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FOREST ROADS AND AQUATIC ECOSYSTEMS:

A REVIEW OF CAUSES, EFFECTS, AND MANAGEMENT PRACTICES

NCASI Forest Watershed Task Group

1.0 INTRODUCTION

The impacts versus values of forest roads have been the subject of recent debate in the United

States. Forest roads historically have had substantial adverse effects on streams. Depending on

how they are managed, roads can continue to impact streams today. The objectives of this paper

are to describe 1) why roads are critical for effective land management; 2) the impacts of

historical road construction practices; and 3) how legacy and current effects of roads can be

systematically evaluated and managed to reduce impacts to acceptable levels.

In 1997, the debate over roads intensified as a result of the Interior Columbia Basin Ecosystem

Management Project (ICBEMP) Assessment of Ecosystem Components in the Interior Columbia

Basin (Quigley and Arbelbide 1997). This assessment found that increasing road densities

(combined with the activities associated with roads) are correlated with declines in anadromous

salmonid species. However, the ICBEMP report also noted that the component contributions

(causes) of effects associated with roads could not be identified, and that they were therefore

“forced to use roads as a catch-all indicator of human disturbance.” Since that time, a number of

road mileage control and reduction efforts have developed. The Forest Service and Bureau of

Land Management (BLM) have accelerated road obliteration activities. The Federal Roadless

Area Initiative would prohibit construction of new roads in “roadless” areas of Forest Service

and BLM lands (implementation is currently in suspension). The Forest Service has also

developed a Road Analysis procedure to assess road conditions and management needs

(USDAFS 1999). The National Marine Fisheries Service’s (1996) “Matrix” includes road

density as a screening criteria for considering whether proposed federal actions will have adverse

effects on threatened and endangered species. The US Environmental Protection Agency has

suggested that road density be used as a means of regulating water quality within its Clean Water

Act Section 303(d) regulation of Total Maximum Daily Loads (USEPA 1999).

The focus of this paper is the interaction of forest roads and aquatic ecosystems, and it is written

from the perspective of private, for-profit, forest management businesses competing in the

international forest products market. We discuss only direct impacts of roads, not secondary

effects such as providing access to sportsmen or poachers – these are not road management

problems, but people management problems. Most of the information provided herein is from

the western U.S. While some of the details may differ slightly for other regions, the fundamental

issues and principles that apply to the West remain applicable across the country.

1.1 Working Definition of a Road for this Paper

The definition of a road may seem self-evident. However, definitions have been constructed that

confuse rather than clarify the relationships of roads and streams. For example, USDA Forest

Service (Gucinski et al. 2000) recently offered this definition: Road “ecosystems” are built and

maintained by people . . ., characterized by open fluxes of energy and matter, and a
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predominance of respiration over photosynthesis – that is, they are heterotrophic and highly

subsidized systems.

The goal of this paper is to clarify road and stream interactions, and an uncomplicated definition

serves this purpose. For this paper: Roads are smooth-surfaced corridors for truck and

automobile transportation.

The corridor includes the entire disturbed “road prism” comprised of the road cutslope, the road

tread, the road fillslope, and any additional widening for ditches, berms, or other disturbed

surfaces that are structural parts of the road right-of-way. Figure 1 is taken from the Forest Road

Management Guidebook (ODF 2000) and diagrams the road prism and its components.

Road prism

Natural

hillslope

Cutslope

Ditch

Surfacing

Fillslope

Toe of fill

Natural

hillslope

Figure 1. Road Prism Structural Features

1.2 Road Types

Individual road segments are built and maintained as part of a network that forms a

transportation system. The construction standard and use of any given road segment depends on

its function within the system.

Primary roads are the most heavily traveled roads and generally originate from paved county

or state highways. They are generally surfaced with rock (“graveled” roads), are built for use

throughout the year, and easily accommodate two-way traffic. The locations of many of

these modern-era truck roads were established during development of the initial (often
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railroad-based) transportation system into entire watersheds; for this reason, and others as

discussed more fully in Section 1.6, they are often located on gentle grades near streams.

Secondary roads generally depart from primary roads and may or may not be graveled. The

road location may have been determined at any time over the last 100 years. These roads are

commonly closed during at least part of the year. Two-way traffic is usually accommodated

by turnouts spaced along the route.

Temporary roads are generally unsurfaced, that is, they usually are not surfaced with gravel,

although gravel surfacing of temporary roads is a common practice in particularly wet areas

of the West Coast and Alaska. At least since development of state forest practices rules and

more environmentally sound practices in the 1970s, these roads are generally closed to traffic

immediately after completion of log hauling and/or silvicultural activities such as slash

disposal, thinning, and tree planting. Active measures are generally also taken to re-establish

vegetation on the road surfaces and to allow the road to maintain itself in a condition of low

erosion and low to no sediment delivery to streams.

1.3 Why Do We Need Roads?

Roads are essential for all land management strategies other than wilderness (Burnett 2001).

They provide access for:

Fire control – Forest roads play two key roles in fire control. First, they provide access for

fire fighting manpower and machinery. Second, they provide firebreaks. The fire protection

plan developed to address repeated and catastrophic wildfires in the Tillamook State Forest

in western Oregon is based on a dual purpose road system that provides 1) rapid access to

hazardous areas; and 2) a pre-constructed system of firebreaks that can be accessed rapidly

by fire control personnel and machinery (ODF 1993).

Grazing – Forest roads are commonly used to disperse cattle and sheep throughout summer

range and to collect them in the fall.

Timber management – Forest roads are an essential asset for active timber management.

They provide cost-effective access for timber stand inventory, forest health assessment,

selection and marking of trees to be harvested, timber harvest personnel and machinery, tree

planting stock and tree planting personnel, and the means for removal of harvested trees from

otherwise remote forests via trucks. Alternative access, such as using helicopter yarding, can

be used effectively, particularly for difficult and unstable landscapes. However, even

helicopters require some road system, because they are economically limited by how far they

can fly from harvest areas to landings on roads. Economical flying distances for helicopters

vary depending on the value of the logs being flown, but rarely exceed 1 mile downhill.

Flying distances must be substantially shorter if helicopters are forced to lift and fly loads

uphill to landings, because of the increased time and fuel needed to lift the loads.

Recreation – Although not generally constructed directly for this purpose, forest roads

provide access for a multitude of recreational activities, including recreational driving

(sightseeing), camping, fishing, hunting, berry picking, and others. For example, over
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200 million recreation activity days per year were made to federal lands in the ICBEMP

assessment area, 45% of which were for sightseeing (Quigley and Arbelbide 1997). Forest

roads also access points of departure for trail uses such as hiking, horseback riding, and

ATVs. In fact, points of departure for wilderness access are often found on low volume

forest roads.

1.4 Economics of Road Networks

Although roads are essential to land management for forest products and other uses such as

recreation, there remain legitimate concerns about where roads should be located and how many

roads are necessary. The number of roads required for active forest management in an area is

determined by both environmental and economic considerations. Once environmental

requirements such as avoidance of unstable slopes and troublesome stream crossings are assessed

and constraints on potential road locations are understood, log yarding costs are compared to

road construction and maintenance costs. Yarding of logs with cable systems is commonly used

on steep slopes for both environmental and cost considerations, but the difficulty increases

rapidly with increasing yarding distance and distance between roads, particularly in steep and/or

highly dissected topography. As a result, cable yarding costs increase rapidly and nonlinearly

with increasing yarding distance. Similar tradeoff considerations also apply to ground-based

tractor skidding operations often used on gentler terrain.

Road construction costs can vary widely, depending on the road standard (see discussion below)

and site conditions (see discussion above). Road construction costs range from less than $10,000

per mile on gentle terrain remote from streams, to over $200,000 per mile on steep slopes where

the design requires features and practices that prevent landslides and delivery of sediment to

streams (Scherer 2000; Clark et al. 2000). Typically, as slopes become steeper and as

environmental hazards such as landslides or road surface erosion and sediment delivery to

streams increase, road design requirements to address these hazards become more and more

expensive (Furniss et al. 1991). In some situations, environmental hazards may be so great that

design and construction requirements become prohibitively expensive, or hazards cannot be

addressed irrespective of design. Alternative but more expensive yarding systems, such as

long-reach skyline cable systems or helicopters, may then be necessary.

In the ideal and theoretically pure economic calculation, additional road is not justified when the

cost of building more road exceeds the savings due to reduced yarding distance. However,

complex terrain, land ownership patterns, existing roads, and/or environmentally unacceptable

locations often dictate road spacing, which in turn often requires road density to increase beyond

an economic optimum.

1.5 Road Management

Road building, upgrading, and maintenance are basic to commercial forestry operations and

require a significant part of company operating budgets. They are crucial in the active

management of the land and movement of forest products off the land. Because of their high

value and potential environmental consequences, road assets are constantly managed.

Management involves seven key steps:
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Transportation system planning – Roads must be located to serve their intended

transportation system objectives while at the same time meeting environmental constraints

and requirements. These dual objectives provide a classic case where neither objective can

be completely optimized, and a satisfactory solution is sought where both economic and

environmental goals can be adequately met. Harvest methods, anticipated traffic, operating

speeds, and safety requirements must be considered. All of these influence road width and

alignment, which affect areas of disturbance and environmental consequences.

Route reconnaissance and location – Based on the constraints identified in the transportation

system planning process, the next step is to determine specific road locations. Alternative

routes are carefully reviewed in the office and in the field using all available information,

including past performance of existing roads in the area or nearby similar areas, aerial

photos, soils data, geology, topographic maps, stream locations, and fisheries information.

Road design – This is the step where various measures to control potential adverse effects of

roads on watershed processes are considered. Road design involves translation of field

location survey and other data into specific plans to guide construction. Practices for control

of surface runoff, erosion, and delivery processes are prescribed at this stage. In addition,

future maintenance needs are considered to assure stability and economical use of the

completed road; if regular maintenance cannot be assured, this must be accounted for in the

design so that erosion and delivery processes are adequately controlled.

Road construction – The best planning and design is useless unless it is incorporated into the

finished product (Megahan 1977). Competent supervision of the construction phase is

required. Important erosion control practices to consider during construction include:

- Keep slope stabilization work as current as possible with road construction.

- Thoroughly clear and grub brush, timber, stumps, and other woody debris from roadbed

and fill areas to prevent potentially serious surface and mass erosion problems.

- Spread cleared vegetation and woody materials over the soil surface below fills to

enhance the sediment trapping and “buffer” characteristics of the slope below the road.

- Keep stream disturbance to an absolute minimum and avoid it altogether during high

flows.

- Limit the work area during construction to small sections to limit exposure of disturbed

area to erosion forces in the event of adverse weather, and keep installation of relief

drains current with sub-grade construction.

Maintenance – Road maintenance is critical in order to provide continued access and control

environmental impacts. Properly maintained roads have a stable surface and an operating

drainage system that drains water from roads as quickly as possible onto the forest floor

instead of directly to streams. Poorly maintained roads are most subject to periodic blockage

or “failure” as transportation systems due to both surface erosion and mass wasting events,

primarily during floods. Erosion and sediment delivery associated with such failures can be

extreme. In addition, roads produce chronic surface erosion impacts, particularly where

poorly located and maintained. Hazard and impact assessments and implementation of
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carefully designed road system maintenance plans can significantly reduce or even eliminate

these impacts (Furniss et al. 1991; ODF 2000). Detailed examples of impact assessment and

road construction and maintenance plan effectiveness are provided in Appendix B

(Section B.5).

Upgrading – Upgrading activities are similar to maintenance. With upgrading, old roads

built to lower standards with lower sensitivity to environmental issues can be brought up to

current standards as forest harvesting occurs in adjacent areas or where priority

environmental concerns are identified (ODF 2000; WFPB 2000).

Closure – Roads that will not be used again in the near future are often closed. This is an

extremely cost-effective measure in cases where environmental concerns do not require

obliteration. At some time in the future, the road may be reconstructed with minimal

disturbance. A key to road closure is achieving self-maintaining drainage. In some cases, for

example where there is significant landslide hazard, old roads may be totally removed from

the landscape. This practice is commonly called obliteration.

1.6 Transportation System History

The system of forest roads in the western US today is the result of over 100 years of human

habitation and use of forest lands. Access for timber harvest and mining were the major driving

forces resulting in the first forest roads, and the location, design, construction, and maintenance

of forest land access has changed dramatically over the last 100 years.

Widespread logging began in the coastal and inland areas of the West in the mid-1800s and early

1900s (Sedell et al. 1991; Bonner School 1976). The earliest logging occurred in locations

adjacent to the ocean, lakes, and rivers where logs could be felled, rolled, or dragged with horses

or steam engines (steam donkeys) directly to the water (Sedell et al. 1991). As water-adjacent

timber ran out, additional water-based horse and steam/cable logging systems were used. These

systems relied on chutes, flumes, and splash dams to move logs downhill and/or downstream.

Horse skid roads, chutes, and many flumes were located in streams, on streambanks, or in

riparian zones. The adverse effects of these early logging practices on stream and channel

characteristics are well documented (Sedell and Luchesa 1982; Sedell et al. 1991). Effects on

erosion and sediment delivery processes are less well documented. However, we know that logs

were commonly dragged downhill directly to streams without erosion control practices, and large

quantities of sediment were undoubtedly delivered to streams in watersheds logged with these

early methods.

Splash damming depended on channel simplification and removal of large wood and boulder

obstructions, as well as artificial and repeated flooding followed by dewatering of channels.

Channel beds and banks were scoured by log-laden flood waters. Use of these practices was

widespread, and in some river systems continued as late as the 1960s (Bisson et al. 1992; Sedell

et al. 1991).

Water-based logging systems were often coupled with railroad logging systems as they were

developed (Robbins 1988). Although some rail routes were located on or near ridgetops, most

were located in valley bottoms and often encroached on the streams, particularly in narrower
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headwater canyons. Railroad logging practices of that era relied on cable logging systems, and

ground-lead and downhill yarding systems were common.

With the advent of more powerful equipment, water and rail-based logging were slowly replaced

by logging truck and logging road-based systems, beginning in the 1930s (Robbins 1988). Both

tractor and cable yarding systems were used to move logs to landings where they could be loaded

onto trucks. Logging roads often occupied old railroad grades, but roadbeds had to be widened,

and in contrast to railroads, truck traffic substantially increases rates of erosion from the

travelway (Reid and Dunne 1984). During this era of ground-based, downhill logging systems,

harvest-related erosion rates have been estimated to exceed background levels by two to three

orders of magnitude (McGreer et al. 1996).

1.7 Interactions with Aquatic Ecosystems

Roads can undoubtedly affect streams and interact with aquatic ecosystems. The linkages of

roads to hydrologic and erosional processes and effects are illustrated schematically in Figure 2.

Erosion

Processes

Hydrologic

Processes

ROAD

EFFECTS

Connectivity

Channel crossings

Gullies

Fish passage Overland flow

(obstructions

 at crossings)

Surface

(fines)

Mass

(fines & coarse)

Water in stream

Peak flows

Scour & fill

Sediment in stream

Water quality

Fish

Channel morphology

Aquatic habitat

Channel

Encroachment

Riparian vegetation

Shade

LWD

Figure 2. Linkages Between Forest Roads and Beneficial Uses
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Managers must address four major potential impacts of roads on aquatic ecosystems. A brief

introduction to each of the effects follows. They are discussed in detail in Sections 2.2 through

2.4, and a discussion of management practices and systems that control such effects can be found

in Appendices B and C.

Hydrologic effects – Roads can change watershed hydrology by intercepting subsurface flow

from hillslopes and by generating overland flow from the road prism. Water may be routed

directly to streams or onto adjacent hillslopes, with the potential effect of changing peak

flows (increases or decreases). If increases in peak flows are large enough, there is potential

for affecting channel morphology and dependent biological systems.

Erosion and delivery of sediment to streams – Both fine and coarse sediment can be

delivered from roads to streams. Runoff from road surfaces often contains fine sediment

(particles of sand size and smaller, usually defined as 2 mm and smaller). This fine sediment

can impact aquatic ecosystems by filling interstitial spaces in streambed gravels and/or by

increasing turbidity levels. Roads can also be a source of coarse sediment that originates

through mass erosion (landslides). Large quantities of coarse sediment introduced to stream

systems during floods can contribute to channel scour, deposition, avulsion (out-of-bank

change of stream course), and other major adjustments in channel morphology.

Channel encroachment – Roads located in valley bottoms, especially in narrow valley

bottoms, may directly impinge on channels. This may result in increases in channel gradient

and reduced opportunity for overbank flow, as well as decreases in desirable habitat area or

alterations in habitat characteristics (e.g., shade, opportunity for large woody debris

recruitment). Road stream crossings can result in channel changes immediately downstream

of the crossing due to the effects of focusing water through a narrow culvert (in comparison

to stream width).

Fish passage – Road culverts may block fish passage where they are too high above the base

channel for fish to jump or where the gradients and velocities in the culverts are too steep and

rapid for fish passage.

1.8 Changes in Road Management

The result of over 100 years of forest access is that most of the roads needed today for

management of private lands have already been built. However, much of today’s existing road

system was designed and built to standards and in locations that would not be used if the system

were built “from scratch” today. Road effects, when aggregated at the landscape scale, are

dependent on road design and road location, and assessment of these effects must consider the

proportion of old roads to new roads that incorporate improved engineering design (Gucinski

et al. 2000). In many cases, major reductions in environmental impacts are possible through

relocation and improvement of old roads, and such improvements are being aggressively pursued

(Furniss et al. 1991). However, these improvements are not accomplished easily or cheaply.

