterized by considerable bed relief.
// (. _i-North channel 

/' ] V\

Headcuts

\ \

-Nail-washer line 

2 KJ

V.SdtO-Headcut * » 

H F

Nail-washer line ^/ ^

B /-^Mass-movement line

/ and fluorescent sand

Iron pins for reservoir 

cross sections

COYOTE C. ARROYO

Roadway ____-~-

FIGURE 145. Drainage basins of Coyote C. Arroyo and Morning Walk Wash; solid circles labelled in bold type are nail-and-washer observation points or iron

pins for resurvey; channel cross-section locations are labeled 1-6.

bO

O Or
206 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

D
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 207

/ m

&

Jr*

f* ,V_ f

i-*fe>"i.*^y*'&

rfjfe ' f __ » ' '» '"? *>"5 Ji.......^^;)!^^^*. -**P .. -^ '.: 

E

FIGURE 146 (Above and left). Photographs illustrating several of the 

individual study areas. A, Slopewash Tributary ; the area shown is 

along the mass-movement line (see fig. 144 for location). B, Slopewash Tributary ; the area shown is within the erosion plot. C, North 

Frijoles Reach, Arroyo de los Frijoles ; the view is downstream from 

above the gaging station. Z>, Locust Tree Reach, Arroyo de los

The riffle is a gravel bar or accumulation which is a 

topographic high, a feature which rises well above the 

mean bed elevation. The pool is a trough below mean 

bed elevation.

In the larger ephemeral streams of the area here 

studied, there is no such relief on the dry streambed., 

In fact the bed is remarkably flat across its width and 

closely resembles a gently inclined plane, for the longitudinal profile is quite straight.

Only in detailed mapping did we become aware of 

the fact that local concentrations of gravel on the sand 

bed correspond in principle to the riffle of the perennial 

river. These' bars, as we call them, are so slightly elevated above mean channel bed elevation that they would 

not be recognizable as a topographic high. Rather, we 

have mapped them merely by inspection of surface texture. Because some gravel particles occur everywhere, 

designation of a bar is rather subjective, but generally 

it implies individual cobbles spaced within several diameters; whereas in areas not called bars the spacing of 

cobbles would be 20-50 diameters or more. Typical 

gravel concentrations are illustrated in figure 152Z>.

SPACING OF GRAVEL BARS

The position of gravel bars in the vicinity of the 

Main Project Reach as mapped each summer during the

F

Frijoles; view upstream; visible In the foreground are rock groups 

from the painted rock experiments. E, Main Project Reach, Arroyo 

de los Frijoles; the view is downstream from above the gaging station. F, Main Project Reach, Arroyo de los Frijoles, looking 

upstream.

period 1958-63 is shown in figure 151. It seems apparent that the position of a gravel bar remains remarkably stable. This is true despite the fact that two or 

three flows of sufficient magnitude to move the material 

on the bars occurred between the successive mappings. 

For example, the largest flow measured during the entire period of study occurred between mappings in 1958 

and 1959, and at that time scour to depths of 0.4-1.4 

feet occurred. Thus all the material of the surface of 

the channel bed moved downstream, yet the bars were 

rebuilt in approximately the same places as before. 

However, with each annual mapping, a few bars are 

missing in the newT map that were present in the old 

map, and also a few new bars appear.

Beginning in 1961, a more intensive effort was made 

to map gravel accumulations. It is this effort, rather 

than an actual increase, which, in figure 151, shows 

more extensive areas of gravel beginning in 1961.

In accordance with observations elsewhere the gravel 

bars are spaced on the average at a distance equal to five 

to seven times the channel width, and this ratio persists 

through all the years of record.

Measurements of gravel size and density on the surface of gravel bars were made at two different times 

separated by major flows. It was found that both the 

size distribution and density of particles greater than 

1 inch in diameter remained almost the same.
208 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

5000

 Synthetic 15-year record

o Main Project, drainage area = 2.87 sq mi 

Locust Tree, drainage area = 1.49 sq mi 

North Frijoles, drainage area = 0.56 sq mi

0.5 1 2

RECURRENCE INTERVAL, IN YEARS

FIGURE 147. Magnitude and frequency of flows, Arroyo de los Frijoles, 1958-62.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 209

-Note: Main stem of North Frijoles extends 

2800 feet farther upstream beyond junction with Slopewash 

Tributary

Slopewash "ributary

DISTANCE DOWNSTREAM FROM DIVIDE ON SLOPEWASH TRIBUTARY, IN THOUSANDS OF FEET 

FIGURE 148. Relation of channel width and drainage area to channel length, Arroyo de los Frijoles.

MOVEMENT OF COARSE PARTICLES

We had hypothesized that gravel bars owe their existence to the fact that particles in juxtaposition are less, 

easily moved by flowing water than when widely separated. Marked cobbles arranged in groups of various 

spacings and collected after individual flows would provide a means of testing under field conditions whether 

this hypothesis would be sustained.

The following procedure was developed: Cobbles 

taken from the channel were completely painted. Each 

was given an indemnification number equal to its weight 

in grams, and this number was painted on the cobble. 

The rocks were placed in the channel in groups, each 

group contained a chosen particle-size distribution and 

comparable groups differed in spacing of the rocks. 

After each flow the entire length of the channel was 

searched for painted rocks. Those found were recorded, 

collected, and replaced to await the next flow. This 

procedure was carried out after each significant, stormflow during the summers of 1958-63, inclusive, and discontinued thereafter.

In these studies a group of particles consisted of 24 

individual rocks arranged in a parallelogram. The 

distance or spacing between particles was one of three 

values, 2 feet, 1 foot, or 0.5 foot.

Except for the initial summer (1958) the individual 

groups included four particles in each of the following 

size (weight) classes:

Weight class 

(grams)

300-500__ 

500-900__

Intermediate

axis, approximate

mean diameter

(mm)

_________ 65

______ 85

900-1,700 _______ 105

1,700-3,300____ 125

3,300-6,500___________ 160

6,500-13,000________ 230

Individual particles in the grid were arranged in a 

Latin Square pattern, in which each line of six particles 

includes one and only one of each of the size classes, 

and in each cross-tier, no rocks of the same size are in 

juxtaposition.
210 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

100

80

60

40

20

U.S. STANDARD SIEVE SIZES

3/4 4 10 20 40 100 200

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"~ 

1

yl.-SIZE DISTRIBUTION FOR SEVERAL OF THE STUDY REACHES

PERCENTAGE OFPARTICL

 £ 00 K>CO>O CD 0

\ 

\

\

Gra\

\ J 

\

kx

el bar, t<

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^

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^v

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\

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N 1

\

\

w

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\

,

ns

S

\

V

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tre

jrf;

^

\

\

am

ce

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V

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end o

mater

avel t

^

^

f gravel b

ial, chann

ar, full ce

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a 

e 1

P*

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56

S

i

an.pi e

10 1 0.1 0.01

GRAIN DIAMETER, IN MILLIMETERS 

B.-SIZE DISTRIBUTION FOR SEVERAL LOCATIONS WITHIN A GIVEN REACH, MAIN PROJECT REACH

0.001

FIGURE 149. Bed-material grain-size distribution, sieve analyses.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 211

8 0

4 6 8 10 12 14 16 18 20 

DISTANCE DOWNSTREAM FROM DIVIDE ON SLOPEWASH TRIBUTARY, IN THOUSANDS OF FEET

FIGURE 150. Downstream distribution of coarsest particle in each 100-foot segment of channel.

Also, for several flows, the experiment included some 

rock groups composed of only one weight class. In this 

arrangement, rocks were spaced on 1, 2, or 3 diameters 

rather than by the absolute distances of 0.5, 1.0, or 2.0 

feet.

At the Main Project where the channel is straight, 

there were initially eight ranges of rock groups about 

110 feet apart. The groups having 1-foot spacing lay 

along the centerline of the channel and the groups having i/o-foot and 2-feet spacing on either side, alternating 

from one range to another. Arrangement of the four 

upstream ranges was the obverse of that for the four 

downstream ranges so as to eliminate bias in across-thechannel variation. The position of each particle was 

individually recorded together with its weight and dimensions of the long, intermediate, and short axes. In 

addition there were two lines of boulders (.as much as 

97,500 g) spaced 9 feet apart across the channel in this 

reach. At various times additional temporary ranges 

of particle groups have been installed at the Main Project Reach, but the eight ranges and two lines of large 

particles described above were maintained during the

entire investigation. After each flow we measured the 

distance that individual particles moved, and in preparation for the next flow, reconstructed each particle 

group in accordance with the specifications described.

Procedure at other readies was basically the same 

as for the Main Project Keach. At the Locust Tree 

Keach there were originally two ranges, three since 1960, 

each including groups having two different spacings, 

and also a line of large rocks spaced 6 feet apart. The 

channel is so narrow at the North Frijoles Keach that 

the groups having different spacings were located along 

the length of the channel rather than along a line perpendicular to it.

At the Railroad Reach there was a single line of angular basalt boulders weighing as much as 111,000 grams 

and spaced 4 feet apart. The Stagger Reach had two 

lines of basalt boulders weighing as much as 47,500 

grams, and spaced 3 feet apart. Basalt is a lithology 

foreign to the drainage basin and was derived from 

highway and railroad fills.

Tracing the downstream movement of painted gravel 

particles during a flow involved certain difficulties. An
212 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

Note: Explanation and scale same as in part B

Buckman Road Bridge 

approximately 1000 ft

1963

4.-SAND AND GRAVEL BARS FROM BELOW BUCKMAN ROAD BRIDGE TO HALF-MILE SECTION

FIGURE 151. Spacing and composition of

initial problem was to find a paint that is weather resistant during long periods of immobility and is abrasion-resistant during transport. Oil-base paints proved 

unsatisfactory because they peeled excessively. Except 

for the first year, water-base masonry paint was used 

with satisfactory results.

Even if the paint remains intact and every particle 

found is identifiable, there are still losses due to burial 

of particles in the sand, entrapment in brushy areas, or 

transport outside the search area. The rocks from a 

given group may move downstream distances ranging 

from a few feet to 3 miles, depending on the magnitude 

of the flow. Because of their bright color, painted 

rocks are plainly visible in the sandy channel unless

completely buried. Many particles are found partly 

buried (fig. 152) and the data on losses indicate that 

others become completely buried. Recoveries range 

from more than 90 percent in small flows to 2 percent 

for one exceptionally large flow. Apparently the losses 

have decreased since adoption of a water-base masonry 

paint, but even under optimum conditions losses of 10- 

30 percent during small flows and 30-50 percent during 

large flows are to be expected. The greatest losses 

occur in the smaller size classes.

Deep burial in the sandy channel seldom occurs in the 

area studied. Many holes 4 feet deep were drilled in 

the channel bed for installation of scour chains, and no 

coarse gravel was encountered. The composition of
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 213

EXPLANATION

Sand and Gravel Outcrop, 

Santa Fe Formation

Sand Gravel 

E.-SAND AND GRAVEL BARS FROM HALF-MILE SECTION TO SAND PLUG REACH 

gravel bars, Arroyo de los Frljoles, 1958-63.

gravel bars lends support to the conclusion that coarse 

particles occur only at or near the channel surface. A 

typical bar (fig. 152Z?) is strewn with coarse gravel, 

and in a typical cross section it is apparent that this is 

only a surface veneer extending at most a few graindiameters deep.

Even when the bed scoured more than a foot in a high 

flow and subsequently filled to the original elevation, 

large gravel particles did not become deeply buried and, 

for the most part, projected slightly above the refilled 

surface.

The explanation of this phenomenon appears to be 

the Bagnold-dispersive-stress (1956) caused by grainto-grain impact during motion. The stress increases

as the diameter squared and the large particles, subjected to highest stress, are forced to the bed surface 

where the dispersive stress is zero.

Subsequent to these observations, some streambeds 

in Maryland (annual precipitation 44 inches) were 

sampled to determine whether similar phenomena occur. It was found that gravel-bed streams in a subhumid region also tend to have a concentration of the 

largest particles at the surface of the channel bed (Leopold and others, 1964, p. 211).

For the purpose of segregating the influence of size 

and spacing on particle movement it is not necessary to 

consider the distance a given rock moved during a flow; 

that is, whether it was actually found downstream or
214 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

A

FIOUEE 152. The painted rock experiments and a naturally occurring accumulation of large particles. A, Main Project Reach, showing Latin 

Square position of painted rock groups in the sandy channel. B, Rocks moved from Main Project Reach during flood of August 4, 1960 ; 

note scour pits around each boulder. C, Detail of rock weighing 7,100 grams at Main Project Reach, partially buried by sand and organic 

debris during flow of August 4, 1960. D, Gravel bar at Sand Plug Reach, Arroyo de los Frijoles, looking upstream.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 215

100

300-500

PARTICLE SIZE CLASS, IN GRAMS 

500-900 900-1700 1700-3300 3300-6500 6500-13,000

A-MAIN PROJECT REACH (DISCHARGE= 1.2 CUBIC FEET PER SECOND PER FOOT; 648 INDIVIDUAL ROCKS)

200 500 1000 2000 5000

PARTICLE WEIGHT, IN GRAMS

B.-NORTH FRIJOLES REACH (DISCHARGE = 7.8 CUBIC FEET PER SECOND PER FOOT; 96 INDIVIDUAL ROCKS) 

FIGDEB 153. The effect of spacing on percentage of rocks moving for a given discharge and particle size.

10,000

was simply missing. The particle had moved and how 

far it had moved was of no consequence. For each flow 

the percentage moved by size class and spacing was 

studied. In all, 14,000 observations were available for 

rock movements. The consistency of the data ranged 

from excellent to poor. A typical set of data are plotted on figure 153 to illustrate. From the set of graphs 

exemplified in this figure, further analysis was made in 

a manner explained in a separate paper by Langbein 

and Leopold. The pertinent results are presented in 

figure 154.

In summary, the results show that a larger flow is required to move particles which are close to one another 

than if they are spaced far apart. The influence of 

spacing decreases with increasing spacing and becomes 

negligible for spacings greater than about eight diameters. For example, a discharge of 11 cfs per ft would 

not move 500-gram particles if spaced at one diameter, 

but the same discharge would move 5,000-gram particles if spaced more than five diameters apart.

