Soilworks products are the industry’s top standard due to our insistence on creating high performance soil stabilization and dust control products that stand up to rigorous testing – both in the lab and in the field. Our commitment to quality and performance has led to our involvement and testing in hundreds of real-world situations. The following library of reports, presentations, specifications, approvals and other similar documents provide you, our customer, the transparency and dependable assurance that is expected from Soilworks.
Over 1.6 million miles of dirt and gravel roads exist within the United States providing a vital part of the nation’s transportation system. Roads crisscross mountains, flat lands, and valleys intercepting streams, meadows, and riparian areas. The ecological effect a road has on the surrounding environment varies greatly depending on location, design, and maintenance. Roads can adversely affect the surrounding environment through erosion, and increased sediment delivery to streams, meadows, and riparian areas. Roads can intercept subsurface flows; increase hillslope drainage density through ditch lines and relief culverts; and create diversion potential at stream crossings. An environmentally sensitive road maintenance practice is a practice that when implemented reduces the adverse effect of a road on the environment by treating the cause of the problem and is in keeping with the natural landscape. The goal of this field guide is to provide examples of environmentally sensitive maintenance practices, which if implemented reduce erosion and sediment, maintain subsurface hydrologic connectivity, restore drainage density to more natural conditions, and eliminate diversion potential. Additionally environmentally sensitive maintenance practices reduce long term maintenance costs and lengthen maintenance cycles. To achieve this goal, the Forest Service, U.S. Department of Agriculture, and Pennsylvania State University’s Center for Dirt and Gravel Roads, have established a simple protocol to help road managers and maintenance practitioners to: carefully assess road conditions; identify problems; determine cause; and select the appropriate environmentally sensitive practices that fit the site conditions.
This field guide is organized to identify visual signs of problems associated with CAUSES and SOLUTIONS for the most commonly encountered road problems. The Keys Section guides the users to specific practices with the guide that is grouped according to the type of problem (road surface, ditch, cutbank, etc). Additional references and links to other useful guides are included in chapter 10.
CHAPTER 1: KEYS TO DIAGNOSING ROAD PROBLEMS
KEYS TO USING THE GUIDE
Don’t address symptoms. Address the problem by identifying the cause of the symptoms. The following keys help identify indicators, determine the cause, and provide potential solutions.
Visual Indicators of Problems: Use this section to identify problems that you see on the road.
Causes: These are common causes of the symptoms listed above.
Potential Solutions: The environmentally sensitive road maintenance practices identified address the causes of the problem.
Figure 1.1—Subsurface water key.
KEYS TO DIAGNOSING ROAD PROBLEMS: SUBSURFACE WATER: SPRINGS, SEEPS, AND WETLANDS
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Subsurface Water: Springs, Seeps and Wetlands
KEYS TO DIAGNOSING ROAD PROBLEMS: ROAD SURFACE DRAINAGE
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Road Surface Drainage
KEYS TO DIAGNOSING ROAD PROBLEMS: ROAD SIDE DITCHES
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Road Side Ditches
KEYS TO DIAGNOSING ROAD PROBLEMS: DITCH OUTLETS
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Ditch Outlets
KEYS TO DIAGNOSING ROAD PROBLEMS: ROAD-STREAM CROSSINGS
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Road-Stream Crossings
KEYS TO DIAGNOSING ROAD PROBLEMS: CUTSLOPES/FILLSLOPES
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Cutslopes/Fillslopes
KEYS TO DIAGNOSING ROAD PROBLEMS: SURFACE AGGREGATE
Visual Indicators of Problems
Photos: Visual Indicators of Road Surface Problems – Surface Aggregate
CHAPTER 2: SUBSURFACE WATER
Figure 2.1—Permeable fill provides for subsurface flows.
Roads often must cross wet areas and can intercept subsurface flows. The degree to which a road intercepts subsurface flow and subsequently redirects it varies from location to location. Wetlands, springs, and seeps can become problem areas if not addressed properly. Left untreated, perpetually wet conditions can expedite road degradation, which requires more frequent maintenance and often times creates hazardous driving conditions.
Most subsurface water is clean, meaning free of sediment (unlike overland flow). Redirecting subsurface water away from the traveled way will dry the road surface and reduce erosion and maintenance costs.
It is important to identify the SOURCE of any water on the road. The environmentally sensitive maintenance practices discussed in this chapter apply to subsurface water only.