Based on an understanding of road impacts and the technology that has developed to address

these impacts, forest managers have changed their approach to managing roads. Some examples

of these changes are:
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Road location – Roads used to be located in the easiest position to construct them, which was

often on floodplains and near streams. Today, new roads tend to be located in mid-slope and

ridgetop locations where channel encroachment, riparian impacts, and delivery of fine

sediments are minimized. Although old roads near streams often caused a disproportionately

high share of landslides due to placement on steep inner gorge slopes, managers learned that

mid-slope roads can also contribute to landslides. Managers now must identify inherently

unstable slopes and either avoid these locations entirely, or construct roads using design and

construction techniques that have been demonstrated to be effective at preventing landslides

for the specific circumstances encountered (Miller et al. 2001).

Road construction – Historically, the development of powerful bulldozers allowed costeffective construction of deeply excavated, wide roads in mid-slope locations. This practice

contributed to many of the landslide problems that have been widely observed throughout the

West and reported in the literature. Roads were commonly engineered and constructed using

“balanced” cuts and fills that led to wide road prisms, large cut and fillslopes, and large

volumes of excavated materials. The excavated materials had to be disposed of, often by

“sidecasting” these materials onto steep slopes below the road travelway or by building the

road fills with them, and were often poorly compacted. These techniques contributed to large

numbers of avoidable failures (Gardner 1979). Today, hydraulic excavators, which can

precisely excavate and place materials (Bechman 1980), have almost universally replaced

bulldozers for road construction on mountain slopes. Roads are now designed to minimize

cut and fill volume by constructing roads no wider than necessary and by fitting them as

closely as possible to the natural topography (Gardner et al. 1978).

Road drainage design – Historically, road drainage systems were designed with the sole

objective of protecting the structural integrity and utility of the road; effects on the

environment were of little concern (Gardner 1979). Large volumes of water were often

allowed to collect from long lengths of road and were then channeled directly into streams, a

practice that contributes to delivery of large volumes of sediment. While protection of road

integrity remains important, environmentally effective road drainage has developed as an

equally important objective during the past 30 to 40 years. Now roads are often fit more

closely to the topography, with rolling grades providing natural drainage, rather than the long

uniform road grades used in the past. Roads are purposefully designed to discharge water

frequently, to minimize length of direct delivery, to discharge at locations chosen to

minimize delivery of water and sediment to streams, and to minimize concentration of water

that could contribute to slope gullying or landslides. Drainage of existing road systems can

also be redesigned to substantially reduce sediment delivery, often to only a fraction of the

original amount, by increasing the frequency of relief drains or other techniques such as

those described in Appendix B (Section B.5.4) and Appendix C (WFPB 2000; McGreer et al.

1998; Packer and Christensen 1964).

Culvert size – Another major improvement in road design and drainage involves the size of

culverts placed in streams at road crossings. For decades, most western states required that

culverts be designed to pass only the 25 year flood – a design that is statistically predicted to

have a 50% probability of overtopping within 17 years of installation. Today, the minimum

design requirement of most state forest practices rules is 50 to 100 years (IDL 2000a; ODF

1994; WFPB 2000).
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Road maintenance – Road maintenance used to be a matter of keeping roads trafficable and

efficient for transportation. Today, maintenance is recognized as a critical component of

both environmental and business performances of roads. Current road maintenance practices

executed to minimize surface erosion and mass wasting include surface grading and

maintenance of road gravel to prevent rutting; ditch cleaning to insure that water remains in

ditches and does not erode the ditch or the running surface; monitoring, cleaning, and

replacement of relief and stream crossing culverts; monitoring and grading of rolling dips;

and treatment of cut and fillslopes to encourage and retain protective vegetation.

Road use – Roads used to be open to access at all times. Today, access control through the

use of gates is commonly practiced to minimize road surface damage during wet periods and

reduce erosion and sediment delivery. The results are often substantial; prevention of ruts in

road surfaces alone can reduce erosion by approximately 50% (Burroughs and King 1989).

Long-term road treatments such as closure, abandonment, and even obliteration are

becoming more common. Reduction of sediment delivery to streams can be particularly

significant where roads in highly erosive materials are located adjacent to streams. For

example, in the Lower East Branch of the LeClerc Creek watershed of northeastern

Washington, closure, rehabilitation, and relocation of 1.5 miles of the 12.7 mile road system

will eliminate 80% of the sediment delivery in the sub-watershed (McGreer et al. 1997;

Stimson Lumber Company 1999).

Appendix A provides a synopsis of the discussion of Sections 1.6 through 1.8, at least in

qualitative terms, through a historical example of the early evolution of logging transportation

systems away from downhill and water-based systems to mid-slope truck-based systems, and the

major reduction of impacts to stream systems that results. Appendix B (Section B.5) provides

examples of transportation system analysis that quantifies sediment delivery reduction due to

road relocation and improved maintenance and design.

2.0 PATHWAY ANALYSIS OF ROAD/AQUATIC ECOSYSTEMS

Roads are a vital part of forest management and an important asset. Yet they have important

interactions with aquatic systems that must be managed to achieve environmental objectives.

The broad changes in road management practices that managers have enacted are a result of the

gradual development of these environmental objectives over the past 40 years or more.

Ultimately, forest managers must determine how much change in existing road systems is

sufficient to meet aquatic goals and how to achieve those changes most efficiently. Answering

these questions involves two elements. First, technical assessments must be framed that connect

road management activities with fish population response. This is called critical pathway

analysis.

The challenge for managers is to understand critical pathways well enough to effectively address

the variability that exists in forest watersheds so that they don’t have to resort to inefficient (and

often ineffective) one-size-fits-all solutions. Pathway analysis and its utility are described in this

section, followed by a detailed discussion of the technical assessment steps within pathway

analysis that allow identification of management impacts on watershed processes, streams, and

fish. This is followed by the second element: “how much is enough” – the interaction of

management practices (specific actions) with management systems (the decision process
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selecting specific actions) and how pathway analysis can be and is being used in forest road

management systems.

Pathway analysis involves connecting management with an understanding of how watersheds

interact with aquatic populations (fish, amphibians, etc.). In an effective pathway analysis, there

is an exchange of information between key levels, including those shown in Figure 3.1

 This

illustration focuses on the major effects of roads: sediment and runoff delivery.

Management System (Directs activity at landscape scale)

Management Practices (BMPs at the site scale)

Watershed Processes

Sediment and Runoff Delivery

Channel and Water Column Conditions

Habitat

Populations

Figure 3. Elements of Critical Pathway Analysis

Although this approach may appear complex, pathway analysis is made efficient by

understanding which questions need to be answered and which ones are less important. By

focusing efforts on information that answers key cause and effect questions, a sound technical

approach is provided without incurring a great deal of unnecessary effort, and without

oversimplifying the problems at hand. Although the understanding of watershed processes is

incomplete, managers and scientists do understand a great deal about the variability of

watersheds and roads, and have developed tools to manage this complexity. Moreover, industry

foresters and watershed specialists continuously work in the watersheds that they manage, and

have opportunities to view processes within them through time and under extreme conditions.

These observations add to the collective understanding of watersheds and fit within the critical

pathway approach, allowing for systematic adjustment of practices where necessary to prevent

undesirable land management impacts.

Cause and effect (critical pathway) linkages between forest roads and aquatic systems are

developed by tracing how roads influence watershed processes (runoff and erosion) in their

vicinity and by determining and quantifying how water and sediment are delivered from roads to

streams and subsequently routed through stream channel systems. Channel responses are then

interpreted in terms of possible effects on stream habitat and fish populations.

 

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 At the lowest level of Figure 3, making the link to populations necessarily involves factors outside the watershed

of local concern (e.g., ocean conditions, commercial harvest, sport fishing, etc.), but such factors are beyond the

scope of this paper, which focuses on the role of roads.
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Contrasting with cause/effect critical pathway analysis are approaches that attempt to regulate

road construction effects with coarse indirect indices such as road density. Such approaches do

not provide efficient means of managing potential effects on downstream beneficial uses,

because they do not link cause and effect, and therefore do not efficiently allocate finite road

management resources to the specific problems (causes) that must be addressed to prevent and

solve problems (effects). These subjects are discussed in more detail in Section 2.7.

The role of management systems and management practices – the steps shown at the top of the

critical pathway in Figure 3 – are then reviewed. Following that is a summary of the effects of

roads on hydrologic and erosion processes in the vicinity of the road prism and how these effects

ultimately link to stream habitat and fish populations (beneficial uses). This knowledge of the

cause and effect linkages between roads and beneficial uses provides a feedback framework to

help determine how road related environmental effects can be systematically managed within

acceptable levels. This hierarchy for illustrating pathway analysis lends itself to visualization of

the adaptive management approach; when channel, habitat, or population objectives are not

achieved, the steps at the top that managers control – management systems and management

practices – are readjusted.

2.1 Management Practices and Systems

Applying appropriate road practices in forest watersheds to reduce negative water quality

impacts requires two elements: a set of management practices for roads which can effectively

reduce water quality impacts; and a management system which ensures that the right practices

are applied in the right places. The management system is used to select and implement

practices chosen from the set of management practice options. The selected practices have been

called Best Management Practices (BMPs). BMPs are determined to be the most effective and

practicable means of controlling pollutants at levels compatible with environmental goals.

However, management systems now go beyond what can be considered identification of

traditional BMPs. These systems not only address current management activities, but may also

identify and treat hazards and impacts that occur due to historic activities, as well as address

existing watershed hazards.

2.1.1 Management Systems

Management systems identify which practices will be applied at which sites. An effective

management system identifies the site characteristics and hazards unique to the area of concern,

and selects appropriate practices to address these hazards. Management systems include state

forest practice rules or BMP-based systems, watershed or landscape analysis systems, and

special issue management systems such as habitat conservation plans or the Oregon Plan for

Salmon and Watersheds. Timber companies have also developed their own road management

systems that incorporate one or more of these approaches.

An effective management system for roads requires several steps. These include an inventory of

road and stream conditions, identification of road sections requiring practices to bring them into

acceptable condition, identification of effective practices and costs, development of priorities and

a schedule of work, appropriate timeframes for implementation and completion of necessary

tasks, implementation monitoring, periodic inspection to determine performance of implemented
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practices, and training to update personnel assessing roads or implementing control practices. A

number of systems already in place or currently being developed to accomplish these steps are

described in Appendix B, along with examples of the effectiveness of several of these systems.

2.1.2 Management Practices

There are a variety of management practices that can be used to reduce impacts from roads, with

emphasis most often placed on those designed to control sediment from roads and to reduce

changes in runoff. Sediment control practices for roads can be categorized as practices that

reduce surface erosion from the road surface, cutslope, or fillslope; practices that avoid

landslides; and practices that reduce delivery of sediment to streams. Runoff control practices

generally attempt to limit the area of road that directs runoff to stream channels. Specific

examples of techniques designed to accomplish each of these goals are described in Appendix C.

Additional examples can be found in the references cited in Appendix C, in the Handbook for

Forest and Ranch Roads (Weaver and Hagans 1994), and in various state forest practice guides

and regulations (IDL 2000a, 1996; Logan 2001; WDNR 1997; WFPB 2000).

2.2 Road Effects on Watershed Processes

2.2.1 Hydrologic Processes

A number of hydrologic processes affected by roads can result in increases in the volume and/or

rate of runoff. These changes in runoff are manifestly from the effects of vegetation removal, as

well as from physical disturbances caused by construction of the road.

2.2.1.1 Vegetation Removal

Removing vegetation from the road right-of-way has effects similar to clearcut timber harvest,

including reduction of evapotranspirational water loss from the soil, reduction of interception of

rain and snow by tree canopies, and increases in snow accumulation and melt rates (Dunne and

Leopold 1978; Troendle 1983; USACE 1956). These effects are permanent for the road running

surface (if they are not closed or abandoned and allowed to revegetate), but are more temporary

for road cuts and fills that may revegetate over time. Changes in these vegetative effects due to

harvesting have been found to be significant in many experimental watersheds where clearcut

harvest has affected 20 to 100% of watershed area. However, roads occupy only a small fraction

of watershed area (typically 2 to 12% – see Table 1). As a result, streamflow effects due to roads

have generally not been detected. In those studies where streamflow effects due to roads have

been detected, the authors generally attribute these to road disturbance effects on soil infiltration,

subsurface and surface flow interception, and concentration and discharge of water from road

drainage structures rather than to effects associated with canopy removal (Burroughs et al. 1972;

Harr et al. 1975; Jones and Grant 1996; King and Tennyson 1984; Megahan 1972).
14

Table 1. Road and Harvest Area Reported for Experimental Watersheds

Study Location

Watershed

area (acres)

Road

area

Harvest

area

Horse Creek central Idaho1 50-370 2-4.5% 21-33%

Alsea Oregon Coast Range2 40-175 3-12% 20-100%

Oregon Cascades Oregon Cascades3 25-250 3-11% 25-100%

H. J. Andrews Oregon Cascades4 250-29,000 5-6% 22-25%

H. J. Andrews Oregon Cascades5 250 8% 22%

Caspar Creek northern California6 1,000 4.5% 60%7

1

 King 1989; King and Tennyson 1984

2

 Krygier and Harr 1972; Harr et al. 1975

3

 Jones 2000

4

 Beschta et al. 2000; Jones and Grant 1996; Thomas and Megahan 1998; Wemple et al. 1996

5

 Rothacher 1970

6

 Keppeler and Ziemer 1990; Wright et al. 1990; Ziemer 1981

7

 60% of timber volume removed

2.2.1.2 Effects of Road Disturbance

Construction of the road prism has additional effects that increase the volume and rate of runoff.

Two processes in particular are reduced infiltration and interception of subsurface flow.

Reduced infiltration is most apparent on the road tread, and the effect can reduce infiltration rates

by an order of magnitude or more compared to undisturbed forest floor. For example, Reid and

Dunne (1984) found an average infiltration rate of 0.5 mm/hr on a graveled road tread surface,

with estimates ranging from 0.3 to 0.8 mm/hr. In contrast, infiltration rates in conifer forest are

typically in excess of 10 mm/hr (Dunne and Leopold 1978; Johnson and Beschta 1980).

Road cut interception of subsurface flow can be very erratic; it is highly dependent on specific

site conditions, and can also be affected by harvest on hillslopes above the road. For example, a

road in the Pine Creek watershed in the Idaho Batholith intercepted 8.4 inches of subsurface flow

from watershed area above the road, which represented about seven times the amount of direct

runoff from the road surface (Megahan 1972). In the Lochsa River drainage in north central

Idaho, a road located several hundred yards downslope of the drainage divide intercepted on the

order of 7 to 8 acre-feet of subsurface flow per day per mile of road and on the order of 5 to

6 acre-feet of overland flow per day per mile of road during the peak snowmelt season in early

June (Burroughs et al. 1972). Conversely, a road in the Olympic Mountains of Washington

intercepted no subsurface flow; there was no cutbank seepage and no base flow in road ditches

(Reid and Dunne 1984). In central Idaho, Megahan (1972) found that one section of road

intercepted more than three times as much water per unit length of road as another road section.

The combined effect of vegetation removal and disturbance due to roads on streamflow volume

and distribution characteristics is discussed in detail in Section 2.5.3.

2.2.2 Erosion Processes and Delivery of Sediment to Streams

Roads increase erosion because of both effects on hydrologic processes and changes in other site

factors that influence erosion rates. Although effects vary greatly depending on specific site
15

conditions, both surface and mass erosion rates often increase with road construction in

mountainous areas.

2.2.2.1 Surface Erosion

Surface erosion is defined as the downslope movement of individual soil particles, including

inter-rill (sheet erosion), rill, and gully erosion. The degree of compaction, soil exposure, slope

length, and slope gradient are the main factors controlling the rate of accelerated erosion

(Wischmeier and Smith 1965). During construction of forest roads, long continuous lengths of

soils are purposefully excavated, exposed, and compacted. In some cases, these surfaces convey

water directly to streams (Packer and Haupt 1965; Pearce undated). Surface erosion is chronic

on forest roads, with rates varying with site conditions, rainfall erosivity, and time since

construction. Surface erosion can also be episodic in the case of culvert failures (plugging) at

channel crossings or at cross drains, usually during large storm events, where water is diverted

onto and erodes road surfaces.

The particle size distribution of material eroded from road surfaces is generally smaller than that

from mass erosion, which includes both fine and coarse materials found throughout the depth of

the failure. Particle sizes of sediments resulting from surface erosion are small (sand and

smaller), and become even smaller depending on the downslope runoff process, sometimes

appearing solely as washload (turbidity). For example, Bilby et al. (1989) found that 80% of

road surface erosion sediment was finer than 0.004 mm, and none was greater than 0.25 mm. In

contrast, Gonsior and Gardner (1971) found that landslide materials generally contained less than

20% finer than 0.05 mm, and 15 to 45% was coarser than 2.5 mm.

A number of factors contribute to increased erosion from forest road surfaces. Soil erodibility is

increased due to disturbance effects of road construction and vehicular traffic. Slope gradients

are increased on cut and fillslopes. Erosion can be increased through increased raindrop impact

due to loss of intercepting vegetation, increased overland flow on road surfaces, and flow

concentration in drainage ditches or road ruts. Finally, erosion is enhanced on clean, bare road

surfaces due to lack of surface protection by vegetation and/or duff.

