Southwest Crown of the Continent 

GRAIP Roads Assessment

Center Horse and Morrell/Trail Project Area, 

Poorman Creek, and Cold Creek

Lolo, Helena, and Flathead National Forests, Montana

August 15, 2014

Richard Cissel1, Tom Black1, Nathan Nelson1, and Charlie Luce2

1Hydrologist

2

Research Hydrologist

U.S. Forest Service

Rocky Mountain Research Station

322 E. Front St, Suite 401

Boise, ID 83702
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Table of Contents

Acknowledgments.........................................................................................................................................8

Executive Summary.......................................................................................................................................9

Center Horse and Morrell/Trail Project Area Summary ...........................................................................9

Poorman Creek Summary .......................................................................................................................11

Cold Creek Summary...............................................................................................................................13

Jammer Roads Summary ........................................................................................................................14

Conclusions.............................................................................................................................................15

1.0 Background .....................................................................................................................................17

2.0 Objectives and Methods.................................................................................................................18

3.0 Study Areas.....................................................................................................................................19

Center Horse and Morrell/Trail Project Area..........................................................................................19

Poorman Creek .......................................................................................................................................21

Cold Creek...............................................................................................................................................23

4.0 Results.............................................................................................................................................25

4.1 Road-Stream Hydrologic Connectivity ........................................................................................25

Center Horse Morrell-Trail Project Area.............................................................................................26

Poorman Creek ...................................................................................................................................26

Cold Creek ...........................................................................................................................................27

4.2 Road Surface Fine Sediment Production and Delivery ...............................................................28

Center Horse Morrell-Trail Project Area.............................................................................................28

Poorman Creek ...................................................................................................................................31

Cold Creek ...........................................................................................................................................33

4.3 Downstream Sediment Accumulation ........................................................................................35

Center Horse Morrell-Trail Project Area.............................................................................................35

Poorman Creek ...................................................................................................................................40

Cold Creek ...........................................................................................................................................44

4.4 Landslides....................................................................................................................................47

Center Horse Morrell-Trail Project Area.............................................................................................47

Poorman Creek ...................................................................................................................................51

Cold Creek ...........................................................................................................................................55

4.5 Gullies and Gully Initiation Risk...................................................................................................59

Center Horse Morrell-Trail Project Area.............................................................................................60

Poorman Creek ...................................................................................................................................63

Cold Creek ...........................................................................................................................................65

4.6 Stream Crossing Failure Risk .......................................................................................................67
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Center Horse Morrell-Trail Project Area.............................................................................................67

Poorman Creek ...................................................................................................................................70

Cold Creek ...........................................................................................................................................72

4.7 Drain Point Condition and Fill Erosion ........................................................................................74

Center Horse Morrell-Trail Project Area.............................................................................................74

Poorman Creek ...................................................................................................................................78

Cold Creek ...........................................................................................................................................81

4.8 Risks by Maintenance Level ........................................................................................................84

5.0 Jammer Road Inventory and Observations.....................................................................................86

5.1 Complete Complex Inventory .....................................................................................................87

5.2 Stream Crossing Survey...............................................................................................................91

6.0 Summary and Conclusions..............................................................................................................95

Center Horse and Morrell/Trail Project Area Summary .........................................................................95

Poorman Creek Summary .......................................................................................................................97

Cold Creek Summary...............................................................................................................................98

Jammer Roads Summary ......................................................................................................................100

Conclusions...........................................................................................................................................101

References ................................................................................................................................................103

Appendix A: Road Risks by Maintenance Level Table...............................................................................106

Appendix B: Glossary of Selected Terms ..................................................................................................107

Appendix C: GRAIP Data Management Plan.............................................................................................109

List of Figures

Figure 1. Location of these watershed inventories and Legacy Roads Monitoring Project sites in Region 1.

....................................................................................................................................................................19

Figure 2. Land ownership and all roads within the Center Horse and Morrell/Trail project area. ............20

Figure 3. Geology of the Center Horse and Morrell/Trail project area. .....................................................20

Figure 4. Elevation and location of inventoried roads within the Center Horse and Morrell-Trail project 

area. ............................................................................................................................................................20

Figure 5. Geology of the Poorman Creek area.. .........................................................................................21

Figure 6. Land ownership and all roads within the Poorman Creek area...................................................22

Figure 7. Elevation and location of inventoried roads within the Poorman Creek area. ...........................22

Figure 8. Geology of the Cold Creek area...................................................................................................23

Figure 9. Land ownership and all roads within the Cold Creek area. .........................................................24

Figure 10. Elevation and location of inventoried roads within the Cold Creek area..................................24

Figure 11. Percent total sediment delivered to streams by percent of drain points. ................................29

Figure 12. Sediment production and delivery by drain point type.............................................................29
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Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Figure 13. Fine sediment delivery to channels by road segment and drain point in the upper Little 

Shanley and Black Canyon Creeks area.......................................................................................................30

Figure 14. Percent total sediment delivered to streams by percent of drain points. ................................32

Figure 15. Sediment production and delivery by drain point type.............................................................32

Figure 16. Fine sediment delivery to channels by road segment and drain point in central roaded portion 

of the Cold Creek area. ...............................................................................................................................32

Figure 17. Percent total sediment delivered to streams by percent of drain points. ................................33

Figure 18. Sediment production and delivery by drain point type.............................................................33

Figure 19. Fine sediment delivery to channels by road segment and drain point in the central roaded 

portion of the Cold Creek area. ..................................................................................................................34

Figure 20. Sediment accumulation from all road-related sediment sources (road surface, gullies, 

landslides, and fill erosion) in the Center Horse and Morrell/Trail project area........................................37

Figure 21. Specific sediment from road surface sediment in the Center Horse and Morrell/Trail project 

area. ............................................................................................................................................................38

Figure 22. Specific sediment from all road-related sediment sources (road surface, gullies, landslides, 

and fill erosion) in the Center Horse and Morrell/Trail project area..........................................................39

Figure 23. Sediment accumulation from all road-related sediment sources (road surface, gullies, 

landslides, and fill erosion) in the Poorman Creek area.............................................................................41

Figure 24. Specific sediment from road surface sediment in the Poorman Creek area.............................41

Figure 25. Specific sediment from all road-related sediment sources (road surface, gullies, landslides, 

and fill erosion) in the Poorman Creek area...............................................................................................43

Figure 26. Sediment accumulation from the road surface in the Cold Creek area. ...................................45

Figure 27. Specific sediment from road surface sediment in the Cold Creek area. ...................................46

Figure 28. Observed landslides in the Spring Creek area of the Center Horse and Morrell/Trail project 

area. ............................................................................................................................................................48

Figure 29. Natural slope stability in the Spring Creek drainage of the Center Horse and Morrell/Trail 

project area.................................................................................................................................................49

Figure 30. Changes in slope stability risk in the Spring Creek drainage of the Center Horse and 

Morrell/Trail project area. ..........................................................................................................................50

Figure 31. Observed landslides in the Poorman Creek area.......................................................................51

Figure 32. Natural slope stability in the central part of the Poorman Creek area. ....................................52

Figure 33. Changes in slope stability risk in the central part of the Poorman Creek area. ........................53

Figure 34. Observed landslides in the Cold Creek area. .............................................................................55

Figure 35. Natural slope stability in the Cold Creek area. ..........................................................................56

Figure 36. Changes in slope stability risk in the central part of the Cold Creek area.................................57

Figure 37. Locations of observed gullies and ESI risk at drain points, western portion of the Center Horse 

area. ............................................................................................................................................................60

Figure 38. Length-slope plot that shows the distribution of gullied and non-gullied drain points............62

Figure 39. Locations of observed gullies and ESI risk at drain points, central portion of the Poorman 

Creek area...................................................................................................................................................63

Figure 40. Locations of observed gullies and ESI risk at drain points, central portion of the Cold Creek 

area. ............................................................................................................................................................65
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Figure 41. Distribution of SBI values for the Center Horse and Morrell/Trail project area. ......................67

Figure 42. The stream crossings with the highest risk of plugging and the most severe consequences of 

failure in the Center Horse and Morrell/Trail project area. .......................................................................68

Figure 43. Spring Creek diversion that delivered 41 Mg of sediment to the stream. ................................69

Figure 44. Distribution of SBI values for the Poorman Creek area.............................................................70

Figure 45. The stream crossings with the highest risk of plugging and the most severe consequences of 

failure in the Poorman Creek area..............................................................................................................70

Figure 46. Stream diversion at a natural ford in the western portion of the Poorman Creek area...........71

Figure 47. Distribution of SBI values for the Cold Creek area. ...................................................................72

Figure 48. The stream crossings with the highest risk of plugging and the most severe consequences of 

failure in the Cold Creek area. ....................................................................................................................72

Figure 49. Specific drain point problems by drain type in the Center Horse and Morrell/Trail project area.

....................................................................................................................................................................75

Figure 50. Drain point problems in the Spring Creek watershed. ..............................................................76

Figure 51. Specific drain point problems by drain type in the Poorman Creek area. ................................78

Figure 52. Drain point problems in the western half of the Poorman Creek area.....................................79

Figure 53. Specific drain point problems by drain type in the Cold Creek area. ........................................81

Figure 54. Drain point problems in the Cold Creek area. ...........................................................................82

Figure 55. Sediment delivery risks for all three areas. ...............................................................................84

Figure 56. Fill erosion total mass and delivered mass for all three project areas......................................85

Figure 57. Gully and landslide risks for the Center Horse and Morrell/Trail project area. ........................85

Figure 58. Drain point problems for all three project areas.......................................................................86

Figure 59. Jammer road locations in the Center Horse and Morrell/Trail project area, with the complete 

surveyed complexes and the stream crossings that we surveyed. ............................................................87

Figure 60. Fine sediment delivery to channels by road segment and drain point in the upper Black 

Canyon jammer road complex....................................................................................................................88

Figure 61. Fill erosion and gullies in the Black Canyon jammer road complex. .........................................89

Figure 62. Stream crossings with observed fill erosion on jammer roads in the Center Horse and 

Morrell/Trail project area. ..........................................................................................................................91

Figure 63. Probability graph output from the local fit regression in R.......................................................93

Figure 64. Stream crossings on jammer roads with problems, including observed overtopping, diversion, 

and culvert problems..................................................................................................................................93

List of Tables

Table A. Summary of GRAIP-predicted road risk predictions, Center Horse and Morrell/Trail project area.

....................................................................................................................................................................10

Table B. Summary of GRAIP-predicted road risk predictions, Poorman Creek area...................................12

Table C. Summary of GRAIP-predicted road risk predictions, Cold Creek area...........................................13

Table D. Summary of observed and predicted jammer road risks..............................................................15
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Table 1. Summary of effective road lengths by drain type for the Center Horse and Morrell/Trail Project 

Area.............................................................................................................................................................25

Table 2. Summary of effective road lengths by drain type for the Poorman Creek area. ..........................26

Table 3. Summary of effective road lengths by drain type for the Cold Creek area...................................27

Table 4. Summary of sediment production and delivery at drain points in the Center Horse and 

Morrell/Trail Project Area...........................................................................................................................29

Table 5. Summary of sediment production and delivery at drain points in the Poorman Creek area........31

Table 6. Summary of sediment production and delivery at drain points in the Cold Creek area. ..............33

Table 7. Observed annual sediment yields for nearby areas......................................................................35

Table 8. Project area streams and sediment accumulation and specific sediment accumulation at the 

stream mouth, calculated using only road surface-related sediment and all road sediment sources 

(landslides, gullies, and fill erosion at drain points)....................................................................................36

Table 9. Project area streams and sediment accumulation and specific sediment accumulation at the 

stream mouth, calculated using only road surface-related sediment and all road sediment sources 

(landslides, gullies, and fill erosion at drain points)....................................................................................40

Table 10. Project area streams and sediment accumulation and specific sediment accumulation at the 

stream mouth, calculated using only road surface-related sediment. .......................................................44

Table 11. Number and types of observed landslides, as well as masses and volumes of sediment 

generated and delivered to the stream channel network in the Center Horse and Morrell/Trail project 

area. ............................................................................................................................................................48

Table 12. Landslide risk changes in the Center Horse and Morrell/Trail project area by category and area.

....................................................................................................................................................................50

Table 13. Number and types of observed landslides, as well as masses and volumes of sediment 

generated and delivered to the stream channel network in the Poorman Creek area...............................51

Table 14. Landslide risk changes in the Poorman Creek area by category and area. ................................54

Table 15. Number and types of observed landslides, as well as masses and volumes of sediment 

generated in the Cold Creek area................................................................................................................56

Table 16. Landslide risk changes in the Cold Creek area by category and area. ........................................58

Table 17. Inventoried gullies in the Center Horse and Morrell/Trail project area......................................61

Table 18. Sediment masses produced and delivered by active gullies in the Center Horse and Morrell/Trail 

project area.................................................................................................................................................61

Table 19. Distribution of drain points by ESI value, Center Horse and Morrell/Trail project area. ............62

Table 20. Further distribution information of drain points by ESI value.....................................................62

Table 21. Inventoried gullies in the Poorman Creek area...........................................................................63

Table 22. Sediment masses produced and delivered by active gullies in the Poorman Creek area. ..........64

Table 23. Drain point and ESI statistics for the Poorman Creek area.........................................................64

Table 24. Inventoried gullies in the Cold Creek area...................................................................................65

Table 25. Drain point and ESI statistics for the Cold Creek area.................................................................66

Table 26. Drain point condition problems and fill erosion below drain points, Center Horse and 

Morrell/Trail project area. ..........................................................................................................................74

Table 27. Fill erosion below drain points, volumes and masses, Center Horse and Morrell/Trail project

area. ............................................................................................................................................................77
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Table 28. Drain point condition problems and fill erosion below drain points, Poorman Creek area........78

Table 29. Fill erosion below drain points, volumes and masses, Poorman Creek area. .............................79

Table 30. Drain point condition problems and fill erosion below drain points, Cold Creek area................81

Table 31. Fill erosion below drain points, volumes and masses, Cold Creek area......................................82

Table 32. Summary of sediment production and delivery at drain points on the jammer road complexes 

that were inventoried with GRAIP in the Center Horse and Morrell/Trail Project Area. ............................88

Table 33. Estimation of sediment delivery from road surfaces for all jammer roads in the Center Horse 

and Morrell/Trail project area, based on the road surface sediment delivery rate per kilometer from the 

inventoried complexes. ...............................................................................................................................89

Table 34. Mass wasting masses and delivery for the observed mass wasting in the Black Canyon jammer 

complex.......................................................................................................................................................90

Table 35. Fill erosion statistics for the jammer road stream crossings observed in the Center Horse and 

Morrell/Trail project area. ..........................................................................................................................92

Table 36. Stream crossings on jammer roads with problems in the Center Horse and Morrell/Trail project 

area. ............................................................................................................................................................94

Table 37. Summary of GRAIP-predicted road risk predictions, Center Horse and Morrell/Trail project area.

....................................................................................................................................................................96

Table 38. Summary of GRAIP-predicted road risk predictions, Poorman Creek area.................................97

Table 39. Summary of GRAIP-predicted road risk predictions, Cold Creek area.........................................99

Table 40. Summary of observed and predicted jammer road risks. .........................................................100
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Acknowledgments

Funding from the Southwest Crown of the Continent Collaborative and from the Great Northern 

Landscape Conservation Cooperative (GNLCC) made this effort possible. We would like to thank the field 

crews (Adrianna Hummer, Benjamin Sundy, Austin Maphis, Ian Reeves, Amberle Keith, Dylan Esmonde, 

Erik Smith, and Hayley Connolly-Newman) for carefully and diligently collecting this data. We would also 

like to thank the Seeley Lake office of the Lolo National Forest, and Amy Vernarsky in particular, the 

Lincoln office of the Helena National Forest, and the Condon office of the Flathead National Forest for 

helping to provide logistical support and bunkhouse space. Thanks also to Anne Carlson, Taylor Greenup, 

Shane Hendrickson, Bruce Rieman, Adam Switalski, Robert Al-chokhachy, and Cameron Thomas.

The full dataset from this project will be available to the public through the GNLCC website, at 

http://greatnorthernlcc.org/. 
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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Executive Summary

This report presents results from three watershed-wide inventories and assessments of roads in the 

Center Horse and Morrell/Trail project area, Poorman Creek watershed, and Cold Creek watershed in 

western Montana using the Geomorphic Road Analysis and Inventory Package (GRAIP). GRAIP is a fieldbased model developed by the Forest Service Rocky Mountain Research Station and Utah State 

University. The primary objectives of the project were to:

• Identify the current level of fine sediment delivery from roads to streams compared to 

reference.

• Identify the types and sources of road-related hydrologic risk in the watershed.

• Select and prioritize future restoration actions to improve watershed conditions and move 

towards an ecologically and economically sustainable road system.

• Establish a pre-treatment condition for comparison to the same roads after treatments have 

been applied in certain areas.

• Compare GRAIP results with modified PACFISH/INFISH Biological Opinion (PIBO) monitoring 

program instream observation data for the watershed, collected concurrently with the GRAIP 

inventory, to investigate the ability to link instream conditions with upslope processes. (This will 

be a separate report).

Field inventory and modeling analysis of the public roads in the Center Horse and Morrell/Trail project 

area, the Poorman Creek watershed area, and the Cold Creek watershed area in the Southwest Crown of 

the Continent in western Montana using the GRAIP model provided detailed, site specific data on 

sediment-related watershed impacts from roads. Impacts are both chronic, in terms of annual sediment 

input to streams, and pulsed, such as during storm events when road connectivity to the channel 

networks is at its maximum. Inventory data was collected on 779 km (484 mi) of road, including 10,835

drain points, by two field crews during the summer months of 2012 and 2013 (June to October).

Additionally, jammer-type logging roads were sampled and their road-stream intersections were 

surveyed in the Center Horse and Morrell/Trail project area.

The GRAIP model was used to predict sediment risk and sediment-related impacts from roads. The 

model predicts road to stream hydrologic connectivity, sediment delivery to streams, downstream 

sediment accumulation, risks of shallow landslides caused by roads, gully initiation risk below drain 

points, and risks to road-stream crossings (Tables A, B, and C). Inventory data is also used to locate and 

describe problems with existing drain points. In addition, GRAIP model data will be compared to instream PIBO monitoring for these project areas in a separate document. 

Center Horse and Morrell/Trail Project Area Summary

In the Center Horse and Morrell/Trail project area, there were 407 km (253 mi) of road and 5061 drain 

points surveyed. Table A presents a summary of the findings for this project area. Hydrologic 

connectivity was found to be a relatively low 4% of all road length at 16 km out of 407 km (10 mi out of 

252 mi). The model predicted 21.4 Mg/yr of delivered road surface fine sediment to stream channels, 

which is 5% of the 456 Mg generated annually by the road surface. This sediment was delivered through 

314 of 5061 (6%) drain points. There was 16.2 Mg/yr of delivery that occurred within 10 m of a stream 

crossing. This is 76% of all sediment delivery and 57% of all sediment produced within 10 m of a stream 

crossing.
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Specific sediment due to road surface-related sediment for the whole Center Horse and Morrell/Trail 

project area was 0.10 Mg/km2/yr, or 1% of the observed total average fine sediment yield for five 

nearby areas as determined by reservoir coring or suspended sediment extrapolations. Including 

sediment delivered to streams through other sources (landslides, gullies, and fill erosion at drain points), 

the specific sediment for the whole project area was 0.21 Mg/km2/yr, or about 2% of the observed 

average fine sediment yield for the nearby areas. Some heavily impacted stream reaches had road 

sediment delivery values as high as 4.9 Mg/km2/yr with only road surface fine sediment, or 18.1 

Mg/km2/yr including mass wasting sediment. Reaches in Shanley, Little Shanley, Blacks Canyon, and 

lower Spring Creeks showed particularly high specific sediment values above 0.3 Mg/km2/yr, or 3% to 

19% above the reference sediment yield.

There were 18 landslides observed by field crews in the course of the inventory, with a total volume of 

1319 m3(1726 yd3). Of those, 10 were road related. It was conservatively estimated that 176 Mg of 

landslide derived sediment has been delivered to streams, which is roughly half the rate of that from 

road surfaces over 20 years (8.8 Mg/yr). It would take about eight years for the fine sediment delivery 

from road surfaces to equal the total mass of delivered sediment from landslides. Calibrated stability 

index modeling with SINMAP conservatively showed that 6 km2(2 mi2), or 3%, of the watershed area 

was put at higher risk of shallow landslide initiation by road drainage.

Gullies were observed at 33 locations by field crews, totaling 208 m3(272 yd3) in volume, and all 

occurring in wet swales. It was estimated that these gullies delivered 217 Mg of sediment to the stream 

channel, equivalent to half the rate of that from road surfaces over 20 years (11 Mg/yr). It would take 

about ten years for the fine sediment delivery from road surfaces to equal the total mass of delivered 

sediment from gullies. Of 3713 applicable drain points, 587 (16%) had an elevated risk of gullying. The 

Table A. Summary of GRAIP-predicted road risk predictions, Center Horse and Morrell/Trail project 

area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4% of road length, 16 km; 6% of drain points connected

Fine Sediment Delivery 5% of sediment produced, 21.4 Mg/yr

Sediment in Streams 0.21 Mg/km2/yr; 2% of average sediment yield for nearby areas

Landslide Risk Estimated 176 Mg of sediment delivered to streams, 3% of 

watershed area with elevated risk due to roads

Gully Risk Estimated 11 Mg/yr of sediment delivered to streams, 16% of 

all drain points exceed ESIcrit threshold

Stream Crossing Risks

 - plug potential 27 sites (23%) with elevated risk (SBI > 2)

 - fill at risk 6843 m3fill at risk, average 60 m3per crossing

 -diversion potential 61 sites (42%) with diversion potential

Drain Point Problems 811 drain points (16% of all drain points) with problems, 61 m3

of fill erosion (2% of drain points), estimated 2.9 Mg/yr of fill 

delivered to streams
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

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11

critical gully initiation index (ESI) was found to be 14. The average ESI for the points without gullies was 

9, while it was 11 for the points with gullies. The gully occurrence rate for drain points that fell above 

the ESI threshold was 1.0% versus 0.5% for points that fell below the ESI threshold.

There were 116 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 1.9. There were 25 crossings with an 

elevated SBI of 3. Two crossings had an SBI of 4, which is the highest possible value. The total calculated 

volume of fill at risk in an overtopping type event was 6840 m3(8950 yd3). There were 55 stream 

crossings with the potential to divert stream flow from a plugged culvert down the road and onto 

unchanneled hillslopes. There were 14 stream crossings with an SBI of 3 or 4 and diversion potential,

four of which were observed to have already failed or be at risk for imminent failure. There was a total 

of 824 m3(1077 yd3) of fill at risk at these points. Six overtopped crossings were observed, five due to 

sediment plugging and one due to wood plugging. Three of those were due to undersized pipes, and one 

delivered 26 m3(910 ft3) to streams.