Figure 2.2—Road intercepts subsurface flows and redirects it down the road as surface runoff.
Figure 2.3—Road crosses meadow without adverse impacts to subsurface flows.
An underdrain is a drainage system installed under a road or road ditch to collect and transport subsurface water. These buried conduits come in a variety of shapes and sizes and are usually wrapped in geotextile fabric, which allows water to enter the conduit while keeping sediment out.
Criteria for Underdrain Use
Important Underdrain Considerations
Figure 2.4—Road ditch with standing water.
Benefits of Underdrains
Types of Underdrains
There are two types of underdrain, prefabricated and constructed. A prefabricated underdrain can be purchased in a variety of shapes and sizes. While it is usually less expensive and easier to install, it will not collect as much water as a constructed underdrain or French drain. French drains, like those used around home foundations, provide greater surface area for water collection.
Figure 2.5—This drain collects water from springs and seeps under the road ditch.
Figure 2.6—Perforated plastic pipe.
Figure 2.7—Free draining stone.
French Drain Construction Sequence
The underdrain shown here collects water from several spring seeps along the cutslope bank and conveys it to the woods in the background.
Figures 2.8a through 2.8d—French drain construction sequence.
Materials required for French drains
Equipment required for French drains
Figure 2.9—Prefabricated wrapped underdrain is inexpensive and easy to use in rocky and sandy soils.
Figure 2.10—This homemade guard will prevent animals from entering the underdrain outlet.
A structure under a road consisting of clean coarse rock wrapped in geotextile fabric through which water can pass freely.
French mattresses are used in extremely wet areas, such as wetlands, to support the roadbed while allowing unrestricted water movement.
Figure 2.11—Side view of a large French mattress.
Figure 2.12—Graphical side view of the mattress components.
Criteria for French Mattress Use
Benefits of French Mattresses
Figure 2.13—This small mattress was built to accommodate several springs and seeps that saturate the road each spring.
Figure 2.14—This is the same mattress outlet after completion. Notice the water flowing out of the mattress below the road.
Important Mattress Considerations
Figure 2.15a—Small mattresses installed to drain several springs and seep.
Figure 2.15b—Large mattress allows wetland flow.
French Mattress Construction Sequence
This is a large mattress using large stone to accommodate a wide wetland.
Figures 2.16a through 2.16d—French mattress construction sequence.
Materials Required for a French Mattress
Equipment Required for a French Mattress
Figures 2.17 and 2.18 (Before and After)—This roadway cuts across a flood plain wetland. A 300-foot-long French mattress was used to provide relief for wetland flows while providing a stable road base and preventing beavers from damming the nearby stream pipe.
Install a permeable fill as part of the road to promote the passage of subsurface and surface flows with minimum flow concentration and maximum spreading across meadows and wetlands. The road fill is permeable because of its construction with relatively large, preferably angular, uniformly graded rock sandwiched between layers of geotextile fabric that preserves voids in the structure and promotes the uninterrupted ground water flow. The permeable fill is similar to the
French mattress, but differs in its ability to spread surface flows with culvert placement.
Criteria for Permeable Fill Use
Figure 2.19—Permeable fill with culverts spreads surface flows.
Important Permeable Fill Considerations
Benefits of Permeable Fills
Kinds of Permeable Fills
Permeable fills can be used alone or in combination with culvert arrays. Place multiple culverts in an array to enable spreading of flood flows and imitate the natural flooding event in the meadow. Culverts may require outlet energy dissipators. In meadows without any surface flow or a small contributing area above the structure can often function well without additional culverts.
Permeable Fill with Culverts
Permeable Fill without Culverts
Figure 2.20—Permeable fill with culverts.
Figure 2.21—Permeable fill without culverts.
Permeable Fill Construction Sequence
Figures 2.22a through 2.22d—Permeable fill construction sequence.
Materials Required for Permeable Fills
Figure 2.23—Geotextile fabric provides support for permeable fill.
Equipment Required for Permeable Fills
Figure 2.24—Track-laying excavator operates in a sensitive meadow environment with little adverse impact.
Figure 2.25—Roller compacts each of lift aggregate.
CHAPTER 3: ROAD SURFACE DRAINAGE
Figure 3.1—The road cross-section should be designed to shed water from the road surface.
Surface drainage provides for the interception, collection, and removal of water from the surface of roads (traveled way).