Surface erosion rates from roads are typically at least an order of magnitude greater than rates

from harvested areas, and three orders of magnitude greater than erosion rates from undisturbed

forest soils. For example, estimates of road surface erosion rates in California, Idaho, and

Washington are generally in the range of 10 to 100 tons/acre/year (Cline et al. 1981; McCashion

and Rice 1983; Vincent 1979; WFPB 1997), with extreme estimates as high as

480 tons/acre/year in Washington’s Olympic Mountains (Reid and Dunne 1984). In contrast,

typical harvest-related rates of surface erosion that have either been measured or used in

modeling procedures range from 0.5 to 5 tons/acre/year (McCashion and Rice 1983; Cline et al.

1981; Potyondy et al. 1991). Natural surface erosion rates in undisturbed forest lands range from

zero to approximately 0.005 to 0.1 tons/acre/year (Clayton and Megahan 1997; Cline et al. 1981;

Dunne and Leopold 1978). Recent research indicates that long-term “natural” erosion rates may

be much higher than previously thought, due to infrequent catastrophic events such as extreme

wildfires (Kirchner et al. 2001).
16

Most of the factors leading to increased surface erosion from roads are manageable by adjusting

road design features, employing erosion control practices, and performing proper road

maintenance. For example (also see Appendices B and C):

Avoid locating roads on steep hillslopes – The road prism disturbed width is three times as

large on a 60% slope as on a 30% hillslope (Megahan 1977, 1976).

Limit road slope – A 13% road gradient produced more than three times as much erosion as a

6% road gradient (Vincent 1979; Luce and Black 1999); the Universal Soil Loss Equation

(USLE) predicts that the erosion rate approximately triples as road gradient doubles (Dunne

and Leopold 1978).

Install and maintain frequent drainage features – Installation of additional road drainage

relief culverts by itself is predicted to reduce sediment delivery to streams by 25 to 85% in

eleven watersheds ranging in size from 5,490 to 69,850 acres (Luce and Black 1999;

McGreer et al. 1998).

Rock the road surface – Graveled tread reduced erosion by 77% over native surface

(Burroughs and King 1985; Luce and Black 1999).

Treat cut and/or fillslopes – Straw applied to fillslopes at a rate of 1 ton/acre reduced fillslope

erosion by approximately 60% (Burroughs and King 1989). Dry seeding and hydromulching

are effective erosion controls on erosive granitic cutslopes (Megahan, Wilson, and Monsen

2001).

Trap eroded sediment – A filter windrow at the toe of the fillslope reduced sediment leaving

the fillslope by approximately 85% (Burroughs and King 1989; Cook and King 1983).

Provide subsurface drainage in high hazard areas (French drains).

2.2.2.2 Mass Erosion

Mass erosion (or mass wasting) is defined as the movement of material en masse, primarily

under the influence of gravity, and in the case of roads is almost always episodic. Large-scale

mass erosion of roads occurs most commonly as debris avalanches, debris flows, and slumps

(Benda et al. 1997; Swanston 1991). Small-scale mass erosion also occurs on roads, especially

cutslopes, from piping, micro-scale debris flow, and dry ravel. The eroded material includes all

particle sizes at the site for the depth of the failure, and is therefore coarser than that for surface

erosion (Gonsior and Gardner 1971).

Roads have typically been the predominant cause of increased rates of mass wasting associated

with forest management, with acceleration factors commonly found to be in the range of five to

one hundred times greater for roads than for harvesting (Swanston and Swanson 1976;

McClelland et al. 1997).

Several factors cause increased mass erosion due to roads. Slope gradients are increased on cut

and fillslopes. Subsurface water flows can be altered, due to both cutslope interception of

subsurface water and changes in water flow on and below fillslopes and hillslopes below the

road. Loss of deep-rooted vegetation on the road right-of-way reduces hillslope stability.

Landslide risk can also be increased by mistakes or oversights during road construction, such as
17

leaving organic debris in fills, over-steepening cut or fillslopes, or failing to recognize local high

hazard situations. These factors often work in combination with each other in ways that are not

well understood. However, several studies report that the road failures most damaging to

streams occur primarily from fill and sidecast failures that develop into debris avalanches on

slopes steeper than 70%, and secondarily from culvert and stream crossing failures (Bush et al.

1997; Fiksdal 1974; Gonsior and Gardner 1971; Gray and Megahan 1981; Megahan et al. 1978;

McClelland et al. 1997; Sidle et al. 1985; Skaugset et al. 1996; Swanson and Dyrness 1975;

Jones et al. 2000).

Rates of mass wasting vary greatly across the landscape, depending on climatic, geologic, and

topographic factors as well as factors associated with management practices. Rates of debris

avalanche occurrence associated with forest roads in westside studies conducted in the early to

mid-1970s ranged from 25 to 344 times the rate in undisturbed forests (Benda et al. 1997; Sidle

et al. 1985). Further demonstrating the variability of results, studies in Oregon, Idaho, and

Washington have reported that anywhere from 27 to 72% of all observed landslides were

associated with roads, 10 to 77% were associated with harvest, and 9 to 63% occurred naturally

(Bush et al. 1997; Dyrness 1967; Fitzgerald and Clifton 1997; Gresswell et al. 1979; McClelland

et al. 1997; Megahan et al. 1978). In terms of mass failure volume, similar studies show 34 to

53% of total failure volume related to roads, 6 to 63% related to harvest, and 3 to 46% occurring

naturally (Dyrness 1967; Gresswell et al. 1979; Ice 1984). In other words, roads are associated

with most failures and failure volume in some studies (in fact, most studies), but certainly not in

all studies and all locations.2

For areas of the inland northwest, few landslide rate studies are reported in the literature.

However, Megahan and Kidd (1972) reported that roads built in small headwater basins in the

1950s and early 1960s in the central Idaho batholith increased rates of mass wasting by a factor

of over 400, but actual numbers of road failures in relation to natural rates were not reported. In

another study in Idaho, Megahan et al. (1978) report that roads constructed prior to 1979

accounted for 56% of all landslides that occurred in a three year period that included an extreme

flood in 1974. More recently, in contrast to Megahan and Kidd’s (1972) results, McClelland et

al. (1997) conducted a survey of all failures greater than 25 cubic yards in volume in nonwilderness areas of north central Idaho’s Clearwater River basin, including large areas of

batholith. Table 2 summarizes their findings.

McClelland et al. (1997) shows that roads had double the rate of mass wasting relative to natural

rates, with smaller effects on landslide volume and volume delivered to streams. Even smaller

increases in rates of mass wasting have been reported for several analyses conducted as part of

watershed assessments in eastern Washington, Idaho, and western Montana (McGreer et al.

 

2

 In contrast to roads, acceleration factors due to harvest range from 2 to 9 over undisturbed conditions in westside

studies, with even lower increase factors for some eastside studies (McGreer et al. 1998). For example, in the H.

J. Andrews Forest in western Oregon for the period 1950 to 1974, Swanson and Dyrness (1975) found a

road-related landslide rate of 4.8 slides/mi2

/year, 0.47 slides/mi2/year from clearcut areas, and 0.15 slides/mi2/year

in undisturbed forest. In terms of slide volume, the same study found approximately 19 tons/acre/year from

road-related slides, 1.7 tons/acre/year from clearcuts, and 0.6 tons/acre/year in undisturbed forest. These results

are reflective of roads constructed prior to most forest practices acts and are consistent with other studies in

western Oregon, Washington, and British Columbia that report road-related slide volumes varying from 2 to

100 tons/acre/year, 0.2 to 2 tons/acre/year from clearcuts, and undisturbed rates of 0.1 to 0.6 tons/acre/year (Ice

1984; Sidle et al. 1985; Swanson and Grant 1982).
18

1998), where landslide rates and hazards are commonly lower than those that occur in areas west

of the Cascade crest (Megahan et al. 1978).

Table 2. Clearwater Basin Landslides Reported by McClelland et al. (1997)

Natural

slides

Road-related

slides

Harvest-related

slides

% of Total Number 29 58 12

% of Total Volume 59 36 5

% of Delivered Volume 71 25 4

Consistent with the general findings of the landslide studies reported in the literature,

McClelland et al. (1997) reported that most road failures were fill failures on steep slopes and

were generally associated with poor construction, maintenance, and/or drainage practices. Road

fill failures, including fill failures associated with culvert blockages and diversions, are the

predominant form of road-associated mass wasting (NCASI 1985; Furniss et al. 1991).

Avoidance of hazardous locations and attention to road fills and drainage are often noted as

means of preventing failures from roads that are to be constructed in the future.

Insufficient stream crossing culvert capacity, often compounded by debris obstruction, has also

been noted as an important cause of culvert failure, resulting in overtopping or diversion from

streambeds onto unstable road fills, with associated mass wasting and severe surface erosion and

gully erosion events (Furniss et al. 1991; McClelland et al. 1997). Although the forest practices

rules of California, Oregon, Idaho, Montana, and Washington now call for stream culvert design

capacity based on the 50 to 100 year flood event, many roads were built when the requirements

were based on the 10 to 25 year event. Thus there is a legacy of undersized culverts that remain

potential site-specific erosion hazards on some roads.

In virtually all the studies reviewed for this paper, the majority of failures observed are from

roads built years ago in locations and with construction methods which later became

unacceptable and/or illegal, and thus road systems pose significant potential for legacy effects.

As practices have improved and as old roads eventually stabilize, this potential can be expected

to decrease; as early as 1984, Ice (1984) noted evidence from westside studies that rates of road

failure were decreasing. In a summary of impacts of the 1996 floods in Oregon, Robison et al.

(1999) reported that “current road management practices are reducing the size of road associated

landslides, as well as the number of landslides.” McClelland et al. (1997) also reported that

following intense rain-on-snow precipitation during the 1996 floods the rate of failure of roads

built in the 1970s through the 1990s was approximately half the rate of failures of roads built in

the 1950s and 1960s.

The risk of mass erosion on forest roads can be reduced through careful road design and location,

proper design of fills, adequate groundwater drains, and control of volume and location of runoff

water. Some of the guidance often reported includes:
19

Avoid locating roads on steep hillslopes – Most failures occur on hillslopes greater than 70%

(Gresswell et al. 1979). The road prism disturbed width is three times as large on a 60%

slope as on a 30% hillslope (Megahan 1977, 1976).

Use full bench/endhaul road construction – In stable sandstone soil types in western Oregon,

sidecast road construction and moderate road gradients resulted in approximately 40 times

more slides per mile of road than full bench/endhaul roads of steeper gradient. The

difference in less stable sandy/gravelly soils was approximately a factor of two (Sessions

et al. 1987).

Install and maintain frequent drainage features and size culverts appropriately (Copstead and

Johansen 1998; Gonsior and Gardner 1971; Furniss et al. 1991).

Compact fills (Gonsior and Gardner 1971).

Provide subsurface drainage in high hazard areas (French drains).

2.2.2.3 Delivery of Water and Sediment to Streams

Reduction and control of road runoff and erosion is important to help maintain road trafficability,

as well as to reduce the potential for downslope delivery of water and sediment. The amount and

timing of delivery of water and/or sediment from roads to streams depends on the type of

geomorphic processes involved, local site conditions, and the nature of road location, design, and

maintenance; the latter three are factors that can be managed.

Runoff from roads generally follows one of four potential pathways: infiltration back into the

hillslope below the road with no delivery to streams; direct delivery at channel crossings (Paths

A, B, and C in Figure 4); direct delivery through gullies formed below relief drains (Path D in

Figure 4); or indirect delivery via overland flow below the road. Direct delivery at channel

crossings is the most common and most rapid form of delivery, and occurs where roadside

ditches (Path B in Figure 4) and/or road tread runoff (Path C in Figure 4) run directly to the

stream crossing structure, whether it is a culvert, bridge, or ford. Delivery at stream crossings is

controlled partly by the spacing of relief drains; i.e., if relief drains are located only a short

distance from the actual crossing, less road surface area will deliver water directly to the

crossing.

Gullies can be formed below road ditch relief drains by erosion at the drain outlet or by

headward extension of the stream channel system. Gullying (Path D in Figure 4) results in

moderately rapid delivery to streams, and is primarily a function of the length of road

contributing to the drain and the hillslope gradient below the outlet (Wemple, Jones, and Grant

1996; Croke and Mockler 2001). Gullies can be caused by excessive runoff through the relief

drain, steep gradient in the cross-drain, a perched drain outlet, and/or lack of armoring below the

drain outlet. Gullying can be controlled by reducing the distance between relief drains and by

employing energy dissipaters or armoring below drain outlets (ODF 2000).
20

stream hillslope

cutslope

ditch

road surface

fillslope

A

B

C

D

ditch relief

 culvert

stream

 crossing

 culvert

Figure 4. Water and Sediment Delivery Paths From Roads

(A) subsurface flow interception

(B) flow through road ditches to streams

(C) flow along road surface to streams

(D) flow through gullies to streams

Overland flow below roads is the slowest form of delivery, and is the least likely to deliver

substantial quantities of water or sediment to streams, due to the slowing effects of intervening

vegetation and other obstructions on the hillslope that trap at least a portion of the road discharge

(Elliott et al. 1997; Megahan and Ketcheson 1996).

The prominence of direct delivery and gullying is documented by research done in western

Washington and Oregon. These studies found that 42 to 66% of road drainage points discharged

to hillslopes with no delivery to streams, 28 to 35% of drains delivered directly to streams, and

17 to 28% delivered via gullies (Bilby et al. 1989; Bowling and Lettenmaier 1997; La Marche

and Lettenmaier 1998; Wemple, Jones, and Grant 1996). More importantly, however, these

same or similar studies have found that 17 to 35% of the total road mileage contributes sediment

to the stream system (Bowling and Lettenmaier 1997; McGreer et al. 1997), or conversely, 65 to

83% of the road mileage did not contribute sediment to streams. Such examples confirm the

ubiquitous “80-20 rule,” in this case, 80% of the problems come from 20% of the roads. This

reveals a key principle: reducing the road mileage that discharges to streams – not merely

reducing road mileage or road density – reduces both the quantity of sediment that reaches

streams and any potential effect that roads may have on peak flows. Comprehensive assessments
21

of road erosion and road drainage to streams can be highly effective in reducing road impacts,

and examples of such assessments and their implementation are provided in Appendix B

(Section B.5).

Sediment delivery from roads due to surface erosion is a function of the volume of water

discharged from the road, the volume of sediment carried by this water, and characteristics of the

path that the water/sediment solution travels (Megahan and Ketcheson 1996). Sediment from

surface erosion near stream crossings is carried directly into the channel, and thus has the

greatest chance for delivery. Likewise, most sediment travelling through cross drains into gullies

connected to a stream is supplied to the stream, although deposition en route is possible.

Elsewhere, sediment in runoff moving downslope as overland flow is transported at low

velocities, and thus is likely to be deposited en route (Brake et al. 1997; Ketcheson and Megahan

1996).

Annual delivery of surface erosion sediment to streams from a given road segment can vary from

zero to tens of tons, depending on such factors as the specific delivery route (stream crossing vs.

gully vs. discharge to hillslope), contributing road length, road gradient, hillslope gradient, road

surfacing (native surface vs. graveled vs. paved), cut and fillslope vegetative cover, and so on

(Elliot et al. 1997; Haupt 1959; WFPB 1997).

Sediment delivery to streams from road surface erosion can be controlled through several

mechanisms that operate synergistically. Erosion and sediment control practices are discussed in

Appendix C.

Sediment supply from mass erosion is episodic, as is the erosion itself, and thus delivers

relatively large volumes of sediment over short periods of time. Sediment supply from mass

wasting is strongly influenced by a number of factors:

Type of mass erosion process (slump vs. debris avalanche vs. debris torrent) – Slumps and

earthflows, which typically penetrate deeper into soil mantles, generally are slower moving

and less likely to deliver sediment than shallow rapid failures such as debris avalanches and

debris flows, particularly when the latter become channelized in headwater draws and

streams. For instance, in the H. J. Andrews Forest of western Oregon, only 14 out of 47

observed events during the winter of 1964/1965 caused channel scour, but those 14 events

represented 64% of the total eroded volume from all 47 events (Dyrness 1967).

Location in the road prism (cut vs. fill) – Road cut failures, which in many areas occur more

commonly than fill failures, often fall to the running surface and are partially or totally

trapped there. For instance, from 1974 to 1976 in the Clearwater National Forest of north

central Idaho, 66% of observed road failures originated from cutslopes but only 47% of the

total failure volume came from cutslope failures, i.e., cutslope failures tended to be smaller

than fillslope failures, and most cutslope failures deposited on the road tread and failed to

reach streams, whereas half of the total fill failure volume was delivered to streams

(Megahan et al. 1978). During the winter of 1964/1965, 32% of road failures in the H. J.

Andrews Forest originated from cutslopes, but nearly half of those cutslope failures

deposited entirely on the road tread (Dyrness 1967).
22

Slope, valley, and channel conditions below the road – Most failures occur on hillslopes

greater than 70% gradient (Gonsior and Gardner 1971; Johnson et al. 2000; Sessions et al.

1987). Road segments near ridgetops (within 100 m) have lower frequency of mass failures;

segments located mid-slope have higher frequency of failures and are more likely to reach

streams sources; segments located in valley bottoms also have high frequency of failures

(Wemple 1999). If failures become debris flows within channels (sometimes called debris

torrents), they are likely to continue downstream until channel gradient becomes less than

6%, a tributary junction angle greater than 70 is reached (Benda and Cundy 1990), or where

slopes are gentle and channels unconfined (Johnson et al. 2000). As a result, debris flows

often reach larger fish-bearing waters.