The effect of spacing on particle movement leads to

the concept that a gravel bar is a kinematic wave caused 

by particle interaction, and is comparable in theory to 

concentrations of cars on a highway.

Owing in part to the phenomenon just described, the 

distance a coarse particle moves during a given flow is 

only slightly related to its size (fig. 155 and table 3). 

Particles lost are assumed to have moved distances comparable to those found. For some flows, all the particles 

recovered, regardless of size, were transported distances 

roughly equal. This is probably related to downstream 

decrease in discharge due to percolation into the channel. The relation of distance moved to maximum discharge during the flow is shown in figure 156. In general, the small particles do not travel materially farther 

than the large ones, and nearly half the flows include 

examples of larger particles moving farther than small 

ones. There is thus no neat progression of transport 

distances inverse to particle size.

SCOUR AND FILL

Scour and fill data from the Arroyo de los Frijoles 

are being collected by means of scour chains buried ver-
216 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

75

PARTICLE SIZE, B-AXIS, IN MILLIMETERS 

118 145

2.37

1.91 C

1.64

1.32

1.17 ±

20,000

0 5 10 15

PARTICLE SPACING, IN DiAMETERS 

fi.-RELATfON OF PARTICLE SPACING AND 

DISCHARGE KEQUiRED FOR MOVEMENT; 

EFFECT OF PARTICLE SIZE ELIMINATED

300 500 700 1000 2000 3000

PARTICLE WEIGHT, IN GRAMS

^.-RELATION BETWEEN DISCHARGE, SIZE, AND SPACING FOR 100 PERCENT OF PARTICLES MOVING

FIGURE 154. Summary of data relating discharge, size, and spacing for painted rock experiments.

tically in the streambed with the top link at or slightly 

above the bed surface. After a flow the elevation of the 

streambed is resurveyed and the bed is dug until the 

chain is exposed. If scour has occurred, a part of the 

chain will be lying horizontally at some depth below the 

channel bed (fig. 157). The difference between the previous streambed elevation and the elevation of the horizontal chain is the depth of scour. The difference between the existing bed elevation and the elevation of the 

horizontal chain is the depth of fill. If no scour has 

occurred the depth of fill is the increase in bed elevation. 

Scour chains, each 4 feet in length, were installed 

along a reach of nearly 6 miles, beginning in Slopewash 

Tributary and ending at Sand Plug Reach. The location of the chains usually followed the low-water channel. Over most of the study reach chains were placed at 

1,000-foot intervals. In the Main Project Reach of

2,000 feet, chains were placed at 100-foot intervals. This 

spacing was believed sufficient to determine any downstream trend in the scour pattern in this arroyo. At 

seven of the chain sections, additional chains were installed across the width of the channel and provide an 

indication of any lateral variation in scour.

Scour-and-fill data are available for most of the 22 

significant flows in the 7-year period, 1958-64. All data 

obtained during the scour-chain record are on file with 

the U.S. Geological Survey, Washington, D.C., 20242. 

However, since some chains were installed before others, 

an equal length of record does not exist for each chain 

location. In addition some chains, usually those in the 

uppermost or lowermost reaches, were not surveyed after 

each flow. These missing segments of data disallow a 

complete picture of scour and fill for individual storms,
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 217

i^U.UUU

10,000 

5000

2000 

1000 

500

20,000 

10,000

C/)

S 

<

OL 

O

z 5000

H 

I 

O

UJ

5 2000

UJ

O

1 

cc

CL 1000 

500

-

F

Discha

!

1

B

NORTH

Ju

rge: 58 cubi 

3.62 cu

1 1 1 1

i

FRIJOLES 

ly 14, 196 

c feet per 

bic feet p

>~

«

REACH 

0 

second 

er seconc

1

^

per foot

1 1 1 1 

 i , <

m

 

1 !

I

I

1

-

I

1 1 1

"

"

1 1 1 1

-

~

1

-

-

-

- Dischc

-

A

LOCUST TREE

A

3EACH

July 14, 1960

arge: 360 cubic feet per second 

9.0 cubic feet per second

A

L

A

A

per foot

A A

A 

A

k A

L

A 

A

A 

A

A

A

1

~

-

-

10,000

5000

2000

1000

500

200

I

-

-

_

-

- MAIN PROJECT REACH

September 13, 1958 '

Discharge: 3060 cubic feet per second

- 38.3 CL bic feet p

1 1 < i ! ! 1

er second per foot

i i 1 ! I 1 i , , II,,

O

0

0

0 0

o

o

0

0" r

o

o

0 

) O

o

o 

on

o

o

D

o

0 0

00

1 1

c

<b

0 CO.

o

o

0

D

°9°. 1 ,

-

-

0

-

-

-

-

-

10 20 50 100 200 500 1000 2000 

TRANSPORT DISTANCE, IN FEET

5000 10,000 20,000

FIGURE 155. Transport distance of coarse particles as a function of particle weight.
218 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

TABLE 3. Relation of transport distance to flow discharge

[Leaders indicate t hat data are insufficient for an average or that category is inapplicable. Distance measurements centered in two columns represent data from adjacent size

classes averaged together]

Location

North Frijoles-.. -...--

Stagger Reach. . . ......

Railroad Reach.. ......

Date

9-13-58 

7-25-62 

7-30-62 

9-18-61 

9-19-61 

8-04-60 

7-08-61 

8-12-61 

7-05-62 

7-14-60 

8-07-59 

7-23-59 

9-19-61 

7-08-61 

7-25-62 

7-30-62 

7-14-60 

8-12-61 

7-05-62 

5-23-59 

8-17-59 

9-06-58 

9-19-61 

5-23-59 

8-12-61 

7-25-62 

7-14-60 

7-08-61 

8-24-59 

9-06-58 

9-19-61 

7-14-60 

7-30-62 

8-12-61 

7-05-62 

7-25-62 

7-08-61 

7-08-61 

7-14-60

Discharge

Cfs

3,060 

1,300 

300 

60 

250 

152 

98 

80-90 

40 

35 

20-25 

10-15 

650 

498 

450 

450 

360 

300-400 

150 

50-75 

20-25 

10 

230 

140 

85 

85 

67 

58 

50 

15-20

Cfs per ft

38.3 

16.3 

3.75 

.75 

3.13 

1.90 

1.22 

1.06 

.50 

.44 

.28 

.16 

16.2 

12.5 

11.2 

11.2 

9.0 

8.8 

3.75 

1.56 

.56 

.25 

14.4 

8.7 

5.32 

5.32 

4.18 

3.62 

3.12 

1.09

Average transport distance, in feet, by size class of particle, in grams

200-300

5,880

I- / "" --

268

300-500

2,336 

1,'

i,:

495 

776 

489 2' 

126 

3 

15 

1,* 

925

9.

225 

397

71

5 4< 

108 

540 

117 

93

500-900

3,862 

71

72

630 

673 

380

 7

103 

11

8 

94 

1,952

2,198

18

247 

299 

73 

J9 

644 

50 

« 

659 

291 

229

900-1, 700

3,500 

It'

7'.

605 

378 

130 

12 

76

7 

1,S 

471

i,;

796 

6S 

2( 

276 

126

6

3

2' 

336 

330 

218

57

1,700- 

3,300

4,537 

62

8

172 

449 

51 

6 

121

0 

95 

841

85

1,116 

2 

56 

230 

29 

29 r4

443 

6 

13 

242 

325 

110

3,300- 

6,500

4,815 

It'

.

136 

194 

83 

2( 

38

0 

1,£ 

1,592

i,:

720 

3] 

8 

107 

34 

8 

& 

124 

1< 

11 

269 

217 

79

6,500- 

13,000

83

0

99 

463 

141 

K) 

24 

0 

0 

 68 

496

20

806 

7 

4

.........

..........

17

78 

12 

9 

78 

159 

48

13,000- 

26,000

1,811 

260

18 

2

0 

0 

0

757

972

170

118 

71

1,313

458 

647 

49 

39 

45

1,665 

381

26, COO52, 000

1,087

0

0 

0

2,140 

304 

191 

199 

61 

35 

14 

43 

260

52,000- 

104,000

363

0 

0 

0

148

Average 

for all 

sizes

4,028 

1,775

784

456 

446 

186 

145 

93 

7 

11 

1,818 

1,123

1,198

1,051 

563 

234 

223 

151 

54 

670 

254 

332 

273 

216 

294 

125 

155 

1,727 

400 

373 

109 

53 

38 

14 

879 

340

but the net change in bed elevation since the time of the 

initial survey may still be obtained.

By 1959 the majority of the chains had been installed 

along the arroyo. Scour-and-fill data for a sample flow, 

for the year 1962, and for the period 1958-62 are shown 

in figure 158. The upper part of the figure shows the 

drainage area of Arroyo de los Frijoles and the general 

location of the chains by chain number. For the two 

individual flows, the lower dashed line represents the 

depth of scour. The upper dashed line represents the 

depth of fill. The heavy solid line represents the net 

change in bed elevation after scour and fill.

The nature of the flash flow is such that the entire 

length of the arroyo may not be flooded with each storm. 

The flow-producing rain may be so located that only 

lower reaches received runoff, or, for a smaller storm 

near the headwaters, a part or possibly the entire flow 

may be absorbed into the ground by percolation before 

is reaches a downstream section. A third possibility remains that a particular chain section may be left dry or 

has very little scour because it was not in the low-water 

path of flow. For a single storm, then there is a considerable variation in the recorded depth of scour from 

section to section. This variation is further exemplified in the Main Project Reach where the chains are

placed at 100-foot intervals. In spite of individual 

variations a general consistency prevails among the 

data, that is, at most sections along the channel there 

is a scour and subsequent fill. All flows produce this 

same pattern; the magnitude of scour is primarily dependent upon hydraulic factors of individual flows, and 

these factors are related to the intensity and total 

amount of rainfall.

North Frijoles, Locust Tree, and Main Project reaches 

of the channel are the objects of special study and are 

also the reaches where flow rates are measured. It is 

within these reaches that the chain sections are located 

to determine cross-channel patterns of scour. The mean 

depth of scour at a section may be determined by averaging the values from the several chains at each of 

the sections. Mean values of scour for each recorded 

flow are tabulated in table 4. The data are plotted in 

figure 159. Despite considerable scatter among the data, 

the mean scour depth appears to be proportional to the 

square root of discharge per unit width of channel.

An increasing depth of scour downstream is not observed in any single profile (fig. 158).

Probably for similar reasons, the depth of scour is 

apparently independent of channel width. Channel 

widths have been illustrated on figure 148. No sys-
100

CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO

r~i i i

219

O Main Project Reach 

Locust Tree Reach 

North Frijoles Reach

0.1

20 50 100 200 500 1000 2000 

TRANSPORT DISTANCE, IN FEET

5000 10.000

FIGURE 156. Average transport distance of coarse particles as a function of discharge (sizes approximately 200-13,000 g).

tematic relation of local depth of scour to the corresponding channel width could be established.

The seven chain sections provided data to study lateral 

variations in scour across the width of the channel. One 

of these sections, chosen as representative of a typical 

reach, is illustrated on figure 160. This figure, illustrating a Main Project section near station 25,000 feet, indicates a net aggradation for the 6-year period. The 

whole width of the channel scours during nearly every 

flow, but the amount of scour and fill varies across the 

width.

The progressive effect of scour and fill over the length 

of the channel is illustrated in figure 161. Except for 

several isolated reaches, aggradation is occurring over 

the entire length of the channel. For the period of 

record, this aggradation amounts to an average of 0.0-4 

ft per yr including those readies which show a net 

scour.

Net scour in individual reaches can be partially explained either by natural or man-caused events. For

examples, at a stationing of 32,000 feet (fig. 161) the 

large flow of 1958 cut through a fan-type deposit (literally a sandplug and hence the name for this reach) 

at, the chain location and indicated a large net scour. 

This fan had earlier been deposited at the mouth of an 

entering tributary. At this sand fan most of the channel width was accumulating a net fill and now, 1964, an 

islandlike deposit over a foot high occupies a large part 

of the channel width. Channel-wide, a net aggradation 

does exist at that location, but because of the placement 

of the chain a net scour shows on the graph of figure 161.

Also, in some of the upstream reaches of the channel, 

excavation of sand by local contractors is responsible, 

at least in part, for the apparent net degradation at 

these sections.

The downstream profiles of the channel bed showing 

progressive accretions of sediment during aggradation 

probably represent as detailed an historical record of 

this process as has been compiled.
220 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

TABLE 4. Mean depth of scour as a function of discharge

FIGURE 157. Horizontal part of chain lying at depth of maximum 

scour, here about half a foot. Vertical part of chain disappears 

below man's hand.

The record demonstrates some nonuniformity along 

a channel 6 miles long, some short reaches not following 

the general trend. The reaches not participating in the 

aggradation do so consistently, but as in the Sand Plug 

Reach at the lower end of the studied length, the reason 

for its deviation relates to special and understandable 

local circumstances. Interestingly, the random pattern 

of storm occurrence does not lead to a random location 

of reaches of sediment accretion, for the increment of 

deposition is rather uniform from year to year.

The exaggeration of scale in figure 161 must be kept 

in mind, and the variations in yearly increments are 

really very small considering the channel length involved. If one short reach aggraded a tenth of a foot 

more than another a thousand feet away, the channel 

slope in the reach would be changed by only 0.0001 foot 

per foot. The variability along the channel due to the 

irregularities of depositional increment are of this order. Thus, despite random character of storms and the 

local loss of flow to channel percolation the mean slope 

of the bed is maintained over long reaches.

A more complete discussion of the records of scour 

is given by Emmett and Leopold (1964). For the present purpose, suffice it to say that scour is associated with 

dilation of the grain bed through the scour depth, but 

that individual particles may move intermittently and 

at a speed much less than that of the water. The volume of material scoured and moved is large. Because 

of its low mean speed downstream, that whole volume 

does not move entirely out of a long reach but, in effect, 

is shifted downstream only a limited distance.

Date of flow

9-6-58... 

9-13-58.. 

5-23-59- 

8-24-59- 

7-14-60... 

11-16-60. 

