Effects of Roads and Well Pads on Erosion in the 

Largo Canyon Watershed, New Mexico, 2001–02

Scientific Investigations Report 2006–5039

Prepared in cooperation with the 

BUREAU OF LAND MANAGEMENT

U.S. Department of the Interior

U.S. Geological Survey
Effects of Roads and Well Pads on Upland 

Erosion in the Largo Canyon Watershed, 

New Mexico, 2001-02

By Anne Marie Matherne

U.S. Department of the Interior 

U.S. Geological Survey

Prepared in cooperation with the

BUREAU OF LAND MANAGEMENT

Scientific Investigations Report 2006–5039
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

For sale by U.S. Geological Survey, Information Services 

Box 25286, Denver Federal Center 

Denver, CO 80225

For more information about the USGS and its products: 

Telephone: 1-888-ASK-USGS 

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.

Suggested citation:

Matherne, A.M., 2006, Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 

2001-02: U.S. Geological Survey Scientific Investigations Report 2006-5039, 42 p.
 iii

Contents

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Previous Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Description of the Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Resource Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Roads and Well Pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Effects of Roads and Well Pads on Upland Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Erosion Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Road and Well-Pad Transects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Field Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Roads Parallel to Topographic Contour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Roads Across Topographic Contour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Well Pads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Processes of Upland Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figures

1-2. Maps showing:

1. Location of study area, study area features, and climatologic stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Road network in the Largo Canyon watershed and locations of the Harris and Palluche 

Canyon road- and pad-analysis areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

3A-3F. Orthophotos showing locations of sediment dams:

3A. In the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

3B. 1A, 1B, 2A–2D, 3A–3G, and 4A–4C, precipitation gage installed for study, and transects 2PN, 

2PS, 3PW, and 3PE, in the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

3C. 5A, 5B, and 6A–6C, precipitation gage installed for study, and transects 5PE, 5PW, 5RE, 5RW, 

6PE, and 6PW, in the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

3D. 7A–7D and transects 7PN and 7PS, in the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

3E. 8A–8C and drainage basin for dam 8A in the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3F. 9A–9H and corresponding drainage basins in the Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4A-4C. Orthophotos showing location of:

4A. Sediment dams, precipitation gage installed for study, and transects in the Palluche 

Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4B. Sediment dams 12A and 12B and transects 12 PN and 12PS in the Palluche Canyon area. . . . . . . . . . . . 13
iv 

4C. Sediment dams 13A and 13B and drainage basin for dam 13A in the Palluche Canyon area. . . . . . . . . . 14

5. Bar graph showing total monthly precipitation at the Farmington Agricultural Science Center,

Bloomfield 3 SE, Otis, and Lybrook National Weather Service cooperative climatological 

stations, March 2001–November 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6. Box plot showing average erosion rates for drainage areas located below roads, 

on hillslopes, or below well pads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7-17. Graphs showing:

7. Land-surface changes for transects (A) 5RE and (B) 5RW in the Harris Canyon area, June 28, 2001–

November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

8. Land-surface changes for transects (A) 17RL, (B) 17RM, and (C) 17RS in the Palluche Canyon area, 

June 28, 2001–November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

9. Land-surface changes for transects (A) 2PN and (B) 2PS, in the Harris Canyon area, June 28, 2001–

November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

10. Land-surface changes for transects (A) 5PE and (B) 5PW in the Harris Canyon area, June 28, 2001–

November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

11. Land-surface changes for transects (A) 6PE and (B) 6PW in the Harris Canyon area, June 28, 2001–

November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

12. Land-surface changes for transects (A) 16PE and (B) 16PW in the Palluche Canyon area, June 28, 

2001–November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

13. Land-surface changes for transects (A) 18PN and (B) 18PS in the Palluche Canyon area, June 28, 

2001–May 4, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

14. Land-surface changes for transects (A) 3PE and (B) 3PW in the Palluche Canyon area, June 28, 

2001–November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

15. Land-surface changes for transects (A) 7PN and (B) 7PS in the Harris Canyon area, June 28, 2001–

November 20, 2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

16. Land-surface changes for transects (A) 12PN and (B) 12PS in the Palluche Canyon area, June 28, 

2001–November 20, 2002.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

17. Land-surface changes for transects (A) 15PE and (B) 15PW in the Palluche Canyon area, June 28, 

2001–November 20, 2002. Location of site 15 shown in figure 4A. View is to the west. . . . . . . . 32

18-29. Photographs showing:

18. Truck on road above area of focused bank erosion, Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

19. Sediment dam 9D and weathered shale and siltstone in the drainage contributing area, Harris 

Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

20. Weathered shale and siltstone in drainage contributing areas of sediment dams 4B and 4C in the 

Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

21. Areas (indicated by arrows) where headcuts in the upslope road berm near sediment dams 8A 

and 8C have extended beyond the road berm and up the hillslope, Harris Canyon area. . . . . . 34

22. Color of sediment on road near sediment dam 1A indicating source of runoff as the weathered shale 

and siltstone, Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

23. Mud cracks as evidence of ponding and sediment deposition behind the road berm at site 4, in the 

Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

24. Sediment dam 3F installed at the downslope edge of a road on a pre-existing drainage in the Harris 

Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

25. Sediment dam 9A overwhelmed by high runoff and partially buried in transported sediment, in the 

Harris Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

26. Splay deposit, formed from sediment transported along across-contour road and subsequently 

eroded by runoff, forms the curved cut in berm of parallel-contour road, Harris 

Canyon area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

27. Sediment erosion from upslope pad berm near sediment dam 2C redeposited on the pad, 

partially burying oil and gas industry equipment, in Harris Canyon area. . . . . . . . . . . . . . . . . . . . . 39

28. Sediment dam 5A and headcuts eroded into downslope pad berm, Harris Canyon area. . . . . . . . . . . . . 40

29. Author standing in a channel cut by focused runoff near site 12 in the Palluche Canyon area. . . . . . . . . 40
 v

Tables

1. Sediment yield, drainage area, erosion rate, slope, land use, and landscape position of sediment 

dams and percentage of sand, silt, and clay of sediment trapped behind sediment dams. . . . . . . . . 16

2. Mean annual precipitation for the Farmington Agricultural Science Center, Bloomfield 3 SE, Otis, 

and Lybrook climatologic stations (2001-02) and the National Weather Service 30-year 

normal precipitation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3. Summary statistics for sediment-dam erosion rate data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4. Number of cuts in upslope and downslope road berms, for road parallel to contour. . . . . . . . . . . . . . . . . . 36

Conversion Factors and Datum

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

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer (hm2) 

is restricted to the measurement of small land or water areas.

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

miles per square mile (mi/mi2) 0.62150 kilometers per square kilometer (km/km2)

Flow rate

cubic foot per year (ft3/y) 0.02832 cubic meter per year (m3/y)

inch per hour (in/h) 0.0254 meter per hour (m/h)
Effects of Roads and Well Pads on Upland Erosion in the 

Largo Canyon Watershed, New Mexico, 2001-02

By Anne Marie Matherne

Abstract

Largo Canyon, located in the San Juan Basin of northwestern New Mexico, is one of the longest dry washes in the world. 

Oil and gas production in the San Juan Basin, which began in 

the 1940's, required the development of an extensive network of 

dirt roads to service the oil and gas wells in the Navajo Reservoir area. Presently, there are about eight wells per square mile, 

and the density of oil and gas wells is expected to increase. 

Potential environmental effects on landscape stability that may 

result from the additional roads and well pads have not been 

documented. In 2001, the U.S. Geological Survey began a study 

in cooperation with the Bureau of Land Management to evaluate the effects of roads and well pads associated with oil and gas 

operations on the erosion potential of Bureau of Land Management lands in the Largo Canyon watershed. 

The effects of roads and well pads on erosion were quantified by installing sediment dams (dams) and by surveying 

transects across roads and well pads. Data from 26 dams were 

used in the analysis. Dams were installed at 43 sites: 21 on hillsides upslope from roads or pads to measure erosion from hillslopes, 11 at the downslope edges of roads to measure erosion 

from roads, and 11 at the downslope edges of well pads to measure erosion from well pads. Pairs of survey transects were 

established at nine well pads and two road locations. 

Sediment-accumulation data for 26 dams, recorded at 17 

measurement intervals, indicate that average erosion rates at the 

dams significantly correlate to size of the contributing area. The 

average erosion rate normalized by drainage area was 0.001 

foot per year below roads, 0.003 foot per year on hillslopes, and 

0.011 foot per year below well pads. Results of a two-sample ttest indicate that there was no significant difference in average 

erosion rates for dams located on hillslopes and below roads, 

whereas average erosion rates were significantly greater for 

dams below well pads than for dams on hillslopes and dams 

below roads.

The average erosion rates estimated from the data collected during this study most likely represent minimum erosion 

rates. Sediment-accumulation data for measurement intervals 

and for dams that were breached during 2002, resulting from the 

large volume of runoff generated by high-intensity storms, were 

not used to compute erosion rates. For this reason, the higher 

range of erosion rates is underrepresented and the results of this 

study are biased toward the lower end of the range of erosion 

rates. 

Measurements along road transects generally indicate that 

sediment is eroded from the top of road berms and redeposited 

at the base of the berms and may be transported downslope 

along the road. Measurements along well-pad transects generally indicate that sediment eroded from hillslopes is transported 

over the surface of the well pad and down the well-pad edges. 