Particle sizes delivered to streams from mass erosion are similar to the size distribution of the

material at the slide initiation site, whether natural soil or road fill, and can include all sizes from

clays to boulders. Because mass wasting generally delivers large volumes over short time

periods and can also deposit large particle sizes, sediment from mass erosion can have

substantial effects on channel morphology over relatively long periods of time (Hogan and

Schwab 1991; Megahan et al. 1980). As discussed in Appendix C, most landslides associated

with roads can be prevented by avoiding hazardous locations and by employing a number of

construction and maintenance practices that have been demonstrated to be effective.

2.3 Channel Encroachment Effects

Channel encroachment due to construction of roads directly adjacent to and within stream

channels is a legacy of past practices. State regulations and forestry BMPs no longer allow roads

to be constructed in these locations (WFPB 2000; IDL 2000a; MDHES 1997; ODF 1994).

Existing roads in valley bottoms, especially in narrow valley bottoms, may directly impinge on

the channel and result in increased channel gradients, reduce the opportunity for overbank flow,

and directly decrease desirable habitat area and characteristics (e.g., reduced stream shading or

large woody debris recruitment). Although no longer a construction consideration, these

potential effects should be addressed when considering road maintenance and closure plans.

2.4 Fish Passage Effects

Road culverts may block passage of juvenile and adult fish where they are too high above the

base channel for fish to jump or where the gradients and velocities in the culverts are too steep

and rapid for fish passage. Passage barriers have been found to be common in a number of road

system inventories, potentially resulting in substantial loss of habitat and population impairment

(Dent and Allen 2000; Hoffman and Sylte 2001; ODF 1999a). Both general and detailed

procedures for judging the adequacy of culvert design and conditions for fish passage are

provided by the Oregon Department of Forestry (ODF 2000; ODF 1999b) and the Washington

Department of Fish and Wildlife (WDFW 1999). A number of active efforts are also under way

to inventory and correct unacceptable culvert conditions (ODF 2000; Plum Creek Timber

Company 2000; Stimson Lumber Company 1999).
23

2.5 Road Effects on Channel and Water Column Conditions

Increases in water or sediment inputs to streams can affect physical channel conditions and water

quality. However, the natural range of variability of stream parameters such as flow, suspended

load, or bedload can be very large, and detecting the potential effects of roads within that wide

range can be difficult. For example, in July 1992, a thunderstorm dropped 2.8 inches of rain in a

gaged sub-watershed of Mica Creek in northern Idaho. Streamflow increased from 0.3 cfs to

10 cfs over a 1 hour period, producing a flood estimated to be between a 2 and 5 year return

period, accompanied by substantial bedload movement.3

 Even in this heavily instrumented

watershed, detecting road effects is very difficult given the degree of natural variability of the

system.

Although individual management activities can increase sediment loads and deposition within

streams and can affect streamflow, more severe effects can result from the simultaneous or

cumulative effects of several sources (NCASI 1999) – effects which are more likely to express

themselves at the watershed scale. Changes in sediment supply and runoff from roads may or

may not be manifested at the watershed scale (i.e., beyond merely locally and just downstream of

the input site), depending on the magnitude and timing of the change in relation to watershed

conditions.

2.5.1 Suspended Sediments

Sediment concentrations depend on the amount of sediment relative to streamflow, with

additional dilution occurring downstream due to additional inflow of water from tributaries and

other sources (NCASI 1999). Forest streams in many regions (but not some parts of the South)

are considered sediment limited, so increases in fine sediment available for transport in the

stream can lead to increased suspended sediment concentrations. Suspended sediment

concentrations are highly variable, varying by as much as two orders of magnitude in

undisturbed watersheds even under similar streamflow conditions (Beschta 1978; Fredriksen

1970; King and Gonsior 1981). This degree of inherent variability or “noise” in the system often

makes it difficult to detect the effects of road construction, especially with increasing distance

downstream from the sediment source.4

 Even in small catchments, effects on sediment

concentrations can be difficult to detect, and the effects decrease over time as surface erosion

rates decrease, often to the point of being non-detectable.

Bearing in mind the difficulty of determining the exact magnitude of potential effects of roads on

sediment relationships, some of the potential effects of roads on water quality include increased

suspended sediment concentrations and turbidity (Beschta 1978; Fredriksen 1970; King and

Gonsior 1981; Rice et al. 1979) and increased deposition of fine sediment in spawning and

rearing habitats (gravels and pools) (Eaglin and Hubert 1993). These relationships are far from

straightforward, however, because in many forest stream systems, other factors such as large

woody debris or bedform are the dominant controls on streambed texture (Buffington 1995).

 

3

 This storm event was used as an example because an increase in peak flow of around 20% can increase the

volume of a 2 year flood to the equivalent of a 5 year event, which is considered to have significant effects on bed

scour and salmonid egg mortality (WFPB 1997). 4

 Bunte and MacDonald (NCASI 1999) provide a more detailed discussion of the variability of suspended sediment

and bedload in streams and the difficulty of detecting management effects with monitoring.
24

In most cases, research in the Northwest has found that suspended sediment concentrations in

streams increase significantly immediately after road construction. Increases reported following

construction of roads in the 1960s and 1970s were as much as 250 times the expected

undisturbed condition (Beschta 1978; Fredriksen 1970; King and Gonsior 1981; Rice et al.

1979). In one study, the increase was attributed to road-related mass failures, as suspended

sediment concentrations in a nearby watershed with no mass failures did not show a significant

increase in suspended sediment in the first year after road building (Beschta 1978). However,

those same studies generally show that suspended sediment concentrations diminish substantially

within 1 to 2 years following construction, often returning to levels similar to those prior to

construction. Furthermore, at least one study reported that most of the additional material was

stored in small channels and was not immediately transported out of the watershed (King and

Gonsior 1981), although transport of “stored” materials to downstream locations eventually

occurs (NCASI 1999).

2.5.2 Bedload Sediments

Bedload transport is even more episodic and variable than suspended sediment (NCASI 1999).

Nonetheless, increased fine and coarse sediment supply, often due to landslides associated with

roads, can cause changes in channel morphology such as widening, shallowing, or braiding

(Lyons and Beschta 1983; Madej 1978).

Bedload sediments from mass erosion usually cause considerable aggradation at the point of

inflow. For example, Benda and Dunne found that debris flow deposits often formed fans that

induced channel bends at the point of deposition. Over time, aggraded sediments are routed

downstream as a function of sediment particle size, streamflow rate, and channel conditions. In

many cases, the majority of sediment from mass erosion is not immediately transported fluvially,

but is stored for considerable periods of time in lower order channels at the point of deposition

and released in episodic events, resulting in higher order channel aggradation/degradation cycles

of 100 to 1000 years (Benda and Dunne 1987).

Sediment residence times and effects on channel morphology and aquatic habitat conditions also

vary depending on the nature of the channel system and its hydrology (Benda and Dunne 1987;

Duncan and Ward 1985). In some cases, deposition of fine or coarse sediment in streams has not

been correlated with road density (Duncan and Ward 1985), new road construction (Fredriksen

1970), or even with specific road sediment input locations (Bilby 1985). However, in some

cases, certain indices such as substrate embeddedness have been correlated with indicators like

the density of stream crossing culverts in the watershed (Eaglin and Hubert 1993). It is possible

to assess channel susceptibility to increased bedload sediments through channel inventories

designed to evaluate effects of past sediment inflows and the hazards and risks of additional

bedload sediments (Montgomery and Buffington 1993).

2.5.3 Effects of Roads on Streamflow

Increases in peak flows, if large enough, can cause increases in scour and fill or bank erosion,

leading to further increases in sediment transport (Roberts 1987; WFPB 1997). Roads

potentially increase peak streamflows by replacing subsurface flow paths with surface flowpaths

through capture of subsurface water in road cuts and by reducing the rate of infiltration into
25

compacted surfaces, thereby generating excess surface flows. However, the role of logging

roads in altering the magnitude and timing of peak flows remains poorly understood (Wemple,

Jones, and Grant 1996).

It has been hypothesized that increases in peak flows from roads may be due to increases in

“drainage density” stemming from connectivity between the road system and the stream network

at channel crossings and through gullies below relief drains (Montgomery 1994; Wemple, Jones,

and Grant 1996; Jones et al. 2000). Although various studies have suggested increases in

“drainage density” of 23 to 60% due to roads (Bowling and Lettenmaier 1997; Montgomery

1994; Wemple, Jones, and Grant 1996), road mileage that drains to streams is not the same as an

increase in the length of streams within the watershed (Jones et al. 2000). Surface water in

streams develops as subsurface flow through the soil and geologic mantle accumulating to the

point of saturation causing channelized surface flow. Roads also intercept subsurface flow, but

interception may be partial, and there is a compensating effect in that runoff from intercepted

subsurface flow is not supplied to the slope below the road, so storm runoff from the portion of

the watershed below the road is reduced (Bowling and Lettenmaier 1997). Furthermore, if

drainage density did actually increase because of road connectivity, relationships developed for

natural drainages linking flood peaks and low flows to drainage density should be suitable for

predicting the flow changes that occur from increased “drainage density” from road construction.

However, studies of road construction effects on experimental watersheds show no such effects

(Harr et al. 1975; Rothacher 1973). Jones et al. (2000) suggested that indices based on the

number of road-stream crossings, particularly at mid-slope locations, may be more reflective of

potential road effects on watershed processes than road density alone.

Arguments are made that runoff from intercepted subsurface flow occurs rapidly as concentrated

overland flow, and therefore tends to increase peak flows (Jones and Grant 1996). This effect

may or may not occur, because subsurface flow often occurs in macropores, where flow

velocities can exceed that of overland flow. In such situations, intercepting overland flow will

reduce peak flows (Bowling and Lettenmaier 1997). In fact, Cheng et al. (1975) reported that

compaction associated with logging in a coastal British Columbia watershed reduced peak flow

magnitude and time to peak because large subsurface channels which normally transported

stormwater were crushed (although no surface flow resulted), forcing stormflow through the soil

matrix at reduced velocity.

Potential effects of roads on peak flows depend on the specific characteristics of the road and the

watershed in question. For example, according to a recent Forest Service document (Gucinski et

al. 2000):

The effects of roads on peak streamflow depend strongly on the size of the watershed.

For example, capture and re-routing of water can dewater one stream while causing major

channel adjustments in the stream receiving the additional water. In large watersheds,

roads constitute a small proportion of the land surface and have relatively insignificant

effects on peak flow.

Road effects on peak flows also depend on road location within the watershed. Jones and Grant

(1996) hypothesized that road construction increases the peak and shifts the hydrograph forward

in time compared to non-roaded watersheds. Assuming this is the case for a sub-basin within a
26

larger watershed, Bowling and Lettenmaier (1997) showed that peak flows are increased at the

larger watershed scale only if the road construction takes place above the centroid (i.e., in the

upper part) of the larger watershed. Road construction near or below the centroid of the larger

basin desynchronizes the runoff hydrograph at the downstream location, leading to decreased

peak flows. Such de-synchronization effects may be responsible for the erratic results from field

studies of the effects of road construction on peak flows in experimental watersheds, some of

which show peak flows increasing, some decreasing, and others showing no statistical change.

In some of the earliest work on road effects on peak flows, Rothacher (1970, 1973) did not detect

any significant increases in mean peak flows or annual water yields due to roads that occupied

8% of a 250 acre western Oregon watershed. In the Oregon Coast Range, Harr et al. (1975)

reported that roads increased mean annual peak flow by 19% in a watershed with 12% of area in

roads, but that watersheds with 3 to 5% of area in roads showed no significant increases in mean

annual peak flows. Ziemer (1981) and Wright et al. (1990) found no significant increases in

peak flows for a 1047 acre watershed in coastal northern California with 5% of the area in roads

and 8% in tractor skid trails. In seven small forested headwater basins in northern Idaho

(ranging in size from 69 to 365 acres) with 1.8 to 4.3% of area in roads, five watersheds

experienced no significant increases in mean annual peak flows, peak flows decreased in one of

the seven basins, and flow during spring snowmelt increased 30% in one watershed with a

mid-slope road occupying 3.9% of the watershed area (King and Tennyson 1984).

In the H. J. Andrews Forest of western Oregon, Jones and Grant (1996) concluded that 6% of the

area occupied by roads in a small (250 acre) watershed caused a (non-significant) 20% increase

in mean annual peak flows. They also argued that roads and clearcutting in large watersheds

(15,000 to 150,000 acre) have caused increases in peak flows in larger basins. They attributed

much of the effect to altered flow paths caused by roads. However, using a different statistical

methodology with the same data set as Jones and Grant (1996), Thomas and Megahan (1998)

found significant increases in peak flows in the small watershed that was roaded and patch-cut,

but only in the first 10 year period following harvest, which implied that the effect was due to

harvest, with little effect from roads, as road effects should be more persistent. Thomas and

Megahan found increases in peak flows of 15 to 40%, but percentage increases in peak flows

decreased with increasing return interval, with no increases detectable for flows greater than the

2 year flow, which is generally considered the flow level where effects on stream channels begin

to occur.

In another re-analysis of the data set used by Jones and Grant (1996), Beschta et al. (2000)

essentially agreed with the conclusions of Thomas and Megahan (1998), but concluded that

“peak flow increases for 0.4 to 5 year return interval events have occurred on small watersheds

as a result of clearcut silviculture and the accompanying effects of roads and broadcast burning

as practiced in the mid-1960s.” They concluded that peak flow increases in the small watershed

were not detectable for flows of 5 year return interval or greater, and they further concluded that

the analysis did not support Jones and Grant’s conclusion that peak flows were increased in

larger basins.

These watershed studies have demonstrated numerous potential effects of roads. However, it is

not practical, or even possible, to evaluate all the effects of road construction using experimental

watershed studies, given the infinite combinations of various site-specific factors and different
27

weather and storm patterns, as well as all of the road design and road location factors that might

affect peak flows. To address this problem, hydrologists develop process-based models that

allow both an examination of a wide variety of circumstances and a determination of the effects

of individual factors.

The Distributed Hydrologic Soil Vegetation Model (DHSVM) is a process-based, hydrologic

model designed to evaluate the effects of road construction and timber harvest on streamflow

(Bowling and Lettenmaier 1997; Wigmosta et al. 1994). Applications of the model to evaluate

effects of forest roads on peak flows (isolated from the effects of forest cutting) in specific

forested watersheds show mixed results, with most studies showing increases in peak flows:

In Hard and Ware Creeks in western Washington (Bowling and Lettenmaier 1997), modeling

showed that road densities of 6 to 8 mi/mi2

, with 17 to 20% of the road mileage connected to

the stream system, increased mean annual peak flows by 11%; flows substantially smaller

than the mean annual peak flow were increased 13 to 17%; 5 year flows increased 9 to 10%,

and 10 year flows increased 8 to 10%.

In the Deschutes River basin in western Washington (La Marche and Lettenmaier 1998),

modeling showed that road densities of 5 to 8 mi/mi2

 increased mean annual peak flows by

2.4 to 10.2%; flows smaller than the mean annual peak flow were increased 1.8 to 10%; and

10 year flows increased 2.5 to 12.2%. For purposes of comparison, it should be noted that

individual annual peak flows in the Deschutes River basin have varied by approximately a

factor of four over a 50 year period of record.

These modeling studies provide an estimate of the potential for road effects on peak flows.

However, the question remains whether the models simulate the entire effects of roads. Whether

such (modeled) peak flow increases are actually measurable in watersheds, and whether

observable effects on stream channel characteristics and aquatic habitat quality occur remains

uncertain. There are virtually no studies that have documented channel effects caused by

increased peak flows attributable to roads. Hydrologic effects of roads on channel morphology

are difficult to predict with models and difficult to isolate and measure in watersheds. As an

illustration, peak flow increases due to roads are generally detectable only for flows less than the

2 to 5 year return interval (Beschta et al. 2000; Thomas and Megahan 1998), while the most

significant channel-forming events are considered to be on the order of the 2 to 10 year return

interval (“bankfull flow”) events or larger (Beschta et al. 2000).

This difficulty is compounded by the fact that other factors also influence channel scour, and

therefore affect channel morphology, often to a greater degree than peak flows. For example:

Sediment size – Scour and fill depths may be more a function of sediment size distribution

than flood magnitude (deVries 1998).

Disturbance history – Channels that received coarse sediment from upstream landslides had

greater scour (Tripp and Poulin 1986).

Flood duration – Some studies have found that flood duration can be as important as flood

magnitude (Costa and O’Connor 1995).
28

Stream characteristics – The size, bedform, slope, and roughness (e.g., rocks, large wood) of

the channel influence scour (Bilby and Ward 1989; Buffington 1995; Keller and Swanson

1979; Megahan 1982).

The effects of these factors, as well as peak flows, on channel morphology will no doubt be the

subject of future research. Nonetheless, the potential effects of roads on peak flows do in part

depend on the mileage of road that drains directly to streams at crossings and through gullies.

Managers should recognize that this mileage can nearly always be controlled through road

drainage design, including insloping versus outsloping and installation of drainage structures at

critical locations.

2.6 Effects on Stream Habitat and Fish Populations

Understanding the effects of roads on erosion, runoff, and delivery processes and the effects of

these inputs on stream channels and water column conditions must be followed by an

understanding of the effects on fish habitat and populations – the last technical steps in Critical

Pathway Analysis. With the technical understanding, albeit imperfect, management systems and

practices designed to limit inputs and effects to acceptable levels are then put in place.