7-08-61- 

9-19-61- 

7-05-62- 

7-30-62.. 

7-20-63- 

9-21-63..

9-13-58. 

5-23-59.. 

8-07-59.. 

7-14-60..

7-08-61.

8-12-61.

9-19-61. 

7-05-62. 

7-30-62. 

7-20-63. 

9-21-63.

8-18-58-

9-13-58- 

5-23-59-

7-23-59..

8-07-59-

7-14-60..

8-04-60- 

7-08-61- 

9-19-61- 

7-25-62.. 

7-20-63- 

9-21-63-

North Fiijoles Reach

Discharge

(cfs)

17.5

194

140

50

67

9

58

230

7

90

10

5

Upper section

Discharge 

(cfs per ft)

0.87

9.7

7.0

2.50

3.50

.40

2.90

11.50

4.50 

.50

.25

Scour 

(It)

0.018

.215

.103

.083

.068

.023

.130

.188

.153

.180

.293

Lower section

Discharge 

(cfs per ft)

I.46 

16.2

II.7 

4.17 

5.59

.67 

4.84 

19.20

.58 

7.50

.83

.42

Scour 

(ft)

0.050

.977

.460

.000

.135

.315

.040

.175

.128

.448

Locust Tree Reach

Discharge

(cfs)

1320

62.5

22.5

360

498

350

650

150

450

15

316

(cfs per ft)

34.0

I.69 

.56

9.0 

12.47

8.75 

16.25

3.75

II.2

.38

7.9

Scour (ft)

Upper 

section

0.820

.132

.196

.260

.464

.194

.280

.274

.272

.134

.314

Middle 

section

0.076

.060

.212

.406

.368

.138

.334

.076

.320

Lower 

section

0.255

.078

.205

.393

.300

.133

.305

Main Project Reach

Discharge 

(cfs)

20

3060

4

12.5

22.5

35

152

98

250

1300

5

391

Upper Reach

Discharge 

(cfs per ft)

0.235

36.0

.047

.147

.265

.412

1.79

1.15

2.94

15.3

.059

4.6

Scour 

(ft)

0.053

.830

.050

.000

.033

.036

.088

.124

.125

.511

.024

.236

Lower Reach

Discharge 

(cfs per ft)

0.286

43.6

.057

.178

.321

.500

2.17

1.40

18.6

.072

5.59

Scour 

(ft)

0.023

.557

.008

.240

.022

.033

.425

.118

.810

.010

.175

Low-water chains

Discharge 

(cfs per ft)

0.050

.156

.282

.439

1.90

1.23

3.13

16.3

.062

4.9

Scour 

(ft)

0.025

.043

.057

.048

.128

.145

.316

.273

.000

.234

HILLSLOPE EROSION 

EROSION PLOT ON SLOPEWASH TRIBUTARY

To measure the rate of hillslope erosion a grid system 

of erosion pins was installed in 1959 on one of the slopes 

in the drainage area of Slopewash Tributary. The general location of this grid system, or erosion plot, is 

shown in figure 144, and the locality is illustrated in 

figure 143. The erosion plot consists of 61 nails with 

washers spaced on 5-foot centers on an area 50 X 50 feet 

having a relief of 5 feet and furrowed by two shallow 

and narrow rills. These rills join midway through the 

grid system into a single larger rill.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 221

Chains 6-13 Chains 20-33 

Chains 14-19

Chains 47-79

Chains 1-5'

I !

C

Locust Tree

Chains 34-46

Chains 84-90

Sand Plug

Nprth 

xFrijoles

^Station .. ../K

-Station 5000

15,000. "

Slopewash^j 

Station 0

2000 0 2000 4000 FEET 

I I I_____|_____I

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A.-LOCATION OF CHAINS ALONG ARROYO DE LOS FRIJOLES

4 6 8 10 12 14 16 18 20 22 24 26 28 

DISTANCE DOWNSTREAM FROM DIVIDE ON SLOPEWASH TRIBUTARY, IN THOUSANDS OF FEET 

B.-SCOUR. FILL, AND NET CHANGE

30 32

FIGURE 158. Downstream pattern of scour, fill, and net change in bed elevation for a single-storm, a 1-year, and a 5-year period, 1958-62.

At the time of the installation, the nails (10-inch 

spikes) were slipped through a large washer and driven 

into the ground in a vertical position until the bottom 

of the washer was flush with the ground surface. Erosion undermines the washer, which then falls down a 

length of the pin. The pin protrudes above the washer 

at a distance equal to the erosion during the intervening period. While maximum erosion is marked by the 

washer, deposition may be recorded as the height of any 

material above the washer, a desirable feature in such 

places as a rill bottom where maximum and net erosion 

generally differ. Figure 162 shows typical erosion nails

on the erosion plot and on transects. Elevations of all 

nail heads were measured and resurveys show that the 

nails remain stable and are not being heaved by frost 

action.

An attempt was made to map erosion values as topographic contours of erosion quantity, but because of the 

short length of record no systematic trend is apparent 

among individual values. At this time it appears that 

the pins on the steeper slopes adjacent to the rills show 

a slightly higher rate of erosion.

Pins in or near rills tend to show some deposition on 

the washer following scour. Depth of overland runoff
222 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

0.01

0.01 0.02 0.05 0.1 0.2 0.5 1.0 2.0 5.0 10 20 

DISCHARGE PER FOOT WIDTH OF CHANNEL, IN CUBIC FEET PER SECOND PER FOOT

100

FIGURE 159. Depth of scour as a function of discharge at chain sections; each point represents an average scour across the channel

bed, based on 4-10 chains per cross-section.

is greater in such locations and it might be that erosion 

occurs during maximum overland flow depth and that 

deposition follows as the flow subsides. But deposition 

is the exception and not the general rule. The majority 

of the pins show very little or no filling on top of the 

w^asher.

Erosion data have been collected in the years 1961-64. 

Data in 1961 included only values of erosion and later, 

both erosion and deposition. The average erosion during the 5-year period, 1959-64, was 0.0117 ft per yr, 

and deposition on some of the pins averaged 0.0041 ft 

per yr a net average rate of erosion of 0.0076 ft per 

jr.

Summary of data C contains data from the erosionpin plot in Slopewash Tributary.

SLOPE-RETREAT PINS ON SLOPEWASH TRIBUTARY

Fifty-seven erosion pins are arranged on four lines 

transverse to the steep sides of Slopewash Tributary. 

These pins are the nail-with-washer just described, and 

are designated as "slope-retreat pins" on the location 

map of figure 144. An enlarged sketch elaborating details of these pins is shown in figure 163.

The pins are arranged in three groups, each group 

consisting of two lines spaced 2 feet apart. Each line, 

with pins spaced at 2-foot intervals, extends down the

steep slopes to the channel bed and, for one pair of lines, 

cuts across the channel and up the steep slopes on the 

opposite side of the tributary. The slopes range in 

steepness from 21 to 38 degrees, and these generalized 

slope angles are marked on figure 163 for identification.

The pins were installed in 1959 and erosion measurements were made once a year in the period 1961-64. Net 

values of erosion for the period are shown below the pin 

numbers on figure 163.

For the 57 pins, the average rate of net erosion is 

0.0142 ft per yr. This figure consists of an average rate 

of maximum erosion of 0.0281 ft per yr and an average 

deposition of 0.0139 ft per yr. Individual measurements varied from a net deposition to an erosion of more 

than 0.08 ft per yr. A summary of all data from the 

slope-retreat lines is included in summary of data D.

Perhaps more meaningful rates of erosion could be 

obtained by dividing the 57 pins into 3 categories. 

Category 1 includes pins 1-29 of the upper line, category 2 includes pins 30-45 of the upper line, and category 3 includes the 12 pins, 46-57, in the lower line. 

Categories 1 and 3 are similar in their physiographic 

locations, but the pins in category 2 differ in that here 

apparent erosion is being disguised by channel deposits 

on some of the pins near the channel edge and by an 

accumulation of sloughed material on some of the lower
CHANGES IN BED ELEVATION, IN FEET ELEVATION ABOVE 

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224 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

I T I I T 

1958

-1

_ -I

6 8 10 12 14 16 18 20 22 24 26 28 

DISTANCE DOWNSTREAM FROM DIVIDE ON SLOPEWASH TRIBUTARY, IN THOUSANDS OF FEET

30 32 34

FIGURE 161. Downstream pattern of accumulative net changes in bed elevation, Arroyo de los Frljoles.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 225

it

FIGURE 162: Erosion pins consisting of 10-inch spike and washer. A, 

Erosion pins in grid system, Slopewash Tributary (scale is a 6-inch 

ruler). B, Erosion pins on slope-retreat line, Slopewash Tributary.

pins on the sloping bank. Thus the 16 pins in this category actually show an average of a net deposition. Most 

likely this apparent deposition is only temporary, as a 

scour of the channel deposit will not only expose the 

lower nails again but will also allow the sloughed material to continue its downslope journey to the channel. 

Rates of net erosion for pins in each of the three categories are: category 1, 0.0210 ft per yr; category 2,

 0.0034 ft per yr (the minus represents net deposition) ; and category 3, 0.0183 ft per yr. More complete 

computations are included at the end of summary of 

data D.

Excepting those pins just mentioned in category 2, 

generally only those pins on the channel bed showed 

consistent deposition above the washer, and the fact that 

in most places these pins were completely buried indicates an aggrading channel. Undoubtedly much of the 

aggraded material is derived from the erosion of the 

steep slopes adjacent to the channel. However, the erosion rate on these slopes more than compensates for the 

volume accumulation of sediment on the channel bed. 

Implicit, then, is that much of the eroded fine-grained 

sediment is being carried further downstream.

Oddly, in the pin lines here discussed, the greatest 

rates of erosion were on the less steep slopes (upper left 

group on fig. 163), but in considering all observations, 

steep slopes generally show a greater rate of erosion 

than less steep slopes. No attempt is made at this time 

to ascribe to either of these two sets of measurements 

the percentage of total sediment which each produces. 

While the gentler slopes have a smaller erosion rate, 

their land area within the watershed is greater. Consequently, in terms of total volume of sediment, the gentler 

slopes may yield the greater amount.

Location and elevation of pins along lines CB and 

BA as well as the net 6-year erosion at each are indicated on the profiles of figure 164. The profiles provide 

an insight to the occasional contradictory data among 

pins. It.appears that the greater steepness in local surface slope (that slope within 1-2 ft of the pin) is accompanied by the greater erosion. The greatest erosion is 

indicated by those pins on the very steep slopes just 

adjacent to, but not in, the channel bed. The pins on a 

locally flat slope, especially those just downhill of a 

steeper slope (see pins 2CB and 3CB, fig. 164) actually 

show a deposition occurring. This deposited material 

was undoubtedly derived in part from the greater erosion on the steeper slopes just uphill, for example, from 

pin 1CB. Pins on relatively unbroken slopes are in general agreement with each other and usually indicate 

about the average rate of erosion. Thirteen of the 17 

pins showed a net erosion and 4 a deposition. If only 

those pins showing a net erosion were considered, the 

average rate of erosion would increase from the reported 

0.0072 ft per yr to 0.017 ft per yr. The former value is 

in agreement with the value from the erosion plot and 

the latter with the value from the slope-retreat lines. 

Generally, the topography along the iron-pin lines is 

intermediate between that of the erosion plot and that 

of the slope-retreat lines.
226 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

\ .Slope crest

K

\

Pin number i 8 9 10 11 12 13 14 \ 37 36 35 34 33 32 31 30

Erosion (ft) <£> , », * * cy" o~ ~ VN* ~ o-' ~ ~ o~

Pin number 15 16 17 18 1^9 20 \ 21 23 23 24 25 26 27 28 29) 45 44 43 42 41 40/39 3_8/ 

Erosion (ft)

Slope angle 26° \ 21

Note: Values of erosion are net change 

during 5- year period 1959-64

Slope angle

2ft

P 14 CN* A° / 6° <£> «P 1° A° A°l /v^ XP xO t^Lf ~\ cx» y

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FIGURE 163. Sketch map showing details of the slope-retreat pins, Slopewash Tributary.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 227

7640

z 7636 -

< 7632 -

7628

7624

Key: 5 CB, designation of pin 

0.10 ft. net erosion

30 40 50 

DISTANCE FROM PIN C, IN FEET

FIGURE 164. Six-year (1958-64) net erosion on iron-pin line CBA, Slope-wash Tributary drainage area.

OTHER MEASUREMENTS OF SLOPE EROSION ON 

SLOPEWASH TRIBUTARY

The second additional set of measurements for rates 

of erosion consists of eight iron pins located at the 

chain-sections below the junction on Slopewash Tributary (see fig. 144 for chain-section locations). These 

are 4-foot lengths of iron reinforcing rod, installed and 

observed as previously described. For each chainsection, a pin was located on each sloping bank and, for 

two of the sections, a pin was situated in the channel 

bed.

Installation was made in 1958 and data were collected 

in 1958-64, excepting 1961. The average rate of erosion for the bank pins is 0.0108 ft per yr and the bed 

pins indicate an average deposition of 0.0033 ft per yr. 

These rates are in agreement with the other observed 

rates for slope erosion and channel aggradation.

EROSION NAILS ON COYOTE C. ARROYO

On slopes leading into the headcut of Coyote C. Arroyo, a total of 65 erosion pins with washers are located 

on 3 lines, as shown in figure 145. The pins were installed in 1961 and have been remeasured yearly to 1964. 

Profiles were run on the pins to determine the slope, 

and also a resurvey of the pin elevations indicates no 

heaving due to either freeze-thaw or wet-dry actions, 

The average of the 65 pins indicates a yearly net erosion 

of 0.0237 foot. All the data for the pins are tabulated 

in summary of data F.

Rates of erosion for each of the three lines were consistent, ranging from 0.021 to 0.027 ft per yr. These 

values approximate the higher values for the sloperetreat pins in Slopewash Tributary, and it is believed 

that they exceed somewhat the average rate of erosion 

for the entire drainage of Coyote C. Arroyo, as is evidenced by a lower value for the grid system than for 

the slope-retreat lines in Slopewash Tributary.