Based on field observations, roads aligned parallel to topographic contours facilitate erosional processes in two ways: (1) 

roads cut across and collect runoff from previously established 

drainages and (2) roads, where they are cut into hillsides or into 

the land surface, provide focal points for the initiation of erosion. Roads aligned across topographic contours can serve as 

conduits to channel runoff but do not constitute a large percentage of the road network.

Introduction

Largo Canyon, located in the San Juan Basin of northwestern New Mexico (fig. 1), is one of the longest dry washes in the 

world. The canyon cuts into the upper strata of the San Juan 

Basin, which consist of sandstone and shale of the Nacimiento 

and San Jose Formations of Tertiary age. Much of the land is 

under the jurisdiction of the Bureau of Land Management 

(BLM), and grazing and recreation are part of the multipurpose 

management strategy for the area. Oil and gas production in the 

San Juan Basin began in the 1940's. Oil and gas production 

increased in the early 1970's and the late 1980's, and an extensive network of dirt roads (fig. 2) was constructed to service the 

wells. Presently, there are approximately eight wells per square 

mile, and the density of oil and gas wells in the Navajo Reservoir area is expected to increase in the next few decades in a 

process known as infilling. The BLM Resource Management 

Plan (Bureau of Land Management, 2003) for the San Juan 

Basin estimates construction of an additional 805 miles of new 

roads over the next 20 years. The potential environmental 

effects on landscape stability that may result from the additional 

roads and well pads have not been documented. In 2001, the 

USGS began a study, in cooperation with the BLM to evaluate 

the effects of upland erosion in the Largo Canyon watershed.
2 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Farmington San Juan River

Navajo Reservoir

Largo Canyon

Palluche

Canyon

Crow Mesa Wildlife

Management Area

Study area

Continental Divide

NEW MEXICO

San Juan Basin

Continental Divide

Palluche Canyon area

(shown in fig. 4A)

Largo Canyon

watershed

EXPLANATION

National Weather Service

cooperative climatologic Lybrook station and name

Lybrook

Otis

Farmington

Agricultural

Science Center Bloomfield

3 SE

108o 00’ 37o

 00’

36o

 30’

36o

 00’

107o

 30’ 107o

 00’

32o

34o

36o

108o 104o 106o

Blanco

0 5 10 15 20

0 5 10 15 20

MILES

KILOMETERS

Harris Canyon area

(shown in fig. 3A)

Base from U.S. Geological Survey digital data, 1993, 1:100,000

Universal Transverse Mercator projection, zone 13

Figure 1. Location of study area, study area features, and climatologic stations.
Introduction 3

36° 20’

36° 40’

107° 40’ 107° 20’ 107° 00’

0 5 10 15 20

0 5 10 15 20

MILES

KILOMETERS

Harris Canyon road- Harris Canyon roadand pad-analysis area and pad-analysis area

Palluche Canyon road- Palluche Canyon roadand pad-analysis area and pad-analysis area

Largo Canyon Largo Canyon

Largo Canyon

watershed

Base from U.S. Geological Survey digital data, 1993, 1:100,000, and

U.S. Geological Survey Digital Orthophoto Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Palluche Palluche

Canyon

Figure 2. Road network in the Largo Canyon watershed and locations of the Harris and Palluche Canyon road- and pad-analysis 

areas.
4 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Purpose and Scope

This report presents the results of a 2-year study to evaluate the effects of roads and well pads associated with oil and gas 

operations on the erosion potential of BLM lands in the Largo 

Canyon watershed, New Mexico. Data are presented for sediment dams on hillslopes and downslope from roads and well 

pads and for surveyed transects across roads and well pads. 

Contributions to erosion from roads and well pads are compared 

to background contributions from the hillslopes. A conceptual 

model of the role of roads and well pads in erosion and sediment-transport processes in an arid landscape is presented.

Previous Investigations

Unsealed or unpaved roads and tracks have been found to 

be the dominant source of surface-runoff generation and transported sediment, on a per unit area basis, on both forested hillslopes and agricultural areas in humid temperate climates 

(Grayson and others, 1993; Croke and others, 1999; Motha and 

others, 2003 and 2004) and in the tropics (Dunne and Dietrich, 

1982; MacDonald and others, 1997; Anderson and MacDonald, 

1998; Ziegler and others, 2000). The infiltration capacity of 

compacted road surfaces is low compared to surrounding areas, 

and the potential for generation of surface runoff and transported sediment from roads is correspondingly higher. 

Although unpaved roads are the primary source areas for erosion-producing surface runoff in response to frequent, lowmagnitude rainfall, surface runoff from agricultural and forested areas becomes a more substantial source of runoff for 

high-intensity or long-duration events because of the larger 

areal extent of forested and agricultural areas compared to road 

surfaces (Ziegler and Giambelluca, 1997). In both Australia 

(Motha and others, 2003) and Thailand (Ziegler and others, 

2000), sediment available for erosion and transport by surface 

runoff was correlated to the disturbance of surface sediment by 

vehicular traffic. On steep, forested hillslopes in Idaho (Megahan, 1974; Megahan and others, 2001), erosion and sediment 

transport are focused on the road prism (cutbank, road surface, 

and fill bank). Erosion rates are highest in the first year after 

road construction and decline thereafter.

At the hillslope scale (less than 33 ft2), Reid and others 

(1999) reported substantial sediment transport and deposition 

on arid hillslopes of piñon-juniper woodland in New Mexico. 

At this scale, large quantities of sediment are eroded, transported, then redeposited on the hillslope primarily by runoff 

from large convective summer storms.

In addition to serving as a source of surface runoff and sediment erosion, a road also can serve as a collecting and focusing 

mechanism for surface runoff. On steep, forested hillslopes 

with thin soil, shallow subsurface ground-water flow can discharge and become surface runoff at road cuts (Megahan, 

1983). Surface runoff collected by roads from many small inlets 

can leave the road at a single, much larger outlet at a discharge 

that often is sufficient to initiate or enlarge a downslope channel 

(Montgomery, 1994). In a survey of the Petroglyph National 

Monument, New Mexico, Gellis (1996) determined that 60 percent of the gullies mapped received runoff from dirt roads. Hillslope erosion associated with roads was found to be mainly 

associated with sites where the roadbed intersected an established drainage channel on the hillslope (Mosley, 1980; Best 

and others, 1995).

Description of the Study Area

Largo Canyon (fig. 1) drains an area of 1,700 mi2. The 

head of Largo Canyon is on the western slope of the Continental 

Divide, trends northwest for about 68 mi, and empties into the 

San Juan River at Blanco, New Mexico. The regional topography is composed of mesas dissected by deep, narrow canyons 

and arroyos. The elevation difference between the mesa top and 

the bottom of Largo Canyon is about 800 ft near the mouth of 

the canyon. Largo Canyon, a broad flat valley that is about 2 mi 

wide near the mouth of the canyon and about 0.5 mi wide in the 

upper canyon, is bounded by steep, rock-faced canyon walls. 

An alluvial channel, eroded by an ephemeral stream, is generally incised 10 to 20 ft into the valley floor. Side canyons commonly are deep and narrow with near-vertical canyon walls. 

Accumulations of talus and colluvial sediment at the base of the 

canyon walls form steep slopes that transition into flat-bottomed arroyos within the canyons. The elevation difference 

between the mesa top and the bottom of the side canyons is generally 300 to 400 ft.

The landscape morphology and erosion potential of the 

Largo Canyon watershed are tied to its underlying geology. 

Rocks of the Nacimiento Formation of Tertiary age are exposed 

at the surface in approximately the lower 20 percent of the canyon's length (Dane and Bachman, 1965). Rocks exposed at the 

surface in most of the watershed are primarily those of the San 

Jose Formation of Tertiary age. Rocks of the Nacimiento and 

San Jose Formations are composed primarily of interbedded 

layers of sandstone and shale of predominantly non-marine origin (Brister and Hoffman, 2002). The cliff-forming sandstones 

are more resistant than the shales but eventually weather into 

their composite sands; the shale is highly erodible and weathers 

into silts and clays, resulting in a highly erodible landscape and 

an abundant sediment supply. Variations in erodibility of the 

different rocks result in a typically southwestern landscape 

dominated by sandstone-capped mesas and deep and narrow 

canyons and arroyos.

The predominant vegetation is sagebrush and grasses with 

a more restricted piñon-juniper association (Dick-Peddie, 

1993). Riparian vegetation, including cottonwood and willow, 

was observed along Largo Canyon and some of the larger tributary canyons.

Climate

The climate of the Largo Canyon watershed is arid, averaging less than 10 in. of rainfall annually. As is typical of the 
Approach 5

southwestern United States monsoonal weather pattern, most 

annual precipitation falls from July through September; October through June is relatively dry. Snow, as measured at the 

Bloomfield 3 SE climatologic station (fig. 1), generally falls 

from December to mid-February and averages less than onehalf inch in depth (Western Region Climate Center, 2004).

Resource Use

BLM land in the Largo Canyon watershed is classified as 

multiple use and is open to recreational and agricultural use. 

Numerous archaeological sites are scattered throughout the canyon. Winter grazing is permitted throughout most of the watershed, but cattle were excluded from portions of the Crow Mesa 

Wildlife Management Area (fig. 1) 7 years prior to the beginning of this study (1994). The Crow Mesa area is one of reduced 

oil and gas activity, compared with other parts of the watershed, 

due to a relative lack of underlying oil and gas reserves (Dale 

Wirth, BLM, oral commun., 2001).

Acknowledgments

Dale Wirth of the Farmington BLM Field Office provided 

support and background information on the study area, which 

has contributed to the understanding of this project.