Management practices and systems are discussed in Section 2.1 and Appendix B.

Changes in hydrology or sediment inputs to streams can affect the physical environment for fish

at various stages of their life history, as well as human uses:

Increases in turbidity can affect the feeding and territorial behavior of fish (Berg and

Northcote 1985; Reiser and Bjornn 1979).

Extremely high turbidities can delay upstream migration of salmonids (Bjornn and Reiser

1991).

Fines in gravels can reduce salmonid embryo survival and/or emergence (Bjornn and Reiser

1991; Cederholm and Salo 1979; Koski 1972; Weaver and Fraley 1990).

Fines in gravels can reduce winter rearing habitat for fish by filling pools and reducing

available cover (Bjornn et al. 1977; Reiser and Bjornn 1979).

Fines in gravels can cause a reduction in the number of benthic invertebrates available as

food for adult salmonids (Bjornn et al. 1977; Cederholm and Salo 1979).

Increases in peak flows can affect the incubation environment for fish where small increases

in scour depths might significantly affect many salmon redds (Montgomery et al. 1996).

Although road construction and timber harvest are not often major factors affecting turbidity

levels of municipal water supplies, in some cases land use factors can contribute to landslides

during major storms, which can increase short-term turbidity levels (Grizzel and Beschta

1993).

Floods can affect human safety and damage structures or property (WFPB 1997).

Generally, although these effects have been demonstrated, translating them to populations has

not been easy to do. Various measures and approaches for translating levels of input of water
29

and sediment to streams to effects on instream habitat conditions and fish populations have been

explored, and this is discussed in Section 2.7.

2.7 Targets and Indices

It is often difficult to determine the acceptable level of impact on stream flows or sediment loads,

or conversely, when impacts to channels, fish habitat, and ultimately to fish populations are

unacceptable. Ideally, and in concert with the concept and final steps in pathway analysis,

targets and indices for these parameters would be determined by use of some ecological metric

that has been established by conclusive experimental research that links level of road input to

degree of ecologic response. Then the level of acceptable impact would cease to be a question to

be answered with science; it would be determined through social and political processes,

suggesting that there may be no one correct and true level of acceptability. Notwithstanding the

difficulty of determining “how much is too much,” approaches relying on somewhat imperfect

science have been emerging that seek to establish targets, indices, and management systems that

limit impacts to levels that are currently judged to be acceptable.

Perhaps the ultimate goal would be to establish targets at the level of input where biologically

detectable acute or chronic effects upon organisms (e.g., fish) do not occur. State water quality

temperature standards provide an example of this approach, albeit levels set to date remain

controversial and are far from settled as pure matters of science. Meaningful targets for sediment

are even more elusive. However, the effects of sediment on water quality, the physical habitat

that organisms depend upon, and ultimately upon the population itself, is highly variable, and

poorly understood quantitatively. Adding to this complexity of biological response are

additional and intermixed effects, both on-site and off, such as those of fishing or exotic

predators, and all manner of activities that affect anadromous and migratory populations

downstream from the area of concern. As a result, most systems for targeting levels of sediment

or flow input avoid linkages to biological response and limit themselves to relationships of input

to physical instream and habitat response.

2.7.1 Reference Streams

One approach that has been implemented to various degrees relies upon “reference streams.”

With the reference stream system, a population of “natural” streams thought to represent a

particular ecosystem is measured for physical and/or biological characteristics. Various

statistical measures of the data are then used to indicate the reference condition for that

ecosystem stream type. For sediment, parameters such as percent surface fines, cobble

embeddedness, or percent pool filling have been used. Metrics used to represent these

parameters include the mean, variance, range of the data, and various other statistical measures.

However, even for a set of streams determined to be within a particular stream type/ecosystem,

variability of sediment metrics is often extreme, even within undisturbed systems. As a result,

pure application of the reference system could judge a stream with a known and perhaps even

extreme past and continuing history of road sediment input to be acceptable. This situation has

led to various means of modifying pure application of the system.

A modified reference stream approach that has been considered restricts the acceptable zone to

only a portion of the full range exhibited by the natural stream population (USEPA 1999). This
30

system has generally been rejected because, by definition, even some natural streams are found

to be out of compliance with the standard. A more promising system reviews the status of an

entire population of streams to see if the distribution of parameter values is different from the

natural distribution. If it is, excess sediment input is indicated. The question remains: what is

(or has been) the source of the sediment? Stand alone application of the reference stream

approach does not answer this question. Application of the critical pathway steps to a reference

stream “goal” begins to build the linkages necessary for achieving a sound cause and effect

understanding that allows identification of appropriate management systems and practices.

One encouraging means of building on the reference stream approach is to couple stream indices

with measures that index road system inputs (in this example, sediment) to the stream. In one

manner or another, this is the system being implemented by various states and companies. In

these systems, instream measures of stream health (physical and/or biological) and evaluations of

road sediment input are coupled in a management system that establishes levels or indices of

sediment input that in turn indicate whether the input is acceptable or not. The target sediment

input level must be decreased until the stream condition, as indicated by indices such as percent

surface fines, channel stability, channel geomorphic type, or similar measures, is judged to be

acceptable. This approach can be based on reference streams or on less rigorously quantitative

approaches such as watershed analysis, which builds “the watershed story” largely from

evidence of process and response observable within the watershed. Either way, the approach

provides integrated watershed and road management systems that allow modification of goals,

indices, and management practices as local and global knowledge bases increase. Such systems

are described in Appendix B.

2.7.2 Sediment and Runoff Indices

In some cases, sediment and runoff targets used to set limits on acceptable change are set at the

input level. For sediment in Washington, the goal is to locate areas in the watershed likely to

experience significant changes in sediment that result in chronic changes in turbidity or

deposition of fines in streambeds affecting aquatic life. Washington requires application of

prescriptive management practices to limit sediment delivery in watersheds where analysis

shows that fine sediment delivery has increased to 50% above natural background rates of

erosion. This is based on evidence that sediment yields increased by 50% or more of the longterm average are detectable with water sampling procedures. Similarly, Washington suggests

that changes in peak flows of up to 10% are difficult to detect or reliably predict. They also

suggest that the 5 year peak flow or larger is the important channel-forming event in mountain

channels, and that an increase of approximately 20% in the 2 year peak flow is needed to

produce the 5 year flow. Accordingly, Washington uses these 10% and 20% figures to index

potentially harmful increases in peak flows, and requires adjustment of management practices in

watersheds where analysis indicates that such increases may be occurring (WFPB 1997).

Similarly, Idaho has set limits that are dependent on instream conditions, and that are designed to

protect beneficial uses based on sediment indices and level of watershed harvest reflective of

potential peak flow effects. Using this system, mass wasting, road surface erosion, and loggingrelated sources of accelerated erosion are indexed, and channel conditions related to sediment are

evaluated and indexed. If both indices considered together indicate that excessive production of

sediment has produced adverse instream conditions, sediment sources in the watershed must be
31

addressed to reduce erosion and delivery. For peak flows, Idaho limits harvest acreage based on

an index of watershed hydrologic condition and stream stability, with acreage more restricted

where streams are less stable and subject to adverse effects on peak flows (IDL 2000b) (see

Figure 5).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

20 30 40 50 60 70 80

Channel Stability Index (CSI)

Canopy Removal Index (CRI)

Low

Moderate

High

Figure 5. Idaho Hydrologic Risk Rating

2.7.3 Road Density Indices

In contrast to approaches that set targets based on cause/effect critical pathway analysis of levels

of input to instream effects, some approaches attempt to regulate road construction effects with

indirect indices such as road density. While a number of studies have shown correlation of road

density to deteriorated instream conditions and fish populations (Gucinski et al. 2000), such

approaches do not provide efficient means of managing potential effects on downstream

beneficial uses, because the lack of a linkage between input and effect does not allow efficient

allocation of finite road management resources to the specific problems (causes) that must be

addressed to prevent and solve impacts (effects). The temptation is to regulate watershed road

density based on correlation to instream conditions that may be due to historic effects or effects

not related to current road sediment and runoff conditions. While indirect effects on fish

populations may indeed be correlated with presence and even density of roads, these impacts are

best controlled through devices such as control of access (road closure and use regulation) or

fishing regulations, and that these effects are not related to watershed processes nor to the direct

effects of roads addressed in this paper. Because quasi-regulatory road density based index

approaches have surfaced, particularly associated with the Federal Endangered Species Act

(NMFS 1996; USDAFS 1993) and Clean Water Act Total Maximum Daily Load (TMDL)
32

processes, it is important to elaborate on the weaknesses of such systems for addressing direct

road impacts.

The scientific literature firmly establishes that forest roads can add significant quantities of

sediment to streams, and in some circumstances have been found to affect streamflow

relationships (Beschta et al. 2000; Bowling and Lettenmaier 1997; Thomas and Megahan 1998).

Roads can also cause a number of additional direct impacts to aquatic habitats. Prior to

development of current forest practices rules and modern operating restrictions, these impacts

included construction of roads within and adjacent to channels, straightening of channels,

permanent removal of shade, and loss of channel-adjacent large woody debris producing

vegetation and growing areas. Most of these impacts are associated with roads that were poorly

located, poorly constructed, or improperly maintained in riparian areas or on steep and unstable

slopes (Brown and Krygier 1971; Fredriksen 1970; Furniss et al. 1991; McGreer et al. 1997;

Megahan and Kidd 1972; Packer 1967; Rice et al. 1979; Swift 1986; Trimble and Sartz 1957).

Proper interpretation of road effects in specific watersheds requires consideration of these

location and road management factors.

Working at very broad scales, where specific factors could not be analyzed, the Interior

Columbia Basin Ecosystem Management Project (ICBEMP) Assessment of Ecosystem

Components in the Interior Columbia Basin (Quigley and Arbelbide 1997) recently stated in the

executive summary that “increasing road densities (combined with the activities associated with

roads) and their attendant effects are associated with declines in the status of four anadromous

salmonid species.” They note that activities associated with roads may affect fish populations,

including fishing, recreation, timber harvest, livestock grazing, and agriculture, and that roads

provide avenues for stocking of non-native fishes. The assessment also stated that,

“Unfortunately, we do not have adequate broad-scale information on many of these attendant

effects to accurately identify their component contributions. Thus, we are forced to use roads as

a catch-all indicator of human disturbance.”

At the broad scales examined by the ICBEMP, it is not surprising that a positive correlation was

found between road density, fish, and habitat quality. Indeed, if impact from all road miles

within any given basin are assumed to be equal, irrespective of road location and management

practices, and if all other factors responsible for effects upon streams and fish within basins are

ignored (the simplifying assumptions relied upon by the ICBEMP assessment), then road

density, stream habitat, and fish declines may be correlated to some degree. However,

widespread experience backed by a vast literature base allows us to avoid such simplifying

assumptions when dealing with management of specific watersheds and allows us to establish

cause and effect relationships between roads, stream habitat features, and fish populations.

Regarding sediment, which is the predominant potential adverse effect of roads on streams (as

long as roads are no longer located within channels), Figure 6 demonstrates that sediment

delivery is not correlated with road density.5

 Figure 6 is based on field inventories and modeling

of road erosion and sediment delivery using Washington watershed assessment procedures

(WFPB 1997) applied to watersheds located throughout the coastal and inland northwest.

 

5

 Although Figure 6 does not indicate the different geologic types encountered in the various watersheds,

categorizing the data by geologic type reveals no discernible trends.
33

0

10

20

30

40

50

60

70

80

012345678

Road density (mi/sq.mi.)

Sediment delivery (tons/sq.mi.)

Figure 6. Road Sediment Delivery vs. Road Density

The explanation for this lack of correlation (and therefore lack of a cause-effect relationship) is,

as discussed earlier, that some but not all roads deliver sediment to streams, and even those roads

that do deliver sediment deliver it at rates that vary by orders of magnitude. Further, where land

managers recognize higher hazards for road erosion they can modify road design and

maintenance practices to minimize impacts (Bourgeois 1978). In many watersheds, specific road

segments are responsible for a disproportionately high share of total road sediment delivery, as

illustrated in Figure 7. These figures help emphasize that if the major stream impacts in a

watershed are associated with sediment discharged from roads, the means of control is to identify

and treat the specific roads that contribute the sediment, not merely to reduce road density.

The realization that not all roads are equal has lately received increased recognition. In

concluding a broad discussion of direct, indirect, and landscape-scale effects, the USDA Forest

Service (Gucinski et al. 2000) states:

Measures of the cumulative effects of roads more closely related to mechanism (for

example, the length of roads connected by direct surface-flow paths to streams or the

miles of potential habitat blocked by culverts) would be more likely to produce stronger

relations between roads and aquatic habitat elements than would road density.
34

0%

20%

40%

60%

80%

100%

0% 20% 40% 60% 80% 100%

% cumulative road mileage

% cumulative road sediment

Upper West Branch Upper East Branch Middle Branch 

Figure 7. LeClerc Creek Watershed Road Sediment Examples

2.8 Habitat/Population Feedback to Management System

When considering potential effects of roads on habitat and populations, the species of concern

are most often fish, typically salmonids. However, managers are increasingly being required to

address all aquatic species, including amphibians and macroinvertebrates (e.g., tailed frogs,

salamanders).

In any case, a knowledge of the cause and effect linkages between roads and beneficial uses, as

discussed in Sections 2.2 through 2.7, provides feedback to help determine how road related

environmental effects can be systematically managed within acceptable levels. The framework

of this feedback is the basis of the adaptive management approach. When habitat or population

objectives are not achieved, adjustments are made in the management practices employed. The

management system is the vehicle used to identify where and how those adjustments are to be

made. Management systems may be based on state forest practice rules or BMPs, watershed or

landscape analysis procedures, special issue management methods, or some combination of

these. Examples of various management systems are described in Appendix B.

3.0 RESEARCH NEEDS

A number of subjects where uncertainty continues to exist regarding the relationship of roads to

stream systems and effects on aquatic ecosystems are discussed herein. Although not a detailed

discussion of these uncertainties and research approaches that might be used to address them, the

most important subjects that require additional research include:

Improve understanding of relationships between input levels, both sediment and water, and

channel responses.
35

Improve understanding of channel response effects on aquatic habitat and population

response.

Develop methods to identify areas with high hazards of excessive sediment or water inputs to

streams.

Monitor the effectiveness of road practices at the project and watershed scale to show that

sediment is appropriately reduced.

Develop and validate targets and indices that relate input levels to channel, habitat, and

population responses.

Validate and improve, where necessary, road sediment erosion and sediment delivery

models.

Validate and improve, where necessary, road water delivery models.

Evaluate the role of culvert water discharge in gully formation and design guidance for its

control.

Quantify how and what types of culverts cause fish passage problems.

4.0 CONCLUSIONS

The impacts and values of forest roads have been the subject of recent debate. Forest roads

historically have produced substantial adverse effects on streams, and depending on how they are

managed, may continue to adversely impact streams today. While there is no doubt that roads

can impact the aquatic environment, roads are also necessary for management of forest lands.

Although roads are essential to land management for forest products, fire control, and other uses

such as recreation, there remain legitimate concerns about where roads should be located and

how many roads are necessary. Roads must be located to serve their intended transportation

system objectives while at the same time meeting environmental constraints and requirements.

These dual objectives provide a classic case where neither objective can be completely

optimized, and a satisfactory solution is sought wherein both economic and environmental goals

can be adequately met. Harvest methods, anticipated traffic, operating speeds, and safety

requirements must be considered. All of these influence road width and alignment, which affect

the area of disturbance and subsequent environmental consequences. Complex terrain, land

ownership patterns, and/or environmentally unacceptable locations often dictate road spacing,

which in turn often requires road density to increase beyond an economic optimum.

Road building, upgrading, and maintenance are basic to commercial forestry operations and

require a significant part of company operating budgets. Because of their high value and

potential environmental consequences, road assets are constantly managed. Management

includes transportation system planning, route reconnaissance and location, road design, road

construction, road maintenance, upgrading, and road closure and obliteration.

Most of the roads needed today for management of private lands have already been built, but

many of these roads were not located, designed, or built to current standards necessary to meet

environmental goals. Assessment of road system effects must consider the proportion of old

roads to new roads that incorporate improved engineering design (Gucinski et al. 2000).
36

Although substantially improved road management practices have evolved during recent years,

managers must continue to address four major potential impacts of roads on aquatic ecosystems.

These potential effects include 1) increased peak flows that, if large enough, may adversely

affect channel morphology and dependent biological systems; 2) erosion and delivery of

sediment to streams through surface erosion processes that can lead to filling of interstitial spaces

in streambed gravels and/or by increasing turbidity levels, and through mass erosion (landslides)

where large quantities of coarse sediment delivery can contribute to channel scour, deposition,

avulsion, and other major affects on channel morphology; 3) channel encroachment, a legacy of

old roads that must be considered in road maintenance, upgrading, and closure plans; and 4) fish

passage at road-stream crossings.

Critical pathway assessment based approaches, like those developed by Washington, Oregon,

and Idaho, are effective management systems that establish the cause-effect linkages between

forest roads and aquatic systems. Applied to roads, critical pathway analysis traces how roads

influence watershed processes (runoff and erosion) in the vicinity of the road, and determine and

quantify how water and sediment are delivered from roads to streams and are routed through the

stream channel system. Channel responses are then interpreted in terms of possible effects on

stream habitat and fish populations. This report contrasts critical pathway analysis with less

effective approaches that attempt to regulate road construction effects with coarse indirect

indices, such as road density, which do not link cause and effect and therefore do not efficiently

allocate finite road management resources to the specific problems that must be addressed to

prevent adverse effects.