Of the 5061 recorded drain points, 811 (16%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Sumps had the highest rate of problems, with 11 

of 24 (46%), followed by ditch relief culverts (155 of 392, 40%). Fill erosion was recorded at 83 drain 

points (2%), with a total volume of 85 m3(3000 ft3). Fill erosion was most common at non-engineered 

drains with 28 instances and 23 m3(820 ft3). Stream crossings had 44 m3(1550 ft3) eroded from 4 of 146 

crossings (2%). It was estimated that fill erosion delivered 87 Mg of sediment to the stream channel, or 

about a quarter of the rate of the of road surface sediment over 20 years (4.4 Mg/yr). It would take 

about four years for the fine sediment delivery from road surfaces to equal the total mass of delivered 

sediment from fill erosion.

Poorman Creek Summary

In the Poorman Creek area, there were 174 km (108 mi) of road and 2190 drain points surveyed. Table B

presents a summary of the findings for this project area. Hydrologic connectivity was found to be a 

relatively low 4.7% of all road length at 8 km out of 174 km (5 mi out of 106 mi). The model predicted 

11.5 Mg/yr of delivered road surface fine sediment to stream channels, which is 4.6% of the 247 Mg 

generated annually by the road surface. This sediment was delivered through 97 of 2190 (4%) drain 

points. There was 5.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 49% of all 

sediment delivery and 77% of all sediment produced within 10 m of a stream crossing.

Specific sediment due to road surface-related sediment for the whole Poorman Creek area was 0.11

Mg/km2/yr, or 1% of the observed total average fine sediment yield for five nearby areas as determined 

by reservoir coring or suspended sediment extrapolations. Including sediment delivered to streams 

through other sources (landslides, gullies, and fill erosion at drain points), the specific sediment for the 

whole project area was 0.19 Mg/km2/yr, or about 2% of the observed average fine sediment yield for 

the nearby areas. The most heavily impacted stream reaches had road sediment delivery values as high 

as 0.8 Mg/km2/yr with only road surface fine sediment, or 4.0 Mg/km2/yr including mass wasting 

sediment.

There were 5 landslides observed by field crews in the course of the inventory, with a total volume of 

252 m3(329 yd3). All were road related. It was conservatively estimated that 91 Mg of landslide derived 

sediment has been delivered to streams, which is roughly half the rate of sediment from road surfaces 
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

12

over 20 years (4.5 Mg/yr). It would take about 8 years for the fine sediment delivery from road surfaces 

to equal the total mass of delivered sediment from landslides. Calibrated stability index modeling with 

SINMAP conservatively showed that 3 km2(1 mi2), or 2%, of the watershed area was put at higher risk of 

shallow landslide initiation by road drainage.

Gullies were observed at 7 locations by field crews, totaling 157 m

3

(206 yd3) in volume, with none 

occurring in wet swales. It was estimated that these gullies delivered 4 Mg of sediment to the stream 

channel, which is negligible compared to the rate of road surfaces over 20 years (0.2 Mg/yr). It would 

take less than one year for the fine sediment delivery from road surfaces to equal the total mass of 

delivered sediment from gullies. There were too few gullies to determine an ESIcrit, suggesting that the 

gully initiation risks here may be very low. The average ESI across the Poorman Creek area was 8.

There were 29 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 1.7. There were 5 crossings with an elevated 

SBI of 3. No crossings had an SBI of 4, which is the highest possible value. The total calculated volume of 

fill at risk in an overtopping type event was 1399 m

3

(1830 yd3). There were eight stream crossings with 

the potential to divert stream flow down the road and onto unchanneled hillslopes. There was one 

stream crossing with an SBI of 3 and diversion potential. There was a total of 21 m3(27 yd3) of fill at risk 

at this point. Two natural ford type crossings were observed to divert flow down the road, though no 

major erosion was observed at the time of the survey.

Of the 2190 recorded drain points, 270 (12%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Ditch relief culverts had the highest rate of 

problems, with 18 of 56 (32%), followed by broad based dips (120 of 412, 29%). Fill erosion was 

recorded at 22 drain points (1%), with a total volume of 11 m

3

(400 ft3). Fill erosion was most common at 

Table B. Summary of GRAIP-predicted road risk predictions, Poorman Creek area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4.7% of road length, 8 km; 4% of drain points connected

Fine Sediment Delivery 4.6% of sediment produced, 11.5 Mg/yr

Sediment in Streams 0.19 Mg/km2/yr; 2% of average sediment yield for nearby areas

Landslide Risk Estimated 91 Mg of sediment delivered to streams, 2.2% of 

watershed area with possible elevated risk due to roads

Gully Risk Estimated 0.2 Mg/yr of sediment delivered to streams, too few 

gullies to determine ESIcrit

Stream Crossing Risks

 - plug potential 5 sites (17%) with elevated risk (SBI > 2)

 - fill at risk 1399 m3fill at risk, average of 48 m3per crossing

 - diversion potential 8 sites (17%) with diversion potential

Drain Point Problems 270 drain points (12% of all drain points) with problems, 11 m3of 

fill erosion (1% of drain points), estimated 0.2 Mg/yr of fill erosion 

delivered to streams
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

13

non-engineered drains with 16 instances and 8 m

3

(300 ft3). It was estimated that fill erosion delivered 3

Mg of sediment to the stream channel, which is negligible compared the amount of road surface 

sediment over 20 years (0.2 Mg/yr).

Cold Creek Summary

In the Cold Creek area, there were 198 km (123 mi) of road and 3584 drain points surveyed. Table C

presents a summary of the findings for this project area. Hydrologic connectivity was found to be a 

relatively low 4% of all road length at 9 km out of 198 km (6 mi out of 123 mi). The model predicted 9.8 

Mg/yr of delivered road surface fine sediment to stream channels, which is 6% of the 162 Mg generated 

annually by the road surface. This sediment was delivered through 205 of 3584 (6%) drain points. There 

was 6.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 67% of all sediment 

delivery and 75% of all sediment produced within 10 m of a stream crossing.

Specific sediment due to road surface-related sediment for the whole Cold Creek area was 0.1 

Mg/km2/yr, or 1% of the observed total average fine sediment yield for five nearby areas as determined 

by reservoir coring or suspended sediment extrapolations. No other sources were observed to deliver 

sediment to streams. The most heavily impacted stream reaches had road sediment delivery values as 

high as 1.1 Mg/km2/yr.

There were 9 landslides observed by field crews in the course of the inventory, with a total volume of 

175 m3(229 yd3). Only one landslide was not road related. No landslide sediment was observed to have 

been delivered to streams. Calibrated stability index modeling with SINMAP conservatively showed that 

Table C. Summary of GRAIP-predicted road risk predictions, Cold Creek area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4% of road length, 9 km; 6% of drain points connected

Fine Sediment Delivery 4% of sediment produced, 9.8 Mg/yr

Sediment in Streams 0.10 Mg/km2/yr; 1% of average sediment yield for nearby areas

Landslide Risk No landslide sediment delivered to streams; 0.6% of watershed 

area with possible elevated risk due to roads

Gully Risk No gully sediment delivered to streams, too few gullies to 

determine ESIcrit

Stream Crossing Risks

 - plug potential 28 sites (39%) with elevated risk (SBI ≥ 2)

 - fill at risk 2095 m3fill at risk, average of 31 m3per crossing

 - diversion potential 39 (34%) sites with diversion potential

Drain Point Problems 284 drain points (8% of all drain points) with problems, 3 m3of fill 

erosion (1% of drain points), estimated 0.005 Mg/yr of fill erosion 

delivered to streams
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

14

0.6 km2(0.2 mi2), or 0.6%, of the watershed area was put at higher risk of shallow landslide initiation by 

road drainage.

Gullies were observed at 3 locations by field crews, totaling 5 m3(7 yd3) in volume, with none occurring 

in wet swales. No gullies were observed to deliver sediment to the stream channel in Cold Creek. There 

were too few gullies to determine an ESIcrit, suggesting that the gully initiation risks here may be very 

low. The average ESI across the Cold Creek area was 4.

There were 71 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 2.3. There were 26 crossings with an 

elevated SBI of 3. Two crossings had an SBI of 4, which is the highest possible value. The total calculated 

volume of fill at risk in an overtopping type event was 2090 m3(2730 yd3). There were 39 stream 

crossings with the potential to divert stream flow from a plugged culvert down the road and onto 

unchanneled hillslopes. There were 14 crossings with an SBI of 3 or 4 and diversion potential. There was 

a total of 332 m3(434 yd3) of fill at risk at these points. Of those 14 crossings, half received the stream 

flow from the ditch, though this appeared to be intentional.

Of the 3584 recorded drain points, 284 (8%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Stream crossings had the highest rate of 

problems, with 45 of 115 (39%), followed by ditch relief culverts (80 of 266, 30%). Fill erosion was 

recorded at 23 drain points (1%), with a total volume of 3 m3(110 ft3). Fill erosion was most common at 

broad based dips with 18 instances and 3 m3(90 ft3). It was estimated that fill erosion delivered 0.5 Mg 

of sediment to the stream channel, which is negligible compared the amount of road surface sediment 

over 20 years (0.005 Mg/yr).

Jammer Roads Summary

Two complete jammer road complexes totaling 19 km (11 mi) of road and 325 drain points in the Center 

Horse project area were inventoried using the GRAIP method. These vegetated and shallow-slope roads 

delivered 0.02 Mg/yr, which is 2% of the 1 Mg/yr generated on the road surfaces (Table D). If this 

delivery rate is applied to all jammer roads in the Center Horse and Morrell/Trail project area, then it 

can be expected that these roads deliver less than 1 Mg/yr from the road surface. A small stream 

diversion was observed that resulted in two delivering gullies (29 Mg) and two non-engineered points 

with fill erosion, one of which delivered to the stream (23 Mg). There were no other observed instances 

of mass wasting, including anything not related to the stream crossing or any landslides.

We conducted a census of all of the stream crossings on jammer roads in the Center Horse and 

Morrell/Trail project area, for a total of 71 crossings. Streams were defined as continuous features with 

a bed, banks, and evidence of flow for some part of most years. There were 61 natural ford-type 

crossings (no infrastructure) and ten crossings with culverts. Nine crossings (13%) were observed to 

have evidence of stream diversion or other problems. There were 31 crossings (44%) with fill erosion, 

totaling 207 m3(7300 ft3), all of which was assumed to deliver (331 Mg). This was roughly equivalent to 

that from road surfaces on non-jammer roads in the Center Horse and Morrell/Trail project area over 20 

years (17 Mg/yr).

The average volume of fill available to erode at each crossing was estimated to be 12 m3(16 yd3) per 

crossing. Of this amount, an average of 3 m3(4 yd3) per crossing has already been eroded, suggesting 
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

15

that 25% of possible erosion has already occurred, and up to 75% remains (about 600 m3or 22,000 ft3). 

Differences in the shape and construction of each stream crossing, and the timing of high flows and 

transport capacity of the streams, suggest that each stream crossing will respond at a different rate, and 

may include some deposition. It was found that on hillslopes of greater than about 40%, every stream 

crossing in the Center Horse area had fill erosion, suggesting that the stream crossings on steeper slopes 

may be at higher risk of failure than those on lower slopes.

Conclusions

Under the observed conditions, the GRAIP inventories in the Southwest Crown of the Continent suggest 

low risk across the measured metrics when considered at the watershed scale. The Center Horse and 

Morrell/Trail project area had the most risk overall. There are two other non-watershed GRAIP sites in 

the northern Rockies; one site in the Clearwater National Forest (Cissel et al. 2011A), and one in the 

Gallatin National Forest (Cissel et al. 2011B). Compared to these sites, these three watersheds fall within 

the typical range for landslide risk, gully risk, stream crossing plugging potential and diversion potential, 

and drain point problems and fill erosion for both sites. The stream crossing fill at risk is slightly higher in 

the Center Horse and Morrell/Trail project area and Poorman Creek, but within the typical range in Cold 

Creek. The Clearwater site had much higher road surface sediment delivery and hydrologic connectivity, 

while this data is in range of the Gallatin site. Compared to a site in the Olympic National Forest in 

western Washington (Cissel et al. 2011C), which is considered to have high risk in all metrics, the Center 

Horse and Morrell/Trail project area has low to moderately low risk in all areas. 

Although sediment delivery risk related to roads is low from the watershed perspective, several road 

segments were identified that may need treatment to minimize sediment delivery effects that are 

significant at the stream reach scale. Depending on downstream habitat and species presence, fine 

Table D. Summary of observed and predicted jammer road risks.

Impact/Risk Type Predicted Risks

Complete Complex Inventory

Fine Sediment Delivery 2% of sediment produced; 0.02 Mg/yr

Estimated Sediment 

Delivery for All Jammer 

Roads

0.4 Mg/yr, using a delivery rate of 0.001 Mg/yr/km

Gullies and Fill Erosion 

Risks

29 Mg delivered to streams from gullies, 23 Mg delivered to 

streams from fill erosion, estimated 3 Mg/yr

Stream Crossing Survey

Fill Erosion Risks, 

Observed

44% of stream crossings with fill erosion, estimated 17 Mg/yr 

delivered to streams

Fill Erosion Risks, Future 

Estimated

25% of estimated risk has been realized, up to 75% (600 m3) 

may remain

Other Problems 9 crossings (13%) with observed stream diversions or other 

problems
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

16

sediment delivery effects may be significant at a stream reach scale. Ongoing work comparing aquatic 

habitat conditions between managed and unmanaged reaches using PIBO data will help refine these 

questions.

Road maintenance level appears to have a small to moderate effect on the various risk metrics. Higher 

maintenance levels (ML 3 and 4; more traffic, more frequent and more intense maintenance) had 

somewhat more sediment delivered from their road surfaces, but mass wasting risks were lower. Lower 

maintenance level roads (ML 1 and 2; little to no traffic, little to no maintenance) had higher mass 

wasting risks. These relationships suggest that traffic has an important effect on road surface fine 

sediment production, but regular more intense maintenance can prevent mass wasting problems. On 

some lower maintenance level roads, it may be beneficial to treat spots that are at high risk of erosion.

The sediment delivery from fill erosion and mass wasting at jammer road-stream intersections in the 

Center Horse and Morrell/Trail project area was on the same scale as the road surface fine sediment 

delivery from non-jammer roads in the same area. The highly vegetated and low slope jammer road 

surfaces themselves did not appear to have significant impacts. Treatments to jammer roads should be 

focused on the roads with stream crossings. However, the consequences of removing vegetation on the 

road surface to access the jammer road stream crossings may increase the contributions of their surface 

fine sediment to streams. Data to be collected in the summer of 2014 may help to further understand 

the causes and distribution of erosion at stream crossings on jammer roads.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

17

1.0 Background

The National Forest Transportation System represents a major public investment and provides many 

benefits to forest managers and the public. Roads, however, also have negative effects on water quality, 

aquatic ecosystems, and other resources. There is currently a large backlog of unfunded maintenance, 

improvement, and decommissioning work needed on National Forest roads. Critical components of the 

infrastructure (e.g., culverts) are also nearing or have exceeded their life-expectancy, adding further risk 

and impacts to watershed and aquatic resources.

The Center Horse and Morrell/Trail project area, and the Poorman Creek and Cold Creek watersheds are

part of an ongoing collaborative project in the southwest Crown of the Continent of western Montana 

designed to assess the impacts of forest roads and jammer-type logging roads on aquatic habitat. 

Collaborators include the Lolo, Helena, and Flathead National Forests; Wildlands CPR; the Clearwater 

Resource Council; The Wilderness Society; and many others. Cottonwood Creek within the Center Horse 

area is listed under a 1996 TMDL for sediment (Montana Department of Environmental Quality 2008).

The GRAIP data collection and analysis procedure provides land managers with field-based data that 

captures the extent to which roads and associated features deliver uncharacteristic amounts of fine 

sediment to the stream network. GRAIP identified precise locations where sediment delivery was 

occurring, where drainage features were compromised, and where road maintenance or 

decommissioning was required. This detailed information can then be used to prioritize actions to 

minimize adverse watershed and aquatic impacts from roads.

All roads that were managed by the Forest Service or were otherwise located on public lands were 

targeted for inventory in 2012 and 2013, including jammer-type roads which were inventoried in 2013. 

Roads on existing geographic information system (GIS) layers were targeted for inventory (about 1280

km, 790 mi in all three areas). However, some additional previously unmapped roads were found and 

inventoried during the course of the study. Jammer-type roads totaled 380 km (230 mi) in existing GIS 

layers, and these were sampled as opposed to completely inventoried. A total of 407 km (253 mi) of 

road was inventoried within the Center Horse and Morrell/Trail project area boundary. Within the 

Poorman Creek area, 174 km (108 mi) were surveyed. Within Cold Creek, there were 198 km (123 mi) of 

road surveyed. In the Center Horse Morrell/Trail project area, 18 km (11 mi) of jammer roads were 

surveyed. The majority of field work has been completed, and work in 2014 includes closer examination 

of jammer road stream crossings. Field work in 2012 began on June 5 and was completed on October 

16. Work began in 2013 on June 5 and was completed on October 25. Two crews collected data by 

vehicle or by foot each season.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

18

2.0 Objectives and Methods

GRAIP is formulated to assess the geomorphic and hydrologic impacts of roads, their physical condition, 

and associated stream connections. It is a relatively intensive field-based method that provides detailed 

information designed to improve understanding of the effect of roads on sediment routing watershed 

processes. Specifically, this project was designed to address the following in the three project areas:

 Identify the current level of fine sediment delivery from roads to streams compared to 

reference.

 Identify the types and sources of road-related sediment risk in the watershed.

 Select and prioritize future restoration actions to improve watershed conditions and move 

towards an ecologically and economically sustainable road system.

 Establish a pre-treatment condition for comparison to the same roads after treatments have 

been applied in certain areas.

 Compare GRAIP results with PIBO data for the watershed collected concurrently with the GRAIP 

inventory to investigate the ability to link instream condition with upslope processes. (This will 

be a separate report).

GRAIP is used to inventory and model the risk profile of each of the road segments and drain point 

features included in the study. The GRAIP system consists of a detailed, field-based road inventory 

protocol combined with a suite of GIS models. The inventory is used to systematically describe the 

hydrology and condition of a road system with Geographic Positioning System (GPS) technology and 

automated data forms (Black et al. 2012). The GIS applications couple field data with GIS terrain analysis 

tools to analyze road-stream hydrologic connectivity, fine sediment production and delivery, 

downstream sediment accumulation, stream sediment input, shallow landslide risk potential with and 

without road drainage, gully initiation risk, and the potential for and consequences of stream crossing 

failures. Detailed information about the performance and condition of the road drainage infrastructure 

is also supplied (Cissel et al. 2012).
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

19

3.0 Study Areas

These three projects areas (Center Horse and Morrell/Trail, Poorman Creek, and Cold Creek) are the first 

watershed-scale GRAIP inventories to be completed in the U.S. Forest Service Northern Region (Region 

1; Figure 1). Other inventories have been completed or are underway in Oregon, Washington, California 

and Idaho (Regions 6, 5, and 4, respectively). Additionally, there is an ongoing region- and western U.S.-

wide Legacy Roads monitoring project, encompassing eight sites in Region 1 where road 

decommissioning, storage, and storm damage risk reduction has been or will be implemented, including 

two sites within the Lolo National Forest (in the Fishtrap Creek watershed) and one site in the Flathead 

National Forest (at Hungry Horse Reservoir).

Center Horse and Morrell/Trail Project Area

The Center Horse and Morrell/Trail project area is located within the Clearwater River watershed, which 

is located east of Seeley Lake, MT, and drains into the Blackfoot River and then the Clark Fork River in 

western Montana. The project area watersheds drain about 220 km2(80 mi2; 53,100 aces), and the 

Clearwater River drains about 3140 km2(1210 mi2; 775,900 acres).

The project area covers two main geologic units (Figure 2). Glacial deposits and other alluvium cover the 

valley bottoms (about 139 km2or 54 mi2), and carbonates and quartzite of the Mesoproterozoic Belt 

Supergroup underlay the valley walls and ridges (131 km2or 51 mi2). There are two faults in the area, 

running roughly northwest-southeast (Ludington et al. 2005). Terrain in the project area is heavily 

influenced by Pleistocene glaciation, with steep valley walls and flat hummocky valley bottoms. 

Elevations in the project area range from 1230 m (4040 ft) to 2620 m (8600 ft), and inventoried roads 

range from 1270 m (4170 ft) to 2360 m (7740 ft). Average annual precipitation in the project area ranges 

from 460 mm/yr (18 in/yr) to 1880 mm/yr (74 in/yr; Montana Department of Environmental Quality 

2011).

Figure 1. Location of these watershed inventories and Legacy Roads Monitoring Project sites in Region 1.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

20

The Center Horse and Morrell/Trail project area is comprised of primarily federally owned and managed 

land (Figure 3). The Forest Service manages 240 km2(90 mi2, 59,300 acres, 94%); 7 km2(3 mi2, 1700 

acres, 3%) is private; the remaining 9 km2(3 mi2, 2200 acres, 4%) managed by the Bureau of Land 

Management and the State of Montana.

Figure 3. Geology of the Center Horse and Morrell/Trail project 

area.

Figure 2. Land ownership and all roads within the Center Horse 

and Morrell/Trail project area. The watershed boundary is 

buffered by 500 m (1640 ft).

Figure 4. Elevation and location 

of inventoried roads within the 

Center Horse and Morrell-Trail 

project area.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

21

All roads on federal and state lands were inventoried, for a total of 407 km (253 mi), with the exception 

of jammer-type logging roads (410 km, 250 mi), which were sampled in 2013 instead of fully 

inventoried. About 30 km (19 mi) of road had been previously mapped, but was found to not exist on 

the ground. Conversely, about 20 km (12 mi) of road was inventoried that was not previously mapped 

(Figure 4). About 10 km (6 mi) of mapped road had been recontoured, and was not inventoried.

Poorman Creek

Poorman Creek is also located within the Blackfoot River watershed, south of Lincoln, MT. The Poorman 

Creek watershed drains about 100 km2(40 mi2, 26,000 acres). The Blackfoot River drains about 6200 

km2(2400 mi2, 1.5 million acres). 

Poorman Creek covers three main geologic units (Figure 5). Alluvium covers the lowest valley bottoms 

(about 8 km2or 3 mi2). Carbonates of the Mesoproterozoic Belt Supergroup (85 km2or 33 mi2) and 

igneous intrusive diorite of possibly Cretaceous origin underlay the bulk of the rest of the watershed (39

km2or 15 mi2; Ludington et al. 2005). Terrain in Poorman Creek is not as heavily influenced by glaciation 

as the other two project areas. Valley walls are shallower, and valley bottoms are less broad. The terrain 

is more dissected by streams. Elevations in the project area range from 1390 m (4550 ft) to 2350 m 

(7720 ft), and inventoried roads range from 1400 m (4600 ft) to 2340 m (7670 ft). Average annual 

precipitation in the project area ranges from 490 mm/yr (19 in/yr) to 760 mm/yr (30 in/yr; Montana 

Department of Environmental Quality 2011).

The Poorman Creek area is comprised of primarily federally owned and managed land (Figure 6). The 

Forest Service manages 96 km2(37 mi2, 23,600 acres, 93%); the remaining 9 km2(3 mi2, 2130 acres, 7%) 

is private.

