THESIS

SEDIMENT PRODUCTION AND DELIVERY FROM HILLSLOPES AND FOREST 

ROADS IN THE SOUTHERN SIERRA NEVADA, CALIFORNIA

Submitted by

Allison K. Stafford 

Department of Forest, Rangeland, and Watershed Stewardship

In partial fulfillment of the requirements

For the Degree of Master of Science

Colorado State University

Fort Collins, Colorado

Spring 2011

Master’s Committee: 

Advisor: Lee MacDonald

John Stednick

Greg Butters
ii

ABSTRACT

SEDIMENT PRODUCTION AND DELIVERY FROM HILLSLOPES AND FOREST 

ROADS IN THE SOUTHERN SIERRA NEVADA, CALIFORNIA

Unpaved roads often are a major source of sediment to streams in forested 

watersheds, and an increase in sediment production and delivery can adversely affect the 

overall health of a stream. The goals of this study were to first quantify the effects of 

climate and soil type on hillslope and road sediment production and delivery, and then 

evaluate the effects of graveling, grading, and waterbar construction on road sediment 

production and delivery. Sediment fences were used to collect 109 fence-years of data 

from water years 2008 and 2009 in the more rain dominated José Basin (800-1200 m) 

and 193 fence-years of data in the snow dominated Kings River Experimental 

Watersheds (KREW) (1485-2420 m), both located in Sierra National Forest (SNF) in 

California. Detailed road surveys assessed road segment characteristics and road-stream 

connectivity.

Mean hillslope sediment production in José Basin was 3.7 x 10-3kg m-2yr-1, 

which was similar to the value of 4.1 x 10-3kg m-2yr-1 in KREW. Native surface road 

segments in José Basin had a mean sediment production rate of 1.8 kg m-2yr-1, and the 

estimated total sediment production from the 67 km of native surface roads is 680 metric 

tons per year. An estimated 30% of the native surface road length is connected to the 
iii

stream network, indicating that up to 210 metric tons of sediment may be delivered to 

streams each year. There was no significant difference in sediment production and 

delivery between road segments in the highly erodible Holland soil and road segments in 

other soil types. Mean sediment production for the native surface road segments in the 

KREW watersheds was 0.13 kg m-2yr-1, which was more than an order of magnitude 

lower than the mean value in José Basin, and road-stream connectivity was only 3%.

There was no significant difference in sediment production from native and gravel 

surface road segments in José Basin due to the high variability and the gravel segments 

still averaged 51% bare soil. The gravel surface segments had shorter drainage features 

than native surface segments, but 40% of the gravel roads were connected as they tended 

to be closer to streams. Graveled roads in the Providence Creek watersheds produced 

0.16 kg m-2 yr

-1

, which was only 22% as much sediment as the native surface roads, and 

had 11% connectivity. 

In José Basin grading initially decreased the mean segment length from 65 m to 

41 m, but one year after grading 22% of the waterbars had failed, leading to a 15% 

increase in mean segment length. Graded road segments in José Basin produced eight 

and three times more sediment per unit area than ungraded segments in WY2008 and 

WY2009, respectively, and this can be attributed to extensive rilling. Sediment 

production rates decreased by 40-60% from the first to the second year after grading. 

Sediment production and delivery from forest roads can be reduced by: 1) using 

more than 30% gravel cover on native surface roads, 2) minimizing grading, and 3) 

improving the construction of waterbars to better withstand and direct overland flow.
iv

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Lee MacDonald for his guidance, as well as 

Dr. John Stednick. I never could have completed this work without the astounding 

support of friends and family. I would especially like to thank Abby Korte for her 

friendship and insight throughout this process. I am very grateful to Alan Gallegos, 

Sierra National Forest, and Carolyn Hunsaker and the Kings River Experimental 

Watershed staff for their guidance, summer housing, and field support. I would also like 

to thank Drew Coe as well as numerous field assistants. This work has been supported 

by grants from the Sierra National Forest and the USDA Forest Service Region 5. 
v

TABLE OF CONTENTS

1. INTRODUCTION .............................................................................................................. 1

1.1. Literature cited ................................................................................................................. 7

2.EFFECTS OF CLIMATE AND SOIL TYPE ON HILLSLOPE AND NATIVE 

SURFACE ROAD SEDIMENT PRODUCTION AND DELIVERY ................................... 12

2.1. Introduction...................................................................................................................... 14

2.2 Background....................................................................................................................... 17

2.3. Objectives ........................................................................................................................ 20

2.4. Methods............................................................................................................................ 21

2.4.1. Site description.............................................................................................................. 21

2.4.2. Precipitation .................................................................................................................. 23

2.4.3. Hillslope sediment production and characteristics ....................................................... 24

2.4.4. Road sediment production ............................................................................................ 26

2.4.5. Road segment characteristics........................................................................................ 26

2.4.6. Road surveys................................................................................................................. 27

2.4.7. Road sediment delivery................................................................................................. 28

2.4.8. Comparison to WEPP:Road.......................................................................................... 29

2.4.9. Statistical analysis......................................................................................................... 30

2.5. Results.............................................................................................................................. 31

2.5.1. Precipitation .................................................................................................................. 31

2.5.2. Hillslope characteristics and sediment production ....................................................... 33

2.5.3. Road segment characteristics and sediment production ............................................... 35

2.5.4. Road sediment delivery................................................................................................. 41

2.5.5. Modeling road sediment production and delivery in José Basin. ................................. 43

2.5.5.1. Predicting sediment production from native surface segments in José Basin. .......... 43

2.5.5.2. Total potential sediment produced and delivered from native surface segments in 

José Basin................................................................................................................................ 44

2.5.5.3. Comparison of WEPP:Road predictions to measured values in José Basin.............. 45

2.6. Discussion........................................................................................................................ 45

2.6.1. Effects of climate on sediment production ................................................................... 45

2.6.2. Predicting road sediment production in José Basin ...................................................... 49

2.7. Conclusions...................................................................................................................... 53

2.8. Literature cited ................................................................................................................. 56

2.9. Tables............................................................................................................................... 61

2.7. Figures.............................................................................................................................. 73

3. EFFECTS OF GRAVELING AND GRADING ON SEDIMENT PRODUCTION AND 

DELIVERY............................................................................................................................. 93

3.1. Introduction...................................................................................................................... 95
vi

3.2 Background....................................................................................................................... 98

3.2.1. Road sediment production and delivery ...................................................................... 98

3.2.2. Effects of graveling on road sediment production and delivery................................ 100

3.2.3. Effects of grading and waterbar installation on road sediment production and delivery

.............................................................................................................................................. 101

3.3. Methods......................................................................................................................... 103

3.3.1. Site description........................................................................................................... 103

3.3.2. Precipitation ............................................................................................................... 105

3.3.3. Sediment production .................................................................................................. 106

3.3.4. Road segment characteristics..................................................................................... 107

3.3.5. Rill volume and contribution to sediment erosion after grading ............................... 109

3.3.6. Sediment delivery ...................................................................................................... 109

3.3.7. Road surveys.............................................................................................................. 111

3.3.8. Statistical analysis...................................................................................................... 111

3.4. Results........................................................................................................................... 112

3.4.1. Precipitation ............................................................................................................... 112

3.4.2. Effects of road surface type on road sediment production and delivery.................... 114

3.4.2.1. Sediment production ............................................................................................... 114

3.4.2.2. Predicting sediment production for gravel surface roads in José Basin ................. 120

3.4.2.3. Sediment delivery ................................................................................................... 122

3.4.3. Effects of grading in José Basin................................................................................. 126

3.4.3.1. Effects of grading on segment characteristics ........................................................ 126

3.4.3.2. Effects of grading on sediment production............................................................. 127

3.4.3.3. Rill erosion after grading ........................................................................................ 130

3.4.3.4. Effects of grading on road surface bulk density ..................................................... 131

3.4.3.5. Effects of grading on sediment delivery ................................................................. 132

3.5. Discussion..................................................................................................................... 133

3.5.1. Effects of graveling on sediment production and delivery ........................................ 133

3.5.2. Effects of grading and waterbar installation in José Basin on sediment proudction and 

delivery ................................................................................................................................ 136

3.6. Conclusions................................................................................................................... 140

3.7. Literature cited .............................................................................................................. 143

3.8. Tables............................................................................................................................ 148

3.9. Figures........................................................................................................................... 160

4. APPENDICES ................................................................................................................. 182

A. Hillslope characteristics and sediment production rates in José Basin, WY2008-2009. 182

B. Hillslope characteristics and sediment production rates in the Providence Creek 

watersheds, WY2004-2009.................................................................................................. 183

C. Hillslope characteristics and sediment production rates in the Providence Creek 

watersheds, WY2004-2009.................................................................................................. 184

D. Native surface road segment characteristics and sediment production rates in José Basin, 

WY2008-2009...................................................................................................................... 185

E. Road segment characteristics and sediment production rates in the Providence Creek 

watersheds, WY2008-2009.................................................................................................. 186
vii

F. Native surface road segment characteristics and sediment production rates in the Bull 

Creek watersheds, WY2008-2009 ....................................................................................... 187

G. Gravel surface road segment characteristics and sediment production rates in José Basin, 

WY2008-2009...................................................................................................................... 188

H. Road characteristics before, immediately after, and one year after grading................... 189

H. Road segment characteristics and sediment production one and two years after grading in 

José Basin, WY2008 and WY2009 ..................................................................................... 190
1. INTRODUCTION

Increased sediment loading adversely impacts streams, as it can affect water 

quality, stream habitat, and aquatic ecosystems (Tagart, 1976; Cederholm et al., 1981; 

Reid and Dunne, 1984; Bilby et al., 1989; Ziegler and Giambelluca, 1997; Kolka and 

Smidt, 2004). Inputs of fine sediment can decrease pool depth and abundance, and 

increase turbidity, both of which can alter the quality and quantity of habitat for 

salmonids and limit reproduction (Harr and Nichols, 1993; Weaver and Hagans, 1999; 

Beechie et al., 2005). Increased sediment loading also affects aquatic organisms by 

altering the temperature and nutrient loads in the stream (Kolka and Smidt, 2004). 

Additionally, increased sediment delivery to reservoirs reduces the usable capacity and 

interferes with piping systems (Minear and Kondolf, 2009). The U.S. Environmental 

Protection Agency lists sediment as the most common impairment to water quality in 

streams and lakes in the United States (EPA, 2010). 

Hillslope sediment production rates in undisturbed forested watersheds are 

typically very low (MacDonald et al., 2003), as forests have a dense surface cover of 

vegetation and litter and a high porosity and infiltration rate (Dunne and Leopold, 1978). 

In contrast, unpaved roads have a low infiltration rate and little to no surface cover, so 

they often are a major sediment source in forested watersheds (Reid and Dunne, 1984; 

Swift, 1988; Bilby et al., 1989; Luce and Black, 1999; Ketcheson et al. 1999; Coe, 2006). 

Studies spanning a variety of differently designed and surfaced roads in rain, rain-onsnow, and snow climates have found that road sediment production rates vary by two to 

three orders of magnitude due to differences in climate, soil type, road surface type and 

design, and road maintenance practices such as grading (Megahan, 1974; Reid and 
2

Dunne, 1984; Kochenderfer and Helvey, 1987; Bilby et al., 1989; Burroughs and King, 

1989; Luce and Black, 1999; Luce and Black, 2001; MacDonald et al., 2001; Ziegler et 

al., 2001; Appelboom et al., 2002; Clinton and Vose, 2003; Motha et al., 2004; RamosScharrón and MacDonald, 2005; Barrett and Tomberlin, 2006; Coe, 2006; Forsyth et al., 

2006; Sheridan and Noske, 2007; Sugden and Woods, 2007; Welsh, 2008). The large 

range found in these studies shows that road sediment production rates are case-specific, 

and rates found in one location cannot necessarily be applied elsewhere.

Road surface sediment production is the result of several erosional and transport 

processes. These include: 1) rainsplash detachment; 2) sheetwash; and 3) rill erosion 

(Zeigler et al., 2000). The absolute and relative magnitudes of these processes depend on 

a number of location-specific climatic and road surface variables. Road runoff and 

sediment production may only be a concern if this material is delivered to a stream or 

other water body. Road sediment delivery is determined by the amount of runoff leaving 

the road surface as well as the location of road drainage points relative to the stream 

network (Megahan and Ketcheson, 1996; Croke and Mockler, 2001; Croke et al., 2005; 

Croke and Hairsine, 2006; Lane et al., 2006). 

Climate is one of the most important controls on road sediment production, as this 

affects the amount, type, and intensity of precipitation (MacDonald et al., 2001). 

Unpaved roads in rain dominated climates should produce much more sediment than 

comparable roads in snow dominated climates, as rainfall is more erosive than snow. In 

mountainous areas, the rain to snow ratio is largely driven by elevation. No one study 

has simultaneously measured and compared sediment production rates across rain, rain-
3

on-snow, and snow dominated climates to quantify the effects of climate in one 

geographic area. 

Soil type is another important control on road sediment production, as this affects 

the particle-size distribution and soil erodibility. Several studies have compared road 

sediment production and delivery between different soil types (Rice and Lewis, 1991; 

Luce and Black, 1999; Sugden and Woods, 2007), but no study has compared hillslope or 

road sediment production and delivery from the highly erosive Holland soil (USDA, 

1983) to other soil types in California’s southern Sierra Nevada. 

 The same factors controlling sediment production on native surface roads also 

control sediment production on gravel surface roads, but the relative magnitude of the 

various processes can differ greatly from native surface roads. Most studies have shown 

sediment production rates from gravel surface roads to be lower than values from 

comparable native surface roads, and this can be largely attributed to the protection from 

rainsplash and reductions in surface erodibility and overland flow velocities 

(Kochenderfer and Helvey, 1987; Burroughs and King, 1989; Appelboom et al., 2002; 

Sheridan and Noske, 2003; Barrett and Tomberlin, 2006; Coe, 2006; Forsyth et al., 2006; 

Korte, in preparation). However, no study has directly compared the relative effects of 

graveling between rain and snow dominated climates in one geographic area.

Grading is an important and common road maintenance technique when surface 

erosion hinders the road’s drivability. Grading is often paired with the construction or reestablishment of waterbars, which drain water off the road surface and reduce the 

contributing area of a road segment, thereby potentially decreasing sediment production 

and delivery. The surface disturbance due to grading increases the supply of material for 
4

transport, thus leading to an initial increase in sediment production (Megahan and Kidd, 

1972; Megahan, 1974; Reid and Dunne, 1984; Megahan et al., 1986; Luce and Black, 

1999; Ziegler et al., 2000; Ziegler et al., 2001; Appelboom et al., 2002; Ramos-Scharrón 

and MacDonald, 2005; Coe, 2006). 

Quantifying the amount and persistence of the increase in sediment production 

after grading is necessary for forest managers to determine the optimal frequency of 

grading versus maintaining the drivability of the road. Quantifying the effect of grading 

on waterbar frequency and performance is necessary to determine how grading affects 

road sediment delivery to streams. The combination of grading and waterbar installation 

or maintenance may result in either an increase or decrease in sediment delivery to the 

stream network, depending on whether delivery is reduced enough to outweigh the 

increase in sediment production; hence it is important that both aspects be examined. 

Forest managers need to identify the key variables for road sediment production 

and delivery to guide road construction and maintenance. Several studies have examined 

these key variables and attempted to predict road sediment production and delivery rates 

(Ziemer et al., 1991; Harden, 1992; Luce and Cundy, 1994; Elliot et al., 1999; Doten et 

al., 2006; Ramos-Scharrón and MacDonald, 2007). As with the magnitude of sediment 

production, the controls on sediment production vary with location and climate, and this 

study will quantify these variables in José Basin, a 78 km2rain dominated watershed in 

the Sierra Nevada of California. 

The present study is building on previous work on road sediment production and 

delivery rates in the Sierra Nevada. The first of these studies was in the Eldorado 

National Forest in the northern Sierra Nevada (Coe, 2006). Sediment production rates 
5

were measured for three water years (WY2000 to WY2002) for 15 native surface road 

segments that were not recently graded, for 2-40 road segments graded within the past 

two years, and for 9-10 gravel surface road segments. Elevations were between 1000 and 

1800 m, so the area has a highly variable mixture of rain and snow. Segment-scale 

measurements and road surveys were used to determine the dominant controlling 

variables and predict road sediment production and delivery (Coe, 2006). 

The second study was in the higher elevation (1485-2420 m), rain-on-snow and 

snow dominated Kings River Experimental Watershed (KREW) in the Sierra National 

Forest (SNF) (Korte, in preparation). This study quantified sediment production rates 

from WY2004 through WY2006 for: 9-20 hillslopes; 23-34 native, gravel, and mixed 

surface road segments; and seven ditches adjacent to paved roads. This study also 

determined key variables for predicting sediment production and used road surveys to 

evaluate sediment delivery pathways and (Korte, in preparation). These data were 

combined with three additional years of monitoring under the present study to allow more 

direct comparisons between KREW and José Basin.

The overall goals of this study were to: 1) compare sediment production rates 

from hillslopes and forest roads in rain and snow dominated climates; 2) evaluate the 

effects of graveling and grading on road sediment production and delivery; and 3) predict 

road sediment production rates in José Basin. Chapter 2 of this thesis quantifies the 

effects of elevation and soil type on sediment production and delivery by: 1) comparing 

sediment production rates from undisturbed hillslopes and native surface road segments 

between the snow dominated KREW watersheds and the rain dominated José Basin; 2) 

comparing sediment production rates from hillslopes and native surface road segments on 
6

Holland soil and other, less erosive soils in José Basin; and 3) estimating sediment 

production and delivery from native surface roads in José Basin. 

Chapter 3 quantifies the effects of graveling, grading, and waterbar construction 

and maintenance on sediment production and delivery by: 1) comparing sediment 

production and delivery between native and gravel surface roads; 2) estimating total 

sediment production and delivery from gravel surface roads in José Basin; and 3) 

quantifying the effect of grading and waterbar installation on road segment 

characteristics, road sediment production, and road sediment delivery in José Basin. 

Forest managers must constantly work to balance public accessibility and forest 

conservation. While roads are necessary for public accessibility and management 

activities, they may negatively affect water quality and stream health. The results of this 

study help quantify the variations in road sediment production and delivery from 

hillslopes and roads in different climates in the SNF, and guide management practices to 

reduce road sediment contributions while maintaining drivability. 
7

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12

2. EFFECTS OF CLIMATE AND SOIL TYPE ON HILLSLOPE AND NATIVE 

SURFACE ROAD SEDIMENT PRODUCTION AND DELIVERY

ABSTRACT:

Sediment is the dominant non-point source pollutant in streams, and unpaved 

roads are often considered to be a major source of sediment in forested watersheds. The 

overall goal of this study was to assess sediment production and delivery from hillslopes 

and roads in two study areas in the southern Sierra Nevada of California. The first study 

area, José Basin, is a 78 km2rain dominated watershed, and the second was the Kings 

River Experimental Watershed (KREW), which contains two groups of four small, snow 

dominated watersheds. Sediment production was measured with sediment fences for two 

water years in José Basin, and up to six water years in KREW. The specific objectives 

were to: 1) quantify the effects of climate on sediment production and delivery rates from 

hillslopes and native surface road segments; 2) quantify the effects of soil type on 

sediment production and delivery rates from hillslopes and native surface road segments 

in José Basin; and 3) estimate the total sediment production and delivery from native 

surface roads in José Basin. 

In José Basin, the mean hillslope sediment production rate was 3.7 x 10-3kg m-2

yr-1, and for native surface roads the value was 1.8 kg m-2yr-1, or nearly 500 times higher. 

Hillslope and road sediment production rates were not significantly different between the 

highly erodible Holland soils and other soil types. Rilled road segments produced 

significantly more sediment than segments without rills. Detailed road surveys and an 

empirical model indicate that native surface roads in José Basin produce 680 metric tons 

yr-1of sediment and potentially deliver 210 metric tons yr-1to the stream network. Much 
13

of this sediment is coming from a relatively few segments with extensive rilling that are 

located close to a stream. 

At the higher elevation KREW sites the mean sediment production rates for 

hillslopes and roads were an order of magnitude lower than in José Basin. The potential 

increase in air temperatures due to climate change and the associated shift from snow to 

rain will increase hillslope road erosion rates as well as sediment delivery to streams. 

Management practices to reduce road sediment production and delivery should focus in 

rain dominated climates where erosion rates are likely to be higher than in snow 

dominated areas. 
14

2.1. Introduction

Increased sediment loading to streams, rivers, and lakes is a major concern, as this 

can adversely affect water quality, stream habitat, and aquatic ecosystems (Bilby et al., 

1989; Ziegler and Giambelluca, 1997; Kolka and Smidt, 2004). Fine sediment also can 

decrease pool depth and abundance, and increase the turbidity of the stream (Beechie et 

al., 2005), both of which can alter the quality and quantity of habitat for salmonids and 

limit reproduction (Harr and Nichols, 1993; Weaver and Hagans, 1999; Beechie et al., 

2005). Increased sediment loading affects aquatic organisms by altering the temperature 

and nutrient loads in the stream (Kolka and Smidt, 2004). Sediment is the most common 

impairment to water quality in streams and lakes in the United States (EPA, 2010). 

Additionally, increased sediment delivery reduces reservoir capacity and can clog or 

damage pipes (Minear and Kondolf, 2009). 

Hillslope sediment production rates in undisturbed forested watersheds are 

typically very low (MacDonald et al., 2004), as forests have a dense surface cover of 

vegetation and litter and a high porosity and infiltration rate (Dunne and Leopold, 1978). 

These characteristics largely prevent soil detachment and overland flow (Dunne and 

Leopold, 1978). Surface disturbances such as fire, concentrated grazing, and road 

construction can expose the mineral soil and greatly reduce the infiltration rate 

(MacDonald et al., 2001; Ramos-Scharrón and MacDonald, 2005). This increases 

rainsplash erosion and the likelihood of erosive overland flow, which can detach soil 

particles and transport them to the stream network.

The surface of an unpaved road is typically dominated by exposed mineral soil, 

and in forested watersheds unpaved roads are often a major source of sediment to streams 
15

(Reid and Dunne, 1984; Swift, 1988; Bilby et al., 1989; Luce and Black, 1999; 

Ketcheson et al. 1999; Coe, 2006). Unpaved roads can deliver a large amount of 

sediment to streams relative to their surface area even during low to moderate rainfall 

events due to their characteristically low infiltration rates (Ziegler and Giambelluca, 

1997; Chappell et al., 1999; Ziegler et al., 2004; Cafferata et al., 2007). 

The amount of road sediment delivered to streams is determined by the amount of 

runoff leaving the road surface as well as the location of drainage points relative to 

streams. While several studies have examined road sediment delivery pathways 

(Megahan and Ketcheson, 1996; Croke and Mockler, 2001; Croke et al., 2005; Croke and 

Hairsine, 2006; Lane et al., 2006), both road sediment production and sediment delivery 

are highly location-specific, as they depend on variables such as climate, soil type, slope, 

and surface cover. Numerous attempts have been made to predict sediment production 

and delivery for a range of climates and types of roads, most notably by using the 

physically-based WEPP:Road model. However, more accurate estimates may be 

obtained by measuring road segment characteristics and sediment production rates for a 

specific area or climate, and developing local empirical models. Alternatively, such data 

also can be used to test the validity of WEPP:Road or other models.

Sediment production and delivery from forest roads has been monitored in the 

Sierra Nevada mountains in California by Colorado State University graduate students 

since 1999. The first study in the Eldorado National Forest in the northern Sierra Nevada 

(Figure 2.1) measured sediment production rates from 15 native surface road segments 

that were not recently graded from water year (WY) 2000 to WY2002 (Coe, 2006). 

Elevations ranged from 1000 to 1800 m, and the area has a mixed rain and snow climate. 
16

Mean annual sediment production from the native surface road segments varied from 

0.22 to 0.81 kg m-2, and road surveys indicated that 25% of the road length was 

hydrologically connected to the stream network (Coe, 2006). .

The second study was located further south in the Sierra National Forest (SNF) in 

the Kings River Experimental Watershed (KREW) (Figure 2.1). This study monitored 

sediment production from 9-18 undisturbed hillslopes and 11-22 native surface road 

segments from WY2004 to WY2006 (Korte, in preparation). Elevations ranged from 

1485 to 2420 m, and the area is snow and rain-on-snow dominated. The mean sediment 

production rate on undisturbed hillslopes was 0.01 kg m-2yr

-1

(s.d. = 0.02 kg m-2yr

-1

), 

and mean annual production rates for hillslopes in the mid-elevation Providence Creek 

watersheds (1485-2005 m) were similar to the mean values for the upper elevation Bull 

Creek watersheds (2050-2420 m). The mean values for native surface road segments 

ranged from 0.0 to 6.2 kg m-2 yr

-1

, and the overall mean road erosion rate of 0.74 kg m-2

yr-1(s.d. = 1.2 kg m-2yr-1) was comparable to the higher values from the Eldorado 

National Forest. In contrast to the hillslopes, the mean annual sediment production rate 

for the native surface road segments in the Providence Creek watersheds was 4-15 times 

the value for the Bull Creek watersheds. The high interannual variability and high 

variability among segments within a water year indicated a need for continued 

monitoring and data analysis.

The present study continued monitoring sediment production rates from 

undisturbed hillslopes and road segments in the KREW watersheds, but the primary focus 

was shifted to José Basin, a 78 km2 watershed located 20 km west of KREW. Road 

sediment production rates in José Basin are expected to be higher than values found by 
17

the two previous studies as the climate is rain rather than snow dominated. Hence the 

goals of this study were to measure sediment production and delivery from hillslopes and 

forest roads in José Basin from different soil types, and use these data to examine the 

effects of climate on sediment production and delivery. 