Roads increase erosion because of effects on hydrologic processes as well as changes in site

factors that influence erosion rates. Although effects vary greatly depending on specific site

conditions, both surface and mass erosion rates and delivery of sediment to streams often

increase with road construction in mountainous areas. Sediment delivery from roads due to

surface erosion is a function of the volume of water discharged from the road, the volume of

sediment carried by that water, and characteristics of the pathway that the water/sediment

solution travels. Sediment delivery due to mass wasting is a function of the characteristics of

slopes where roads may be located, as well as road designs and construction. By understanding

these processes as they apply to the specific circumstances of watersheds, as established by

watershed assessment and road inventory procedures, managers can effectively reduce and

control impacts to levels established as acceptable by current standards. Uncertainty exists

regarding these standards and the targets and indices that reflect them, and future research will be

needed to refine them through time. Similarly, although potential effects of roads on peak flows

and channel morphology are probably limited to effects within small watersheds, and the

magnitude of such effects remains uncertain, they can be managed through regulation of the

amount of road “connected” to stream systems.

Applying appropriate road practices in forest watersheds to reduce negative water quality

impacts requires two elements: a set of management practices for roads which can effectively

reduce water quality impacts; and a management system which ensures that the right practices

are applied in the right places. The management system is used to select and implement

practices chosen from the set of management practice options. Both current management

activities and watershed hazards, as well as hazards and impacts that occur due to historic

activities, must be addressed.
37

Effective management systems for roads require several steps. These include inventory of road

and stream conditions, identification of road sections requiring practices to bring them into

acceptable condition, identification of effective practices and costs, development of priorities and

a schedule of work, appropriate timeframes for implementation and completion of necessary

tasks, implementation monitoring, inspection to determine performance of implemented

practices, and personnel training. Building on state forest practice rule BMP-based systems,

western states including Oregon, Washington, and Idaho have developed watershed analysis

systems that address watershed conditions on a site-specific basis. Habitat conservation plans

and other special issue management systems, including those developed by a number of forest

products companies, have also been developed to meet current environmental objectives and

standards.

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APPENDIX A

MICA CREEK EXAMPLE OF HISTORIC LOGGING METHODS AND IMPACTS

The transformation from rail and water-based forms of logging and transport to modern era

logging methods and the road location and design that facilitate them are illustrated by the

history of activity in the Mica Creek watershed, a 38 mi2

 watershed tributary to the St. Joe River

in northern Idaho. This watershed was extensively logged in the 1920s and early 1930s. The

transportation and logging system patterns and methods used are evident from 1933 stereo aerial

photography. Evidence of these early activities also remains in the watershed today, and

includes old railroad grades, trestles, trenches from ground skidding, flumes, splash dams, log

chutes, and log corduroyed skid trails.

Timber in the lower portions of slopes near streams was skidded downslope to the valley

bottoms. The typical pattern was to skid logs by dragging them with horses to timber chutes that

were constructed in the first and second order draws that led to the valley bottoms of larger

streams. Some of these larger streams were covered with log corduroy roads where logs were

skidded with horses and wheeled carriages. At that point the logs were channeled into wooden

flumes located in and adjacent to the main third and fourth order tributaries of the watershed.

The flumes joined downstream and extended for several miles down the mainstem of Mica Creek

until they reached a narrow valley constriction where a splash dam was constructed that

periodically flushed logs for several more miles to the St. Joe River.

It is not hard to imagine that downhill skidding to instream and stream-adjacent transportation

corridors without benefit of erosion control caused tremendous impacts to the stream network of

Mica Creek. These impacts included stream dewatering, direct physical disturbance of stream

morphology, destruction of riparian vegetation, solar exposure, removal of instream large wood,

and introduction of sediment in quantities that exceeded natural rates of watershed erosion by an

estimated two to three orders of magnitude for a period of several years.

Conversion of railroad grades to truck roads in the 1940s and 1950s resulted in the location of

mainline roads that accessed major watersheds adjacent to rivers and streams. Because the

mainlines were located in the valley bottoms, the remainder of the road transportation system

was constructed to lead downslope to it, and often these roads were also constructed on old

railroad grades or original locations that followed tributary stream courses. The result is that

extensive road systems have developed that lie in stream-adjacent locations. A second, and often

equally important, effect is that after leaving valley bottoms, roads could be built on steep slopes.

These early mid-slope roads were often constructed with bulldozers and excavated materials

were sidecast onto steep and unstable slopes, resulting in numerous landslides in many

watersheds (Sidle 1985).

Construction machinery and techniques and road location requirements that consider landslide

hazards have eliminated many of these problems during the past 30 years, but a legacy of old

road problems remains. In many cases, these legacy problems can be systematically eliminated,

or at least reduced in severity, and formal regulatory and non-regulatory programs to reduce

these legacy effects have been implemented in recent years throughout much of the western

forest lands. Examples of such programs include road maintenance and abandonment
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requirements of Washington’s “Forest and Fish Agreement,” forest practices act rules (WFPB

2000), Oregon State’s Plan for Salmon and Watersheds (ODF 2000), and Plum Creek Timber

Company’s Native Fish Habitat Conservation Plan (Plum Creek Timber Company 2000).

Seventy to eighty years have passed since the early logging in Mica Creek. The watershed is

once again densely forested, and streams have recovered to a remarkable degree. For example, a

striking array of sediment-intolerant macroinvertebrates currently populates Mica Creek. To

facilitate logging planned for the headwater areas of the watershed in 2001, new forest roads

have been constructed. The new road system allows virtually all areas of the headwaters to be

logged by ground-based systems on moderate to gentle slopes and ridgetops above the roads, and

by aerial cable systems below the roads. Of particular relevance to the subject of this paper, this

road system was located with great care to minimize stream crossings or other locations where

sediment delivery to streams is likely.

The effect of roads and logging in the Mica Creek watershed is being monitored in a research

setting by Potlatch Corporation and NCASI (McGreer et al. 1995). The nature of the road

locations and construction standards, as well as preliminary results following road construction,

lead to an estimate that sediment delivery to streams will be no more than 10% to 50% above

natural watershed rates of erosion, decreasing to even lower rates within one to two years

following logging. In fact, a detailed analysis of sediment sampling from Mica Creek showed no

increase in suspended sediment in the first year following road construction (Mosier 1999). The

contrast between historic and modern methods is huge, and while details vary from one

watershed to the next, the Mica Creek history is representative of similar watershed histories

throughout the west.

References

McGreer, D.J., Cundy, T.W., and Gravelle, J.A. 1995. Mica Creek cumulative watershed

effects study. In: Watershed Management Planning for the 21st Century. August 14-16,

1995, San Antonio, TX. Watershed Management Committee of the Water Resources

Engineering Division/ASCE. p. 300-309.

Mosier, D.D. 1999. Influence of road construction on stream water quality in the Mica Creek

watershed, Shoshone County, Idaho. Master’s thesis. Moscow, ID: University of Idaho,

Geological Engineering Department.

Oregon Department of Forestry (ODF). 2000. Forest road management guidebook:

Maintenance and repairs to protect fish habitat and water quality. Salem, OR: Oregon

Department of Forestry. 32 p.

Plum Creek Timber Company. 2000. Native Fish Habitat Conservation Plan. Seattle, WA:

Plum Creek Timber Company.

Sidle, R.C. 1985. Factors influencing the stability of slopes. In: Proceedings of a Workshop on

Slope Stability: Problems and Solutions in Forest Management. General Technical Report

PNW-180. United States Department of Agriculture Forest Service, Pacific Northwest

Forest and Range Experiment Station. p. 17-25.
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Washington Forest Practices Board (WFPB). 2000. Forest Practices Act Board Manual.

Olympia, WA: Washington Department of Natural Resources. 212 p.
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APPENDIX B

MANAGEMENT SYSTEMS AND EFFECTIVENESS

B.1 State BMP Management Systems

Nearly all state forest practices BMP programs, including state forest practices acts, were

initially developed in response to the requirements of Section 208 of the 1972 Federal Clean

Water Act. Accordingly, each state’s BMPs share the basic objective and requirement of

maintaining the beneficial uses of the water and meeting the state’s water quality standards.

However, there are substantial differences between these BMPs and the state forest practice

management systems designed to implement these rules.

Oregon and Idaho have forest practice notification programs that are designed to alert state

agencies to proposed operations. Notification allows for pre-harvest inspections where there are

priority risks and where special protection may be needed. In Oregon, where there are special

risks associated with activities in areas with a high risk of landslide or near fish-bearing streams

and wetlands, written plans are required. The Oregon and Idaho forest practice rules also allow

for special protection rules in watersheds that are water quality limited.

Washington uses a permit program, and there are several levels of review based on the risk

category of the management activity proposed. The permit process is streamlined for activities

where a watershed analysis has been conducted and approved by the Washington Department of

Natural Resources (also see Section B.3), wherein management practices for the watershed have

been developed cooperatively between scientists and managers.

In California, comprehensive timber harvest plans are subject to an exhaustive review process by

state agencies and the public. Only licensed professional foresters who have sufficient education

and professional training and have passed an exam can submit timber harvest plans. Like

Washington, streamlined approval can occur for operations covered by Sustained Yield Plans.

These plans cover the sustainability of timber and public resources over large management areas.

Special rule packages can be developed for individual counties or watersheds with endangered

species or other risks.

As discussed in Section B.5.1, the effectiveness and levels of compliance with BMPs have been

formally evaluated by some states.

B.2 Company Based Management Systems

There is a range of management systems that companies or non-industrial private landowners

may use to manage roads. At the base level is compliance with state forest practice rules and

BMPs. These are considered the minimum standards needed to protect public resources.

Repeated assessments have shown that compliance with state BMPs and forest practice rules

prevents major water quality impacts under most circumstances (Ethridge and Heffernan 2000).

Compliance with all state BMPs is a commitment of all industrial timber companies who are

members of the American Forest and Paper Association and who have committed to the

Sustainable Forestry Initiative (SFI) (AF&PA 2000). One of the objectives of SFI is to “protect
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the water quality in streams, lakes, and other waterbodies.” A key performance measure is

“program participants will meet or exceed all established Best Management Practices (BMPs)

approved by EPA, all applicable state water quality laws and regulations, and the requirements of

the Clean Water Act for forestland.”

However, state BMPs can be inefficient, because they are designed to protect resources under the

general circumstances encountered in the area regulated. The result is that state BMPs

over-protect in some cases (wasting resources that could be applied to higher priorities) and

under-protect in others (allowing undesired impacts). For this reason, some states have

customized BMPs to regions within the state. States with diverse geographies and complex

terrain, such as Washington, Oregon, and Idaho, have promoted various forms of watershed

assessment to tailor BMPs more closely to the watershed and site conditions (see Section B.3).

Most timber companies have much more complex management systems than mere compliance

with state BMPs. An example of the many levels of management systems is Plum Creek Timber

Company’s Habitat Conservation Plan for Native Fish (Plum Creek Timber Company 2000). In

addition to a commitment to meeting state regulations, Plum Creek developed an internal

conservation plan, which goes well beyond state BMPs in order to systematically address special

management issues – in this case, issues that arise due to the presence of threatened, endangered,

or otherwise sensitive fish species.

B.2.1 Plum Creek Timber Company’s Native Fish HCP

Plum Creek Timber Company (PCTC) developed a Habitat Conservation Plan (HCP) for 17

species of native fish on 1.6 million acres of company ownership, most of which is in Montana.

The plan was approved by both US Fish and Wildlife Service and National Marine Fisheries

Service as meeting the requirements of the Federal Endangered Species Act and will be in effect

for 30 years. The HCP includes 56 commitments on the part of PCTC, covering all facets of

their forest management system. A summary of these levels of commitment is provided in

Appendix 1 of the Plum Creek HCP summary (Plum Creek Timber Company 2000).

With regard to roads, the HCP requires as a base prescription that the company comply with all

forestry BMPs. In Montana, BMPs are currently managed as a non-regulatory program.

Because Montana’s forestry BMPs have only been in place since 1989, the majority of PTCT’s

road system was constructed without the benefit of modern standards, including those for road

drainage, erosion control, and fish passage through culverts. The HCP will require the company

to inspect its entire road system in the next 5 years, and bring all old roads into compliance with

contemporary BMPs within 10 to 15 years. Once in compliance, the HCP sets maximum

intervals for road re-inspection and necessary maintenance.

Roads that PCTC does not need for long-term forest management (i.e., surplus roads) will be

“abandoned” within the same 10 to 15 years as road upgrades. To be abandoned, several criteria

need to be met. These include blocking the road to vehicles, removing culverts and pulling back

and reshaping fills at stream crossings, revegetating road surfaces and adding extensive road

tread drainage, and stabilizing landslide prone segments through total or partial recontouring.
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Finally, the plan also requires extensive research and monitoring to see that the road

management system specified in the HCP is working to reduce sediment delivery to streams.

This will include preparing sediment budgets in numerous watersheds, monitoring trends in

spawning gravel, and validating coefficients used in road sediment models.

B.3 Watershed/Landscape Assessment Approaches

The basic premise of watershed and landscape based assessment and management systems is that

trained evaluators can develop an understanding of watershed and stream processes at work, and

an understanding of cause-and-effect relationships between disturbance and stream conditions

based on direct observation of stream and watershed conditions, both historic and current, and

application of observations within predictive models where appropriate. Current stream

conditions are determined, effects of future forest practices are anticipated, and management

practices that correct or prevent adverse conditions are developed.

B.3.1 Washington Watershed Assessment Process

Washington’s watershed analysis approach to watershed management is based on biological and

physical inventories of watershed conditions. It is a collaborative process involving resource

scientists and managers representing landowners, agencies, tribes, and other interested citizens.

Both the assessment and the management process based on assessment findings are highly

structured and defined within the Forest Practices Act and its implementing rules, and are

designed to be repeated and adaptive, as illustrated in Figure B.1.

Public Resources

Resource Assessment Prescription Process

Effectiveness

Monitoring

Feedback for Adaptive Improvement

Watershed Processes

Information

Area-specific

prescriptions

– regulatory

– voluntary

activities

(BMPs)

watershed

processes

resources

Management

Actions

Predictions and

hypotheses of

mgmt. actions on

resources

Figure B.1. The Major Components of Washington Watershed Analysis

In Washington’s system for management of road erosion and sediment delivery impacts, roads

are field inventoried and the data are used with simple spreadsheet based models that quantify
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erosion and sediment delivery in comparison to estimates of natural background watershed

sediment delivery. When delivery is considered to be too high, an adverse condition exists that

must be addressed with management prescriptions designed to alleviate the condition (see

Section 2.7). These prescriptions are developed by local land managers and agencies, must

address the specific areas of hazard and resource concern identified by the scientific assessments,

and are subject to public review and appeal prior to final acceptance of the plan.

B.3.2 Idaho Cumulative Watershed Effects Process

The objective of Idaho’s Cumulative Watershed Effects (CWE) assessment and forest practices

management process is to lead landowners to conduct future forest practices according to three

“staged” criteria (IDL 2000b):

1) In watersheds where beneficial uses are not supported as a result of forest practices and are

not improving, mitigation and rehabilitation activities must be conducted in conjunction with

current forest practice activities so that, in balance, a generally improving trend is maintained

until adverse conditions no longer exist.

2) In watersheds where beneficial uses are not supported as a result of forest practices but

conditions are improving, activities must be conducted in a way that does not interrupt this

improving trend.

3) In watersheds where beneficial uses are supported, forest practices will be designed to

prevent loss of this support.

The Idaho assessment procedures are designed to detect the presence of adverse watershed or

stream conditions, to identify causes for the conditions, and to identify actions that will correct

and prevent existing and potential future problems. The result of implementation of the CWE

process in a watershed is the development of mandatory special rules for the watershed, called

Cumulative Watershed Effects Management Practices, that are authorized by the state’s Forest

Practices Act and are enforced by the Idaho Department of Lands (IDL). As in Washington,

roads in Idaho watersheds are inventoried, and although based on a qualitative rating of erosion

and delivery of sediment to streams, road conditions leading to adverse instream conditions must

be corrected until the qualitative rating score is reduced to within the range considered to be

acceptable.

B.3.3 California Sustained Yield Plans

In California, a Sustained Yield Plan (SYP) is an option for the landowner to supplement the

Timber Harvest Plan (THP) process, but does not replace the THP. The SYP provides analysis

of long-term issues across the landscape, such as sustained timber production, cumulative

watershed effects, and fish and wildlife concerns.

The watershed assessment portion of the SYP must include an analysis of potential adverse

impacts of planned forestry operations, including impacts on water quality. Specifically, the

SYP must include 1) identification of unstable areas and unstable soils that are either actively or

potentially discharging sediment; 2) a map of existing roads and the approximate location and

mileage of proposed new, reconstructed, and abandoned roads; and 3) a general description of
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existing sources of erosion and areas known to be sensitive to ground disturbance. The SYP

must also provide a discussion of feasible measures to avoid significant adverse impacts.

Once the SYP is approved by the California Department of Forestry, the THP can incorporate

findings of the SYP to address issues that were identified. The THP may rely on the SYP

analysis as long as the THP is consistent with the measures set forth in the SYP. If the THP

involves issues not discussed in the SYP, the THP must address those issues and conform to the

Forest Practices Rules.