One can minimize erosion from road surfaces with proper road building and maintenance practices. The road surface should be shaped to shed water and keep it from accumulating. Standing water and flowing water will weaken the subgrade and result in rutted, potholed, and washboarded roads that generate more sediment and require more frequent maintenance.
The road’s template (cross section) whether crown, insloped, or outsloped, is the first line of defense against erosion. The road-surface shape may vary with changes in topography, hillslope position, road gradient, and surface and subsurface drainage features. The road-surface shape criteria includes environmental and resource considerations, safety, traffic requirements, and traffic-service levels.
There are several environmentally sensitive road maintenance practices that ensure the road surface quickly sheds the water and avoids concentrating drainage, which reduces erosion, restores hillslope hydrology, and lowers long-term maintenance costs.
Figure 3.2—Road surface templates (Insloped vs. Outsloped vs. Crown)
ROAD SURFACE SHAPE
Importance of Road-Surface Shape
The road-surface shape (template) dictates the necessity for certain road drainage design elements and structures including ditches, cross-drain culverts, rolling dips, grade breaks, as well as the road’s ability to intercept, collect, and remove water from the road surface. It is important to identify the road-surface shape and assess that design elements are in place and functioning as designed. If any of the visual indicators identified earlier are apparent, the road surface may need maintenance or an environmentally sensitive practice, such as modifying the road-surface shape or the installation of surface-drainage structures.
Crown, insloped, and outsloped road shapes are slowly lost over time due to traffic, erosion, and maintenance activities.
Prior to maintaining a road, drive the segment and identify the road-surface shape. For example an insloped road generally has cross-drain relief culverts and an inside ditch. An outsloped road has no ditches or cross-drain culverts, and a crowned road often has ditches on the sides and cross-drain relief culverts. The effectiveness of a crown, inslope, or outslope in shedding water should be one of the major factors in determining when to grade a road.
Proper Road-Surface Shape
Crowned Road Considerations
Figure 3.3—Crowned road.
Outsloped Road Considerations
Figure 3.4a—Outsloped road disperses flow.
Figure 3.4b—Outsloped roads eliminates ditches.
Insloped Road Considerations
Figure 3.5—Insloped road.
How Much Crown or Cross Slope?
Unpaved roads require more sideslope than asphalt roads because the road surface is permeable and the roughness slows runoff. Steeper roads require a more pronounced crown to ensure that water flows off to the side instead of down the road surface. As a general rule, there should be at least 1/2 inch to 3/4 inch of fall per foot across the road (4 to 6 percent).
Figure 3.6—A road’s sideslope can be measured using a level and tape measure. The road should drop 2 to 3 inches over the 4-foot length of the level used in the picture above.
A grade break is an intentional increase in road elevation or change in road grade to create an undulating road profile (rolling grade). It is designed to shorten the contributing area and force water off the road surface into stabilized ditches or outlets on either side of the road. Grade breaks shed water toward the shoulders and are not meant to carry concentrated flow across the traveled way.
Benefits of Grade Break
Criteria for Grade Break Use
Materials Required For a Grade Break
Equipment Required For a Grade Break
Grade Break Considerations
Figure 3.7—The two grade breaks pictured here prevent water from flowing down the road, even if the road’s crown were to be lost.
Figure 3.8—A grade break, such as the one pictured in the distance, should be big enough to
shed water, but gentle enough to allow traffic passage.
BROAD-BASED DIP (ROLLING DIP)
Dips are designed and constructed to divert water off the road surface, disperse surface water flows, and reduce erosion.
The road profile (vertical alignment) is changed by simultaneously constructing a dip and raising the grade by placing fill material in the road below the dip. The slightly skewed dip turns surface flows and disperses runoff away from the road surface. Broad-based dips have an intended flow channel are meant to carry water across the road surface on low-traffic roadways.
Benefits of Broad-Based Dips
Criteria for Broad-Based-Dip Use
Figure 3.9—Diagram of dip.
Broad-Based Dip Versus Grade Break
Materials Required for a Broad-Based Dip
Equipment Required for a Broad-Based Dip
Figure 3.10—The broad-based dip pictured here conveys water from the road surface and upslope ditch into a vegetative filter area on the right.
Broad-Based Dip Considerations
Figure 3.11—Broad-based dip breaks up contributing area and reduces maintenance frequency.
A belt diversion is a structure used on low-volume roads to divert water off the road surface. The diversion consists of a piece of used conveyor belt bolted to treated lumber and buried in the road.
