# Monitoring Road Decommissioning in the Mann

Creek Watershed
Payette National Forest

April 27 , 2010

Nathan Nelson 1

, Tom Black 1 , and Richard Cissel 1

1 Hydrologi st

US Forest Service Rocky Mountain Research Station 322 East Front Street, Suite 401 Boise, Idaho, 837022



## Table of Contents

Executive Summary

................................ ................................ ................................ .................. 4

Acknowledgements

................................ ................................ ................................ .................. 5

1.0 Background

................................ ................................ ................................ .................... 6

2.0 Study Objectives

................................ ................................ ................................ ............ 6

3.0 Methods

................................ ................................ ................................ ........................ 7

4.0 Monitoring Locations

................................ ................................ ................................ ..... 7 Regional Monitoring Sites

................................ ................................ ................................ .............. 7
Mann Creek Sites

................................ ................................ ................................ ............................ 9

5.0 Results

................................ ................................ ................................ ......................... 11

5.1 Road

- stream Hydrologic Connectivity

................................ ................................ .............. 12

5.2 Fine Sediment Production & Delivery

................................ ................................ ............... 12

Pre

- treatment

................................ ................................ ................................ ............................ 13

Post

- treatment

................................ ................................ ................................ .......................... 14

5.3 Landslide Risk

................................ ................................ ................................ .................... 16 Existing Landslides

................................ ................................ ................................ ..................... 16 Changes in Landslide Risk

................................ ................................ ................................ .......... 17

5.4 Gully Initiation Risk

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

5.5 St ream Crossing Failure Risk

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

5.6 Drain Point Condition

................................ ................................ ................................ ........ 25

6.0 Summary & Conclusions

................................ ................................ ............................... 26

References

................................ ................................ ................................ ............................. 28

Appendix A

– Glossary

................................ ................................ ................................ ............ 30



## List of Tables

Table 1. The locations and types of road treatments monitored.

................................ ................... 8
Table 2. Decommissioning treatments applied by road number.

................................ .................. 11
Table 3. Summary of sediment production and delivery at drain points, pre

- treatment road.

.... 14
Table 4. Summary of sediment production and delivery at drain points, post

- treatment road.

.. 15
Table 5. Changes in sediment production and delivery, pre

- treatment vs. post

- treatment.

........ 16
Table 6. ESI population statistics for pre

- decommissioning and post

- decommissioning road
networks.

................................ ................................ ................................ ................................ ... 19
Table 7. Channel slope and sediment size characteristics at excavated stream crossings in Mann
Creek.

................................ ................................ ................................ ................................ ......... 24
Table 8. Drain point condition problems and fill erosion below drain points, pre

- and post

treatment.

................................ ................................ ................................ ................................ . 25
Table 9. Summary of GRAIP model r isk predictions for the Mann Creek road decommissioning project.

................................ ................................ ................................ ................................ ...... 273



## List of Figures

Figure 1. Locations of monitored sites in Region 4.

................................ ................................ ......... 8 Figure 2. Map of road locations within the Mann Creek watershed.

................................ ............ 10 Figure 3. Fine sediment production and delivery to channels by road segment and drain point,

pre

- treatment road.

................................ ................................ ................................ .................. 13 Figure 4. Photo of a typical rocky, fully recontoured road with straw mulch.

............................... 15 Figure 5. Estimated natural slope stability index classes.

................................ .............................. 17 Figure 6. Stability index for hillslopes in the vicinity of road 501641000.

................................ ..... 18 Figure 7. Distribution of Stream Blocking Index values for pre

- treatment group.

........................ 20 Figure 8. SBI values on the 2300

- 100 and 2300

- 130 road st ream crossings.

................................ . 21 Figure 9. Examples of stream bed grain

- size distributions.

................................ ............................ 23 Figure 10. Example of an excavated stream crossing.

................................ ................................ .... 244

Executive Summary

The USFS, Rocky Mountain Research Station (RMRS) and Intermountain (INT) Region, Pacific Northwest Region (PNW), Pacific Southwest Region (PSW) and the Northern Region (NR) are monitoring a sample of the road decommissioning and maintenance projects to assess their
effectiveness in reducing impacts and r isks to key watershed processes. Risk profiles are being developed and compared, before and after road treatments, with the Geomorphic Road Analysis and Inventory Package (http://www.fs.fed.us/GRAIP). This suite of robust inventory and analysis
tools eva luates the following road impacts and risks: road

- stream hydrologic connectivity, fine sediment production and delivery, shallow landslid e risk , gully initiation risk, stream crossing failure risk, and drain point condition.