2.2. Background 

Water-driven erosion at the road segment scale depends on several interacting 

erosion and transport processes, including rainsplash, sheetwash, and rill erosion (Zeigler 

et al., 2000). Rainsplash detachment occurs when the impact from a falling raindrop 

detaches sediment particles (Zeigler et al., 2000). The rate of rainsplash detachment is 

highly dependent on the rainfall erosivity, which in turn is a function of the precipitation 

intensity and the drop size distribution (Lal, 1988; Renard et al., 1997). Snowfall has 

minimal erosive energy, as it is lighter and falls much more slowly than rain. Rainsplash 

is minimal on forested, undisturbed hillslopes, as the surface is protected by vegetation 

and litter (Dunne and Leopold, 1978), but it can play a major role in sediment production 

from native surface roads (Ziegler et al., 2000). In Thailand, which has a monsoonal 

rainfall climate, rainsplash detachment accounted for 38-45% of sediment production 

from the road surface, even though the surface was highly compacted (Ziegler et al., 

2000). 

When rainfall intensity exceeds the infiltration capacity of a surface, water flows 

downslope as infiltration-excess or Horton overland flow (HOF), which can result in 

sheetwash and/or rill erosion (Dunne and Leopold, 1978). Sheetwash occurs when water 

flows across the surface in a sheet, detaching and transporting sediment (Dunne and 
18

Leopold, 1978). Rill erosion is when water collects into channels due to the surface’s 

micro-topography. The concentrated flow can detach and transport sediment from the rill 

bed and sides (Dunne and Leopold, 1978). 

Both sheetwash and rill erosion occur when the shear stress applied by the flow 

exceeds the resistance of the surface (Dunne and Leopold, 1978; Luce and Black, 1999; 

Croke and Hairsine, 2006). The shear stress of a given flow is given by

τ = γdS (equation 2.1)

where τ is the shear stress (Newtons m-1), γ is the fluid density (Newtons m-2), d is the 

depth of flow (m), and S is the surface slope (m m-1). The depth of flow is a function of 

the duration and intensity of a given precipitation event relative to the infiltration rate. In 

the Sierra Nevada, snowmelt rates are typically much lower than rainfall intensities, 

allowing more time for the snowmelt to infiltrate and resulting in a much lower 

likelihood of HOF. 

Infiltration rates on undisturbed, forested hillslopes are high, and HOF rarely 

occurs (Dunne and Leopold, 1978). Infiltration rates for unpaved roads tend to be very 

low; values in Idaho, Colorado, and Montana varied between 5 x 10-5and 8.8 mm h-1

with a geometric mean of 0.11 mm h-1(Luce and Cundy, 1994). Therefore, assuming a 

spatially uniform precipitation rate, the discharge from a road segment is directly 

proportional to the area of that segment, while the velocity of the flow is directly 

proportional to the slope of a road segment (Ramos-Scharrón and MacDonald, 2007). 

The rainsplash detachment, shear stress of HOF, and resulting transport capacity are 

direct functions of the precipitation characteristics and the contributing area and slope of 

a road segment (Anderson and MacDonald, 1998; MacDonald et al., 2004).
19

As runoff becomes channelized into rills, the detachment and transport capacity 

increases because the flow is deeper and faster (Merz and Bryan, 1993; Brunton and 

Bryan, 2000). The extent of rilling will vary with soil properties and precipitation 

characteristics (Brunton and Bryan, 2000). In Colorado, road sediment production was 

strongly related to rill density (R2= 0.57, p < 0.0001) (Welsh, 2008). In agricultural and 

burned areas, rill erosion may be more important than sheetwash erosion (Pietraszek, 

2006), but few data are available on the balance between sheetwash and rill erosion for 

unpaved roads.

Soil type is another important control on road sediment production, as this affects

the soil erodibility. Soil erodibility is one of the controlling factors in the Revised 

Universal Soil Loss Equation (RUSLE), and this is calculated from the soil texture, 

organic matter content, structure, and permeability (Renard et al., 1997). In José Basin, 

the soils in the Holland series are notably more erosive as the soil erodibility (K factor) in 

RUSLE is 0.28. This is higher than the values of 0.20 or less for all other soil types 

(USDA, 1983). Exposure of the sandy clay loam B horizon is thought to especially lead 

to surface erosion. This has led to more extensive rocking and other treatments on roads 

in Holland soils (A. Gallegos, pers. comm., USDA Forest Service, 2007).

Road-stream connectivity determines the hydrologic effects of roads at the 

watershed scale (Wemple et al., 1996; La Marche and Lettenmaier, 2001; Bowling and 

Lettenmaier, 2001). Sediment from roads is contributed to the stream network when 

sediment produced exits the road surface and flows into a stream (Croke and Mockler, 

2001), such as at stream crossings (Wemple et al., 1996; Croke and Mockler, 2001; Coe, 

2006). Road-stream crossings are rare in the two study areas, so most of the road-stream 
20

connectivity is due to the concentrated runoff from a road extending to a stream as 

evidenced by a sediment plume or small channel (Montgomery, 1994; Wemple et al., 

1996; Croke and Mockler, 2001; La Marche and Lettenmaier, 2001; Bowling and 

Lettenmaier, 2001).

Road sediment production and delivery modeling is necessary to estimate the 

amount of sediment delivered from roads to streams, and modeling also can help direct 

management practices to those road segments with the highest potential for sediment 

delivery. The most common road sediment production and delivery model is 

WEPP:Road, a web-based interface based on the Water Erosion Prediction Project 

(WEPP). This is designed to predict sediment production and delivery from road 

segments, compacted landings, compacted skid trails, and compacted foot, cattle, or offroad vehicle trails (Elliot, 1999). WEPP:Road is a process-based model which only 

requires users to specify key variables, namely the climate, soil type, gravel cover, local 

topography, segment length, segment slope, road design, surface conditions, ditch 

conditions, and distance to streams. 

2.3. Objectives

Given this background, the specific objectives were to: 1) measure sediment 

production rates from undisturbed hillslopes and native surface road segments in KREW 

and José Basin; 2) use these data to quantify the effects of climate on sediment 

production and delivery; 3) quantify the effects of soil type on hillslope and road 

sediment production and delivery in José Basin; 4) estimate the basin-wide annual native 

surface road sediment production and delivery rate for José Basin; and 5) compare the 
21

measured road sediment production rates to modeled values using WEPP:Road. Working 

hypotheses were that road sediment production rates would be higher in rain dominated 

climates than in snow dominated climates, and higher on roads in Holland soils than 

other soil types. Sediment production rates from undisturbed hillslopes also were 

expected to be significantly less than values from native surface roads. 

2.4. Methods

2.4.1. Site description

José Basin

José Basin is a 78 km2 watershed in Sierra National Forest, located in the southern 

Sierra Nevada of California (Figure 2.1). Elevations range from 450 to 1950 m (Figure 

2.2), although most of the study sites were located between 800 and 1200 m. The area 

has a Mediterranean-type climate with dry summers and wet winters. Most precipitation 

at the lower elevations falls as rain, and in the upper portions of the basin there is usually 

a seasonal snowpack and rain-on-snow events occur frequently due to diurnal and 

seasonal fluctuations (A. Gallegos, USFS, pers. comm., 2008). 

The middle and upper elevations in José Basin are dominated by conifers, 

particularly ponderosa pine (Pinus ponderosa) and incense cedar (Libocedrus decurrens). 

At lower elevations, brush stands are more common, and these contain ceanothus 

(Ceanothus spp.), manzanita (Arctostaphylos spp.), and other species. Primary soil types 

are the Shaver, Tollhouse, Chawanakee, and Holland series (USDA, 1983). As stated 

earlier, Holland soils are regarded as being particularly susceptible to surface erosion (A. 

Gallegos, USFS, pers. comm., 2007). 
22

There are 447 km of stream channels in José Basin and the drainage density is 5.7 

km km-2(Figure 2.3) (SNF data base, accessed via A. Gallegos, 2007). The basin has an 

extensive road network, with 159 km of mapped roads for a relatively high road density 

of 2.0 km km-2(Figure 2.3) (SNF data base, accessed via A. Gallegos, 2007). The mean 

road width is approximately 2.6 m, indicating that roads occupy only 0.53% of the total 

surface area. Much of the basin is managed by the SNF, but there are extensive private 

land holdings. Road access is crucial in José Basin as there are scattered houses in some 

areas, and the basin is heavily used for grazing, logging, and recreational uses such as 

hunting and off-highway vehicles. 

Providence and Bull Creek Watersheds, KREW

The Kings River Experimental Watershed (KREW) is 20 km east of José Basin, 

and is also in the SNF (Figure 2.1). KREW contains two groups of four watersheds; the 

lower elevation group is the Providence Creek watersheds (1485 to 2005 m) (Figure 

2.4a), and the higher elevation group is the Bull Creek watersheds (2050 to 2420 m) 

(Figure 2.4b). The eight watersheds range in size from 0.53 to 2.27 km2. Average annual 

precipitation is 1240 mm, with approximately 90% of the precipitation falling as snow, 

and the Bull Creek watersheds typically have a higher snow to rain ratio than the 

Providence Creek watersheds (Korte and MacDonald, 2007). Vegetation in the 

Providence Creek watersheds is primarily Sierra mixed-conifer forest, while the Bull 

Creek watersheds have Sierra mixed-conifer forest that grades into red fir (Abies 

magnifica) at higher elevations. The KREW watersheds have primarily Gerle, Cagwin, 
23

and Shaver series soils, which are coarse sandy loam and loamy sand soils with granitic 

lithology (USDA, 1983).

2.4.2. Precipitation

José Basin

Five tipping bucket rain gages were installed in José Basin (Figure 2.2), but 

equipment problems and vandalism meant that valid data were collected from four rain 

gages in WY2008 and three gages in WY2009. Annual precipitation and annual erosivity 

were calculated using the RF program for each gage for WY2008 and WY2009 

(Petkovsek, 2001). No correlation was found between elevation and annual precipitation 

or annual erosivity for either water year, so data from the nearest functioning rain gage 

were assigned to each site where sediment production was measured.

The precipitation data from José Basin was put in historical context by using the 

95 years of precipitation data from the Auberry climate station, which is the closest longterm station. The elevation of the Auberry station is 640 m and it is approximately 10 km 

west of José Basin (Figure 2.1). Annual precipitation from the rain gages in José Basin 

was compared to the long-term mean annual precipitation and the measured precipitation 

at Auberry for WY2008 and WY2009.

Providence Creek and Bull Creek watersheds, KREW

Precipitation data were collected at 15-minute intervals at upper and lower 

climate stations in both the Providence Creek and Bull Creek watersheds for WY2008 

and WY2009 (Table 2.1). The precipitation gages in the Providence Creek watersheds 
24

are at 1750 m and 1985 m, while the gages in the Bull Creek watersheds are at 2195 m 

and 2463 m. Annual erosivity was calculated. Regression equations between elevation 

and either annual precipitation or annual erosivity were calculated separately for the 

Providence Creek and Bull Creek watersheds, and these equations were used to calculate 

the annual precipitation and erosivity for each of the hillslopes and road segments where 

sediment production was being monitored. In WY2009 the data for the lower Bull Creek 

precipitation gage were incomplete, so data from the upper gage were used for all of the 

sites in the Bull Creek watersheds.

2.4.3. Hillslope sediment production and characteristics 

Hillslope sediment production and characteristics were measured for 9-18 

undisturbed convergent hillslopes in KREW and 10 hillslopes in José Basin. Sediment 

production was measured by installing a sediment fence in each convergent swale (Figure 

2.5). These were constructed of a geotextile fabric attached to 1.2 m long pieces of 1.3 

cm diameter rebar that were pounded 0.3-0.5 m into the ground (Robichaud and Brown, 

2002). The leading edge of the fabric was attached to the ground with landscape staples 

to prevent underflow. 

Annual sediment production was determined by removing and weighing the 

sediment captured in each fence to the nearest 0.5 kg. Two representative samples of this 

material were analyzed for percent moisture (Gardner, 1986) and percent organic matter 

(Ben-dor and Banin, 1989). The mean moisture and organic matter values from each 

fence were used to convert the field weights to a dry mass of mineral sediment. Annual 
25

sediment production was the dry mass of mineral sediment divided by the contributing 

area. 

Hillslope characteristics were measured and related to sediment production (Table 

2.2). The drainage area for each hillslope was determined by walking and flagging the 

perimeter and then recording these points with a GPS and downloading these data into 

ArcMap. The axis and sideslope gradients were measured with a clinometer and the axis 

length was measured with a cloth tape. The dominant soil type was determined by 

digging a hole up to approximately one meter deep to observe whether there was the 

distinctive red-colored B horizon of a Holland soil. Soil type was grouped into either 

Holland or other. Other soil types included the Shaver, Tollhouse, and Chawanakee 

series (USDA, 1983).

The thickness of the O horizon was measured at three evenly-spaced locations 

along each of three evenly-spaced lateral transects. Percent cover was determined by 

classifying the surface at a minimum of 100 systematically-spaced points along the three 

transects using the categories listed in Table 2.2. 

Sediment production was measured for ten hillslopes in José Basin in WY2008 

and WY2009 (Table 2.3). Three hillslopes were in Holland soil and seven hillslopes 

were in other soil types. Sediment production also was measured from 9-10 hillslopes in 

the Providence Creek watersheds and 6-8 hillslopes in the Bull Creek watersheds in 

WY2008 and WY2009 (Table 2.4). 
26

2.4.4. Road sediment production

Sediment production from native surface road segments with a well-defined 

drainage area and a single outlet was measured using sediment fences (Robichaud and 

Brown, 2002) (Figure 2.6). When necessary, additional fences were constructed directly 

downslope of the original fence to increase storage capacity and catch efficiency. The 

sediment production rates were calculated in the same manner as described for the 

hillslopes, assuming that all the sediment was derived from the road. 

Sediment fences in the Providence and Bull Creek watersheds were installed by 

Colorado State University students prior to the current study, and annual sediment 

production rates for road segments in the Providence Creek watersheds were measured 

for WY2008 and WY2009 (Table 2.4). In José Basin road sediment production was 

measured from 5-12 segments in other soil types and 8-18 segments in Holland soil in 

WY2008 and WY2009 (Table 2.3). More than half of the sediment fences in José Basin 

overtopped in WY2008, and sediment production from overtopped fences were not 

included in the sample sizes or the mean sediment production rates.

2.4.5. Road segment characteristics

Key characteristics were measured or classified for each road segment with a 

sediment fence (Table 2.5). The length of each segment was measured with a meter 

wheel. The active width is the width of the road that is regularly driven on, while the 

total width is the width from the bottom of the cutslope to the top of the fillslope. Road 

segment area was the segment length times the active width. Segment slope was 
27

measured with a clinometer for each change of slope within the segment, and the segment 

slope was the length-weighted slope. 

The percent surface cover was determined by classifying the surface at a 

minimum of 100 systematically spaced points sampled along a zigzag transect on the 

active road surface. Each point was classified as bare soil, gravel (defined as rock with a 

secondary axis greater than 1.0 cm), litter, or live vegetation. Native surface segments 

were defined by having less than 20% gravel cover.

Traffic levels were estimated by determining the branch order of the road relative 

to a main road. The traffic level of each segment was classified as very low, indicating 

that vehicles very rarely travelled on the road, low, medium, or high. Drain types and 

drain features were classified following the categories in Table 2.6. The elevation and 

location of the drainage point of each segment was determined using a GPS unit. The 

soil type of the segment was determined for each segment in José Basin by using soil 

maps and verifying the classification in the field. Soil types were grouped into either 

Holland or other, which included the Shaver, Tollhouse, and Chawanakee series (USDA, 

1983). Road segment characteristics in the Providence and Bull Creek watersheds were 

measured by A. Korte (in preparation) prior to this study, though road surface cover was 

re-measured in summer 2009.

2.4.6. Road surveys

Detailed road surveys were conducted on 10.9 km of roads in José Basin between 

2007 and 2009 to: 1) determine how well the fenced segments represented the road 

network in José Basin; and 2) estimate total annual sediment production and delivery 
28

from native surface roads in José Basin. The detailed surveys measured or estimated the 

same characteristics as were observed on road segments with sediment fences (Table 

2.5), with the exception that the percent bare soil and gravel on the surface of the road 

were estimated in the surveys rather than determined with cover counts. The sections to 

be surveyed in José Basin were identified by breaking the road network into 269 sections 

that were 300 to 900 m long using ArcGIS, and selecting 20% of the road sections using 

a random number generator (Figure 2.7). The selected sections were surveyed unless 

they were paved or not accessible as they were on private land holdings. Surveys were 

conducted on all of the road segments in the Providence Creek and Bull Creek 

watersheds by A. Korte (in preparation) prior to the current study. 

2.4.7. Road sediment delivery

The potential for runoff and sediment to be delivered to the stream network for 

each monitored and surveyed road segment was evaluated by identifying and following 

any sediment plume or drainage rill, hereafter referred to as drainage features (Coe, 

2006). The length and slope of each drainage feature was measured (Table 2.5). The 

roughness of the drainage pathway was classified from one to four, with class one being 

very smooth pathways and class four paths having some combination of live vegetation, 

large woody debris, or larger litter accumulations, such as pine cones, to disrupt the flow 

and effectively trap the runoff and sediment. 

The presence or absence of pushouts at the drainage point of the road segment 

was recorded (Table 2.5). Pushouts were classified as no longer intact either if they were 

filled with too much deposition for the water to continue to drain at that point, or the road 
29

drainage was no longer directed to the pushout. The presence or absence of large, round 

rocks used as armoring at the drainage point or a small channel over the road was also 

recorded. This drain armoring was classified as intact if it remained in the correct 

location to slow flow and trap sediment, and it also was noted whether the armoring was 

buried under sediment. The locations of culverts were noted, and the percent of the 

culvert that was plugged with sediment or large woody debris was estimated. The 

presence and volume of scour at the downstream end of each culvert was measured. 

Each road segment was also put in a connectivity class according to the drainage 

feature length and whether it extended to within 10 m of a stream (Table 2.7). Segments 

with a connectivity class of one have very little potential to deliver runoff and sediment 

to a stream channel, while segments with a connectivity class of four have a high delivery 

potential. 

2.4.8. Comparison to WEPP:Road

The measured sediment production values for the native surface road segments in 

José Basin in WY2009 were compared to the values predicted by WEPP:Road (n = 43). 

The northing, westing, and elevation for each fence as demarcated by a GPS unit were 

entered into the PRISM model for calculating the mean monthly rainfall for each native 

surface segment with a sediment fence. Segments on Holland soil were classified as clay 

loam, while segments on other soil types were classified as loam. The road surface for 

each segment was classified as native. Percent rock was calculated from the cover counts 

conducted on each monitored segment, and the road gradient, length, and width were all 

measured in the field. Insloped segments and segments that were a mixture of insloped 
30

and planar were classified as ―insloped with a bare ditch‖. Outsloped segments with 

berms and planar segments were classified as ―outslope, rutted‖ since these segments 

generally had at least some wheel ruts. . Low and medium traffic levels were set as low, 

while very low traffic levels were set as none. The length of the simulated climate was 

set to one year. WEPP:Road was validated by comparing predicted rates to measured 

values.

2.4.9. Statistical analysis

The main dependent variable was the annual sediment production rate from 

hillslopes and native surface road segments (kg m-2yr

-1

). Pairwise comparisons of 

hillslope and road segment sediment production rates for WY2008 and WY2009 were 

made between each of the study areas: José Basin, the Providence Creek watersheds, and 

the Bull Creek watersheds. The effect of soil type on hillslope and road sediment 

production in José Basin also was evaluated by pairwise comparisons between Holland 

and other soil types for WY2008 and WY2009. The validity of each comparison was 

assessed by comparing other key variables (e.g., slope, area, percent bare soil) between 

groups. 

ANOVA tables and regressions were used to assess the relationships between 

each independent variable and the measured sediment production rates from native 

surface road segments in José Basin from WY2008 and WY2009. A multivariate linear 

regression model to predict sediment production from native surface road segments in 

José Basin was constructed using a backward elimination procedure and a selection 
31

criteria of α = 0.10. The multivariate model was evaluated by comparing predicted 

sediment production rates to measured values. 

2.5. Results

2.5.1. Precipitation

José Basin

Mean annual precipitation for the past 95 years at the Auberry rain gage is 611 

mm (California Department of Water Resources, 2010). In WY2008 the annual 

precipitation at Auberry was only 458 mm or 75% of the mean. Mean precipitation for 

the four functioning rain gages in José Basin in WY2008 was 519 mm (standard 

deviation (s.d.) = 50 mm), or approximately 60 mm more than at Auberry (Figure 2.8). 

Annual precipitation was not significantly correlated with elevation in José Basin for 

WY2008 (R2= 0.03, p = 0.84). The mean erosivity of the four gages in WY2008 was 

630 MJ ha-1 mm hr-1(s.d. = 90 MJ ha-1 mm hr-1).

In WY2009 the annual precipitation at Auberry was 526 mm, or 86% of the mean. 

Mean precipitation for the three functioning rain gages in José Basin was 554 mm, which 

was 35 mm more than at Auberry, but the values in José Basin were more variable than in 

WY2008 as the standard deviation was 139 mm. Again the measured precipitation in 

José Basin was not significantly correlated with elevation (R2= 0.81, p = 0.29). The 

mean erosivity in WY2009 was 390 MJ ha-1 mm hr-1(s.d. = 210 MJ ha-1 mm hr-1), or 

38% less than the value in WY2008. There was no significant difference in annual 

precipitation between WY2008 and WY2009 (p = 0.66), but annual erosivity in WY2008 

was significantly lower than the WY2009 value (p = 0.09). 
32

Providence Creek and Bull Creek watersheds, KREW

Precipitation in the KREW watersheds falls largely as snow, although there can 

be summer rain storms as well as rain-on-snow events. The mean annual precipitation 

for the four KREW stations is 1240 mm per year (Korte and MacDonald, 2007), or more 

than double the mean value for the Auberry station. In WY2008 the Providence Creek 

watersheds received 83% of the mean annual precipitation, as compared to annual 

precipitation measuring 75% of the mean value at Auberry. Total precipitation was only 

913 mm at the lowest gage, while the other three gages all had very similar totals of 1116 

to 1148 mm, regardless of elevation (Figure 2.9). Annual precipitation was assumed to 

be directly correlated with elevation in both the Providence Creek and the Bull Creek 

watersheds in WY2008.

In WY2009 the mean precipitation at the Providence Creek rain gages was 962 

mm (s.d. = 6 mm), or 78% of the mean annual precipitation for KREW (Figure 2.9). 

Precipitation at the upper Bull Creek rain gage was 1081 mm, which was only 12% more 

than the mean precipitation in the Providence Creek watersheds. Again, a direct 

correlation was assumed between annual precipitation and elevation in the Providence 

Creek watersheds. However, the lower Bull Creek precipitation gage did not collect 

sufficient data due to equipment malfunctions, and so it was assumed that all sediment 

fences in the Bull Creek watersheds received the same precipitation as the Upper Bull 

Creek rain gage. 
33

2.5.2. Hillslope characteristics and sediment production 

José Basin

The mean contributing area of the ten hillslopes with sediment fences in José 

Basin was 0.42 ha, but the standard deviation was relatively large at 0.32 ha (Table 2.8, 

Appendix A). The mean elevation of the ten sediment fences was 1100 m (s.d. = 107 m), 

and values ranged from 947 m to 1225 m. The hillslope surface areas were typically well 

covered, as litter covered more than half of the ground surface (mean = 56%, s.d. = 11%), 

while live vegetation averaged 25% (s.d. = 12%) and woody debris averaged 13% (s.d. = 

7%). Percent bare soil and rock accounted for only 4% and 2% of the surface on average, 

respectively. Seven hillslopes were classified as other soil types and only three hillslopes 

were in Holland soil. Hillslopes in Holland soils and other soil types were not 

significantly different in area, slope, or surface cover. 

Mean hillslope sediment production in José Basin was 7.4 x 10-3kg m-2(s.d. = 2.1 

x 10-2kg m-2) in WY2008 (Table 2.8). The mean sediment production rate for the three 

hillslopes in Holland soil was only 6.7 x 10-5kg m-2(s.d. = 9.4 x 10-5kg m-2), or more 

than three orders of magnitude lower than the mean rate for other soil types (1.1 x 10-2kg 

m

-2

, s.d. = 2.5 x 10-2kg m-2) (Appendix A). The latter value was highly skewed by the 

sediment production rate for one hillslope, JHS10, which was an order of magnitude 

higher than any other hillslope. The relatively high variability and small number of 

hillslopes on Holland soil meant that there was no significant difference in hillslope 

sediment production rates with soil type (p = 0.50). In WY2009 no sediment was 

produced from any of the hillslopes in José Basin, which exemplifies the large potential 
34

interannual variability of hillslope sediment production as well as the typically low 

erosion rates found in forests with high percent surface cover. 

Providence Creek and Bull Creek watersheds, KREW

The mean elevation of the hillslope sediment fences in the Providence Creek 

watersheds was 1915 m (s.d. = 54 m) (Appendix B), or 815 m higher than the mean 

elevation of the hillslope fences in José Basin, while the hillslope sediment fences in the 

Bull Creek watersheds had a mean elevation of 2320 m (s.d. = 131 m) (Appendix C). 

The mean area of the monitored hillslopes in the Providence Creek watersheds was 0.55 

ha (s.d. = 0.37 ha), which was only slightly larger than the mean area for hillslopes in 

José Basin. However, the mean area for the monitored hillslopes in the Bull Creek 

watersheds was nearly four times the mean value for the Providence Creek hillslopes (p <

0.0001). 

In WY2008 the mean sediment production rate for the ten hillslopes in the 

Providence Creek watershed was 7.9 x 10-4kg m-2(s.d. = 1.0 x 10-3kg m-2) (Appendix 

B), which was an order of magnitude lower than the mean value in José Basin. The mean 

sediment production rate for the four hillslopes in the Bull Creek watersheds was 58% of 

the value from the Providence Creek watersheds, but this difference was not significant 

(p = 0.43) (Appendix C). There was no significant difference in hillslope sediment 

production between José Basin and either the Providence Creek or the Bull Creek 

watersheds in WY2008 (p ≥ 0.33). 