Figure 5. Geology of the 

Poorman Creek area. The 

alluvium shown in the 

southern side of the valley 

is probably actually 

located on the valley floor.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

22

All roads on federal and state lands were inventoried, for a total of 174 km (106 mi). About 47 km (29 

mi) of road had been previously mapped, but was found to not exist on the ground. Many of these may 

be ATV trails. Conversely, about 20 km (12 mi) of road was inventoried that was not previously mapped 

(Figure 7).

Figure 7. Elevation and location of inventoried roads within the Poorman Creek area.

Figure 6. Land ownership 

and all roads within the 

Poorman Creek area. The 

watershed boundary is 

buffered by 500 m.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

23

Cold Creek

Cold Creek is located within the Swan River watershed, and is located west of Condon, MT. The Swan 

River drains into the Flathead River. The Cold Creek watershed drains about 90 km2(30 mi2, 21,000 

acres), and the Swan River drains about 1810 km2(700 mi2, 448,000 acres).

Cold Creek covers two main geologic units (Figure 8). Glacial deposits and other alluvium cover the 

valley bottoms (about 28 km2or 11 mi2), and carbonates and quartzite of the Mesoproterozoic Belt 

Supergroup underlay the higher elevations (104 km2or 40 mi2; Ludington et al. 2005). Terrain in the 

project area is heavily influenced by Pleistocene glaciation, with steep valley walls and flat hummocky 

valley bottoms. The bulk of the roads in Cold Creek are in the hummocky zone. Elevations in the project 

area range from 1070 m (3520 ft) to 2580 m (8470 ft), and inventoried roads range from 1080 m (3540

ft) to 1730 m (5670 ft). Average annual precipitation in the project area ranges from 560 mm/yr (22

in/yr) to 1830 mm/yr (72 in/yr; Montana Department of Environmental Quality 2011).

The Cold Creek area is comprised of primarily federally owned and managed land (Figure 9). The Forest 

Service manages 116 km2(45 mi2, 28,660 acres, 93%); the remaining 9 km2(3 mi2, 2130 acres, 7%) is 

private.

Figure 8. Geology of the Cold Creek area.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

24

All roads on federal and state lands were inventoried, for a total of 198 km (123 mi). About 27 km (17

mi) of road had been previously mapped, but was found to not exist on the ground. Conversely, the 

same length of road was inventoried that was not previously mapped (27 km or 17 mi; Figure 10). Some 

of this may be on private land.

Figure 9. Land ownership and all roads within the Cold Creek area. The watershed 

boundary is buffered by 500 m.

Figure 10. Elevation and location of inventoried roads within the Cold Creek area.
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

25

4.0 Results

A total of 10,835 drain points, 14,912 road lines, and 3110 other associated features (including 44

gullies, 32 landslides, and 1880 photo points) were inventoried in nine months of field work over the 

summers of 2012 and 2013 by two field crews. Each crew collected an average of 3 km (1.8 mi) of road 

per day. Data analysis provides specific information on the condition and function of 779 km (484 mi) of 

roads (Figures 4, 7, and 10). These results are for the non-jammer roads in the three areas. Jammer 

roads are discussed in in section 5.0. GRAIP inventory and data modeling tools were used to characterize 

the following types of impacts and risks:

 Road-stream hydrologic connectivity

 Fine sediment production and delivery

 Downstream sediment accumulation

 Shallow landslide risk

 Gully initiation risk

 Stream crossing failure risk

 Drain point condition

4.1 Road-Stream Hydrologic Connectivity

Roads can intercept shallow groundwater and convert it to surface runoff, resulting in local hydrologic 

impacts when that water is discharged directly to channels (Wemple et al. 1996). Additional runoff is 

also produced from the compacted road surface. Basin-scale studies in the Oregon Cascades suggest 

that a high degree of integration between the road drainage system and the channel network can 

increase peak flows (Jones and Grant 1996).

Table 1. Summary of effective road lengths by drain type for the Center Horse and Morrell/Trail Project Area. Sumps cannot be 

stream connected, while streams crossings are stream connected by definition.

Drain Type

All Drain Points Connected Drain Points Not Connected Drain Points

% Length 

Count Connected

Average 

Contributing 

Length (m)

∑ 

Contributing 

Length (m)

Count

Average 

Contributing 

Length (m)

∑ 

Contributing 

Length (m)

Count

Average 

Contributing 

Length (m)

∑ 

Contributing 

Length (m)

Broad Based Dip 1413 110 157,650 42 110 4490 1371 110 153,160 3%

Diffuse Drain 931 90 84,710 11 60 700 920 90 84,010 0.8%

Ditch Relief 

Culvert

392 60 24,160 30 30 1020 362 60 23,140 4%

Excavated 

Stream Crossing

4 50 180 4 50 180 0 0 0 100%

Lead Off Ditch 135 70 9640 13 50 580 122 70 9050 6%

Non-Engineered 

Drain

1102 60 67,090 39 60 2300 1063 60 64,780 3%

Stream Crossing 146 40 5680 146 40 5680 0 0 0 100%

Sump 24 140 3280 0 0 0 24 140 3280 0%

Water Bar 914 60 54,850 29 50 1470 885 60 53,3780 3%

All Drains 5061 80 407,230 314 50 16,420 4747 80 390,800 4%
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

26

The hydrologically-connected portion of the road system is calculated in GRAIP using field observations 

of connection at each drain point and a road segment flow routing system. The flow path below each 

drain point is followed until evidence of overland flow ceases or the flow path reaches a channel.

Center Horse Morrell-Trail Project Area

In the Center Horse and Morrell-Trail project area, a total of 16.4 km (10.2 mi) out of 407 km (252 mi) of 

inventoried road (4%) was hydrologically connected to the stream network. Broad based dips and nonengineered drains were the most common types of drainage features (1413 and 1102 features, 

respectively), and, along with diffusely draining road segments (931 features) and water bars (914 

features), drained 90% (364 km, 226 mi) of the road network (Table 1). The bulk of the hydrologic 

connectivity occurred at stream crossings and broad based dips. There were 146 stream crossings, and 

they drained 6 km (4 mi) of the road network, all of which was connected. The broad based dips drained 

158 km (98 mi) of the road network, 4 km (2 mi) of which was connected to the stream network.

Poorman Creek

In Poorman Creek, a total of 8.1 km (5.0 mi) out of 174 km (108 mi) of inventoried road (5%) was 

hydrologically connected to the stream network. Broad based dips (412 features), diffuse drains (417

features), non-engineered drains (693 features), and water bars (549 features) were the most common 

types of drainage features, and drained 92% (160 km, 100 mi) of the road network (Table 2). The bulk of 

the hydrologic connectivity occurred at stream crossings, ditch relief culverts, and non-engineered 

drains. There were 53 stream crossings, and they drained 4 km (2 mi) of the road network, all of which 

was connected. The ditch relief culverts drained 9 km (5 mi) of the road network, 2 km (1 mi) of which 

Table 2. Summary of effective road lengths by drain type for the Poorman Creek area. Sumps cannot be stream connected, while 

streams crossings are stream connected by definition.

Drain Type

All Drain Points Connected Drain Points Not Connected Drain Points

% Length 

Count Connected

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Count

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Count

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Broad Based Dip 412 120 49,750 8 120 930 404 120 48,820 2%

Diffuse Drain 417 110 47,210 2 50 100 415 110 47,110 0.2%

Ditch Relief 

Culvert 56 160 8710 9 170 1550 47 150 7160 18%

Lead Off Ditch 8 120 950 0 0 0 8 120 950 0%

Non-Engineered 

Drain 693 60 42,830 24 70 1600 669 60 41,220 4%

Stream Crossing 53 70 3900 53 70 3900 0 0 0 100%

Sump 2 60 130 0 0 0 2 60 130 0%

Water bar 549 40 20,620 1 30 30 548 40 20,590 0.1%

All Drains 2190 80 174,090 97 80 8110 2093 80 165,980 5%
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were connected to the stream network. The non-engineered drains drained 43 km (27 mi) of the road 

network, 2 km (1 mi) of which was connected to the stream network.

Cold Creek

In the Cold Creek area, a total of 8.7 km (5.4 mi) out of 198 km (123 mi) of inventoried road (4%) was 

hydrologically connected to the stream network. Broad based dips and non-engineered drains were the 

most common types of drainage features (1050 and 1097 features, respectively), and, along with 

diffusely draining road segments (670 features) and ditch relief culverts (266 features), drained 90% 

(178 km, 111 mi) of the road network (Table 3). The bulk of the hydrologic connectivity occurred at 

stream crossings, ditch relief culverts, and broad based dips. There were 115 stream crossings, and they 

drained 4 km (3 mi) of the road network, all of which was connected. The ditch relief culverts (266 

features) drained 17 km (10 mi) of the road network, 2 km (1 mi) of which was connected (13%). The 

broad based dips drained 70 km (44 mi) of the road network, 1 km (0.8 mi) of which was connected to 

the stream network (2%).

Table 3. Summary of effective road lengths by drain type for the Cold Creek area. Sumps cannot be stream connected, while 

streams crossings are stream connected by definition.

Drain Type

All Drain Points Connected Drain Points Not Connected Drain 

Points % Length 

Connected

Count

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Count

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Count

Mean 

Contributing 

Length (m)

Σ 

Contributing 

Length (m)

Broad Based Dip 1050 70 70,030 23 60 1320 1027 70 68,710 2%

Diffuse Drain 670 80 50,180 0 0 0 670 80 50,180 0%

Ditch Relief 

Culvert 266 60 16,870 44 50 2240 222 70 14,630 13%

Lead Off Ditch 139 50 7110 9 40 360 130 50 6750 5%

Non-Engineered 

Drain 1097 40 41,270 10 40 360 1087 40 40,910 1%

Stream Crossing 115 40 4320 115 40 4320 0 0 0 100%

Sump 1 130 130 0 0 0 1 130 130 0%

Water Bar 246 30 7940 4 30 110 242 30 7830 1%

All Drains 3584 55 197,860 205 40 8720 3379 60 189,140 4%
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4.2 Road Surface Fine Sediment Production and Delivery

Fine sediment production at a drain point ( ) is estimated with a base erosion rate and the properties of 

two flow paths along the road (Luce and Black 1999, Cissel et al. 2012, Prasad 2007), as shown below.

 

 is the base erosion rate1(kg/m)

 is the road length (m) contributing to the drain point

 is the slope of the road contributing to the drain point (m/m)

 is the vegetation cover factor for the flow path

 is the road surfacing factor

Delivery of eroded sediment to the channel network is determined by observations of each place that 

water leaves the road. Each of these drain points is classified as either delivering or not delivering. No 

estimate of fractional delivery is made, because there is insignificant hillslope sediment storage in 

locations where there is a clear connection to the channel under most circumstances.

Delivery of fine sediment occurs through a mix of road drainage features, including broad based dips, 

diffuse road segments, ditch relief culverts, non-engineered drains, water bars, and others (Appendix A). 

In the tables below, sediment delivery is broken out by drain type to assess their effectiveness in 

preventing sediment from entering the channel.

Center Horse Morrell-Trail Project Area

There were 5061 drain points observed in the Center Horse and Morrell/Trail Project Area, 314 of which 

delivered sediment to stream channels (Table 4). Model predictions indicate that these points delivered 

an estimated 21.4 Mg/yr, or 4% of the 456 Mg/yr generated on the road surfaces and ditches (Figure 

11). Broad based dips and non-engineered drains delivered the most sediment (6.8 Mg/yr and 7.4

Mg/yr, respectively; Figure 12). There was 16.2 Mg/yr of delivery that occurred within 10 m of a stream 

crossing. This is 76% of all sediment delivery and 57% of all sediment produced within 10 m of a stream 

crossing (compared to the 4% delivery rate for all sediment). A map of the road surface sediment 

delivery and the accumulated sediment delivered through each drain point is shown for upper Little 

Shanley Creek and upper Black Canyon Creek in the Center Horse project area (Figure 13).

The fraction of sediment produced and delivered from the road system can also be evaluated in the 

context of road length. Of the 407 km (252 mi) of total inventoried road length, 16.4 km (10.2 mi, 4%) 

deliver sediment to streams (Table 4).

 

1

For this analysis, base erosion rates of 17 kg/meter of road elevation for open roads and 1 kg/meter of road 

elevation for closed roads was used, based on observations at eight local sediment plots over two years (Black and 

Luce 2013). These numbers may be revised once more data can be collected. Sugden and Woods (2007) measured 

erosion on open roads in western Montana and found low to moderate rates that equate to GRAIP base rates of 7 

kg/meter of road elevation for Belt geology and 11 kg/meter of road elevation for glacial till.
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Table 4. Summary of sediment production and delivery at drain points in the Center Horse and Morrell/Trail Project 

Area.

Drain Type Count

Σ 

Sediment 

Production 

(kg/yr)

Σ 

Sediment 

Delivery 

(kg/yr)

% 

Sediment 

Delivery

Length 

Connected 

(m)

% Length 

Connected

Broad Based Dip 1413 163,010 6860 4% 4490 3%

Diffuse Drain 931 104,870 1010 1% 700 1%

Ditch Relief Culvert 392 13,400 830 6% 1020 4%

Excavated Stream Crossing 4 110 110 100% 180 100%

Lead Off Ditch 135 7800 810 10% 580 6%

Non-Engineered Drain 1102 97,430 7410 8% 2300 3%

Stream Crossing 146 3140 3140 100% 5670 100%

Sump 24 1520 0 0% 0 0%

Water Bar 914 64,920 1190 2% 1470 3%

Discharge at Stream 

Crossings* 241 28,280 16,170 57% 10,150 60%

All Drains 5061 456,200 21,360 5% 16,420 4%

* includes stream crossings, excavated stream crossings, and any other drain point within 10 m of stream crossings

Figure 11. Percent total sediment delivered to streams 

by percent of drain points. 4% of all drain points deliver 

100% of the delivered sediment.

Figure 12. Sediment production and delivery by drain 

point type.
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Figure 13. Fine sediment delivery to channels by road segment and drain point in the upper Little Shanley and 

Black Canyon Creeks area. The road lines are colored to indicate the mass of fine sediment delivered to channels.
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Poorman Creek

There were 2190 drain points observed in the Poorman Creek area, 97 of which delivered sediment to 

stream channels (Table 5). Model predictions indicate that these points delivered an estimated 11.5

Mg/yr, or 5% of the 247 Mg/yr generated on the road surfaces and ditches (Figure 14). Non-engineered 

drains and stream crossings delivered the most sediment (4.4 Mg/yr and 4.0 Mg/yr, respectively; Figure 

15). A map of the road surface sediment delivery and the accumulated sediment delivered through each 

drain point is shown for the central part of the Poorman Creek area (Figure 16).

There was 5.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 49% of all 

sediment delivery and 77% of all sediment produced within 10 m of a stream crossing (compared to the 

5% delivery rate for all sediment).

The fraction of sediment produced and delivered from the road system can also be evaluated in the 

context of road length. Of the 174 km (108 mi) of total inventoried road length, 8.1 km (5.0 mi, 5%) 

deliver sediment to streams (Table 2).

Table 5. Summary of sediment production and delivery at drain points in the Poorman Creek area.

Drain Type Count

Σ 

Sediment 

Production 

(kg/yr)

Σ 

Sediment 

Delivery 

(kg/yr)

% 

Sediment 

Delivery

Length 

Connected 

(m)

% Length 

Connected

Broad Based Dip 412 70,320 2280 3% 930 2%

Diffuse Drain 417 47,010 160 0.3% 100 0.2%

Ditch Relief Culvert 56 7960 670 8% 1550 18%

Lead Off Ditch 8 710 0 0% 0 0%

Non-Engineered Drain 693 77,330 4420 6% 1600 4%

Stream Crossing 53 3960 3960 100% 3900 100%

Sump 2 80 0 0% 0 0%

Water bar 549 40,060 20 0.04% 30 0.1%

Discharge at Stream 

Crossings* 75 7260 5600 77% 4580 87%

All Drains 2190 247,420 11,500 5% 8110 5%

* includes stream crossings and any other drain point within 10 m of stream crossings
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Figure 14. Percent total sediment delivered to streams by 

percent of drain points. 3% of all drain points deliver 100% of 

the delivered sediment.

Figure 15. Sediment production and delivery by drain point type.

Figure 16. Fine sediment delivery to channels by road segment and drain point in central roaded portion of the Cold Creek area. 

The road lines are colored to indicate the mass of fine sediment delivered to channels.
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Cold Creek

There were 3584 drain points observed in the Cold Creek area, 205 of which delivered sediment to 

stream channels (Table 6). Model predictions indicate that these points delivered an estimated 9.8

Mg/yr, or 4% of the 162 Mg/yr generated on the road surfaces and ditches (Figure 17). Broad based dips

and stream crossings delivered the most (3.3 Mg/yr and 3.8 Mg/yr, respectively; Figure 18). A map of 

the road surface sediment delivery and the accumulated sediment delivered through each drain point is 

shown for the central part of the Cold Creek area (Figure 19).

Table 6. Summary of sediment production and delivery at drain points in the Cold Creek area.

Drain Type Count

Σ 

Sediment 

Production 

(kg/yr)

Σ 

Sediment 

Delivery 

(kg/yr)

% 

Sediment 

Delivery

Length 

Connected 

(m)

% Length 

Connected

Broad Based Dip 1050 64,750 3350 5% 1320 2%

Diffuse Drain 670 30,070 0 0% 0 0%

Ditch Relief Culvert 266 12,750 1780 14% 2240 13%

Lead Off Ditch 139 5000 200 4% 360 5%

Non-Engineered Drain 1097 377,340 300 1% 360 1%

Stream Crossing 115 3840 3840 100% 4320 100%

Sump 1 110 0 0% 0 0%

Water Bar 246 7590 350 5% 110 1%

Discharge at Stream 

Crossings* 180 8760 6570 75% 5210 75%

All Drains 3584 161,840 9810 6% 8720 4%

* includes stream crossings and any other drain point within 10 m of stream crossings

Figure 17. Percent total sediment delivered to streams 

by percent of drain points. 6% of all drain points deliver 

100% of the delivered sediment.

Figure 18. Sediment production and delivery by drain point 

type.
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There was 6.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 67% of all 

sediment delivery and 75% of all sediment produced within 10 m of a stream crossing (compared to the 

4% delivery rate for all sediment). 

The fraction of sediment produced and delivered from the road system can also be evaluated in the 

context of road length. Of the 198 km (123 mi) of total inventoried road length, 8.7 km (5.4 mi, 4%) 

deliver sediment to streams (Table 3).

Figure 19. Fine sediment delivery to channels by road segment and drain point in the central roaded portion of the 

Cold Creek area. The road lines are colored to indicate the mass of fine sediment delivered to channels.
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4.3 Downstream Sediment Accumulation

Road surface derived fine sediment enters the stream network below connected drain points. Roadrelated sediment accumulates in streams and is routed through the network. GRAIP calculates two 

measures of road sediment for each stream segment. The first measure, sediment accumulation (Figures

20, 23, and 26, below), is the mass of road-related sediment that passes through each stream segment 

per year. In the absence of detailed information on sediment routing, the assumption is that road 

surface-related fine sediment has a residence time of less than one year. The second measure, specific 

sediment accumulation (Figures 21, 24, and 26, below), is the mass of road-related sediment normalized 

by the contributing area. In this metric, area is used as a proxy for discharge, allowing us to compare the 

sediment impacts to channel segments with differing contributing areas.

Observed annual sediment yields for nearby areas (Table 7) range from 2.8 Mg/km2/yr to 122.6 

Mg/km2/yr. Time-scales and data types varied. Not including the outlying data from Gibson Reservoir, 

the measured average sediment yield for nearby areas was 9.2 Mg/km2/yr, similar to short-term rates 

for the northern Rocky Mountains as reported by Kirchner (2001).

Center Horse Morrell-Trail Project Area

Road surface-related sediment at the mouth of the various creeks within the Center Horse and MorrellTrail project area ranged from 0.03 Mg/yr (Lost Creek) to 11.6 Mg/yr (Cottonwood Creek; Figure 20; 

Table 8). Specific sediment ranged from 0.01 Mg/km2/yr (North Fork Cottonwood Creek) to 1.80

Mg/km2/yr (Little Shanley Creek). Using the total road surface sediment delivered and the drainage area 

for the whole Center Horse and Morrell/Trail project area, the specific sediment was 0.10 Mg/km2/yr

(Figure 21).

Including the sediment from road-related landslides (not including cutslope failures), gullies, and fill 

erosion at drain points (see Sections 4.4, 4.5, and 4.7), in addition to that from the road surface, the 

total annual road sediment accumulation at the mouth of the various creeks within the Center Horse 

Table 7. Observed annual sediment yields for nearby areas. Sampling methods and time scales vary.

Location Citation

Length of 

Record

Type of Data

Specific Sediment 

(Mg/km2/yr)

North Fork Blackfoot River, MT

Lolo National Forest 

2009

18 years Suspended sediment 2.8

Blackfoot River at Bonner, MT

USGS 2012; Lambing 

and Sando 2008

15 of 22 

years

Suspended sediment 7.5

Nevada Creek Reservoir, MT USDA 1978 36 years Reservoir core samples 7.7

Lower Willow Creek Reservoir, MT USDA 1978 11 years Reservoir core samples 11.9

Flathead Lake, MT Hoffman et al. 2006 7600 years Seismic survey 16.3

Gibson Reservoir, MT USDA 1978 43 years Reservoir core samples 122.6

Average, no outlier 9.2
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and Morrell-Trail project area ranged from 0.03 Mg/yr (Lost Creek) to 20.5 Mg/yr (Cottonwood Creek). 

Specific sediment with mass wasting sediment ranged from 0.01 Mg/km2/yr (North Fork Cottonwood 

Creek) to 1.80 Mg/km2/yr (Little Shanley Creek) with large increases in some other areas (Cottonwood, 

Shanley, Spring, and Blind Canyon Creeks). Using the total sediment including mass wasting delivered

and the drainage area for the whole Center Horse and Morrell/Trail project area, the specific sediment 

was 0.21 Mg/km2/yr (Figure 22).

At the stream reach scale, road sediment impacts may be more pronounced due to high local delivery 

rates from gullies, landslides, road fill or surface erosion, and due to limitations on available transport 

energy. Reaches in lower Spring, Black Canyon, Shanley, and Little Shanley Creeks may be in this group 

(Figure 22).

Road-related sediment both with and without mass wasting ranged from about 0.1% to about 20% of 

the estimated average annual observed sediment yield for this geographic region. Using the total 

sediment delivered and the drainage area for the whole Center Horse and Morrell/Trail project area, the 

specific sediment was 1% of the estimated average annual observed sediment yield with road-surface 

sediment only, and 2% of the estimated average annual observed sediment yield including mass wasting 

sediment.

Table 8. Project area streams and sediment accumulation and specific sediment accumulation at the stream mouth, 

calculated using only road surface-related sediment and all road sediment sources (landslides, gullies, and fill 

erosion at drain points).