In FY 2009 , pre

- treatment inven tories have been conducted at five site s in the Intermountain Region. A site consists of a group of road segments totaling four miles treated with either decommissioning or Storm Damage Risk Reduction (i.e., stormproofing ) . Inventories were also completed on four miles of control sites for each locale

. Four post

- treatment inventories were also executed. This status report focuses only on decommissioning work implemented by the Payette National Forest i n the Mann Creek wa tershed. At the Mann Creek sites, treatments included removal of culverts and fills at stream crossings and recontouring of the road prism

.

Before

- after comparisons using GRAIP indicate that decommissioning treatments resulted in a large reduction of most impact

- risk metrics. Road

- stream connectivity was reduced by 97 %

, from 3, 000

m of connected road to 77 m. Delivery of fine sediment was re duced by 97.6 %

, from

41.7 tonne s/year to 1.0 tonne /year. Values of a stream blocking index were reduced from an average of 2 before treatment to zero after treatment (n=1 3 ), indicating the risk of stream crossings becoming plugged was completely eliminate d by excavation and removal of culverts and associated fills. While former crossings sites may contribute fine sediment to streams in the short term, the restoration treatments removed over 807 m 3 of earthen material from areas with a high potential for failure and delivery to stream channels. Diversion potential was eliminated at all

stream crossing sites.

The slope stability risk below drain point locations on the original road was reduced to n early
natural conditions as water was redistributed across the hillslope by diffuse drainage

.

R eductions in gully risk

, as determined by a gully initiation index (ESI) , were relatively low prior to treatment, and were reduced to negligible values by conversion to diffuse drainage. Current calculations are based on conservative assumptions, so the actual performance of the treatments may exceed these initial expectation s. Such assumptions will be assessed duri ng future post

storm monitoring.

Before treatment, inventoried road segments had problems at 35 % of 102 inventoried drainage

po ints. Post

- treatment monitoring indicate s that these problems were entirely eliminated by the decommissioning treatments and that most replacement drainage features are less
vulnerable to failure.5

Taken collectively, preliminary results indicate the decommissioning treatments should be
effective in significantly reducing most hydrogeomorphic impacts and risks to aquatic
ecosystems.

Summary of GRAIP road risk predictions for the Mann Creek watershed decommissioning project. IMPACT/RISK TYPE EFFECT OF TREATMENT:

INITIAL GRAIP PREDIC TION EFFECT OF TREATMENT:

POST

- STORM

VALIDATION

Road

- Stream Hydrologic Connectivity - 97%,

- 2,923 m of connected road To be determined.

Fine Sediment Delivery

- 98 %,

- 40.7 tonne s/year To be determined.

Landslide Risk Restored to near natural condition To be determined.

Gully Risk Reduced from low to negligible To be determined.

Stream Crossing Risk

- plug potential

- 100% (eliminated at 13 sites) To be determined.

- fill at risk

- 100% (807 m 3 removed) To be determined.

- diversion potential

- 100% (eliminated at 8 sites) To be determined.

Drain Point Problems

- 100% (0% vs. 35% of drain points) To be determined.

Acknowledgements

We would like to thank the field crews (Laura Hutchinson, Jim Peterson, Matt Steiger, and Jim Bitzenberg) for collecting the data. We would also like to thank Dave Kennell and Tom Crawford of the Payette National Forest for help in selecting these sites and logistical support during a very busy field season. Thanks also to Rick H o p son and the Region 4 staff for supporting this monitoring effort.6



### 1.0 Background

The National Forest Transportation System is vast and represents an enormous investment of human and financial capital. This road and trail network provides numerous bene fits to forest managers and the public

, but can have adverse effects on water quality, aquatic ecosystems, and other resources. There is currently a large backlog of unfunded maintenance, improvement, and decommissioning work on national forest roads

, and many critical components of the network (e.g., culverts) are nearing or have exceeded their life

- expectancy. This significantly elevates risks to aquatic resources. Many I ntermountain R egion forests have been actively addressing known road issues in critical resource areas. Various road treatment techniques and restoration activities are being applied throughout the region to address the resource risks posed by forest roads.

The USFS , Rocky M ountain Research Station (RMRS), Intermountain ( INT ) Region , Pacific Northwest Region, Pacific Southwest Region and the Northern Region are implementi ng a roads m onitoring p roject to evaluate the effectiveness and to learn from the successes of
road restoration treatments being implemented on national forests thro ughout the regions. As of February 2009, post

- storm event data has been collected at one site, post

- treatment data has been collected on 16 sites with partial datasets collected at 17 additional sites.

This report briefly describes the overall objecti ves of the r egional

- scale study and the methods being used. Specific r esults presented herein , however, are focused only on road decommissioning work completed by the Payette National Forest ( P NF) in the Mann Creek
watershed in FY200 9 . As other data become available, similar reports will be developed for
additional sites. In addition, syntheses of results at multiple sites will be produced throughout and at the end of this monitoring project.



### 2.0 Study Objectives

The monitoring project is designed to assess the effectiveness of decommissioning and maintenance projects in reducing road impacts and risks to several key watershed processes. Specifically, the project is intended to address the following questions.