In WY2009 the mean hillslope sediment production rate in the Providence Creek 

watersheds was 7.0 x 10-6kg m-2(s.d. = 2.2 x 10-5kg m

-2

), which was two orders of 
35

magnitude lower than the value the previous year. The mean value in the Bull Creek 

watersheds was 54 times the mean value for the Providence Creek watersheds, but this 

difference was not significant (p = 0.23) (Table 2.8). The high mean value for the Bull 

Creek hillslopes was largely due to one hillslope, BH1, which produced 2.5 x 10-3kg m-2, 

and was one of only two hillslopes in the Bull Creek watersheds that produced sediment 

in WY2009. Similarly to WY2008, there was no significant difference in sediment 

production between hillslopes in José Basin and hillslopes in either the Providence Creek 

or the Bull Creek watersheds in WY2009 (p ≥ 0.22). 

2.5.3. Road segment characteristics and sediment production

José Basin

Native surface roads accounted for 7.2 km or 66% of the surveyed road length. 

The mean length of the 133 native surface segments was 82 m, but this varied widely 

with a standard deviation of 124 m. The median value of 51 m is perhaps a better 

representation of the native surface segments in José Basin, as the mean value was 

skewed by the longest segment, which was 1.2 kilometers long. When weighted by 

length, the mean width of the native surface roads in José Basin was 2.5 m (s.d. = 0.5 m). 

The mean length-weighted slope was 8% (s.d. = 4%). Seventy-six percent of the 

segments were planar, and 21% were a combination of planar, outsloped with a berm, 

and insloped. The remaining segments were outsloped with a berm. The majority of the 

segments (65%) had either waterbars or dips as the main drainage feature, and none of 

the segments had diffuse drainage. Three of the native surface segments had stream 

crossings across road surface. Twenty-nine percent of the native surface road length had 
36

fillslope erosion at the drainage point. Of the 10.8 km, 1.4 km did not have any 

waterbars or dips as part of their drainage system. Of the remaining 9.4 km, 51% of the 

road length had effective waterbars or dips, while the remaining 49% had ineffective 

waterbars or dips. There were a total of 77 ineffective bars or dips on the 10.8 km of 

road, for a total of seven ineffective bars or dips per kilometer of native surface road.

Segments were mostly bare, as the mean surface cover due to gravel, litter, or 

vegetation was only 8% (s.d. = 14%). Forty-one percent of the surveyed road length had 

little to no traffic, while 26% was classified as having low traffic, and 33% was classified 

as having medium traffic. Thirty-eight percent of the surveyed road length was on 

Holland soil.

Rill erosion with a mean depth of at least five centimeters was observed on 45% 

of the native surface segments surveyed in José Basin. The mean segment length of the 

segments without rills was 61 m (s.d. = 50 m), while the value for segments with rills was 

nearly double at 116 m (s.d. = 114 m) (p = 0.004). The total rill length was 2.7 km, for 

an overall rill to road length ratio of 0.38. The mean rill length was 72 m (s.d. = 107 m) 

and the mean rill volume was 5.7 m3(s.d. = 13.7 m3). The mean slope weighted by 

segment length for segments with rills was 10%, while the mean slope for segments 

without rills was only 4% (p < 0.0001). 

The mean elevation of the 34 native surface road segments with sediment fences 

in José Basin was 1056 m (s.d. = 82 m), and the range was from 913 m to 1254 m. The 

native surface road segments with sediment fences in José Basin had a mean length of 44 

m (s.d. = 16 m), which is 51% of the mean length of the surveyed segments (p = 0.08). 

This significant difference is not surprising given that the segments selected for 
37

monitoring are required to have a discrete top and bottom, and that very few of the 

monitored segments had broken waterbars in comparison to the surveyed segments. 

The mean slope of the native surface segments with sediment fences in José Basin 

was 9% (s.d. = 3%), and the range was from 2% to 16%. The mean value of 9% is 

significantly higher than the mean slope of the surveyed segments (p < 0.0001). The 

much larger area but lower slope of the surveyed segments resulted in a mean area*slope 

factor that was only 17% larger than the segments with sediment fences (p = 0.55). The 

segments with sediment fences in José Basin averaged 30% (s.d. = 15%) surface cover or 

70% bare soil, and this was significantly less bare soil than the surveyed segments (p < 

0.0001). Only 5% of the monitored segments had very little to no traffic, while 52% 

were characterized as having a low amount of traffic. The remaining 43% had a medium 

traffic level.

In WY2008 the mean sediment production rate for the 12 native surface road 

segments in José Basin was 1.4 kg m-2(s.d. = 2.3 kg m-2) (Figure 2.10). Production rates 

varied widely, with the lowest rate occurring on JNO6 (0.042 kg m-2) and the highest on 

JBT14 (7.9 kg m-2). Relatively few segments produced the majority of the sediment, 

with 25% of the road length monitored producing 75% of the sediment (Figure 2.11).

In WY2009 the mean sediment production rate for the 29 native surface road 

segments in José Basin increased by 50% to 2.1 kg m-2(s.d. = 3.1 kg m-2) (Figure 2.10). 

Sediment production values varied by even more than in WY2008, as rates ranged from 

0.0050 to 12.9 kg m-2. This high variability helps explain why sediment production from 

native surface road segments was not significantly different between WY2008 and 

WY2009 despite the 50% increase (p = 0.51) (Figure 2.10). As in WY2009, relatively 
38

few segments produced large amounts of sediment in WY2009, with 25% of the road 

length monitored producing 75% of the sediment (Figure 2.11).

Stratification of the data by soil type showed that there were 21 road segments 

with sediment fences in Holland soil and 12 road segments in other soil types. The mean 

elevation of the Holland segments with sediment fences was 1109 m (s.d. = 66 m), while 

the mean value for the segments in other soil was 982 m (s.d. = 52 m) (p < 0.0001). 

However, elevation within José Basin was not significantly correlated to sediment 

production (p = 0.92). The mean length and area of segments were similar for both soil 

types, while the mean slope of the segments in Holland soil was 10% (s.d. = 3%) as 

compared to the mean value of 8% (s.d. = 3%) for the segments in other soil, and this 

difference was nearly significant (p = 0.11). The segments in Holland soil averaged 65% 

bare soil, which was significantly less than the mean of 79% for the segments in other 

soil types (p = 0.0008). 

In WY2008 the mean sediment production rate for the five native surface 

segments in other soil types was 0.5 kg m-2(s.d. = 0.7 kg m-2) (Figure 2.12). Mean 

sediment production for the eight road segments in Holland soil averaged 1.9 kg m-2, or 

nearly four times higher, but the standard deviation of 2.7 kg m-2 was 42% larger than the 

mean (Appendix D). The small sample sizes and high variability meant that road 

sediment production did not significantly differ by soil type for WY2008 (p = 0.28). 

In WY2009 the mean sediment production rate for the 12 native surface segments 

in other soil types was 2.7 kg m-2(s.d. = 4.1 kg m-2), which was 5.4 times higher than in 

WY2008 (p = 0.25) (Figure 2.12). Almost half of this increase is due to JNO3, which 

produced 12.9 kg m-2in WY2009. If this segment is excluded, the mean sediment 
39

production rate drops to 1.7 kg m-2(s.d. = 2.4 kg m-2), although this is still 3.4 times 

higher than the mean value from WY2008. The mean sediment production rate for the 18 

road segments in Holland soil was 1.6 kg m-2yr-1, which was 16% lower than WY2008 

(Figure 2.12). The explanation for the surprising contrast between the increase in 

sediment production from WY2008 to WY2009 for segments in other soil types as 

compared to the decrease in values for segments in Holland soil is unknown. As in 

WY2008, road sediment production in WY2009 was not significantly different by soil 

type (p = 0.32). 

For the native surface segments in José Basin, sediment production was 

significantly correlated with segment slope (R2= 0.11; p = 0.03) (Figure 2.13). When 

sediment production was normalized by segment slope to account for the significantly 

steeper segments in Holland soil than in other soil types, the road segments on Holland 

soil still did not produce significantly more sediment than the road segments on other soil 

types for WY2008 or WY2009 (p = 0.24 and p = 0.21, respectively).

Providence Creek and Bull Creek watersheds, KREW

In the Providence Creek watersheds, the mean elevation of the six native surface 

road segments was 1859 (s.d. = 85 m), which is 800 m higher than the mean elevation of 

the native surface segments in José Basin. The mean area and slope of the segments with 

sediment fences in the Providence Creek watersheds generally were similar to the mean 

values in José Basin (Table 2.9). The main difference was that the native surface 

segments in the Providence Creek watersheds averaged only 48% bare soil (s.d. = 17%) 
40

as compared to 70% in José Basin (p < 0.0001). The remaining 52% was comprised of 

35% litter (s.d. = 22%), 10% gravel (s.d. = 10%), and 7% live vegetation (s.d. = 6%). 

In WY2008 the mean sediment production rate for the six native surface road 

segments in the Providence Creek watersheds was 0.12 kg m-2(s.d. = 0.14 kg m-2) 

(Figure 2.10; Appendix E), and ranged over an order of magnitude from 0.01 to 0.4 kg 

m

-2

. The mean rate was an order of magnitude lower than mean rate from native surface 

segments in José Basin, but the mean rates were not significantly different (p = 0.22) due 

to the high variability between segments. 

The mean value of 0.14 kg m-2(s.d. = 0.12 kg m-2) in WY2009 was very similar 

to the previous year (Figure 2.10). Similar to WY2008, the mean value in the Providence 

Creek watersheds was only 7% of the mean rate in José Basin. However, again due to 

high variability, there was no significant difference between values in the Providence 

Creek watersheds and José Basin (p = 0.14).

In the Bull Creek watersheds, the mean elevation of the nine native surface road 

segments was 2292 m (s.d. = 62 m), 433 m higher than the mean elevation in the 

Providence Creek watersheds. The mean length was 57 m (s.d. = 25 m), and this was 

significantly longer than the mean segment length in José Basin (p = 0.01) and nearly 

significantly longer than the mean segment length in the Providence Creek watersheds (p 

= 0.12). Mean segment slope in the Bull Creek watersheds was 9% (s.d. = 3%), which is 

similar to the values in both José Basin and the Providence Creek watersheds. Percent 

bare soil for the native surface segments in the Bull Creek watersheds averaged 53% (s.d. 

= 21%), which was similar to the mean value in the Providence Creek watersheds. 

However, the mean gravel cover of 7% (s.d. = 5%) was significantly more than the mean 
41

value of 2% in the Providence Creek watersheds (s.d. = 1%) (p = 0.001) and nearly 

significantly more than the mean gravel cover of 4% in José Basin (s.d. = 8%) (p = 0.11).

The mean road sediment production rate in the Bull Creek watersheds was 0.042 

kg m-2(s.d. = 0.067 kg m-2) in WY2008 (Appendix F), or 35% of the mean value from 

the Providence Creek watersheds and only 3% of the mean value from José Basin. The 

differences between road sediment production in the Bull Creek watersheds and the 

Providence Creek watersheds and José Basin were nearly significant in WY2008 at p = 

0.19 and p = 0.11, respectively. 

In WY2009 the mean sediment production rate for native surface road segments 

in the Bull Creek watersheds was 0.23 kg m-2(s.d. = 0.27 kg m-2), which was 5.5 times 

the value from WY2008; this increase was nearly identical to the increase for the 

hillslope sediment fences in the Bull Creek watersheds in WY2009. Unlike the previous 

year, road sediment production in the Bull Creek watersheds in WY2009 was 38% 

greater than in the Providence Creek watersheds, though this difference was not 

significant (p = 0.48). The mean road sediment production of 0.23 kg m2in the Bull 

Creek watersheds was only 9% of the mean value for José Basin, and this difference was 

significant (p = 0.09). 

2.5.4. Road sediment delivery

José Basin

Forty-five percent of the 7.2 km of surveyed native surface road length or 42% of 

the segments had no visible drainage feature (Figure 2.14). Sediment plumes accounted 

for the majority of the drainage features, although occasionally there was a drainage rill. 
42

Drainage features tended to be relatively short, as only seven of the 57 segments, or 16% 

of the road length, had drainage features greater than 20 m long. The longest drainage 

feature in José Basin was 105 m long, and this came from a 246 m long segment. 

Forty-six percent of the native surface road length in José Basin had a 

connectivity class of one, while 30% of the road length was directly connected to the 

stream network (Figure 2.15). The relatively high connectivity given the average plume 

length of only 16 m can be explained by the proximity of many roads to the stream 

channel. Of the 14 surveyed segments that were connected to a stream, seven segments 

or 500 m of road had plume lengths of zero meters, as the discharge points were directly 

into a stream.

The effect of soil type on sediment delivery was evaluated from the detailed data 

for 38 road segments prior to installing sediment fences. Thirteen of these segments were 

in other soil types, and 25 were on Holland soil. Twelve of the 13 segments in other soil 

types had a drainage feature, and the mean drainage feature length was 25 m (s.d. = 19 m) 

with a range of three to 60 m. Thirty percent of the road length on other soil types had a 

connectivity class of one, while 28% of the road length was connected to the stream 

(Figure 2.16).

Similarly to the segments in other soil types, only two of the 25 segments in 

Holland soil had no visible drainage features. Also similarly to segments in other soil 

types, the mean drainage feature length for segments in Holland soil was 27 m (s.d. = 17 

m) and values ranged from six to 65 m. The similarities in plume length between 

segments in other soil types and segments in Holland soil indicate that native surface 

segments on Holland soil are no more likely to have a longer drainage feature than 
43

segments in other soil types. However, the percent of connected road length on Holland 

soil was 18%, which was slightly lower than the value for other soil types (Figure 2.16). 

This 10% difference is likely due to a higher proximity of other soil types to stream 

channels than Holland soils. 

Providence Creek watersheds

In the Providence Creek watersheds, 27% of the 7.8 km of native surface road 

length had no visible drainage feature, and this is lower than the value of 45% for native 

surface segments in José Basin (Figure 2.14). However, only 3% of the native surface 

road length in the Providence Creek watersheds was directly connected to the stream 

network, which is only a tenth of the value for José Basin (Figure 2.15).

2.5.5. Modeling road sediment production and delivery in José Basin.

2.5.5.1. Predicting sediment production from native surface segments in José Basin

The univariate analysis showed that sediment production was significantly and 

positively correlated with segment slope, the length of rills on the segment, and the 

volume of rills on the segment (Table 2.10). Rill length was the most significant variable 

(p = 0.0004) and explained 39% of the variability in annual road sediment production. 

The empirical multivariate model constructed using the survey data to predict 

sediment production from the native surface road segments in José Basin included rill 

length (R in m), area (A in m2), percent Holland B horizon on the surface of the road 

segment (B), and annual precipitation (P in mm): 

 SP = 0.010 + 0.11*R – 0.016*A – 0.029*B + 0.0056*P (equation 2.2)
44

where SP equals the sediment production rate in kg m-2yr-1(R = 0.59) (Table 2.11). The 

model tended to over-estimate the lower sediment production rates and under-estimate

the higher sediment production rates (Figure 2.17). The predicted sediment production 

rates from the multivariate model again confirm that relatively few segments typically 

produce a large amount of sediment, as only 12% of the segments were predicted to have 

sediment production rates greater than 4 kg m-2yr-1. The variables included did make 

physical sense except that sediment production decreased with increasing segment area. 

Equation 2.2 could not be used to predict road sediment production for all the 

surveyed road segments because the surveys did not attempt to estimate the percent of 

Holland B horizon on the road surface. The simplified equation used to predict road 

sediment production from the surveyed native surface segments was:

 SP = 0.010 – 0.016*A + 0.0056*P + 0.11*R (equation 2.3),

which has an R2of 0.49.

2.5.5.2. Total potential sediment produced and delivered from native surface segments in 

José Basin

The road survey showed that 42% of the 159 km of roads in José Basin were 

native surface, 18% were gravel surface, and 41% were paved. Mean annual 

precipitation for the seven gage-years of data in José Basin was 534 mm. Using the 

characteristics measured in the random survey and equation 2.3, the predicted mean 

sediment production rate for the 11 km of surveyed native surface roads in José Basin 

was 1.8 kg m-2yr-1. Given that there are an estimated 67 km of native surface roads in 
45

José Basin, the estimated total sediment production is approximately 680 metric tons per 

water year, or 10 metric tons per kilometer of road length. 

The road survey showed that 30% of the native surface road length in José Basin 

was directly connected to a stream. Multiplying this percentage by the estimated total 

sediment production indicates that up to 210 metric tons of sediment from native surface 

roads are being delivered each year to the stream network in José Basin. 

2.5.5.3. Comparison of WEPP:Road predictions to measured values in José Basin

WEPP:Road poorly predicted sediment production rates for native surface road 

segments in José Basin (R2= 0.03, n = 43) (Figure 2.18). The general tendency was for 

WEPP:Road to under-predict annual sediment production, as the predicted sediment 

production rates were less than half of the measured values for 74% of the data. For 30% 

of the data the predicted sediment production rates were more than an order of magnitude 

lower than the observed values.

2.6. Discussion

2.6.1. Effects of climate on sediment production

The comparison of data between study sites provides a unique opportunity to 

evaluate the effect of elevation and climate on hillslope and road sediment production. 

There were no significant differences between hillslope sediment production rates in José 

Basin, the Providence Creek watersheds, or the Bull Creek watersheds in WY2008, and 

in WY2009 the highest elevation Bull Creek hillslopes produced the most sediment. The 

dense cover of vegetation and duff on the hillslopes protects the surface from rainsplash 
46

erosion and increases infiltration, reducing erosive overland flow. The ability of ground 

cover to minimize surface erosion rates applies whether the surface is in a rain or snow 

dominated area. 

Roads are more susceptible to rainsplash detachment and erosive overland flow, 

and therefore have much higher sediment production rates than hillslopes. The lack of 

cover on a native road surface also makes the surface more susceptible to an increase in 

erosion with an increase in the ratio of rain to snow. Areas with much higher annual 

precipitation and annual erosivities generally have much higher road sediment production 

rates. On the Olympic Peninsula mean annual precipitation is 6.4 times the value in José 

Basin, and the mean sediment production rate was 41 Mg km-1yr

-1

, or four times the 

mean rate in José Basin (Table 2.12). The mean annual precipitation on St. John in the 

U.S. Virgin Islands is 1.5 to 2.3 times the value in José Basin, while road sediment 

production rates were 5-15 kg-2m

-2

yr

-1

(Ramos-Scharrón and MacDonald, 2005) or 2.8 

to 8.3 times the mean rate in José Basin (Table 2.12). The much higher erosion rates on 

St. John can be attributed to the annual erosivity on St. John being approximately 25 

times higher than in José Basin (Ramos-Scharrón and MacDonald, 2005), and this 

indicates the potentially greater usefulness of erosivity for predicting erosion than total 

precipitation. 

In northwestern California, the Jackson Demonstration State Forest receives 

approximately 1400 mm yr-1of precipitation, which is twice the value for José Basin, but 

the annual erosivities are not as different (Renard et al., 1997). As the road sediment 

production rates of 0.5 to 4 kg m-2yr-1(Barrett and Tomberlin, 2006) were similar to 
47

values in José Basin, and this again indicates the greater utility of erosivity relative to 

total precipitation. 

In the Sierra, like many areas, an increase in elevation typically increases the 

amount of snow relative to rain. This decreases the erosivity, as snowfall has minimal 

erosive energy, precipitation intensities are lower, and snowmelt rates are low in 

comparison to rainfall intensities, resulting in less overland flow. Hence road sediment 

production rates are typically lower in areas with snow or mixed snow-and-rain. Mean 

annual precipitation in the Providence Creek watersheds in WY2008 and WY2009 was 

approximately twice the value in José Basin, but due to the preponderance of snow, the 

annual erosivity was much lower. This explains why the mean sediment production rate 

in the Providence Creek watersheds for native surface roads was 0.13 kg m-2 yr

-1

(s.d. = 

0.13 kg m-2yr

-1

), or just 7% of the mean value in José Basin. 

In the higher elevation Bull Creek watersheds the mean road sediment production 

rate in WY2008 was 35% of the value from the Providence Creek watersheds, while in 

WY2009 the mean road sediment production rate in the Bull Creek watersheds was 1.6 

times the value in the Providence Creek watersheds. The higher sediment production in 

the Bull Creek watersheds in WY2009 can be attributed to a relatively rare localized 

summer rainstorm, which can drastically increase the annual erosivity. 

Road sediment production rates in the Eldorado National Forest (ENF) (Figure 

2.1), which has a mixed rain-on-snow climate, provide further insight into the role of 

elevation and climate on road sediment production. On the ENF annual precipitation was 

2.5 times higher than in José Basin, but the study area was snow dominated and the mean 

road sediment production rate of 0.22 to 0.81 kg m-2yr-1(Coe, 2006) was only 12-45% of 
48

the mean value from José Basin. Similarly, annual precipitation in the Idaho batholith is 

approximately 720 mm, with 60% falling as snow, and the mean sediment production 

rate from native surface road segments was 0.48 kg m-2yr-1(Megahan, 1974). This is 

very similar to the mean value for the ENF but only 27% of the mean value from José 

Basin. The lower road sediment production rates on the ENF and the Idaho batholith can 

be explained by the lower erosivity due to the greater proportion of snow. These 

comparisons to other studies in rain, rain-on-snow, and snow dominated climates suggest 

that road sediment production varies with annual precipitation in rain dominated areas, 

but that annual erosivity is a much better predictor of road erosion rates when the 

precipitation is a mixture of rain and snow. 

The exact effect of potential global climate change on the amount of precipitation 

in the Southern Sierra is uncertain, but overall global warming is a potential outcome 

(IPCC, 2007). Warmer temperatures will increase the rain to snow ratio in the southern 

Sierra and other mountainous areas. This warming will increase sediment production 

from native surface roads in the KREW watersheds, which will reduce the current 10-fold 

difference in mean sediment production rates between the mixed-climate Providence 

Creek watersheds and the rain dominated José Basin. The potential shift to more rain the 

Providence Creek watersheds also will likely increase sediment delivery by increasing 

the amount of runoff and erosion from native surface road segments. Similar increases 

can be expected in other areas that are at or just above the rain-snow boundary.
49

2.6.2. Assessing and reducing road sediment production in José Basin

A crude estimate of the relative importance of unpaved roads to total sediment 

production in José Basin can be made by comparing the estimated hillslope sediment 

yields to the sediment production and delivery from native surface roads. The mean 

sediment production rate for hillslopes in José Basin was only 0.0037 kg m-2 yr-1(s.d. = 

0.015 kg m-2yr-1). If this rate is multiplied by the area of the basin and 100% 

connectivity is assumed, the background sediment yield is 290 tons yr-1. Road surveys 

and the multivariate road sediment production model predicted that native surface roads 

would generate 680 tons of sediment per year. Since 30% of the native surface road 

length is connected to a stream, native surface segments in José Basin could deliver up to 

210 tons of sediment per year to the stream network. This is 72% of the estimated 

hillslope sediment yield, indicating that road erosion is a major contributor of sediment to 

streams in José Basin, especially since they occupy less than one percent of the land area.

Unpaved roads also have been identified as a major source of sediment in forested 

watersheds in other locations (Reid and Dunne, 1984; Swift, 1988; Bilby et al., 1989; 

Luce and Black, 1999; Ketcheson et al., 1999; Coe, 2006). On St. John, unpaved roads 

delivered more sediment to the streams than all of the natural sources, including bank 

erosion, treethrow, and erosion from undisturbed hillslopes (Ramos-Scharrón and 

MacDonald, 2005). In Australia unsealed roads and logging tracks were identified as the 

most hydrologically active areas within a logged forest, and these are often significant 

sediment sources (Croke and Hairsine, 2006). Because excessive sediment reduces water 

and habitat quality (Bilby et al., 1989; Ziegler and Giambelluca, 1997; Kolka and Smidt, 
50

2004), forest managers need to consider means for reducing road sediment production 

and delivery.

The results presented in this study can help guide best management practices for 

reducing road sediment production and delivery in José Basin. The significant variables 

in the multivariate model for predicting sediment production from native surface road 

segments were rill length (m), annual precipitation (mm), segment area (m2), and the 

percent Holland soil B horizon on the road surface (Table 2.11). The positive

correlations of sediment production with rill length and annual precipitation make 

physical sense, and the former has direct implications for management. However, the 

negative coefficients for segment area and percent Holland soil B horizon merit further

explanation. 

In WY2008 and WY2009 rilled segments respectively produced ten and six times 

more sediment per unit area than unrilled segments when normalized by slope (p < 

0.0001 and p = 0.007) (Figure 2.19). Other studies have shown that surface runoff can 

detach and transport more sediment once it is channeled into a rill (Meyer et al., 1975; 

Loch and Donnellan, 1983; Poesen, 1987). These results indicate that rills are a major 

source of sediment from native surface road segments relative to rainsplash and 

sheetwash erosion. Rilling readily occurs on native surface roads due to the depressions 

caused by tire tracks that concentrate the flow. The recognized management practice to 

reduce rilling and road sediment production is to restrict driving in wet conditions, and 

this study supports this practice. 

An analysis of the segments with rills versus segments without rills also can be 

used to pinpoint where rills are most likely to form, and hence when waterbars or the 
51

application of gravel could help minimize rilling. The mean segment area for rilled 

segments was 130 m2(s.d. = 50 m2) as compared to 100 m2(s.d. = 40 m2) for segments 

without rills. This was significant at p = 0.07, indicating that rills form on longer or 

wider segments. Rilled and unrilled segments were more clearly separated by the product 

of road segment area times segment slope, as the area*slope factor for rilled roads 

averaged 1330 m2m m-1(s.d. = 560 m2m m-1) as compared to only 880 m2m m-1(s.d. = 

560 m2 m m-1) for unrilled segments (p = 0.02). This indicates that larger, steeper 

segments should be broken into smaller segments by installing waterbars when the 

area*slope factor exceeds about 1000 m2m m

-1

. 