Stream Name

Road Surface 

Sediment at 

Mouth 

(Mg/yr)

Specific Road 

Surface Sediment at 

Mouth (Mg/km2/yr)

All Road 

Sediment at 

Mouth 

(Mg/yr)

All Specific Road 

Sediment at 

Mouth 

(Mg/km2/yr)

Shanley Creek 0.8 0.06 3.0 0.21

Lost Creek 0.03 0.03 0.03 0.03

Dry Cottonwood Creek 0.3 0.05 0.3 0.05

Black Canyon Creek 2.4 0.43 2.4 0.43

Cottonwood Creek 11.6 0.19 20.5 0.33

Spring Creek 2.2 0.17 11.0 0.88

Little Shanley Creek 7.3 1.80 7.3 1.80

North Fork Cottonwood 

Creek 0.3 0.01 0.3 0.01

Morrell Creek 3.6 0.05 3.9 0.06

Trail Creek 1.6 0.03 4.1 0.08

Swamp Creek 0.3 0.03 0.4 0.04

Blind Canyon Creek 0.9 0.04 3.3 0.14

Center Horse and 

Morrell/Trail Project 

Area

21.4 0.10 45.2 0.21
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Figure 20. Sediment accumulation from all road-related sediment sources (road surface, gullies, landslides, and fill 

erosion) in the Center Horse and Morrell/Trail project area.
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Figure 21. Specific sediment from road surface sediment in the Center Horse and Morrell/Trail project area.
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Figure 22. Specific sediment from all road-related sediment sources (road surface, gullies, landslides, and fill 

erosion) in the Center Horse and Morrell/Trail project area.
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Poorman Creek

Road surface-related sediment at the mouth of the two named creeks within the Poorman Creek area 

ranged from 0.1 Mg/yr (Canyon Creek) to 0.8 Mg/yr (South Fork Poorman Creek; Figure 23; Table 9). 

Specific sediment ranged from 0.04 Mg/km2/yr (Canyon Creek) to 0.05 Mg/km2/yr (South Fork Poorman 

Creek). Using the total road surface sediment delivered and the drainage area for the whole Poorman 

Creek area, the specific sediment was 0.11 Mg/km2/yr (Figure 24).

Including the sediment from road-related landslides (not including cutslope failures), gullies, and fill 

erosion at drain points (see Sections 4.4, 4.5, and 4.7), in addition to that from the road surface, the 

total annual road sediment accumulation at the mouth of Poorman Creek was 19.6 Mg/yr. Specific 

sediment with mass wasting sediment for the entire Poorman Creek area was 0.19 Mg/km2/yr (Figure 

25).

At the stream reach scale, road sediment impacts may be more pronounced due to high local delivery 

rates from gullies, landslides, road fill or surface erosion, and due to limitations on available transport 

energy. Reaches in upper Poorman Creek may be in this group (Figure 25).

Road-related sediment both with and without mass wasting ranges from about 0.4% to about 0.5% of 

the estimated average annual observed sediment yield for this geographic region. Using the total 

sediment delivered and the drainage area for the whole Poorman Creek area, the specific sediment is 

1% of the estimated average annual observed sediment yield with road-surface sediment only, and 2% 

of the estimated average annual observed sediment yield including mass wasting sediment.

Table 9. Project area streams and sediment accumulation and specific sediment accumulation at the 

stream mouth, calculated using only road surface-related sediment and all road sediment sources 

(landslides, gullies, and fill erosion at drain points).

Stream Name

Road 

Surface 

Sediment 

at Mouth 

(Mg/yr)

Specific Road 

Surface 

Sediment at 

Mouth 

(Mg/km2/yr)

All Road 

Sediment 

at Mouth 

(Mg/yr)

All Specific 

Road 

Sediment at 

Mouth 

(Mg/km2/yr)

South Fork Poorman Creek 0.8 0.05 1.1 0.03

Canyon Creek 0.1 0.04 0.1 0.04

Poorman Creek (Project Area) 11.5 0.11 19.6 0.19
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Figure 23. Sediment accumulation from all road-related sediment sources (road surface, gullies, landslides, and fill erosion) in 

the Poorman Creek area.
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Figure 25. Specific sediment from all road-related sediment sources (road surface, gullies, landslides, and fill erosion) in the 

Poorman Creek area.
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Cold Creek

Road surface-related sediment at the mouth of the two forks of Cold Creek ranged from 0.4 Mg/yr 

(North Fork Cold Creek) to 3.8 Mg/yr (South Fork Cold Creek; Figure 26; Table 10). Specific sediment 

ranged from 0.04 Mg/km2/yr (North Fork Cold Creek) to 0.14 Mg/km2/yr (South Fork Cold Creek). Using 

the total road surface sediment delivered and the drainage area for the whole Cold Creek area, the 

specific sediment was 0.10 Mg/km2/yr (Figure 27). There were no instances of delivering gullies or 

landslides, and only two instances of delivering fill erosion, totaling roughly 0.02 Mg/yr, so mass wasting 

was not routed downstream in Cold Creek.

Table 10. Project area streams and sediment accumulation and specific sediment accumulation 

at the stream mouth, calculated using only road surface-related sediment. There was no mass 

wasting that was observed to deliver sediment to the stream in Cold Creek.

Name

Road Surface 

Sediment at 

Mouth 

(Mg/yr)

Specific Road 

Surface Sediment at 

Mouth (Mg/km2/yr)

Additional 

Sediment from 

Mass Wasting at 

Mouth (Mg/yr)

South Fork Cold Creek 3.8 0.14 0

North Fork Cold Creek 0.4 0.04 0

Cold Creek (Main Stem) 8.7 0.09 0

Cold Creek Project 

Area 9.8 0.10 0

At the stream reach scale, road sediment impacts may be more pronounced due to high local delivery 

rates, road surface erosion, and due to limitations on available transport energy. Reaches in the South 

Fork Cold Creek may be in this group (Figure 27).

Road-related sediment ranged from about 0.4% to about 1.5% of the estimated average annual 

observed sediment yield for this geographic region. Using the total sediment delivered and the drainage 

area for the whole Cold Creek area, the specific sediment was 1% of the estimated average annual 

observed sediment yield.
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Figure 26. Sediment accumulation from the road surface in the Cold Creek area. There were no instances of mass wasting that were 

observed to deliver sediment to streams in Cold Creek.
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Figure 27. Specific sediment from road surface sediment in the Cold Creek area.
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4.4 Landslides

At each landslide location, the type, location, and volume are observed. Landslides can be determined to 

be connected to the channel network if an associated drain point above the landslide is connected to 

the channel network, if an associated road surface flow path that would be expected to intercept the 

landslide sediment is connected to the network, or if the landslide is observed in the field to be 

connected to the network. In most cases, shallow landslides initiate during large storm events when 

soils become saturated, and deliver sediment to the channel over a limited time frame. This represents a 

pulsed as opposed to chronic sediment input to the streams. Delivered landslide masses are distributed 

over a 20 year time span in order to compare their approximate magnitude with that of the road surface 

fine sediment (a chronic sediment source). Twenty years is used because, in most places, that is roughly 

the maximum age of a feature still easily observable in the field. In any given year, the amount of 

sediment delivered to streams from landslides is likely to be higher or lower than the rate we calculate.

The risk of shallow landslide initiation is predicted using SINMAP 2.0 (Pack at al. 2005, 

http://hydrology.neng.usu.edu/sinmap2/), modified to account for contributions of road surface runoff, 

and locally calibrated to known locations of landslides (where available). SINMAP has its basis in the 

infinite plane slope stability model and produces raster grids that illustrate slope stability based on 

hillslope and specific catchment area at each DEM grid cell. Un-roaded and roaded risk grids are 

subjected to a series of mathematical operations that result in grids that show the important changes to 

landslide risk due to the presence of the roads. These change grids are compared to the natural 

landslide risk grid to show how the roads affect slope stability in the context of the background risks (i.e. 

the risks without the influence of road drainage). Important grid cell changes are those un-roaded to 

roaded differences that show a risk change from stable to unstable, or the areas that were unstable 

without roads and became less stable after road construction.

Center Horse Morrell-Trail Project Area

Existing Landslides

The Center Horse and Morrell/Trail project area has a low incidence of road-related shallow landsliding. 

Most road miles are located on the shallow slopes of the glaciated valley bottoms. Landslide volume was 

estimated for all landslides visible from the road greater than a minimum threshold of six feet in slope 

length and slope width. The inventory recorded 18 landslides (Table 11), totaling 1319 m3(1726 yd3). 

There were nine landslides estimated to be less than five years of age, three between five and ten years 

old, and six landslides were between ten and 15 years old. There were ten that were related to the road 

in some way; road-related landslides totaled 307 m3(402 yd3). Including non-road related landslides, 

there were nine cutslope failures (257 m3, 336 yd3), four hillslope failures (614 m3, 803 yd3), and five 

fillslope failures (449 m

3

, 587 yd3). Figure 28 shows the locations of the observed landslides in the Spring 

Creek area of the Center Horse and Morrell/Trail project area.

There were two landslides (11%) found to be stream connected; one road related fillslope failure and 

one non-road related cutslope failure. The cutslope failure may not be fully connected due to the 

common removal of eroded cutslope material during road maintenance and uncertainty surrounding 

timing and discharge of intercepting flow paths. The stream in which the fillslope failure discharged may 

lead to a lake. 
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Using a bulk density for road fill of 1.6 Mg/m3(Madej 2001), the total mass of sediment generated was 

expected to be 2111 Mg, with 176 Mg delivering to streams, not including the cutslope failure. This is 

about 10% of all landslide-generated mass (Table 11). Over a 20-year period, about 8.8 Mg/yr (again 

without the cutslope failure) have been delivered to streams. This is roughly half the rate of the annual 

road surface fine sediment delivery. It would take about eight years for the fine sediment delivery from 

road surfaces to equal the total mass of delivered sediment from landslides. Estimates here do not 

account for partial delivery of landslide sediments (i.e. not all sediment from a road related landslide is 

likely to be delivered, even if some of the sediment is), so actual volumes may be lower.

Table 11. Number and types of observed landslides, as well as masses and volumes of sediment generated 

and delivered to the stream channel network in the Center Horse and Morrell/Trail project area.

Location Count

Volume 

(yd3)

Volume 

(m3)

Mass 

Produced 

(Mg)

Mass 

Delivered 

(Mg)

Average Delivery 

Rate Over 20 Years 

Road Related (Mg/yr)

Cutslope 9 336 257 411 109 5.4

Not Road Related 3 156 119 190 109 5.4

Road Related 6 180 138 221 0 0

Fillslope 5 587 449 718 176 8.8

Not Road Related 3 421 322 515 0 0

Road Related 2 166 127 203 176 8.8

Hillslope 4 803 614 982 0 0

Not Road Related 2 747 571 914 0 0

Road Related 2 55 42 68 0 0

Totals, Not Considering Cutslope Failures 1700 176 8.8

Totals 18 1726 1319 2111 284 14.2

Not Road Related 8 1324 1012 1620 109 5.4

Road Related 10 402 307 491 176 8.8

Figure 28. Observed 

landslides in the Spring 

Creek area of the 

Center Horse and 

Morrell/Trail project 

area.
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Changes to Landslide Risk Due to Roads

SIMNAP calibration was completed using eight known locations of landslides in the local area obtained 

from forest personnel (S. Hendrickson, personal communication 2013). Figures 29 and 30 illustrate the 

risk and change in risk in the area. SINMAP was calibrated and run initially to determine the intrinsic 

stability of the slopes over which the road traverses and to identify locations that are at a high risk of 

failure without the road (Figure 29). 

A second calibrated stability index run was performed to address the effects of road water contribution 

to drain points. In Figure 30, the areas in the Spring Creek drainage in the southern part of the project 

area where the road changed the risk from the stable category (stable, moderately stable, quasi-stable 

from Figure 29, above) to the unstable category (lower threshold, upper threshold, defended) are 

shown in red. These are areas where road drainage was installed over naturally stable slopes, and the 

added water moved the area into the unstable category. The orange cells are areas where the risk 

increased (became less stable) after road construction, and the terrain was unstable prior to road 

construction. This is due to the installation of road drainage over naturally unstable slopes. Risk may not 

extend as far downslope as is shown.

Figure 29. Natural slope stability in the Spring Creek drainage of the Center Horse and Morrell/Trail 

project area. The yellow, blue, and green cells are generally considered to be stable, while the pink, 

red, and dark tan cells are generally considered to be unstable. The star indicates a stream-connected 

landslide in a creek that discharges into a lake.
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Figure 30 also shows the locations of observed landslides. Over the whole area, nine of the 18 landslides 

(50%) occurred on destabilized slopes. As shown and described above, some of these points are fillslope 

or cutslope failures, and may not correlate well with the SINMAP risk which is designed to predict 

hillslope risks rather than risks within the road prism. Additionally, there were only eight calibration 

landslide points; a good calibration dataset should include at least 50 points. Given these considerations, 

there is a reasonably high level of correlation between observed and expected landslide locations.

Of the 216 km2(83 mi2) that comprise the Center Horse and Morrell/Trail project area, 2.6 km2(1 mi2, 

1%) was stable before road construction and is now unstable, and 3.7 km2(1.4 mi2, 2%) was unstable 

before road construction and is now less stable due to road drainage (Table 12). This is a total of 6.3 km2

(2.4 mi2, 3%) of the watershed that has experienced an increase in landslide risk due to road hydrology. 

This can be compared to 7.8% of the North Fork Siuslaw River watershed in western Oregon that 

experienced an increase in landslide risk due to roads, and has a high incidence of road related shallow 

landsliding.

Table 12. Landslide risk changes in the Center Horse and Morrell/Trail project area 

by category and area.

Total Area of Watershed (m2) 215,620,000 100%

Area Stable Before Roads, Now Unstable (m2) 2,646,600 1%

Area Unstable Before Roads, Now Less Stable (m2) 3,686,400 2%

Total Area Affected by Roads (m2) 6,336,000 3%

Figure 30. Changes in slope stability risk in the Spring Creek drainage of the Center Horse and 

Morrell/Trail project area. The red and orange areas are where the risk increased.
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Poorman Creek

Existing Landslides

The Poorman Creek area has a low incidence of road-related shallow landsliding. Hillslopes in Poorman 

Creek are generally shallow. Landslide volume was estimated for all landslides visible from the road 

greater than a minimum threshold of six feet in slope length and slope width. The inventory recorded 

five landslides (Table 13), totaling 252 m

3

(329 yd3). Three landslides were estimated to be less than five 

years of age, and two landslides were between ten and 15 years old. All five were related to the road in 

some way. There were three cutslope failures (95 m

3

, 124 yd3), one hillslope failure (153 m

3

, 200 yd3), 

and one fillslope failure (4 m

3

, 5 yd3). Figure 31 shows the locations of the observed landslides in the 

Poorman Creek area.

Table 13. Number and types of observed landslides, as well as masses and volumes of 

sediment generated and delivered to the stream channel network in the Poorman Creek

area.

Location* Count Volume 

(yd3)

Volume 

(m3)

Mass 

Produced 

(Mg)

Mass 

Delivered 

(Mg)

Average 

Delivery Rate 

Over 20 Years 

(Mg/yr)

Cutslope 3 124 95 152 91 4.5

Fillslope 1 5 4 6 0 0

Hillslope 1 200 153 245 0 0

Total 5 329 252 403 91 4.5

* all observed landslides were road related

Figure 31. Observed landslides in the Poorman Creek area. The dotted line was collected in 2014.
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There was one landslide that was found to be stream connected. This cutslope failure occurred directly 

above a culvert, and the culvert was connected to a stream. Though it is likely that some sediment from 

this failure moved across the road and was not delivered, or was removed by maintenance equipment, 

observations suggest that most of the sediment entered the culvert and therefore delivered to the 

stream.

Using a bulk density for road fill of 1.6 Mg/m3(Madej 2001), the total mass of sediment generated was 

expected to be 403 Mg, with 91 Mg delivering to streams. This is about 20% of all landslide-generated 

mass (Table 13). Over a 20-year period, about 4.5 Mg/yr have been delivered to streams. This is roughly 

half the annual road surface fine sediment delivery rate. It would take about 8 years for the fine 

sediment delivery from road surfaces to equal the total mass of delivered sediment from landslides. 

Estimates here do not account for partial delivery of landslide sediments (i.e. not all sediment from a 

road related landslide is likely to be delivered, even if some of the sediment is), so actual volumes may 

be lower.

Changes to Landslide Risk Due To Roads

SIMNAP calibration was completed using the same eight known locations of landslides in the Center 

Horse and Morrell/Trail project area obtained from forest personnel (S. Hendrickson, personal 

communication 2013). Figures 32 and 33 illustrate the risk and change in risk in the area. SINMAP was 

calibrated and run initially to determine the intrinsic stability of the slopes over which the road traverses 

and to identify locations that are at a high risk of failure without the road (Figure 32). 

Figure 32. Natural slope stability in the central part of the Poorman Creek area. The yellow, blue, and 

green cells are generally considered to be stable, while the pink, red, and dark tan cells are generally 

considered to be unstable. The dotted line was collected in 2014.
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A second calibrated stability index run was performed to address the effects of road water contribution 

to drain points. In Figure 33, the areas in the central portion of the Poorman Creek area where the road 

changed the risk from the stable category (stable, moderately stable, quasi-stable from Figure 32, 

above) to the unstable category (lower threshold, upper threshold, defended) are shown in red. These 

are areas where road drainage was installed over naturally stable slopes, and the added water moved 

the area into the unstable category. The orange cells are areas where the risk increased (became less 

stable) after road construction, and the terrain was unstable prior to road construction. This is due to 

the installation of road drainage over naturally unstable slopes. Risk may not extend as far downslope as 

is shown.

Figure 33 also shows the locations of observed landslides. Over the whole area, the only landslide that 

occurred over a destabilized slope was the hillslope failure. Fillslope and cutslope failures may not 

correlate well with the SINMAP risk which is designed to predict hillslope risks rather than risks within 

the road prism. Additionally, there were only eight calibration landslide points, and they were located in 

somewhat dissimilar geology in a relatively spatially distant locale; a good calibration dataset should 

include at least 50 points and be within a nearby area of similar soils and geology. Given these 

considerations, it is reasonable to expect poor correlation between observed and expected landslide 

locations.

Of the 130 km

2

(50 mi2) that comprise the Poorman Creek area, 1.4 km2(0.5 mi2, 1%) was stable before 

road construction and is now unstable, and 1.5 km2(0.6 mi2, 1%) was unstable before road construction 

and is now less stable due to road drainage (Table 12). This is a total of 2.9 km2(1.1 mi2, 2%) of the 

watershed that has experienced an increase in landslide risk due to road hydrology. This can be 

Figure 33. Changes in slope stability risk in the central part of the Poorman Creek area. The red and 

orange areas are where the risk increased. The dotted line was collected in 2014.
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compared to 7.8% of the North Fork Siuslaw River watershed in western Oregon that experienced an 

increase in landslide risk due to roads, and has a high incidence of road related shallow landsliding.

Table 14. Landslide risk changes in the Poorman Creek area by category and area.

Total Area of Watershed (m2) 130,484,000 100%

Area Stable Before Roads, Now Unstable (m2) 1,351,100 1%

Area Unstable Before Roads, Now Less Stable (m2) 1,519,560 1%

Total Area Affected by Roads (m2) 2,870,670 2%
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Cold Creek

Existing Landslides

The Cold Creek area has a low incidence of road-related shallow landsliding (Figure 34). Most road miles 

are located on the shallow slopes of the glaciated valley bottom. Landslide volume was estimated for all 

landslides visible from the road greater than a minimum threshold of six feet in slope length and slope 

width. The inventory recorded nine landslides (Table 15), totaling 175 m

3

(229 yd3). Two landslides were 

estimated to be less than five years of age, one landslide was estimated to be between five and ten 

years old, and six landslides were between ten and 15 years old or older. There were eight that were 

related to the road in some way; road-related landslides totaled 141 m

3

(184 yd3). Including the nonroad related landslide, there were five cutslope failures (80 m

3

, 105 yd3, and four fillslope failures (94

m

3

, 123 yd3).

Figure 34 shows the locations of each of the observed landslides in the Cold Creek area. No landslides 

were found to be connected to the stream network. Using a bulk density for road fill of 1.6 Mg/m3

(Madej 2001), the total mass of sediment generated was expected to be 280 Mg (Table 15). 

Figure 34. Observed landslides in the Cold Creek area.
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Changes to Landslide Risk Due To Roads

SIMNAP calibration was completed using the same eight known locations of landslides in the Center 

Horse and Morrell/Trail project area obtained from forest personnel (S. Hendrickson, personal 

communication 2013). Figures 35 and 36 illustrate the risk and change in risk in the area. SINMAP was 

Table 15. Number and types of observed landslides, as well as masses and 

volumes of sediment generated in the Cold Creek area.

Location Count Volume 

(yd3)

Volume 

(m3)

Mass 

Produced 

(Mg)

Mass 

Delivered 

Road Related (Mg)

Cutslope 5 105 80 129 0

Road Related 5 105 80 129 0

Fillslope 4 123 94 151 0

Not Road Related 1 44 34 54 0

Road Related 3 79 60 97 0

Totals, Not Considering Cutslope Failures 151 0

Totals 9 229 175 280 0

Not Road Related 1 44 34 54 0

Road Related 8 184 141 225 0

Figure 35. Natural slope stability in the Cold Creek area. The yellow, blue, and green cells are generally 

considered to be stable, while the pink, red, and dark tan cells are generally considered to be unstable.
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calibrated and run initially to determine the intrinsic stability of the slopes over which the road traverses 

and to identify locations that are at a high risk of failure without the road (Figure 35). 

A second calibrated stability index run was performed to address the effects of road water contribution 

to drain points. In Figure 36, the areas in the Cold Creek area where the road changed the risk from the 

stable category (stable, moderately stable, quasi-stable from Figure 35, above) to the unstable category 

(lower threshold, upper threshold, defended) are shown in red. These are areas where road drainage 

was installed over naturally stable slopes, and the added water moved the area into the unstable 

category. The orange cells are areas where the risk increased (became less stable) after road 

construction, and the terrain was unstable prior to road construction. This is due to the installation of 

road drainage over naturally unstable slopes. Risk may not extend as far downslope as is shown. The 

areas of elevated risk may be limited to the upper part of the road network, where valley walls are 

steeper. Most of the road network in the Cold Creek area is in the lower part of the watershed, where 

hillslopes are generally very shallow.

Figure 36 also shows the locations of observed landslides. Over the whole area, the only landslide that 

occurred over a destabilized slope was a cutslope failure. There were no observed hillslope failures, and 

fillslope and cutslope failures may not correlate well with the SINMAP risk which is designed to predict 

hillslope risks rather than risks within the road prism. Additionally, there were only eight calibration 

Figure 36. Changes in slope stability risk in the central part of the Cold Creek area. The red and orange 

areas are where the risk increased.
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landslide points, and they were located in a relatively spatially distant locale; a good calibration dataset 

should include at least 50 points and be nearby to the area of interest. Given these considerations, it is 

reasonable to expect poor correlation between observed and expected landslide locations.