Attempts to correlate individual rates of erosion with 

individual local ground slopes did not result in a neat 

regression of erosion rates with lessening slopes. To 

the observer on the ground, it appears rather instinctive that greater erosion is occurring on the steeper 

slopes; however, the disparity in the data is sufficient 

to mask attempts to illustrate graphically the relation 

of slope to rate of erosion.

TRACING OF FLUORESCENT SAND

A fluorescent sand (ASTM mesh size 40) was placed 

along three lines in two of the study areas to trace the 

movement of individual fine-grained sediment. One line 

was along the hillcrest of Morning Walk Wash (see 

fig. 139). The other two lines were in Coyote C. Arroyo, one along the nail line ED and the other along 

the mass-movement line (see fig. 145).

The sand was placed in 1961 and the initial position 

was marked. In 1962 the movement of this sand was 

determined by searching for grains at night with a 

black light. Despite a relatively large amount of erosion indicated by the erosion nails, the individual sand
228 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

grains appeared remarkably stable. For the short distance of 5-10 feet individual grains moved in quantity. 

However, for distances greater than this very few grains 

could be found. Maximum distance at which we found 

a grain was about 50 feet.

The original concentration of the grains was not recorded and it is not known how many of the grains had 

actually moved but could not be found. The concentration of grains in the initial position was still large 

in 1962. However, it is believed that many grains, 

either by moving completely out of the searched area 

or by being covered, were not found.

In 1964 a second attempt was made to trace the 

movements of the fluorescent sand. The concentration 

at the original placement area had considerably lessened 

over that observed in 1962. Many grains were found 

within 50 feet of the original line and a few were found 

between 50 and 100 feet. Below 100 feet, but within 

several hundred feet, a few grains were found which 

fluoresced with the same characteristics as the placed 

grains, but comparison of these with grains from other 

observations indicated that they probably were native 

fluorescent minerals.

If any conclusion may be drawn from these experiments it would be that grains on the flat of a watershed 

divide are moved very slowly but that, once they are on 

the steeper slopes and within an area capable of overland flow, they are moved much more rapidly. This 

conclusion is supported by a 1-year set of data for erosion pins on a transect across a divide near the houses 

of Las Dos. These pins are referred in the project 

files as Corral Flat nail and washer line, but because of 

the short period of record are not elsewhere presented 

in this report. The 1-year of data show no erosion or 

deposition exceeding 0.005 foot, and the average for the 

line indicates little or no systematic movement of individual grains.

CHANNEL ENLARGEMENT IN SLOPEWASH TRIBUTARY

Although the slope retreat pins give an indication 

for the rate of channel enlargement, another set of 

measurements was designed specifically to provide rates 

of bank recession and channel aggradation-degradation. This set of measurements, designated as nail sections A-J (location shown on fig. 144, consists of 10 

observation sections spaced approximately at 50-foot 

intervals along Slopewrash Tributary. At each section 

a nail with washer was located on each sloping bank 

and one at the center of the channel bed. Rates of erosion and deposition were observed as previously 

described.

The sections were installed in 1959. Data have been 

collected yearly to 1964, excepting 1960. These data

show that the average rate of bank erosion for the side 

pins is 0.0248 ft per yr. Deposition occurring at some 

of these pins averages 0.0058 ft per yr. The net bank 

recession is then equal to 0.0190 ft per yr. The channel 

bed pins indicate an eroded depth of 0.0694 ft per yr. 

This depth probably occurs as scour while surface runoff is flowing in the channel. Subsequent fill amounts 

to 0.1024 ft per yr. This leaves a net deposition of 

0.0330 ft per yr, indicating an aggrading channel. This 

observation is consistent with other measurements indicating a channel aggradation. The channel aggradation is not confined to lower reaches of the channel but 

also extends upstream into the uppermost headwater 

rills. All nails in the channel on sections A-H show 

net deposition, and these vary in distance to watershed 

divide from 400 to 800 feet. Still, the amount of deposition in the small channels does not account for the volume eroded from upslope surfaces.

This excess of sediment is being supplied to the main 

streams and accounts for the aggradation observed 

there and reported in the section on scour and fill.

A summary of data for the nail sections are included 

in summary of data G.

SOIL CREEP OR MASS MOVEMENT 

SLOPEWASH TRIBUTARY

To measure the magnitude of downslope soil movement occurring as soil creep, lines of mass-movement 

pins were installed in Slopewash Tributary and in 

Coyote C. basin (see figs. 144 and 145 for locations). 

The line in Slopewash Tributary is along the east fork 

some 100 feet above the junction of the tributaries. The 

line chosen crosses the meandering channel several 

times, and thus the pins are on the steep slopes (about 

1:1) of the channel banks, alternately on one side and 

the other of the tributary. In figure 146 the photograph 

was taken with the camera at the north end of the line 

and the man is standing at the south end.

The two ends of the line are monumented and located 

in such a place that the monuments themselves are subject to no downhill movement. Iron rods, 4-feet long, 

were used to monument these end points. Generally 

at 5-foot spacings along the length of the line, ^-inch 

galvanized iron pipes, 10 inches long, were driven vertically into the ground. At the time of installation they 

generally protruded about 0.1 foot, above the ground 

surface. A transit was set up over the center of the 

monument on the north end of the line, oriented to the 

center of the monument at the south end of the line, 

and the distance of each pin away from the line of sight 

was recorded. Similar measurements are made on a 

resurvey except that the angle of the pin from the ver-
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 229

tical and any increase in protrusion above the ground 

surface are also recorded.

Resurveys were made annually from 1961 to 1964. 

The average rate of downslope creep of the pin tops is 

0.225 in. per yr. Considerable variations exist among 

individual measurements. However, all pins show net 

downhill movement for the 5-year period. Individual 

variations probably reflect local influences of the particular pin location; for examples, a twig, rock, local 

slope, or proximity to the channel.

All of the soil profile to the full depth of the pin is 

not moving as fast as the average rate reported. Most 

pins are rotating downhill, indicating that the top 

layers of soil creep at a faster rate than the lower layers. 

The average rotation of the pins is 1.4° per year. For 

seven of the pins the pin angles themselves explain all 

the observed downslope creep, the point of rotation being very nearly at, or slightly above, the bottom of the 

pin. For the other eight pins the center of rotation 

is a short distance below the bottom of the pin. For this 

latter set of pins it follows then that the entire soil 

profile, at least to the depth of these pins, must move 

downslope some distance. An average value of the 

downhill movement for the bottom of all pins is 0.003 in. 

per yr (a computed, not an observed value). This value, 

being so nearly equal to zero, indicates that only about 

the top 8 inches of soil are involved in mass-movement 

and that the soil nearest the surface has the greatest 

movement.

Since the pins are leaning downhill and some of the 

pin length protrudes above the ground surface, a more 

meaningful value of downhill creep would be that computed for the pin at the ground surface rather than at 

the pin top. These computations show the average rate 

of soil creep at the ground surface as 0.205 in. per yr, 

slightly less than the 0.225 in. per yr attributed to the 

tops.

Movement at the ground surface and at the pin base, 

along with the depth of inserted pin, allows computation of the volume of material moving. This value is 

0.87 cu in. per in. of slope base per year, or 32 cu ft per 

mile of slope base per year.

The increasing protrusion above the ground surface 

observed at the mass-movement pins was also used to 

study erosion rates. The average rate of erosion for 

these pins is 0.025 ft per yr. Generally, these are the 

steepest slopes (approximately 45°) for which erosion 

values were obtained and they show the largest rate of 

erosion.

A summary of the downhill movement of the pin tops, 

rotation of the pins, and erosion at the pins are included in summary of data H.

COYOTE C. ARROYO

A mass-movement line of pins as just described was 

also installed along a tributary to Coyote C. Arroyo 

(location shown on fig. 145). The average downhill 

movement of the pin tops for the period 1961-64 was 

0.267 in. per yr. During the period one pin showed an 

unexplained uphill movement.

The average downhill pin rotation during the period 

of observation was 1.7° per year. The relation of downhill movement to pin rotation is the same for these pins 

as for the pins in Slopewash Tributary.

The pins on this line showed greater erosion than 

those in Slopewash Tributary. Thus, computations for 

the rate of downhill movement at the ground surface 

used a value for the length of pin exposed equal to the 

original protrusion plus one-half of the erosion. Computations show the average rate of movement at the 

surface as 0.202 in. per yr, a figure remarkably close to 

that obtained in Slopewash Tributary. The volume rate 

is somewhat less than that in Slopewash owing to a 

smaller depth of soil movement, here 7.5 inches. The 

computed volume rate of mass-movement is 25.5 cu ft 

per mile of slope base per year.

A summary of data for the mass-movement line in 

Coyote C. Arroyo is included in summary of data I.

HEADCUT ENLARGEMENT 

FENCE LINE HEADCUT

Fence Line Headcut is a tributary to the Arroyo de 

los Frijoles, entering on the left bank about 1,500 feet 

below the Main Project Reach. Figure 165 is a photograph of this headcut in 1964. In 1960 the headcut was 

staked with six iron pins, each 4 feet in length. The 

rate of enlargement of the headcut is determined by

FIGUBE 165. Fence Line Headcut.
230 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

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FIGURE 166. Aspects of the drainage area of Coyote C. Arroyo. A, The largest headcut, cut in valley alluvium of Coyote C. Arroyo (also see map of 

fig. 167). E, Channel of Coyote C. Arroyo about 800 feet downstream from headcut pictured in A; man points with shovel to position 

where C1* sample was obtained to date the Coyote terrace deposits. C, View near the watershed divide of Coyote C. Arroyo; note the lag 

gravel typical of headwater areas not covered by colluvium. D, Typical view of the valley alluvium; coarse particles are found here only in 

watercourses, as in that in foreground.

measuring the distance from the iron pins to the vertical walls of the cut. Resurveys indicate that the headcut is slowly enlarging at all points of measurements, 

but that the greatest rate of enlargement is at the upstream end where the headcut is advancing nearly 1.5 ft 

per yr. Height of the vertical walls of the cut averages 

6 feet.

The average volume of sediment discharged by this 

one gully is estimated at over 500 cu ft per yr, mostly 

from headward advancing.

COYOTE C. ARROYO HEADCUT

Coyote C. Arroyo is a discontinuous gully involving 

four headcuts. About 2,000 feet below the headwater 

divide is the largest of the headcuts, below which the 

gully is continuous to the master stream. The area 

around this largest headcut has been studied in detail 

and figure 166 includes photographs of the vicinity. 

Rate of headcut enlargement is being recorded by yearly 

planetable mapping and by measurements from iron 

pins driven at known distances from the vertical walls.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 231

_Pin B

-Erosion lines

Pin 2

15 + 50

6610

6606

6602

O 6598

16 + 50 

No vertical banks downstream from

15 + 00 16 + 00 17 + 00 18+00 

CHANNEL STATIONING UPSTREAM, IN FEET

19+00

FIGUEE 167. Topographic map and profile of Coyote C. Arroyo headcut.

The planetable map of 1962 is shown in figure 167 and, 

as a dashed line, the outline of the headcut as it appeared 

the previous year. Most of the headcut has retreated 

some and the greatest amount of retreat is recorded in 

extremities which extend either up the primary direction of the channel or in the direction of tributary 

swales. Measurements from the pins to the cut bank 

indicate a lateral retreat of 0.4 ft per yr and a retreat at 

the most head ward extreme of 2.6 ft per yr. Thus, while 

the map of figure 167 provides some insights about

headcut retreat, mapping is not sufficiently accurate to 

delineate the relatively minute retreats which are occurring.

The initial 400 feet of channel profile is shown below 

the headcut map to provide an indication of channel 

slope and the sloughed material associated with the 

headcut. The average slope of the channel here is 0.03 

ft per ft compared to 0.02 ft per ft in the channel 1,000 

feet downstream. The volume of material contributed 

to the stream by the enlargement of this headcut has
232 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

been computed to be 1,650 cu ft per yr for the period 

1961-64.

MOVEMENT OF LARGE PARTICLES IN HEADWATER 

RILLS

SLOPEWASH TRIBUTARY

Two of the channels that have been studied in detail 

with respect to movement of individual rocks, Green 

Kock Gulch and Little Green Rock Gulch, are shown 

in figure 144. The former is also illustrated in figure 

168. Starting at or near the mouth of these two channels individual rocks, each 3-6 inches in diameter, were 

completely painted. They were then replaced in the 

rills at measured distances from the mouth. This distance, in feet, was painted on each rock for identification and the total number of rocks at each distance was 

recorded. A total of 250 rocks was painted in Green 

Rock Gulch and placed at distances of 1-47 feet upstream of the mouth. Forty rocks were painted in 

Little Green Rock Gulch and placed from 21 to 36 feet 

upstream of the mouth.

The initial placement was in 1959 and resurveys were 

made annually. At the time of the resurveys the movements of the individual rocks were easily discernible 

because identification numbers on the painted rocks 

were no longer in consecutive order nor at the distance 

corresponding to their number.

Although the number of rocks moving has not been 

large, the recovery percentage is high. In 1964, 5 years 

after placement, 88 and 78 percent respectively of the 

rocks in the two gulches are still accounted for. Missing rocks are usually those that moved but later were 

obscured by either vegetation or a sand covering, that 

is, they were not buried in place. This is suggested 

by some of the rocks in the main study which were reFIGUKB 168. Green Rock Gulch, a tributary to Slopewash Tributary. 

Rocks wash into this minor rill from the lag gravel covering some of 

the hillslopes seen in the background.

ported as missing in a given flow but wrere found after 

a subsequent flow.

The data have not been sufficient to describe a trend 

in movement. Both the upper and the lower halves of 

the reach on Green Rock Gulch show about 25 percent 

of their rocks moving or missing. Because of the large 

number of rocks not moving and the large variability 

in distance of those moving, the data are perhaps not 

yet meaningful. However, the longest distances recorded to date are of rocks originally placed in the 

lower 10 feet of channel and these have moved as much 

as 540 feet.

GUNSHOT ARROYO

Gunshot Arroyo is the first tributary entering Arroyo 

de los Frijoles below the sweeping S-curve half-mile 

downstream of the Main Project Reach. Measurements 

in Gunshot Arroyo include the tracing of large particle 

movements in the channel bed and on a steep sloping 

bank of the channel, the retreat of a knickpoint formed 

in the channel by an outcropping of semiresistant Santa 

Fe formation, channel enlargement, and degradationaggradation studies.