Benefits of Belt Diversions
Criteria for Belt-Diversion Use
Figure 3.12—Low-volume access roads, such as the one pictured here, are ideal candidates for diversions.
Figure 3.13—Conveyor-belt diversion on a farm lane (road).
Figure 3.14—On most roads a completed diversion should leave no more than 4 inches of belt exposed.
Figure 3.15—A completed diversion directs surface drainage off the roadway and into a field.
Materials Required for Belt Diversions
Equipment Required for Belt Diversions
Figure 3.16—Schematic view of conveyor belt diversion. This schematic assumes the diversion is long enough that two separate pieces of lumber need to be joined end to end to span the road. On narrow roads, the diversion may be constructed using a single piece of 2-by 6-inch material.
Figure 3.17—Construction of a 24-foot-length diversion. Note that the belt has been cut in half lengthwise. A 4-foot board on top of the belt spans the lumber joint of two 12-foot boards.
Belt Diversion Construction Sequence
Figures 3.18a through 3.18d—Belt diversion construction sequence.
CHAPTER 4: ROADSIDE DITCHES
Figure 4.1—Eroded ditch caused by excessive volume and velocity of water.
Ditches collect and carry road-surface water, water from springs or seeps, and water from run-on sources to designated discharge locations. Criteria for using a roadside ditch include (1) water expressed in the cutbank needs to be prevented from reaching the traveled way; (2) safety concerns dictate an insloped road with a berm on roads traversing steep sideslopes; and (3) high-standard roads require a road template shape that is super-elevated to accommodate higher speeds. All other roads should be outsloped or crown to reduce the road-drainage density, to restore natural surface drainage patterns, and to reduce maintenance costs.
Roads that do require a ditch often have downcut and degraded ditch lines. Too often, traditional practices designed to fix ditches address only the symptom (erosion) rather than the problem (water volume and steep road gradient), which causes increased water power. Many low-volume roads are modeled after urban storm sewers, collecting water and transporting it to the nearest stream, which can adversely affect water quality and aquatic habitat. A change in philosophy, away from collecting water, and towards dispersing water, is what is desired to reduce environmental impacts and simplify road maintenance.
This chapter focuses on managing ditches to reduce the volume of water in the road drainage system and to allow it to infiltrate naturally. Environmentally sensitive road maintenance practices that eliminate ditches or maximize the number of ditch outlets are effective techniques to disperse road drainage and reduce long-term maintenance costs.
READING THE DITCH
The practice of reading the ditch is an art that requires looking at historical evidence and paying special attention to the cause of ditch problems. To properly read the ditch requires training your eyes to detect subtle changes in the landscape and road. Reading the ditch involves determining when and where to use an environmentally sensitive maintenance practice, such as raising the road profile or installing rolling dips. Road drainage can be designed and/or modified to allow for more infiltration and dispersion of flows by observing how the road lies across the landscape and intercepts natural drainages. Instead of relying on standard tables or guides, reading the ditch requires observation to determine when and where to use environmentally sensitive maintenance practices based on your knowledge, experience, and site-specific conditions.
Benefits of Reading the Road Ditch
Criteria for reading the road ditch
Factors Affecting Ditch Stability
Figure 4.2—This photograph is taken only 300 feet from the top of the hill, yet the road ditch is over 5 feet deep.
Further investigation of the site revealed a large amount of water emptying out of a meadow and into the road ditch.
This water should be either diverted before it reaches the road or handled as quickly as possible and not allowed to flow down the road ditch.
Figure 4.3—Length of ditch and contributing area must be evaluated.
How Do You Read The Ditch?
Figure 4.4—This eroded ditch is a symptom. The problem is excessive water volume for this road gradient and soil, and must be managed upslope.
Figure 4.5—Near the top of a hill, this ditch is starting to erode. The team looks for drainage options.
Figure 4.6—Eroded ditches are a common problem.
RAISING THE ROAD PROFILE
The process of raising the road profile starts with filling the road cross section to an elevation that more closely resembles the natural topography, allowing for sheet flow from the downslope side of the road, and additional culverts to drain the upslope side of the road.
Understanding the Entrenched Road Problem
Many low-volume roads have become entrenched, or lower than the surrounding terrain on either side, over time due to traffic, maintenance, and erosion. Entrenched roads collect drainage from the surrounding area and trap it in the road corridor. This can lead to a host of drainage problems on the road. Raising the road profile is an environmentally sensitive practice that addresses the problem (the road is lower than the surrounding topography and concentrates runoff) instead of the symptoms (eroded ditches, cutbanks, and road surfaces).