Approach

Variables considered for examining the effects of roads 

and well pads on upland erosion in the Largo Canyon watershed 

included geology and soil type, position of the road or well pad 

within the landscape, and the presence or absence of cattle grazing. Because roads and well pads were in active use, it was necessary to develop methods of measurement that did not impede 

traffic. Based on field reconnaissance, study sites were selected 

to represent a range of observed variables. The objective was to 

instrument enough study sites so a representative data set could 

be collected. Most study sites were located within the Harris 

Canyon area where cattle are allowed to graze and in the Palluche Canyon area within the ungrazed portion of the Crow 

Mesa Wildlife Management Area (fig. 1). Sites included dams, 

transects, or a combination of both (figs. 3-4). Dams were used 

to collect runoff from a defined drainage area, and transects 

were used to measure change in elevation across well pads or 

roads. For a given site, a dam is designated by the site number 

followed by a single letter. A transect is designated by the site 

number, R or P (road or well pad), and N, S, E, or W (north, 

south, east, or west), reflecting relative position of the site 

transects on the landscape. 

Dams

Sediment dams (dams) were installed at 43 sites. Of the 43 

dams, 21 were installed on hillsides upslope from roads or well 

pads, 11 at the downslope edges of roads, and 11 at the downslope edges of well pads (figs. 3A-F and 4A-C). The placement 

of dams was designed to measure the amount of eroded sediment entering and leaving roads and well pads from both the 

sandstone and shale source areas. Hillslope erosion was measured by dams placed upslope from roads and well pads, and 

road and well-pad erosion was measured by dams placed 

downslope from roads and well pads. In part, dam placement 

was designed to test the limits of dams to measure erosion; it 

was anticipated that not all locations would be successful at 

trapping transported sediment. Fewer locations for dam placement downslope from roads were available than upslope from 

roads. Locations identified were pre-existing drainages with 

drainage areas often exceeding the trapping capacity of the 

dams. Adequately stabilizing the dams in the downslope locations was not possible; even when a net accumulation of sediment was recorded over a measurement interval, sediment loss 

from the dams was sometimes substantial. Many of these dams 

worked well until runoff during large monsoonal storms of the 

second summer (2002) produced sufficient runoff to overwhelm the dams.

Initial attempts to measure sediment accumulation using 

dams made of straw bales were abandoned when the straw 

proved to be an irresistible draw to hungry cattle. These straw 

bale dams were replaced with dams made of black woven-polyethylene silt fence (commonly used during road construction to 

limit sediment transport from disturbed-soil areas). Dams constructed of silt fence were less sturdy than those constructed of 

straw bales and required regular maintenance because of persistent gusty winds. The dams were reinforced with closely spaced 

wood lathe and were lined with chicken wire for stability. The 

bottom edges of the silt fence material were buried about 0.5 ft 

below land surface to minimize piping and sediment loss under 

the dams. Hydraulic forces during large runoff events, however, 

still caused piping beneath some dams and the consequent erosion and loss of sediment.

Dam sizes and shapes, adapted to local topography, averaged 4 ft wide. The volume of sediment accumulation behind 

each dam was measured using 4-ft lengths of steel construction 

reinforcement bar (rebar) that generally were placed 2 ft apart 

in a three by three grid (depending on the size of the dam). Each 

section of rebar was hammered about 2 ft into the ground. The 

elevations of the top of each section of rebar and of each reinforcing wood lathe were surveyed to within 0.003 ft and were 

referenced to a stable elevation reference marker nearby. The 

horizontal spacing between the rebar and lathe and the initial 

height of each piece of rebar and lathe above ground surface 

were measured to within 0.05 ft. Subsequently, the height of 

each rebar and lathe above ground surface was measured to 

determine the volume of sediment that had accumulated behind 

the dam. The interval between successive measurements was 4-
6 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

EXPLANATION

11 Sediment dam and number

10

11

AREA SHOWN

IN FIGURE 3B AREA SHOWN

IN FIGURE 3D

AREA SHOWN

IN FIGURE 3F

AREA SHOWN

IN FIGURE 3E

AREA SHOWN

IN FIGURE 3C

107° 47’ 107° 46’ 107° 45’

36°

42’

36°

41’

0 1,000 2,000 3,000 4,000

0 250 500 750 1,000 METERS

FEET

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 3A. Location of sediment dams in the Harris Canyon area.
Approach 7

2B

2C

2D

2A

1A

1B

4A 3G

4C 4B

3F

3E

3C 3D

3B 3A

2PN

2PS

EXPLANATION

1A Sediment dam and number

Precipitation gage installed

for study

2PS

Transect and number

3PW 3PE

107° 47’ 05” 107° 47’ 107° 47’ 55” 107° 47’ 50”

36°

40’

45”

36°

40’

40”

0 100 200 300 400 500

0 25 50 75 100 125

FEET

METERS

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 3B. Location of sediment dams 1A, 1B, 2A–2D, 3A–3G, and 4A–4C, precipitation gage installed for study, and transects 2PN, 

2PS, 3PW, and 3PE, in the Harris Canyon area.
8 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

6A

6B

6C

5B

5A

5PW

5PE

5RE

5RW

6PW 6PE

107° 46’

0 100 200 300 400 500

0 25 50 75 100 125 METERS

FEET

Sediment dam and number

EXPLANATION

5A

Precipitation gage installed

for study

5PW Transect and number

Base from U.S. Geological Survey Digital Orthophoto

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

107° 45’ 55” 107° 45’ 50”

36° 

41’ 15”

36° 

41’ 10”

36° 

41’ 05”

Figure 3C. Location of sediment dams 5A, 5B, and 6A–6C, precipitation gage installed for study, and 

transects 5PE, 5PW, 5RE, 5RW, 6PE, and 6PW, in the Harris Canyon area.
Approach 9

7A

7B 7C

7D

7PN

7PS

7A Sediment dam and number

EXPLANATION

7PS Transect and number

107° 46’ 04” 107° 46’ 107° 45’ 56” 107° 45’ 52”

36°

40’

44”

36°

40’

40”

36°

40’

36”

0 100 200 300 400 500

0 25 50 75 100 125 METERS

FEET

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 3D. Location of sediment dams 7A–7D and transects 7PN and 7PS, in the Harris Canyon area.
10 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

8B

8C

8A

Sediment dam and number

EXPLANATION

8A

Drainage basin for Dam 8A

107° 45’ 56” 107° 45’ 48” 107° 45’ 40”

36°

40’

56”

36°

40’

48”

0 100 200 300 400 500

0 25 50 75 100 125 METERS

FEET

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 3E. Location of sediment dams 8A–8C and drainage basin for dam 8A in the Harris Canyon area.
Approach 11

Sediment dam and number

EXPLANATION

9H 0 25 50 75 100 125 METERS

0 100 200 300 400 500 FEET

107° 45’ 40” 107° 45’ 36” 107° 45’ 32” 107° 45’ 28”

36°

40’

32”

36°

40’

28”

9A

9B

9C

9D

9E

9F

9G 9H

DAM 9H drainage basin

DAM 9G drainage basin

DAM 9C

drainage basin

DAM 9B drainage basin

Dam

9D drainage

DAM 9F

drainage

basin

DAM 9E drainage basin

Dam 9A drainage basin

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 3F. Location of sediment dams 9A–9H and corresponding drainage basins in the Harris Canyon area.
12 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

AREA SHOWN

IN FIGURE 4B

AREA SHOWN

IN FIGURE 4C

14

16

15

18

17

107° 37’ 107° 36’ 107° 35’

36°

24’

36°

23’

Sediment dam and number

EXPLANATION

14

Precipitation gage installed

for study

Location of transects and 

site number 15

0 1,000 2,000 3,000 4,000

0 250 500 750 1,000

FEET

METERS

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 4A. Location of sediment dams, precipitation gage installed for study, and transects in the Palluche Canyon area.
Approach 13

12B

12A

Sediment dam and number

EXPLANATION

12A

12PS Transect and number

12PN

12PS

107° 35’ 08” 107° 35’ 04” 107° 35’

36°

23’

28”

36°

23’

24”

0 100 200 300

0 25 50 75

FEET

METERS

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 4B. Location of sediment dams 12A and 12B and transects 12 PN and 12PS in the Palluche Canyon area.
14 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

13A 13B

Drainage basin for dam 13A

Sediment dam and number

EXPLANATION

13A

0 100 200 300

0 25 50 75

FEET

METERS

107° 35’ 08” 107° 35’ 04” 107° 35’

36°

22’

48”

36°

22’

44”

Base from U.S. Geological Survey Digital Orthophoto 

Quarter Quadrangle, 1997, 1:10,000

Universal Transverse Mercator projection, zone 13

Figure 4C. Location of sediment dams 13A and 13B and drainage basin for dam 13A in the Palluche Canyon area.
Approach 15

6 weeks, and the accuracy of each measurement was within 0.02 

ft. 

Changes in sediment volume between successive measurements were calculated using the Surfer contouring program 

(Golden Software, Inc., 2002). Data for individual measurement intervals over which there was a net loss of sediment due 

to dam failure were discarded from the data set. All data for a 

dam were eliminated if data for more than 50 percent of the 

measurement intervals indicated a net loss of sediment. Using 

these criteria, data for 26 of 43 dams were retained for analysis 

(table 1).