Segment slope was a significant continuous variable in the univariate analysis, but 

the R2 was low and slope was not a significant variable in the multivariate model for 

predicting road sediment production. Figure 2.13 suggests a simple categorical 

classification of sediment production versus slope, and Figure 2.20 shows that mean 

sediment production for segments with slopes greater than 7% was an order of magnitude 

higher than for segments with slopes less than 7% (p = 0.18 and 0.06 for WY2008 and 

WY2009, respectively). This indicates that management practices to reduce sediment 

production, such as graveling or installing waterbars, should focus on road segments that 

are steeper than 7%.

The multivariate model predicted that road sediment production in José Basin is 

significantly correlated to annual precipitation (p = 0.06). Other studies also have shown 

that annual precipitation, or more importantly annual erosivity, is a significant variable in 

predicting road sediment production (Ramos-Scharrón and MacDonald, 2005; Coe, 2006; 

Sugden and Woods, 2007; Welsh, 2008; Fu et al., 2010). This study shows that 
52

management practices to reduce road sediment production are much more important in 

rain dominated areas.

The multivariate model predicts a decrease in sediment production with 

increasing segment area, which is counter-intuitive. However, this can be explained by 

the greater potential for sediment deposition on many of the larger segments. For 

segments with areas greater than 150 m2, the mean slope of the bottom ten meters 

averaged 6% (s.d. = 2%) as compared to 8% (s.d. = 3%) for the segments with areas less 

than 100 m2, and this difference was significant at p = 0.04. Road segments with slopes 

less than 7% were already shown to have lower sediment production rates than segments

steeper than 7%. These results indicate that the flatter sections at the ends of the longer 

segments can act as depositional areas, and this can explain the negative correlation 

between segment area and sediment production in the multivariate model. 

The multivariate model also predicts a decrease in sediment production with an 

increasing percent Holland B horizon on the road surface, but this is most likely a 

statistical artifact. As previously described, the Holland B horizon is a highly erodible 

layer, and in theory sediment production should increase with an increase in the percent 

B horizon. However, the univariate analysis did not find any correlation between 

sediment production and the percent B horizon, and there was no significant difference in 

sediment production between roads in Holland soil and roads in other soil types. 

According to the data gathered in this study, there is no clear justification for focusing 

road sediment reduction efforts on Holland soils.

The very large variability in sediment production rates between sites makes it 

inefficient to universally apply management practices to reduce road sediment 
53

production, as just a few segments often account for most of the road-related sediment 

being delivered to the stream network. For example, segment JNO3 in José Basin had a 

sediment production rate of 12.9 kg m2yr-1in WY2009, which was nearly an order of 

magnitude more than any of the other segments in either water year. JNO3 had an 

extensive rill system, with 53 m of rills on a 35 m long segment, giving it a higher rill 

density than any other segment, and it had a moderate to high delivery potential. A best 

management practice to reduce sediment contributions from native surface road segments 

should begin with pinpointing the ―trouble‖ segments and road sections that are apt to 

deliver the most sediment to the stream network. The data collected in this thesis indicate 

that management efforts should focus on those segments with extensive rill erosion, 

segments with area*slope factors greater than 1000 m2m m

-1

, and segments with slopes 

greater than 7%. Sediment production on these segments can be reduced through 

graveling or paving as examined in the next chapter. Sediment delivery can be reduced 

by installing waterbars that direct flow away from streams, which also will be examined 

in more detail in the following chapter. 

2.7. Conclusions

This project monitored hillslope and road sediment production in the low 

elevation José Basin (800-1200 m), the mid-elevation Providence Creek watersheds 

(1485-2005 m), and the upper elevation Bull Creek watersheds (2050-2420 m) in the 

Sierra National Forest, California in WY2008 and WY2009. The mean hillslope 

sediment production rate in José Basin in WY2008 was 7.4 x 10-3 kg m-2. While 

sediment production rates for hillslopes in the Providence Creek and Bull Creek 
54

watersheds were at least an order of magnitude less than values from José Basin in 

WY2008, there was no significant difference in values between the three areas. In 

WY2009 none of the hillslopes in José Basin produced any sediment, and rates in the 

Bull Creek watersheds were higher than values in the Providence Creek watersheds. 

According to these data, sediment production from hillslopes was not significantly higher 

in rain dominated areas than snow dominated areas, and this can be attributed to the 

dense cover of vegetation and litter protecting the hillslope from rainsplash and erosive 

overland flow. 

The mean road sediment production rate in José Basin was 1.8 kg m-2yr

-1

, with 

values from individual segments ranging from zero to 12.9 kg m-2yr

-1

. There was no 

significant difference in road sediment production between hillslopes and road segments 

in Holland soils and in other soil types. Thirty percent of the native surface road length 

in José Basin was directly connected to the stream network. 

While WEPP:Road performed poorly in predicting sediment production from 

native surface roads in José Basin, an empirical multivariate model predicted road 

sediment production to increase with increasing in annual precipitation and total rill 

length on the road surface, and decrease with an increase in road segment area. Using 

this model, native surface roads in José Basin are estimated to produce 680 tons yr-1of 

sediment, and up to 210 tons yr-1are delivered to the stream network. In contrast, 

hillslopes, which occupy orders of magnitude more area than roads, are estimated to 

contribute 290 tons yr-1. This indicates that native surface roads are a major contributor 

of sediment in José Basin. 
55

Mean road sediment production in the Providence Creek watersheds was 0.13 kg 

m

-2

yr-1, which was more than an order of magnitude lower than in José Basin. Only 3% 

of the road length was connected to a stream, so road sediment delivery to streams is very 

low. Mean road sediment production in the Bull Creek watersheds was similar to the 

values from the Providence Creek watersheds. The results show that road sediment 

production is much higher in rain dominated areas than in snow dominated areas, as the 

bare surface subjected to rainsplash and higher rates of overland flow. Road sediment 

production rates in the Providence Creek watersheds would likely experience a ten-fold 

increase if the dominant precipitation were to switch from snow to rain.

Road sediment production was proportional to the total length of rills on a 

segment, indicating the importance of rilling for road sediment production. An important 

management implication is to restrict driving during wet conditions to reduce tire 

depressions, which in turn can reduce rilling and sediment production. Rilling was more 

extensive on longer, steeper segments, and erosion control efforts and best management 

practices should target these segments. Practices that aim to reduce sediment production 

and delivery such as graveling, paving, grading, and installing waterbars are examined in 

the following chapter. 
56

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61

2.9. Tables

Table 2.1. Elevations and annual precipitation for WY2008 and WY2009 for the four 

climate stations in the KREW watersheds. There are no data for the lower Bull Creek 

rain gage in WY2009.

Annual precipitation 

(mm)

Climate station Elevation (m) WY2008 WY2009

Lower Providence 1749 913 966

Upper Providence 1984 1148 958

Lower Bull 2194 1116 -- --

Upper Bull 2463 1133 1081

Mean (s.d.) 2098 (304) 1078 (110) 1002 (69)
62

Table 2.2. Hillslope characteristics and surface cover categories measured for each 

hillslope with a sediment fence in José Basin. The O horizon depth was measured at nine 

systematically-spaced points on each hillslope.

Hillslope characteristics Hillslope surface cover categories

Dominant soil type (Holland, other) Bare soil

Area (m2) Litter

Axis length (m) Woody debris (>1 cm diameter)

Axis gradient (%) Live vegetation

Mean right and left sideslope gradients (%) Rock (>1 cm diameter)

Presence of rills (Y/N) Bedrock

Total rill length (m)

Mean rill width (m)

Mean rill depth (m)

Shortest distance from rill to fence (m)

O horizon depth (m)
63

Table 2.3. Number of hillslopes and native surface road segments with valid sediment 

production data in Holland soil and other soil types in José Basin for WY2008 and 

WY2009.

Hillslopes Native surface road segments

Water year Other soil types Holland soil Other soil types Holland soil

2008 7 3 5 8

2009 7 3 12 18

Totals 14 6 17 26
64

Table 2.4. Number of hillslopes and native surface road segments with valid sediment 

production data in the Providence Creek and Bull Creek watersheds from WY2004 

through WY2009. 

Providence Creek watersheds Bull Creek watersheds

Water 

year Hillslopes

Native surface 

segments Hillslopes

Native surface 

segments

2008 10 6 6 9

2009 10 6 6 9

Totals 59 55 34 45
65

Table 2.5. Road segment characteristics measured, estimated, or observed for each 

segment with a sediment fence and the surveyed road segments. ―/E‖ indicates that the 

characteristic was estimated rather than measured for the segments that were not 

monitored for sediment production.

Characteristic Measured (M), 

estimated (E), or 

observed (O)

Continuous variable 

(C) or categorical 

group (G)

Method of 

measurement

Segment length (m) M C Meter wheel

Surface type (Native, gravel) O G

Active width (m) M C Cloth tape

Total width (m) M C Cloth tape

Segment slope (%) M C Clinometer

Bare soil (%) M / E C Cover count

Gravel cover (%) M / E C Cover count

Traffic level (Very low, low, medium) E G

Evidence of past surface rocking (Y/N) O G

Cutslope height (m) E C

Cutslope gradient (%) M C Clinometer

Cutslope percent bare soil (%) E C

Slope of upper hillslope (%) M C Clinometer

Slope of lower hillslope (%) M C Clinometer

Ditch width (m) M C Cloth tape

Ditch slope (%) M C Clinometer

Maximum rill length (m) M C Cloth tape

Mean rill width (m) M C Ruler

Mean rill depth (m) M C Ruler

Drain type (see Table 2.6) O G

Drain feature (see Table 2.6) O G

Drain armoring (Y/N) O G

Water cross armoring (Y/N) O G

Armoring buried (Y/N) O G

Armoring intact (Y/N) O G

Pushout present (Y/N) O G

Pushout effective (Y/N) O G

Fillslope erosion (Y/N) O G

Maximum fillslope rill depth (m) M C Ruler

Multiple fillslope rills (Y/N) O G

Drainage feature length (m) M C Cloth tape

Drainage feature slope (%) M C Clinometer

Drainage feature roughness (1,2,3,4) O C

Connectivity class (1,2,3,4) O G

Culvert present (Y/N) O G

Culvert plugged (%) E C

Scour at culvert outlet (Y/N) O G

Volume of scour at culvert outlet (m3) M C Cloth tape
66

Table 2.6. Drain type and drain feature categories used to describe each road segment. 

Slashes indicate a mixture of types or features within a road segment. *Sediment 

production was not measured on segments that were either completely or partially 

outsloped or had any diffuse drainage.

Drain types Drain features

Insloped Diffuse*

Outsloped (diffuse)* Dip

Outsloped (with a berm) Pushout

Planar Waterbar

Through cut Stream crossing

Insloped/Planar Cattle guard

Insloped/Outsloped with a berm On segment deposition

Outsloped with a berm/Planar Intersection

Planar/Outsloped* Diffuse/Dip*

Insloped/Outsloped/Planar* Diffuse/Waterbar*

Diffuse/Pushout*

Diffuse/Intersection*

Diffuse/On segment deposition*

Dip/Pushout

Dip/On segment deposition

Intersection/On segment deposition
67

Table 2.7. Definitions of connectivity classes and the associated potential for sediment to 

be delivered to the stream network.

Connectivity Drainage Potential for 

class characteristics sediment delivery

1 Drainage feature <10 m long. Very low

2 Drainage feature <20 m long. Low/moderate

3 Drainage feature >20 m long but more than 

10 m from a stream channel.

Moderate/high

4 Drainage feature to within 10 m of a stream 

channel, regardless of length.

High
68

Table 2.8. Mean elevation, area, and sediment production rates for hillslopes in José Basin and the Providence Creek and Bull 

Creek watersheds for WY2008 and WY2009. None of the monitored hillslopes in José Basin produced sediment in WY2009.

Mean sediment production rate (kg m-2yr

-1

)

Study site Elevation (m) Area (ha) WY2008 WY2009

Mean s.d. Mean s.d. n Mean s.d. n Mean s.d.

José Basin 1100 8104 0.42 0.32 10 7.4 x 10-32.1 x 10-210 0 0

Providence Creek watersheds 1915 54 0.55 0.37 10 7.9 x 10-41.0 x 10-311 7.0 x 10-62.2 x 10-5

Bull Creek watersheds 2320 131 2.08 0.84 4 4.6 x 10-49.1 x 10-47 3.8 x 10-49.5 x 10-4
69

Table 2.9. Mean elevation, area, slope, and sediment production rates for native surface road segments in José Basin and the

Providence Creek and Bull Creek watersheds for WY2008 and WY2009.

Mean sediment production rate 

(kg m-2 yr-1)

Basin or watersheds

Elevation 

(m)

Area 

(m2)

Slope 

(m m-1) WY2008 WY2009

Mean s.d. Mean s.d. Mean s.d. n Mean s.d. n Mean s.d.

José Basin 1056 82 115 44 9 3 12 1.4 2.3 29 2.1 3.1

Providence Creek watersheds 1859 85 102 36 10 3 6 0.12 0.14 6 0.14 0.12

Bull Creek watersheds 2292 62 117 48 9 3 9 0.042 0.067 9 0.23 0.27
70

Table 2.10. Correlation coefficients, coefficients of determination, and p-values for the 

site variables included in the univariate analysis of annual sediment production from 

native surface road segments in José Basin (n = 43). Values in bold are significant at p ≤ 

0.10.

Variable r R

2

p-value

Length (m) -0.13 0.02 0.53

Area (m2) -0.14 0.02 0.65

Slope (m m-1) 0.30 0.09 0.03

Area*Slope (m2m m-1) 0.08 0.01 0.33

Annual precipitation (mm) 0.04 0.00 0.22

Annual erosivity (MJ ha-1 mm hr-1) -0.01 0.00 0.35

Percent bare soil 0.27 0.07 0.15

Percent gravel cover -0.09 0.01 0.26

Percent Holland soil B horizon -0.10 0.01 0.72

Elevation (m) -0.18 0.03 0.92

Rill length (m) 0.62 0.39 0.0004

Rill volume (m3) 0.49 0.24 0.0016
71

Table 2.11. Coefficients and p-values for significant variables in the multivariate model 

for predicting annual sediment production from native surface road segments in José 

Basin.

Variable Coefficient p-value

Rill length (m) 0.11 <0.0001

Segment area (m2) - 0.016 0.02

Percent Holland soil B horizon on segment surface - 0.029 0.03

Annual precipitation (mm) 0.0056 0.06

Intercept 0.010
72

Table 2.12. Sediment production rates from five other studies in snow, mixed rain and snow, and rain climates. Data from the 

current study are in italics.

Dominant 

precipitation Study

Annual

precipitation

Annual sediment production 

from native surface roads

mm kg m

-2 Mg km-1

Snow Bull Creek watersheds 1000 0.13

Mixed rain 

and snow

Providence Creek watersheds 1100 0.14

Coe, 2006 1300 0.32 1.6

Megahan, 1974 700 0.48

Rain

José Basin 530 1.8 10

Barrett and Tomberlin, 2006 1400 0.5 to 4

Ramos-Scharrón and MacDonald, 2005 900-1400 5 to 15

Reid and Dunne, 1984 3900 41
73

2.10. Figures

Figure 2.1. Location of the national forests in California, including the Eldorado and the 

Sierra National Forest (SNF). Inset of the SNF shows José Basin and the Kings River 

Experimental Watershed (KREW). X indicates the location of the Auberry precipitation 

gage (CA map from http://www.fs.fed.us/r5/forests.shtml).
74

Figure 2.2. Elevation contours and the location of the five rain gages (JRG1-JRG5) in 

José Basin (derived from digital elevation maps in the SNF data base, accessed via A. 

Gallegos, 2007).
75

Figure 2.3. Roads (in black) and streams (in blue) in José Basin (data from the SNF data 

base, accessed via A. Gallegos, 2007). Colored areas in the background represent 

convergent areas that are likely wet or contain flow during the wet season from 

approximately October through May. 
76

Figure 2.4. The King’s River Experimental Watershed (KREW) contains two sets of four 

watersheds. The lower elevation Providence Creek watersheds (a) have elevations 

ranging from 1485 to 2005 m, while the higher elevation Bull Creek watersheds (b) range 

from 2050 to 2420 m (Korte, 2005). Sediment fences on roads are indicated by yellow 

circles, and sediment fences on hillslopes are indicated by yellow circles with attached 

contributing areas in blue (figures from Korte, in preparation).
77

Figure 2.5. Sediment fences were installed on undisturbed, convergent swales in José 

Basin and the Providence Creek and Bull Creek watersheds. The fabric floor facilitates 

sediment removal and the accuracy of the measurement (photo by A. Korte).
78

Figure 2.6. Sediment fences were installed at the drainage point of native surface road 

segments in José Basin as well as the Providence Creek and Bull Creek watersheds. This 

fence was installed just below a waterbar draining a native surface road segment in José 

Basin in summer 2007.
79

Figure 2.7. Location of the road sections (in black) in José Basin that were randomly 

selected to be surveyed. The remainder of the road network is shown in grey.
80

0

250

500

750

2008 2009

Water year Precipitation (mm)

JRG1

JRG2

JRG3

JRG4

JRG5

Figure 2.8. Annual precipitation for the rain gages in José Basin. Four rain gages 

functioned during WY2008 and three gages in WY2009.
81 y = 1.0x - 840

Providence Creek

watersheds

y = 0.063x + 980

Bull Creek 

watersheds

800

1000

1200

1700 1900 2100 2300 2500

Elevation (m) Precipitation (mm)

a)

y = -0.034x + 1030

Providence Creek

watersheds

800

1000

1200

1700 1900 2100 2300 2500

Elevation (m) Precipitation (mm)

 Bull Creek 

watersheds

b)

Figure 2.9. Precipitation versus elevation for the Providence Creek and Bull Creek 

watersheds for (a) WY2008 and (b) WY2009. 
82

0

2

4

6

2008 Water year Sediment production (kg m-2

)

José Basin

Providence Creek watersheds

Bull Creek watersheds

2009

Figure 2.10. Mean sediment production rates for native surface road segments in José 

Basin, the Providence Creek watersheds, and the Bull Creek watersheds for WY2008 and 

WY2009. Error bars display one standard deviation.
83

0.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00

Cumulative proportion of road length Cumulative proportion of sediment produced

WY2008

WY2009

Figure 2.11. A relatively small proportion of the road length monitored produced 75% of 

the sediment in both WY2008 and WY2009.
84

Figure 2.12. Mean sediment production rates for native surface road segments in José 

Basin in other soil types and in Holland soil for WY2008 and WY2009. Error bars 

indicate one standard deviation.
85 y = 0.25x - 0.43

R

2

 = 0.09

p = 0.03

0

3

6

9

12

15

0 3 6 9 12 15 18

Segment slope (%) Sediment production (kg m-2 yr-1

)

Figure 2.13. Annual sediment production and segment slope were significantly 

correlated for native surface road segments in José Basin (p = 0.03).
86

0.0

0.2

0.4

0.6

0.8

1.0

0 15 30 45 60 75 90 105

Drainage feature length (m) Cumulative proportion 

José Basin 

Providence Creek watersheds

Figure 2.14. Cumulative proportion of road length by drainage feature length for native 

surface road segments in José Basin and the Providence Creek watersheds.
87

0%

20%

40%

60%

80%

100%

José Basin Providence Creek

watersheds Cumulative percent

1 2

3 4

Connectivity 

class

Figure 2.15. Cumulative percent of road length by hydrologic connectivity class for 

native surface segments in José Basin and the Providence Creek watersheds.
88

0%

20%

40%

60%

80%

100%

Other soil

types

Holland soil Cumulative percent

1 2

3 4

Connectivity

class

Figure 2.16. Cumulative percent of native surface road length in José Basin by 

hydrologic connectivity class for other soil types and Holland soil. 
89

1:1

R

2

 = 0.59

0

2

4

6

8

0 3 6 9 12 15

Measured (kg m-2 yr

-1) Predicted (kg m-2 yr-1

)

Figure 2.17. Predicted versus measured sediment production rates using the empirical 

multivariate model developed for native surface road segments in José Basin. 
90

0

1

2

3

0 3 6 9 12 15

Measured (kg m-2 yr

-1) Predicted (kg m-2 yr-1

)

1:1 

Figure 2.18. Comparison of the predicted road sediment production using WEPP:Road to 

the values measured in José Basin (n = 43).
91

0.0

0.3

0.6

0.9

2008 2009

Water year Sediment production normalized by slope (kg m-2 yr-1

)

No rills present

Rills present

Figure 2.19. Mean sediment production rates normalized by slope for native surface 

segments with and without rills in José Basin for WY2008 and WY2009 (p < 0.0001 and 

p = 0.007, respectively). Error bars represent one standard deviation.
92

0

2

4

6

2008 2009 Water year Sediment production (kg m-2

)

Segments with slopes less than 7%

Segments with slopes greater 7%

Figure 2.20. Mean sediment production rates in José Basin for native surface segments 

with slopes less than and greater than 7% for WY208 and WY2009 (p = 0.18 and 0.06, 

respectively).
93

3. EFFECTS OF GRAVELING AND GRADING ON SEDIMENT PRODUCTION 

AND DELIVERY

ABSTRACT:

Rocking, grading, and installing waterbars are common road maintenance 

techniques for unpaved roads, and these are intended to improve drivability and reduce 

both sediment production and sediment delivery to streams. A study in the Sierra 

National Forest, California was conducted to compare sediment production and delivery 

from: 1) native and gravel surface road segments in the lower elevation José Basin (800-

1200 m) and the higher elevation Providence Creek watersheds (1485-1205 m); and 2) 

ungraded and graded native surface road segments in José Basin. Sediment fences were 

used to measure annual sediment production rates. Road segment characteristics such as 

segment length and slope were measured, and road sediment delivery was estimated by 

assessing each drainage feature. 

For water year (WY) 2004 through WY2006, the mean sediment production rate 

for gravel surface segments was 0.23 kg m2yr-1in the Providence Creek watersheds, or 

14-29% of the value for native surface segments, and this difference was significant. 

There was no significant difference in WY2007 due to very low precipitation and road 

erosion rates, or in WY2008 and WY2009 due to very high sediment production rates 

from one gravel segment. In José Basin, gravel surface roads produced significantly 

more sediment than native surface segments in WY2008, and there was no significant 

difference in WY2009. Gravel surface segments in José Basin have only 29% gravel 

cover on average, which is inadequate to significantly reduce rainsplash and sheetwash 

erosion.
94

Pre- and post-treatment surveys of approximately eight kilometers of roads in 

José Basin indicated that grading and waterbar installation decreased the mean segment 

length from 65 to 41 m, but 22% of the waterbars that were installed or reconstructed 

failed within the first year after grading, resulting in a 15% increase in segment length. 

Rills developed on 31% of the segments within the first year after grading. Different 

comparisons in different years indicated that graded road segments produced 2.6 to 7.6 

times more sediment than ungraded segments. Though grading reduced the length of 

road directly connected to the stream network by half, the net result was a 20-320% 

increase in the estimated sediment delivery to streams.

The results indicate that the frequency of grading should be reduced as much as 

possible to prevent an increase in sediment delivery. Waterbars need to be compacted 

and high with adequate cross-slope to direct water off the surface. Restricting traffic 

under wet conditions can reduce the occurrence of waterbar failure and the need for 

grading.
95

3.1. Introduction

Increased sediment loading to streams, rivers, and lakes is a major concern, as this 

can adversely affect water quality, stream habitat, and aquatic ecosystems (Bilby et al., 

1989; Ziegler and Giambelluca, 1997; Kolka and Smidt, 2004). The EPA lists sediment 

as the most common impairment to water quality in streams and lakes in the United 

States (EPA, 2010). Fine sediment also can decrease pool depth and abundance, and 

increase the turbidity of the stream (Beechie et al., 2005), both of which can alter the 

quality and quantity of habitat for salmonids and limit reproduction (Harr and Nichols, 

1993; Weaver and Hagans, 1999; Beechie et al., 2005). Increased sediment loading also 

can affect aquatic organisms by altering stream temperatures and nutrient loads (Kolka 

and Smidt, 2004). The U.S.D.A. Forest Service lists sediment as one of the primary 

impairments to water quality in North American forests, along with pathogenic 

organisms, organic material, nutrients, dissolved solids, and toxics (Brown and Binkley, 

1994). 

Sediment loading in streams occurs when surfaces that are hydrologically 

connected to the stream erode. Hillslope sediment production rates in undisturbed 

forested watersheds are typically very low (MacDonald et al., 2004), as forests have a 

dense surface cover of vegetation and litter and a high porosity and infiltration rate. 

These characteristics largely prevent soil detachment and overland flow (Dunne and 

Leopold, 1978). Surface disturbances such as fire, concentrated grazing, or road 

construction can expose the mineral soil and reduce the infiltration rate (MacDonald et 

al., 2001; Ramos-Scharrón and MacDonald, 2005). This can result in a higher likelihood 
96

for the occurrence of erosive overland flow, which can detach the exposed mineral soil 

particles and transport them to the stream network.

Unpaved roads typically have a high percentage of exposed mineral soil that is 

susceptible to detachment and transport. In forested watersheds, unpaved roads are often 

a major source of sediment to streams (Reid and Dunne, 1984; Swift, 1988; Bilby et al., 

1989; Luce and Black, 1999; Ketcheson et al. 1999; Coe, 2006). Roads can deliver a 

large amount of sediment to streams relative to their surface area even during low to 

moderate rainfall events (Ziegler and Giambelluca, 1997; Chappell et al., 1999; Ziegler et 

al., 2004; Cafferata et al., 2007). Road sediment production can vary greatly both interannually and among road segments, which are defined as sections of the road that have 

clearly defined contributing areas and discrete drainage points or are outsloped (Coe, 

2006; Korte, in preparation).

Rocking, grading, and installing waterbars are common treatments to reduce road 

sediment production, reduce road sediment delivery, and maintain road drivability. 