In 1960 the initial survey and installations included 

the -selection, painting, and replacing of rocks in the 

channel. The rocks, ranging in diameter from about 

3 to 10 inches, were completely painted and numbered 

with the distance in feet corresponding to the initial 

position upstream of the junction with Arroyo de los 

Frijoles. The largest number is 880 and the watershed 

divide is located at station 1,150 feet. The rocks were 

placed at 10-foot intervals.

In 1962 a complete resurvey was made of the existing measurements and a longitudinal-profile survey was 

run from 150 feet below the mouth of the arroyo to and 

over the watershed divide. This profile is shown on 

figure 169. No vertical or cut banks were observed above 

station 620 feet and the channel disappeared above station 1,050 feet.

Superposed on the profile of figure 169 is a schematic 

illustration of the rock movements as recorded in 1962. 

Each rock position is identified as to moving, missing, 

or stationary. For those rocks which were found, the 

distance moved in feet is indicated by the number above 

the original position of the rock.

Most rocks below station 750 feet moved. Downstream from station 750 feet to station 450 feet, most 

of the moving rocks were found. Below station 450 

feet a large percentage of the rocks were reported missing. The upper of the two mentioned subreaches has 

a gravel bed and the lower a sand bed. In the lower 

reaches of the channel most rocks that had moved were 

found partly buried in sand and, with few exceptions, 

those which had traversed the length of the tributary
6800

6790

6780

6770

6760

6750

6740

6730

6720 -

6710

-2+00 -1+00

EXPLANATION

23

Transport distance, in feet, of particles 

moving and found

o 

Particles moving, but not found

Particles not moving

Value of channel slope in each 100-f

length of channel, in feet per feet

Arroyo de los Frijoles

1+00 2 + 00 3 + 00 4 + 00 5 + 00 6 + 00 7+00 

CHANNEL STATIONING UPSTREAM OF MOUTH, IN FEET

8 + 00 9 + 00 1

FIGURE 169. .Profile of Gunshot Arroyo illustrating movement of coarse particles, 1960-62. 

intermediate-axis diameter of particles is 150 mm.

Average B- or
234 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

and into the channel of Arroyo de los Frijoles were not 

found. The rocks above station 750 feet were consistent 

in that none had moved despite the fact that these 

were on the steepest slopes.

At the time of the 1962 survey the rocks moving and 

found averaged a transport distance of 39 feet; the 

maximum distance recorded was 120 feet. If consideration were given to the missing rocks, which probably 

were transported entirely out of the tributary, these 

distances would be considerably increased. Of the rocks 

originally placed, 37 percent were missing and 22 percent had not moved.

After the 1962 survey the rocks found were returned 

to their original position, but the missing positions were 

not filled. Resurveys in 1963 and 1964 of these remaining rocks recovered only one rock reported missing in

1962. This adds credence to the probability that missing rocks were transported entirely out of the tributary. 

In 1963 the number of total missing rocks increased 

to 82 per cent, and all but 2 of the 55 rocks remaining 

after the 1962 survey had moved. Of these 14 were 

found and averaged a transport distance of 218 feet and 

a maximum distance of 930 feet. The large ~ increase in

percentage of missing rocks is probably attributable to 

the storm which caused a 1,300 cfs flow at Main Project 

and which occurred between the surveys of 1962 and

1963. Most rocks remaining for the latter survey were 

from upstream positions and had longer distances to 

travel before being exposed to the greater chance of 

loss in the main channel. By 1964 the number of missing rocks had increased to 85 per cent.

Painted rocks on a typical steep slope (approximately 

45°) at station 190 feet were resurveyed in 1962, 1963, 

and 1964. The rocks painted were native to the slope 

and generally ranged in intermediate-axis diameter 

from 1 to 3 inches. On an uncounted number of rocks 

painted in 1960,175 remained in 1962 and 164 remained 

in 1964. Thus, in the last 2 years only 6 per cent have

moved off the slope and have become lost in the channel. 

Between annual surveys an average of only 3 per cent 

of the rocks (excluding those missing) moved over one 

foot, but a gradual slumping was noticeable. In 1964, 

118 rocks (72 per cent) had slumped downhill a measurable amount, and this slumping averaged 0.6 foot for 

the 4-year period. It appears that the effects of gravity, 

aided by such processes as freeze-thaw and wet-dry, 

have an appreciable influence on coarse particles on 

steep slopes.

The monumented knickpoint in the Santa Fe formation at station 417 feet averages about 1.3 feet in height, 

and between 1960 and 1964 no measurable amount of 

upstream retreat was recorded.

Scour chains placed in the arroyo bed at station 25 

feet, 230 feet, and 468 feet indicate the channel is aggrading at a rate of 0.06 ft per yr for the 2-year period 

1962-64. Although this is a short-term record, the value 

is in agreement with that of the main arroyo, 0.04 ft per

yr.

MORNING WALK WASH

In 1961, painted rocks were placed at 10-foot intervals 

in the channel of Morning Walk Wash near Las Dos 

(fig. 139). The painted rocks ranged in diameter from 

3 to 5 inches, the average rock size native to the gullies. 

A total of 166 such rocks were placed along the thalwegs 

of the two main channels and a smaller rill draining the 

hillslope.

A resurvey in 1962 indicated a very large percentage 

of the-rocks had moved. Table 5 is a condensed presentation of the rock movements between 1961 and 1962. 

For example, in the north gully three times as many 

rocks had moved in the lower reaches than in the 

upper reaches and the rocks in the lower reaches tended 

to move greater distances. Many of the rocks were 

found in a fan deposit at the mouth of the channel.

As in Gunshot Arroyo the rocks found during the

TABLE 5. Summary of particle movement Morning Walk Wash, 1961-62 

[L, lower reach; 17, upper reach]

Particles

Total originally placed. ______ _______

Percent moving, on basis of: 

Total found. _____ .___.__._.._______.__

Total found plus total missing _ __ ... ___

Distance moved, in feet, on basis of total found:

South gully

L

44

41 

93

48

177 

473

U

43

40 

63

77

339 

723

Total or 

average

87

40

78 

62

258

South 

rill

12

25 

25 

100

211 

'613

North gully

L

34

77 

91

U

33

12 

30

Total or 

average

67

45 

61

1 Lower reach.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 235

survey were returned to their original position to await 

movement during subsequent flows, but the missing positions were not filled with new rocks. Thus data after 

1962 became less meaningful except to determine the 

depletion rate of the originally placed rocks. Data for 

one of the painted rock experiments in headwater channels are included in summary of data J for 1961-64.

The condition of the paint on the rocks found indicates that the rocks are transported with only little 

abrasive action, that is, they are not broken up in place 

and removed as smaller particles, this despite the rolling 

and tumbling over other rocks in their trip downstream.

Two monumented cross sections of the channels were 

installed in 1961 and resurveyed yearly to 1964. During this period the upper section, 170 feet above channel 

mouth, showed no significant changes, while the lower 

section at the mouth showed about 0.2 foot of deposition in each channel bed. This value is consistent with 

other observations for channel aggradation.

SEDIMENTATION IN CHANNELS AND RESERVOIRS

About 1937, at the lower end of Coyote C. Arroyo 

some 1,900 feet downstream of the present position of

the largest headcut, an earth dam was constructed across 

the arroyo. In 1961 the reservoir behind the dam was 

topographically mapped by planetable, and it was 

planned that resurveys would allow the determination 

of the amount of fill accumulating within the reservoir. 

Contours of equal deposition occurring during 1961-62, 

as well as original topography, are shown in figure 170.

Computations determining the volume amount of sediment collected in the reservoir during the period 1961- 

64 are shown in table 6. This amount totals 6,245 cu 

ft or 2,082 cu ft per yr. If the average rate of erosion 

shown by the erosion nails is assumed as a basin-wide 

average, the reservoir is shown to collect only about 5 

percent of the total eroded sediment. However, the 

computation of this percentage may be of only academic 

interest because, as was remarked previously, values 

of the erosion rate computed from the pins installed 

in this basin are believed to be too large for the basin 

as a whole. Most of the sedimentation was in the year 

1961-62.

The field-sketch map of figure 145 shows six channel 

cross sections at various distances up the arroyo. These 

cross sections were first surveyed in 1961; they have

25

CONTOUR INTERVAL 

TOPOGRAPHY: 1 FOOT 

DEPOSITION: 0.25 FOOT

FlGUBE 170. Topography of dam and reservoir on Coyote C. Arroyo and contours of deposition, 1981-82.
236 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

TABLE 6. Observed sedimentation in reservoir behind dam on Coyote C. Arroyo, 1961-64

Cross section

1 - .- .

2 - . .- .._

3.. -- - ..

4 - . -.

5 __

6 --- - ......

7 --.--. ......

End pins

BM 2-6 

BM 2-5 

BM 2-4 1-5 

1-4 

1-3 

1-2

Decrease in area of cross section 

due to deposition (sq ft)

1961-62

10.0 

28.3 

29.0 

30.5 

34.0 

15.5 

51.5

1961-63

10.0 

26.2 

38.0 

50.5 

68.0 

8.5 

44.5

1961-64

10.4 

24.3 

39.0 

55.5 

73.0 

14.5 

39.5

Effective 

width of 

section 

(ft)

30 

43 

53 

55 

60 

35 

40

Average depth of deposition (ft)

1961-62

0.33 

.54 

.55 

.55

.57 

.44 

1.29

1961-63

0.33 

.61

.72 

.92 

1.13 

.24 

1.11

1961-64

0.35 

.56 

.74 

1.01 

1.22 

.42 

.99

Effective 

area of 

reservoir 

(sq ft)

1,000 

825 

900 

913 

1,436 

1,850 

1,336

Total - _ - -- - 

Rate cu ft i

Amount of sedimentation > (cu ft)

1961-62

330 

445 

500 

505 

820 

815 

1,725

5,140 

5,140

1961-63

330 

505 

650 

840 

1,620 

445 

1,485

5,875 

2,938

1961-64

350 

460 

665 

920 

1,750 

775 

1,325

6,245 

2,082

1 Amount of sediment contributed from basin (40.8 acres): 

2082

40.8X43,560 =0.0012 ft per yr

been resurveyed yearly to 1964 and allow computation 

of deposition in the channel. Stationing and channel 

changes are summarized in table 7. The volume accumulations of sediment in the 1,435-foot reach included by the sections are also shown in the table. 

These data indicate that 3,192 cu ft per yr of sediment 

is deposited in this reach, which corresponds to channel 

aggradation of about 0.10 ft per yr. This value represents about 8 percent of the total eroded sediment indicated by the erosion pins.

The percentages of total eroded sediment accounted 

for by the surveys in the reservoir and in the lower 

reach of channel are not total reservoir and channel 

storage of sediment for the entire basin. Our studies 

have indicated that even headwater rills are aggrading, 

thus there is much more channel length in the basin 

available for sedimentation processes. Although the 

surveyed reservoir is the only man-built barrier, other 

natural reservoirs are also available. The discontinuous nature of the channels provides many alluvial fans

and flats which may be considered as natural reservoirs ; at least, sedimentation rather than erosion is occurring in these areas.

ANALYSIS OF SEDIMENT BUDGET

To account for sediment volumes contributed by erosion and to compile a balance sheet is not easy, because 

of the variance within the measurement data. With regard to what appears to be the main process contributing debris (sheet or surface erosion), the problem is how 

to average the rates observed by the nail and washer 

data at various localities and derive a figure applicable 

to the whole contributing area. To use the data on volumes contributed by headcuts presents little problem 

because there are only a few headcuts per square mile in 

the study area. Bank cutting and consequent channel 

enlargement is not an important source of sediment, as 

indicated by measured cross sections of channels. The 

data on mass-movement pins present a special problem 

because, lacking knowledge of certain details of the

TABLE 7. Observed rates of channel changes in Coyote C. Arroyo

Section

1. ____-_. _

2__._ ..__._.__.__.__

3____.___ ..-_._. .__

4.. .__._._.._.__ .

5____. _______________

6__________.___

Channel 

stationing

(ft)

30 

210 

365 

650 

955 

1,435

Change in channel shape 

( + , deposition; , scour; 

(sq ft)

1961-62

+30. 75 

+ 8.75 

+ 16. 75 

-2.70 

+ .70 

-1.30

1961-63

+ 29. 00 

+ 10. 00 

+ 14. 10 

-.50 

+ .80 

-.25

1961-64

+ 28. 25 

+ 11. 00 

+ 14. 75 

. 00 

+ 1. 10 

+ .50

Length 

of reach

(ft)

120 

165 

225 

290 

395 

240

Total.... _ _ __ _

Rate cu ft T-i^r VI*

Volume of sediment ' (cu ft)

1961-62

3,690 

1,445 

3,770 

-785 

265 

-310

8,075 

8,075

1961-63

3,480 

2, 100 

3, 180 

-145 

315 

-60

8,870 

4,435

1961-64

3,390 

2,310 

3,320 

0 

435 

120

9,575 

3, 192

; Amount of sediment contributed from basin (40.8 acres):

3192 40.8X43.560° a0018ftperyr
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 237

process, the total area subject to effective sediment contribution from this source is difficult to estimate.

No great problem is presented by channel aggradation, for these measurements are far more complete 

than for other processes. Two important sources of possible error remain the unmeasured volume of debris 

passing out of the basin as bedload or suspended load, 

and the trap efficiency of the reservoirs.

These difficulties face any investigator who is constructing a sediment budget. No perfect solution is 

available, but at least the assumptions made in the computations can be stated and the implications of the assumptions can be analysed. Although the quantities are 

only roughly approximate, a summary of debris inflow, 

outflow, and storage is attempted. Table 8 summarizes 

the average values of the measurement quantities. 

These values are arithmetic averages of individual readings taken over the period of measurement at the respective measurement points. Because comparison of 

mean and median values shows no great disparity, we 

used mean values exclusively in this report.

The main assumptions enter the computations in progressing from average-measurement data, table 8, to 

computations of average rates of erosion and deposition 

summarized in table 9.