Of the 101 km2(39 mi2) that comprise the Cold Creek area, 0.3 km2(0.1 mi2, 0.3%) was stable before 

road construction and is now unstable, and 0.3 km2(0.1 mi2, 0.3%) was unstable before road 

construction and is now less stable due to road drainage (Table 16). This is a total of 0.6 km2(0.3 mi2, 

0.6%) of the watershed that has experienced an increase in landslide risk due to road hydrology. This 

can be compared to 7.8% of the North Fork Siuslaw River watershed in western Oregon that 

experienced an increase in landslide risk due to roads, and has a high incidence of road related shallow 

landsliding.

Table 16. Landslide risk changes in the Cold Creek area by category and area.

Total Area of Watershed (m2) 100,642,000 100%

Area Stable Before Roads, Now Unstable (m2) 308,900 0.3%

Area Unstable Before Roads, Now Less Stable (m2) 338,000 0.3%

Total Area Affected by Roads (m2) 646,900 0.6%
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4.5 Gullies and Gully Initiation Risk

Gullying at drain points below roads can be a substantial source of sediment to stream channels. At each 

gully location we measured or estimated the volume of the gully, and observed properties such as its

location, any other contributing factors such as groundwater interception, and whether or not it was 

associated in any way with the road. To distinguish between road-related gullies and natural incipient 

channel heads, we mapped features as a gully if they occurred below the road drain points, but were 

absent on the uphill side of the road. A gully was defined as a linear erosional feature at least ten feet 

long and six inches deep. Gullies can be determined to be connected to the stream channel network if

an associated drain point that discharges through the gully is connected to the channel. This mass is 

both pulsed (as the gully initiates) and chronic (as continued erosion by road surface-derived water), but 

it is not known what proportion belongs to each category. Delivered gully masses are distributed over a 

20 year time span in order to compare their magnitude with that of the road surface fine sediment (a 

chronic sediment source). Twenty years is used because, in most places, that is roughly the maximum 

age of a feature still easily observable in the field. In any given year, the amount of sediment delivered 

to streams from gullies is likely to be higher or lower than the rate we calculate.

Gully initiation occurs when the shear stress applied by runoff exceeds the strength of the soil surface 

on the hillslope. GRAIP computes the Erosion Sensitivity Index (ESI; Istanbulluoglu et al. 2003), as shown 

below, at each drain point.

 

 

 is the contributing road length at the drain point (m)

 is the slope of the hillslope below the drain point (%)

Calculated ESI values are compared to a calibrated critical ESI threshold (ESIcrit) to identify areas with a

high risk of gully formation (i.e., where ESI > ESIcrit). Calibrations are completed using a logistical 

regression technique (local fit, locfit) in the R statistical computing environment and a length-slope plot 

of the drain points with and without gullies (Figure 38, below). An easy way to conceptualize this is to 

think of these distributions as densities. That is, while the density of non-gully drain points decreases as 

ESI gets larger, the density of gullied points increases relative to the non-gullied drain points. For more 

information on ESI in GRAIP, see Cissel et al. (2012), specifically, pages 105-109 and page 126.

Diffuse drain points, stream crossings, and drain points that do not have an associated road surface flow 

path (i.e. orphan drain points, Appendix A) are not included in the ESI analysis, because these types of 

drain points do not behave in such a way that the ESI is a useful metric. Diffuse points represent a road 

segment that does not concentrate flow, and so does not pose a gully risk. Streams have their own, and 

often non-road related, controls on their propensity to incise, and so cannot be treated the same as 

other drain points. Orphan drain points have a contributing length of zero, and so have an ESI of zero, 

which throws off a meaningful average.
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Center Horse Morrell-Trail Project Area

Existing Gullies

The Center Horse and Morrell/Trail project area has a medium to low incidence of road related gullies. 

There were 33 gullies observed during the course of the survey, with a total volume of 208 m3(272 yd3, 

Table 17). There were 13 gullies that occurred only on the hillslope (44 m3, 58 yd3), four that occurred 

only on the fillslope (2 m3, 3 yd3), and ten that occurred on both the fillslope and hillslope below a drain 

point (131 m3, 172 yd3). All 33 gullies occurred in wet swales. Three gullies were no longer actively 

eroding, while 30 were actively eroding. Figure 37 shows the locations of the gullies in the western 

portion of the Center Horse area, as well as gully initiation risk information (see below).

There were ten gullies (30%) that were determined to be connected to the channel. Using a bulk density 

for road fill of 1.6 Mg/m3(Madej 2001), the mass of sediment generated at all connected gullies was 217

Mg (Table 18). This was 65% of the mass generated at all gullies. Over a 20 year period, 11 Mg/yr of 

sediment was delivered to stream channels, or roughly half of the rate of road surface fine sediment 

delivered to stream channels annually. It would take about ten years for the fine sediment delivery from 

Figure 37. Locations of 

observed gullies and ESI 

risk at drain points, 

western portion of the 

Center Horse area.
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road surfaces to equal the total mass of delivered sediment from gullies. Actual annual sediment 

delivery from gullies is likely higher or lower than these estimates in any given year.

Gully Initiation Risk

The ESIcrit was empirically derived for the Center Horse and Morrell/Trail project area using inventoried 

gullies, and is the ESI value above which the risk of gully formation increases significantly (Figure 38). 

Here, ESIcrit = 14, as the risk of gully formation roughly doubles above that value (Table 19). There was 

one orphan drain point with a gully, and seven gullies without an associated drain point. 

Table 17. Inventoried gullies in the Center Horse and Morrell/Trail project area.

Location of Gully

Count

Volume 

(yd3)

Volume 

(m3)

Number That Occur 

in Wet Swale

Average Delivery Rate 

Activity of Gully Over 20 Years (Mg/yr)

Above Road 6 39 30 6 0

Not Active 1 1.8 1.4 1 0

Still Eroding 5 38 29 5 0

Fillslope 4 2.7 2.1 4 9

Not Active 2 1.3 1.0 2 9

Still Eroding 2 1.4 1.1 2 0

Hillslope 13 58 44 13 0

Still Eroding 13 58 44 13 0

Fill and Hill 10 172 131 10 2

Still Eroding 10 172 131 10 2

Totals 33 272 208 33 11

Table 18. Sediment masses produced and delivered by active gullies in the Center Horse and Morrell/Trail project area.

Mass Produced 

(Mg)

Mass Delivered 

(Mg)

% Sediment 

Delivery

Average Delivery Rate Over 20 

Years (Mg/yr)

Fillslope 3 0 0% 0

Hillslope 71 45 64% 2

Fillslope and Hillslope 210 172 82% 9

Totals 332 217 65% 11
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The average ESI across the Center Horse and Morrell/Trail project area was 9, with an average 

contributing road length of 85 m (280 ft, Table 20). There were 587 (16%) non-diffuse non-stream 

crossing non-orphan drain points where ESI exceeded ESIcrit, leaving 3126 drain points (84%) with an ESI 

value below the threshold. Of the drain points with gullies, six (26%) had an ESI value in excess of ESIcrit. 

This leaves 17 gullied drain points (74%) with an ESI that fell under the critical threshold. The gully rate 

for all points above ESIcrit was 1.0%, and it was 0.5% for points below ESIcrit (Table 19). Drain points that 

had gullies drained 1.8 km (1.1 mi) of road length. The average ESI of drain points with gullies was 11, 

while the average ESI of drain points without gullies was 9. The average contributing length at drain 

points with gullies was 77 m (250 ft), and similarly 85 m (280 ft) at drain points without gullies. Figure 37

shows the distribution of gully risk in the western portion of the Center Horse area.

Table 19. Distribution of drain points by ESI value, Center Horse and Morrell/Trail 

project area. ESIcrit = 14. Eight observed gullies did not have an associated drain point 

or occurred below an orphan drain point, and so are not counted.

< ESIcrit > ESIcrit

ESI Value < 14 14 - 50 50 - 100 > 100

# Sites With Gullies 17 4 2 0

# Sites Without Gullies 3109 440 106 35

% of Total With Gullies 74% 17% 9% 0%

% of Total Without Gullies 84% 12% 3% 1%

Gully Rate (# Gullied / # Total in %) 0.5% 1.0%

Table 20. Further distribution information of drain points by ESI value.

Contributing Length (m)

Average ESI

Where ESI > ESIcrit Total 

Total Average Total Percent Number

Drain Points With Gullies 1770 77 11 6 26% 23

Drain Points Without Gullies 315,070 85 9 581 16% 3690

All Drain Points 316,840 85 9 587 16% 3713

Figure 38. Length-slope plot that shows the 

distribution of gullied and non-gullied drain 

points. Notice that there are more nongullied points towards the center of the 

graph. As the ESI gets larger (upper right part 

of the distribution), there are fewer nongullied points, but there are relatively more 

gullied points. Above the blue ESIcrit = 14 line, 

there is a 1.0% chance of a point being 

gullied, while below the ESIcrit line, there is a 

0.5% chance.
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Poorman Creek

Existing Gullies

The Poorman Creek area has a low incidence of road related gullies. There were four gullies observed 

during the course of the survey, with a total volume of 151 m

3

(197 yd3, Table 21). There were two

gullies that occurred only on the hillslope (150 m

3

, 196 yd3), and two that occurred only on the fillslope 

(0.7 m

3

, 0.9 yd3). No gullies occurred in wet swales. The gullies located on the hillslope were no longer 

actively eroding, while both gullies that occurred on the fillslope were actively eroding. Figure 39 shows 

the locations of the gullies in the central portion of the Poorman Creek area, as well as gully initiation 

Table 21. Inventoried gullies in the Poorman Creek area.

Location of Gully

Count Volume 

(yd3)

Volume 

(m3)

Number That 

Occur in Wet 

Swale

Average Delivery 

Rate Over 20 Years 

(Mg/yr) Activity of Gully

Fill and Hill 1 0.3 0.2 0 0.02

Still Eroding 1 0.3 0.2 0 0.02

Fillslope 4 9 7 0 0.2

Still Eroding 4 9 7 0 0.2

Hillslope 2 196 150 0 0

Not Active 2 196 150 0 0

Totals 7 206 157 0 0.2

Figure 39. Locations of observed gullies and ESI risk at drain points, central portion of the Poorman Creek area.
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risk information (see below). No gullies were determined to be connected to the channel. Using a bulk 

density for road fill of 1.6 Mg/m3(Madej 2001), the mass of sediment generated at all gullies was 241 

Mg.

There were two gullies (29%) that were determined to be connected to the channel. Using a bulk density 

for road fill of 1.6 Mg/m3(Madej 2001), the mass of sediment generated at all connected gullies was 4

Mg (Table 22). This was 2% of the mass generated at all gullies. Over a 20 year period, 0.2 Mg/yr of 

sediment was delivered to stream channels, which is insignificant compared to the rate of road surface 

fine sediment delivered to stream channels annually. It would take less than one year for the fine 

sediment delivery from road surfaces to equal the total mass of delivered sediment from gullies. Actual 

annual sediment delivery from gullies is likely higher or lower than these estimates in any given year.

Gully Initiation Risk

In the Poorman Creek area, there were too few gullies to determine an ESIcrit, suggesting that the gully 

initiation risks here may be very low. The average ESI across the Poorman Creek area was 8, with an 

average contributing road length of 79 m (259 ft, Table 23). Drain points that had gullies drained 1.2 km 

(0.8 mi) of road length. Figure 39 shows the distribution of gully risk in the central portion of the 

Poorman Creek area.

Table 23. Drain point and ESI statistics for the Poorman Creek area

Contributing Length (m) Average 

ESI

Total 

Total Average Number

Drain Points With Gullies 1222 204 5 6

Drain Points Without Gullies 172864 79 8 2184

All Drain Points 174086 79 8 2190

Table 22. Sediment masses produced and delivered by active gullies in the Poorman Creek area.

Mass 

Produced 

(Mg)

Mass 

Delivered 

(Mg)

% Sediment 

Delivery

Average Delivery 

Rate Over 20 

Years (Mg/yr)

Fillslope 11 4 31% 0.2

Hillslope 240 0 0% 0

Fillslope and Hillslope 0.3 0.3 100% 0.02

Totals 252 4 2% 0.2
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65

Cold Creek

Existing Gullies

The Cold Creek area has a low incidence of road related gullies. There were three gullies observed 

during the course of the survey, with a total volume of 5 m

3

(7 yd3, Table 24). There were two gullies 

that occurred only on the hillslope (4 m

3

, 5 yd3), and two that occurred only on the fillslope (2 m

3

, 2 yd3). 

No gullies occurred in wet swales. All gullies were actively eroding. Figure 40 shows the locations of the 

gullies in the Cold Creek area, as well as gully initiation risk information (see below). No gullies were 

determined to be connected to the channel. Using a bulk density for road fill of 1.6 Mg/m3(Madej 

2001), the mass of sediment generated at all gullies was 9 Mg.

Table 24. Inventoried gullies in the Cold Creek area.

Location of Gully

Count Volume 

(yd3)

Volume 

(m3)

Mass 

Produced 

(Mg)

% Sediment 

Delivery

Number That 

Occur in Wet 

Swale Activity of Gully

Fillslope 1 2 2 2 0% 0

Still Eroding 1 2 2 2 0% 0

Hillslope 2 5 4 6 0% 0

Still Eroding 2 5 4 6 0% 0

Totals 3 7 5 9 0% 0

Figure 40. Locations of observed gullies and ESI risk at drain points, central portion of the Cold Creek area.
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66

Gully Initiation Risk

In the Cold Creek area, there were too few gullies to determine an ESIcrit, suggesting that the gully 

initiation risks here may be very low. The average ESI across the Cold Creek area was 4, with an average 

contributing road length of 55 m (180 ft, Table 25). Drain points that had gullies drained 0.2 km (0.1 mi) 

of road length. Figure 40 shows the distribution of gully risk in the Cold Creek area.

Table 25. Drain point and ESI statistics for the Cold Creek area.

Contributing Length (m)

Average ESI Total 

Total Average Number

Drain Points With Gullies 157 52 4.3 3

Drain Points Without Gullies 197,699 55 4.0 3581

All Drain Points 197,856 55 4.0 3584
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67

4.6 Stream Crossing Failure Risk

Besides contributing fine sediment to streams through surface erosion, stream crossings may fail 

catastrophically when blocked and deliver large sediment pulses to stream channels. Stream crossing 

failure risks were assessed using the Stream Blocking Index (SBI, Flanagan et al. 1998). The SBI 

characterizes the risk of plugging by woody debris by calculating the ratio of the culvert diameter to the 

upstream channel width and the skew angle between the channel and the pipe inlet. The SBI is out of a 

range of one to four, where one suggests low risk of blockage, and four suggests a high risk of blockage.

The risk of stream crossing failure can also be viewed in the context of the consequences of failure 

(Flanagan et al. 1998). A consequence of concern at these stream crossings is the erosion of fill material 

into the stream channel. We calculated the fill material that would likely be excavated in an overtopping 

type failure. We modeled the prism of fill at risk as bounded at the base by an area 1.2 times the 

channel width, with side slopes climbing to the road surface at a slope of 33%.

Another consequence of concern at failed stream crossings is the diversion of stream flow onto road 

surfaces and unchanneled hillslopes. Once a crossing becomes occluded and begins to act as a dam, 

failure can occur in one of several ways. If the road grade dips into and rises out of the crossing, the 

failure is likely to be limited to a localized overtopping of the stream crossing. However, if the road 

grades away from the crossing in one or more directions, the flow may be diverted down the road and 

ditch and onto adjacent hillslopes, where it can cause gullying and/or landsliding (Furniss et al. 1997, 

Best et al. 1995). In these situations, volumes of sediment far exceeding those at the crossing can be at 

risk. GRAIP addresses this issue by classifying the potential for stream crossings to divert streamflow 

down the adjacent road as: no potential, potential to divert in one direction, or potential to divert in two 

directions.

The highest risk crossings in these areas have high SBI and diversion potential in one or both directions.

These are generally the crossings that should be addressed first.

Center Horse Morrell-Trail Project Area

Field crews recorded 150 stream crossings in the Center Horse and Morrell/Trail project area. Only the 

116 crossings with a culvert were included in the SBI calculations. The 34 crossings that did not have a 

culvert were bridges (seven crossings), were natural fords (23), or were excavated crossings (four), and 

were not included. Risk of pipe plugging is not a factor at these crossings.

Figure 41. Distribution of SBI values for 

the Center Horse and Morrell/Trail 

project area.
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68

The SBI values for the Center Horse and Morrell/Trail project area had an average of 1.9 for the 116 

stream crossings. There were two stream crossings with an SBI of 4, 25 crossings with an SBI of 3, 53 

crossings with an SBI of 2, and 36 crossings with an SBI of 1 (Figure 41). Of the crossings with values of 

three and four, 24 of 27 had a pipe diameter to channel width ratio of 0.5 or less (small pipe, large 

stream), and 14 had a pipe that was 1/3 or less than the width of the stream, and seven pipes were 

partially or totally blocked. Six crossings with an SBI of 2 had a pipe that was half the width of the 

channel.

The total fill volume at risk for all the stream crossings was 6844 m3(8951 yd3). Fill volumes ranged from 

5 m3(7 yd3) to 875 m3(1144 yd3), and had a mean volume of 60 m3(78 yd3). This is similar to previous 

findings for the middle Blackfoot River at 38 stream crossings, which had an average of 116 tons of fill 

per crossing (Montana Department of Environmental Quality 2008). Overtopping-type fill failure will not 

occur at bridges, so no fill volume risk was calculated at these locations. In the Center Horse and 

Morrell/Trail project area, 55 of 146 stream crossings (38%) had the potential to divert streamflow down 

the road in one or more directions. Bridges also had no diversion potential.

There were 14 crossings with an SBI of 3 or 4 and diversion potential (Figure 42). There was a total of 

824 m3(1077 yd3) of fill at risk at these points. Two have more than 100 m3of fill at risk, and four had 

some major issue (e.g. observed overtopping) or were at imminent risk of a major issue (e.g. partial 

blockage or sediment plume moving downstream to the pipe). These crossings should have the highest 

priority for risk reduction treatments. The 13 crossings with a high SBI but no diversion had 1028 m3

Figure 42. The stream crossings with the highest risk of plugging and 

the most severe consequences of failure in the Center Horse and 

Morrell/Trail project area.
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69

(1345 yd3) of fill at risk, and the 47 crossings with diversion but a low SBI had 1835 m3(2400 yd3) of fill at 

risk.

Several stream crossings were observed to have overtopped or diverted flow in the course of the survey. 

Two crossings, along road 4353 (Morrell Creek) and road 602 (Shanley Creek), were plugged by 

sediment, but the water from both diversions infiltrated before connecting to a stream. These crossings 

had SBIs of 1 and 2. One crossing, along road 17506 (Blind Canyon Creek), was plugged by sediment and 

connected, but had minimal erosion and had an SBI of 2. Two crossings, along road 16654 (connecting 

Morrell Creek roads with Trail Creek roads) and along road 4359 (minor Morrell Creek tributary), were 

plugged by sediment and delivered to a stream, but had minimal erosion. These crossings had SBI values 

of 3 and 4 (orange dots on Figure 42). One diversion, along road 56079 (Spring Creek, Figure 43), was 

plugged by wood and diverted roughly 100 m down the road. The resulting erosion of the road surface 

delivered about 910 ft3(25.6 m3, 41.0 Mg) to Spring Creek (accounted for in the fill erosion piece, 

Section 4.7). That particular crossing pipe had an SBI value of 3 (orange dot on Figure 42). The diversion 

was repaired by a passing fire crew. 

Figure 43. Spring Creek diversion that delivered 41 Mg of sediment to the stream.
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70

Poorman Creek

Field crews recorded 53 stream crossings in the Poorman Creek area. Only the 29 crossings with a 

culvert were included in the SBI calculations. The 24 crossings that did not have a culvert were bridges 

(eight crossings) or were natural fords (16) and were not included. Risk of pipe plugging is not a factor at 

these crossings.

The SBI values for the Poorman Creek area had an average of 1.7 for the 29 stream crossings. There 

were no stream crossings with an SBI of 4, five crossings with an SBI of 3, nine crossings with an SBI of 2, 

and 15 crossings with an SBI of 1 (Figure 44). All five of the crossings with values of three had a pipe 

diameter to channel width ratio of 0.4 or less (small pipe, large stream), and two had a pipe that was 1/3 

or less than the width of the stream. Two crossings with an SBI of 2 had a pipe that was half the width of 

the channel.

The total fill volume at risk for all the stream crossings was 1399 m

3

(1830 yd3). Fill volumes ranged from 

6 m

3

(8 yd3) to 318 m

3

(416 yd3), and had a mean volume of 48 m

3

(63 yd3). This is similar to previous 

findings for the middle Blackfoot River at 38 stream crossings, which had an average of 116 tons of fill 

per crossing (Montana Department of Environmental Quality 2008). Overtopping-type fill failure will not 

occur at bridges, so no fill volume risk was calculated at these locations. In the Poorman Creek area, 

eight of 53 stream crossings (15%), including three natural fords, had the potential to divert streamflow 

down the road in one or more directions. Bridges also had no diversion potential.

Figure 45. The stream 

crossings with the highest 

risk of plugging and the 

most severe consequences 

of failure in the Poorman 

Creek area.

Figure 44. Distribution of SBI values for 

the Poorman Creek area.
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71

There was one crossing with an SBI of 3 and diversion potential (Figure 45). There was a total of 21 m

3

(27 yd3) of fill at risk at this point. There were no problems already apparent at this location. The three

crossings with a high SBI but no diversion had 582 m

3

(761 yd3) of fill at risk, and the seven crossings 

with diversion but a low SBI had 142 m

3

(186 yd3) of fill at risk.

There were two natural ford type crossings in the western portion of the Poorman Creek area on road 

1842-A2 that were observed to divert flow down the road, though no major erosion was observed at the 

time of the survey (Figure 46).

Figure 46. Stream diversion at a natural ford in the western portion of the Poorman 

Creek area. No major erosion was observed.
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72

Cold Creek

Field crews recorded 115 stream crossings in the Cold Creek area. Only the 71 crossings with a culvert 

were included in the SBI calculations. The 42 crossings that did not have a culvert were bridges (six 

crossings), natural fords (36) or log culverts (two) and were not included. Risk of pipe plugging is not a 

factor at bridges and fords, and log culverts are generally considered to be blocked by design.

The SBI values for the Cold Creek area had an average of 2.3 for the 71 stream crossings. There were 

two stream crossings with an SBI of 4, 26 crossings with an SBI of 3, 31 crossings with an SBI of 2, and 12

crossings with an SBI of 1 (Figure 47). Of the 26 crossings with an SBI of 3, 17 had a pipe diameter to 

channel width ratio of 0.5 or less (small pipe, large stream), and five had a pipe that was 1/3 or less than 

the width of the stream. Nine crossings with an SBI of 2 had a pipe that was half the width of the 

channel.

The total fill volume at risk for all the stream crossings was 2095 m

3

(2740 yd3). Fill volumes ranged from 

4 m

3

(5 yd3) to 268 m

3

(351 yd3), and had a mean volume of 31 m

3

(41 yd3). This is similar to previous 

findings for the nearby middle Blackfoot River at 38 stream crossings, which had an average of 116 tons 

Figure 47. Distribution of SBI values 

for the Cold Creek area.