Rocking reduces sediment production by covering the bare mineral soil, thereby reducing 

rainsplash detachment, and also reduces the velocity of overland flow, which further 

reduces detachment and sediment transport (Megahan et al., 1991; Poesen et al., 1994; 

Appelboom et al., 2002; Sheridan and Noske, 2007; Rivera et al., 2009). Grading, while 

maintaining drivability, typically increases the supply of finer soil particles that can be 

readily detached by rainsplash and sheetwash and thereby often increases sediment 

production (Megahan and Kidd, 1972; Megahan, 1974; Reid and Dunne, 1984; Megahan 

et al., 1986; Luce and Black, 1999; Ziegler et al., 2000; Ziegler et al., 2001; Appelboom 

et al., 2002; Ramos-Scharrón and MacDonald, 2005; Coe, 2006). If flow becomes 
97

concentrated, severe rilling may occur, which can increase sediment production and 

reduce road drivability. Installing waterbars reduces the contributing area of a road 

segment, which should decrease the amount of concentrated runoff and sediment 

production (Chapter 2). By altering segment length and drainage from a road, waterbar 

construction and maintenance can reduce road-stream connectivity and sediment delivery 

to the stream network.

These issues are of particular concern on National Forest lands in the Sierra 

Nevada, and the present study follows from two earlier projects. The first study in the 

Eldorado National Forest in the northern Sierra Nevada (Figure 3.1) measured sediment 

production rates from 15 native surface road segments that were not recently graded, 2-40 

recently graded road segments, and 9-10 ungraded gravel surface road segments from 

water year (WY) 2000 to 2002 (Coe, 2006).

The second study was centered on the Kings River Experimental Watershed 

(KREW) in the Sierra National Forest (SNF) in the southern Sierra Nevada (Figure 3.1). 

In this area precipitation falls mainly as snow, although occasional rain or rain-on-snow 

events may occur. From WY2004 to WY2006, sediment production was measured from 

11-13 native surface, seven gravel surface, and four mixed surface road segments as well 

as from seven ditches adjacent to paved roads (Korte, in preparation). Both of these 

studies also conducted extensive road surveys to characterize the road network and 

evaluate road-stream connectivity.

This study continued the measurements of road sediment production from 

different road surface types in the KREW watersheds, but the primary focus was shifted 

to the lower elevation José Basin, which is also located in the SNF. José Basin is a 78 
98

km2 watershed approximately 20 km west of KREW (Figure 3.1), and here the 

precipitation falls primarily as rain. The specific objectives of this portion of the study 

were to: 1) quantify the effect of road surface type on sediment production and delivery 

in KREW under a range of climatic conditions; 2) quantify the effect of graveling on road 

sediment production and delivery in José Basin; 3) predict the total sediment delivered 

from gravel surface roads to the stream network in José Basin; 4) quantify the effect of 

grading and waterbar installation on road segment characteristics, road sediment 

production, and road sediment delivery in José Basin; and 5) quantify the effect of rill 

erosion on sediment production following grading in José Basin.

3.2. Background

3.2.1. Road sediment production and delivery

Road surface sediment production is the result of several erosional and transport 

processes. These include: 1) rainsplash detachment, 2) sheetwash, and 3) rill erosion 

(Zeigler et al., 2000). Rainsplash detachment occurs when the impact of a raindrop 

detaches fine sediment from the road surface (Zeigler et al., 2000). The rate of rainsplash 

detachment is highly dependent on the rainfall erosivity, which in turn is a function of the 

precipitation intensity and the drop size distribution (Lal, 1988; Renard et al., 1997). 

When rainfall intensity exceeds the infiltration capacity of a surface, water flows 

downslope as infiltration-excess or Horton overland flow (HOF) (Dunne and Leopold, 

1978). Sheetwash and rill erosion occur when the shear stress applied by this overland 

flow exceeds the resistance of the surface (Dunne and Leopold, 1978). 
99

The amount of sheetwash and rill erosion is directly related to the force of the 

flow and the surface erodibility (Luce and Black, 1999; Croke and Hairsine, 2006). The 

force of a given flow is related to the depth and velocity of flow (Dunne and Leopold, 

1978). The depth and velocity of flow are functions of the duration and intensity of a 

given precipitation event relative to the infiltration rate (Dunne and Leopold, 1978).

Infiltration rates on unpaved roads tend to be very low due to compaction. Values 

in Idaho, Colorado, and Montana ranged from 5 x 10-5to 8.8 mm h-1 with a geometric 

mean of 0.11 mm h-1(Luce and Cundy, 1994). Given a spatially uniform precipitation 

rate and no contribution from the adjacent hillslope, the discharge from a road segment is 

a direct function of the area of that segment (Leopold et al., 1964). Given a discharge, 

the slope and roughness of a road segment determines the flow velocity and hence the 

erosive energy of the discharge (Dunne and Leopold, 1978). Therefore the detachment, 

shear stress, and sediment transport capacity of overland flow are direct functions of the 

precipitation characteristics (Dunne and Leopold, 1978), the contributing area and slope 

of a road segment, and the road surface characteristics (Anderson and MacDonald, 1998; 

MacDonald et al., 2004; Coe, 2006).

As the runoff becomes channelized into rills, the detachment and transport 

capacity increases because the flow is deeper and faster (Merz and Bryan, 1993; Brunton 

and Bryan, 2000). It follows that the amount of rilling varies with precipitation 

characteristics and soil properties (Brunton and Bryan, 2000). Road sediment production 

was found to be strongly related to rill density in Colorado (R2= 0.57, p < 0.0001) 

(Welsh, 2008), and on exposed hillslopes rill erosion can be the primary sediment source 

rather than sheetwash (Pietraszek, 2006). Excessive rilling on unpaved roads reduces 
100

drivability and grading may be needed to restore a smooth, drivable surface. Excessive 

rill erosion following grading may result in the need for repetitive grading, and previous 

studies have not quantified the contribution of rill erosion to sediment production after 

grading. 

The effects of unpaved roads on runoff and erosion may not be a concern unless a 

road is hydrologically connected to a stream, lake, or other area of concern (Wemple et 

al., 1996; La Marche and Lettenmaier, 2001; Bowling and Lettenmaier, 2001). In some 

areas most of the connected segments are due to road-stream crossings (Wemple et al., 

1996; Croke and Mockler, 2001; Coe, 2006), but road-stream crossings are not common 

in either KREW or José Basin. In these areas road-stream connectivity is primarily due 

to HOF from the road surface forming a small channel or sediment plume that extends to 

the stream network (Montgomery, 1994; Wemple et al., 1996; Croke and Mockler, 2001; 

La Marche and Lettenmaier, 2001; Bowling and Lettenmaier, 2001). The overall 

increase or decrease in sediment contributed to the stream after any type of road 

maintenance is therefore the combination of the impact on sediment production and the 

impact on sediment delivery.

3.2.2. Effects of graveling on road sediment production and delivery

The same factors that affect sediment production on native surface roads also 

affect sediment production on gravel surface roads, as they are subject to the same set of 

runoff and erosional processes (Sheridan and Noske, 2007). However, the relative 

magnitude of these processes will differ from native surface roads, so sediment 

production rates from gravel surface roads are typically lower than comparable native 
101

surface road segments. Much of this difference is due to the large reduction in both 

rainsplash and sheetwash erosion (Poesen et al., 1994; Megahan et al., 1991; Rivera et al., 

2009). 

The reduction in rainsplash erosion is because the surface gravel shields the finer, 

more easily detached sediment particles from raindrop impact. Graveling greatly reduces 

sheetwash erosion by reducing the velocity of flow over a road surface and shielding the 

finer particles from the shear stress of the overland flow. Graveling also can reduce the 

amount of runoff by providing a more porous surface (Appelboom et al., 2002) and 

possibly allowing more infiltration into the underlying native material by reducing 

compaction. The reduction in velocity also allows more time for water to infiltrate, 

which will reduce surface runoff. In Australia mean runoff ratios for gravel surface roads 

were only 0.55 as compared to 0.66 for native surface segments (Sheridan and Noske, 

2007). In North Carolina, the runoff volume for older and newly graveled road segments 

respectively averaged 45% and 39% less than native surface road segments (Appelboom 

et al., 2002). This reduction in runoff will result in shorter drainage features, potentially 

reducing road-stream connectivity.

3.2.3. Effects of grading and waterbar installation on sediment production and delivery 

The effects of grading and waterbar installation are often believed to be beneficial 

in terms of reducing sediment delivery to streams, but this is a complex issue. Grading 

disturbs the road surface and increases the supply of material for transport, which can 

lead to an initial increase in sediment production (Megahan and Kidd, 1972; Megahan, 

1974; Reid and Dunne, 1984; Megahan et al., 1986; Luce and Black, 1999; Ziegler et al., 
102

2000; Ziegler et al., 2001; Appelboom et al., 2002; Ramos-Scharrón and MacDonald, 

2005; Coe, 2006). As the time since grading increases, the fine material on the road 

surface is eroded away and a coarser armor layer forms, which is more resistant to both 

rainsplash and sheetwash erosion (Ziegler et al., 2000; Ramos-Scharrón and MacDonald, 

2005). The resulting reduction in sediment production rates following grading has been 

modeled by the equation:

 Et = En + kSe-kt (equation 3.1)

where Et is the sediment production rate (Mg km-2day-1), En is the sediment production 

rate that would be approached if no disturbance occurred (Mg km-2day-1), k is an index 

of the decline in erosion following grading (days-1), S is the total rate of material 

available for erosion immediately after grading (Mg km-2day-1), and t is the time since 

disturbance in days (Megahan, 1974).

In the northern Sierra Nevada, road segments that were graded within the past two 

years produced approximately twice as much sediment as segments that had not been 

recently graded (Coe, 2006). This increase was more prevalent at elevations below 1400 

m, where a greater proportion of the precipitation fell as rain rather than snow (Coe, 

2006). There was no apparent decline in sediment production between the first and the 

second year after grading (Coe, 2006). On St. John in the U.S. Virgin Islands, recently 

graded road segments produced 2.5 times more sediment per unit precipitation than 

comparable non-graded roads (Ramos-Scharrón and MacDonald, 2005). In the Oregon 

Coast Range, grading of ditches and cutslopes resulted in a seven-fold increase in 

sediment production (Luce and Black, 1999). 
103

Waterbars are often constructed or rebuilt when grading occurs. Waterbars direct 

flow off the road surface, which should reduce sediment production by reducing the 

length and hence the contributing area of a segment. However, waterbars can fail due to 

flow depths that exceed the waterbar height, sediment deposition upslope of the waterbar, 

or rill erosion through the waterbar. The strategic placement of waterbars can reduce 

road-stream connectivity by reducing the amount of runoff and sediment production from 

a single drainage point, directing flow off of the road where it can infiltrate, and 

disconnecting segments that would otherwise flow directly into a stream. There are very 

few data on the effects of waterbar failure on segment contributing length and sediment 

delivery, and this study will examine these effects in José Basin.

3.3. Methods

3.3.1. Site description

Providence Creek watersheds, KREW

The Kings River Experimental Watershed (KREW) contains four mid-elevation 

(1485 to 2005 m) watersheds ranging from 0.49 km2to 1.32 km2 within the Providence 

Creek watershed (Figure 3.2). The area has a Mediterranean-type climate with dry 

summers and wet winters. Average annual precipitation is 1240 mm, with approximately 

90% of the precipitation falling as snow (Korte and MacDonald, 2007). Vegetation is 

primarily Sierra mixed-conifer forest (Eagan et al., 2007). The area has a granitic 

lithology with coarse sandy loam and loamy sand soils of the Gerle, Cagwin, and Shaver 

series (USDA, 1983; Korte and MacDonald, 2007).
104

There are 12.6 kilometers of road in the Providence Creek watersheds, with half 

these being native surface. There are 1.5 km of gravel surface roads and 1.9 km of paved 

roads, and the latter are generally insloped with ditches. The remaining roads are 

classified as mixed surface roads, as they are a complex intermixing of native surface, 

gravel, and old pavement.

In recent years very little road maintenance work has been done in the Providence 

Creek watersheds. The majority of the graveling was done at least ten years ago, with 

only small patches of gravel or other maintenance practices being put into place on an as 

needed basis. No grading has been done in the Providence Creek watersheds in the past 

ten years. 

José Basin

The primary study area was José Basin, and this is approximately 20 km west of 

KREW (Figure 3.1). Elevations range from 450 m to 1950 m, though most of the study 

sites were between 800 m and 1200 m elevation. Most precipitation at the lower 

elevations falls as rain, and in the upper portions of the basin there is usually a seasonal 

snowpack (A. Gallegos, USDA Forest Service, pers. comm., 2008). Rain-on-snow 

events can occur at any elevation depending on the sequence of warm and cold storms 

and the diurnal fluctuations in temperature. 

There are 447 km of stream channels in José Basin and the drainage density is 5.7 

km km-2(Figure 3.3). The basin has 159 km of mapped roads for a relatively high road 

density of 2.0 km km-2(Figure 3.3). Road drivability is crucial in José Basin, as there are 

scattered houses in some areas, and the basin is heavily used for grazing, logging, and 
105

recreational uses such as hunting and off highway vehicles. Approximately one third of 

the unpaved roads in José Basin have at least 20% gravel cover. 

Road maintenance is relatively common in José Basin to maintain drivability. 

Box-drag grading is performed at least annually or more by residents on at least one road 

section, and more intensive grading is done by Southern California Edison to maintain 

road access to its properties and power lines. Less frequent grading projects with 

waterbar installation and reconstruction are done on an as-needed basis by the SNF to 

maintain drivability and decrease sediment delivery. 

3.3.2. Precipitation

Providence Creek watersheds

KREW staff operates two climate stations in the Providence Creek watersheds—

one at 1750 m and another at 1984 m. Fifteen-minute precipitation data have been 

collected from water year 2004 (WY2004) through WY2009. Annual precipitation was 

calculated for both climate stations. Regression equations relating elevation to annual 

precipitation were developed for each water year and used to estimate the annual 

precipitation for each site where road sediment production was being measured. 

José Basin

Five tipping bucket rain gages were installed in José Basin, but equipment 

problems and vandalism meant that valid data were obtained from four rain gages in 

WY2008 and three gages in WY2009. Annual precipitation and erosivity were 

calculated using the RF program for each gage for each year (Petkovsek, 2001). No 
106

correlation was found between elevation and annual precipitation or erosivity for either 

water year, so data from the nearest functioning rain gage was assigned to each segment 

where sediment production was measured.

The precipitation data from José Basin was put in historical context by using data 

from the Auberry climate station, which is the closest long-term station. The Auberry 

station is at 640 m and about one kilometer west of José Basin (Figure 3.1). The mean 

annual precipitation at Auberry was calculated using the 95 year record. Annual

precipitation in José Basin was compared to annual precipitation at Auberry for WY2008 

and WY2009.

3.3.3. Sediment production

Sediment production from discrete road segments was measured using sediment 

fences (Robichaud and Brown, 2002) (Figure 3.4). Fences were constructed of a 

geotextile fabric attached to 1-2 m long pieces of 1.3 cm diameter rebar pounded 0.3-0.5 

m into the ground. The leading edge of the fabric was attached to the ground with 

landscape staples to prevent underflow. The captured sediment was removed during the 

dry season and weighed in the field to the nearest 0.5 kg. Two representative samples of 

about 500 g were collected to determine percent moisture (Gardner, 1986) and percent 

organic matter (Ben-dor and Banin, 1989). The mean percent moisture and organic 

matter values were used to convert the field weights to a dry mass of mineral sediment. 

The annual sediment production rate (kg m-2 yr-1) was determined by dividing the 

calculated dry mass of mineral sediment by the contributing area of the road surface. 
107

In the Providence Creek watersheds, annual sediment production rates for native, 

gravel, and mixed surface road segments as well as ditches adjacent to paved roads were 

measured and calculated by A. Korte for WY2004 through WY2006 (in preparation). 

Sediment production continued to be monitored in the Providence Creek watersheds 

through WY2009, though the sample size for native surface segments decreased in 

WY2007 due to the removal of seven sediment fences that were located on Southern 

California Edison land (Table 3.1). 

In José Basin, sediment production was measured in WY2008 and WY2009 from 

13-30 native surface road segments that were not recently graded (―ungraded‖ segments), 

5-11 gravel surface segments, and 3-24 native surface segments for one and two water 

years after grading (Table 3.2). More than half of the sediment fences in José Basin 

overtopped in WY2008, and sediment production values from the overtopped fences 

were excluded from all calculations. In WY2009 sediment production was measured 

from six matched pairs of road segments, where one segment was graded in summer 

2008 while the other segment was left ungraded. These pairs also were included in the 

larger pool of ungraded and graded segments (Table 3.2). 

3.3.4. Road segment characteristics 

The key characteristics for each road segment with a sediment fence were 

measured or classified (Table 3.3) to help compare and explain sediment production and 

potential sediment delivery. The length of each segment was measured with a meter 

wheel. A cloth tape was used to measure the active width, which is the width of the road 

that is regularly driven on, and the total width, which was defined as the width from the 
108

bottom of the cutslope to the top of the fillslope. The area of the road segment was the 

segment length times the active width. A clinometer was used to measure the segment 

slope or each change of slope if the segment was not uniform, and the segment slope was 

then calculated as the length-weighted slope. 

Percent surface cover was determined by classifying the surface at a minimum of 

100 systematically spaced points sampled along a zigzag transect on the active road 

surface. Each point was classified as bare soil, gravel (rock with a secondary axis greater 

than one centimeter), litter, or live vegetation. Segments with less than 20% gravel cover 

were classified as native surface segments while segments with greater than 20% gravel 

cover were classified as gravel segments. 

Traffic was classified by determining the branch order of the road relative to a 

main road and visual inspection. Classes ranged from very low, indicating that vehicles 

very rarely travelled on the road, to low, medium, and high. Drain types and drain 

features were classified following the categories in Table 3.4. The elevation and location 

of the drainage point of each segment was determined using a GPS unit. All road surveys 

in the Providence Creek watersheds were completed by A. Korte (in preparation) prior to 

this study.

The bulk density of 13 segments prior to grading was measured by the excavation 

method (Grossman and Reinsch, 2002). Three pits approximately 7 cm by 7 cm were 

dug on the road segment to the depth of the deepest rill. The excavated sediment was 

collected, dried for 24 hours at 105°C , and weighed. The volume of the pit was 

determined from the volume of 30 grade silicon sand used to fill each pit. The bulk 

density was calculated by dividing the mass of the excavated sediment by the pit volume, 
109

and then averaging the three measurements. Bulk density was re-measured immediately 

after grading using the same procedure and again one year after grading. 

3.3.5. Rill volume and contribution to sediment erosion after grading

Field observations confirmed that grading results in a planar road surface. The 

length and volume of rills that developed in the first year after grading was measured by 

placing a straight edge across the road surface and measuring the rill depth at 3-4 evenly 

spaced locations across the rill. The cross-sectional area at that location was the average 

depth times the rill width. The cross-sectional area was measured for every major change 

in rill depth and/or width along the length of the rill, and the rill volume was calculated 

by: 

 

n

i

i i a l

1

 (equation 3.2)

where a is equal to the cross-sectional area (m2) and l is equal to the rill length (m) 

represented by that cross-section. The mass of sediment from rill erosion for each graded 

segment was calculated by multiplying the mean bulk density after grading by the total 

rill volume, and this value was compared to the mass of sediment captured by the 

corresponding sediment fence to determine the proportion derived from rill erosion 

(Pietraszek, 2006).

3.3.6. Sediment delivery

The potential for runoff and sediment to be delivered to the stream network was 

evaluated for each monitored road segment by identifying and following any drainage 

feature, such as a sediment plume or a rill originating from the drainage point of a road 
110

segment (Coe, 2006). The maximum length and mean slope of each drainage feature was 

measured in the same manner as for the road segments (Table 3.3). The roughness of the 

drainage pathway was classified on a scale of one to four, with class one being very 

smooth and class four having a large amount of live vegetation, logs, woody debris, or 

rocks trapping or dispersing the surface runoff and sediment. 

The presence or absence of pushouts at the drainage point of the road segment 

was observed (Table 3.3). Pushouts were classified as no longer intact if they were too 

filled with sediment for the water to drain, or if the surface drainage no longer directed 

flow to the pushout. The presence or absence of large rocks to armor either the drainage 

point or the road surface at a stream crossing also was observed. This drain armoring 

was classified as intact if it was still in place, but it was also noted whether the armoring 

was exposed or buried under deposited sediment. The locations of culverts were noted, 

and the percent of the cross-sectional area that was plugged with sediment or large woody 

debris was estimated. The presence of scour at the downstream end of each culvert was 

noted and measured if present. 

The connectivity class of each road segment was determined according to the 

length of the drainage feature and whether this extended to within 10 m of a defined 

channel (Table 3.5). Segments with a connectivity class of one have very little potential 

to deliver runoff and sediment to a stream channel, while segments with a connectivity 

class of four have a high potential. Road connectivity was evaluated for the Providence 

Creek watersheds prior to this study (A. Korte, in preparation). The potential amount of 

road sediment contributed to the stream in the Providence Creek watersheds was 

estimated by multiplying the mean sediment production rate by the total length of the 
111

road of a given surface, the mean width of the road, and the percent directly connected. 

In José Basin, the potential amount of road sediment contributed to the stream was 

estimated using a multivariate model predicting sediment production and multiplying the 

total potential sediment production from gravel surface roads by the percent of road 

length directly connected to the stream.

3.3.7. Road surveys

Road surveys were conducted on 7.7 kilometers of roads in José Basin between 

2007 and 2009 (Table 3.3). The sections to be surveyed were identified after using 

ArcGIS to break the road network into 269 sections that were 300 to 900 m in length. 

The sections were numbered and 20% of the sections were randomly selected (Figure 

3.5). Each of the selected sections was surveyed following Tables 3.3 to 3.5 unless it was 

paved or inaccessible because it was a private road. The percent bare soil and gravel 

surface were estimated for road sections surveyed that did not have sediment fences.

Repeated road surveys also were conducted on approximately eight kilometers of 

roads in José Basin that were graded in the summer of 2008 to determine the effect of 

grading on segment characteristics. The first survey was conducted prior to grading, and 

this was repeated immediately after grading and again in summer 2009 to determine the 

changes that occurred over one water year. 

3.3.8. Statistical analysis

The main dependent variable was the annual sediment production rate from road 

segments (kg m-2yr-1). Pairwise comparisons of road sediment production rates within a 
112

given water year were made between different road surface types in José Basin and in the 

Providence Creek watersheds. The effect of grading on road sediment production in José 

Basin was evaluated by pairwise comparisons for each water year. The validity of each 

comparison was assessed by comparing other key variables (e.g., segment slope, area, 

and percent bare soil) between groups. Pairwise comparisons also were made between 

bulk density values for each segment pre- and post-grading, and between immediately 

post-grading and one year after grading.

ANOVA tables were used to assess the relationships between each independent 

variable and the measured sediment production rates from gravel surface segments in 

José Basin. A multivariate linear regression model to predict sediment production from 

gravel surface road segments in José Basin was constructed using backward elimination 

procedures and a selection criteria of α = 0.10, and the validity of the model was assessed 

by comparing predicted sediment production rates to observed values.

3.4. Results

3.4.1. Precipitation

Precipitation in the KREW watersheds falls largely as snow, though there is the 

potential for both rain and rain on snow events. Mean annual precipitation is 

approximately 1240 mm per year (Figure 3.6). In WY2004 annual precipitation in the 

Providence Creek watersheds was only 72% of normal, while annual precipitation was 

141% of normal in WY2005 and 163% of normal in WY2006. WY2007 was the driest 

year with only 62% of the mean annual precipitation. WY2008 and WY2009 were 17% 

and 22% below normal, respectively. 
113

Mean annual precipitation for the Auberry rain gage is only 611 mm (California 

Department of Water Resources, 2010), or 49% of the mean annual precipitation for the 

Providence Creek watersheds. In WY2008 the annual precipitation at Auberry was only 

458 mm or 75% of the mean, and this is consistent with the below normal precipitation in 

the Providence Creek watersheds. Mean precipitation for the four functioning rain gages 

in José Basin was 519 mm (standard deviation (s.d.) = 50 mm), or approximately 60 mm 

more than at Auberry (Table 3.6). Annual precipitation was not significantly correlated 

with elevation in José Basin for WY2008 (R2= 0.03, p = 0.84). The mean erosivity of 

the four gages in WY2008 was 630 MJ ha-1 mm hr-1(s.d. = 90 MJ ha-1 mm hr-1). 

Erosivity was not correlated with elevation in WY2008 (R2= 0.008, p = 0.91). 

In WY2009 the annual precipitation at Auberry was 526 mm, or 86% of the mean. 

Mean precipitation for the three functioning rain gages in José Basin was 554 mm, which 

was 35 mm more than at Auberry, but the values in José Basin were more variable than in 

WY2008 as the standard deviation was 139 mm. Again the measured precipitation in 

José Basin was not significantly correlated with elevation (R2= 0.81, p = 0.29). There 

was no significant difference in annual precipitation between WY2008 and WY2009 in 

José Basin (p = 0.66). The mean erosivity in WY2009 was only 390 MJ ha-1 mm hr-1

(s.d. = 210 MJ ha-1 mm hr-1), and erosivity was again not correlated with elevation in 

WY2009 (R2= 0.15, p = 0.74). Erosivity in WY2009 was 38% of, and significantly less 

than, the erosivity in WY2008 (p = 0.09). 
114

3.4.2. Effects of road surface type on road sediment production and delivery

3.4.2.1. Sediment production

Providence Creek watersheds

The 6-13 native surface road segments with sediment fences had a mean elevation 

of 1860 m (s.d. = 85 m) and a range of 1750 m to 1960 m. Mean segment length was 45 

m (s.d. = 13 m), and the mean slope was 10% (s.d. = 3%) (Appendix E). The segments 

averaged 49% bare soil (s.d. = 22%), while the remaining cover consisted of duff (mean 

= 35%, s.d. = 22%), gravel (mean = 10%, s.d. = 22%), and live vegetation (mean = 7%, 

s.d. = 6%). 

In WY2004 the mean sediment production rate of the 11 native surface road 

segments in the Providence Creek watersheds was 0.30 kg m-2yr

-1

(s.d. = 0.38 kg m-2yr

-

1

) (Figure 3.7; Appendix E). In WY2005 two more segments were monitored, and the 

mean sediment production rate was nearly three times greater than the prior year (p = 

0.25). This increase can be attributed to the 95% increase in precipitation (Figure 3.6) 

rather than the additional segments, as the two new segments had smaller sediment 

production rates than the mean value for the remaining 11 segments. 