Sediment cores were collected for grain size analysis from 

material inside and about 1 foot from the face of each dam. A 1-

inch-diameter hand auger was used and sediment was cored to 

a depth of 8 to 12 inches. Sediment density (weight per unit volume) was determined for each core sample. A single end-member sample was collected from both a sandstone and a shale outcrop. The material was analyzed by the USGS Sediment 

Laboratory in Iowa using a combination of sieve, visual accumulation (VA) tube, and pipet analysis (Guy, 1969). The cores 

sampled material deeper than the sediment collected during the 

study. Dams were installed without altering the ground surface 

or drainage, and material collected was assumed to be representative of prior sediment deposition at the site.

The erosion rate for each measurement interval was 

expressed as volume of sediment accumulated (in cubic feet) 

divided by the accumulation interval (expressed as fraction of a 

year). The drainage area of each dam was measured at the end 

of the data-collection period, using either a survey tape or a Global Positioning System (GPS) receiver to establish dimensions. 

Drainage area boundaries determined using a GPS receiver are 

shown in figures 3 and 4. Slope was determined using an inclinometer. The percentage of bedrock in each drainage area was 

estimated by visual inspection in the field. Sediment contributing area is defined as the non-bedrock part of the drainage area.

Roads and Well Pads

Erosion of roads and well pads was measured directly 

using repeated surveys of monumented transects. This technique was used to monitor broad areal extents of roads and pads, 

supplementing the sediment-accumulation point measurements 

at dams. Pairs of survey transects (transects) were established 

across opposite sides of nine well pads (figs. 3B-D; fig. 4B). 

Dams were installed at six of these pads. At two road locations 

(figs. 3 and 4A), transects were used to monitor surface changes 

on road segments lacking natural drainage outlets suitable for 

dams. The ends of each transect were monumented with rebar, 

and intermediate measurement points were marked with whisker flagging generally placed at 6-ft intervals across the pad. 

Road transects were measured at 1-ft intervals determined by 

stretching a survey tape between the rebar monuments. Groundsurface elevations along transects were determined by level survey.

Transects were measured three times during the study. 

Each level survey was closed to within 0.003 ft (vertical). 

Where the horizontal measuring points were marked by whisker 

flagging, the accuracy of using the same horizontal measuring 

points as used in previous surveys was within 0.01 ft. When 

flagging was lost, a survey tape was used to determine the horizontal measuring points along the transect between the rebar 

monuments. The horizontal measurement error was +/- 0.5 ft. 

Changes in cross-sectional areas between surveys are reported 

to 1.0 ft2.

Incipient erosion from road berms was characterized by 

counting the number of erosion cuts per specified length of the 

berm on both sides of the road surface. Erosion cuts were 

defined as vertical erosion cuts down the berm face at least 0.5 

in. deep. The specified length of a berm was dependent on the 

road configuration and the length of road for which geomorphic 

conditions remained similar. 

Roads and well pads in the Harris Canyon and Palluche 

Canyon road- and pad-analysis areas (fig. 2) were digitized 

from USGS Digital Orthophoto Quarter Quadrangles 

(DOQQ's), 1:10,000-scale to the North American Datum of 

1983 (NAD83) on a Universal Transverse Mercator (UTM) 

projection. The aerial photographs upon which the DOQQ's are 

based were taken in October 1997. The ground resolution of the 

DOQQ's is 1 m (3.3 ft).

Precipitation

Graduated plastic rain gages were installed near dams 1A 

and 6C (figs. 3B and 3C) in the Harris Canyon area and near 

dam 14 (fig. 4A) in the Palluche Canyon area and were read 

when the dams were measured. Cork in the gages gave a reading 

of maximum total recorded during the measurement period but 

did not control for evaporation. Tipping-bucket rain gages were 

installed at the same locations during the second year and 

recorded precipitation data from June 26 to November 26, 2002.

Statistical Analysis

Average erosion rate from each of the three landscape 

positions was tested against each of the potential influencing 

parameters using regression analysis. Regression analysis 

relates a dependent variable to one or more independent causative variables, evaluated by the standard error and the coefficient of determination, R2 (Minitab, 2003). R2 is the proportion 

of the variation in the dependent variable Y explained by the 

regression equation. The adjusted R2 adjusts the calculation of 

the coefficient of determination for a population with a small 

number of observations. A p-value, calculated for each independent variable, represents the probability that the relation of 

that variable in the regression is due to chance, with values less 

than or equal to 0.05 defining a statistically significant variable.

Mann-Whitney is a non-parametric two-sample t-test used 

to compare the means of two populations of samples with 

unequal variances (Minitab, 2003). This statistic was used to
Table 1. Sediment yield, drainage area, erosion rate, slope, land use, and landscape position of sediment dams and percentage of sand, silt, and clay 

sediment dams. [Due to sediment losses, data for 26 dams were retained for analysis] Sediment dams (figs. 3 and 4) Average sediment yield from drainage basin, in cubic feet per year Drainage area, in square feet Drainage area, in acres Percentage of drainage area that is bedrock Contributing area (drainage area minus bedrock area), in square feet Normalized average erosion rate, in feet per year Slope of contributing area, in percent Land use Landscape position Percentage of sand, silt, c

1A 79.9 128,000 2.9 61 49,700 0.00165 6 Grazed Below road 74.2 15.3 

1B 39.1 9,300 0.2 0 9,300 0.00411 39 Grazed Hillslope 70.9 14.8 

2A 9.3 500 0.0 0 500 0.01877 14 Grazed Below well pad 83 9 

2B 9.9 2,300 0.1 0 2,300 0.00429 10 Grazed Below well pad 76 12 

2D 45.8 332,000 7.6 85 46,600 0.00098 35 Grazed Hillslope 91 5 3A 24.5 1,800 0.0 0 1,800 0.01336 5 Grazed Below well pad 85 8 

3B 6.5 590 0.0 0 590 0.01098 17 Grazed Below well pad 85 7 

3D 3.5 2,500 0.1 0 2,500 0.00142 43 Grazed Hillslope 76 11 4A 9.5 76,800 1.8 48 40,000 0.00024 11 Grazed Below road 59 23 

4B 3.3 35,300 0.8 18 28,900 0.00011 34 Grazed Hillslope 49 30 4C 2.7 29,600 0.7 43 16,800 0.00016 28 Grazed Hillslope 50 28 

5A 13.2 1,000 0.0 0 1,000 0.01338 8 Grazed Below well pad 82 9 

6C 11.2 680 0.0 0 680 0.01653 26 Grazed Hillslope 87 8 7B 3.6 580 0.0 0 590 0.00613 11 Grazed Below well pad 83 9 7C 3.4 4,900 0.1 0 4,900 0.00070 26 Grazed Hillslope 33 36 

7D 10.6 4,500 0.1 0 4,500 0.00237 30 Grazed Hillslope 85 10 

8B 12.1 3,500 0.1 0 3,500 0.00344 22 Grazed Hillslope 88 7 8C 8.9 3,400 0.1 0 3,400 0.00259 22 Grazed Hillslope 88 7 

9D 8.2 4,900 0.1 0 5,000 0.00165 20 Grazed Hillslope 56 25 

9E 2.4 470 0.0 0 470 0.00502 20 Grazed Hillslope 77 9 

9F 4.7 5,000 0.1 15 4,200 0.00111 20 Grazed Hillslope 80 9 

9H 11.2 32,000 0.7 30 22,400 0.00050 6 Grazed Below road 86 6 

12A 2.8 340 0.0 0 340 0.00828 4 Ungrazed Below well pad 4 55 

12B 4.7 300 0.0 0 300 0.01548 4 Ungrazed Below well pad 11 45 13B 8.2 5,800 0.1 0 5,800 0.00142 2 Ungrazed Below road 73 14 

14 4.8 4,100 0.1 0 4,100 0.00117 1 Ungrazed Below road 58 18 
Effects of Roads and Well Pads on Upland Erosion 17

test for a statistical difference between the average erosion rate 

of the three landscape positions with each of the other two positions. A p-value less than or equal to 0.05 was considered to represent a significant difference in erosion rates.

Effects of Roads and Well Pads on 

Upland Erosion

In the following sections, data collected during this study 

are used to establish minimum erosion rates for hillslopes, the 

downslope edges of roads, and well pads. Field observations 

made during this study are used to develop a conceptual model 

of processes of upland erosion in the study area that incorporates the effects of roads and well pads on the erosion process.

Based on the October 1997 DOQQ's, the Harris Canyon 

road- and pad-analysis area (fig. 2) contains 108 well pads with 

a combined area of 0.1 mi2, or 64.5 acres, and 84 mi of roads 

with a road density of 2.5 mi/mi2. The Palluche Canyon roadand pad-analysis area (fig. 2) contains 114 well pads with a 

combined area of 0.04 mi2, or 28.8 acres, and 114 mi of roads 

with a road density of 2.2 mi/mi2. With the exception of countymaintained roads, the roads are not crowned or ditched and 

were graded only occasionally when heavy use on wet roads 

resulted in a rutted surface.

Precipitation

Precipitation at four National Weather Service climatological stations (fig. 1) for the 2001-02 study period generally followed the seasonal monsoonal pattern but with an unusually dry 

spring in 2002 and little rain recorded for the first 6 months of 

that year (fig. 5). Mean annual precipitation at the four stations 

was below normal for 2001-02 (table 2). During 2001 precipitation was generally of low intensity. During the 2002 monsoon 

season, however, precipitation of high intensity fell several 

times. The first high-intensity precipitation that fell in the Palluche Canyon area on July 9, 2002, totaled 0.82 in., with a maximum intensity of 0.71 in./hr. The second high-intensity precipitation that fell on July 23, 2002, in the Harris Canyon area 

totaled 1.4 in. over about 4 hours, with a maximum intensity of 

0.68 in./hr. Although precipitation data were not recovered for 

tipping-bucket rain gages in the Harris Canyon area in August 

2002 due to an equipment malfunction, data from the four 

National Weather Service climatological stations and from the 

Palluche Canyon area tipping-bucket rain gage indicate sparse 

precipitation. Three major rains fell during September 2002, the 

largest a storm totaling 0.47 in. over 32 minutes near the end of 

the month.