Problems Stemming from Entrenched Roads
Because entrenched roads collect and trap water, many problems can result including:
Figure 4.7—Example of an entrenched roadway.
Figure 4.8—Over time, the elevation of many roads, especially unpaved roads, is lowered due to traffic, maintenance, and erosion. When roads become lower than the surrounding terrain, they are referred to as entrenched, and water often is trapped in the road traveled way.
How Does Raising the Road Profile Work?
Raising the road profile uses imported fill material to build up the entrenched road. Ideally, the final road elevation will be high enough to restore natural drainage patterns by eliminating the downslope ditch and providing cover for crossdrain pipes to effectively drain the uphill ditch. Raising the road profile is sometimes the only long-term solution to many entrenched road problems.
Raising the Road Profile Considerations
Figures 4.9 and 4.10 (Before and After)—This entrenched roadway was a constant source of maintenance and pollution. The road was filled over 6 feet in places to eliminate the ditch on the left and provide elevation and cover for cross pipe to drain the ditch on the right.
Benefits of Raising the Road Profile
Criteria for Raising the Road Profile
Figures 4.11 and 4.12 (Before and After)—This entrenched roadway trapped runoff in the ditches and emptied into a small headwater stream. The road was elevated up to 5 feet in places in order to eliminate the ditch on the left and provide elevation and cover for several cross pipes.
Materials Required for Raising the Road Profile
Equipment Required For Raising the Road Profile
Figures 4.13a through 4.13d—Raising the road profile construction sequence.
Raising the Road Profile Construction Sequence
The process of removing an unnecessary berm, windrow, or false shoulder on the downslope side of the road provides dispersed sheet flow off the road surface.
What Is a Road Berm?
A berm is a mound of soil material, parallel to the roadway on the downslope side that has been placed or accumulated over time due to road traffic or maintenance activities (grader can windrow material). Road berms may be several inches or several feet high, but once a berm forms, it traps runoff on the road surface causing accelerated erosion of the road surface.
Removing the Berm
Berm removal is a straightforward process. Many berms can be eliminated using small earthmoving equipment. A truck may be needed to take excess berm material to a suitable location. Depending on the size and composition of the berm, the material generated from removal may even be used to as road fill or surface material.
Figure 4.14—Berms can range from several feet high to only a few inches high as pictured here. The small partially vegetated berm on the left is preventing runoff from exiting the road surface. A stable vegetated buffer exists to the left, but the berm is causing an unnecessary ditch to form at the road edge.
Benefits of Berm Removal
Criteria for Berm Removal
Materials and Equipment Required for Berm Removal
Berm Removal Considerations
Figure 4.15—The berm was created by recent grading. Removing the berm and crowning the road allows sheet flow into the vegetation to the left.
There are several strategies and guidelines outlined below for reducing maintenance needs and erosion problems associated with roadside ditches.
Characteristics of Low-Maintenance Ditches
STRATEGIES FOR LOW-MAINTENANCE DITCHES
Using the Side of the Bucket to Determine Ditch Shape
As viewed from the side, the back and bottom of a typical backhoe bucket is an ideal shape for a wide, shallow ditch line. The bucket can be dragged along small sections of ditch to achieve the proper shape. The required size of the ditch is dependent upon the volume of water it must manage. More frequent ditch outlets reduces the need for large ditches.
Cleaning ditches while grading, or pulling ditches, often leads to deep ditches that are ”V” shaped and unstable. Consider alternative methods or equipment to clean the ditch other than a grader, such as the one pictured here. Also consider using a separate piece of equipment to clean the ditches after grading.
Figure 4.16—This bucket is a good parabolic shape for ditch construction.
Leaf Blowers and Vacuums
In locations with deciduous vegetation, graders are often used to remove fallen leaves from the ditch in order to prevent plugging of cross-drain culverts. However, it is difficult to remove leaves with a grader without disturbing the soil in the ditchline. Pull-behind or threepoint- hitch leaf blowers are inexpensive and multiuse tools that remove dead vegetation without disturbing the soil. Leaf blowers can be attached to a small tractor and are easy to operate. If ditch cleaning, not reshaping, is the issue, then a leaf blower can accomplish the task faster, cheaper, and with less soil disturbance than a grader. Leaf vacuums have the added advantage of not blowing leaves up onto the uphill bank that could return to the road ditch.