Precipitation and mean sediment production was higher in WY2006 than any of 

the other five years, as the mean production rate for the 13 native surface segments was 

1.8 kg m-2yr-1(s.d. = 1.8 kg m-2yr-1) (Figure 3.7). In WY2007 precipitation was lower 

than in any other year and the mean sediment production rate for the six remaining native 

surface segments was only 0.039 kg m-2yr-1(s.d.= 0.091) or 2% of the value in WY2006 

(p = 0.0019) (Figure 3.7). This was the lowest value for the six years of monitoring. 
115

Sediment production rates were similar for the final two water years, averaging 0.12 and 

0.14 kg m-2yr-1, respectively (s.d. = 0.14 and 0.12 kg m-2yr-1). 

The seven gravel surface segments in the Providence Creek watersheds had 32% 

gravel cover on average (s.d. = 8%), which was more than three times the amount of 

gravel on the native surface segments. Consequently, the gravel surface segments 

averaged only 19% (s.d. = 9%) bare soil as compared to 48% for the native surface 

segments. The remaining road surface was covered with duff (mean = 40%, s.d. = s.d. = 

14%) and vegetation (mean = 10%, s.d. = 8%). The gravel surface segments had similar 

segment areas and slopes as the native surface segments (Appendix E).

Mean annual sediment production for the seven gravel surface segments in the 

Providence Creek watersheds in WY2004 and WY2005 was respectively 13% and 17% 

of the mean rate for the native surface segments, and this difference was significant (p = 

0.017 and 0.045) (Figure 3.7). In WY2006 the mean sediment production rate from 

gravel surface segments was 29% of the mean rate from native surface segments, which 

was a smaller but still significant difference compared to the native surface segments (p = 

0.018). In WY2007 and WY2009 the mean sediment production rate from gravel surface 

segments was equal to the mean rate from native surface segments, while in WY2008 the 

mean sediment production rate from gravel surface segments was 49% of the mean rate 

from native surface segments (p = 0.30).

The interannual pattern for sediment production rates from gravel surface 

segments was generally very similar to the pattern for values from native surface 

segments. In WY2004 the mean sediment production rate for the gravel surface 

segments was 0.04 kg m-2yr-1, while in WY2005 and WY2006 the mean value was 3.5 
116

and 3.7 times larger, respectively. This is similar to the 2.8- and 2.2-fold increases for 

the mean values from native surface segments for the same two water years. Similar to 

the native surface segments, the mean sediment production rate for gravel surface 

segments was highest in WY2006, the wettest year, and lowest in WY2007, the driest 

year. A different pattern was only evident in WY2008 and WY2009, when sediment 

production rates from native surface segments were nearly equal while there was a 2.5-

fold increase in mean sediment production for the gravel surface segments. 

The four mixed surface road segments in the Providence Creek watersheds 

averaged 23% bare soil (s.d. = 15%), 21% gravel (s.d. = 8%), 21% pavement (s.d. = 7%), 

and 38% duff (s.d. = 19%). Their mean length was 95 m (s.d. = 38 m), or 2.1 times the 

mean length of the native surface segments, while their mean slope was 10% (s.d. = 1%), 

which was the same value as the native surface segments (Appendix E). 

Sediment production from the four mixed surface road segments tended to be 

binary, with PM1 and PM5 having sediment production rates typically one to three orders 

of magnitude higher than PM3 and PM4. Rills at least 8 m long formed on the two 

segments with higher sediment production rates, though a rill that was 16 m long and 0.8 

m deep also formed on PM4. Mean annual sediment production rates from mixed surface 

segments were 43-62% that of native surface segments from WY2004 to WY2007. In 

WY2008 the mean annual sediment production rate for mixed surface roads was 0.31 kg 

m

-2

yr

-1

(s.d. = 0.26 kg m-2yr

-1

), or 4.3 times that of the native surface segments. Though 

precise measurements were not taken, a significant amount of erosion was observed at the 

knickpoint of the largest rill on PM1, which had a sediment production rate of 0.58 kg m2

yr-1, or 1.7 times any of the native surface segments in that year (Appendix E). In 
117

WY2009 the mean sediment production rates from native, gravel, and mixed surface 

segments were nearly identical (Figure 3.7). 

The ditches with sediment fences were on insloped, paved road segments that 

averaged 90 m long (s.d. = 50 m), twice as long as the native and gravel surface road 

segments. The mean segment slope was 7% (s.d. = 3%), which is slightly lower than the 

mean slope of 8-11% for the three other surface types. In each segment the ditches 

extended the entire length of the segment, and the mean ditch width was 1.0 m (s.d. = 0.2 

m). 

In each year, the mean sediment production from the ditches was at least an order 

of magnitude lower than the mean values for any of the other three road surface types 

(Figure 3.7). The six-year average was only 0.020 kg m-2yr

-1

(s.d. = 0.090 kg m-2yr

-1

), 

but in the wettest year (WY2006) this more than quadrupled to 0.090 kg m-2yr

-1

(s.d. = 

0.22 kg m-2yr

-1

). The interannual variations were similar to the other road surface types, 

as the values increased from WY2004 to WY2006. The smallest value was in the driest 

year (WY2007), when none of the ditches produced any sediment.

José Basin

The number of native surface road segments with valid sediment production 

measurements ranged from 13 in WY2008 to 30 in WY2009. The mean elevation of 

these segments was 1056 m (s.d. = 83 m), 800 m lower than the mean elevation of the 

native surface segments in the Providence Creek watersheds. Mean segment area was 

115 m2(s.d. = 44 m

2

), which is less than the value of 168 m2for native surface segments 

in the Providence Creek watersheds (p = 0.37). Mean segment slope was 9% (s.d. = 4%), 
118

which is very similar to the mean value of 8% for the Providence Creek watersheds. 

Other than elevation, the only other major difference was that the native surface segments 

in José Basin averaged 70% bare soil (s.d. = 15%), as compared to 48% (s.d. = 17%) bare 

soil for the native surface segments in the Providence Creek watersheds (p < 0.0001). 

In WY2008 the mean sediment production rate for the native surface segments in 

José Basin was 1.4 kg m-2yr-1, but this was highly variable as the standard deviation was 

2.2 kg m-2yr-1(Figure 3.8; Appendix D). This is 2.5 times the mean value for the native 

surface segments in the Providence Creek watersheds, but the true difference would be 

even greater since 19 of the 32 sediment fences in José Basin overtopped. 

In WY2009 the mean sediment production rate for the 30 native surface segments 

in José Basin was 2.0 kg m-2yr

-1

(s.d. = 3.1 kg m-2yr

-1

), or 43% higher than in WY2008 

(Figure 3.8), even though the mean precipitation was only 6% greater (Table 3.6). The 

coefficient of variation was nearly identical at 155%. In WY2009 the mean sediment 

production from native surface road segments in José Basin was 14 times the mean value 

from the Providence Creek watersheds. This ratio is believed to be more representative 

than in WY2008 as no sediment fences overtopped.

The number of gravel surface segments in José Basin with valid sediment 

production values ranged from five in WY2008 to 11 in WY2009. The mean area of the 

gravel surface road segments was 114 m2(s.d = 44 m2), and this was only nearly identical 

to the mean value for native surface segments in José Basin. However, the mean slope of 

the gravel surface segments was 13% (s.d. = 3%) as compared to 9% (s.d. = 3%) for the 

native surface segments, and this difference was significant (p = 0.0001). As expected, 

the gravel surface segments averaged 29% gravel (s.d. = 7%) and 51% bare soil (s.d. = 
119

12%) as compared to 4% gravel (s.d. = 8%) and 70% bare soil (s.d. = 15%) for the native 

surface segments (p < 0.0001 in each case). The remaining cover was mostly duff (mean 

= 19%) and only 1% live vegetation. The mean elevation of the graveled segments was 

70 m higher than the mean elevation of the native surface segments (p = 0.0040), but this 

difference is not believed to have a significant effect on sediment production (Chapter 2).

In WY2008 the mean sediment production for gravel surface segments in José 

Basin was 3.6 kg m-2 yr-1(s.d. = 1.9 kg m-2yr-1), or 2.6 times the value for native surface

segments (p = 0.06) (Figure 3.8, Appendix G). All five segments had sediment 

production rates greater than 1.0 kg m-2yr

-1

. JGH5 had a sediment production rate of 6.6 

kg m-2yr

-1

, which was the highest sediment production rate for a gravel surface segment. 

JGH5 had only 23% gravel cover, as compared to 27-40% gravel cover for the other four 

segments with valid sediment data. 

In WY2009 the mean sediment production for gravel surface segments was only 

0.7 kg m-2yr-1(s.d. = 1.0 kg m-2yr-1), or 35% of the value for the native surface segments 

(Figure 3.8). The value of 0.7 kg m-2yr-1also was only 19% of the value for WY2008. 

Sediment production from the five segments with valid data in WY2008 produced only 

2-51% as much sediment in WY2009, despite the lack of a significant difference in 

annual precipitation. The low sediment production from gravel segments in WY2009 can 

probably be attributed to their location within José Basin, as eight of the 11 gravel 

segments were located near JRG2, which had an annual erosivity of only 160 MJ ha-1mm 

hr-1. This was 290 MJ ha-1 mm hr-1less than the WY2009 values for any of the other 

gages. Sediment production for each of these eight segments was less than 1.0 kg m-2yr1

, while each of the remaining three segments were located near JRG4, which had an 
120

annual erosivity of 570 MJ ha-1 mm hr-1in WY2009, and they each produced more than 

1.0 kg m-2yr-1and.

In WY2008 the mean sediment production rate for gravel surface segments in 

José Basin was 60 times the mean value for the Providence Creek watersheds, and in 

WY2009 there was a five-fold difference (Figure 3.9). These large differences can be 

largely attributed to the difference in elevation and thus climate, as the mean length of the 

gravel surface segments in José Basin was 20% less than the gravel segments in the 

Providence Creek watersheds (p = 0.44). The mean slope was only slightly steeper at 

13% (s.d. = 3%) as compared to 11% (s.d. = 6%) for the gravel segments in the 

Providence Creek watersheds (p = 0.21). The gravel surface segments in José Basin did 

average 51% bare soil, which was much more than the mean value of 19% for the 

Providence Creek watersheds (p = 0.0001), but the gravel surface segments in both areas 

averaged 29% gravel cover.

3.4.2.2. Predicting sediment production for gravel surface segments in José Basin

Univariate analyses showed that annual sediment production from the gravel 

surface road segments in José Basin (n = 16) was significantly related to segment slope, 

segment area times slope (A*S), annual precipitation, annual erosivity, and percent bare 

soil (Table 3.7). The positive correlations between road sediment production and annual 

erosivity, annual precipitation, and the percent bare soil make physical sense. Annual 

erosivity had the strongest relationship with an R2of 0.45 (p < 0.01), and annual 

precipitation was also marginally significant at p = 0.08. The negative correlations 

between road sediment production and segment slope and area*slope did not make 
121

physical sense, and may be due to the location of longer, steeper fences in areas with 

higher annual erosivities. The multivariate model predicted annual sediment production 

from segment area (A in m2), segment slope (S in m m-1), percent bare (B), annual 

precipitation (P in mm), annual erosivity (E in MJ ha-1 mm hr-1), and segment area times 

slope (AS in m2 m m-1) (Table 3.8):

SP = 17 – 0.11*A – 0.83*S + 5.63*B + 0.009*E+ 0.006*AS (equation 3.3)

where SP is sediment production (kg m-2) (Figure 3.10). The coefficients for most of 

these variables make physical sense, as sediment production is predicted to increase with 

increasing percent bare soil, erosivity, and segment area times slope. The negative 

relationship with area also was observed for native surface segments, as longer segments 

tended to have a flatter depositional area at the bottom. The predicted decrease in 

sediment production with an increase in slope does not make physical sense and is likely 

a statistical artifact. Therefore the multivariate model for predicting sediment production 

from gravel surface segments in José Basin is:

SP = -1.3 – 0.005*A + 0.004*E + 4.4*B – 0.0003*AS (equation 3.4).

This explains 57% of the variability in sediment production from gravel surface segments 

(Figure 3.10). The application of this model to the 2.5 km of surveyed gravel surface 

segments in José Basin yields a predicted sediment production rate of seven tons per 

year, or 2.8 tons per kilometer. On this basis the 29 km of gravel surface roads in José 

Basin are predicted to produce approximately 80 tons of sediment each year. In 

comparison, the multivariate model for predicting sediment production from native 

surface segments predicted that monitored native surface segments produced 10 tons per 
122

kilometer, and the 67 km of native surface roads in José Basin are predicted to produce 

680 tons of sediment each year. 

3.4.2.3. Sediment delivery

Providence Creek watersheds

Fifty-five percent of the 13.9 km of roads in the Providence Creek watersheds are 

native surface. Drainage features were present for 114 segments or 74% of the native 

surface road length, and the remaining 31 segments had no visible signs of sediment 

discharge. The mean length of the 114 drainage features was 20.4 m (s.d. = 14.6 m), but 

the mean was highly skewed by six drainage features over 50 m in length. The longest 

drainage feature was 94 m and this emanated from an 84 m long segment. 

Despite the frequency of drainage features, only eight segments or 4% of the 

native surface road length was directly connected to a stream (Figure 3.11). Multiplying 

the mean sediment production rate from native surface roads by the total native surface 

road length, the mean road width, and the percent that is directly connected to a stream, 

the potential sediment delivered from native surface roads in the Providence Creek 

watersheds was 470 kg yr-1. This is 35% of the total potential sediment delivered to 

streams from roads (Table 3.9). 

Only 11% of the roads in the Providence Creek watersheds are gravel surface. 

Drainage features were present for 76% of the gravel surface road length, which is very 

similar to the 74% value for native surface roads. The mean length of the drainage 

features was 16.5 m (s.d. = 15.9), which was 19% less than the mean length from the 

native surface roads (p = 0.21). There were fewer long drainage features, as drainage 
123

features longer than 20 m were found for only 21% of the road length. The longest 

plume was 88 m long from a 51 m segment, but this was the only drainage feature from a 

gravel surface road that was longer than 30 m. 

Eleven percent of the gravel surface road length was directly connected to the 

stream network as compared to 4% for the native surface roads (Figure 3.11). Gravel 

surface segments are estimated to contribute just 60 kg yr-1to the stream network in the 

Providence Creek watersheds, which is only 4% of the total estimated sediment delivery 

from roads (Table 3.9).

Mixed surface roads accounted for 20% of the road network in the Providence 

Creek watersheds. Drainage features were present for 71% of the road length, and this 

was similar to native and gravel surface roads. The mean length of the 33 drainage 

features was 20.9 m (s.d. = 15.6 m), which again is nearly equal to the value for native 

surface roads. The mixed surface roads, like native surface roads, had several longer 

drainage features, with 29% of the road length having drainage features longer than 25 m. 

Three segments had drainage features between 30 m and 40 m long, and one 34 m long 

segment had a drainage feature that was 90 m long. 

Thirty-one percent of the mixed surface roads were directly connected to the 

stream network, and this was eight and three times more than the native and gravel 

surface roads, respectively (Figure 3.11; Table 3.9). The high sediment production rate 

and high connectivity means that mixed surface roads are estimated to contribute nearly 

800 kg yr-1of sediment to streams in the Providence Creek watersheds, or 59% of the 

total (Table 3.9). Graveling all of the native surface roads in the Providence Creek 

watersheds could reduce their sediment production by 78%. 
124

Fifteen percent of the Providence Creek road network is paved, and the paved 

roads are typically insloped with adjacent ditches. Only 21% of the paved road length

had a sediment plume or rill, and three of the six drainage features were less than 10 m 

long. The longest drainage feature was nearly 43 m long, and this discharged from an 81 

m long segment. 

Surprisingly, 16% of the paved roads were directly connected to the stream 

network, which was four times the rate of native surface roads (Figure 3.11). Since the 

sediment production rates are lower for ditches than any of the three road surface types, 

the ditches are estimated to contribute only 23 kg yr-1of sediment to the stream network, 

or 1% of the total.

José Basin

The road survey showed that 42% of the 159 km of roads in José Basin were 

native surface, 18% were gravel surface, and 41% were paved. Only 52 native surface 

segments, or 54% of the surveyed native surface road length, had a drainage feature 

(Figure 3.12). Drainage features from native surface road segments in José Basin were 

typically short, as only four segments had drainage features longer than 30 m. The mean 

length was 13.6 m (s.d. = 17.8 m), or 33% less than the mean length of drainage features 

from native surface roads in the Providence Creek watersheds. The longest drainage 

feature was 105 m and emanated from a 246 m long segment. 

Thirty percent of the native surface road length was directly connected to the 

stream network, which is nearly an order of magnitude more than in the Providence 

Creek watersheds (Figure 3.13). The higher connectivity in José Basin is because many 
125

of the roads are located near streams; the mean drainage feature length of the connected 

segments was only 6.1 m (s.d. = 10.8 m). 

Gravel surface roads accounted for 41% of the road length surveyed in José 

Basin. Eighty-four percent of the gravel surface road length had a drainage feature as 

compared to 54% for the native surface roads (Figure 3.12). Drainage feature lengths for 

the gravel surface segments were typically short, as 87% of the gravel surface road length 

had drainage features less than 10 m long. The longest drainage feature was only 22 m 

long, and this came from a 45 m long segment. The connectivity classes for gravel 

surface roads also had a binary distribution, as 55% of the road length had a connectivity 

class of one and 40% of the road length was directly connected to the stream network 

(Figure 3.13). 

3.4.2.4. Total potential sediment delivered from gravel surface segments in José Basin

As calculated in the previous chapter using the multivariate model for predicting 

sediment production from native surface roads,, native surface roads are estimated to 

contribute 210 tons of sediment per year to the stream network in José Basin (Table 3.9). 

This is 87% of the total potential sediment delivered from roads to streams (Table 3.9), 

and more than two orders of magnitude more than native surface segments in the 

Providence Creek watersheds. Native surface segments in José Basin are estimated to 

contribute 

As calculated using the multivariate model for predicting sediment production 

from gravel surface roads, the 29 km of gravel surface roads in José Basin are predicted 

to produce 80 tons of sediment per year. Since 40% of the gravel surface segments are 
126

connected, up to 32 tons yr-1of sediment are delivered to the stream network from gravel 

surface roads. This is just 13% of the estimated sediment delivery from native surface 

segments. Since the gravel surface segments in José Basin have comparable sediment 

production rates and a 33% higher connectivity, most of the eight-fold difference in 

sediment delivery between gravel and native surface roads is due to the much greater 

amount of native surface roads (67 km vs. 29 km). The remaining 3.2-fold difference is 

due to differences in the derived models as well as differences in the representativeness 

of the monitored segments to all of the native and gravel surface segments in José Basin. 

3.4.3. Effects of grading in José Basin

3.4.3.1. Effects of grading on segment characteristics 

Approximately eight kilometers were graded along six different roads in José 

Basin in summer 2008. Prior to grading, the mean length of the 124 segments was 65 m, 

but the variability was very high as the standard deviation was 104 m (Figure 3.14; 

Appendix H). Thirteen segments were greater than 100 m long, and the longest was 1124 

m. There were 109 waterbars on these road segments, but the field assessment indicated 

that only 53% of the waterbars were functioning properly. Waterbar failure was due to 

on-segment deposition on the upslope side of the waterbar, rill erosion through the 

waterbar, and flow depth that exceeded the height of the waterbar. 

During grading 128 waterbars were either installed or reconstructed, and this 

decreased the mean segment length from 65 m to 41 m (Figure 3.14). Segment length 

became much more uniform as the overall standard deviation dropped from 104 m to 26 

m. Only six segments were longer than 100 m, and the longest segment was 175 m. 
127

The repeat survey one year after grading showed an overall increase in mean 

segment length of 15% to 47 m, and a 31% increase in the overall standard deviation. 

The increase in mean segment length was true for all six roads. The increase in mean 

length and standard deviation was due to the failure of 28 waterbars, or 22% of the 128 

waterbars installed or reconstructed in summer 2008. Waterbar failure resulted in ten 

segments that were more than 100 m long and two segments longer than 200 m. 

Waterbar failure was again due to on-segment deposition, rill erosion, and flow depths 

exceeding the height of the waterbar.

3.4.3.2. Effects of grading on sediment production

The ungraded and graded native surface segments in José Basin had similar 

lengths and areas (Figure 3.15), but the two groups differed in slope and surface cover. 

The ungraded segments had an average of 9% slope (s.d. = 4%), while the graded 

segments averaged 14% slope, and this difference was highly significant (p < 0.0001) 

(Figure 3.15). The ungraded segments had 71% bare soil on average (s.d. = 15%), and 

the graded segments had 81% bare soil (s.d. = 14%). This significant difference (p = 

0.0048) is due to the blading technique used in grading, which scrapes accumulated duff 

and vegetation growth off of the road surface. The ungraded and graded segments had 

only 4% and 5% gravel cover, respectively (s.d. = 8% and 6%). 

In WY2008 the 13 ungraded native surface segments in José Basin had a mean 

sediment production rate of 1.4 kg m-2yr-1, but the data were highly skewed as indicated 

by the high standard deviation of 2.2 kg m-2 yr-1(Figure 3.8; Appendix D). One ungraded 

segment (JNO6) did not produce any sediment and 11 of the 13 ungraded segments had 
128

sediment production rates less than 2 kg m-2yr-1, but one segment (JBT14) produced 

nearly 7.9 kg m-2yr-1. 

In WY2008, valid sediment production data were obtained from only three of the 

nine graded segments in WY2008, as the sediment eroded from the other six segments 

overtopped the sediment fences. The mean sediment production rate for these three 

segments was 10.6 kg m-2yr-1(s.d. = 3.9 kg m-2yr-1), or 7.7 times higher than the mean 

value for the ungraded segments (p < 0.0001) (Figure 3.8; Appendix I). The range of 

values was from 6.1 to 13.0 kg m-2yr-1.

In WY2009 the mean sediment production rate from the 30 ungraded native 

surface segments was 2.0 kg m-2 yr

-1

(s.d. = 3.1 kg m-2 yr

-1

), or 43% higher than in 

WY2008 (Figure 3.8). One third of the segments had sediment production rates greater 

than 2 kg m-2yr

-1

. The sediment production rate for JNO3 was 12.9 kg m-2yr

-1

, which 

was the highest sediment production rate for an ungraded native surface road segment in 

either WY2008 or WY2009. 

In WY2009 the mean sediment production for the 24 graded segments was 5.1 kg 

m

-2

yr-1(s.d. = 4.9 kg m-2yr-1), which is 2.6 times the mean value for the ungraded native 

surface segments (p = 0.0007) (Figure 3.8). Nine of the 24 graded segments had 

sediment production rates greater than 5 kg m-2yr-1. The sediment production rate for 

JBT19 was 20.4 kg m-2yr-1, which was the highest rate among the 297 segment-years of 

data collected in this study between WY2004 and WY2009.

Sediment production from the ungraded and graded road segments was 

significantly related to segment slope (R2= 0.36, p < 0.0001) (Figure 3.16). After 

normalizing sediment production by segment slope to account for the differences in 
129

slopes between the ungraded and graded road segments, the graded road segments still 

produced 4.2 times more sediment per unit area than the ungraded segments in WY2008 

(p = 0.01) and 1.6 times more sediment in WY2009 (p = 0.06) (Figure 3.17). 

With respect to the six matched pairs of graded and ungraded segments (Table 

3.10), the graded segments generally produced about five times more sediment than the 

ungraded segments (Figure 3.18). In one case, the graded segment generated 4.1 kg m2

yr-1 while the ungraded segment produced no sediment. For the other five pairs the 

graded segments produced three to nine times more sediment than the ungraded 

segments. The graded segments did have 21% more area, 1% higher slope, and 40% 

more bare soil (Table 3.10), but these differences only account for 42% of the observed 

differences using equation 3.4.

The third comparison between graded and ungraded road segments was for four 

segments with one year of data prior to grading (WY2008) and one year of data after 

grading (WY2009). Sediment production for segments JBT2 and JBT4 was three and 

nearly seven times greater in the year after grading, which is much more than the overall 

increase in sediment production of 47% for ungraded segments from WY2008 to 

WY2009. In contrast, sediment production for segments JBT1 and JNU1 was much 

lower for the year after grading than the year before grading (Figure 3.19). The largest 

decline was for JNU1, which was graded by Southern California Edison, while the other 

three segments were graded by SNF. This variability is not readily explained, and 

indicates the need for sufficient replication in order to detect a significant effect. 

The change in sediment production after grading was evaluated over time for the 

three native surface road segments graded in summer 2007. Sediment production 
130

decreased sharply from the first to the second year after grading for all three segments 

(Figure 3.20), as the mean value dropped from 10.6 kg m-2yr-1(s.d. = 3.9 kg m-2yr-1) in 

the first year after grading to 5.3 kg m-2yr-1(s.d. = 3.9 kg m-2yr-1) in the second year, or 

a mean decline of 52%. This decline occurred despite the 47% increase in sediment 

production for ungraded, native surface segments from WY2008 to WY2009. 

3.4.3.3. Rill erosion after grading

Rills at least five centimeters deep formed on 31% of the 172 graded road 

segments within one year after grading. The length of the segments with newly-formed 

rills ranged from 16 m to 243 m (mean = 55 m, s.d. = 45 m), and the mean length of the 

segments with rills was 28% longer than the segments without rills (p = 0.03) (Table 

3.11). The segments with rills had a significantly higher mean slope of 11% (s.d. = 4%) 

as compared to the mean slope of 8% for segments without rills (p = 0.0004) (Table 

3.11). The amount of bare soil was very similar for the segments with and without rills, 

but the segments with rills had a mean gravel cover of only 7% (s.d. = 11%), which was 

half of the mean value for the segments without rills (p = 0.017) (Table 3.11). 