The main source of data on sheet erosion is the pinand-washer installations. More variance is noted between successive years than among the respective pins 

in the same year. Within a given group of nails the 

mean rate of erosion for the 3-year period was plotted 

by individual pins against the local ground surface 

slope at the pin, but no correlation was found. This 

lack of correlation is attributed to the fact that each 

group of nails applied to only a small range of slope 

values. Some influence of slope probably can be seen 

in the comparison of values of surface erosion in table 

8. For example, the average land slope on the erosion 

plot of Slopewash Tributary is less than on the nail 

lines of Coyote C., and the corresponding net erosion 

rates are 0.008 and 0.024 ft per yr respectively.

But it appeared unjustifiable to correlate these net 

erosion values for different localities merely with slope 

because many other factors probably are also operative. 

The significance could not be tested statistically with 

only seven localities.

The average value of surface erosion for the whole 

basin (0.015 ft per yr; see table 9) represents our best 

judgment of the order of magnitude. This value is in 

agreement with the result obtained by equal weighting 

of number of pins and number of years of data, 0.0145.

Two values of volume eroded by headcut retreat are 

available. Approximately the average of these two was

TABLE 8. Data on measured rates of erosion and deposition

[SWT, Slopewash Tributary]

Erosion

Surface erosion:

Erosion plot, SWT:

Pins_________ . 61 

Years________ 5 

Net erosion ft per yr 0. 008 

Slope-retreat pins, SWT:

Pins_________ . 57 

Years_____ 5 

Net erosion ft per yr 0. 014 

Nail lines, Coyote C. Arroyo :

Pins_________ 65

Years_ 3 

Net erosion ft per yr______ 0. 024

Nail sections, bank, SWT:

Pins____________.__ 20 

Years_______ 5 

Net erosion ft per yr 0. 019 

Mass-movement pins, SWT:

Pins_________ - 15 

Years______ 5 

Net erosion ft per yr_____ 0. 025

Iron pins, SWT:

Pins_________ . 19 

Years_____ 6 

Net erosion ft per yr 0. 007 

Chain section pins, on banks, SWT :

Pins . 8 

Years____ 6 

Net erosion ft per yr 0. Oil 

Gully erosion:

Coyote headcut:

Years________ 3

Retreat (ft peryr) :

Laterally_______ - 0. 4 

Headward_______________- 2. 6 

Volume of material eroded cu ft per yr__ 1, 650 

Fence line headcut:

Years_____________ 4 

Retreat (ft peryr) :

Laterally______________ - 0.15 

Headward__ 1- 5 

Volume of material eroded cu ft per yr_ 500 

Mass movement (soil creep) : 

Slopewash Tributary:

Pins________ 15 

Years________ . -- 5 

Downhill movement at ground surface in. 

per yr_________ 0.205

Volume of material moved cu ft per mile of

slope base per yr 32 

Coyote C. Basin:

Pins______ - 12

Years __ 3 

Downhill movement at ground surface in.

per yr_ 0. 202 

Volume of material moved cu ft per mile

of slope base per yr 25 

Movement of individual rocks: 

Morning Walk Tributary: 

South gully and rill:

Rocks_ 99 

Years_ 3 

Rocks moved percent 75 

Average distance moved ft per yr 190
238 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

TABLE 8. Data on measured rates of erosion and deposition 

Continued

Erosion Continued

Movement of individual rocks Continued 

Morning Walk Tributary Continued 

North Gully:

Rocks_______.______________

Years_______.._______________

Rocks moved percent_____________

Average distance moved ft per yr_ 

Gunshot Arroyo:

Rocks______________________. 

Years ___________________.

Rocks moved percent___________. 

Average distance moved ft per yr____. 

Green Rock Gulch:

Rocks___________.__________. 

Years_____________________________

Rocks moved percent__________. 

Average distance moved ft per yr___. 

Little Green Rock Gulch :

Rocks______________________. 

Years ____________________. 

Rocks moved percent___________. 

Average distance moved ft per yr____

Deposition

Aggradation of channels: 

Slopewash Tributary: 

Nail section:

Number of chains, pins or sections_______

Yearn_______________________

Average net aggradation ft per yr_____

Pins at chain section :

Number of chains, pins, or sections______

Years____________________________

Average net aggradation ft per yr______

Arroyo Frijoles, mainstem: including North 

Branch:

Number of chains, pins, or sections_________

Years__________..____________________

Average net aggradation ft per yr_________

Coyote C. Arroyo:

Number of chains, pins, or sections__________

Years____________ .________________

Average net aggradation ft per yr________

Gunshot Arroyo:

Number of chains, pins, or sections__________

Years____________________________

Average net aggradation ft per yr________

Filling of small reservoirs: 

Coyote C. Arroyo Dam :

Drainage area sq mile____________________

Years_____________________________________

Volume deposition cu ft___________________

Sediment collected ton per sq mile per yr___ 

Big Sweat Dam:

Drainage area sq mile________________

Years________________._____________

Volume deposition cu ft__________________

Sediment collected ton per sq mile per yr___

67

3

67

4

100

93

250

5

23

59

40

5

32

1

10

5

0.033

0.003

90

6

0.040

3

0.100

3

2

0.060

0.064

3

6,245

1,633

0.0060

1.2

95.3

660

applied to the number of headcuts per square mile estimated from detailed knowledge of the area.

Mass-movement pins are installed on sloping gully 

walls which are steeper than the hillslopes in general. 

Though when the measurements were begun we had not 

expected downhill creep to be of significance in a semiarid climate, our observations and those of others (for

TABLE 9. Average rates of erosion and deposition

Erosion 

Surface erosion:

Average rate ft. per yr 0. 015

Percentage of total basin contributing 65 

Erosion rate tons per sq mi per yr 13, 600

Gully erosion:

Average volume per headcut cu ft per yr 1, 000 

Headcuts per sq mi____ _ 4 

Erosion rate tons per sq mi per yr 200

Mass movement:

Average downhill rate at ground surface in. 

per yr_____________________________ 0. 20

Length of channel affected mi per sq mi _ 35. 6 

Average volume eroded cu ft per sq mi per yr 1, 960 

Total volume tons per sq mi per yr _ 98

Total erosion tons per sq mi per yr__ 13, 900

Deposition

Aggradation of channels:

Channel area sq ft per sq mi__ .

Average rate of deposition ft per yr.

Deposition tons per sq mi per yr____ 

Collected in dams tons per sq mi per yr_. 

Total deposition tons per sq mi per yr___.

579X10*

0.05

1,440

1,663

3,073

summary see Leopold and others, 1964, p. 349-353) indicate that it is a process which cannot be disregarded. 

Mass wasting should deliver debris to the rills and channels in proportion to the rate of downhill creep and to 

the total length of channel in a given area. A drainage 

density was computed by using a Horton analysis of the 

number and lengths of channels. In a square mile the 

order of the largest channel including rills is seven. The 

number and lengths of various orders are as follows:

Order

7__ 

6. _ 

5_ - 

4 - --

3

2. -

!__-_ -----------

Total ------

Number

1 

3.5 

11

45 

140 

400 

1,200

Length 

(miles)

1.2 

.70 

.22 

.11 

.05 

.02S 

.01

Adjustment to channel segments

Length 

(mile)

0.50 

.48 

.11 

.06 

.027 

.013 

.01

Number

1 

4.5 

14.5 

56 

185 

540 

1,600

Number 

X length 

(miles)

0.5 

2.2 

1.6 

3.3 

5.0 

7.0 

16.0

35.6

By this estimate there are about 35 miles of channel and rill in a square mile area, and because there are 

two banks of a channel, the length of channel boundary 

possibly subject to debris production by creep is some 

70 miles. Using an average of 28 cu ft per mile of slopebase per year,

28 X 70=1,960 cu ft per yr per sq mi, 

which at 100 Ibs per cu ft is 98 tons per sq mi per yr.

Movement of individual rocks was not included as a 

separate item of contribution to sediment production.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 239

Depositional data consisted of channel aggradation 

which was computed into tons per square mile as follows:

Order

7---. 

6----. -- -----

5- - - 

4

3--- - -- -- 

2

1... ....

Total 

Segment 

length 

(miles)

0.5

2.2

1.6

3.3

5.0

7.0

16.0

Width 

(ft)

28

16

8

3.5

2.5

1.3

.9

Channel 

area (sq ft)

75,000

186, 000

67, 000

61, 000

66, 000

48, 000

76, 000

579, 000

Then 579 X103 sq ft of channel area aggrading at 0.05 ft 

per yr is 28,900 cu ft; at 100 pounds it equals 1,440 tons 

per sq mi per yr.

The collection of sediment behind the dam in Coyote 

C. Arroyo gave a figure of 1,633 tons per sq mi per yr. 

The production and trapping of sediment may be summarized as follows:

Surface erosion- - 

Gully erosion._ 

Mass movement.

TotaL--__.

Total sediment Sediment

(tons per sq production

mi per yr) (percent)

13, 600 97. 8

200 1.4

98 .7

13,900 100±

Deposition in channelsTrapped in reservoir.-_

1,440

1,633

10

12

Total. 3,073 22 ±

By far the largest contribution of sediment is by sheet 

erosion. Channel deposition is only about half of the 

total sediment trapped, the latter being only about one-' 

quarter of that produced. It is recognized that if the 

budget were correct and the reservoir trap efficiency 

were 100 percent, the total of deposition in channels and 

trapped in the reservoir would equal sediment production. It is our opinion that the sediment moved as 

sheet erosion does not all get into the channel, but is 

temporarily stored in thin deposits widely dispersed 

over the colluvial area, and that furthermore, there is 

a very low trap efficiency to the reservoir.

Other measurements of sediment accumulation in 

western United States give values of 1,200 to 2,400 tons 

per sq mi per yr (Brown, 1945).

To our knowledge, of the published reports on sediment yield from semiarid drainage basins, by far the 

most excellent is that of Hadley and Schumm (1961), 

who measured, among other things, sediment accumulation in a large number of stock ponds and small reservoirs. These data were studied in relation to geologic formation, runoff, and various geomorphic characteristics of basins. Their data are far more comprehensive than ours insofar as sediment accumulation in 

reservoirs is concerned. The only unique feature of 

the present data is that we attempt to assess the relative 

importance of different processes of sediment production.

Despite their deficiencies, our data bear comparison 

with the more extensive values published by Hadley 

and Schumm, as in the following:

Sediment accumulation:

Coyote C. Arroyo (0.064 sq mi) accumulation in reservoir and channel.---_--__-_----------------

Average curve for all lithologies, for 

0.06 sq mi area (Hadley and 

Schumm) _____________________

Based on 100 Ibs per cu ft.

Acre ft per

sq mi per

yr

1.41

Tons per

sq mi pr

yr 1

3,073

3,930

For small basins the sediment accumulation observed 

by us in New Mexico is of the same order of magnitude 

as in basins of similar size in Wyoming underlain by 

shale or other lithologies high in silt content. Hadley 

and Schumm (fig. 30, p. 173) showed that for the Cheyenne Basin sediment accumulation was related to relief ratio (basin relief divided by basin length). The 

average relief ratio for our Coyote C. and Slopewash 

tributaries is 0.59. Entering this value in the HadleySchumm curve for all lithologies, the estimated value 

of sediment accumulation is 2.4 acre ft per sq mi per 

yr, and in the curve of those authors applicable to Fort 

Union formation only, the value is about 2.5. These 

values are slightly higher than the 1.41 observed in 

Coyote C. Arroyo but still of the right order of magnitude.

The finding of Hadley and Schumm (fig. 26, p. 163) 

that sediment accumulation per unit area of basin decreases rapidly with increasing drainage area is in keeping with our result that sheet erosion basin-wide estimated from erosion pins gives a value of sediment production about 4.5 times larger than can be accounted 

for in channel aggradation and reservoir accumulation. 

This feature is probably related in part to the same 

cause postulated by those authors: absorption of water 

in the dry channel beds below areas affected by local 

storms. But the fact remains that even in our detailed 

study of deposition, sediment spread thinly over colluvial areas does not show up in measurement data.

Another interesting comparison is with data on sediment production by dry sliding of debris on the steep
240 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

slopes of southern California. Kramnies (1960) measured debris in metal troughs laid on contour in burned 

and unburned areas in San Dimas Experimental Forest 

near Glendora. He found a sediment yield of 24.7 tons 

per acre per year (15,800 tons per sq mi per yr) after 

a brush fire, which compared with 2.69 (1,720 tons per 

sq mi per yr) before the fire had denuded the slopes. 

Of the total annual yield 89 percent of the debris was 

contributed during nonrain periods by dry sliding. The 

figure for prefire condition is about half the sediment 

yield observed by us in New Mexico, but the postfire 

figure is five times larger than our value.

Returning to the question posed earlier in this report, 

it appears that in semiarid areas of the type studied 

sheet erosion not only predominates as a sediment source 

but also seems quite capable of providing the sediment 

making up the bulk of alluvial fills during periods of 

aggradation. Indeed, the present channels are aggrading, and at 0.05 ft per yr the observed rate would eventuate in a fill as deep as the Coyote alluvium under the 

high terrace in 100-200 years. No doubt such a rate 

would not be sustained as an average for so long a period 

because in a century there would be some years, no 

doubt, during which net degradation would occur.

Nonetheless, the present processes and their rates appear quite capable of resulting in deposition of alluvial 

fills comparable to those of past periods which filled 

major valleys. The present is, then, a reasonable picture of conditions during which valley aggradation 

occurred in post-Pleistocene time.

The importance of sheet erosion makes it quite possible that aggradation can occur in tributaries, even in 

small channels only a few hundred feet from the'watershed divide. Gully or rill erosion was probably insignificant or absent during the deposition of the principal 

alluvial fills in these valleys. Gully erosion assumes its 

important role during periods of valley trenching or 

arroyo cutting as was observed in the post-1880 period.