Figure 4.17—A leaf blower clears dead vegetation without disturbing the soil.
When the entire length of a ditch is cleaned or reshaped at once, it creates an easy source and pathway for sediment to get into waterways. An alternative is to clean or reshape ditches in sections, skipping every other section each year. The unmaintained section will have residual vegetation and a rougher shape. These unmaintained sections can function as a filter area, slowing the water flowing in the ditch before it enters the cleaned, less stable section of ditch. This strategy can be employed in locations where ditch discharge to the stream cannot be avoided.
Figure 4.18—Homemade ditch cleaner for a grader.
DISCONNECTING DITCHES AND STREAMS
Ditch lines that drain directly to the stream are hydrologically connected to the stream and become efficient conduits of sediment to the stream channel. Environmentally sensitive maintenance practices identify opportunities to reduce sediment delivery and restore more natural hydrologic conditions by decreasing ditch connectivity and encouraging infiltration.
Criteria for Disconnecting Ditches and Streams
How to Disconnect Ditches from Streams
Benefits of Disconnecting Ditches and Streams
Figure 4.19—Unstable ditch. This ditch presents a safety, maintenance, and environmental concern. It is too deep, too wide, unvegetated, and can route sediment to the stream.
Reprofiling Ditches at Stream Crossings
In broader valleys or relatively flat landscapes, it is often possible to make road ditches flow away from the stream crossing. To accomplish this, fill material is added to the area around the crossing to raise the grade. The ditch is regraded to force water to flow away from the stream crossing into stable vegetated outlets.
Figure 4.20—Traditional urban stormwater approaches collect and convey ditches directly to streams, as pictured above. Modern rural stormwater management should disconnect the road and stream by avoiding concentrated discharges to streams and encourage drainage dispersal.
Figure 4.21—Aerial depiction of road-stream crossing. The left side of the diagram shows the traditional practice of discharging water to the stream. The right side of the diagram shows material added to redirect ditch flow and outlet water away from the stream.
Figure 4.22a—Before: A typical crossing with ditches armored with rock and draining directly into the stream.
Figure 4.22b—After: Material has been added and the ditch has been reprofiled to drain away from the stream through a new cross pipe and into the woods.
CHAPTER 5: DITCH OUTLETS
Figure 5.1—Culvert placed below the natural elevation requires frequent maintenance and long ditch outlets.
Roads with cross-drain culverts or lead-out ditches can show signs of accelerated erosion at the outlet. Accelerated erosion at the outlet is a symptom of excess volume or velocity of water being discharged as well as the soil type that the concentrated flow is placed on. The location and condition of the ditch outlets can be an indicator of how much erosion and sediment reaches nearby streams. Whenever possible, ditch and culvert outlets should be strategically located to disperse road runoff and sediment into well-vegetated buffer areas away from streams. Unfortunately many roads are located in areas immediately adjacent to streams and lack adequate buffers, or exist on steep hillslopes where concentrated discharge scours the fillslope causing accelerated erosion. Environmentally sensitive road maintenance practices are designed to first identify the cause of the problem and then implement practices to reduce the adverse effects of ditch and culvert outlet drainage as it leaves the road. The overall intent is a well-designed, low-maintenance road that has minimal impact to soil, water, and aquatic resources.
Figure 5.2—Shotgun culverts causes accelerated erosion.
Figure 5.3—Culvert outlet is well armoured.
SHALLOW CROSS PIPES (DITCH-RELIEF CULVERTS)
A ditch-relief culvert installed at the natural ground elevation, avoids the need for an excavated outlet trench or tail ditch.
Deep: Traditional deep culvert where pipe cover is obtained by digging a trench and backfilling with compacted fill to the original road-grade elevation.
Shallow: The shallow culvert is placed at the natural ground elevation and fill is imported to provide pipe cover above the original road-grade elevation.
Figure 5.4—Side-view schematic, looking through cross pipe from the outlet, compares the deep and shallow pipe placements on the road. The deep pipes are bedded below the natural ground elevation line and require outlet trenches to function. The shallow pipe placement is at natural ground elevation and uses imported fill to achieve pipe cover.
Problems Associated with Traditional Deep Pipes
When a pipe outlet is placed below ground surface, it often creates the need for continual maintenance of a tail ditch to keep water flowing away from the road.