How effective are USFS road restoration projects in :

1) reducing or eliminating:

a. the risk of increased peak flows resulting from road

- stream connectivity ?

b. fine sediment production and delivery to stream channels ?

c. shallow landslide risk ?

d. gully initiation risk?

e. the risk and consequences of stream crossing failures?

2) improving the performance of the road drainage system ?7



### 3.0 Methods

The Geomorphic Road Analysis and Inventory Package ( GRAIP

, Prasad et al. 2007

, http://www.fs.fed.us/GRAIP ) is being used to inventory and model the risk profile of each of the road segments included in the study. The GRAIP system consists of a detailed, field

- based road inventory protocol combined with a suite of geographic informat ion system ( GIS ) models. The inventory is used to systematically describe the hydrology and condition of a road system using Geographic Positioning S ystem ( GPS ) technology and automated data forms (Black et al , 200 9,
Cissel et al 2009 )

. The GIS models use these data to analyze road

- stream hydrologic connectivity, fine sediment production and delivery, shallow landslide potential with and without road drainage, gully initiation risk, and the potential for and consequences of stream crossin g failures. Detailed information about the performance and condition of the road drainage infrastructure is also supplied.

Risk profiles are being developed and compared at untreated control segments and treated
segments before and after road projects

. At a given site, m onitored road segments typically comprise 4 miles of both treated and control sites. Control sites were selected based on the ir
similar ity to treated sites with respect to road construction methods , maintenance levels, geology,
and hydrologic regimes

. Each site also includes a final v alidation evaluation at both treatment and
control sites following a substantial storm event ( 5

- 10 year re currance interval) . This will allow testing of the initial GRAIP risk predictions and provide an unbiased comparison between the
treated and the untreated roads.



### 4 .0 Monitoring Locations

Regional Monitoring Sites

In FY2009, pre

- treatment evaluations were completed at five sites 1 on four national forests in the Intermountain Region. Decommissioning was implemented at four of these sites and one other site was treated with Storm Damage Risk Reduction 2 ” (Figure 1, Table 1). Four post

- treatment inventories were also completed in FY 2009. The final post

- treatment inventory will be completed in 2010. The post

- storm evaluations will be completed at the remaining sites as conditions allow in the coming years. In addition, evaluations will be initiated at five new sites, the locations o f which have not yet been determined

.

1 Each site will include the following evaluations: pre

- treatment, post

- treatment, and post

- storm validation on treated road segments; and pre

- treatment and post

- storm validation on control segments.

2 “ Storm Damage Risk R eduction (SDRR) is used to refer to relatively low

- cost treatments applied across extensive portions of the road network with the objective of protecting aquatic resources and infrastructure. These treatments are intended to reduce the chronic effects of roads (e.g., fine sediment delivery) and significantly reduce the likelihood and consequences of catastrophic failures (e.g., diversion of stream flow onto roads) associated with large storm events. A variety of tools may be used to achieve these objectiv es, depending on site

- specific conditions. These include diversion potential dips at road

stream crossings, water bars, and broad

- based drain dips. These simple, extensive treatments are intended to compliment the use of more intensive treatments (e.g., decommissioning, road realignments) that are typically implemented on relatively small segments of the network.8

Figure 1

. Locations of monitored sites in Region 4.

Table 1

. The locations and types of road treatments monitored

. National Forest Treatment Watershed

Payette Decommissioning Mann Creek

Payette Decommissioning Calf Creek

Boise Decommissioning Squaw Creek

Caribou

- Targee Other Treatments Island Park

Storm Damage Risk Reduction Island Park9

Mann Creek Sites

During the summer and fall of 200 9

, field crews inventoried decommissioning sites in the Intermountain Region, including the Mann Creek watershed (Table 1, Figure 1). This watershed is p rincipally underlain by basalt s, with Columbia River Group basalts dominating the mid

elevation band. The higher elevations are underlain by sedimentary rocks of the Olds Ferry and Izee terranes as well as mafic plutons of the Blue Mountains island arc terrane

. The average
annual precipitation for the basin ranges from 10

- 30 inches per year. The waters hed is managed for multiple uses including timber harvest, grazing, and recreation. The inventoried
sites are located between 4,800 and 6,000 feet above sea level just east of the Snake River

. The Mann Creek watershed is located in Washington county between U.S. Highway 95 and the Snake River. Mann Creek Reservoir, located near the mouth of the watershed, is about halfway between Weiser and Cambridge.