Figure 48. The stream 

crossings with the highest 

risk of plugging and the 

most severe consequences 

of failure in the Cold Creek 

area.
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73

of fill per crossing (Montana Department of Environmental Quality 2008). Overtopping-type fill failure 

will not occur at bridges, so no fill volume risk was calculated at these locations. In the Cold Creek area, 

39 of all 115 stream crossings (34%), had the potential to divert streamflow down the road in one or 

more directions.

There were 14 crossings with an SBI of 3 or 4 and diversion potential (Figure 48). There was a total of 

332 m

3

(434 yd3) of fill at risk at this points. Of those 14 crossings, half received the stream flow from the 

ditch, though this appeared to be intentional (streams were intercepted by the ditch and discharged 

through the next culvert down road 90509). No other problems were already apparent at these

locations. The 14 crossings with a high SBI but no diversion had 427 m

3

(558 yd3) of fill at risk, and the 25

crossings with diversion but a low SBI had 234 m

3

(306 yd3) of fill at risk.
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74

4.7 Drain Point Condition and Fill Erosion

The GRAIP inventory involves an assessment of the condition of each drain point and a determination of 

how well it is performing its intended function. Problems with drain point condition are pre-defined for 

each drain type. Broad based dips are considered to be in poor condition if they are insufficiently 

outsloped and pond water on the road. Culverts are defined to be in poor condition if they have more 

than 20% occlusion of the inlet by sediment, substantial inlet crushing, significant rust, or flow around 

the pipe. Lead off ditches are considered problematic if they have excess deposition or gullying. Nonengineered features are almost always a problem due to a blocked ditch, a gully, or a broken outside 

berm, but are not considered problematic if they occur due to an outsloped road and do not have any 

fill erosion. Stream crossings culverts are considered a problem if they are blocked by sediment or wood, 

crushed or rusted significantly, incising, scouring, losing much water from flow around the pipe, or have 

a high SBI with diversion potential (see Section 4.6 for more detail on SBI and diversion). Sumps are a 

problem if they pond water on the road surface or cause fill saturation. Water bars that are damaged, 

under-sized, or do not drain properly are defined as problematic. Diffuse drains (outsloped roads) are 

rarely observed to have drain point problems.

If a drain point is observed to have fill erosion, the volume is estimated. Fill erosion can be determined 

to be connected to the stream channel network if its associated drain point is connected to the channel. 

This mass of sediment may be pulsed (if the fill failure happens at once), chronic (if the fill gradually 

erodes), or pulsed and then chronic (initial failure, followed by more gradual erosion); it is unknown 

what proportion of this mass belongs to each category. Delivered masses of fill erosion are distributed 

over a 20 year time span in order to compare their magnitude with that of the road surface fine 

sediment (a chronic sediment source). Twenty years is used because, in most places, that is roughly the 

maximum age of a feature still easily observable in the field. In any given year, the amount of sediment 

delivered to streams from gullies is likely to be higher or lower than the rate we calculate.

Table 26. Drain point condition problems and fill erosion below drain points, Center Horse and 

Morrell/Trail project area.

Drain Type Count

Problems Fill Erosion

Number % of Total Number % of Total

Broad Based Dip 1413 387 27% 6 0.4%

Diffuse Drain 931 0 0% 13 1%

Ditch Relief Culvert 392 155 40% 11 3%

Excavated Stream Crossing 4 0 0% 0 0%

Lead Off Ditch 135 1 0.7% 0 0%

Non-Engineered Drain 1102 113 10% 28 3%

Stream Crossing 146 44 30% 4 3%

Sump 24 11 46% 0 0%

Water Bar 914 100 11% 21 2%

All Drains 5061 811 16% 83 2%
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75

Center Horse Morrell-Trail Project Area

Within the Center Horse and Morrell/Trail project area, 16% of all drain points (811 of 5061) had one or 

more problem of some type (Table 26; Figures 49 and 50). Sumps had the highest rate of problems (11 

of 24, 46%), followed by ditch relief culverts (155 of 392, 40%), stream crossings (44 of 146, 30%), and 

broad based dips (387 of 1413, 27%). Diffuse road segments (931 features total) and excavated stream 

crossings (four features total) did not have any problems. Water bars had problems at 100 of 914 

locations (11%) and non-engineered drains had problems at 113 of 1102 locations (10%).

Fill erosion was present at 2% of all drain points, totaling 85 m3(3000 ft3; Table 27). Fill erosion was 

most common at non-engineered drains, with 28 of 1102 (3%) eroding 23 m3(820 ft3). Water bars had 

fill erosion at 21 of 914 locations (2%; 8 m3; 280 ft3); diffuse drains at 13 of 931 locations (1%; 2 m3; 80 

ft3); and ditch relief culverts at 11 of 392 locations (3%; 4 m3; 150 ft3). Stream crossings had the most 

mass of fill erosion of 44 m3(1550 ft3) eroded from four crossings. More than half of this mass was from 

the Spring Creek flow diversion. Using the same bulk density as above, fill erosion at drain points that 

were connected to the stream channel network totaled 87 Mg, most of which occurred at stream 

crossings (70 Mg) and non-engineered drains (13 Mg). This was 64% of the sediment produced by fill 

erosion at drain points. Over a 20 year period, 4.4 Mg/yr of sediment were delivered to stream 

channels, or roughly one quarter of the rate of road surface fine sediment delivered to stream channels 

annually. It would take about four years for the fine sediment delivery from road surfaces to equal the 

Figure 49. Specific drain point problems by drain type in the Center Horse and Morrell/Trail project area.
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76

total mass of delivered sediment from fill erosion. Actual annual sediment delivery from fill erosion is 

likely higher or lower than these estimates in any given year, and when the largest failures occur, they 

are often repaired and quickly become difficult to record accurately.

Figure 50. Drain point problems in the Spring Creek watershed.
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Table 27. Fill erosion below drain points, volumes and masses, Center Horse and Morrell/Trail project area.

Drain Type Count

Number 

With 

Fill 

Erosion

% of 

Total

Total 

Volume 

Mass 

Sediment 

Produced 

(Mg)

Mass 

Sediment 

Delivered 

(Mg)

% 

Sediment 

Delivery

Average 

Delivery Rate 

Over 20 Years 

(Mg/yr) (m3

) (ft3)

Broad Based Dip 1413 6 0.4% 4 140 6 2 30% 0.1

Diffuse Drain 931 13 1% 2 80 3 0 0% 0

Ditch Relief Culvert 392 11 3% 4 150 7 0.1 2% 0.01

Excavated Stream 

Crossing

4 0 0% 0 0 0 0 0% 0

Lead Off Ditch 135 0 0% 0 0 0 0 0% 0

Non-Engineered Drain 1102 28 3% 23 820 37 13 36% 1

Stream Crossing 146 4 3% 44 1550 70 70 100% 4

Sump 24 0 0% 0 0 0 0 0% 0

Water Bar 914 21 2% 8 280 13 2 15% 0.1

All Drains 5061 83 2% 85 3000 136 87 64% 4
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78

Poorman Creek

Within the Poorman Creek area, 12% of all drain points (270 of 2190) had one or more problem of some 

type (Table 28; Figures 51 and 52). Ditch relief culverts had the highest rate of problems (18 of 56, 32%), 

followed by broad based dips (120 of 412, 29%); sumps had a rate of 50%, but there were only two 

Table 28. Drain point condition problems and fill erosion below drain points, Poorman Creek area.

Count

Problems Fill Erosion

Number % of Total Number % of Total

Broad Based Dip 412 120 29% 2 0.5%

Diffuse Drain 417 0 0% 1 0.2%

Ditch Relief Culvert 56 18 32% 1 2%

Lead Off Ditch 8 0 0% 0 0%

Non-Engineered Drain 693 63 9% 16 2%

Stream Crossing 53 7 13% 0 0%

Sump 2 1 50% 0 0%

Water bar 549 61 11% 2 0.4%

All Drains 2190 270 12% 22 1%

Figure 51. Specific drain point problems by drain type in the Poorman Creek area.
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79

sumps recorded. Diffuse road segments (417 features total) and lead off ditches (eight features) did not 

have any problems. Stream crossings had problems at seven of 53 locations (13%), water bars had 

problems at 61 of 549 locations (11%) and non-engineered drains had problems at 63 of 693 locations

(9%).

Table 29. Fill erosion below drain points, volumes and masses, Poorman Creek area.

Drain Type Count

Number 

With 

Fill 

Erosion

% of 

Total

Total Volume Mass 

Sediment 

Produced 

(Mg)

Mass 

Sediment 

Delivered 

(Mg)

% 

Sediment 

Delivery

Average 

Delivery 

Rate Over 

20 Years 

(Mg/yr)

(m3) (ft3)

Broad Based Dip 412 2 0.5% 1 50 2 0.5 20% 0.02

Diffuse Drain 417 1 0.2% 0.1 10 0.2 0 0% 0

Ditch Relief Culvert 56 1 2% 0.3 10 0.5 0 0% 0

Lead Off Ditch 8 0 0% 0 0 0 0 0% 0

Non-Engineered Drain 693 16 2% 8 300 13 3 22% 0.1

Stream Crossing 53 0 0% 0 0 0 0 0% 0

Sump 2 0 0% 0 0 0 0 0% 0

Water bar 549 2 0.4% 1 40 2 0 0% 0

All Drains 2190 22 1% 11 400 18 3.4 19% 0.2

Figure 52. Drain point problems in the western half of the Poorman Creek area.
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Fill erosion was present at 1% of all drain points, totaling 11 m

3

(403 ft3; Table 29). Fill erosion was most 

common at non-engineered drains, with 16 of 693 (2%) eroding 8 m

3

(296 ft3). Water bars had fill 

erosion at two of 549 locations (0.4%; 1 m

3

; 40 ft3); broad based dips at two of 412 locations (0.5%; 1

m

3

; 50 ft3); and ditch relief culverts at 1 of 56 locations (2%; 0.3 m

3

; 12 ft3). Non-engineered drains had 

the most mass of fill erosion. Using the same bulk density as above, fill erosion at drain points that were 

connected to the stream channel network totaled 3.4 Mg, 3 Mg of which occurred at non-engineered

drains. This was 19% of the sediment produced by fill erosion at drain points. Over a 20 year period, 0.2

Mg/yr of sediment were delivered to stream channels, which is negligible compared to other sources.

Actual annual sediment delivery from fill erosion is likely higher or lower than these estimates in any 

given year, and when the largest failures occur, they are often repaired and quickly become difficult to 

record accurately.
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Cold Creek

Within the Cold Creek area, 8% of all drain points (284 of 3584) had one or more problem of some type 

(Table 30; Figures 53 and 54). Stream crossings had the highest rate of problems (45 of 115, 39%),

followed by ditch relief culverts (80 of 266, 30%). Diffuse road segments (670 features total), lead off 

Table 30. Drain point condition problems and fill erosion below drain points, Cold Creek area.

Drain Type Count

Problems Fill Erosion

Number % of Total Number % of Total

Broad Based Dip 1050 14 1% 18 2%

Diffuse Drain 670 0 0% 0 0%

Ditch Relief Culvert 266 80 30% 1 0.4%

Lead Off Ditch 139 0 0% 0 0%

Non-Engineered Drain 1097 127 12% 3 0.3%

Stream Crossing 115 45 39% 1 1%

Sump 1 0 0% 0 0%

Water Bar 246 18 7% 0 0%

All Drains 3584 284 8% 23 1%

Figure 53. Specific drain point problems by drain type in the Cold Creek area.
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ditches (139 features total), and sumps (one feature total) did not have any problems. Non-engineered 

drains had problems at 127 of 1097 locations (12%), water bars had problems at 18 of 246 locations 

(7%), and broad based dips had problems at 14 of 1050 locations (1%).

Table 31. Fill erosion below drain points, volumes and masses, Cold Creek area.

Drain Type Count

Number 

With 

Fill 

Erosion

% of 

Total

Total 

Volume

Mass 

Sediment 

Produced 

(Mg)

Mass 

Sediment 

Delivered 

(Mg)

% 

Sediment 

Delivery

Average 

Delivery 

Rate Over 

20 Years 

(Mg/yr)

(m3) (ft3)

Broad Based Dip 1050 18 2% 3 90 4 0 0% 0

Diffuse Drain 670 0 0% 0 0 0 0 0% 0

Ditch Relief Culvert 266 1 0.4% 0.03 1 0.05 0 0% 0

Lead Off Ditch 139 0 0% 0 0 0 0 0% 0

Non-Engineered Drain 1097 3 0.3% 0.4 20 1 0.2 33% 0.02

Stream Crossing 115 1 1% 0.2 10 0.3 0.3 100% 0.05

Sump 1 0 0% 0 0 0 0 0% 0

Water Bar 246 0 0% 0 0 0 0 0% 0

All Drains 3584 23 1% 3 114 5 0.5 10% 0.005

Figure 54. Drain point problems in the Cold Creek area.
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83

Fill erosion was present at 1% of all drain points, totaling 3 m

3

(110 ft3; Table 31). Fill erosion was most 

common at broad based dips, with 18 of 1050 (2%) eroding 3 m

3

(90 ft3). Non-engineered drains had fill 

erosion at 3 of 1097 locations (0.3%; 0.4 m

3

; 20 ft3); stream crossings at 1 of 115 locations (1%; 0.2 m

3

; 

10 ft3); and ditch relief culverts at 1 of 266 locations (0.4%; 0.03 m

3

; 1 ft3). Broad based dips had the 

most mass of fill erosion. Using the same bulk density as above, fill erosion at drain points that were 

connected to the stream channel network totaled 0.5 Mg, which occurred at stream crossings (0.3 Mg) 

and non-engineered drains (0.2 Mg). This was 10% of the sediment produced by fill erosion at drain 

points. Over a 20 year period, 0.005 Mg/yr of sediment were delivered to stream channels, which is 

negligible compared to other sources. Actual annual sediment delivery from fill erosion is likely higher or 

lower than these estimates in any given year, and when the largest failures occur, they are often 

repaired and quickly become difficult to record accurately.
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4.8 Risks by Maintenance Level

Sediment production and delivery, connected length of road, drain point problems, and fill erosion were 

analyzed by road maintenance level for the three areas. Gully and landslide risks were analyzed for the

Center Horse and Morrell/ Trail project area. Poorman Creek and Cold Creek did not have enough gullies 

or landslides for this analysis. Road surface fine sediment delivery risks were hypothesized to be higher 

on roads that received more maintenance (Maintenance Levels 3 and 4), and lower on roads that 

received less maintenance (ML 1 and 2), due to the positive correlation of maintenance level with 

traffic. Mass wasting risks and other infrastructure problems were hypothesized to be higher on roads 

that received less maintenance (ML 1 and 2), as many of these issues may be preventable. Unclassified 

roads are usually small and seldom used, and are generally equivalent to ML 1 or 2. Appendix A shows 

these risks for each of the three areas and summarized for all three.

For all three areas, there was roughly twice as much total sediment delivery on the ML 3 roads as on any 

of the ML 1 or 2 or unclassified roads (Figure 55, note the logarithmic scale). Sediment production, as 

well, was higher on the higher maintenance level roads. Specific sediment delivery (delivery normalized 

by length of road in each ML category) was almost five times higher on the ML 3 roads than any of the 

ML 1 or 2 or unclassified roads. For sediment delivery as a percentage of production, each maintenance 

level was roughly equivalent, though the ML 3 roads had the highest percent, suggesting that the higher 

delivery on the higher maintenance levels was due to the higher production.

Figure 55. Sediment delivery risks for all three areas. Note that the logarithmic scale begins at 10. Only the Center 

Horse and Morrell/Trail project area had ML 4 roads, so these were omitted from these graphs. Specific sediment 

is normalized by road length in each ML category.
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In the Center Horse and Morrell/Trail project area, there were more landslides with more mass on the 

lower maintenance level roads than the higher (Figure 56). The number, mass, and delivered mass of 

gullies exhibited a similar pattern in this area. This pattern is stronger when the delivered mass from 

gullies is normalized by total road length in each ML category, with a roughly ten-fold difference 

between the unclassified and ML 1 roads and the ML 2, 3, and 4 roads. Fill erosion mass, delivered mass, 

specific delivered mass, and percent mass delivered were also higher on the lower maintenance level 

roads in all three areas (Figure 57). Regular maintenance may address the road problems that lead to 

mass wasting. An alternative hypothesis is that the higher maintenance level roads tend to cross less 

steep slopes in the valley bottom, which is less conducive to mass wasting. In the Center Horse and 

Morrell/Trail project area, the average slope that the ML 4 roads traversed was about half of the 

average slope that the ML 1, 2, and 3 roads traversed.

Figure 57. Gully and landslide risks for the Center Horse and Morrell/Trail project area. Note the logarithmic scale. The 

other two areas did not have enough gullies or landslides for this analysis.

Figure 56. Fill erosion total mass and delivered mass for all three project areas. Note the change in axis scale for Specific Fill Erosion 

Delivery on the left graph.
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Drain point problems did not fit the expected pattern, as although there were more drain points with 

problems on the lower maintenance level roads, the higher maintenance level roads had a higher 

percentage of drain points with problems (Figure 58). Heavier traffic may result in wear on 

infrastructure that outpaces the effects of neglect on the lower maintenance level roads, though given 

enough time, the effects of neglect may be larger. Additionally, different types of drain points 

preferentially occur on the different maintenance levels, and each type of drain point has a different 

overall problem rate.

Figure 58. Drain point problems for all three project areas.
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5.0 Jammer Road Inventory and Observations

Jammer roads are decades-old closely-spaced unsurfaced logging roads built to a low standard that 

contour along the hillslope roughly every 30 m (100 ft) of slope length. In the Center Horse and 

Morrell/Trail project area, there were 380 km (230 mi) of jammer roads concentrated in 20 to 25 

complexes that encompass 0.25 mi2to 1 mi2each (Figure 59). This is about the same total length as 

there were regular, non-jammer roads.

Though these roads were generally unmaintained since they were in use as logging roads, the risks they 

may pose to aquatic systems in the future were unknown. On the one hand, most of these roads were

heavily vegetated and initially appeared to be stable; on the other hand, infrastructure along these 

roads was old and likely to fail or to have already failed. Prior field observations suggested that most of 

the sediment delivery and mass wasting risks from jammer roads occurred at stream crossings. In order 

to evaluate these risks, we inventoried two complexes in the Center Horse project area using GRAIP

(section 5.1, below), and conducted a census of every jammer road-stream intersection in both project 

areas (section 5.2. below). 

5.1 Complete Complex Inventory

Two complete jammer road complexes totaling 18.5 km in the Center Horse project area were 

inventoried using the GRAIP method. The eastern complex was located in upper Black Canyon (13.3 km, 

Figure 59. Jammer road locations in the Center Horse and Morrell/Trail project area, with the complete surveyed complexes and the stream

crossings that we surveyed.
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8.3 mi), and the western complex was located on the south face of Morrell Mountain (5.1 km, 3.2 mi; 

Figure 59). The Black Canyon complex may be treated at some point in the future, and the GRAIP 

method will be used to monitor the outcomes of the treatment. 

There were 325 drainage points recorded. Drainage on these roads occurred mostly through diffuse 

road segments (158 points) and non-engineered drains (124 points). Most of the road surfaces were 

undrivable and covered in grass, herbaceous vegetation, or small to medium sized trees (17.9 of 18.4 

km; 97%).

Table 32. Summary of sediment production and delivery at drain points on the jammer road complexes that were 

inventoried with GRAIP in the Center Horse and Morrell/Trail Project Area.

Drain Point Type Count

Sediment 

Production 

(kg/yr)

Sediment 

Delivery 

(kg/yr)

% 

Sediment 

Delivery

Length 

Connected 

(m)

% Length 

Connected

Broad Based Dip 28 90 0 0% 0 0%

Diffuse Drain 158 560 2 0.4% 20 0.1%

Ditch Relief Culvert 1 0 0 0% 0 0%

Lead Off Ditch 0 0 0 0% 0 0%

Non-Engineered Drain 124 350 6 2% 50 1%

Stream Crossing 9 10 10 100% 100 100%

Sump 0 0 0 0% 0 0%

Water Bar 5 8 0 0% 0 0%

All Drains 325 1020 18 2% 160 1%

Figure 60. Fine sediment delivery to 

channels by road segment and drain point 

in the upper Black Canyon jammer road 

complex. The road lines and drain points 

are colored to indicate the mass of fine 

sediment delivered to channels.
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Overall, both complexes had very low sediment production and delivery (Table 32). Roads were highly 

vegetated and had low slopes. Sediment production totaled 1 Mg/yr for both complexes. There were no 

delivering drain points in the Morrell Mountain complex. In the Black Canyon complex, there was 0.02 

Mg/yr of fine sediment delivered from the road surface to the stream from 0.2 km of road length (2% of 

all sediment produced from 1% of total length; Figure 60). An estimate of total road surface fine 

sediment delivery for the Center Horse and Morrell/Trail project area was made by applying the road 

surface delivery rate from these two complexes to the entire length of jammer roads (Table 33). The 

estimated total road surface fine sediment delivery was 0.4 Mg/yr.

Table 33. Estimation of sediment delivery from road surfaces for 

all jammer roads in the Center Horse and Morrell/Trail project 

area, based on the road surface sediment delivery rate per 

kilometer from the inventoried complexes.

Length of Road Surveyed (km | mi) 19 11

Total Length of Jammer Roads in Center 

Horse and Morrell/Trail (km | mi) 376 234

Total Road Surface Sediment Delivery 

(Mg/yr) 0.02

Road Surface Delivery Rate for Surveyed 

Roads (Mg/yr/km) 0.001

Estimated Road Surface Delivery for All 

Jammer Roads (Mg/yr) 0.4

In the Black Canyon complex, there was a natural ford stream diversion from a two foot wide sidechannel onto the road. As a result of this diversion, there were two gullies observed, totaling 29 Mg 

(Figure 61; Table 34). Both gullies delivered their sediment to the stream. Also as a result of the stream 

diversion, there were two non-engineered drains observed to have fill erosion totaling 25 Mg. One of 

Figure 61. Fill erosion and gullies in the Black 

Canyon jammer road complex. All mass 

wasting was due to a diverted stream crossing. 

There was no other mass wasting observed in 

either inventoried jammer complex.
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the two drain points with fill erosion delivered to the stream, totaling 23 Mg. This mass wasting totaled 

53 Mg, with 51 Mg delivered to the stream. Averaged over 20 years, the mass wasting delivery totaled 3 

Mg/yr. There were no other observed instances of mass wasting, including landslides, in either complex.

Table 34. Mass wasting masses and 

delivery for the observed mass wasting 

in the Black Canyon jammer complex. 

No mass wasting was observed in the 

Morrell Mountain complex.

Landslide Mass (Mg) 0

Gully Mass (Mg) 29

Fill Erosion Mass (Mg) 25

Total Mass Wasting (Mg) 53

Mass Wasting Delivery (Mg) 51

Mass Wasting Delivery Over 

20 Years (Mg/yr) 3

The Black Canyon complex was chosen for this inventory because it was thought to have a high rate of 

and potential for sediment delivery and other problems. Based on other field observations at other 

complexes, as well as the stream diversion in the Black Canyon complex, most delivery of sediment from 

jammer roads probably occurs at stream crossings when the fill erodes into the stream or diverts down 

the road (see below). Other mass wasting, particularly that delivers to the stream channel, is probably 

rare.