Problems with tail ditches include:
Figure 5.5—Traditional deep pipe. It has a long outlet trench requiring continual maintenance.
Shallow Cross Pipes
A shallow cross-pipe installation uses the natural ground elevation at the pipe outlet to determine the cross-pipe elevation. Any additional pipe cover is obtained by importing fill over the pipe, rather than by digging deeper into the road base.
Figure 5.6—Shallow pipe. Placing the outlet at the natural ground elevation reduces maintenance and helps disperse flows.
In contrast, typical deep cross pipes use the existing road elevation to determine pipe installation depth.
Benefits of Shallow Cross Pipes
Criteria for use of shallow cross pipes
Figure 5.7—A shallow cross pipe being installed: The cross pipe shown is partially installed. Notice that the pipe outlet is at the elevation of the existing ground, no outlet trench or tail ditch is required. The top of the pipe is ABOVE the existing road surface. The required pipe cover is obtained by importing fill. When completed, the fill will create a grade break over the pipe.
Procedure for Installing a Shallow Cross Pipe
Figure 5.8—The same pipe is shown here covered with fill, before final compaction. Arrow denotes headwall or pipe inlet.
A pipe placed in the downslope ditch to carry drainage through the downslope bank and away from the road.
Figure 5.9—The through-the-bank pipe provides an outlet for road drainage that is trapped in the road corridor by road banks. The pipe inlet is located in the road ditch, and the outlet is at the natural ground elevation where the water can drain away from the road.
Benefits of Through-the-Bank Pipes
Criteria for Using Through-the-Bank Pipes
Materials Required for a Though-the-Bank Pipe
Equipment Required for a Through-the-Bank Pipe
Through-the-Bank Pipe Installation
Figure 5.10—The inlet of a through-the-bank pipe shown during installation before the pipe is covered.
HEADWALLS AND ENDWALLS
A wall built around a pipe opening to support the road and protect the road from erosion caused by excessive velocities and turbulence. A wall at a pipe inlet is a headwall and the wall at a pipe outlet is an endwall. Headwalls vary depending on the physical conditions at each installation site and may include wingwalls, debris fins, and aprons.
Figure 5.11—Headwalls come in various shapes, sizes, and materials, based on the situation and material available.
Benefits of Headwalls and Endwalls
Criteria for Headwall Endwall Use
Headwall and Endwall Considerations
Figure 5.12—Plan views of a stone headwall. Note that the base width should be equal to the height, the face should be sloped or canted back, seams should be overlapped like bricks, and stone should be placed under the pipe.
Figure 5.13—A properly constructed natural stone headwall can last for decades.
Figure 5.14—Headwall with wingwalls.
CHAPTER 6: ROAD-STREAM CROSSINGS
Figure 6.1—Consequence of poor road location results in loss of road and increases sediment delivery.
The road-stream crossing is a critical area to assess for opportunities to reduce erosion and sediment delivery. Roads often are hydrologically connected to streams and contribute sediment from the ditch and the road surface. This direct roadstream connection causes deteriorated water quality and adverse impacts to aquatic species, animals, and humans. Chapter 6 provides environmentally sensitive practices for reducing sediment and maintenance costs associated with stream crossings of all forms including bridges, pipes, and low-water crossings. The type of crossing at a given location depends on many factors, such as stream type, road use, and available funding.
This chapter does not cover the sizing and installation procedures for bridges or pipes. Many sources exist to provide more in-depth guidance on designing, selecting, and installing bridges and major culverts. This chapter addresses alternative maintenance practices, especially designed for use on low-volume roads, which can reduce sediment and erosion at stream crossings and lower maintenance frequency.
Figure 6.3—This direct road-stream connection causes deteriorated water quality and adverse impacts to aquatic species, animals, and humans.
An intentionally designed flat, low-lying section of reinforced road that serves as an emergency spillway to allow water to flow over the road with minimal damage during high, but anticipated, flow events.
Figure 6.3—The road illustrated here will allow water from extreme events to flow over the reinforced bypass.
Benefits of High-Water Bypass
Criteria for Use
Figures 6.4a through 6.4d—Construction sequence for high-water-bypass.
IMPROVED FORDS AND LOW-WATER CROSSINGS
A stream crossing at or near streambed elevation can be shaped and surfaced with many types of materials (rock, concrete, etc.). A small channel or slot may be included in the structure’s low point to pass very low flows and aquatic animals. The downstream roadway edge may be stabilized and buttressed with boulders, gabions, or concrete jersey barriers (K-rails).