Data were collected on roads in the s pring of 2009 before the decomissioning treatments began, and once again in s ummer of 2009 once the treatments were completed (Figure 2)

. Pre

treatment roads were native or gravel surface roads that were generally in good shape. With the exception of road 501641000 , the roads were classed as maintenance level 2 or 3. The
maintenance class of road 501641000 is unknown , as the forest did not classify it , though it

appears to be similar to maintenance level 2 based on photographs and comparisons to descriptions of roa d maintenance classes. Flow on the roads was generally contained in wheel
tracks or a ditch. Both treatment and control sites included roads on a range of hillslope positions , though dominantly valley

- bottom, and included frequent live stream crossings. The
watershed has moderately steep topogr aphy, so stream crossing fills are not typically large.

Decommissioning treatments were performed by USFS equipment and staff, and involved removing stream crossing culverts and fills and partially to full y recontouring the road prism

.10

Figure 2

. Map of road locations within the Mann Creek watershed

.11

Table 2

. Decommissioning treatments applied by road number.

Decommissioned Road Control Road

Road # Maintenance

Level Treatment Road # Maintenance
Level Treatment

50007 2 Stream crossing extraction, recontouring, and culvert
removal 50029

50473? 2 None

50029 2 Stream crossing extraction, recontouring, and culvert
removal 50029

50473? 2 None

50470 1 Stream crossing extraction, recontouring, and culvert
removal 50029

50473? 2 None

50019
Old 51189 3 Stream crossing extraction, recontouring, and culvert
removal 50019

Old 51189 3 None

50164100

0 Unclassified Stream crossing extraction, recontouring, and culvert
removal 500100500 Unclassified None



### 5.0 Results

GRAIP inventory and modeling tools were used to characterize the following types of impacts
and risks , all of which were expected to be reduced by the decommissioning treatments:

 Road

- stream hydrologic c onnectivity

 Fine s ediment d elivery

 Landslide r isk

 Gully i nitiation r isk

 Stream crossing f ailur e risk

 Drain point p roblems12

5 .1 Road

- stream Hydrologic C onnectivity

R oads 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 suggests that a high deg ree of integration between the road drainage system and the channel network can increase peak flows (Jones and Grant 1996).

GRAIP calculates the hydrologically

- connected portion of the road using the field assessment of drain point connection 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
natural channel. In Mann Creek , the decommissioning treatments de creased the total number of drain points and re distributed water back o nto the hillslope through diffuse drainage

. This substantially reduced t he length of road surface connected to the channel. Prior to the treatments, 3, 000 m out of the 8,100 m of inventoried road ( 37 %) were hydrologically connected to stream. After the treatments, 77 m of the 8,100 m of monitored
road ( 1%) were connected. Thus, t he treatments resulted in a net reduction of 2, 923 m of hydrologically

- connected road , which is 97 % less than the pre

- treatment condition.

5

. 2 Fine S ediment P roduction & D elivery

Fine s ediment production for a road segment ( ) is estimated based on a base erosion rate and the properties of the road (Luce and Black 1999) , as shown below.

is the base erosion rate 3 ( k g/m) is the road length (m) contributing to the drain point is the slope of the road segment (m/m) contributing to the drain point
is the vegetation cover factor for the flow path is the road surfacing factor

Delivery of fine sediment occurs through a mix of road drainage features including ditch relief culverts, non

- engineered drain points, stream crossings and others

. D elivery of eroded
sediment to the channel network is determined by observ ations of each place that water leaves
the road . Each of these drain point s is classified as delivering, not delivering, or uncertain

. No estimate of fractional delivery is made because , under most circumstances, there is in significant hillslope sediment storage in locations where there is a clear connection to the channel ; all sediment is assumed to be delivered to the stream if a connection is present

. For this analysis,

u n certain observations were treated as delivering

. A map of the road surface sediment

3 For this analysis, a base erosion rate of 79 kg/m of road length was assumed, based on observations in the Oregon Coast Range (Luce and Black 1999). Further work could determine if this rate is appropriate for this climate, geology and road system.13

production and the accumulated sediment delivered through drain points is shown for the 50007, 50029, and 50470 roads (Figure 3 ).

Figure 3

. Fine sediment production and delivery to channels by road segment and drain point,

pre

- treatment road . The road line is colored to indicate the mass of fine sediment that is generated on the road. The size of the circle indicates the accumulated mass o f sediment delivered to the stream network at each drain point.

Pre

- treatment

S ediment delivery is broken out by drain type to assess their effectiveness in preventing sediment from entering the channel (Table 3)

. However, t he sample size , a total of 102 drain points, collected for the Mann Creek study is too small for extensive statisti cal analysis to determine trends by drain point type

. One

- hundred and two drain points were documented

, 37 % of which were hydrologically connected to stream channel s . These points delivered 41.7

tonne s /year of sediment

, or 31 % of the sediment generated by the road surface s and ditch es

.14

Table 3

. Summary of sediment production and delivery at drain points, pre

- treatment road.