The mean total rill length for the 53 segments with rills was 19.2 m and the 

standard deviation was relatively high at 27.5 m. The mean was skewed by two segments 

with more than 110 m of rills. If these two segments are excluded, the mean rill length is 

9.7 m. The mean rill volume for the 53 segments was 0.22 m3(s.d. = 0.41 m3), while the 

median was 0.08 m3. A survey of 17 segments in summer 2008 showed a mean road 

segment length above the rill initiation point of 9.0 m (s.d. = 7.1) and a range of 0 m to 

24 m. Rills beginning at the very top of the segment were likely headcut after initiation. 
131

The slope of the road above the rill initiation point also was highly variable, as this 

ranged from three to 24% (mean = 13%, s.d. = 7%). For the area above the rill, the 

visually estimated percent bare soil ranged from 65-100% and the percent gravel cover 

was from 0-35%. 

Rills formed in the first wet season after grading on all three segments with valid 

sediment production values. Rill volume was measured on two of these segments, and 

the mean value was 0.15 m3(s.d. = 0.05 m3). The estimated mass of rill erosion was 196 

kg or 46% of the measured sediment production on segment JBT8, and 319 kg or 49% of 

the measured sediment production on JBT9 (Table 3.12). 

In WY2009, 19 of the 24 graded segments with sediment fences developed rills. 

The 19 segments with rills had a mean sediment production rate of 2.1 kg m-2yr

-1

(s.d. = 

2.3 kg m-2 yr

-1

), which was slightly higher than the mean value for the five graded road 

segments without rills (mean = 1.9 kg m-2yr

-1

, s.d. = 1.4 kg m-2yr

-1

). The mean 

estimated mass of rill erosion from the 19 segments with rills was 98% (s.d. = 115%) of 

the measured sediment production (Table 3.12), but in six cases the estimated rill erosion 

was more than the measured sediment production. The high values may be partially due 

to deposition of the eroded sediment before reaching the sediment fence. Hence the 

median value of 47% may more accurately indicate the proportion of sediment that is due 

to rill erosion, and this value is very similar to the mean value in WY2008.

3.4.3.4. Effects of grading on road surface bulk density

The mean bulk density for the 13 native surface road segments in José Basin 

immediately before grading was 1.56 g cm-3(s.d. = 0.17 g cm-3). Immediately after 
132

grading the mean bulk density was 1.52 g cm-3(s.d. = 0.20 g cm-3), which is only 

marginally lower (p = 0.66). The pairwise comparison for segments prior to and after 

grading showed that the mean bulk density for four segments decreased, the values for 

six segments stayed approximately equal, and the values for the remaining three 

segments increased (Figure 3.21). 

One year after grading the mean bulk density for the same 13 segments was 1.54 

g cm-3(s.d. = 0.19 g cm-3). Again, the pairwise comparison shows considerable variation 

among segments as bulk density decreased on three segments, increased on five 

segments, and was effectively unchanged for the other five segments (Figure 3.21). 

3.4.3.5. Effects of grading on sediment delivery

The survey of approximately six kilometers of road prior to grading showed that 

32% of the road length was directly connected to the stream network, while 41% of the 

surveyed length had no visible drainage feature. The mean drainage feature length was 

14 m, but this was highly variable as the standard deviation was 18 m. 

Road-stream connectivity decreased by more than half one year after grading, as 

only 13% of the surveyed road length was directly connected to a stream (Figure 3.22). 

This decrease is largely due to the breaking up of longer, hydrologically connected 

segments into shorter segments with no drainage feature. 
133

3.5. Discussion

3.5.1. Effects of graveling on sediment production and delivery

Graveling is typically successful at reducing road sediment production in the 

Providence Creek watersheds, but there was considerable variability in the magnitude of 

its effectiveness between segments and between years. This variability can be attributed 

to variations in climate, surface cover, ad hoc maintenance, and segment characteristics. 

Over the six years of monitoring the mean sediment production rate for gravel 

surface segments was only 22% of the mean value for native surface segments. In 

WY2004 and WY2005 the gravel segments produced only 13-17% as much sediment as 

the native surface segments, but this value increased to 29% in WY2006, which was the 

wettest year in the study (Figure 3.7). In WY2007, which was a very dry year, there was 

no significant difference in sediment production between the gravel and native surface 

segments (Figure 3.7). However, one segment, PG3, produced 0.23 kg m-2in WY2007, 

which was more than an order of magnitude greater than any other gravel surface 

segment in WY2007. The cause of this high value is unknown, as this segment did not 

produce significantly more sediment than the other gravel surface segments in any of the 

other five years of monitoring. If this datum from segment PG3 is excluded, the mean 

sediment production from the gravel surface segments in WY2007 was again 18% of the 

mean value from the native surface segments, or very similar to the values from WY2004 

and WY2005. 

In WY2008 and WY2009 there was no significant difference in the mean 

sediment production rate between the native and gravel surface road segments. The 

sediment production from gravel surface segments among sites varied widely, with 
134

values ranging from zero to 0.3 kg m-2in WY2008 and 0.01 to 0.4 kg m-2in WY2009. In 

both years the sediment production from one graveled segment (PG2) was two to three 

times higher than any of the other graveled segments. The sediment fence for this 

segment was constructed 10-15 meters downslope of the road, and rilling between the 

fence and the road probably increased the amount of sediment captured in the sediment 

fence. If this segment is excluded, the mean sediment production from gravel surface 

segments in WY2008 was 18% of the mean value for native surface segments, which 

again is nearly identical to values in WY2004 and WY2005, and this difference was 

nearly significant (p = 0.12).

In WY2009 there was some ad hoc road maintenance on two gravel surface 

segments, PG1 and the afore-mentioned PG2. This included digging trenches for 

drainage and filling deep ruts with logs, and the sediment production from these two 

segments was respectively 2.6 and 5.3 times the mean value of 0.08 kg m-2 (s.d. = 0.07 kg 

m

-2

) from the other five gravel segments. The increased sediment production for these 

two segments indicates that even small disturbances to the road surface can increase road 

sediment production. A third gravel segment, PG7, had a sediment production rate that 

was an order of magnitude higher than the maximum value for the other four untreated

gravel surface segments (0.19 kg m-2versus 0.05 kg m-2). As with segment PG3 in 

WY2007, segment PG7 did not produce more sediment in the other five water years than 

the mean value from the other gravel segments. The increase in sediment production 

from this segment may be due to concentrated flow in the tire treads observed on this 

segment, or possibly cutslope erosion. The outliers in WY2007 and WY2009 serve as 
135

reminders that there is a great deal of uncertainty in predicting road sediment production,

and the inclusion or omission of one or two sites can greatly alter the results.

Gravel should reduce road sediment production by protecting the underlying road 

surface from rainsplash and reducing shear stress by slowing overland flow velocities. 

The five-fold reduction in sediment production on the gravel segments in the Providence 

Creek watersheds was surprising as the percent gravel cover averaged only 29% and was 

generally only one rock deep. However, the runoff rates in the Providence Creek 

watersheds are generally low as the area is snow dominated, and a thin gravel layer may 

be relatively effective in reducing road surface runoff. As runoff rates increase, the 

effectiveness of this thin layer of gravel may be expected to decline, as the runoff is able 

to erode through, or detach and transport, the thin gravel layer. 

Sediment production from gravel surface roads was much higher in the rain 

dominated José Basin than in the Providence Creek watersheds. Mean annual sediment 

production for gravel segments in José Basin were 60 and 5 times higher in WY2008 and 

WY2009, respectively. This difference is consistent with the 12-13 fold difference in 

mean sediment production between the native surface segments in José Basin and the 

native surface segments in the Providence Creek watersheds (Chapter 2). 

Unlike the Providence Creek watersheds, graveling was not successful in 

reducing road sediment production in José Basin, even though the mean gravel cover was 

29% in each study area. The two-year mean sediment production rate for the gravel 

segments in José Basin was nearly equal to the mean value for the native surface 

segments. The muted effect of graveling in José Basin can be attributed to higher annual 

erosivities and the average of 51% bare soil on the road surface as compared to only 18% 
136

bare soil for the gravel segments in the Providence Creek watersheds. The lower percent 

bare soil for the gravel segments in the Providence Creek watersheds can be attributed to 

the denser forest cover at the higher elevations and the very low traffic levels, resulting in 

40% litter cover. Like gravel, litter can protect the surface from rainsplash detachment 

and can slow the flow velocity, reducing sheetwash and rill erosion. 

To be effective the gravel must be sized so that it is not easily detached by 

rainsplash or overland flow, and have interlocking faces rather than rounded. It also 

should cover the entire travelway and any inside ditch. The highest shear stress can be 

approximated from the rainfall intensity, contributing area, and slope, as road surface 

infiltration is negligible (Luce and Black, 1999). The ineffectiveness of graveling in José 

Basin indicates the need for more than 30% gravel cover and a gravel cover that is more 

resistant to the predicted shear stress based on the design rainfall intensity. With climate 

change the amount and intensity of rainfall in the Providence Creek watersheds may 

increase, and the existing gravel cover can be expected to be less effective in reducing 

road sediment production.

3.5.2. Effects of grading and waterbar installation in José Basin on sediment production 

and delivery

Grading is a routine maintenance technique for increasing drivability, but the 

results show that this greatly increases sediment production and can lead to an increase in 

the amount of sediment delivered to the stream network. In José Basin graded roads 

produced eight and three times more sediment per unit area than the ungraded road 

segments in WY2008 and WY2009, respectively. Among the matched pairs grading 
137

increased sediment production by three to nine times. A smaller increase was measured 

in the northern Sierra Nevada, where recently-graded road segments produced 

approximately two times more sediment per unit erosivity (p = 0.02) (Coe, 2006), and in 

the U.S. Virgin Islands, where graded segments produced 2.5 times more sediment per 

unit precipitation than comparable ungraded road segments (Ramos-Scharrón and 

MacDonald, 2005). 

As with graveling, the effects of grading appear to vary with climate as this 

affects the amount and type of precipitation. In the Eldorado National Forest, graded 

segments produced eight times more sediment than ungraded segments at elevations 

below 1400 m (p = 0.0008), while at elevations above 1400 m there was no significant 

difference in sediment production between graded and ungraded roads (Coe, 2006). The 

large difference found at the more rain dominated lower elevations is directly comparable 

to the large differences observed in José Basin, which also is below 1400 m. Since no 

grading was done in the KREW watersheds, it is not possible to determine how the 

grading effect would differ with elevation and climate, but the six-year record of road 

sediment production in the KREW watersheds would provide an excellent opportunity to 

quantify the effects of grading. 

The results indicate that whenever possible, the frequency of grading should be 

reduced to decrease the frequency of the increase in sediment production. Furthermore, 

the effect of grading is of particular concern in wetter, rain dominated areas because the 

potential increase in sediment production is likely to be higher than in higher elevation, 

snowmelt dominated areas.
138

While grading usually increases sediment production, it can decrease sediment 

delivery by the associated installation and repair of waterbars. Waterbars can both reduce 

sediment production by breaking up longer segments, and reduce sediment delivery by 

directing road discharge onto hillslopes and away from the streams. In José Basin, 32% 

of the road length was connected to the stream prior to grading, while after grading only 

13% of the road length was connected. This 2.5-fold decrease in delivery did not fully 

compensate for the three to eight-fold increase in sediment production, suggesting that 

grading would result in a potential 20-320% increase in sediment delivery. 

Grading may have been more successful in reducing road sediment delivery in 

José Basin if less than 22% of the newly installed and repaired waterbars had not failed

the first year after grading. The failure of the waterbars was due to wheel ruts or rill 

erosion through the waterbars, sediment deposition upslope of the waterbar, and flow 

depths that exceeded the height of the waterbar. The management implications are that 

waterbars should: 1) be as high and as densely compacted as possible while continuing to 

allow traffic in order to maximize the likelihood that they will be effective over time; and 

2) they must have a sufficient cross-slope gradient to carry the sediment off the road 

instead of allowing it to accumulate on the road upslope of the waterbar. Restricting 

driving in wet conditions will also reduce waterbar failure, as this is will greatly reduce 

the chance of wheel ruts cutting through the waterbar. 

The larger increases in sediment production relative to the decrease in sediment 

delivery suggest that grading should be minimized in José Basin. A reduction in the 

frequency of grading to reduce sediment production rates also was recommended for 

roads on St. John (Ramos-Scharrón and MacDonald, 2005), state forest roads in Oregon 
139

(Mills et al., 2007), and roads in western Montana (Sugden and Woods, 2007). The need 

for grading also can be reduced by restricting road use and construction during wet 

periods, as this reduces rut formation and helps maintain the drivability of the road 

(Barrett and Conroy, 2002; Sugden and Woods, 2007). 

3.5.3. Monitoring and management

The relative variability in sediment production between years and between sites 

can be used to help determine the most efficient strategy for measuring road sediment 

production—is it better to monitor more sites for fewer years, or fewer sites for more 

years? The mean annual sediment production from gravel surface segments for the six 

years of monitoring in the Providence Creek watersheds ranged from 0.04 kg m-2to 0.15 

kg m-2, and the coefficient of variation for the mean annual sediment production was 1.2. 

These annual mean values were very similar to the annual mean values of 0.01 kg m-2to 

0.21 kg m-2 measured for gravel road segments in the Idaho batholith (Burroughs and 

King, 1989). 

The coefficient of variation between sites within years varied from 0.8 to 2.2 and 

averaged 1.4 (s.d. = 0.5). Sediment production from native surface segments in the 

Providence Creek watersheds was skewed, as the overall mean was 0.72 kg m-2yr-1, 

while the median was only 0.21 kg m-2yr-1. In the northern Sierra Nevada, mean erosion 

rates were also skewed by a select few gravel surface segments, so that the median value 

for the 30 segment-years was 0.0009 kg m-2yr-1 while the mean value was over an order 

of magnitude higher at 0.12 kg m-2yr-1(Coe, 2006). The slightly higher coefficient of 

variation between sites than between years in the Providence Creek watersheds suggests 
140

that the most efficient strategy for measuring road sediment production may be to have 

more sites with fewer years of monitoring, although multiple years are needed to capture 

at least some of the interannual variability and more extreme values. 

The skew and high inter-site variability also indicates that it is often just a few 

segments that contribute the highest sediment yields to the stream, and so practices to 

reduce road sediment delivery first need to pinpoint segments with high sediment 

production and delivery potential. As previously discussed, the higher-producing 

segments are typically larger, steeper segments with extensive rilling. These types of 

segments that feed into stream crossings or are in close proximity to streams should be 

the highest priority for treatment. Segments with cutslope erosion and segments with tire 

treads that can concentrate overland flow also should be targeted. Sediment reduction 

strategies should focus on rocking and/or outsloping these segments, and reducing the 

accumulation and delivery of overland flow by outsloping or installing waterbars. 

3.6. Conclusions

Sediment production and delivery from forest roads was monitored for 249 road 

segment-years in the southern Sierra Nevada of California. From WY2004 through 

WY2009, sediment production rates were monitored on native, gravel, and mixed surface 

roads, as well as from ditches adjacent to paved roads in the Providence Creek 

watersheds (1485 m to 2005 m) of the Kings River Experimental Watershed. For two 

water years, sediment production rates also were monitored from native surface, gravel 

surface, and recently-graded road segments in José Basin, which is a lower elevation, rain 

dominated watershed. Road characteristics were surveyed in the two areas, and potential 
141

delivery was determined by surveying drainage features leaving the road surface and 

determining road-stream connectivity.

In the Providence Creek watersheds, graveling was typically successful at 

reducing road sediment production, but this difference was sometimes muted by 

individual segments with high values. Graveling all of the native surface roads in the 

Providence Creek watersheds could reduce their sediment production by 78%. In 

contrast, the gravel surface segments in José Basin did not produce significantly less 

sediment than the native surface segments. The thin gravel layer found in the study areas 

is less or ineffective at reducing road sediment production in wet years and areas with 

higher annual erosivity. To be effective, the gravel segments in José Basin will need 

more than 30% gravel cover and gravel that is either deeper or larger. 

The graded road segments in José Basin produced three to eight times more 

sediment than ungraded segments. Rill erosion is estimated to account for approximately 

half of the sediment produced in the first year after grading. Grading initially decreased 

the mean segment length by 37%, but mean segment length increased 15% in the first 

year after grading due to the failure of 22% of the constructed and reinstalled waterbars. 

The large increase in sediment production coupled with the smaller decrease in 

connectivity resulted in an estimated 20-320% increase in sediment delivery in the year 

after grading.

The frequency of grading should be reduced as much as possible in José Basin to 

decrease the occurrence of a sediment pulse to the stream network. Waterbars of 

adequate height and cross-slope must be constructed or repaired during grading to reduce 

delivery. Perhaps the most beneficial best management practice to reduce sediment 
142

production from roads is to restrict traffic under wet conditions, as this will reduce 

waterbar failure and the need for grading.
143

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production using a vector geographic information system. Earth Surface Processes and

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Management practices for sediment reduction from forest roads in the coastal plains. 

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Barret, J.C., and W.J. Conroy. 2002. Improved practices for controlling both point and 

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Conference, Fort Worth, Texas, USA. Pp. 301-306.

Beechie, T.J., C.N. Veldhuisen, E.M. Beamer, D.E. Schuett-Hames, R.H. Conrad, and P. 

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Fisheries Society, Bethesda, MD, USA. Pp. 35-65.

Ben-dor, E., and A. Banin. 1989. Determination of organic matter content in arid zone 

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Analysis 20(15-16): 1675-1695.

Bilby, R.E., K. Sullivan, and S.H. Duncan. 1989. The generation and fate of roadsurface sediment in forested watersheds of southwestern Washington. Forest Science 35: 

453-468.

Bowling, L.C., and D.P. Lettenmaier. 2001. The effects of forest roads and harvest on 

catchment hydrology in a mountainous maritime environment. In: Land Use and 

Watersheds: Human Influence on Hydrology and Geomorphology in Urban and Forest 

Areas. Wigmosta, M.S., and S. Burges (eds.). Water Science and Application 2. 

American Geophysical Union, Washington, DC, USA. Pp. 145-164.

Brown, T.C., and D. Binkley. 1994. Effect of management on water quality in North 

American forests. USDA Forest Service GTR-RM-248, Fort Collins, CO, USA. 27 pp.

Brunton, D.A., and R.B. Bryan. 2000. Rill network development and sediment budgets. 

Earth Surface Processes and Landforms 25: 783-800.

Burroughs, E.R., and J.G. King. 1989. Reduction of soil erosion on forest roads. USDA 

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148

3.8. Tables

Table 3.1. Number of native, gravel, and mixed surface road segments and ditches 

adjacent to paved roads that were monitored for sediment production in the Providence 

Creek watersheds from WY2004 to WY2009.

Water year

200

4 2005 2006 2007 2008 2009

Total

s

Native surface road segments 11 13 13 6 6 6 55

Gravel surface road segments 7 7 7 7 7 7 42

Mixed surface road segments 4 4 4 4 4 4 24

Ditches adjacent to paved roads 7 7 7 7 7 7 42
149

Table 3.2. Number of native, gravel, and graded road segments in José Basin with valid 

sediment production values in WY2008 and WY2009.

Water year

2008 2009 Totals

Native surface road segments 13 30 43

Gravel surface road segments 5 11 16

First year post-grading 3 24 27

Second year post-grading 0 3 3
150

Table 3.3. Road segment characteristics measured, estimated, or observed for each 

segment with a sediment fence and the surveyed road segments. /E indicates that the 

characteristic was estimated rather than measured in the surveys conducted on segments 

that were not monitored for sediment production.

Characteristic Measured (M), 

estimated (E), or 

observed (O)

Continuous (C) 

or categorical 

group (G)

Method of 

measurement

Length (m) M C Meter wheel

Surface type (Native, Gravel) O G

Active width (m) M C Cloth tape

Total width (m) M C Cloth tape

Slope (%) M C Clinometer

Bare soil (%) M / E C Cover count

Gravel cover (%) M / E C Cover count

Traffic level (Very low, Low, Medium) E G

Evidence of past surface rocking (Y/N) O G

Cutslope height (m) E C

Cutslope gradient (%) M C Clinometer

Cutslope percent bare soil (%) E C

Slope of upper hillslope (%) M C Clinometer

Slope of lower hillslope (%) M C Clinometer

Ditch width (m) M C Cloth tape

Ditch slope (%) M C Clinometer

Rill length (m) M C Cloth tape

Rill width (m) M C Ruler

Rill depth (m) M C Ruler

Drain type (see Table 3.4) O G

Drain feature (see Table 3.4) O G

Drain armoring (Y/N) O G

Water cross armoring (Y/N) O G

Armoring buried (Y/N) O G

Armoring intact (Y/N) O G

Pushout present (Y/N) O G

Pushout effective (Y/N) O G

Fillslope erosion (Y/N) O G

Maximum fillslope rill depth (m) M C Ruler

Multiple fillslope rills (Y/N) O G

Drainage feature length (m) M C Cloth tape

Drainage feature slope (%) M C Clinometer

Drainage feature roughness (1,2,3,4) O C

Connectivity class (1,2,3,4) O G

Culvert present (Y/N) O G

Culvert plugged (%) E C

Scour at culvert outlet (Y/N) O G

Volume of scour at culvert outlet (m3) M C Cloth tape
151

Table 3.4. Drain type and drain feature categories used to describe each road segment. 

Slashes indicate a mixture of types or features within a road segment where flow was 

restricted to one discrete drainage point by berms and/or the cutslope. 

Drain types Drain features

Insloped Diffuse

Outsloped (diffuse) Dip

Outsloped (with a berm) Pushout

Planar Waterbar

Through cut Stream crossing

Insloped/Planar Cattle guard

Insloped/Outsloped with a berm On segment deposition

Outsloped with a berm/Planar Intersection

Planar/Outsloped Diffuse/Dip

Insloped/Outsloped/Planar Diffuse/Waterbar

Diffuse/Pushout

Diffuse/Intersection

Diffuse/On segment deposition

Dip/Pushout

Dip/On segment deposition

Cattle guard/Pushout

Intersection/On segment deposition
152

Table 3.5. Definition of each connectivity class and the associated potential for runoff 

and sediment to be delivered to the stream network.

Connectivity Definition Potential for 

class sediment delivery

1 Drainage feature <10 m long. Very low

2 Drainage feature <20 m long. Low/moderate

3 Drainage feature >20 m long but more than 

10 m from a stream channel.

Moderate/high

4 Drainage feature to within 10 m of a stream 

channel, regardless of length.

High
153

Table 3.6. Elevation and annual precipitation and erosivity for the functioning rain gages 

in José Basin in WY2008 and WY2009. – indicates that the gage did not collect valid 

data for that water year.

Rain gage Elevation (m) Precipitation (mm) Erosivity (MJ ha-1 mm hr-1)

WY2008 WY2009 WY2008 WY2009

JRG1 1050 462 -- 674 --

JRG2 1100 581 403 732 160

JRG3 1120 501 -- 522 --

JRG4 1250 -- 677 -- 568

JRG5 1000 533 582 603 449

Mean (s.d.) 1100 (90) 519 (50) 554 (139) 633 (91) 393 (210)
154

Table 3.7. Correlation coefficients, coefficients of determination, and p values for the 

regressions between key site variables and annual sediment production from gravel 

surface road segments in José Basin. Values in bold are significant at p ≤ 0.10.

Variable r R

2

p value

Length (m) -0.40 0.17 0.12

Area (m2) -0.42 0.17 0.11

Slope (%) -0.48 0.23 0.06

Area*slope (m2) -0.54 0.29 0.03

Percent bare soil 0.48 0.23 0.06

Percent gravel cover -0.05 0.00 0.90

Elevation (m) -0.40 0.16 0.13

Annual precipitation (mm) 0.44 0.20 0.08

Erosivity (MJ ha-1 mm hr-1) 0.67 0.45 <0.01

Rill length (m) -0.37 0.14 0.15

Rill volume (m3) -0.29 0.09 0.27
155

Table 3.8. Significance of the variables in the multivariate model for predicting sediment 

production from gravel surface road segments in José Basin.

Variable p value

Annual erosivity (MJ ha-1 mm hr-1) 0.0003

Segment area (m2) 0.0004

Segment slope (%) 0.0008

Segment area*slope (m2m m-1) 0.0014
156

Table 3.9. Mean sediment production rate, road length, mean width, and proportion of the road surface directly connected to 

the stream network for native, gravel, mixed surface roads, and road ditches in the Providence Creek watersheds. *The 

potential sediment delivered and the proportion of total potential delivered sediment in José Basin were predicted by the 

multivariate models, rather than by using mean sediment production rates. 

Mean sediment 

production rate 

(kg m-2yr-1)

Road 

length 

(km)

Mean road 

width (m)

Proportion 

connected

Potential 

sediment 

delivery

(kg yr-1)

Proportion of 

total potential 

delivered 

sediment 

Providence Creek watersheds

Native surface roads 0.78 7.6 2.2 0.04 470 0.35

Gravel surface roads 0.16 1.5 2.3 0.11 60 0.04

Mixed surface roads 0.35 2.8 2.6 0.31 800 0.59

Ditches adjacent to paved roads 0.02 2.1 3.5 0.16 20 0.02

Total sediment contribution from roads 1,350

José Basin

Native surface roads 1.7 67 2.6 0.30 210,000 0.88

Gravel surface roads 1.6 29 2.6 0.40 30,000 0.13

Total sediment contribution from roads 240,000
157

Table 3.10. Characteristics of and sediment production rates for the six matched pairs of ungraded and graded road segments in 

José Basin.