Farmington Agricultural Science Center

Bloomfield 3 SE

Otis

Lybrook

PRECIPITATION, IN INCHES

Lybrook

data missing

2001

MAM J J A S O ND

2002

J FM A M J J A S O N

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

Figure 5. Total monthly precipitation at the Farmington Agricultural Science Center, Bloomfield 3 SE, Otis, and Lybrook National 

Weather Service cooperative climatological stations, March 2001–November 2002. Data obtained from Western Region Climate 

Center, 2004.
18 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Table 2. Mean annual precipitation for the Farmington Agricultural Science Center, Bloomfield 3 SE, Otis, and Lybrook climatologic stations (2001-02) and the National Weather Service 30-year (1971-2000) normal precipitation.

[Data obtained from Western Region Climate Center, 2004]

Time period

Precipitation, in inches

Farmington 

Agricultural 

Science 

Center

Bloomfield 3 

SE Otis Lybrook

Mean annual 

precipitation 

for the four 

climatologic 

stations

2001 7.54 7.09 12.34 10.49 9.37

2002 7.69 7.30 8.39 9.89 8.32

30-year normal 8.39 9.18 10.23 10.20 9.50

Erosion Rate

Sediment accumulation behind dams, recorded for 17 

intervals of time (measurement intervals), was used to determine the average erosion rate for each dam in cubic feet per 

year. To compare erosion rates among dams collecting sediment from drainage areas of varying sizes, the erosion rate was 

normalized by dividing by the contributing area (table 1) so that 

erosion rate is expressed as volume of sediment per unit area per 

year (cubic feet per square foot per year or feet per year). Other 

factors considered to influence erosion rates are intensity and 

amount of precipitation, percentage of bedrock in the total 

drainage area, slope of the contributing area, land use (grazed or 

ungrazed), grain size of the accumulated sediment (indicative of 

source material), and landscape position of the dam and drainage area on the landscape (hillslope, below a road, or below a 

well pad). 

No attempt was made to relate precipitation intensity and 

amount to erosion rate for a measurement interval because the 

4-6 weeks between measurements did not allow correlation of 

individual precipitation events to individual erosion events. 

Similarly, the measurement interval did not allow for the establishment of thresholds for erosion based on the intensity and 

duration of precipitation. In addition, given the highly variable 

annual and interannual precipitation patterns in an arid environment, measuring a representative sample of events in a 2-year 

period to establish thresholds of sediment movement is not possible.

Average erosion rates at the dams significantly related to 

size of the contributing drainage area (p = 0.004) and account 

for 28 percent of the regression variability in the data. The percentage of bedrock in the drainage area of a dam also significantly related to average erosion rate (R2 (adjusted) = 30 percent, p = 0.003). The parameters percent bedrock and 

contributing area significantly relate to each other 

(R2 (adjusted) = 78 percent, p = 0.000), so a multiple linear 

regression of these two parameters to estimate erosion rate does 

not improve the regression. Because of the complex physical 

environment and difficult sampling conditions, the final data set 

consisting of measurements from 26 dams (table 1) was insufficient to draw relationships between erosion rates and selected 

geomorphic parameters. However, the average erosion rate differs significantly for dams in certain landscape positions. The 

average erosion rate normalized by drainage area was about 

0.001 ft/yr below roads, 0.003 ft/yr on hillslopes, and 0.011 ft/yr 

below well pads (fig. 6; table 3). With use of a two-sample t-test 

to compare the means of two populations of samples with 

unequal variances, there was no significant difference in the 

average erosion rate for dams located on hillslopes and below 

roads, whereas average erosion rates for dams below well pads 

were significantly larger than for dams in the other two landscape positions.

The average erosion rates estimated from the data collected during this study most likely represent minimum erosion 

rates. Sediment-accumulation data for measurement intervals 

during which dams were breached during 2002, as a result of the 

large volume of runoff generated by high-intensity storms, were 

not used to compute erosion rates. For this reason, the higher 

range of erosion rates is underrepresented and the results of this 

study are biased toward the lower end of the range of erosion 

rates. 
Effects of Roads and Well Pads on Upland Erosion 19

Average

75th percentile

25th percentile

Median (50th percentile)

1.5 times the interquartile

range or the largest value

-1.5 times the interquartile

range or the smallest value

Sample size (8)

Outlier

Far outlier

EXPLANATION

BELOW ROAD HILLSLOPE BELOW WELL PAD

0

0.005

0.01

0.015

0.02

0.025

(5)

(13)

(8)

AVERAGE EROSION RATE, IN FEET PER YEAR

0.011 (table 3)

0.003 (table 3)

0.001 (table 3)

Figure 6. Average erosion rates for drainage areas located below roads, on hillslopes, or below well pads.
Effects of Roads and Well Pads on Upland Erosion 20

Table 3. Summary statistics for sediment-dam erosion rate data. P-values refers to statistical comparison of average erosion rate between two landscape positions. Below road is repeated to show p-value statistical comparison to below well pad.

Landscape position Average, in feet per year Standard deviation p-value

Below road 0.001 0.001

0.111

Hillslope 0.003 0.004

0.002

Below well pad 0.011 0.005

0.001

Below road 0.001 0.001

Road and Well-Pad Transects

Land-surface transects were located at two road sites and 

nine well pads. Although road and well-pad transects were, for 

the most part, surveyed three times during the study, most of the 

following discussion focuses on the overall change in land surface between the first (June 28, 2001) and last (November 20, 

2002) surveys. All sites are discussed, but only selected sites are 

illustrated.

Road transects 5RE and 5RW (fig. 7), in the Harris Canyon area, were located on a sandy stretch of road with a 3-percent slope that connects well pad 5 with the feeder-road network (fig. 3C). The tops of the road berms are about 2 ft above 

the road surface (fig. 7), and the land slopes away from the road 

berms on both sides. In general, both transects show apparent 

downslope sediment movement from the road berms, erosion 

from the upper part of the berms, and redeposition on the road 

at the base of the berms. There is infilling of a road rut in 

transect 5RW, but no substantial net change in road surface elevation on either transect. Road transects 17RL, 17RM, and 

17RS (fig. 8), located in the Palluche Canyon area (within area 

17 in fig. 4A), cross a flat section of road through an open area 

adjacent to an area of badlands topography. Sandstone is adjacent to the upslope end of transect 17RS, whereas shale crops 

out about 200 ft from the road at the uphill end of transect 17RL. 

The transects are about 300 ft apart. Transect 17RL is the farthest upslope transect and 17RS is the farthest downslope 

transect. Site 17 was chosen because silt, identified by color, 

was observed during field reconnaissance to have been transported from the weathered outcrops across a hillslope with a 2-

percent gradient and deposited across and on the far side of the 

road. The three transects together support sediment movement 

downslope toward the road; a larger volume of movement was 

noted in steeper portions. The transects also indicate erosion 

and transport of sediment downslope and along the road once 

the sediment reaches the road.

Well-pad transects 2PN, 2PS, 5PE, 5PW, 6PE, and 6PW 

(figs. 9, 10, and 11), in the Harris Canyon area, were located on 

sandy material. The site 2 well pad (fig. 3B), the head of a side 

canyon, lies downslope from colluvial sediment deposits and 

bedrock cliffs that potentially can supply large volumes of sediment. A loss of sediment from June 28, 2001, to November 

2002 generally was shown for transects 2PN and 2PS from the 

hillslope above the pad and from the pad, although some sediment was deposited in transect 2PN on the pad (fig. 9). Erosion 

from the downslope edge of the pad is shown in transect 2PN, 

whereas deposition is shown in transect 2PS. The pattern of net 

gain and loss of sediment between successive surveys suggests 

downslope transport and redeposition of sediment from the hillslope, over the surface of the well pad, and down the well-pad 

edges.
Effects of Roads and Well Pads on Upland Erosion 21

DISTANCE ALONG TRANSECT, IN FEET

0 5 10 15 20 25 30

5

6

7

8

9

10

11

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET

0 5 10 15 20 25

5

6

7

8

9

10

11

A (5RE)

B (5RW)

ELEVATION, IN FEET

Road berm

Road berm

Road berm

Road berm

Road surface

Road surface

Vertical Exaggeration X 2.1

Vertical Exaggeration X 2.6

Figure 7. Land-surface changes for transects (A) 5RE and (B) 5RW in the Harris Canyon area, June 28, 2001–November 20, 

2002. Transect locations shown in figure 3C. View is to the northeast.
22 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

0 10 20 30 40 50 60 70

8

9

10

11

12

13

0 10 20 30 40 50 60 70 80

9

10

11

12

0 5 10 15 20 25 30

12

13

14

15

16

A (17RL)

B (17RM)

C (17RS)

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET

Road

berm

Road surface

Road surface

Road surface

Road

berm

Road

berm

Road

berm

Road

berm

Road

berm

Hillslope

Hillslope

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 4.9

Vertical Exaggeration X 2.6

Vertical Exaggeration X 2.5

Figure 8. Land-surface changes for transects (A) 17RL, (B) 17RM, and (C) 17RS in the Palluche Canyon area, June 28, 2001–

November 20, 2002. Transect locations shown in figure 4A. View is to the west.
Effects of Roads and Well Pads on Upland Erosion 23

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

9

10

11

12

13

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

9

10

11

12

13

A (2PN)

B (2PS)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Hillslope

Hillslope

Well pad

Vehicle rut at

measurement

point

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 9.5

Vertical Exaggeration X 9.5

Well pad

Figure 9. Land-surface changes for transects (A) 2PN and (B) 2PS, in the Harris Canyon area, June 28, 2001–November 20, 2002. 