Drain Type Count Sediment
Received at Drain

Point ( k g) Sediment Delivered

by Drain Point ( k g) % S ed iment

Del ivery % Effective

L ength

C onnected Broad Based Dip 3 15,230 0 0% 0%
Diffuse Drain 32 27,601 1,619 6 % 7 %
Ditch Relief Culvert 2 0 8,272 2,201 27 % 32 %
Lead Off Ditch 3 823 251 30% 33%

Non

- Engineered 29 55,977 16,847 30 % 46 % Stream Crossing 14 20,764 20,764 100% 100% Sump 0 0 0 0% 0%
Waterbar 1 7,919 0 0 % 0 %
All Drains 102 136,586 41,682 31 % 37 %

Post

- treatment

Decommissioned roads in the Mann Creek watershed were, for the most part, recontoured ( F igure 4) , though some short sections were tilled. The recontoured surface is intended to mimic the natural hillslope hydrology and result in increased infiltration and diffuse flow and
minimized surface drainage from the road. A heavy application of straw was applied in addition to the use of locally available organic matter and transplant material. The disturbed, recontoured surface is likely to generate higher sediment production prior to revegetation ; however, the disturbed surface is substantially disconnected from the stream network. Without the previous stream connections, the decommissioned roads do not deliver nearly as
much sediment (Table 4)

. Nineteen (29%) of the drain points were found t o be connected to
the stream network . However only five of these nineteen drain points are likely to actively deliver sediment due to the redesign and treatment ; the other fourteen are orphans . The total
sediment delivered is reduced to 1 tonne /year (2% of the sediment delivered before

treatment ).15

Figure 4

. Photo of a typical rocky , fully recontoured road with straw mulch.

Table 4

. Summary of sediment production and delivery at drain points, post

- treatment road

. Drain Type Count Sediment Received

at Drain Point (k g) Sediment

Deliver ed by

Drain Point (kg) % Sediment

Delivery % Effective

L ength

C onnected
Broad Based Dip 1 0 0 0 % 0 %
Diffuse Drain 47 59,999 528 0.9 % 0.6 %
Ditch Relief Culvert 0 0 0 0% 0%
Lead Off Ditch 0 0 0 0% 0%

Non

- Engineered 0 0 0 0% 0% Stream Crossing 1 4 486 486 100% 100% Sump 0 0 0 0% 0%
Waterbar 4 0 0 0 % 0 %
All Drains 66 60,485 1014 1.7 % 0.9 %

The modeled change in sediment delivery following the treatments indicates a decline from

41.7 tonne s /year to 1.0 tonne /year , a decrease of over 40 tonnes (Table 5) . The largest
reduction s occurred at stream crossings (through shortening of contributing s egments) and16

non

- engineered features (through removal of the features), with sma ller reductions from the
removal of ditch relief culverts. There was a n increase i n the number of diffuse drains ( 15 ) ; diffuse drains and water bars were the only drain type s to mark an increase in total number

. Even with the increased number, and increase in sediment received by diffuse drains (117%), sediment delivery decreased by 67% because diffuse drains rarely connect (Table 5)

. Rapid revegetation of recontoured sit es is expected to reduce the production estimates substantially
in the future

.

Table 5

. Changes in sediment production and delivery, pre

- treatment vs. post

- treatment.

Drain Type Count Sediment Production (kg) Sediment

Delivery (kg) Sediment

Production (%) Sediment

Delivery (%) Broad Based Dip

- 2

- 15,230 0

- 100 % 0 %
Diffuse Drain 15 32,398

- 1090 117 %

- 67 %
Ditch Relief Culvert

- 20

- 8,272

- 2,201

- 100%

- 100%
Lead Off Ditch

- 3

- 823

- 251

- 100%

- 100%

Non

- Engineered

- 29

- 55,977

- 16,847

- 100%

- 100% Stream Crossing 0

- 20,278

- 20,278

- 97.7%

- 97.7% Sump 0 0 0 0% 0%
Waterbar 3

- 7,919 0

- 100% 0%
All Drains

- 36

- 76,101

- 40,668

- 55.7%

- 97.6%

5.3 Landslide Risk

Existing Landslides

No road related landslides were reported by field crews working in the Mann Creek watershed. The risk of shallow landslide initiation was predicted using SINMAP 2.0 (Pack et al., 2008, http://hydrology.neng.usu.edu/sin map2/ ). SINMAP was run initially to determine the intrinsic stability of the slopes over which the road traverses and to identify locations that are at high risk of failure without a road (Figure 5 ).17

Figure 5

. Estimated natural slope stability index classes. Slope stability was modeled using
default values in SINMAP 2.0. Rectangle indicates area shown in Figure 6.

Changes in Landslide Risk

A second stability index (SI) run was performed to address the effects of road water
contribution to drain points on the original road network (Figure 6 , left)

. This example
illustrates the effect of water being concentrated and discharged at a swale. The swale
location s ( indicated by arrow s ) w ere previously mapped as being moderately stable to quasi

stable; the increased water discharged from the road decreased stability into the lower
threshold category

.