Road

segment

Ungraded 

or Graded 

Length 

(m)

Width 

(m)

Area 

(m2)

Slope 

(%) A*S

Percent 

bare soil

Percent 

gravel

Sediment 

production rate 

(kg m-2yr

-1

)

JNH5 Ungraded 36 2.5 89 12 1068 66 1 0.0

JNH4 Graded 44 2.6 114 13 1482 84 2 4.1

JPS15 Ungraded 31 2.7 84 4 336 73 0 0.2

JPS16 Graded 45 3.4 153 5 765 94 0 0.7

JPS18 Ungraded 70 2.4 168 8 1344 46 0 0.1

JPS17 Graded 85 2.4 204 10 2040 78 0 0.6

JPS19 Ungraded 28 2.5 70 10 700 49 0 0.2

JPS20 Graded 16 2.7 43 10 430 94 0 0.8

JPS21 Ungraded 28 2.2 62 10 620 54 1 0.3

JPS22 Graded 32 2.8 90 10 900 82 1 3.0

JNH11 Ungraded 30 3 90 10 900 73 10 0.4

JPS23 Graded 29 2.7 78 13 1014 73 13 1.7

Mean (s.d.) Ungraded 37 (16) 2.6 (0.3) 94 (38) 9 (3) 828 (355) 60 (12) 2 (4) 0.2 (0.1)

Graded 42 (24) 2.8 (0.3) 114 (58) 10 (3) 1105 (572) 84 (8) 3 (5) 1.8 (1.4)
158

Table 3.11. Segment and rill characteristics for 119 unrilled road segments and 53 rilled road segments one year after grading, 

and the p values for each comparison.

Segment Segment Percent Percent Drainage Ineffective Rill Rill

length slope bare gravel feature length bars/dips length volume

(m) (%) (m) per km (m) (m3)

No rills present (5,144 m)

Mean 43 8 82 14 10 2.3 -- --

s.d. 27 4 19 18 14 -- --

Rills present (2,934 m)

Mean 55 11 86 7 17 5.5 19 0.22

s.d. 45 4 12 11 15 28 0.41

p values 0.03 0.0004 0.19 0.02 0.01 -- --
159

Table 3.12. Rill volume, bulk density, rill erosion, measured sediment production, and the 

ratio of rill erosion relative to the mass of sediment collected in the sediment fence. All 

segments were graded one year earlier, and NA indicates that no rill erosion was present.

Year Road Rill Bulk Rill Sediment Ratio of rill erosion

graded segment volume density mass production to sediment

(m3) (g cm-3) (kg) (kg) production

2008

JBT8 0.12 1.69 196 428 0.46

JBT9 0.18 1.74 319 658 0.48

2009

JBT1 0.04 1.66 66 89 0.74

JBT2 0.81 1.66 1344 1025 1.31

JBT3 0.08 1.79 141 470 0.30

JBT4 0.1 1.79 178 818 0.22

JBT5 0.21 1.8 380 622 0.61

JBT6 0.07 1.3 87 76 1.14

JBT7 0.17 1.57 260 831 0.31

JBT11 0.91 1.56 1421 2480 0.57

JBT12 0.7 1.32 922 433 2.13

JBT13 NA 1.38 NA 258 NA

JBT14 0.11 1.38 157 333 0.47

JBT17 0.46 2.34 1089 862 1.26

JBT18 3.05 1.37 4184 1375 3.04

JBT19 4.44 1.61 7140 1549 4.61

JBT20 NA 1.75 NA 201 NA

JBT21 0.34 1.33 456 1090 0.42

JNH4 0.06 1.35 84 367 0.23

JNH6 0.14 1.35 189 553 0.34

JNU1 NA 1.29 NA 10 NA

JNU2 NA 1.59 NA 115 NA

PS16 0.01 1.16 16 103 0.16

PS17 NA 1.43 NA 132 NA

PS20 NA 1.43 NA 34 NA

PS22 0.06 1.67 99 269 0.37

PS23 0.04 1.52 55 136 0.40

Mean 0.58 1.55 894 567 0.93

s.d. 1.11 0.24 1706 565 1.10
160

3.9. Figures

Figure 3.1. Location of the national forests in California, including the Eldorado and the 

Sierra National Forest (SNF). Inset is Sierra National Forest, showing José Basin and the 

Kings River Experimental Watersheds (KREW). X indicates the location of the Auberry 

precipitation gage (CA map from http://www.fs.fed.us/r5/forests.shtml).
161

Figure 3.2. Map of the four Providence Creek watersheds in the Kings River 

Experimental Watersheds (KREW) and the sediment fences used to monitor hillslope and 

road sediment production. Contributing areas for the hillslope sediment fences are shown 

in blue. The sediment fences along the main east-west road in the upper part of the map 

are measuring sediment production from the ditches adjacent to this insloped, paved road. 

(Map courtesy A. Korte).
162

Figure 3.3. Roads (in black) and streams (in blue) in José Basin. 
163

Figure 3.4. One or more sediment fences were installed at the drainage point of road 

segments in José Basin and the Providence Creek watersheds. The fence in the 

foreground was installed in summer 2007 in José Basin just below a waterbar draining a 

native surface road segment, and the second fence was added in summer 2008 to prevent 

overtopping.
164

Figur

e 3.5. Twenty percent of the road network in José Basin was randomly selected and 

surveyed. Selected sections are black and the remainder of the road network is shown in 

grey. 
165

0

400

800

1200

1600

2000

2004 2005 2006 2007 2008 2009

Water year Precipitation (mm)

Mean annual precipitation

Figure 3.6. Mean annual precipitation for the Providence Creek watersheds for WY2004 

to WY2009. Error bars represent one standard deviation.
166

0

1

2

3

4

2004 2005 2006 2007 2008 2009

Water year Sediment production (kg m-2 yr-1

)

Native surface road segments

Gravel surface road segments

Mixed surface road segments

Ditches adjacent to paved roads

Figure 3.7. Mean annual sediment production in the Providence Creek watersheds for 

WY2004 through WY2009 for native, gravel, and mixed surface road segments as well 

as ditches adjacent to paved, insloped road segments. Error bars represent one standard 

deviation.
167

Figure 3.8. Mean sediment production rates in José Basin for WY2008 and WY2009 for 

ungraded native surface road segments, gravel surface road segments, and road segments 

one and two water years after grading, respectively. Error bars indicate one standard 

deviation.
Figure 3.9. Mean sediment production rate for native and gravel surface road segments 

in José Basin and the Providence Creek watersheds for WY2008 and WY2009. Error 

bars indicate one standard deviation.
169

0

1

2

3

4

0 1 2 3 4 5 6 7

Observed rate (kg m-2 yr

-1) Predicted rate (kg m-2 yr-1

)

R

2

 = 0.57

Figure 3.10. Observed versus predicted sediment production rates (kg m-2yr-1) for gravel 

surface segments in José Basin. Line shows a 1:1 relationship.
170

0%

20%

40%

60%

80%

100%

Native

surface

segments

Gravel

surface

segments

Mixed

surface

segments

Ditches

adjacent to

paved roads Cumulative percent 

1 2

3 4

Connectivity 

class

Figure 3.11. Hydrologic connectivity classes for native, gravel, and mixed surface road 

segments in the Providence Creek watersheds as well as ditches adjacent to paved roads. 

1 indicates a drainage feature less than 10 m long and at least 10 m from a stream 

channel, and 4 indicates that a segment is connected to the stream channel.
171

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100 120

Drainage feature length (m)

Cumulative proportion

Native surface roads

Gravel surface roads

Figure 3.12. Cumulative proportion of road length versus drainage feature length for 

native and gravel surface roads in José Basin.
172

0%

20%

40%

60%

80%

100%

Native surface roads Gravel surface roads Cumulative percent

1 2

3 4

Connectivity 

class

Figure 3.13. Hydrologic connectivity classes for native and gravel surface roads in José 

Basin. 1 indicates a drainage feature less than 10 m long and at least 10 m from a stream 

channel, and 4 indicates a segment is connected to the stream channel.
173

0

50

100

150

200

9S61 9S307 9S304 9S304A 9S61B 9S307A Total

Road Segment length (m)

Prior to grading

Immediately following grading

One year after grading

Figure 3.14. Mean segment lengths for six roads in José Basin prior to grading, 

immediately after grading, and one water year after grading. Error bars indicate one 

standard deviation. The standard deviation on 9S307 prior to grading was 300 m.
174

Figure 3.15. Box and whisker plots of a) segment areas and b) segment slopes for the 

ungraded and graded road segments with valid sediment production data in José Basin. 

Boxes represent the 25% and 75% quartiles, lines represent the medians, plus signs 

represent the means, and the whiskers represent minimums and maximums.
175 y = 0.56x - 2.7

R

2

 = 0.36

p < 0.0001

0

5

10

15

20

25

0 5 10 15 20 25

Segment slope (%) Sediment production rate (kg m-2 yr-1

)

Figure 3.16. Annual sediment production versus segment slope for the ungraded and 

graded native surface segments in José Basin for WY2008 and WY2009.
176

0.0

0.2

0.4

0.6

0.8

1.0

2008 Water year 2009 Sediment production normalized by slope (kg m-2 yr-1

)

Ungraded road segments

Graded road segments

Figure 3.17. Mean sediment production rates normalized by slope for ungraded and 

graded segments in WY2008 and WY2009. The differences were significant for both 

WY2008 (p = 0.01) and WY2009 (p = 0.04).
177

0

1

2

3

4

5

1 2 3 4 5 6

Pair number Sediment production (kg m-2 yr-1

)

Ungraded segments

Graded segments

Figure 3.18. Sediment production for WY2009 for each of the six matched pairs of 

ungraded and graded segments in José Basin. 
178

0

2

4

6

8

10

JBT1 JBT2 JBT4 JNU1

Road segment Sediment production (kg m-2

)

One year before grading (WY2008)

One year after grading (WY2009)

Figure 3.19. Annual sediment production for four segments in José Basin for the year 

prior to grading (WY2008) and the year after grading (WY2009).
179

0

5

10

15

JBT8 JBT9 JBT10

Road segment Sediment production (kg m-2 yr-1

)

First year after grading

(WY2008)

Second year after grading

(WY2009)

Figure 3.20. Sediment production rates in the first and second water year after grading 

for three segments in José Basin. 
180

0.0

0.5

1.0

1.5

2.0

2.5

JBT1JBT2JBT3JBT4JBT5JBT6JBT7

JBT11JBT12JBT13JBT14

JNH4

PS16

Road segment Bulk density (g cm-3

)

Prior to grading

Post grading

One year after grading

Figure 3.21. Mean bulk density for 13 road segments prior to grading, immediately after 

grading, and one year after grading. Error bars display one standard deviation.
181

0%

20%

40%

60%

80%

100%

Prior to grading One year after grading Cumulative percent

1 2

3 4

Connectivity

class

Figure 3.22. Hydrologic connectivity classes for six kilometers of road in José Basin 

prior to grading and one year after grading. 1 indicates a drainage feature less than 10 m 

long and at least 10 m from a stream channel, and 4 indicates a segment is connected to 

the stream channel.
182

5. Appendices

Appendix A. Characteristics and sediment production rates for hillslopes in José Basin 

by soil type.

Hillslope

Axis 

Area

Axis Mean Fence Sediment 

length slope side slope elevation production rate

(m) (m2) (%) (%) (m) (kg m-2yr-1)

Hillslopes in Holland soil WY2008 WY2009

JHS4 117 5500 25 11 1037 0.0002 0.0000

JHS7 84 3200 38 20 1225 0.0000 0.0000

JHS9 134 6700 31 13 1174 0.0000 0.0000

Mean 112 5100 31 14 1145 0.0001 0.0000

s.d. 23 1600 6 5 87 0.0001 0.0000

Hillslopes in other soil types

JHS1 120 3600 55 45 1167 0.0014 0.0000

JHS2 67 1100 55 38 1165 0.0009 0.0000

JHS3 249 11700 20 13 947 0.0001 0.0000

JHS5 82 3000 33 9 1133 0.0000 0.0000

JHS8 96 4200 50 27 1206 0.0000 0.0000

JHS10 84 1300 30 15 979 0.0668 0.0000

JHS11 67 1200 25 20 962 0.0045 0.0000

Mean 109 3700 38 24 1080 0.0105 0.0000

s.d. 62 3600 14 13 108 0.0249 0.0000
183

Appendix B. Area, elevation, and sediment production rates for hillslopes in the 

Providence Creek watersheds for WY2004 through WY2009. ―NA‖ indicates that the 

fence did not collect valid data for that water year or was not yet constructed. ―**‖ 

indicates missing data for that water year.

Hillslope Area

(m2)

Fence 

elevation 

(m)

Sediment production rate (kg m-2 yr-1)

WY2004 WY2005 WY2006 WY2007 WY2008 WY2009

PH1 3973 1970 0.0000 0.0000 0.0127 0.0000 0.0001 0.0000

PH2 3922 1973 0.0000 0.0000 0.0178 0.0000 0.0000 0.0000

PH3 4109 1914 0.0000 0.0000 0.1142 0.0000 0.0013 0.0000

PH4 14738 1925 0.0000 0.0000 0.0251 0.0000 0.0000 0.0001

PH5 6078 1904 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

PH6 7124 1916 0.0000 0.0006 0.0072 0.0000 0.0001 0.0000

PH7 12194 1942 0.0000 0.0000 0.0180 0.0000 ** 0.0000

PH8 4201 1960 0.0000 0.0015 0.0919 0.0000 0.0030 0.0000

PH9 2986 1957 0.0000 0.0046 0.0523 0.0000 0.0005 0.0000

PH10 1814 1808 NA 0.0000 0.0230 0.0000 0.0008 **

PH11 1504 1833 NA 0.0000 0.0000 0.0000 0.0020 0.0000

Mean 5700 1918 0.0000 0.0006 0.0329 0.0000 0.0008 0.0000

s.d. 4200 54 0.0000 0.0014 0.0378 0.0000 0.0010 0.0000
184

Appendix C. Area, elevation, and sediment production rates for hillslopes in the Bull 

Creek watersheds for WY2004 through WY2009. ―NA‖ indicates that the fence was not 

yet constructed or did not collect valid data for that water year. ―**‖ indicates missing 

data.

Hillslope Area

(m2)

Fence 

elevation (m)

Sediment production rate (kg m-2yr-1)

WY2005 WY2006 WY2007 WY2008 WY2009

BH1 14892 2294 0.0023 0.0002 0.0000 0.0000 **

BH2 12606 2332 0.0029 0.0037 0.0001 0.0018 0.0025

BH4 26186 2252 0.0017 0.0003 0.0000 ** 0.0000

BH5 22726 2361 0.0019 0.0022 0.0000 ** 0.0000

BH6 18562 2414 0.0013 0.0008 0.0000 0.0000 0.0001

BH7 38445 2426 0.0002 0.0001 0.0000 0.0000 0.0000

BH8 12182 ** NA 0.0000 0.0000  

BH9 18235 **  NA 0.0014 0.0000 ** 0.0000

Mean 20500 2347 0.0017 0.0011 0.0000 0.0005 0.0004

s.d. 8700 68 0.0009 0.0013 0.0000 0.0009 0.0010
185

Appendix D. Characteristics and sediment production rates for native surface road 

segments in Holland soil and other soil types in José Basin for WY2008 and WY2009. 

―NA‖ indicates that the fence did not collect valid data for that water year, the fence was 

not yet constructed, or the segment was graded. ―**‖ indicates missing data.

Segment Length Area Slope Fence elevation Sediment production rate 

(m) (m2) (%) (m) (kg m-2yr-1)

Native surface road segments in Holland soil WY2008 WY2009

JBT1 44 96 9 986 3.8 NA

JBT14 43 91 10 1018 7.9 NA

JNH5 36 89 12 1181 0.1 0.0

JNH7 32 96 2 1083 0.2 0.0

JNH8 30 59 14 1014 1.7 0.1

JNH10 37 99 10 1124 0.2 0.1

JNH12 50 125 10 1141 0.1 0.4

JNH13 60 168 8 1137 1.5 0.1

JNH3 40 99 16 1215 NA 4.9

JNH6 29 75 10 1102 NA 7.4

JNH9 37 99 15 1025 NA 2.1

JNH11 30 90 12 1176 NA 0.4

JNH14 71 200 10 1137 NA 3.6

JPS11 40 120 10 1014 NA 5.2

JPS12 36 72 6 1134 NA 0.0

JPS14 53 164 12 1093 NA 2.9

JPS15 31 84 5 1129 NA 0.2

JPS18 70 168 9 1114 NA 0.1

JPS19 28 70 10 1105 NA 0.2

JPS21 28 62 12 1087 NA 0.3

Mean 42 108 10 1109 1.9 1.6

s.d. 13 38 3 65 2.7 2.3

Native surface road segments in other soil types

JNO4 56 151 4 1011 0.1 0.1

JNO6 31 83 5 982 0.0 0.1

JNO8 37 100 6 958 0.1 0.0

JNO9 32 102 11 920 0.6 4.2

JNU1 28 65 10 1102 NA 1.7

JNO1 48 115 4 ** NA 0.1

JNO3 35 76 11 1015 NA 12.9

JNO5 50 156 14 960 NA 1.3

JNO7 35 94 11 970 NA 8.7

JPS1 45 167 10 913 NA 3.0

JPS3 80 208 8 1034 NA 0.1

JPS4 51 153 3 968 NA 1.6

JPS5 88 246 10 954 NA 0.6

Mean 45 127 8 979 0.2 2.6

s.d. 17 48 3 47 0.3 3.9
186

Appendix E. Characteristics and sediment production rates for native, gravel, and mixed 

surface road segments as well as ditches adjacent to paved roads in the Providence Creek 

watersheds for WY2004 through WY2009. ―NA‖ indicates that the fence was not yet 

constructed or was removed for that water year.

Segment Length

(m)

Area

(m2)

Slope

(%)

Elevation

(m)

Sediment production rate (kg m-2yr-1)

WY2004 WY2005 WY2006 WY2007 WY2008 WY2009

Native surface road segments

PN1 35.0 95 6 1859 0.00 0.00 0.19 NA NA NA

PN2 52.6 140 9 1846 0.52 1.90 3.99 NA NA NA

PN3 23.9 69 4 1837 0.08 0.10 1.24 NA NA NA

PN4 70.3 232 4 1865 0.12 0.93 0.89 NA NA NA

PN5 139.3 514 7 1869 0.97 1.75 2.22 NA NA NA

PN6 31.1 87 12 1961 0.17 0.12 0.89 0.00 0.21 0.24

PN7 54.9 179 7 1964 0.11 0.51 2.69 NA NA NA

PN8 46.8 150 13 1747 1.07 4.24 6.17 0.22 0.04 0.29

PN9 40.7 148 7 1770 0.04 0.00 0.32 0.00 0.01 0.01

PN10 49.3 164 9 1844 0.15 0.03 0.35 0.00 0.02 0.23

PN11 31.7 94 13 1878 0.11 0.19 0.69 0.00 0.08 0.06

PN12 36.3 98 11 1838 NA 0.75 3.42 NA NA NA

PN13 68.0 218 7 1952 NA 0.24 0.51 0.01 0.37 0.03

Mean 52 168 8 1864 0.30 0.83 1.81 0.04 0.12 0.14

s.d. 30 115 3 66 0.38 1.21 1.81 0.09 0.14 0.12

Gravel surface road segments

PG1 54.3 174 11 1965 0.14 0.30 1.02 0.02 0.02 0.21

PG2 26.0 73 19 1964 0.07 0.18 0.65 0.02 0.28 0.42

PG3 71.4 255 5 1748 0.00 0.04 0.16 0.23 0.00 0.01

PG4 67.3 244 3 1761 0.01 0.01 0.07 0.01 0.00 0.02

PG5 21.5 80 14 1766 0.03 0.12 0.87 0.00 0.03 0.09

PG6 67.1 239 13 1838 0.03 0.12 0.09 0.00 0.05 0.09

PG7 39.9 134 14 1871 0.02 0.20 0.74 0.00 0.02 0.19

Mean 50 171 11 1845 0.04 0.14 0.52 0.04 0.06 0.15

s.d. 21 78 6 93 0.05 0.10 0.40 0.09 0.10 0.14

Mixed surface road segments

PM1 90.5 434 9 1822 0.19 0.79 2.63 0.07 0.58 0.16

PM3 150.7 652 9 1738 0.00 0.00 0.01 0.00 0.02 0.00

PM4 64.3 312 10 1760 0.02 0.21 0.37 0.00 0.18 0.01

PM5 75.6 288 12 1841 0.34 0.43 1.48 0.00 0.44 0.36

Mean 95 422 10 1790 0.14 0.36 1.12 0.02 0.30 0.13

s.d. 38 167 1 49 0.16 0.34 1.19 0.03 0.26 0.17

Ditches adjacent to paved roads

PDi1 80.8 372 6 1941 0.000 0.014 0.018 0.000 0.011 0.004

PDi2 178.6 925 9 1948 0.000 0.000 0.000 0.000 0.000 0.000

PDi3 36.8 162 4 1910 0.000 0.000 0.000 0.000 0.000 0.000

PDi4 116.8 594 10 1891 0.000 0.014 0.064 0.000 0.001 0.002

PDi5 45.9 237 4 1894 0.000 0.000 0.000 0.000 0.017 0.004

PDi6 57.9 311 11 1758 0.010 0.020 0.581 0.000 0.046 0.031

PDi7 110.3 467 7 1822 0.000 0.000 0.000 0.000 0.000 0.001

Mean 90 438 7 1880 0.001 0.007 0.095 0.000 0.011 0.006

s.d. 50 258 3 68 0.003 0.008 0.216 0.000 0.017 0.011
187

Appendix F. Characteristics and sediment production rates for native surface road 

segments in the Bull Creek watersheds for WY2005 through WY2009.

Segment Length Area Slope Fence elevation Sediment production rate (kg m-2 yr-1)

(m) (m2) (%) (m) WY2005 WY2006 WY2007 WY2008 WY2009

BN1 33.9 88 13 2237 0.33 0.09 0.00 0.09 0.39

BN2 58.5 152 10 2245 0.28 0.11 0.00 0.04 0.68

BN3 54.2 201 5 2251 0.11 0.18 0.00 0.01 0.06

BN4 112.8 384 8 2248 0.56 0.56 0.00 0.03 0.24

BN5 76.5 252 10 2285 0.17 0.02 0.00 0.00 0.00

BN6 47.5 176 7 2374 0.03 0.00 0.00 0.00 0.03

BN7 36.6 149 8 2403 0.17 0.08 0.00 0.00 0.05

BN8 67.8 251 12 2247 0.30 0.04 0.00 0.20 0.62

BN9 29.4 92 4 2340 0.00 0.00 0.00 0.00 0.00

Mean 57.5 194 9 2292 0.22 0.12 0.00 0.04 0.23

s.d. 26.0 92 3 64 0.17 0.18 0.00 0.07 0.27
188

Appendix G. Characteristics and sediment production rates for gravel surface segments 

in José Basin for WY2008 and WY2009. ―NA‖ indicates that the fence did not collect 

valid sediment production data for that year.

Segment Length Area Slope Fence elevation Sediment production rate (kg m-2yr-1)

ID (m) (m2) (%) (m) WY2008 WY2009

JGH3 37 89 12 1106 3.4 1.1

JGH4 22 57 14 1080 3.5 1.4

JGH5 26 66 10 1071 6.6 3.4

JGH6 55 137 9 1115 3.3 0.1

JGH10 39 119 12 1219 1.4 0.0

JGH7 80 192 17 1071 NA 0.3

JGH8 60 173 11 1115 NA 0.3

JGH9 45 112 16 1164 NA 0.1

JGH11 29 68 15 1199 NA 0.6

JGH12 49 114 20 1134 NA 0.3

JGH13 25 55 19 1108 NA 0.1

Mean 42 107 14 1126 3.6 0.7

s.d. 18 46 4 50 1.9 1.0
Appendix H. Mean segment characteristics and waterbar data for six different road sections in José Basin prior to, 

immediately after, and one water year following grading.

Prior to grading Immediately after grading One year after grading

Segment length Waterbars Segment length Segment length Waterbars

Road n Total Mean s.d. n % failed n Total Mean s.d. n Total Mean s.d. Total % failed

9S61 71 3657 52 31 72 33 99 3670 37 20 83 3646 44 25 74 19

9S307 13 1864 143 302 17 82 44 1858 42 29 38 1841 45 38 10 50

9S304 21 1216 58 33 0 0 24 1239 52 33 23 1294 56 37 3 33

9S304A 4 225 56 37 6 83 6 220 37 14 9 222 25 10 32 25

9S61B 4 253 63 10 3 33 6 201 34 13 5 235 47 27 4 0

9S307A 11 860 78 71 11 64 18 847 47 37 14 840 60 57 5 0

Total 124 8075 65 104 109 47 197 8035 41 26 172 8078 47 34 128 22
190

Appendix I. Characteristics and sediment production rates for road segments one and 

two years after grading in José Basin. * indicates that the production data are from 

WY2008, while all of the other data are from WY2009.

Fence Length Area Slope Fence elevation Sediment production rate

(m) (m2) (%) (m) (kg m-2yr-1)

One water year after grading

JBT8* 32 70 6 1013 6.1

JBT9* 23 51 5 1007 12.8

JBT10* 24 60 8 988 13.0

JBT1 44 96 3 980 0.9

JBT2 46 150 6 982 6.8

JBT3 47 107 4 1002 4.4

JBT4 32 83 7 1036 9.9

JBT5 39 113 9 1034 5.5

JBT6 60 145 3 979 0.5

JBT7 41 119 3 969 7.0

JBT11 83 200 4 993 12.4

JBT12 56 118 7 1018 3.7

JBT13 37 82 5 1019 3.2

JBT14 43 91 2 1032 3.7

JBT17 25 69 14 1004 12.5

JBT18 49 147 60 998 9.4

JBT19 30 76 15 1009 20.4

JBT20 23 64 20 1022 3.1

JBT21 58 151 13 1022 7.2

JNH4 41 90 9 1254 4.1

JNU1 28 65 1 1134 0.2

JNU2 29 67 3 1144 1.7

JPS16 45 153 2 1112 0.7

JPS17 85 204 5 1101 0.6

JPS20 16 43 8 1105 0.8

JPS22 32 90 3 1155 3.0

JPS23 29 78 5 1191 1.7

Mean 41 103 9 1048 5.7

s.d. 17 43 11 74 5.1

Two water years after grading

JBT8 32 70 17 1156 2.4

JBT9 23 51 18 918 5.1

JBT10 24 60 14 847 8.2

Mean 26 60 16 974 5.3

s.d. 5 10 2 162 2.9