Transect locations shown in figure 3B. View is to the south.
24 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

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

9

10

11

12

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

9

10

11

12

A (5PE)

B (5PW)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Hillslope

Well pad

Hillslope

Well pad

Vehicle rut at

measurement

point

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 12.8

Vertical Exaggeration X 12.8

Figure 10. Land-surface changes for transects (A) 5PE and (B) 5PW in the Harris Canyon area, June 28, 2001–November 20, 

2002. Transect locations shown in figure 3C. View is to the northeast.
Effects of Roads and Well Pads on Upland Erosion 25

0 20 40 60 80 100 120 130

9

10

11

12

13

14

15

16

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

9

10

11

12

13

14

15

A (6PE)

B (6PW)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Sandy embankment

Sandy embankment

Well pad

Earth deposited

during constuction

Earth deposited

during constuction

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 4.6

Vertical Exaggeration X 4.1

Figure 11. Land-surface changes for transects (A) 6PE and (B) 6PW in the Harris Canyon area, June 28, 2001–November 20, 

2002. Transect locations shown in figure 3C. View is to the northwest.
26 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

An intervening low area separates the site 5 well pad from 

the nearby hillslope, and the site 6 well pad is adjacent to a 

sandy embankment (fig. 3C). In transects 5PE and 5PW, a fairly 

stable surface configuration and some downslope sediment 

movement and redeposition at the edges of the well pads are 

shown, with the exception of vehicle ruts in the surface at 

transect 5PW (fig. 10). The site 6 well pad showed a similarly 

stable surface configuration between the first and second 

transect surveys (June 28, 2001, and May 7, 2002; not shown). 

Increases in surface elevation caused by earth movement during 

construction are shown in transects 6PE and 6PW (fig. 11), 

which compares the first and the third survey. 

Sites 16 and 18 in the Palluche Canyon area (fig. 4A) also 

were located on sandy material. Comparison of the June 28, 

2001, and November 20, 2002, survey measurements indicates 

a net gain of sediment on the site 16 well pad in transects 16PE 

and 16PW (fig. 12). The well pad at site 18 (fig. 13) was 

regraded before the November 20, 2002, survey, which resulted 

in the loss of the survey reference monument. However, a comparison of the June 28, 2001, and the May 4, 2002, survey measurements indicates a net gain of sediment at the site 18 well pad 

(fig. 13).

Well-pad sites 3 and 7 in the Harris Canyon area (figs. 3B 

and 3D) and sites 12 and 15 well pads in the Palluche Canyon 

area (figs. 4A and 4B) were adjacent to clay source areas. Only 

the June 28, 2001, and November 20, 2002, survey measurements are available for site 3 well-pad transects (fig. 14). Wellpad sites 3 and site 7 abut a weathered shale slope of about 35-

percent grade. Transect 3PE is downslope from transect 3PW. 

Dam measurements and field observations following storm runoff at sites 3 and 7 indicate downslope transport of sediment 

from the hillslope and across the well pad. Transect survey measurements indicate transport across the well pad, especially at 

transect 3PW. 

Net differences in land-surface elevation at transects 7PN 

and 7PS in the Harris Canyon area (fig. 3D) were small (fig. 

15). At transect 7PN, the cross section was stable for all surveys. Exceptions were a slump deposition on the upslope end of 

the well pad and a tire rut near the center of the pad, both of 

which were absent by the May 2002 survey (not shown). Landsurface elevation changed little between May and November 

2002. At transect 7PS, sediment deposition was equivalent to 

about a 3-in. increase in land-surface elevation across the 

transect between June 2001 and May 2002 (not shown). This 3-

in. increase had largely disappeared by November 2002, resulting in a minor difference in land-surface elevation compared 

with the original 2001 survey.

Data collected for well-pad transects 12PN and 12PS (figs. 

4A and 4B; fig. 16) in the Palluche Canyon area indicate sediment erosion near the upslope edge of the pad and redeposition 

on the well pad. Measurements for well-pad transects 15PE and 

15PW (fig. 4A) in the Palluche Canyon area indicate erosion 

and redeposition at the upslope edge of the well pad and, in general, erosion near the downslope edge of the well pad (fig. 17).

Field Observations 

To draw meaningful conclusions, data obtained through 

measurements at point locations need to be generalized over a 

broad spatial area. Erosion in an arid landscape, however, is not 

a spatially generalized process but is focused at point locations 

that are a function of any of several variables interacting in 

complex ways that can focus energy and increase erosion potential. These variables include slope, cohesiveness of source 

material, elevation differences between points in the drainage 

area, vegetative cover, and the proximity of these variables to 

each other and to the point of measurement. For this reason, 

field observations, although not quantitative, can be valuable 

for understanding processes and interactions on the landscape. 

Some of the observed processes were quite dramatic, such as 

focused bank erosion (fig. 18), whereas other processes, such as 

sediment-color differences that show sediment-transport patterns, are more subtle. Field observations can elucidate processes not well captured by point measurements. The following 

discussion of field observations focuses on roads aligned generally parallel to topographic contour, roads that cross topographic contour, and well pads.

Roads Parallel to Topographic Contour

Dams on hillslopes upslope from roads at sites 3, 4, and 9 

in the Harris Canyon area (figs. 3B and 3F) accumulated sediment transported from nearby shale and siltstone source areas 

(figs. 19 and 20), whereas dams at sites 8 (fig. 21) and 6 in the 

Harris Canyon area accumulated sediment transported from 

sandy hillslopes. Despite the differences in source rock material, observations at these sites indicate that both sandstone and 

siltstone weather to provide an abundant sediment supply. In 

the Harris Canyon area and in the flatter, more open Palluche 

Canyon area, bedrock, where it composes a large percentage of 

the drainage area, forms an impermeable surface that can contribute large volumes of runoff and increase the sediment-transport potential of runoff entering a dam.

Color differences between sediments derived from sandy 

and shaley and silty source areas clearly delineated surface-runoff flow lines. In the narrower canyons in the Harris Canyon 

area and in the flatter and broader canyons in the Palluche Canyon area, sediment was transported from the surrounding land 

and deposited on the road surface by runoff. Differences in sediment color indicate that some of the greenish sediment trapped 

by dam 1A originated from a shale and siltstone source area at 

the base of the canyon wall and was transported across the road 

to the dam (fig. 22). Transverse erosion across the road surface, 

evident in figure 22, indicates a sediment contribution from 

upslope of the road. Prior to the large rainfall in 2002, sediment 

from upslope of the road was captured by the road berm on the 

upslope right side of the road.

Unlike at sites at which bedrock was part of the contributing area, the drainage at the site 14 dam in the Palluche Canyon 

area was well defined, collecting runoff primarily from the road 
Effects of Roads and Well Pads on Upland Erosion 27

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

6

7

8

9

10

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

7

8

9

10

11

A (16PE)

B (16PW)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Mounded earth near 

center of well pad

Mounded earth near 

center of well pad

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 19

Vertical Exaggeration X 19

Figure 12. Land-surface changes for transects (A) 16PE and (B) 16PW in the Palluche Canyon area, June 28, 2001–November 20, 2002. Location of site 16 shown in figure 4A. View is to the northwest.
28 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

0 10 20 30 40 50 60 70 80 90

9

10

11

0 10 20 30 40 50 60 70 80 90

9

10

11

A (18PN)

B (18PS)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 25.5

Vertical Exaggeration X 25.5

Figure 13. Land-surface changes for transects (A) 18PN and (B) 18PS in the Palluche Canyon area, June 28, 2001–

May 4, 2002. Location of site 18 shown in figure 4A. View is to the south.
Effects of Roads and Well Pads on Upland Erosion 29

0 10 20 30 40 50 60 70 80 90

4

5

6

7

0 10 20 30 40 50 60 70 80 90

3

4

5

6

A (3PE)

B (3PW)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 17

Vertical Exaggeration X 15.8

Figure 14. Land-surface changes for transects (A) 3PE and (B) 3PW in the Palluche Canyon area, June 28, 2001–November 20, 2002. Transect locations shown in figure 4A. View is to the west.
30 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

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

9

10

11

12

13

14

15

16

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

9

10

11

12

13

14

15

16

A (7PN)

B (7PS)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Slump deposit

Tire rut at

measurement point

Tire rut at

measurement point

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 10.5

Vertical Exaggeration X 10.5

Figure 15. Land-surface changes for transects (A) 7PN and (B) 7PS in the Harris Canyon area, June 28, 2001–November 

20, 2002. Transect locations shown in figure 3D. View is to the south.
Effects of Roads and Well Pads on Upland Erosion 31

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

9

10

11

12

13

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

9

10

11

12

13

A (12PN)

B (12PS)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Slump Deposit

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 19.2

Vertical Exaggeration X 15.2

Figure 16. Land-surface changes for transects (A) 12PN and (B) 12PS in the Palluche Canyon area, June 28, 2001–November 20, 

2002. Transect locations shown in figure 4B. View is to the south.
32 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

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

2

3

4

5

6

7

8

9

10

11

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

2

3

4

5

6

7

8

9

10

11

A (15PE)

B (15PW)

DISTANCE ALONG TRANSECT, IN FEET

DISTANCE ALONG TRANSECT, IN FEET

ELEVATION, IN FEET ELEVATION, IN FEET

Well pad

Well pad

Elevation along transect, June 28, 2001

Elevation along transect, November 20, 2002

EXPLANATION

Vertical Exaggeration X 8.5

Vertical Exaggeration X 11

Figure 17. Land-surface changes for transects (A) 12PN and (B) 12PS in the Palluche Canyon area, June 28, 2001–November 20, 2002. Transect locations shown in figure 4B. View is to the south.
Effects of Roads and Well Pads on Upland Erosion 33

SHALE AND

SILTSTONE

Figure 18. Truck on road above area of focused bank erosion. Note the fence posts hanging from fence 

wire. Road is near site 9, Harris Canyon area. View is to the northeast.