Other than sediment from stream crossing-related erosion, jammer roads in the Center Horse and 

Morrell/Trail project area are probably not a major sediment source. Non-stream crossing risks are 

observed and estimated to be very low. However, it is unknown what the response of these roads may 

be after a forest fire. Without vegetation, there may be a greater sediment supply, more runoff, and a 

greater chance of mass wasting. Stream crossings risks are evaluated in the following section.
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5.2 Stream Crossing Survey

Prior field observations suggested that most of the risk present on the jammer roads in the Center Horse 

and Morrell/Trail project area occurred at stream crossings. In order to evaluate this risk, we conducted 

a census of all of the stream crossings on jammer roads in the area (Figure 59). Crews followed streams 

up to each consecutive stacked road until the stream channel head was reached or there were no more 

upslope roads. Streams were defined as continuous features with a bed, banks, and evidence of flow for 

some part of most years. No minimum size was used in this definition because even small features can 

cause problems under the right conditions. TauDEM 4.0 (http://hydrology.usu.edu/taudem/taudem4.0) 

was used to model the probable stream locations. There were a number of modeled streams that were 

not present in the field, and streams that were found in the field that were not present in the model. 

There were 71 stream crossings on jammer roads surveyed in the course of the census. There were 61 

natural ford-type crossings (no infrastructure) and ten crossings with culverts. Some of the natural fords 

may have been log culverts at one time, but the evidence has likely decomposed. Observations at each 

crossing included channel width, presence of problems such as a blocked culvert or scoured road, 

volume of fill erosion, and presence of stream diversion. Fill erosion risks were further analyzed to 

evaluate the rough probability and amount of remaining risk.

Figure 62. Stream crossings with observed fill erosion on jammer roads in the Center 

Horse and Morrell/Trail project area. The largest fill erosion volume was due to a 

stream diversion.
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There were 31 stream crossings with fill erosion (44% of all crossings on jammer roads), totaling 207 m3

(7310 ft3, 331 Mg; Figure 62; Table 35). One crossing in lower Black Canyon in the Center Horse project 

area with a stream diversion had more than half of the total fill erosion (3980 ft3, 113 m3, 180 Mg). Most 

crossings with fill erosion had under 300 ft3(10 m3, 15 Mg). The average fill erosion per crossing was 100

ft3(3 m

3

, 5 Mg). Without the largest outlier volume of fill erosion, the average fill erosion per crossing 

was 50 ft3(1 m

3

, 2 Mg). Since this fill erosion occurred at stream crossings, all of it delivered to the 

stream. Averaged over 20 years, the fill erosion totaled 17 Mg/yr, which is roughly equivalent to the 

road surface fine sediment delivery for the non-jammer roads in the Center Horse and Morrell/Trail 

project area. Without the largest outlier mass of fill erosion, the delivery rate over 20 years was 8 Mg/yr.

Table 35. Fill erosion statistics for 

the jammer road stream crossings 

observed in the Center Horse and 

Morrell/Trail project area.

Number Surveyed 71

Number With Fill Erosion 31

% Fill Erosion 44%

Volume Fill Erosion (ft3) 7310

Volume Fill Erosion (m3) 207

Mass Fill Erosion (Mg) 331

Fill Erosion Delivery Over 

20 Years (Mg/yr) 17

Mean Fill Erosion Per 

Crossing (m3)

3

Estimated Mean Total 

Original Fill Volume at

Each Crossing (m3)

12

% of Estimated Original 

Fill Volume Eroded (m3)

25%

The volume of fill was estimated at each crossing as being bounded at the base by an area 1.2 times the 

channel width, with side slopes climbing to the road surface at a slope of 33%. We assumed a road 

width of 14 ft, and a fill depth of five feet. The slope of the hillslope was used to determine the length of 

the crossing bottom according to the slopes given by Megahan (1976), modified to account for the

narrower road. The estimated average volume of fill at each crossing was 12 m3(420 ft3; Figure 62). 

Using the average volume of fill erosion per crossing, it is estimated that about 25% of the possible fill 

erosion has already been eroded, with 75% (about 600 m

3

or 22,000 ft3) remaining. Much of the 

observed fill erosion included volumes eroded from stream diversions, so the observed fill erosion 

volume may be larger than the estimated available volume. There may be more than 75% of the 

available fill remaining. However, the process of the stream channel cutting through what amounts to a 

flat step in its longitudinal profile takes time, and will happen episodically during high flow events. Each 

stream crossing will respond at a different rate due to the available transport capacity of the stream, 

and may include some deposition.
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In order to prioritize the stream crossings with the greatest risk of future fill erosion, we used a logistical 

regression technique (local fit, locfit) in the R statistical computing environment that compared the 

stream crossings in the Center Horse project area with fill erosion to those without, according to the 

slope of the hillslope on which the stream runs (Figure 63). The sample includes all crossings with fill 

erosion, but may be too small to draw broad conclusions. It was found that on hillslopes of greater than 

about 40%, every stream crossing in the Center Horse area had fill erosion.

Figure 63. Probability graph output from the local fit 

regression in R. Fill Erosion Probability is a yes/no field 

(specific volumes are not accounted for). Though fill 

erosion occurs throughout the slope range, above about 

40% slope, all have fill erosion.

Figure 64. Stream crossings on jammer roads with problems, including observed overtopping, diversion, and culvert problems.
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Other problems were observed at the inventoried jammer road stream crossings. Five of the crossings 

(7%) had evidence of current or recent stream diversions (Figure 64; Table 36). Ten natural ford type 

crossings were observed to have one direction of possible diversion (two of them already had diversions 

observed). One other crossing with a culvert and one diversion direction was observed to have been 

overtopped in the past. Four other crossings (6%) were observed to have other problems, including 

scoured road surfaces above the crossings and blocked or failing culverts. This is nine crossings in total, 

or 13%.

Table 36. Stream crossings on jammer 

roads with problems in the Center Horse 

and Morrell/Trail project area.

Number of Crossings With 

Stream Diversion Evidence 5

% of Crossings With Stream 

Diversion Evidence 7%

Number of Crossings With 

Other Problems 4

% of Crossings With Problems 6%
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6.0 Summary and Conclusions

Field inventory and modeling analysis of the public roads in the Center Horse and Morrell/Trail project 

area, the Poorman Creek watershed area, and the Cold Creek watershed area in the Southwest Crown of 

the Continent in western Montana using the GRAIP model provided detailed, site specific data on 

sediment-related watershed impacts from roads. Impacts are both chronic, in terms of annual sediment 

input to streams, and pulsed, such as during storm events when road connectivity to the channel 

networks is at its maximum. Inventory data was collected on 769 km (478 mi) of road, including 10,759

drain points, by two field crews during the summer months of 2012 and 2013 (June to October).

Additionally, jammer-type logging roads were sampled and their road-stream intersections were 

surveyed in the Center Horse and Morrell/Trail project area.

The GRAIP model was used to predict sediment risk and sediment-related impacts from roads. The 

model predicts road to stream hydrologic connectivity, sediment delivery to streams, downstream 

sediment accumulation, risks of shallow landslides caused by roads, gully initiation risk below drain 

points, and risks to road-stream crossings (Tables 37, 38, and 39). Inventory data is also used to locate 

and describe problems with existing drain points. In addition, GRAIP model data will be compared to instream PIBO monitoring for these project areas in a separate document. 

Center Horse and Morrell/Trail Project Area Summary

In the Center Horse and Morrell/Trail project area, there were 407 km (253 mi) of road and 5061 drain 

points surveyed. Table 37 presents a summary of the findings for this project area. Hydrologic 

connectivity was found to be a relatively low 4% of all road length at 16 km out of 407 km (10 mi out of 

252 mi). The model predicted 21.4 Mg/yr of delivered road surface fine sediment to stream channels, 

which is 5% of the 456 Mg generated annually by the road surface. This sediment was delivered through 

314 of 5061 (6%) drain points. There was 16.2 Mg/yr of delivery that occurred within 10 m of a stream 

crossing. This is 76% of all sediment delivery and 57% of all sediment produced within 10 m of a stream 

crossing.

Specific sediment due to road surface-related sediment for the whole Center Horse and Morrell/Trail 

project area was 0.10 Mg/km2/yr, or 1% of the observed total average fine sediment yield for five 

nearby areas as determined by reservoir coring or suspended sediment extrapolations. Including 

sediment delivered to streams through other sources (landslides, gullies, and fill erosion at drain points), 

the specific sediment for the whole project area was 0.21 Mg/km2/yr, or about 2% of the observed 

average fine sediment yield for the nearby areas. Some heavily impacted stream reaches had road 

sediment delivery values as high as 4.9 Mg/km2/yr with only road surface fine sediment, or 18.1

Mg/km2/yr including mass wasting sediment. Reaches in Shanley, Little Shanley, Blacks Canyon, and 

lower Spring Creeks showed particularly high specific sediment values above 0.3 Mg/km2/yr, or 3% to 

19% above the reference sediment yield.

There were 18 landslides observed by field crews in the course of the inventory, with a total volume of 

1319 m3(1726 yd3). Of those, 10 were road related. It was conservatively estimated that 176 Mg of 

landslide derived sediment has been delivered to streams, which is roughly half the rate of that from 

road surfaces over 20 years (8.8 Mg/yr). It would take about eight years for the fine sediment delivery 

from road surfaces to equal the total mass of delivered sediment from landslides. Calibrated stability 
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index modeling with SINMAP conservatively showed that 6 km2(2 mi2), or 3%, of the watershed area 

was put at higher risk of shallow landslide initiation by road drainage.

Gullies were observed at 33 locations by field crews, totaling 208 m3(272 yd3) in volume, and all 

occurring in wet swales. It was estimated that these gullies delivered 217 Mg of sediment to the stream 

channel, equivalent to half the rate of that from road surfaces over 20 years (11 Mg/yr). It would take 

about ten years for the fine sediment delivery from road surfaces to equal the total mass of delivered 

sediment from gullies. Of 3713 applicable drain points, 587 (16%) had an elevated risk of gullying. The 

critical gully initiation index (ESI) was found to be 14. The average ESI for the points without gullies was 

9, while it was 11 for the points with gullies. The gully occurrence rate for drain points that fell above 

the ESI threshold was 1.0% versus 0.5% for points that fell below the ESI threshold.

There were 116 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 1.9. There were 25 crossings with an 

elevated SBI of 3. Two crossings had an SBI of 4, which is the highest possible value. The total calculated 

volume of fill at risk in an overtopping type event was 6840 m3(8950 yd3). There were 55 stream 

crossings with the potential to divert stream flow from a plugged culvert down the road and onto 

unchanneled hillslopes. There were 14 stream crossings with an SBI of 3 or 4 and diversion potential,

four of which were observed to have already failed or be at risk for imminent failure. There was a total 

of 824 m3(1077 yd3) of fill at risk at these points. Six overtopped crossings were observed, five due to 

sediment plugging and one due to wood plugging. Three of those were due to undersized pipes, and one 

delivered 26 m3(910 ft3) to streams.

Table 37. Summary of GRAIP-predicted road risk predictions, Center Horse and Morrell/Trail 

project area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4% of road length, 16 km; 6% of drain points connected

Fine Sediment Delivery 5% of sediment produced, 21.4 Mg/yr

Sediment in Streams 0.21 Mg/km2/yr; 2% of average sediment yield for nearby areas

Landslide Risk Estimated 176 Mg of sediment delivered to streams, 3% of 

watershed area with elevated risk due to roads

Gully Risk Estimated 11 Mg/yr of sediment delivered to streams, 16% of 

all drain points exceed ESIcrit threshold

Stream Crossing Risks

 - plug potential 27 sites (23%) with elevated risk (SBI > 2)

 - fill at risk 6843 m3fill at risk, average 60 m3per crossing

 -diversion potential 61 sites (42%) with diversion potential

Drain Point Problems 811 drain points (16% of all drain points) with problems, 61 m3

of fill erosion (2% of drain points), estimated 2.9 Mg/yr of fill 

delivered to streams
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Of the 5061 recorded drain points, 811 (16%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Sumps had the highest rate of problems, with 11 

of 24 (46%), followed by ditch relief culverts (155 of 392, 40%). Fill erosion was recorded at 83 drain 

points (2%), with a total volume of 85 m3(3000 ft3). Fill erosion was most common at non-engineered 

drains with 28 instances and 23 m3(820 ft3). Stream crossings had 44 m3(1550 ft3) eroded from 4 of 146 

crossings (2%). It was estimated that fill erosion delivered 87 Mg of sediment to the stream channel, or 

about a quarter of the rate of the of road surface sediment over 20 years (4.4 Mg/yr). It would take 

about four years for the fine sediment delivery from road surfaces to equal the total mass of delivered 

sediment from fill erosion.

Poorman Creek Summary

In the Poorman Creek area, there were 174 km (108 mi) of road and 2190 drain points surveyed. Table B

presents a summary of the findings for this project area. Hydrologic connectivity was found to be a 

relatively low 4.7% of all road length at 8 km out of 174 km (5 mi out of 106 mi). The model predicted 

11.5 Mg/yr of delivered road surface fine sediment to stream channels, which is 4.6% of the 247 Mg 

generated annually by the road surface. This sediment was delivered through 97 of 2190 (4%) drain 

points. There was 5.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 49% of all 

sediment delivery and 77% of all sediment produced within 10 m of a stream crossing.

Specific sediment due to road surface-related sediment for the whole Poorman Creek area was 0.11 

Mg/km2/yr, or 1% of the observed total average fine sediment yield for five nearby areas as determined 

by reservoir coring or suspended sediment extrapolations. Including sediment delivered to streams 

through other sources (landslides, gullies, and fill erosion at drain points), the specific sediment for the 

Table 38. Summary of GRAIP-predicted road risk predictions, Poorman Creek area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4.7% of road length, 8 km; 4% of drain points connected

Fine Sediment Delivery 4.6% of sediment produced, 11.5 Mg/yr

Sediment in Streams 0.19 Mg/km2/yr; 2% of average sediment yield for nearby areas

Landslide Risk Estimated 91 Mg of sediment delivered to streams, 2.2% of 

watershed area with possible elevated risk due to roads

Gully Risk Estimated 0.2 Mg/yr of sediment delivered to streams, too few 

gullies to determine ESIcrit

Stream Crossing Risks

 - plug potential 5 sites (17%) with elevated risk (SBI > 2)

 - fill at risk 1399 m3fill at risk, average of 48 m3per crossing

 - diversion potential 8 sites (17%) with diversion potential

Drain Point Problems 270 drain points (12% of all drain points) with problems, 11 m3of 

fill erosion (1% of drain points), estimated 0.2 Mg/yr of fill erosion 

delivered to streams
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whole project area was 0.19 Mg/km2/yr, or about 2% of the observed average fine sediment yield for 

the nearby areas. The most heavily impacted stream reaches had road sediment delivery values as high 

as 0.8 Mg/km2/yr with only road surface fine sediment, or 4.0 Mg/km2/yr including mass wasting 

sediment.

There were 5 landslides observed by field crews in the course of the inventory, with a total volume of 

252 m3(329 yd3). All were road related. It was conservatively estimated that 91 Mg of landslide derived 

sediment has been delivered to streams, which is roughly half the rate of sediment from road surfaces 

over 20 years (4.5 Mg/yr). It would take about 8 years for the fine sediment delivery from road surfaces 

to equal the total mass of delivered sediment from landslides. Calibrated stability index modeling with 

SINMAP conservatively showed that 3 km2(1 mi2), or 2%, of the watershed area was put at higher risk of 

shallow landslide initiation by road drainage.

Gullies were observed at 7 locations by field crews, totaling 157 m3(206 yd3) in volume, with none 

occurring in wet swales. It was estimated that these gullies delivered 4 Mg of sediment to the stream 

channel, which is negligible compared to the rate of road surfaces over 20 years (0.2 Mg/yr). It would 

take less than one year for the fine sediment delivery from road surfaces to equal the total mass of 

delivered sediment from gullies. There were too few gullies to determine an ESIcrit, suggesting that the 

gully initiation risks here may be very low. The average ESI across the Poorman Creek area was 8. 

There were 29 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 1.7. There were 5 crossings with an elevated 

SBI of 3. No crossings had an SBI of 4, which is the highest possible value. The total calculated volume of 

fill at risk in an overtopping type event was 1399 m3(1830 yd3). There were eight stream crossings with 

the potential to divert stream flow down the road and onto unchanneled hillslopes. There was one 

stream crossing with an SBI of 3 and diversion potential. There was a total of 21 m3(27 yd3) of fill at risk 

at this point. Two natural ford type crossings were observed to divert flow down the road, though no 

major erosion was observed at the time of the survey.

Of the 2190 recorded drain points, 270 (12%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Ditch relief culverts had the highest rate of 

problems, with 18 of 56 (32%), followed by broad based dips (120 of 412, 29%). Fill erosion was 

recorded at 22 drain points (1%), with a total volume of 11 m3(400 ft3). Fill erosion was most common at 

non-engineered drains with 16 instances and 8 m3(300 ft3). It was estimated that fill erosion delivered 3 

Mg of sediment to the stream channel, which is negligible compared the amount of road surface 

sediment over 20 years (0.2 Mg/yr).

Cold Creek Summary

In the Cold Creek area, there were 198 km (123 mi) of road and 3584 drain points surveyed. Table 39

presents a summary of the findings for this project area. Hydrologic connectivity was found to be a 

relatively low 4% of all road length at 9 km out of 198 km (6 mi out of 123 mi). The model predicted 9.8 

Mg/yr of delivered road surface fine sediment to stream channels, which is 6% of the 162 Mg generated 

annually by the road surface. This sediment was delivered through 205 of 3584 (6%) drain points. There 

was 6.6 Mg/yr of delivery that occurred within 10 m of a stream crossing. This is 67% of all sediment 

delivery and 75% of all sediment produced within 10 m of a stream crossing.
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99

Specific sediment due to road surface-related sediment for the whole Cold Creek area was 0.1

Mg/km2/yr, or 1% of the observed total average fine sediment yield for five nearby areas as determined 

by reservoir coring or suspended sediment extrapolations. No other sources were observed to deliver 

sediment to streams. The most heavily impacted stream reaches had road sediment delivery values as 

high as 1.1 Mg/km2/yr.

There were 9 landslides observed by field crews in the course of the inventory, with a total volume of 

175 m

3

(229 yd3). Only one landslide was not road related. No landslide sediment was observed to have

been delivered to streams. Calibrated stability index modeling with SINMAP conservatively showed that 

0.6 km2(0.2 mi2), or 0.6%, of the watershed area was put at higher risk of shallow landslide initiation by 

road drainage.

Table 39. Summary of GRAIP-predicted road risk predictions, Cold Creek area.

Impact/Risk Type GRAIP Predicted Risks

Road-Stream 

Hydrologic Connectivity

4% of road length, 9 km; 6% of drain points connected

Fine Sediment Delivery 4% of sediment produced, 9.8 Mg/yr

Sediment in Streams 0.10 Mg/km2/yr; 1% of average sediment yield for nearby areas

Landslide Risk No landslide sediment delivered to streams; 0.6% of watershed 

area with possible elevated risk due to roads

Gully Risk No gully sediment delivered to streams, too few gullies to 

determine ESIcrit

Stream Crossing Risks

 - plug potential 28 sites (39%) with elevated risk (SBI ≥ 2)

 - fill at risk 2095 m3fill at risk, average of 31 m3per crossing

 - diversion potential 39 (34%) sites with diversion potential

Drain Point Problems 284 drain points (8% of all drain points) with problems, 3 m3of fill 

erosion (1% of drain points), estimated 0.005 Mg/yr of fill erosion 

delivered to streams

Gullies were observed at 3 locations by field crews, totaling 5 m

3

(7 yd3) in volume, with none occurring 

in wet swales. No gullies were observed to deliver sediment to the stream channel in Cold Creek. There 

were too few gullies to determine an ESIcrit, suggesting that the gully initiation risks here may be very 

low. The average ESI across the Cold Creek area was 4.

There were 71 stream crossings with culverts (as opposed to bridges or fords) recorded. The average 

blocking index (SBI) for these points was a moderate to low 2.3. There were 26 crossings with an 

elevated SBI of 3. Two crossings had an SBI of 4, which is the highest possible value. The total calculated 

volume of fill at risk in an overtopping type event was 2090 m

3

(2730 yd3). There were 39 stream 

crossings with the potential to divert stream flow from a plugged culvert down the road and onto 

unchanneled hillslopes. There were 14 crossings with an SBI of 3 or 4 and diversion potential. There was 

a total of 332 m3(434 yd3) of fill at risk at these points. Of those 14 crossings, half received the stream 

flow from the ditch, though this appeared to be intentional.
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100

Of the 3584 recorded drain points, 284 (8%) had one or more problem of some type (e.g. blocked or 

crushed culvert, excess puddling on the road surface). Stream crossings had the highest rate of 

problems, with 45 of 115 (39%), followed by ditch relief culverts (80 of 266, 30%). Fill erosion was 

recorded at 23 drain points (1%), with a total volume of 3 m

3

(110 ft3). Fill erosion was most common at 

broad based dips with 18 instances and 3 m

3

(90 ft3). It was estimated that fill erosion delivered 0.5 Mg 

of sediment to the stream channel, which is negligible compared the amount of road surface sediment 

over 20 years (0.005 Mg/yr).

Jammer Roads Summary

Two complete jammer road complexes totaling 19 km (11 mi) of road and 325 drain points in the Center 

Horse project area were inventoried using the GRAIP method. These vegetated and shallow-slope roads 

delivered 0.02 Mg/yr, which is 2% of the 1 Mg/yr generated on the road surfaces (Table 40). If this 

delivery rate is applied to all jammer roads, then it can be expected that these roads deliver less than 1 

Mg/yr from the road surface. A a small stream diversion was observed that resulted in two delivering 

gullies (29 Mg) and two non-engineered points with fill erosion, one of which delivered to the stream 

(23 Mg). There were no other observed instances of mass wasting, including anything not related to the 

stream crossing or any landslides.

Table 40. Summary of observed and predicted jammer road risks.

Impact/Risk Type Predicted Risks

Complete Complex Inventory

Fine Sediment Delivery 2% of sediment produced; 0.02 Mg/yr

Estimated Sediment 

Delivery for All Jammer 

Roads

0.4 Mg/yr, using a delivery rate of 0.001 Mg/yr/km

Gullies and Fill Erosion 

Risks

29 Mg delivered to streams from gullies, 23 Mg delivered to 

streams from fill erosion, estimated 3 Mg/yr

Stream Crossing Survey

Fill Erosion Risks, 

Observed

44% of stream crossings with fill erosion, estimated 17 Mg/yr 

delivered to streams

Fill Erosion Risks, Future 

Estimated

25% of estimated risk has been realized, up to 75% (600 m3) 

may remain

Other Problems 9 crossings (13%) with observed stream diversions or other 

problems

We conducted a census of all of the stream crossings on jammer roads in the Center Horse and 

Morrell/Trail project area, for a total of 71 crossings. Streams were defined as continuous features with 

a bed, banks, and evidence of flow for some part of most years. There were 61 natural ford-type 

crossings (no infrastructure) and ten crossings with culverts. Nine crossings (13%) were observed to 

have evidence of stream diversion or other problems. There were 31 crossings (44%) with fill erosion, 
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101

totaling 207 m

3

(7300 ft3), all of which was assumed to deliver (331 Mg). This was roughly equivalent to 

that from road surfaces on non-jammer roads in the Center Horse and Morrell/Trail project area over 20 

years (17 Mg/yr).