B.3.4 Oregon Watershed Assessment Process

The Oregon watershed assessment process is designed to identify how natural processes and

human activities affect fish habitat and water quality, and to evaluate the cumulative effects of

land management practices over time. Although the process does not include development of

site specific watershed management prescriptions, it provides the information necessary for

development of action plans and monitoring strategies for protecting and improving fish habitat

and water quality. The assessment provides broad-scale screening and is developed by local

citizens with some assistance from technical experts using the assessment manual’s “cookbook”

procedures for compilation and evaluation of information about watersheds. The procedure

concludes with development of a Watershed Condition Evaluation and Monitoring Plan. A

standard list of Critical Questions is addressed for each of six watershed characterization

modules, as shown in Figure B.2.

Watershed Watershed Watershed

Description Characterization Assessment

Hydrology and

Water Use

Riparian/

Wetlands

Sediment Sources

Channel

Modification

Water Quality

Start-up and

Identification of

Watershed Issues

Watershed

Condition

Evaluation

Monitoring Plan

Historical

conditions

Channel

Habitat Type

Classification

Fish and

Fish Habitat

Figure B.2. Oregon’s Watershed Assessment Approach
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Road erosion and sediment delivery are evaluated as a component of a broad sediment source

assessment that identifies where human caused sediment increases are most severe, as well as

priority restoration opportunities. The assessment manual provides highly structured and

organized procedures for evaluation of landslide hazards, road surface erosion, and stream

culvert capacity and condition. Roads are inventoried using Oregon Department of Forestry

procedures that are available online at www.odf.state.or.us/FP/default.htm.

B.4 Special Issue Management Systems

In some cases, management systems evolve around a specific issue or certain species of concern.

Examples of this include Habitat Conservation Plans (HCPs), the Oregon Plan for Salmon and

Watersheds, Washington State’s Forest and Fish Agreement, and the Idaho Antidegradation

Agreement.

B.4.1 Habitat Conservation Plans

Section 9 of the 1973 Endangered Species Act (ESA) notes that it is unlawful to “take”

endangered species, with the definition of “take” including, “...harass, harm, pursue, hunt, shoot,

wound, kill, trap, capture or collect...” Regulations under Section 4 of the Act clarify that

“harm” in the definition of “take” includes “significant habitat modification.” In one of the few

amendments to the 1973 ESA, Congress modified Section 10 in 1982 to permit “take” for listed

species incidental to such otherwise lawful activities as grazing, farming, or logging. Each

application for such an incidental take permit must be accompanied by a “conservation plan.”

There is no requirement that any landowner or agency seek a Habitat Conservation Plan (HCP),

but the process is intended to be proactive and creative, with the landowner taking the initiative

to obtain the HCP and suggest the habitat conservation measures designed to avoid take. The

legal assurances provided by an HCP are not without cost – both in terms of the cash outlay

necessary for the completion of the agreement and the delays and modifications to land uses that

might be required in exchange for the HCP.

The HCP for native fish species developed by Plum Creek Timber Company as described in

Section B.2.1 is one example of an HCP that addresses existing and potential future road impacts

through comprehensive assessment and inventory followed by implementation of forceful (and

expensive) road maintenance and construction requirements.

B.4.2 Oregon Plan for Salmon and Watersheds

Several Evolutionarily Significant Units of salmon and steelhead have been listed in recent years

under the ESA in numerous rivers of coastal and interior Oregon. Under sponsorship of the

state’s Governor, Oregon has developed its Plan for Salmon and Watersheds. The key elements

of the Oregon Plan are: 1) an ecosystem approach that requires systematic consideration of the

full range of attributes of aquatic health; 2) a focus on reversing factors for decline and meeting

objectives that address those factors; 3) use of adaptive management and a comprehensive

monitoring strategy; and 4) building citizens and constituent groups into the restoration process.

Several forest land initiatives have been implemented, including development of the watershed

assessment process (OWEB 1999), development of standard road inventory and assessment

procedures (ODF undated), and development of training materials for landowners, including the
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Forest Road Management Handbook (ODF 2000). These procedures emphasize design and

construction of culverts to ensure fish passage, along with road maintenance and repairs to

prevent surface erosion, washouts, and road failure associated landslides.

Several watershed assessments using the Oregon procedures have been completed and many

more are in progress. Many members of the Oregon Forest Industry Council and smaller forest

landowners have voluntarily completed the required inventories and have initiated rehabilitation

of road systems to address existing adverse circumstances (ODF 2000).

B.4.3 Washington Forest and Fish Agreement

In 1986, the timber industry, tribes, the state, and the environmental community agreed to

resolve contentious forest practices problems through negotiations, resulting in Washington’s

watershed assessment process and several stream and landscape research efforts. As a result of

research findings and common findings within many of the completed watershed analyses, the

Timber/Fish/Wildlife (TFW) parties, expanded to include federal and local governments, began

working together again to address ESA listings, 660 streams included on the 303(d) list of water

quality limited water bodies, and the cost and uncertainty attendant upon timber acquisitions and

harvest activities. Agreement was reached and recommended to the Forest Practices Board and

the Governor’s Salmon Recovery Office in February 1999. The recommendations were

subsequently adopted as Emergency Forest Practices Rules. These rules substantially modified

the then-existing forest practices rules in such important areas as stream classification, riparian

management requirements, management of unstable slopes, and road management.

Under the agreement and the subsequent Emergency Rules, the road management policy is to

maintain or provide passage for fish in all life stages, provide for the passage of some woody

debris, meet water quality standards, control sediment delivery, protect streambank stability, and

divert most road runoff to the forest floor. Perhaps the most comprehensive of these new rules is

that all landowners are now required to develop and submit for public review and Washington

Department of Natural Resources approval formal road maintenance and abandonment plans for

their entire ownership and road system within specified time frames. Requirements to inventory

all stream crossing culverts and to replace or correct those with fish passage problems are

included. Culverts not passing the now-required 100 year flood flow must be replaced at the end

of their useful life. The new rules also contain comprehensive location, design, maintenance,

and abandonment requirements for prevention of both mass and surface erosion.

B.4.4 Idaho Antidegradation Agreement

The quality of surface water in Idaho and the regulatory scheme for managing it are defined in

three “tiers.” The first category is those streams where the quality of the water exceeds that

which is necessary to support such existing “beneficial uses” as salmonid spawning or cold water

biota. For these streams, the state’s antidegradation policy allows some lowering of water

quality to accommodate logging or other economic activities, as long as the quality is never

lowered below that necessary to achieve the beneficial use. The second category of stream

includes those where the beneficial uses are not fully supported. These are the waterbodies

where state and federal law requires that a TMDL be completed in order to reduce all sources of

pollutants to a level where the beneficial uses are once again fully supported. For the portions
B8

within forested watersheds, forestry BMPs are more stringent than for the first tier of streams.

“Outstanding resource waters” constitute the third tier of streams. For these streams, water

quality cannot be lowered as the result of any point source discharge or nonpoint activity.

Two efforts by the Idaho Department of Environmental Quality (IDEQ) and the Idaho

Department of Lands (IDL) are key to determining the level of forestry BMPs appropriate to

each tier of water quality protection. The rules of Idaho’s Forest Practices Act require a

“default” level of BMPs applicable across the state. Every four years, these two agencies

conduct an audit of the BMPs to determine if they were effective in maintaining water quality,

and rule changes are developed to address instances where practices have been found to be

inadequate.

IDEQ also monitors streams to determine if beneficial uses are being met. For streams where the

uses are fully supported and there is a history of land uses, the BMPs associated with those uses

are, in a general sense, judged to have been effective. For streams where the beneficial uses are

not fully supported, a TMDL may be required, and a technical advisory team and citizen group

work together to select and implement the BMPs needed to assure improvement in water quality.

B.5 Effectiveness of Control Practices and Management Systems

The effectiveness of BMP based state regulatory systems has been evaluated periodically over

the past 20 or so years in some states. Recently, more quantitative procedures have been used to

evaluate the effectiveness of company and special issue management systems. This section

reviews the effectiveness of state BMPs, then recounts a few examples of how special

management systems have been applied that have substantially reduced delivery of sediment and

runoff to stream systems.

B.5.1 Effectiveness of State BMPs

As part of their state/EPA agreements, Idaho, Washington, and Montana have conducted formal

forest practices water quality audits approximately every four years. More recently, Oregon and

California have also begun conducting similar audits. These state audits have assessed both rule

compliance and effects on water quality.

Idaho and Montana have found that hillslope erosion does not contribute sediment to streams

except where disturbance has occurred adjacent to streams, which in most cases has occurred

only where activities were found to have been out of compliance with the rules.6

 In some cases,

however, roads were found to have contributed sediment to streams in quantities estimated to be

potentially harmful to beneficial uses. As a result, rule improvements have been recommended

and enacted (Zaroban et al. 1997; IDL 2000a; WFPB 2000).

In Idaho, the 1992 IDEQ Water Quality Audit (Hoelscher et al. 1993) concluded that “BMP’s . .

were judged to effectively prevent pollutant delivery to streams 99% of the time,” but that when

BMPs were not applied, pollutants, primarily sediment, were delivered to streams 75% of the

time. Similarly, the 1996 audit (Zaroban et al. 1997) concluded that “when properly applied and

maintained, the management practices described in the Idaho forest practices rules are effective

 

6

 Washington only reports effects associated with rule violations.
B9

99% of the time.” However, the most frequent area of non-compliance was related to road

construction and/or maintenance; 69% of all cases of non-compliance were associated with road

rules. Delivered sediment “was primarily from roads with comparatively minor contributions

from harvest systems.” Road rules were cited in 84% of those cases where sediment delivery

occurred.

In Montana, the state has conducted biennial audits of BMP implementation and effectiveness

since 1990 (Schultz 1990, 1992; Frank 1994; Mathieus 1996; Fortunate et al. 1998; Ethridge and

Heffernan 2000). Over the course of these audits, BMP compliance has continually improved,

with statewide BMP application rates of 79%, 88%, 91%, 92%, 94%, and 96% in 1990, 1992,

1994, 1996, 1998, and 2000, respectively. This increase in compliance in Montana is thought to

be the result of increased education of landowners, loggers, and forestry professionals (Patrick

Heffernan, personal communication). With this increasing level of BMP application over time,

water quality impacts have steadily declined and are infrequent where BMPs are fully

implemented (Schultz 1990, 1992; Frank 1994; Mathieus 1996; Ethridge and Heffernan 2000).

Like Idaho, the most common BMPs that were not fully or properly applied dealt with road

drainage and road erosion control.

In Washington, the Washington Forest Practices Compliance Report (TFW 1991) does not report

any conclusions regarding the effectiveness of properly applied BMPs; it only reports instances

of non-compliance and the number of cases in which such non-compliance was judged to result

in damage to public resources. The non-compliance rate for harvest related activities was lower

than that for roads (62 instances of non-compliance for harvest activities vs. 95 for roads), and

the number of cases in which damage to public resources occurred was also lower for harvest

than it was for roads (10 instances of damage for harvest vs. 21 for roads).7

 Since 1991, there

have been no forest practices audit reports completed for Washington.

In Oregon, BMP compliance rates from 1987 to 1996 averaged between 96 and 98% (Dent and

Robben 1999). As in Idaho and Montana, the most frequent areas of non-compliance found in

the 1998 ODF monitoring were in road construction and/or maintenance (Dent and Robben

1999). Of 20 non-compliant road-related practices, 9 resulted in sediment delivery to streams.

The specific non-compliant practices that had the greatest impacts on streams were related to

road drainage or temporary crossings. Of 22 sediment sources identified, 19 were associated

with roads; 6 of the 22 sediment sources were estimated to be “incidental” (<1 cubic yard), 10

were “moderate” (1 to 10 cubic yards), and 6 were judged to be “significant” (>10 cubic yards).

Additional monitoring by ODF indicated that 31% of the surveyed road length potentially

delivered sediment to streams, and that two-thirds of that potential delivery length occurred

immediately upslope of live stream crossings (Skaugset and Allen 1998). However, less than

half (40%) of that potential delivery length occurred where surface drain spacing exceeded

recommended criteria, suggesting that drainage spacing is not sufficient by itself to adequately

control sediment delivery from roads.

In California, the forest practice rules were generally found to be sufficient to prevent erosion,

and 97% of the 727 erosion problem points identified were associated with departures from rule

 

7

 In the majority of cases, damage was judged to be “slight” for both harvest and roads.
B10

requirements (CBOF 1999). Rules related to roads had greater than 90% compliance, and most

road rule departures were related to drainage and maintenance. However, of 35 mass erosion

events documented, 27 were related to timber management activities, with 24 of those associated

with roads, most often fillslope failures. One of the major conclusions of the monitoring was

that “roads and their associated crossings were found to have the greatest potential for delivery

of sediment to watercourses,” and that “where roads are built will remain critical for reducing the

likelihood of producing significant sediment input to channels.” Recommendations therefore

included greater attention to and better implementation of rules related to drainage, crossing

design, and maintenance.

Collectively, these state reports demonstrate that while compliance with BMPs is high, most

excursions are associated with roads, and that when road BMPs are not properly applied,

sediment delivery to streams is likely. However, even with full application of state BMPs,

sediment delivery from roads can occur. The questions then are “How much sediment

delivery?” and “What is its significance?” Watershed assessments are designed to address these

questions and, where necessary, to reduce impacts to acceptable levels.

B.5.2 LeClerc Creek Mass Wasting

A watershed analysis completed by Stimson Lumber Company for the LeClerc Creek watershed

provides an example of mass wasting assessment, development and implementation of mass

wasting hazard management prescriptions, and adjustment (adaptive management) of

prescriptions with improved information following major runoff events in 1998 and 1999.

Forty-six landslides were located and several moderate to high hazard mass wasting management

units were identified and mapped in 1996 as part of the LeClerc Creek Watershed Assessment

(McGreer et al. 1997). One area of the watershed had experienced two road fill failures that

resulted in relatively small debris torrents confined to first and second order tributary streams.

Based on these failures and characteristics of surrounding areas, a moderate hazard area was

designated and mapped in several discontinuous blocks totaling several hundred acres.

Management prescriptions for the roads in these units required detailed inspection and

preparation of road maintenance plans, installation of additional drainage, and other upgrade

measures. However, before these measures could be implemented, two additional road failures

occurred in the same area as the previous two. Subsequent detailed assessment of the area

resulted in a new prescription that required total obliteration of all roads and no construction of

new roads that lay within the area of particular hazard, as identified by geomorphic

characteristics. No subsequent failures have occurred in the watershed.

B.5.3 Plum Creek Timber Company HCP

As the technical foundation for its Native Fish HCP, PCTC evaluated the potential effectiveness

of rigorous sediment delivery control through road upgrading. Several measures were proposed.

The most significant upgrade and the measure that could be analyzed most rigorously was

addition of road drainage structures. Using an iterative analysis process, road culvert and surface

drain structure spacing was specified that would substantially limit sediment delivery (McGreer

et al. 1998). The effectiveness of the approach was then applied to the road systems inventoried

in eleven watersheds in Montana, Idaho, and Washington where detailed road erosion
B11

assessments had been recently completed. The analysis indicated that construction of additional

drainage structures near stream crossings would eliminate 25 to 85% of road sediment delivered

to streams in the eleven watersheds evaluated. These measures are now being applied to the

1.7 million acres of PCTC ownership covered by the HCP, where similar results are expected.

Implementation and effectiveness monitoring are required by the terms of the HCP to evaluate

the effectiveness of these habitat conservation measures.

B.5.4 Spruce Creek Road Location and Construction

Assessment of an extensive road system in the Spruce Creek watershed of northern Idaho using

Washington watershed assessment procedures resulted in estimated sediment delivery from roads

of 257 tons/year. Further analysis of site-specific conditions revealed that addition of drainage

relief structures near streams would reduce delivery from this existing road system by 149 tons,

from 257 tons to 108 tons (McGreer and Schult 1996). Potential sediment delivery from

additional roads planned for construction in the watershed was subsequently assessed based on

the Washington procedures, coupled with sediment delivery prediction methodology from

Megahan and Ketcheson (1996) and based on detailed field data collection for each road segment

(McGreer and Schult 1997).

Based on standard design measures consistent with state regulations, three miles of new fullyinsloped road was projected to increase sediment delivery for the watershed by 12% beyond

delivery from the existing road system. However, analysis also revealed that delivery could be

reduced by 24%, from 32.0 to 24.3 tons/year, by adding surfacing rock to those sections of road

that drain via road ditches directly to streams (i.e., rocking the crossings), and nearly an

equivalent reduction (23%) could be achieved with the addition of relief culverts to certain

specific road segments. Rocked crossings combined with additional culverts reduced projected

sediment delivery to 17.1 tons/year, a 47% reduction, which represents a 7% increase over the

amount delivered from the existing road system. In summary, the landowner could choose a

number of options for control of sediment from existing and proposed roads that would

substantially decrease future sediment delivery to the watershed’s streams while logging and

road construction proceeded.

References

American Forest and Paper Association (AF&PA). 2000. Sustainable Forestry Initiative SM

standard - principles and objectives. Washington, DC: American Forest and Paper

Association. 5 p.

California State Board of Forestry (CBOF). 1999. Hillslope monitoring program: Monitoring

results from 1996 through 1998. Sacramento, CA: California State Board of Forestry. 70 p.

Dent, L., and Robben, J. 1999. Forest practices compliance monitoring project: 1998 pilot

study results. Salem, OR: Oregon Department of Forestry.