Figure 19. Sediment dam 9D and weathered shale and siltstone in the drainage contributing area, Harris 

Canyon area. Location of dam 9D shown in figure 3F. View is to the northwest.
34 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Dam 4C

Dam 4B

SHALE AND

SILTSTONE

DAM 8A

DAM 8C

Figure 21. Areas (indicated by arrows) where headcuts in the upslope road berm near sediment 

dams 8A and 8C have extended beyond the road berm and up the hillslope, Harris Canyon area. 

Locations of dams 8A and 8C shown in figure 3E. View is to the northwest.

Dam 4C

Dam 4B

SHALE AND

SILTSTONE

DAM 8A

DAM 8C

Figure 20. Weathered shale and siltstone in drainage contributing areas of sediment dams 4B 

and 4C in the Harris Canyon area. Locations of dams 4B and 4C shown in figure 3B. View is to the 

northwest.
Effects of Roads and Well Pads on Upland Erosion 35

Figure 22. Color of sediment on road near sediment dam 1A indicating source of runoff as the weathered shale and siltstone (shown in the upper right of photograph), Harris Canyon area. Locations of 

dams 1A and 1B shown in figure 3B. View is to the west. 

surface. Site 14 differed from sites in the northern part of the 

study area and is characterized by a flatter surrounding terrain 

and a greater distance to the bedrock cliffs. The road at site 14 

(fig. 4A) appeared to be fed more diffusely than the road in the 

steeper canyons with occasional flow focused by plant roots 

onto the road, but much of the runoff remained confined on the 

hillslope side of the road berm.

At sites where land on either side of the road was flat, there 

commonly was evidence of flow and sediment transport across 

land surface for a distance of several feet without downcutting 

or rill formation. The road berm sometimes acted as a dam, trapping sediment above the road (fig. 23). However, higher intensity rainfall caused sheet-flow runoff, transporting sediment 

over the berm onto the road. Lower intensity rainfall transported sediment by focused flow, entering the road through 2- 

to 3-in.-wide headcuts in the road berms (fig. 23). For roads parallel to contour, road-berm headcuts generally were focused on 

the upslope side of the roadbed, with a range of 15-65 headcuts 

per 100 ft of road on the upslope side and 0-2 headcuts per 100 

ft of road on the downslope side (table 4).

At many locations, road-berm cuts reached only a few 

tenths of a foot headward from the road berm and were fed by 

downward movement of sediment from the area upslope from 

the cut (fig. 23). Some cuts, however, were observed to have 

eroded headward for several feet, forming a distinct channel 

(fig. 21). The principal input of runoff to roads parallel to contour was focused by established rills or channels on the adjacent 

hillslopes. Where the road intersected a pre-existing drainage, 

runoff flowed directly across the road and exited on the downslope side of the road (fig. 24), usually after transport of a few to 

several hundred feet along the road itself. 

Most of the locations at which dams could be placed to trap 

sediment draining from roads were selected because they were 

established drainage channels (fig. 24). For rainfall of smaller 

magnitude and intensity these dams worked well, but rainfall of 

larger magnitude and intensity (large enough to integrate flow 

paths in the entire drainage area) generated large volumes of 

runoff that overwhelmed the capacity of these dams (fig. 25), 

caused erosion along the sides and back of the dam, and contributed to deepening of the channel below the road. The erosive 

force associated with large magnitude and intensity runoff was 

at times sufficient to erode the downslope edge of the road surface. During one rainfall, focused flow through the dam caused 

development of a channel below the road that was not present 

when the dam was established. No erosion rates were estimated 

for the larger runoff events that breached dams.

Based on observations, roads aligned parallel to contour 

facilitate erosional processes in two ways: (1) roads cut across 

and collect runoff from previously established drainages and (2) 

roads, where cut into hillsides or into the land surface, provide 

focal points for the initiation of erosion. In the first process, runoff and sediment from pre-existing small drainages may be 
36 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Table 4. Number of cuts in upslope and downslope road berms, for road parallel to contour.

Nearby 

sediment 

dam or 

transects 

(figs. 3

and 4)

Soil 

composition

Length of road 

examined, 

in feet

Number of cuts in berm / number 

of cuts per 100 feet of road

Upslope side 

of road

Downslope side 

of road

1A-B Silty sand 200 65 / 32.5 0 / 0

4A-C Silty sand 148 23 / 15.5 2 / 1.4

3G-F Silty sand 200 47 / 23.5 20 / 10

8A-C Sand 400 37 / 9.3 2 / 0.5

5RW-5RE Sand 400 46 / 11.5 0 / 0

9A-B Silty sand 180 15 / 8.3 1 / 0.6

9C-E Silty sand 242 37 / 15.3 1 / 0.4

9F-G Silty sand 76 3 / 3.9 3 / 3.9

13A-B Silty sand 289 29 / 10.0 1 / 0.3

14A-B Sand 200 20 / 10.0 38 / 19.0

Average number of cuts in berm per 100 feet of road 14 3.6

Figure 23. Mud cracks (in upper left of photograph) as evidence of ponding and sediment deposition 

behind the road berm at site 4. Headcuts, formed in the road berm where runoff overflowed the 

berm, do not extend upslope from berm. Pen in middle foreground for scale. Near site 4 in the Harris 

Canyon area.
Effects of Roads and Well Pads on Upland Erosion 37

DAM 3F

Figure 25. Sediment dam 9A overwhelmed by high runoff and partially buried in transported sediment. Location of dam 9A, in the Harris Canyon area, shown in figure 3F. View is to the east.

Figure 24. Sediment dam 3F installed at the downslope edge of a road on a pre-existing drainage 

in the Harris Canyon area. The channel deepened and widened, with concurrent deterioration of 

the road edge, over the 2-year course of this study. Location of dam 3F shown in figure 3B. View 

is to the south.
38 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

intercepted by and transported along the road (figs. 3E and 3F) 

to an outlet point (fig. 21, dam 8A; fig. 25, dam 9A). The outlet 

point may be a new or pre-existing drainage at some distance 

down the road from the numerous small drainages contributing 

runoff to the road. Sediment is deposited on the road from accumulated runoff originating from a segment of the hillslope. This 

accumulated runoff and sediment are channeled by the road bed 

to a single outlet point on the downslope side of the road (figs. 

21 and 25). Because flow from the hillslope drainages is concentrated into a larger flow along the road, the potential erosive 

capacity of the runoff is magnified, the degree of magnification 

depending on the slope and topography at the point. The second 

way in which roads facilitate erosional processes is in providing 

focal points for the initiation of erosion on freshly exposed or 

disturbed surfaces. Road berms, created when level roads are 

cut into hillslopes, provide oversteepened slopes on which 

enough potential energy is available to initiate headcut erosion 

during runoff. Headcut erosion occurs naturally on weathered 

surfaces where rills form at slope breaks and erode headward. 

Periodic grading of the roads sustains the heights of the berms 

and maintains the potential energy needed to initiate rill formation and headcut erosion. In contrast to roads adjacent to hillslopes, roads through flatter landscapes, such as parts of the 

Palluche Canyon area, show little evidence of headcut erosion 

extending upslope from road berms.

Roads Across Topographic Contour

Roads across topographic contour generally are well-pad 

access roads or roads that cross drainage divides and can serve 

to integrate parts of the watershed as a secondary drainage network; however, roads across topographic contour constitute a 

small percentage of the road network. Although no sediment 

dams were installed on across-contour roads, depositional features, such as splay deposits formed where roads across contour 

intersect roads parallel to contour (fig. 26), indicate that roads 

across contour serve as downslope conduits for sediment transport.

Well Pads

Base material at well-pad sites 2 and 5 (figs. 3B and 3C) 

was primarily sandy, whereas base material at well-pad sites 3, 

7, and 12 (figs. 3B, 3D, and 4B) was primarily silty. Well pads 

typically were flat surfaces cut into the adjacent hillslope. 

Because the pads were wider than the roads, the upslope cut 

face and downslope berm generally were much higher than road 

berms. Areas upslope from well pads supplied sediment to the 

well pad, and sometimes fan deposits formed at the base of the 

well-pad berm (fig. 27). Dams below the downslope well-pad 

berm trapped sediment mainly from the well-pad slope itself; 

drainages developed over time at some places and captured runoff from the well-pad surface (fig. 28). Like roads, well pads 

can provide conditions for focusing runoff and locally increasing erosion. At site 3, a 4-ft-deep channel was cut between the 

embankment surrounding the well pad and the cliff face, where 

runoff from the mesa was focused at this point. At site 12, a similar focus of runoff from the hillslope by an embankment stabilizing the well pad led to development of a deep channel incised 

into the road (fig. 29).