CLIMATOLOGICAL OBSERVATIONS DURING 

AGGRADATION

From the archeologic materials and a C14 date, it is 

computed that the upper part of the Tesuque formation 

accumulated in the Tesuque Valley, a few miles from 

our study area, at an average rate of 104-156 yr per ft 

(Miller and Wendorf, 1958, p. 190). During the period 

1958-64 we observed an average rate of channel bed 

change that would result in aggradation at the rate of 

about 25 yr per ft. The present landscape is similar to 

that under conditions which probably prevailed in the 

same area, let us say, in the first centuries of the Christian era. But the land at present has hardly begun to 

recover from widespread devastation of the overgrazing

in the late 19th century. The combination of a grazed 

range and the present climatic swing provides comparable rainfall-runoff conditions to those caused by a somewhat more unfavorable climate but uncomplicated by 

the effects of grazing animals.

What are the salient aspects of climate in relation to 

vegetation which create the difference between a period 

of aggradation and one of degradation in valleys ? This 

question has merited the attention of many geomorphologists and has been answered tentatively in a variety of 

ways. Considerable evidence points to a coincidence 

of increasing aridity with degradation and increasing 

humidity with aggradation, but there are opposite 

views. Reaching a firm conclusion will have to await 

continuation of just the kinds of observations being here 

reported. Because we cannot hope to obtain a definitive 

answer to the question with 7 years of measurement, we 

are publishing our results principally to encourage 

others to join us in similar programs of simple measurement over a period of time in order that there will gradually become available concurrent data on rate of channel change, precipitation, and runoff.

The precipitation record for Santa Fe, N. Mex., is the 

longest in the United States. This record has been 

analysed in detail for its relation to the erosion problem 

(Leopold, 1951) and even then, 14 years ago, the difficulty of analysis lay not in the length of the precipitation record but in the lack of quantitative data on land 

erosion and channel changes. Our measurement data 

are not yet enough, but the nature of the problem can 

be more clearly seen than was possible without them, as 

will now be explained.

Leopold (1951) showed that the mean annual precipitation at Santa Fe did not significantly change between the first and second half of the century of record, 

but the frequency of daily rainfall amounts did change. 

In the present discussion we will review briefly that 

argument and bring the analysis up to date of the present writing, 1964.

Three graphs are presented in figure 171. Graph A, 

the annual march of yearly precipitation totals, is 

plotted without any averaging. Graphs B and O show 

that part of the annual amounts contributed in summer 

(July-Sept, incl.) months. The mean summer total of 

6.06 inches consists mostly of thunderstorm rainfall 

which each season begins about July 15 after a relatively dry late spring and early summer. Thunderstorms are nearly daily occurrences in the nearby mountains from mid-July to early September. Graph O 

shows that part of the summer rainfall made up by rains 

totalling one inch or more in a day.

In the three parts of figure 171, trends in the 114 

years are not easily discernible without the use of mov-
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 241

A. INDIVIDUAL YEARLY RAINFALL

Mean annual rainfall. Long-term 

average= 13.72 inches

B. INDIVIDUAL' SUMMER 

RAINFALL

C. INDIVIDUAL SUMMER RAINFALL FROM RAINS EQUAL 

TO OR GREATER THAN 1.00 INCH PER DAY

Mean annual rainfall. Long-term 

average=6.06 inches

YEAR 

FIGURE 171. Precipitation, Santa Fe, N. Mex.

ing averages. Inspection of the graphs reveals the dry 

period of the 1940's and early 1950's and the heavy 

summer rainfalls of the early 1850's.

Figures 172 and 17o break the precipitation record 

into its summer and nonsummer components, and then

again into the number of rains of different categories of 

size of daily rainfalls. The secular change in number 

of nonsummer rains of less than 0.5 inch in a day so 

prominent in Leopold's analysis is obvious here, figure 

A more subdued but parallel trend is seen also

50

40

75 30

20

10

i i i r

A. TOTAL NUMBER OF RAINY DAYS

B. RAINS, INTENSITY 0.01-0.49 INCH PER DAY

C. RAINS, INTENSITY 0.49-0.99 INCH PER DAY

D. RAINS, INTENSITY EQUAL TO OR GREATER THAN 1.00 INCH PER DAY

YEAR

FIGUEB 172. Number of individual summer rains (July-Sept, incl.), Santa Fe, N. Mex.
242 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

40 I I T 

A. TOTAL NUMBER OF RAINY DAYS

30

20

10

B. RAINS, INTENSITY 0.01-0.49 INCH PER DAY

C. RAINS, INTENSITY 0.50-0.99 INCH PER DAY

£vj£j<__h£> y'-'\_w.v\-v

D. RAINS, INTENSITY EQUAL TO OR GREATER THAN 1.00 INCH PER DAY

YEAR

FIOUBB 173. (Number of individual nonsummer rains, Santa Fe, N. Mex.

in the number of summer rains less than 0.5 inch per 

day. These secular changes leave the general impression 

that the last 25 years were more similar to the first 

25 years of record than to the middle of the record 

period; that is, 1942-57 seems to resemble 1853-72.

This impression is strengthened by examination of 

figure 174 which shows the annual march of the average 

intensity of rain expressed as inches per day per rainy 

day, that is, the number of inches of rain in a year divided by the number of rainy days that year. The rains 

of the early and final part of the record were more intense than during the middle of the record.

Similar analysis led Leopold (1951) to argue that the 

period coincident with the advent of heaviest grazing, 

1850-80, was characterized by a deficiency of the lowintensity rains which succor vegetation and by more 

than the average number of heavy rains which could 

act upon a weakened vegetal cover and promote erosion. 

This argument is a reasonable one, but to demonstrate

its validity one needs concurrent and detailed data on 

erosion rates. Such concurrent data are now available 

for the 7-year period 1958-64, but this period includes 

years of both high and low intensity rainfall. The precipitation data are not clearly of the character that one 

could say unequivocally that erosion should be large or 

should be small. In short, the 7-year record is not long 

enough.

But the nature of the question ought to be clear from 

the data presented. Geomorphologists must make 

quantitative observations of erosion rates and channel 

changes over a long enough period to be clearly related 

to the concurrent precipitation record.

It is our hope that the presentation even of the short 

record now available will spur our colleagues to establish similar areas and continue simple measurements 

over a period of time so that those who follow us will 

have more to work with in analysis of this hydrologic 

and geomorphic problem.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 243

0.40

0.30

o

- 0.20

0.10

Long-term average=0.183 inch

YEAR

FIGURE 174. Average annual intensity of rainfall, Santa Fe, N. Mex.

REFERENCES

Bagnold, R. A., 1956, The flow of cohesionless grains in fluids:

Royal Soc. [London] Philos. Trans., ser., A no. 964, v. 249, p.

235-297.

Brown, C. B., 1945, Rates of sediment production in Southwestern United States: U.S. Soil Conserv. Service, SCSTP-65, 40 p. 

Emmett, W. W., and Leopold, L. B., 1964, Downstream Pattern

of River-Bed Scour and Fill: Proc., Federal Inter-Agency

Conf. on Sedimentation, Jackson, Miss. 

Hadley, R. F., and Schumm, S. A., 1961, Hydrology of the upper

Cheyenne River Basin: U.S. Geol. Survey Water-Supply

Paper 1531-B, 198 p. 

Krammes, J. S., 1960, Erosion from mountain side slopes after

fire in southern California: U.S. Forest Service, Pacific S.

W. Forest and Range Expt. Sta., Research Note 171. 

Leopold, L. B., 1951, Rainfall frequency, an aspect of climatic

variation: Am. Geophys. Union Trans., v. 32, no. 3, p. 347-

357.

Leopold, L. B., and Miller, J. P., 1954, A post-glacial chronology 

for some alluvial valleys in Wyoming: U.S. Geol. Survey 

Water-Supply Paper 1261 89 p.

 1956 Ephemeral streams hydraulic factors and their 

relation to the drainage net: U.S. Geol. Survey Prof. Paper 

282-A, 37 p.

Leopold, L. B., Wolman, M. G., and Miller, J. P. 1964, Fluvial 

processes in geomorphology: San Francisco, W. H. Freeman 

Co., 522 p.

Miller, J. P., and Wendorf, F., 1958, Alluvial chronology of the 

Tesuque Valley, New Mexico: Jour. Geol., v. 66, no. 2, p. 

177-194.

Miller, J. P., Montgomery A., and Sutherland, P. K., 1963, Geology of part of the Southern Sangre de Cristo Mountains, 

New Mexico: New Mex. Inst. of Mining and Tech. Mem. 

11, 106 p.

Wolman, M. G., 1955, The natural channel of Brandywine Creek, 

Pennsylvania: U.S. Geol. Survey Prof. Paper 271, 56 p.

SUMMARY OF DATA

CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 247

A. Summary of nonrecorded rain-gage data, Arroyo de los Frijoles, 1959-6S 

[Date of observation may be several days after storm date. Record should not be considered as annual precipitation. Tr., trace amount. Gage locations shown on fig. 143]

Date of observation

8-07-59 

8 19-59

8-24-59. 

in_of\_cQ

7 i Ei-fin

0 (\K Cf\

10-17-60 

5-23-61 -

6-16-61 

6-29-61... 

7 Ifl fil

8-14-61- _- --- - -- 

ft 1Q_fi1

7-02-62.- - 

7 nO A9

T 97_fi9

8-01-62 

6-13-63 

6-17-63 

7 1rt_A^

7-22-63 

8-27-63 

9-23-63

Precipitation, in inches, at rain-gage1

0.80 

.25 

.50 

1.00

.76 

.50 

.20 

1.30

.00 

.20 

.00 

.10 

.60 

1.00 

1.10 

1.20

.20

.40 

.79

.20 

Tr. 

1.00 

.15 

1.30

2

1.13

.25 

.58

.70 

.00 

1.00 

2.70

.00 

.20 

.40 

.20 

.10 

1.20 

1.10 

.88

.20 

.50 

2.00 

.90

.35

.00 

.20 

1.30

3

0.80

.50 

1.45

.85 

.80 

.80 

2.40

.00 

.40 

.00 

.40 

.80 

1.30 

1.15 

1.40

.70 

.35 

.50 

1.10

1.20

.02 

.75 

.20 

1.40

4

0.80

.35 

1.40

.80 

.65

1.90

.00 

.30 

.00 

.30 

.90 

1.00 

1.10 

.95

1.30 

.50

.90 

.40 

Tr. 

.50 

.40 

1.10

5

0.88

.32

.85 

.35 

.75 

2.20

.00 

.20 

.00 

.50 

.40 

1.10 

.90 

.87

1.20 

.30 

.60

.20 

.40 

Tr. 

.30 

.30 

1.00

6

1.05

.36 

1.40

.80 

Tr. 

.50 

2.30

.00 

.20 

.20 

.40 

.60 

1.00 

1.00 

1.00

.20 

.80 

.00

.75 

.60 

.00 

.35 

.30 

1.10

7

0.80

1.38

.90 

Tr. 

.65 

2.20

Tr. 

.20 

Tr. 

.50 

.60 

1.30 

.80 

.82

.20 

.60 

.60

.80 

.75 

Tr. 

.20 

.35 

1.30

8

1.20

.90 

Tr. 

.45 

2.30

.10 

.20 

.20 

.50 

.80 

1.20 

.80 

1.00

.30 

.70 

.50

.72 

.75 

Tr. 

.10 

.40 

1.30

9

1.20 

.20

.30

1.05 

.00 

.25 

2.40

.30 

.20 

.10 

.30 

.90 

1.30 

.96 

.79

.20 

1.00 

.20

.71 

.60 

Tr. 

.00 

.20 

1.20

10

0.80

1.32

.94 

.00 

1.10 

2.50

.10 

.30 

.20 

.10 

.60 

1.40 

1.10 

.89

1.10 

.00

.55 

.55 

Tr. 

.00 

.25 

1.30

11

1.00

.48 

1.30

1.10 

.00 

.35 

2.50

.20 

.20 

Tr. 

Tr. 

.60 

1.20 

.85 

.75

.40 

.90 

.00

.50 

.55 

Tr. 

.00 

.20 

1.10

12

1.06 

.30 

.65 

1.26

1.10 

1.02 

.81 

1.89

.51 

.16 

.87 

1.33 

1.13 

1.35

.90 

1.09 

1.50 

.00

.67 

.35 

.20 

.07 

.40 

1.67

B.- -Summary of recording rain-gage data, Arroyo de los 

Frijoles, 1959-62

[Date of observation is within several days of major precipitation, but total precipitation includes also that between observations. Records should not be considered 

complete for use as annual precipitation. Gage located at Main Project Reach; see 

fig. 143]

Date of observation 

8-07-59__. ______

8-20-59.. _ _ -.

8-24-59. _______

8-26-59 ____ __

10-02-59 _ _ _. ._

10-30-59. - 

11-13-59... ______

12-17-59 . 

1-21-60 

2-29-60 _ _ __ -

5-18-60 _ ___ ._

6-10-60... _..._.

7-15-60 - .-

8-05-60 ____ .-

8-23-60 _ ___..-

10-07-60 _ --__-.

10-17-60. 

12-12-60.- -_....

1-12-61. ...._...

4-03-61- ______ -

4-18-61.. ______

6-16-61... -.__..

6-19-61 _ __

6-29-61 _ .____.

Precipitation 

(inches)

____ 1.06

_.__ .26

_.._ .80

..__ .23

--__ .08

____ 1.50

.___ .50

____ .01

- _ .50

---_ .50

____ .00

_ _ 1.10

__-_ 1.20

__._ .81

..-_ .25

__-_ .70

__ . 1.89

.___ .60

__._ .10

_.-. 1.30

_.. _ .38

20

___. .60

-___ .30

Date of observation 

7-08-61- _ ______

7-28-61 _ _. __

8-13-61 

8-15-61 _________

8-23-61 _ ..-__

9-12-61 

9-19-61 ___ _..

 9-20-61. 

10-27-61 _______

12-06-61 -

1-16-62 _ ______

3-09-62 _ . .

3-26-62 _ ______

5-01-62... ._ _ .. -

6-11-62 

6-30-62... ______

7-02-62- ____ .

7-09-62.. .. .__.-

7-23-62 .

7-26-62._. __ .

7-30-62 - .

8-02-62. _ _ _ .

8-28-62. __ _ . .

9-17-62.- .--.