Ethridge, R., and Heffernan, P. 2000. Montana forestry best management practices monitoring

– The 2000 forestry BMP audit report. Missoula, MT: Montana Department of Natural

Resources and Conservation, Forestry Division. 69 p.
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Fortunate, N., Heffernan, P., Sanger, K., and Tootell, C. 1998. Montana forestry best

management practices implementation monitoring. 1998 forestry BMP audits final report.

Missoula, MT: Montana Department of Natural Resources and Conservation, Forestry

Division.

Frank, G. 1994. Montana forestry best management practices implementation monitoring.

1994 forestry BMP audits final report. Missoula, MT: Montana Department of Natural

Resources and Conservation, Forestry Division.

Hoelscher, B., Colla, J., Hanson, M., Heimer, J., McGreer, D., Poirier, S., and Rice, J. 1993.

Forest practices water quality audit 1992. Boise, ID: Idaho Department of Health and

Welfare, Division of Environmental Quality. 27 p. plus appendices.

Idaho Department of Lands (IDL). 2000a. Rules pertaining to the Idaho Forest Practices Act,

Title 38, Chapter 13, Idaho code. Coeur d’Alene, ID: Idaho Department of Lands. 39 p.

Idaho Department of Lands (IDL). 2000b. Forest Practices Cumulative Watershed Effects

Process for Idaho; Idaho Forest Practices Act. Coeur d’Alene, ID: Idaho Department of

Lands.

Mathieus, G. 1996. Montana forestry best management practices implementation monitoring.

1996 forestry BMP audits final report. Missoula, MT: Montana Department of Natural

Resources and Conservation, Forestry Division.

McGreer, D.J., and Schult, D.T. 1997. Spruce Creek sediment delivery; proposed roads.

Project completion report for Plum Creek Timber Company. Lewiston, ID: Western

Watershed Analysts. 6 p.

McGreer, D.J., and Schult, D.T. 1996. Road sediment assessment for existing roads in the

Spruce Creek watershed, northern Idaho. Project completion report for Plum Creek Timber

Company. Lewiston, ID: Western Watershed Analysts.

McGreer, D.J., Sugden, B., Doughty, K., Metzler, J., and Watson, G. 1997. LeClerc Creek

Watershed Assessment. Lewiston, ID: Western Watershed Analysts. 300 p.

McGreer, D.J., Sugden, B., and Schult, D. 1998. Surface Erosion and Mass Wasting

Assessment and Management Strategies for Plum Creek’s Native Fish Habitat Conservation

Plan. Technical Report #3. Columbia Falls, MT: Plum Creek Timber Company. 50 p.

Megahan, W.F., and Ketcheson, G.L. 1996. Predicting downslope travel of granitic sediments

from forest roads in Idaho. Water Resources Bulletin 32(2): 371-382.

Oregon Department of Forestry (ODF). 2000. Forest road management guidebook:

Maintenance and repairs to protect fish habitat and water quality. Salem, OR: Oregon

Department of Forestry. 32 p.

Oregon Department of Forestry (ODF). Undated. Forest road hazard inventory protocol.

Salem, OR: Oregon Department of Forestry. 8 p. plus appendices.
B13

Oregon Watershed Enhancement Board (OWEB). 1999. Oregon watershed assessment manual.

Salem, OR: Oregon Watershed Enhancement Board.

Plum Creek Timber Company. 2000. Native Fish Habitat Conservation Plan. Seattle, WA:

Plum Creek Timber Company.

Schultz, B. 1992. Montana forestry best management practices implementation monitoring.

1992 forestry BMP audits final report. Missoula, MT: Montana Department of Natural

Resources and Conservation, Forestry Division.

Schultz, B. 1990. Montana forestry best management practices implementation monitoring.

1990 forestry BMP audits final report. Missoula, MT: Montana Department of Natural

Resources and Conservation, Forestry Division.

Skaugset, A., and Allen, M. 1998. Forest road sediment and drainage monitoring project

report for private and state lands in western Oregon. Salem, OR: Oregon Department of

Forestry. 20 p.

Timber/Fish/Wildlife Field Implementation Committee (TFW). 1991. 1991 forest practice

compliance survey. Olympia, WA: Washington Department of Natural Resources. 25 p.

plus appendices.

Washington Forest Practices Board (WFPB). 2000. Forest Practices Act Board Manual.

Olympia, WA: Washington Department of Natural Resources. 212 p.

Zaroban, D.W., Love, B., Colla, J., Lesch, G., Heimer, J., Lehner, J., Lukens, B., Poirier, S., Lee,

B., and David, K. 1997. Forest practices water quality audit 1996. Boise, ID: Idaho

Department of Health and Welfare, Division of Environmental Quality. 32 p. plus

appendices.
C1

APPENDIX C

EXAMPLES OF SPECIFIC MANAGEMENT PRACTICES

C.1 Surface Erosion Control

Substantial research has been conducted that provides techniques for reduction of forest road

erosion (Trimble and Sartz 1957; Packer 1967; Gonsior and Gardner 1971; Burroughs et al.

1976; Berglund 1976; Megahan 1977; Yee and Roelofs 1980; Burroughs and King 1989).

Systematic quantification of the benefits of various control techniques have been built from this

research (Burroughs and King 1989; Cline et al. 1981; Potyondy et al. 1991; Ketcheson and

Megahan 1996; Elliot et al. 1997). Practices are available for effective treatment of erosion

hazards for all major road prism components, e.g., cutslopes, running surfaces, road ditches,

fillslopes, and even the area downslope from roads.

An excellent summary of road erosion control effectiveness is provided by Burroughs and King

(1989), who show that erosion from the entire road prism can be reduced by over 90%. These

techniques with a high degree of erosion reduction have practical application for roads located

where sediment delivery to streams is of particular concern. Burroughs and King (1989) is a

particularly helpful reference to road managers because the percent effectiveness of individual

practices is reported, providing road managers with the means of choosing practices that are

most practicable and cost effective for their particular location and circumstances. Relationships

illustrated by Burroughs and King (1989) include:

With increasing application rates and percent ground cover achieved, treatment of cut and

fillslopes with straw, wood chips, rock, hydromulching, or erosion mats can reduce erosion

by 80 to 100%, depending on the treatment applied. For instance, straw applied to fillslopes

at a rate of 1 ton/acre reduces fillslope erosion by approximately 60%.

Treating road travel surfaces reduces tread erosion by 43 to 77% (see also Burroughs and

King 1985; Foltz and Truebe 1995). Surfacing can be a particularly important treatment,

because tread erosion usually comprises 50% or more of total delivered road prism erosion,

with increasing importance as road traffic increases. Moreover, sediment reduction due to

rock surfacing can vary by several-fold depending on hardness and quality of the rock (also

Foltz and Burroughs 1990).

Erosion from ditches can be eliminated with rock, and Burroughs and King summarize

design principles and criteria.

Development of wheel ruts in roads approximately doubles erosion; surfacing and/or traffic

control prevents ruts (see also Foltz and Burroughs 1990; Foltz, Evans, and Truebe 2000).

C.2 Landslide Avoidance

Landslides have been reported to be the predominant form of erosion from roads in several

studies of steep, hazardous (as evidenced by presence of natural failures) terrain (Megahan and

Kidd 1972; Fiksdal 1974; Morrison 1975; O’Loughlin 1972; Swanson and Dyrness 1975).
C2

Landslides from road fills or sidecast are the most common type of failure, tend to form debris

avalanches or debris flows (often down steep draws and small streams), and are the most

destructive to downstream fish-bearing channels (Benda et al. 1997; Furniss et al. 1991; Gonsior

and Gardner 1971; Morrison 1975; O’Loughlin 1972; Dyrness 1967). Cutslope failures often

block road ditches and divert concentrated water onto fillslopes, contributing to their failure

(Dyrness 1967), and discharge of concentrated road drainage water, usually from ditches through

relief culverts, onto road fills or naturally unstable bedrock hollows also contributes to many

failures (Benda et al. 1987). These mechanisms point to the solutions:

Avoid slopes and locations with a landslide history.

Avoid headwall and bedrock hollow locations.

Avoid inner valley gorges (the oversteepened slopes adjacent to streams).

Avoid large cuts and fills; minimize volume.

Don’t incorporate woody debris in fills.

Carefully size culverts and install trash racks to prevent plugging, particularly where fill

failure could lead to downstream debris flow.

Drain water frequently to avoid concentration on or below fills and to help avoid further

concentration in the event of cutslope failure.

Outslope roads where practical, and consider reshaping insloped roads to outsloped prisms

with surface drains when they become inactive.

Eliminate sidecast on steep slopes (those over 50%).

Excellent and concise guidelines for recognition of hazardous terrain and landslide prevention

are provided by Benda et al. (1997) and Furniss et al. (1991).

C.3 Sediment Delivery Reduction

The most important step in minimizing the impacts of roads on streams, including both surface

and mass erosion (landslides), usually occurs during reconnaissance and route selection. Many,

if not most, landslides can be avoided by identifying hazardous slopes and avoiding them.

Much, if not most, surface erosion can be prevented from reaching streams by constructing roads

in locations where sediment will not reach streams.

For sediment from surface erosion, in addition to practices that reduce eroded volume, practices

that regulate road runoff amount and distribution or that trap runoff prior to it reaching streams

are particularly effective. For example:

Locate the road farther from the stream (Megahan and Ketcheson 1996; Packer 1967; Elliot

et al. 1997).

Reducing the length of road that drains directly to streams via ditches at road crossings can

substantially reduce total road system sediment delivery (ODF 2000; McGreer et al. 1998).
C3

Reducing the length of road segment contributing to a relief drain reduces sediment delivery

to streams, because the distance the water and sediment travel downslope before being

trapped and infiltrated decreases due to decreasing source area for water supplied to the road

segment in question (i.e., the volume of water and sediment discharged is smaller and is

therefore trapped or infiltrated sooner) (Megahan and Ketcheson 1996; Packer 1967; Elliot et

al. 1997).

Increasing obstructions (e.g., rocks, logs, stumps, slash, etc.) on the hillslope below a drain

reduces sediment delivery because of increased opportunity for sediment deposition and

reduced sediment travel distance (Brake et al. 1997; Megahan and Ketcheson 1996).

Filter windrows constructed at the toe of fillslopes reduce sediment leaving the fillslope by

approximately 85% (Burroughs and King 1989).

C.4 Runoff Control

Runoff control practices are designed to minimize changes in the hydrograph caused by the road.

These involve minimization of the area of road that directs runoff to stream channels as surface

flow. The basic approach involves road prism and drainage system design that prevents

concentration of drainage waters and puts water back on forest soils where the runoff infiltrates

the soil and sediment can be deposited on slopes before it reaches streams. Practices that

accomplish this objective include:

Outslope the road system and eliminate road prisms that are insloped to a ditch.

Locate road systems to minimize stream crossings.

Locate relief culverts or surface drains strategically to minimize the length of the ditch that

discharges to streams at crossings. Space them frequently to prevent concentration of

discharged water; the larger the volume discharged, the further downslope it travels towards

streams prior to infiltration (Ketcheson and Megahan 1996).

References

Benda, L., Veldhuisen, C., Miller, D., and Miller, L.R. 1997. Slope instability and forest land

managers, a primer and field guide. Seattle, WA: Earth Systems Institute. 74 p.

Berglund, E.R. 1976. Seeding to control erosion along forest roads. Extension Circular 885.

Corvallis, OR: Oregon State University Extension Service. 19 p.

Brake, D., Molnau, M., and King, J.G. 1997. Sediment transport distances and culvert spacing

on logging roads within the Oregon coast mountain range. Minneapolis, MN: ASAE Annual

International Meeting, August 10-14, 1997. 12 p.

Burroughs, E.R., Chalfant, G.R., and Townsend, M.A. 1976. Slope stability in road

construction. Portland, OR: United States Department of the Interior Bureau of Land

Management. 102 p.
C4

Burroughs, E.R. Jr., and King, J.G. 1989. Reduction of soil erosion on forest roads. General

Technical Report INT-264. Ogden, UT: United States Department of Agriculture Forest

Service, Intermountain Research Station. 21 p.

Burroughs, E.R. Jr., and King, J.G. 1985. Surface erosion control on roads in granitic soils. In:

Proceedings of Symposium Sponsored by Committee on Watershed Management/Irrigation

and Drainage Division, ASCE, April 30-May 1, 1985, Denver, CO. p. 183-190.

Cline, R., Cole, G., Megahan, W., Patten, R., and Potyondy, J. 1981. Guide for predicting

sediment yields from forested watersheds. United States Department of Agriculture Forest

Service, Northern and Intermountain Regions.

Dyrness, C.T. 1967. Mass soil movements in the H. J. Andrews Experimental Forest. Research

Paper PNW-42. United States Department of Agriculture Forest Service, Pacific Northwest

Forest and Range Experiment Station. 12 p.

Elliot, W.J., Graves, S.M., and Hall, D.E. 1997 (draft). Technical documentation to the crossdrain spacing/sediment yield application (X-Drain). Moscow, ID: United States Department

of Agriculture Forest Service, Rocky Mountain Research Station. 10 p.

Fiksdal, A.J. 1974. A landslide survey of the Stequaleho Creek watershed. Supplement to Final

Report FRI-UW-7404. Seattle, WA: University of Washington, Fisheries Research Institute.

7 p.

Foltz, R.B., and Burroughs, E.R. 1990. Sediment production from forest roads in wheel ruts.

In: Proceedings, Watershed Planning and Analysis in Action Symposium, Irrigation and

Drainage Conference, American Society of Civil Engineers. Durango, CO. p. 266-275.

Foltz, R.B., and Truebe, M.A. 1995. Effect of aggregate quality on sediment production from a

forest road. In: Proceedings of the Sixth International Conference on Low-Volume Roads.

June 25-29, 1995, Minneapolis, MN. p. 49-58.

Foltz, R.B., Evans, G.L., and Truebe, M.A. 2000 Relationship of forest toad aggregate test

properties to sediment production. In Proceedings ASCE Conference on Watershed

Management, June 20-24,2000. Fort Collins, CO: Colorado State University.

Furniss, M.J., Roelofs, T.D., and Yee, C.S. 1991. Road construction and maintenance. In:

W.R. Meehan (ed). Influences of Forest and Rangeland Management on Salmonid Fishes

and Their Habitats. American Fisheries Society Special Publication 19. p. 297-323.

Gonsior, M.J., and Gardner, R.B. 1971. Investigation of slope failures in the Idaho Batholith.

Research Paper INT-97. Ogden, UT: United States Department of Agriculture Forest

Service, Intermountain Forest and Range Experiment Station. 34 p.

Ketcheson, G.L., and Megahan, W.F. 1996. Sediment production and downslope sediment

transport from forest roads in granitic watersheds. Research Paper INT-RP-486. Ogden,

UT: United States Department of Agriculture Forest Service, Intermountain Research

Station. 11 p.
C5

McGreer, D.J., Sugden, B., and Schult, D. 1998. Surface Erosion and Mass Wasting

Assessment and Management Strategies for Plum Creek’s Native Fish Habitat Conservation

Plan. Technical Report #3. Columbia Falls, MT: Plum Creek Timber Company. 50 p.

Megahan, W.F. 1977. Reducing erosional impacts of roads. In: Guidelines for Watershed

Management, FAO Conservation Guide. Rome: Food and Agriculture Organization of the

United Nations.

Megahan, W.F., and Ketcheson, G.L. 1996. Predicting downslope travel of granitic sediments

from forest roads in Idaho. Water Resources Bulletin 32(2): 371-382.

Megahan, W.F., and Kidd, W.J. 1972. Effect of logging roads on sediment production rates in

the Idaho Batholith. Research Paper INT-123. Ogden, UT: United States Department of

Agriculture Forest Service, Intermountain Forest and Range Experiment Station. 14 p.

Morrison, P.H. 1975. Ecological and geomorphological consequences of mass movements in

the Alder Creek watershed and implications for forest land management. Bachelor’s thesis.

Eugene, OR: University of Oregon. 102 p.

O’Loughlin, C.L. 1972. The stability of steepland forest soils in the coast mountains, southwest

British Columbia. Doctoral dissertation. Vancouver, BC: University of British Columbia.

147 p.

Oregon Department of Forestry (ODF). 2000. Forest road management guidebook:

Maintenance and repairs to protect fish habitat and water quality. Salem, OR: Oregon

Department of Forestry. 32 p.

Packer, P.E. 1967. Criteria for designing and locating logging roads to control sediment. Forest

Science 13(1): 2-18.

Potyondy, J.P., Cole, G.F., and Megahan, W.F. 1991. A procedure for estimating sediment

yields from forested watersheds. In: S.S. Fan and Y.H. Kiuo (eds). Proceedings of the Fifth

Federal Interagency Sedimentation Conference, March 18-21, 1991, Las Vegas, NV. p. 12-

46 thru 12-54.

Swanson, F.J., and Dyrness, C.T. 1975. Impact of clear-cutting and road construction on soil

erosion by landslides in the western Cascade Range, Oregon. Geology 3(7): 393-396.

Trimble, G.R., and Sartz, R.S. 1957. How far from a stream should a logging road be located?

Journal of Forestry 55: 339-341.

Yee, C.S., and Roelofs, T.D. 1980. Planning forest roads to protect salmonid habitat. General

Technical Report PNW-109. Portland, OR: United States Department of Agriculture Forest

Service, Pacific Northwest Forest and Range Experiment Station. 26 p.