A third model run was performed to illustrate the change in risk of shallow landsliding with the modified road drainage system resulting from the restoration treatments (Figure 6 , center ).

Recont ouring treatments replaced a concentrated surface flow path with a diffuse flowpath . The18

design is intended to reduce the concentration of surface and groundwater and to mimic as much as possible the natural hillslope hydrology. If this treatment is successful it may return the slope stability to near the un

- roaded, natural co ndition.

P ost

- storm monitoring will help calibrate the S I values used in this analysis and refine these initial
results

. Question s to be evaluated include the amount of runoff still intercepted by cutslopes and runoff generated from treated surfaces.

Figure 6

. Stability index for hillslopes in the vicinity of road 501641000. Left: Stability Index classes prior to road decommissioning. Arrows point to swales affected by road drainage. Center: Stability Index classes after road decommissioning. Right: Amount of change in stability index values between pre

- and post

- decommissioning. Positive values indicate a predicted increase in slope stability following road decommissioning.19

5.4 Gully Initiation Risk

Gullying at drain points below road s can be a substantial source of sediment to stream channels. 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 drainage point.

, where:

is the road length contributing to the drain point
is the average slope of the hillslope below the drain point

Calculated ESI values are then compared to a critical ESI threshold ( ESI crit ) to identify areas with a high risk of gully formation (i.e., where ESI > ESI crit ). ESI crit is empirically

- derived for each study area using inventoried gullies. In this study, only one gully was located by the field

crews , and that gully is located along one of the control roads rather than along a road to be
decommissioned. Hence, it is not possible to, nor is it relevant to, calculate a value for ESI crit
. While gully formation appeared to be uncommon prior to decommissioning the roads, it has become far less likely following road decommissioning (Table 6).

Table 6

. ESI population statistics for pre

- decommissioning and post

- decommissioning road
networks

.

ESI Value Minimum Maximum Average Standard
Deviation

Pre

- Decom 0 47.6 2.87 7.18

Post

- Decom 0 0.569 0. 047 .143 Change 0

- 47.0

- 2. 82

- 7.04

5

. 5 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 channel s

. Stream crossing failure risks were assessed using the Stream B locking I ndex (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 (w*) and the skew angle between the channel and the pipe inlet.

The SBI values for the pre

- treatment stream crossings were relatively high with an average
value of 2 for the 1 3 stream crossings (Figure 7 ) , not counting one excavated crossing . This is out of a range of 0 to 4, where 0 suggests no risk of blockage and v alues of 3 or 4 indicate a high20

risk of blockage . The stream crossings with value of 3 all had culvert to channel width ratios of
<1. All 1 3 stream crossing pipes were removed during decommissioning, which completely eliminated the risk of pipe plugging (Figure 8 ). GRAIP calculates an SBI of 0 for crossings without a pipe.

Figure 7

. Distribution of Stream Blocking Index values for pre

- treatment group.
Post

- treatment values were zero for all sites

.

0 1 2 3 4 5 6

1 2 3 Count

Stream Blocking Index (SBI)21

Figure 8

. SBI values on the 2300

- 100 and 2300

- 130 road stream crossings. Left: pre

treatment. Right: post

- treatment. All post treatment values are shown as 0.

The risk of a stream crossing failure can also be viewed in the context o f the consequences of failure ( Flanagan et al

. 199 8 ). A consequence of concern at these stream crossings is the
erosion of fill material , a total of 807.2 m 3

, into the stream channel. This material was excavated during the restoration work

.

A second, and perhaps greater, consequence of concern at failed stream crossings is the diversion of stream flow onto road surfaces and unchannelled hillslopes. Once a crossing becomes occluded and begins to act as a dam, failure can occur in several ways . If the road grade dips into and r i ses out of the crossing, the failure is likely to be limited to a localized overtopping of the stream crossing. However, i f the road grades away from the stream crossing in one or more directions, the flow may be diver ted down the road and ditch and onto adjacent hillsopes, where it can cause gullying and/or landsliding ( Furniss et al. 1998

, 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. At this site, 57 % ( 8 of 1 4 ) of the stream crossings on t he22

original road s had the potential to diver t streamflow down the road in one direction. The

r estoration treatments eliminated these risks at all sites.

GRAIP field crews also took more detailed measurements at excavated stream crossings during the post

- treatment assessment. These metrics include the length and grade of side slopes,
Wolman pebble counts both in the crossing and in an upstream reach, and m easurements of

mass

- wasting volumes, if any. These measurements are intended to provide baseline metrics against which the amount and type of future stream crossing adjustment can be gauged.