Processes of Upland Erosion

As studies in forested humid temperate watersheds have 

shown, unpaved roads are considered a major source of sediment in undeveloped areas, serving both as sources of sediment 

and as conduits for transporting accumulated sediment out of 

the basin of origin. In these humid temperate areas, which have 

a ground cover of litter and duff, roads and associated road cuts 

constitute a substantial percentage of total open and bare 

ground. By contrast, canyons dissecting sandstone and shale 

characterize the Largo Canyon watershed, and much of the land 

surface is unvegetated ground interspersed with shrubs or rock. 

The area of bare land surface constituted by roads is relatively 

small compared with the area of bare and easily erodible landscape.

Northwest New Mexico represents a different climate and 

landscape than that in which the observations about the role of 

roads in landscape erosion were developed. In arid climates, 

extreme runoff events shape the landscape and do most of the 

work of transporting sediment (Graf, 1998). The effects of 

extreme runoff events remain evident in the subsequent configuration of the landscape; subsequent, milder runoff events do 

not account for the existing configuration of the landscape. 

Even if, in the arid Largo Canyon watershed, roads do play an 

important role in landscape erosion, the mechanisms by which 

roads contribute to erosion in arid climates would be expected 

to differ from those in humid, temperate forested climates 

because erosion processes reflect the climate and landscape in 

which they occur.

Roads across contour can serve as a downslope conduit for 

runoff and transported sediment but constitute a small percentage of total road area. Roads constructed parallel to contour can 

minimize erosion potential compared with roads constructed 

across contour. Roads parallel to contour, however, contribute 

to erosion by more indirect processes in two ways: (1) initiating 

headcut erosion at the upslope road berm and (2) concentrating 

small inflows upslope into a larger flow with increased erosion 

potential at the downslope road berm. Variations of this conceptual model are a function of slope, orientation to contour, and 

position with respect to other landscape features.

On the upslope side of roads parallel to contour, weathered 

shale slopes were observed to develop more extensive rill networks than did weathered sandstone slopes. For a given source 

material, steepness of the adjacent topography and proximity to 

a cliff or mesa determines the degree of rill or channel formation and runoff accumulation onto the land surface. The upslope 

roadside berm acts as a dam for low runoff events and when 

adjacent topography is relatively flat compared to the hillslope, 

accumulating eroded sediment upslope from the road surface. 
Effects of Roads and Well Pads on Upland Erosion 39

CURVED CUT

IN ROAD BERM

DIRECTION OF

FLOW FROM

ACROSS-CONTOUR

ROAD

Figure 27. Sediment erosion from upslope pad berm near sediment dam 2C redeposited on the 

pad, partially burying oil and gas industry equipment. Location of dam 2C in Harris Canyon area is 

shown on figure 3B. View is to the southwest.

Figure 26. Splay deposit, formed from sediment transported along across-contour road and subsequently eroded by runoff, forms the curved cut in berm of parallel-contour road. Across-contour road connects from lower left of photograph, Harris Canyon area. View is to the southwest.
40 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Figure 29. Author standing in a channel cut by focused runoff near site 12 in the Palluche Canyon 

area. Location of site 12 shown in figure 4B. View is to the southwest.

Figure 28. Sediment dam 5A and headcuts eroded into downslope pad berm. Headward erosion 

has extended the headcuts up onto the surface of the well pad. Transect 5PNE whisker flagging 

crosses the well pad behind author and in front of vehicle (arrow points along transect). Location 

of dam 5A in Harris Canyon area shown in figure 3C. View is to the northwest.
Summary 41

Headcuts initiated from road berms may subsequently release 

this sediment from temporary storage. The number of established rills and drainage networks that may cross the road and 

continue downslope on the other side is greater on steeper hillslopes or outcrops.

On the downslope side of a road parallel to contour, accumulated runoff from the adjacent hillslope concentrates and discharges to an existing or newly formed gully or arroyo. The 

degree of downcutting depends on the elevation difference 

between the road and the gully or arroyo. Deep channels were 

observed cutting headward into the roadbed where an arroyo 

was more than 10 feet below the road. Where roads were of low 

grade along the valley axis or downslope across contour, the 

road served more as a conduit for runoff.

Well pads function in the erosion process in a way similar 

to roads parallel to contour by providing opportunities for headcut erosion or focusing of flow. Erosion rates for well pads are 

greater than for roads, but the total area of well pads is much 

smaller than that of roads, so the overall contribution to total 

sediment erosion is smaller. Where the construction of a well 

pad focuses runoff from bedrock portions of the drainage area, 

well pads can contribute to dramatic local erosion (figs. 27 and 

29). Transect surveys of well pads indicate small net sediment 

losses and gains and a consistent downslope movement of sediment by erosion and redeposition. Redeposition of sediment 

probably heals many small, newly formed rills and may explain 

the general lack of permanent rill development upslope from the 

well pads and road berms because the redeposition indicates 

that runoff and sediment movement are large enough to successively form and heal rills.

Summary

Largo Canyon, located in the San Juan Basin of northwestern New Mexico, is one of the longest dry washes in the world. 

Largo Canyon drains an area of 1,700 mi2. The head of Largo 

Canyon is on the western slope of the Continental Divide. The 

regional topography is composed of sandstone-capped mesas 

dissected by deep, narrow canyons and arroyos. Weathering of 

shale and sandstone results in a highly erodible landscape and 

an abundant sediment supply.

Oil and gas production in the San Juan Basin has required 

the development of an extensive network of dirt roads to service 

the oil and gas wells. Presently, there are about eight wells per 

square mile; the density of wells is expected to increase. Potential environmental effects on landscape stability that may result 

from construction of additional oil- and gas-well service roads 

and well pads have not been documented.

The Harris Canyon road- and well-pad analysis area contains 108 well pads with a combined area of 0.1 mi2, or 64.5 

acres, and 84 miles of road with a road density of 2.5 mi/mi2. 

The Palluche Canyon road- and well-pad analysis area contains 

114 well pads with a combined area of 0.04 mi2, or 28.8 acres, 

and 114 miles of roads with a road density of 2.2 mi/mi2.

Sediment dams were installed at 43 sites: 21 on hillsides 

upslope from roads or pads, 11 at the downslope edges of roads, 

and 11 at the downslope edges of well pads to measure hillslope, road and well-pad erosion. Data from 26 dams were used 

in the analysis. Erosion of roads and well pads was measured 

directly using repeated surveys of monumented survey 

transects. Measurements of sediment accumulation behind 26 

dams, recorded at 4- to 6-week measurement intervals, indicate 

that average erosion rates at the dams significantly correlate to 

size of the contributing drainage area, and the average erosion 

rate is significantly different for dams in certain landscape positions. The average erosion rate normalized by drainage area was 

about 0.001 ft/yr below roads, 0.003 ft/yr on the hillslopes, and 

0.011 ft/yr below well pads.

Results of a two-sample t-test indicated that for dams 

located at the downslope edges of well pads, average erosion 

rates were significantly larger than for dams below roads and on 

hillslopes. No significant difference in average erosion rate was 

indicated, however, for dams below roads compared with dams 

located on hillslopes.

Sediment-accumulation data for measurement intervals 

over which dams were breached during 2002, resulting from the 

large volume of runoff generated by high-intensity storms, were 

not used to compute erosion rates. For this reason, the higher 

range of erosion rates is underrepresented and the results are 

biased toward the lower end of the range of erosion rates in this 

study. 

Measurements along road transects generally indicate that 

sediment is eroded from the top of road berms and redeposited 

at the base of the berms and may be transported downslope 

along the road. Measurements along well-pad transects generally indicate that sediment eroded from hillslopes is transported 

over the surface of the well pad and down the well-pad edges. 

Based on field observations, roads aligned parallel to contour facilitate erosional processes in two ways: (1) roads cut 

across and collect runoff from previously established drainages 

and (2) roads, where they are cut into hillsides or into the land 

surface, provide focal points for the initiation of erosion. Runoff 

and sediment from pre-existing small drainages may be intercepted by and transported along the road to an outlet point 

where the potential erosive capacity of the runoff is magnified 

by the accumulation of runoff. Roads also facilitate erosional 

processes by providing focal points along road berms for the 

initiation of headcut erosion. Periodic grading of roads maintains the heights of the berms and the potential energy conditions needed to initiate rill formation and headcut erosion. 

Across-contour roads can serve as conduits for sediment 

transport, but constitute a small percentage of the road network. 

Well-pad berms generally were much higher than road berms, 

and fan deposits were observed to form at the base of some upslope well-pad berms. Dams below the downslope side of well 

pads trapped sediment mainly from the well-pad slope itself, 

with drainages sometimes developing over time to capture runoff from the well-pad surface. Like roads, well pads can provide 

conditions for focusing runoff and locally increasing erosion. 
42 Effects of Roads and Well Pads on Upland Erosion in the Largo Canyon Watershed, New Mexico, 2001-02

Well pads function in the erosion process in a way similar 

to roads parallel to contour by providing areas for headcut erosion or focusing of flow. Erosion rates for well pads are greater 

than for roads, but the total area of well pads is much smaller 

than that of roads, so the overall contribution to total sediment 

erosion from well pads is smaller.

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