11-26-62. _

Precipitation 

(inches)

____ .60

____ .31

__ ._ 1.33

.10

 1.13

____ .70

__ ._ .80

--_. .10

 __ .70

__._ .10

___. .30

___. .20

____ .20

____ .10

____ .10

_.__ 1.10

____ .00

_. _. 1.09

.. _. .70

... _ 1.50

.00

__ __ .00

__.. .20

____ .50

.. .30
248 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

C. Summary of data, erosion-pin plot in Slopewash Tributary, 1959-64 

[Minus values in the net change columns represent deposition rather than erosion]

Pin

1........ _ ............................

2 

3

4 

5

6. ---- ----- --- ----- ---------

7 

8 

9 

10

11 

12 

13..-. ---------------

14 

15

16

17 

18 

19.-. . -. ----------------

20 

21.. -------------------

22.- -- ----- ------------

23. 

24 

25.. -------------------------

26.----.----- ---------------

27 

28 ----------------------

29 

30

31 

32 

33

34.- .......... .. .....-... ......

35 

36. ....... . 

37. - -- ----------

38 

39

40 -. -----

41 

42 . 

43

44

45-.- 

46 

47 --------------------

48

49 - .--...-

50 

51 -. ..- -------------

52 

53 

54.-- - . - -------

55 --------------- ----------

56 

57... ----------------------------

58-. -----------------------------

59.- ---------------------------

60 - --

61

1959-61

Erosion (ft)

0.02 

.01 

.01 

.04 

.03

.02 

.02 

.02 

.02 

.02

.04 

.01 

.03 

.02 

.03

.01 

.01 

.02 

.02 

.02

.03 

.03 

.02 

.02 

.03

.05 

.01 

.01 

.01 

.02

.01 

.02 

.01 

.02 

.02

.01 

.01 

.01 

.02 

.03

.02 

.02 

.03 

.04 

.01

.01 

.01 

.07 

.04 

.03

.03 

.03 

.02 

.01 

.01

.02 

.04 

.02 

.01 

.01

.02

1959-62

Erosion (ft)

0.00 

.03 

.00 

.05 

.06

.04 

.04 

.03 

.03 

.03

.13 

.00 

.05 

.03 

.05

.03 

.02 

.02 

.03 

.04

.05 

.05 

.06 

.03 

.04

.06 

.02 

.02 

.03 

.03

.03 

.00 

.00 

.04 

.03

.01 

.02 

.02 

.04 

.05

.00 

.04 

.02 

.07 

.02

.03 

.03 

.10 

.05 

.05

.04 

.03 

.07 

.02 

.02

.03 

.07 

.04 

.04 

.00

.03

Deposition 

(ft)

0.01 

.00 

.01 

.01 

.00

.03 

.00 

.00 

.03 

.00

.11 

.00 

.02 

.00 

.00

.00 

.00 

.00 

.00 

.02

.00 

.00 

.00 

.04 

.03

.00 

.00 

.00 

.00 

.00

.01 

.01 

.04 

.02 

.00

.00 

.00 

.00 

.00 

.05

.02 

.00 

.00 

.00 

.02

.00 

.00 

.07 

.00 

.00

.00 

.03 

.00 

.00 

.00

.00 

.07 

.00 

.00 

.00

.02

1959-63

Erosion (ft)

0.04 

.03 

.02 

.05 

.05

.04 

.04 

.04 

.035 

.025

.11 

.015 

.045 

.03 

.05

.02 

.02 

.02 

.03 

.03

.05 

.05 

.075 

.03 

.04

.09 

.02 

.02 

.03 

.03

.04 

.02 

.00 

.035 

.02

.02 

.02 

.02 

.04 

.05

.03 

.06 

.03 

.08 

.02

.02 

.03 

.11 

.05 

.05

.035 

.04 

.10 

.02 

.02

.03 

.06 

.03 

.03 

.02

.035

Deposition

(ft)

0.04 

.03 

.02 

.00 

.00

.01 

.04 

.01 

.04 

.00

.11 

.00 

.03 

.02 

.00

.01 

.00 

.01 

.00 

.01

.00 

.01 

.00 

.03 

.00

.00 

.00 

.00 

.00 

.00

.01 

.02 

.07 

.035 

.01

.00 

.00 

.00 

.00 

.03

.03

.01 

.00 

.00 

.02

.00 

.00 

.07 

.01 

.00

.00 

.01 

.00 

.00 

.00

.01 

.03 

.01 

.00 

.06

.00

1959-64

Erosion (ft)

0.015 

.025 

.010 

.040 

.045

.040 

.010 

.030 

.010 

.045

.020 

.020 

.020 

.025 

.125

.035 

.020 

.015 

.030 

.025

.050 

.055 

.115 

.020 

.145

.130 

.025 

.030 

.045 

.050

.035 

.035

.025 

.015

.025 

.035 

.040 

.065 

.040

.030 

.075 

.050 

.080 

.015

.025 

.030 

.065 

.055 

.055

.035 

.030 

.175 

.025 

.025

.040 

.055 

.020 

.035 

.010

.035

Deposition 

(ft)

0.020 

.005 

.005 

.000 

.000

.005 

.025 

.000 

.040 

.000

.025 

.000 

.005 

.000 

.000

.000 

.005 

.000 

.005 

.005

.005 

.000 

.000 

.000 

.000

.000 

.005 

.005 

.005 

.000

.000 

.000

.000 

.000

.ooc 

.ooc

.000 

.000 

.005

.035 

.005 

.000 

.000 

.020

.000 

.000 

.005 

.005 

.000

.005 

.000 

.000 

.005 

.000

.000 

.005 

.005 

.005 

.035

.000

Net change 1959-64

Total (ft)

-0.005 

.020 

.005 

.040 

.045

.035 

-.015 

.030 

.030 

.045

-.005 

.020 

.015 

.025 

.125

.035 

.015 

.015 

.025 

.020

.045 

.055 

.115 

.020 

.145

.130 

.020 

.025 

.040 

.050

.035 

.035

.025 

.015

.025 

.035 

.040 

.065 

.035

-.005 

.070 

.050 

.080 

-.005

.025 

.030 

.060 

.050 

.050

.030 

.030 

.175 

.020 

.025

.040 

.050 

.015 

.030 

-.025

.035

Yearly 

average 

(ft per yr)

-0.001 

.004 

.001 

.008 

.009

.007 

-.003 

.006 

.006 

.009

-.001 

.004 

.003 

.005 

.025

.007 

.003 

.003 

.005 

.004

.009 

.011 

.023 

.004 

.029

.026 

.004 

.005 

.008 

.010

.007 

.007

.005 

.003

.005 

.007 

.008 

.013 

.007

-.001 

.014 

.010 

.018 

-.001

.005 

.006 

.012 

.010 

.010

.006 

.006 

.035 

.004 

.005

.008 

.010 

.003 

.006 

-.005

.007

Summary

Average erosion, 0.0117 ft per yr. 

Average deposition, 0.0041 ft per yr. 

Net average erosion, 0.0076 ft per yr.
CHANNEL AND HILLSLOPE PROCESSES, SEMIARID AREA, NEW MEXICO 249

D. Summary of data, slope-retreat pins in Slopewash Tributary, 1959-64

(Minus values in the net change columns represent deposition rather than erosion]

Pin

4.-.. ............. ..

5 

6... . ----------

7.-. ----------------

8- . -----------

9 

10 -------------

11. 

12. ... ------------

13 

14 

15--..- -------

16 . -------

17 --- -------

18- - ---------

19 

20 

21 

22. 

23.-- - --- --

25 - -- --

26 

28. -------------

9Q

30 

31.-- 

32

33--- ---------

34 

35- -

36.---..- -------

37 

38 

39 

40.-. --------------

41 - 

42--... --------

43- ---------

44 --------------

45 

46-. -------------

47. ----------------

48 -----------

49. ----------------

50. . ----------------

51 --------------

52 

53... ---------------

54. 

55 -------------

56.-. ------

57

1959-61

Erosion 

(ft)

0.01 

.06 

.05 

.04 

.07

.17 

.01 

.01 

.02 

.03

.03 

.02 

.01 

.04 

.00

.04 

.04 

.15

.29 

.08

.00 

.03 

.02 

.01 

.02

.04 

.03 

.02 

.03

.02 

.02 

.03 

.04 

.01

.02 

.02

.03 

.03

.02 

.01 

.00 

.01 

.01

Deposition

(ft)

0.00 

.00 

.00 

.00 

.00

.00 

.16 

.00 

.00 

.00

.00 

.03 

.00 

.00 

.00

.00 

.00 

.00

.00 

.00

.18 

.00 

.04 

.03 

.00

.00 

.00 

.00 

.00

.00 

.00 

.00 

.00 

.00

.00 

.00

.00 

.00

.00 

.00 

.00 

.00 

.00

1961-62

Erosion 

(ft)

0.03 

.04 

.03 

.06 

.04

.03 

.21 

.03 

.02 

.01

.01 

.08 

.02 

.02 

.02

.02 

.03 

.11

.13

.07

.22 

.03 

.06

.02

.01 

.02 

.02 

.01

.01 

.00 

.00

.00 

.01

.00 

.02 

.03 

.06 

.05

.11 

.05 

.03 

.04

.02 

.03 

.03 

.10 

.02

.10 

.09

Deposition

(ft)

0.00 

.00 

.00 

.00 

.00

.00 

.17 

.00 

.00 

.00

.00 

.07 

.00 

.00 

.00

.00 

.00 

.00

.00 

.00

.10 

.00 

.02

.00

.03 

.00 

.00 

.01

.04 

.09 

.01

.02 

.00

.01 

.05 

.06 

.04 

.00

.00 

.00 

.00 

.00

.00 

.00 

.00 

.05 

.01

.04 

.04

1962-63

Erosion 

(ft)

0.01 

.02 

.01 

.01 

.02

.02 

.03 

.00 

.09 

.04

.06 

.03 

.06 

.03 

.025

.015 

.035 

.03

.02 

.04

.03 

.03 

.04 

.04 

.05

.175 

.05 

.04 

.02

.01 

.01 

.02 

.01 

.00

.02 

.03

.02 

.04

.03 

.02 

.01 

.01 

; 02

.19 

.00 

.00 

.01 

.00

.02 

.08 

.07 

.01 

.01

.00 

.00

Deposition 

(ft)

0.01 

.01 

.03 

.01 

.01

.02

.06 

.01 

.01

.02 

.02

.025

.03

.02 

.04

.03

.04 

.04 

.05 

.05

.05

.07 

.09 

.07 

.02 

.02

.03

.02

.13

.11

.00 

.03 

.01 

.00 

.01

.04 

.04 

.03 

.00 

.02

.02 

.00 

.00 

.00 

.00

.15 

.02

1963-64

Erosion 

(ft)

0.025 

.03 

.035 

.015 

.015

.030 

.080 

.070 

.030 

.015

.040 

.015 

.005 

.005 

.020

.035 

.035 

.040

.020 

.025

.030 

.050 

.030 

.070 

.020

.035 

.035 

.000 

.020

.055 

.080 

.075 

.025 

.030

.030 

.015

.090 

.050

.030 

.050 

.080 

.040 

.030

.050 

.110 

.010 

.000 

.020

.000 

.090 

.070 

.030 

.070

.210 

.060

Deposition 

(ft)

0.000 

.000 

.015 

.000 

.000

.000 

.000 

.030 

.000 

.000

.000 

.000 

.000 

.000 

.015

.000 

.000 

.040

.020 

.025

.040 

.005 

.020 

.000 

.000

.000 

.005 

.040 

.000

.135 

.085 

.145 

.045 

.080

.005 

.000

.110 

.080

.000 

.000 

.000 

.000 

.000

.000 

.000 

.000 

.040 

.020

.010 

.000 

.000 

.000 

.000

.000 

.000

1959-64

Erosion 

(ft)

0.075 

.150 

.125 

.125 

.145

.250 

.330 

.110 

.160 

.095

.140 

.145 

.095 

.095 

.065

.110 

.140 

.330

.460 

.215

.280 

.140 

.150 

.120 

.110

.260 

.135 

.080 

.080

.085 

.110 

.135 

.075 

.040

.070 

.075

.140 

.120

.080 

.100 

.120 

.120 

.110

.140 

.220 

.060 

.040 

.060

.040 

.200 

.170 

.140 

.100

.310 

.150

Deposition 

(ft)

0.010 

.010 

.045 

.010 

.010

.020 

.330 

.090 

.010 

.010

.000 

.120 

.020 

.000 

.040

.000 

.000 

.070

.040 

.065

.350 

.045 

.120 

.080 

.050

.030 

.055 

.040 

.010

.205 

.175 

.255 

.155 

.110

.055 

.020

.240 

.190

.010 

.080 

.070 

.040 

.010

.040 

.040 

.030 

.040 

.040

.030 

.000 

.000 

.050 

.010

.190 

.060

Net change 1959-64

Total 

(ft)

0.065 

.140 

.080 

.115 

.135

.230

.000 

.020 

.150 

.080

.140 

.025 

.075 

.095 

.025

.110 

.140 

.260

.420 

.150

-.070 

.095 

.030 

.040 

.060

.230 

.080 

.040 

.070

-.120 

.065 

-.120 

-.080 

-.070

.015 

.055

 .100 

 .070

.070 

.020 

.050 

.080 

.100

.100 

.180 

.030 

.000 

.020

.010 

.200 

.170 

.090 

.090

.120 

.090

Yearly 

average

(ft per yr)

0.013 

.028 

.016 

.023 

.027

.046 

.000 

.004 

.030 

.016

.028' 

.005 

.015 

.019 

.005

.022 

.028 

.052

.084 

.030

-.014 

.019 

.006 

.008 

.012

.046 

.016 

.008 

.014

-.024 

-.013 

-.024 

-.016 

-.014

.003 

.011

-.020 

 .014

.014 

.004 

.010 

.016 

.020

.020 

.036 

.006 

.000 

.004

.002 

.040 

.034 

.018 

.018

.024 

.018

Pins 

1-29.. 

30-45.

Summary of erosion rates, in foot per year

Erosion

0.0326

.0197

Deposition

0.0116

.0231

Net erosion

0. 0210

.0034

Pins

46-57.

1-57..

Erosion Deposition

0. 0272 0.0089

.0281 .0139

Net erosion 

0.0183 

.0142