Measurements of channel slope and sediment characteristics ca n be used to evaluate how well the excavated crossing mimics the natural channel characteristics. Most of the excavated crossings show some fining of bed materials compared to the upstream reach (Table 7 ; Figure 9 )

, though the D84 increased at four of the stream crossings

. Since the material at these excavated crossings appears the same as on adjacent recontoured road segments, it is likely that the armoring effect is not intentional ; armoring may prevent excessive incision or lateral erosion at
the crossing

. We would expect that over time, grain size distributions will shift toward those recorded in upstream reaches as fine sediment is removed.

Three of the crossings were found to have channel slopes that differed from upstream channel slopes by 5% or more. In all three cases, measured slopes in the crossing are less than those observed upstream. Such crossings may be prone to greater amounts of incision as the stream adjusts its bed.23

Figure 9

. Examples of s tream bed grain

- size distributions. Top : The crossing shows marked fining of sediments compared to the upstream reach . Bottom: Possible armoring occurring with marked fining.24

Table 7

. Channel slope and sediment size characteristics at e xcavated stream crossings in
Mann Creek.

Crossing

# Slope % Grain Size (mm)

In Crossing Upstream Crossing Upstream

D16 D50 D84 D16 D50 D84

1541 5

- 1 35 172 32 70 217

1706 10

- 0.5 27 167 20 52 118

1141 8 32 0.5 6 71 5 25 130

942 8 13 14 32 109 15 38 74

1012 23 38 0.5 14 90 0.5 25 140

1151 11 10 0.5 0.5 30 3 24 91

1345 14 18 0.5 7 40 2 18 69

1539 11 10 0.5 18 73 5 16 54

1146 9 8 0.5 6.5 139 0.5 23 59

Figure 10

. Example of an excavated stream crossing.25

5 .6 Drain Point Condition

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 insufficient ly outslope d and pond water on the road. Culverts are d efined 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. N on

- engineered features are almost always a problem due to a blocked ditch, a gully, or a broken outside berm. Stream crossings are considered a problem if they are blocked by sediment or wood, crushed or rusted significantly, incising, scouring or loosing much water from flow around the pipe. Sumps are a problem if they pond water on the road surface or cause fill saturation. Waterbars that are damaged, under sized, or do not drain properly are defined a s problem atic

. Diffuse drains (outsloped roads) ar e rarely observed to have drain point problems.

At this site, n on

- engineered features and broad

- based dips were observed to have the highest rate of problems ( 93 % and 67 % , respectively )

, while diffusely drained roads were least likely to have problems (Table 8 ). So far, no problems have been observed after the decommissioning treatments. However, there has been little time for such problems to develop as a result of significant storms. Therefore, final conclusions regarding the new drainage system cannot be made until the post

- storm validation monitoring is completed.

Table 8

. Drain point condition problems and fill erosion below drain points, pre

- and post

treatment.

PRE

- TREATMENT POST

- TREATMENT Drain Type Count Problems Fill Erosion Count Problems Fill Erosion Broad Based Dip 3 67 % 0 % 1 0% 0 %
Diffuse Drain 32 0% 3 % 47 0% 0%
Ditch Relief 20 10 % 15 % 0 0 % 0%
Lead Off 3 33% 0% 0 0% 0%

Non

- Engineered 29 93 % 1 7% 0 0% 0% Stream Crossing 1 4 29 % 0% 14 0% 0% Sump 0 0 % 0% 0 0% 0%
Waterbar 1 0% 100 % 4 0% 0%
Total 102 35 % 10% 66 0 % 0%26



### 6 .0 Summary & Conclusions

Rocky Mountain Research Station began a regional road monitoring program in FY 2008 and included the Intermountain Region in FY 2009. As part of t he study, field crews inventoried road
segments on the Payette Nationa l Forest , before and after decommission ing treatments, as well
as a set of con trol roads . These roads received high

- intensity t reatments that included removal
of culverts and fills at stream crossings and recontouring of the road itself.

The GRAIP model was used to predict the change in level of impact/ risk between the pre

- existing
road and the decommissioned road. The restoration treatments reduced the length of the sampled road that was hydrologically connected to streams by 2, 923 m, or 97 %

, from pretreatment conditions. The model predicts that fine sediment delivery was reduced by 98 %,
from 41.7 tonne s to 1.0 tonne annually . The risks presented by stream crossings becoming plugged by debris and sediment were completely eliminated by the excavation and removal of
the culvert s and fill s . These locations will contribute fine sedim ent to the channel in the short

term until they become vegetated

. The potential for streamflow to be diverted onto roads and unchannelled hillslopes was also eliminated

.

The slope stability risk below drain point locations on the original road was reduced as water was redistributed across the hillslope by diffuse drainage. Treatments are predicted to return slope stability to near natural levels

. Gully initiation risks, already low prior to treatment,

were re duced to near negligible values

. E xisting drain point problems , which were present at

35 % of inventoried sites, appear to have been entirely eliminated by the restoration effor t s.
T hese new drainage features

, however, have not yet been evaluated after a large storm

event.