The average volume of fill available to erode at each crossing was estimated to be 12 m3(16 yd3) per 

crossing. Of this amount, an average of 3 m3(4 yd3) per crossing has already been eroded, suggesting

that 25% of possible erosion has already occurred, and up to 75% remains (about 600 m3or 22,000 ft3).

Differences in the shape and construction of each stream crossing, and the timing of high flows and 

transport capacity of the streams, suggest that each stream crossing will respond at a different rate, and 

may include some deposition. It was found that on hillslopes of greater than about 40%, every stream 

crossing in the Center Horse area had fill erosion, suggesting that the stream crossings on steeper slopes 

may be at higher risk of failure than those on lower slopes.

Conclusions

Under the observed conditions, the GRAIP inventories in the Southwest Crown of the Continent suggest 

low risk across the measured metrics when considered at the watershed scale. The Center Horse and 

Morrell/Trail project area had the most risk overall. There are two other non-watershed GRAIP sites in 

the northern Rockies; one site in the Clearwater National Forest (Cissel et al. 2011A), and one in the 

Gallatin National Forest (Cissel et al. 2011B). Compared to these sites, these three watersheds fall within 

the typical range for landslide risk, gully risk, stream crossing plugging potential and diversion potential, 

and drain point problems and fill erosion for both sites. The stream crossing fill at risk is slightly higher in 

the Center Horse and Morrell/Trail project area and Poorman Creek, but within the typical range in Cold 

Creek. The Clearwater site had much higher road surface sediment delivery and hydrologic connectivity, 

while this data is in range of the Gallatin site. Compared to a site in the Olympic National Forest in 

western Washington (Cissel et al. 2011C), which is considered to have high risk in all metrics, the Center 

Horse and Morrell/Trail project area has low to moderately low risk in all areas.

Although sediment delivery risk related to roads is low from the watershed perspective, several road 

segments were identified that may need treatment to minimize sediment delivery effects that are 

significant at the stream reach scale. Depending on downstream habitat and species presence, fine 

sediment delivery effects may be significant at a stream reach scale. Ongoing work comparing aquatic 

habitat conditions between managed and unmanaged reaches using PIBO data will help refine these 

questions.

Road maintenance level appears to have a small to moderate effect on the various risk metrics. Higher 

maintenance levels (ML 3 and 4; more traffic, more frequent and more intense maintenance) had 

somewhat more sediment delivered from their road surfaces, but mass wasting risks were lower. Lower 

maintenance level roads (ML 1 and 2; little to no traffic, little to no maintenance) had higher mass 

wasting risks. These relationships suggest that traffic has an important effect on road surface fine 

sediment production, but regular more intense maintenance can prevent mass wasting problems. On 

some lower maintenance level roads, it may be beneficial to treat spots that are at high risk of erosion.

The sediment delivery from fill erosion and mass wasting at jammer road-stream intersections in the 

Center Horse and Morrell/Trail project area was on the same scale as the road surface fine sediment 

delivery from non-jammer roads in the same area. The highly vegetated and low slope jammer road 

surfaces themselves did not appear to have significant impacts. Treatments to jammer roads should be 
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102

focused on the roads with stream crossings. However, the consequences of removing vegetation on the 

road surface to access the jammer road stream crossings may increase the contributions of their surface 

fine sediment to streams. Data to be collected in the summer of 2014 may help to further understand 

the causes and distribution of erosion at stream crossings on jammer roads.
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References

Best, D. W., Kelsey, H. M., Hagans, D.K. and Alpert, M. 1995. Role of fluvial hillslope erosion and road 

construction in the sediment budget of Garret Creek, Humboldt County, California. In Geomorphic 

Process and Aquatic Habitat in the Redwood Creek Basin, Northwestern California. Nolan, K. M., 

Kelsey, H. M., and Marron, D. C. editors. USGS professional paper #1454. pp: m1-m9.

Black, T. A., Cissel, R. and Luce, C. H. 2012. The Geomorphic Road Analysis and Inventory Package 

(GRAIP) Volume 1: Data Collection Method. Gen. Tech. Rep. RMRS-GTR-280WWW. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

Black, T. A. and Luce, C. H. 2013. Measuring Water and Sediment Discharge from a Road Plot with a

Settling Basin and Tipping Bucket. Gen. Tech. Rep. RMRS-GTR-287. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Cissel, R. M., Black, T. B., and Luce, C. H. 2011A. Legacy Roads and Trail Monitoring Project, Road 

Decommissioning in the Lolo Creek Watershed, Clearwater National Forest. USDA Forest Service 

Rocky Mountain Research Station, Boise Aquatic Science Lab.

Cissel, R. M., Black, T. B., and Luce, C. H. 2011B. Legacy Roads and Trail Monitoring Project, Road 

Decommissioning in the Mill Creek Watershed, Gallatin National Forest. USDA Forest Service 

Rocky Mountain Research Station, Boise Aquatic Science Lab.

Cissel, R., Black, T., Luce, C., and Staab, B. 2011C. Legacy Roads and Trails Monitoring Project, Storm 

Damage Risk Reduction in the Skokomish River Watershed, Olympic National Forest. USDA Forest 

Service Rocky Mountain Research Station, Boise Aquatic Science Lab.

Cissel, R. M., Black, T. A., Schreuders, K. A. T., Prasad, A., Luce, C. H., Nelson, N.A., Tarboton, D.G., and 

Nelson, N. A. 2012A. The Geomorphic Road Analysis and Inventory Package (GRAIP) Volume 2: 

Office Procedures. Gen. Tech. Rep. RMRS-GTR-281WWW. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station.

Flanagan, S. A., Furniss, M. J., Theisen, S., Love, M., Moore, K., and Ory, J. 1998. Methods for Inventory 

and Environmental Risk Assessment of Road Drainage Crossings. USDA Forest Service Technology 

and Development Program 9877-1809-SDTDC 45pp

Fly, C.M., Grover-Weir, K., Thornton, J., Black, T.A., and Luce, C.M. 2010. Bear Valley Road Inventory 

(GRAIP) Report; Bear Valley Category 4b Assessment, Boise National Forest. USDA Forest Service, 

Boise National Forest.

Furniss, M. J., Love, M., and Flanagan, S. A. 1997. Diversion Potential at Road Stream Crossings. USDA 

Forest Service Technology and Development Program 9777-1814-SDTDC 12pp.

Hofmann, M. H., Hendrix, M. S., Moore, J. N., and Sperazza, M. 2006. Late Pleistocene History of 

Sediments in Flathead Lake, MT: Evidence from High-resolution Seismic Reflection Interpretation. 

Sedimentary Geology. Vol. 184, pp:111-131.
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Istanbulluoglu, E., Tarboton, D.G., Pack, R.T., and Luce, C.H. 2003. A sediment transport model for 

incision of gullies on steep topography. Water Resources Research. Vol. 39, No. 4, pp: 1103-1117. 

Jones, J. A., and Grant, G. E. 1996. Peak flow responses to clear-cutting and roads in small and large 

basins, western Cascades, Oregon, Water Resour. Res. Vol. 32, pp: 959-974.

Kirchner, J. W., Finkel, R. C., Riebe, C. S., Granger, D. E., Clayton, J. L., King, J. G., and Megahan, W. F. 

2001. Mountain Erosion Over 10 yr, 10 ky, and 10 my Time Scales. Geology. Vol. 29, No. 7, pp:591-

594.

Lambing, J. H., and Sando, S. K. 2008. Estimated Loads of Suspended Sediment and Selected Trace 

Elements Transported through Milltown Reservoir in the Upper Clark Fork Basin, Montana, Water 

Years 2004-07. U.S. Geological Survey Scientific Investigations Report 2008-5080.

Lolo National Forest Soil and Water Program. 2009. Unpublished stream gage data from the North Fork 

Blackfoot River located at 47.103N, -112.961W. Missoula, MT.

Luce, C.H., and Black, T. 1999. Sediment production from forest roads in western Oregon. Water 

Resources Research. Vol. 35, No. 8, pp: 2561-2570.

Ludington, S., Moring, B. C., Miller, R.J., Flynn, K.S., and Hopkins, M. J. 2005. Western States Geology 

shapefiles. Accessed online in 2009 from http://pubs.usgs.gov/of/2005/1305.

Madej, M. A. 2001. Erosion and Sediment Delivery Following Removal of Forest Roads, Earth Surface 

Landforms and Processes, Vol. 26, No. 2, pp: 175-190.

Megahan, W.F. 1976. Tables for geometry for low-standard roads for watershed management 

considerations, slope staking, and end areas. Gen. Tech. Rep. INT-32. U.S. Department of 

Agriculture, Forest Service, Intermountain Forest and Range Experiment Station.

Moll, J. 1997. Glossary of Water/Road Interaction Terminology for Water/Road Interaction Technology 

Series. USDA Forest Service Technology and Development Program 9777-1806-SDTDC 14pp.

Montana Department of Environmental Quality. 2008. Middle Blackfoot-Nevada Creek Total Maximum 

Daily Loads and Water Quality Improvement Plan. Accessed online April 18th, 2013 from 

http://www.deq.mt.gov/wqinfo/tmdl/finalreports.mcpx.

Montana Department of Environmental Quality. 2011. Montana Average Annual Precipitation 1981 –

2010 shapefiles. Accessed online April 4, 2013 from http://nris.mt.gov/nsdi/nris/mdb/mt_1981-

2010_AveAnnPrecip.zip.

Pack, R. T., Tarboton, D.G., Goodwin, C.N. and Prasad, A.. 2005. SINMAP 2. A Stability Index Approach to 

Terrain Stability Hazard Mapping, technical description and user’s guide for version 2.0, Utah State 

University.

Prasad, A. 2007. A tool to analyze environmental impacts of road on forest watersheds. MS Thesis. Utah 

State University, USA.
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Sugden, B. D. and S. W.Woods 2007. Sediment production from forest roads in Western Montana. 

Journal of the American Water Resources Association. Vol. 43, No. 1, pp: 193-206.

U.S. Department of Agriculture. 1978. Sediment Deposition in U.S. Reservoirs: Summary of Data 

Reported Through 1975. Miscellaneous Publication Number 1362. Compiled by F. E. Dendy and W. 

A. Champion. Agricultural Research Service, USDA Sedimentation Laboratory, Oxford, MS.

U.S. Geological Survey. 2012. National Water Information System data available on the World Wide Web 

(USGS Water Data for the Nation) for USGS Station 12340000 Blackfoot at Bonner. Accessed April, 

2013, at URL http://waterdata.usgs.gov/nwis/.

Wemple, B. C., Jones, J. A., and Grant, G. E. 1996. Channel network extension by logging roads in two 

basins, western Cascades, Oregon, Water Resources Bulletin. Vol. 32, pp: 1195-1207. 
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Appendix A: Road Risks by Maintenance Level Table Road risk table for all three project areas, broken out by road maintenance level. There were not enough gullies or landslides in Poorman Creek or Cold Creek to perform this analysis, so they are omitted. See section 4.8 for more information.
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Appendix B: Glossary of Selected Terms

Below is a list of terms, mostly of drainage point types, but also of some other commonly used terms, 

for the purpose of clarification. Adapted from Black, et al. (2012), Fly, et al (2010), and Moll (1997).

Broad based dip. Constructed: Grade reversal designed into the road for the purpose of draining water 

from the road surface or ditch (also called dip, sag, rolling grade, rolling dip, roll and go, drainage dip, 

grade dip). Natural: A broad based dip point is collected at the low point where two hillslopes meet, 

generally in a natural swale or valley. This is a natural low point in the road that would cause water on 

the surface of the road to drain out of the road prism. 

Cross drain. This is not a feature collected specifically in GRAIP, and it can refer to a number of other 

drainage features. It is characterized by any structure that is designed to capture and remove water 

from the road surface or ditch. Ditch relief culverts, waterbars, and broad based dips can all be called 

cross drains.

Diffuse drain. This is a point that is characterized by a road segment that does not exhibit concentrated 

flow off the road. Outsloped roads or crowned roads often drain half or all of the surface water diffusely 

off the fillslope. Although collected as a drain point, this feature is representative of an area or a road 

segment rather than a concentrated point where water is discharged from the road prism. A drop of 

water that lands on a diffuse road segment will not flow down the road or into the ditch, but more or 

less perpendicular to the centerline off the road surface and out of the road prism. Also called sheet 

drainage or inter-rill flow.

Ditch relief culvert. This drain point is characterized by a conduit under the road surface, generally 

made of metal, cement, or wood, for the purpose of removing ditch water from the road prism. This 

feature drains water from the ditch or inboard side of the road, and not from a continuous stream 

channel.

Flow path. This is the course flowing water takes, or would take if present, within the road prism. It is 

where water is being concentrated and flowing along the road from the place where it enters the road 

prism, to where it leaves the road prism. This can be either on the road surface, or in the ditch.

Lead off ditch. This drain point is characterized by a ditch that moves flow from the roadside ditch and 

leads it onto the hillslope. Occurs most often on sharp curves where the cutslope switches from one side 

of the road to the other. Also known as a daylight ditch, mitre drain, or a ditch out (though this term can 

also describe other types of drainage features).

Mg, megagrams. This unit is equivalent to 1 metric tonne, 1000 kg, and 1,000,000 g. Equivalent to 2204 

lbs, and 10% larger than 1 U.S. short ton (2000 lbs).

Non-engineered drainage. This drain point describes any drainage feature where water leaves the road 

surface in an unplanned manner. This can occur where a ditch is dammed by debris, and the water from 

the ditch flows across the road, where a gully crosses the road, where a wheel rut flow path is diverted 

off the road due to a slight change in road grade, or where a berm is broken and water flows through. 

This is different from a diffuse drain point, which describes a long section of road that sheds water 

without the water concentrating, whereas this point describes a single point where a concentrated flow 

path leaves the road.

Orphan drain point. This is any drain point that does not drain any water from the road at the time of 

data collection. Examples include a buried ditch relief culvert, or a water bar that has been installed on a 

road that drains diffusely.

Stream crossing. This drain point is characterized by a stream channel that intersects the road. This 

feature may drain water from the ditch or road surface, but its primary purpose is to route stream water 

under or over the road via a culvert, bridge, or ford. A stream for the purposes of GRAIP has an armored 
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108

channel at least one foot wide with defined bed and banks that is continuous above and below the road 

and shows evidence of flow for at least some part of most years.

Sump. Intentional: A closed depression where water is intentionally sent to infiltrate. Unintentional:

Any place where road water enters and infiltrates, such as a cattle guard with no outlet, or a low point 

on a flat road.

Waterbar. This drain point is characterized by any linear feature that is perpendicular to the road that 

drains water from the road surface and/or ditch out of the road prism or into the ditch. Waterbars may 

be constructed by dipping the grader blade for a short segment, or adding a partly buried log or rubber 

belt across the road. Some road closure features may also act as a waterbar, such as a tank trap (also 

known as a closure berm or Kelly hump). Cattle guards that have an outlet that allows water to flow out 

are also considered to be water bars. These features may also be known as scratch ditches if they drain 

water into the ditch.
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109

Appendix C: GRAIP Data Management Plan

Project Title: A new model of watershed-scale aquatic monitoring from the Crown of the 

Continent: Quantifying the benefits of watershed restoration in the face of climate change

Data Input-New Collection

1 General 

Description Road Inventory data and output from the 

Geomorphic Road Analysis and Inventory Package 

(GRAIP)

Budget

Format Grids, and shapefiles

Data Processing & Scientific 

Workflow

See The Geomorphic Road Analysis and Inventory 

Package (GRAIP) Volume 1 Data Collection Method 

and Volume 2: Office Procedures. Rocky Mountain 

Research Station General Technical Report RMRSGTR-280WWW 

http://www.treesearch.fs.fed.us/pubs/40654 and 

281WWW

http://www.treesearch.fs.fed.us/pubs/40655

Protocols See The Geomorphic Road Analysis and Inventory 

Package (GRAIP) Volume 1 Data Collection Method 

and Volume 2: Office Procedures. Rocky Mountain 

Research Station General Technical Report RMRSGTR-280WWW and 281WWW

Backup and Storage The original input data were copied to a local PC at 

RMRS Boise and backed up on second hard-drive 

and a local server. 

QA/QC See field and office manuals above

Metadata With each output file

Volume Estimate 2 GB

Archive Orgs Final data to be archived on DVD at RMRS Boise 

and sent to GNLCC web portal for archiving.

Access and Sharing Data will be shared with partners and cooperators 

as it is collected, analyzed, and published.

Exclusive Use We request a maximum of a two year extension 

following the conclusion of the funding period to 

write manuscripts and publish our results. During 

this time data will be shared with cooperators and 

upon request with non-project related researchers 

and data and project managers. After the 

extension period, no restrictions to the data 

access. 
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110

Restrictions We do not anticipate restrictive use of the data 

after publication. Proper reference to source 

required. 

Citation TBD

TBD NA

Contact Tom Black USDA Forest Service Rocky Mountain 

Research Station, Boise.

tblack@fs.fed,us

Data Inputs

1 Elevation data (DEM)

Description 30 meter DEM

Format Raster Data-Grid

Data Processing & Scientific 

Workflow

Use as acquired, resampled to 5 meter using 

bilinear resampling

Source National Elevation Dataset (NED)

Protocols See The Geomorphic Road Analysis and Inventory 

Package (GRAIP) Volume 2: Office Procedures. 

Rocky Mountain Research Station General 

Technical Report RMRS-GTR-281WWW

Backup and Storage The original input data were copied to a local PC at 

RMRS Boise and backed up on second hard-drive 

and a local server. 

Volume Estimate 50 MB

Access and Sharing Free 

Restrictions Unrestricted use

2 GRAIP Road Inventory Field Data

Description A GPS referenced field inventory documenting the 

hydrology and geomorphology of the road 

network

Format ArcGIS 9.3 shapefiles

Data Processing & Scientific 

Workflow

These files have been exported from the GPS 

device, differentially corrected in Pathfinder 

Office, edited to minimize GPS errors in road 

alignment and combined and exported as 

shapefiles. See The Geomorphic Road Analysis 

and Inventory Package (GRAIP) Volume 1 Data 

Collection Method and Volume 2: Office 

Procedures. Rocky Mountain Research Station 

General Technical Report RMRS-GTR-280WWW 
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111

and 281WWW

Protocols Data is collected following the protocol in the field 

manual by persons receiving a two week intensive 

training course teaching the material in the Field 

manual, (see above).

Backup and Storage The original input data were exported from field 

devices to a field laptop. Files are then copied to a 

PC at RMRS Boise and backed up on second harddrive and a local server. 

QA/QC Field and Office QA/QC documented in the 

manuals, see above

Metadata With each file and directory

Volume Estimate 5-20 MB

Data Outputs

1 GRAIP Model Output Shapefiles

Description Road line, Drain point and stream shapefiles that 

contain observed and modeled sediment 

production, delivery and other geomorphic and 

hydrologic attribute data.

Format ArcGIS 9.3 shapefiles

Data Processing & Scientific 

Workflow

See office manuals

Protocols See office manuals

Backup and Storage Files are produced on a PC at RMRS Boise and 

backed up on second hard-drive and a local server. 

QA/QC See office manuals

Metadata Associated with each file and directory

Volume Estimate 10-50 MB

Archive Orgs Final data to be archived on DVD at RMRS Boise 

and sent to GNLCC web portal for archiving.

Access and Sharing Data will be shared with partners and cooperators 

as it is collected, analyzed, and published.

Exclusive Use We request a maximum of a two year extension 

following the conclusion of the funding period to 

write manuscripts and publish our results. During 

this time data will be shared with cooperators and 

upon request with non-project related researchers 

and data and project managers. After the 

extension period, no restrictions to the data 

access. 

Restrictions We do not anticipate restrictive use of the data 

after publication. Proper reference to source 

required. 

Citation TBD
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112

Digital Object Identified (DOI) Link TBD

Contact Tom Black USDA Forest Service Rocky Mountain 

Research Station, Boise.

tblack@fs.fed,us

2 GRAIP Model Intermediate and Output GRIDS

Description GRAIP uses various grids created by the programs 

TauDEM to route sediment and create a channel 

network. The program SinMap makes slope 

stability predictions from the DEM. These grids 

are called on and updated by GRAIP.

Format ArcGIS 9.3 grids

Data Processing & Scientific 

Workflow

See office manuals

Protocols See office manuals

Backup and Storage Files are produced on a PC at RMRS Boise and 

backed up on second hard-drive and a local server. 

QA/QC See office manuals

Metadata Associated with each directory and in the office 

manual

Volume Estimate 20-50 MB

Archive Orgs Final data to be archived on DVD at RMRS Boise 

and sent to GNLCC web portal for archiving.

Access and Sharing Data will be shared with partners and cooperators 

as it is collected, analyzed, and published.

Exclusive Use We request a maximum of a two year extension 

following the conclusion of the funding period to 

write manuscripts and publish our results. During 

this time data will be shared with cooperators and 

upon request with non-project related researchers 

and data and project managers. After the 

extension period, no restrictions to the data 

access. 

Restrictions We do not anticipate restrictive use of the data 

after publication. Proper reference to source 

required. 

Citation TBD

Digital Object Identified (DOI) Link TBD

Contact Tom Black USDA Forest Service Rocky Mountain 

Research Station, Boise.

tblack@fs.fed,us

Software

1 GRAIP 

Description GRAIP is a free software package that runs as an 
Southwest Crown of the Continent GRAIP Watersheds Roads Assessment

Blackfoot and Swan River Watersheds; Lolo, Helena, and Flathead National Forests; Montana

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extension in ArcGIS 9.3 (at present). It performs 

the calculations of road sediment and routes the 

sediment to streams in addition to calculating a 

variety of road hydro-geomorphic risk metrics.

Restrictions This software is in the public domain.

Fees Free

Source/Link http://www.neng.usu.edu/cee/faculty/dtarb/graip/

2 TauDEM 

Description TauDEM is a tool that runs in Arc GIS to calculate 

hydrologic attributes of a landscape using a DEM 

Restrictions This software is in the public domain.

Fees Free

Source/Link http://www.neng.usu.edu/cee/faculty/dtarb/graip/

3 SINMAP 2.0 

Description GRAIP 

Restrictions This software is in the public domain.

Fees Free

Source/Link http://www.neng.usu.edu/cee/faculty/dtarb/graip/

4 ArcGIS 9.3 

Description Geographic Information System Software

Restrictions This software is available for purchase form ESRI

Fees TBD

Source/Link http://www.ESRI.com