As a whole , these initial results indicate that the decommissioning work in the Mann Creek
watershed s hould be effectiv e in greatly reducing many of the hydrogeomorphic impacts and
risks th at these roads posed t o aquatic ecosystems. The final post storm inventory assessment will enable a closer examination of the hydrologic function of the newly decommissioned road system and will answer important questions about runoff generation,

stream c rossing stability, gully initiation thresholds

, and landslide risk. This report will be updated when these data become available.27

Table 9

. Summary of GRAIP model risk predictions for the Mann Creek road decommissioning project. IMPACT/RISK TYPE EFFECT OF TREATMENT:

INITIAL GRAIP PREDIC TION EFFECT OF TREATMENT:

POST

- STORM

VALIDATION

Road

- Stream Hydrologic Connectivity - 97 %,

- 2, 923 m of connected road To be determined.

Fine Sediment Delivery

- 98 %,

- 40.7 tonne s/year To be determined.

Landslide Risk Restored to near natural condition To be determined.

Gully Risk Reduced from low to negligible To be determined.

Stream Crossing Risk

- plug potential

- 100% (eliminated at 1 3 sites) To be determined.

- fill at risk

- 100% (807 m 3 removed) To be determined.

- diversion potential

- 100 % (eliminated at 8 s ites) To be determined.

Drain Point Problems

- 100 % ( 0 % vs. 35 % of drain points) To be determined.28



### References

Best, D. W., Kelsey, H. M., Hagans, D.K

. and M. Alpert. 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 Ba sin, 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. 200 9 . The Geomorphic Road Analysis and Inventory Package (GRAIP) Data Collection Met hod. USDA Forest Service Rocky Mountain Research Station, Boise Aquatic Science Lab.

Cissel, R., Black, T. A., Luce, C. H

,, Tarboton, D. G., Schreuders, K. A., and Prasad, A 2009 . The Geomorphic Road Analysis and Inventory Package (GRAIP) Office Procedure Manual. USDA Forest Service Rocky Mountain Research Station, Boise Aquatic Science Lab.

Flanagan, S. A., Furniss, M. J., Theisen, S., Love, M., Moore, K., and J. Ory. 1998. Methods for Inventory and Environmental Risk Assessment of Road Draina ge Crossings. USDA Forest Service Technology and Development Program 9877

- 1809

- SDTDC 45pp.

Furniss, M. J., Love, M., and S. A. Flanagan

. 1997 Diversion Potential at Road Stream Crossings. USDA Forest Service Technology and Development Program 9777

- 1814

- S DTDC 12pp.

Istanbulluoglu, E

., Tarboton, D

. G.

, Pack, R. T.

, Luce, C

. H. 2003. A sediment transport model for incision of gullies on steep topography. Water R esources Research. 39(4): 1103

- 1117. Jones, J. A., and G. E. Grant, 1996. Peak flow responses to clear

- cutting and roads in small and large basins, western Cascades, Oregon, Water Resour. Res., 32, 959

- 974.

Luce, C. H. , and T. Black . 1999. Sediment production from forest roads in western Oregon. Water Resources Research. 35(8): 2561

- 2570.

Madej, Mary A. 2001

. Erosion and Sediment Delivery Following Removal of Forest Roads, Earth Surface Landforms and Processes, 26(2) pp.175

- 190.

Pack, R. T., Tarboton, D.G., Goodwin, C.N. and A. Prasad, 2005

. SINMAP 2. A Stability Index Approach to Terrain Stability Hazard Ma pping, technical description and users guide for version 2.0, Utah State University.

Pr asad, A. 2007. A tool to analyze environmental impacts of road on forest watersheds. MS Thesis. Utah State University, USA.

Prasad, A

, , Tarboton, D. G., Schreuders, K. A., Luce, C. H. , and T.A. Black. 2007. GRAIP1.0 Geomorphic Road Analysis and Inventory Package: A tool to analyze the environmental impact of
roads on forested watersheds. Tutorial and Reference Manual. http://WWW.engineering.usu.edu/dtarb/graip

.29

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, 32, 1195

- 1207.30

Appendix A

– Glossary

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. (2009), Fly, et al (2010), and Moll (1997).

Broad based dip . Constructed: Grade reversal des igned 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 dips). Natural: A broad based dip point is collected at the low point where two hillslopes meet, g enerally 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 numb er 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
featur e is representative of an area or a road segment that 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

perpe ndicular 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, withi n 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 di tch out (though this term can also describe other types of drainage features).

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
de bris, 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 water31

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 channe l 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 channel at le ast 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 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 se gment, 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 ar e also considered to be water bars. These features may also be known as scratch ditches