Criteria for Low-Water-Crossing Use
Important Low-Water-Crossing Considerations
Figure 6.5—Concrete ford crossing.
Figure 6.6— Low-water crossing.
Benefits of Low-Water Crossings
Low-water crossings fall into two general categories: (1) simple, unimproved or improved unvented fords with a natural or hardened bottom, and (2) vented fords with culverts or vents to bypass very low flows. Ideally these two types match the natural channel shape. Occasionally low-water bridges are used for broad streams or rivers with extreme flow fluctuations.
Figure 6.7—Vented ford or low-water bridge.
Figure 6.8—Gabion ford crossing.
Simple Boulder Fords or Concrete Jersey Barriers
Construction Sequence for a Boulder Ford
Figure 6.9—Boulder ford on Stanislaus National Forest in California has had no maintenance since construction in 1997.
Construction Sequence for a Jersey-Barrier Ford
Figure 6.10—Jersey barrier in Arizona provides safe, low maintenance access to forest roads.
IMPROVED STREAM CROSSINGS
This section identifies practices to improve existing stream crossings in order to reduce erosion and sediment delivery to the stream. Often erosion and sediment delivery to streams is due to undersized culverts. Culvert sizing is part of road design and generally requires several disciplines and resource objectives prior to designing a stream crossing. This guide focuses on road maintenance practices that can be implemented easily by road crews. Therefore, only brief summaries are presented here with links for additional resources.
Better Pipe Alignment
Pipes are often placed perpendicular to the road in order to save on pipe lengths. However, this can cause streambank erosion if the stream is forced to turn at hard angles as it enters and exits the pipe. When this is the case, a better strategy is to use a longer section of pipe to create a better alignment of the crossing with the natural stream channel.
Figure 6.11—Better pipe alignment.
Arch pipes are bolted to concrete footers that run along each side of the stream channel.
They can be purchased already assembled, or in plates that can be assembled onsite.
Benefits of Bottomless-Arch Pipes
Figure 6.12—A bottomless arch pipe has just been installed over a currently dry stream channel.
Paving Bridge Approaches
Road aggregate should never be graded onto, or allowed to sit on, bridge decks. In addition to falling easily into the stream, the aggregate holds water, impedes drainage, and reduces the bridge load limit. Another solution is to pave the bridge approaches to reduce sediment delivery to the bridge and stream. Carefully review the sediment contributing area and extend the pavement to the break in slope.
Figure 6.13—Paved bridge approach reduces sediment delivery to the stream.
Sometimes the best solution for the road and the stream is to relocate the road out of the stream corridor. The forest road shown here was relocated because it frequently flooded and eroded the road. The new road was located away from the stream. Road relocation can restore the natural hillslope hydrology and allow for recovery of native and riparian vegetation.
Figure 6.14—This road is constantly being eroded and flooded. Relocating the road away from the stream, while initially costly, will pay for itself in a few years of reduced flooding and repair costs.
CHAPTER 7: CUTSLOPES/FILLSLOPES
Figure 7.1— Figure 7.1—Unvegetated cutslopes are a source of sediment.
This chapter addresses stability problems associated with road cutslopes (backslope) and fillslopes. Unstable road
cutslopes can disrupt road drainage, adversely impact water quality, create safety hazards, and increase maintenance frequency and cost. Addressing unstable cutslopes involves correctly identifying the source of the problem. Common cutslope problems originate from several sources; undermining of the cutslope, intercepting subsurface flows, and run-on from offsite sources.
NATURALIZE BANK SHAPES
Naturalize Bank Shape. A simple practice designed to mimic the natural landscape and create a stable roughened cutslope or fillslope.
Why Naturalize The Bank Shape?
Traditionally, equipment operators try to create roadbanks that are smooth and uniform. The banks are often composed of subsoil or rock, which is seeded with grass. In the natural world, slopes are rarely uniform. By incorporating features to roughen the slope, erosion is reduced and an environment rich in diversity of plant species is created.
Criteria for Use
When building or maintaining road cutslopes and fillslopes, allow for surface roughness by leaving grade imperfections and debris in place. These imperfections reduce erosion, create tortuous flow paths, increase infiltration, and provide small niches for different types of plants to grow. Heavy equipment grousers (cleats) run perpendicular to the slope to provide additional surface roughness. Their tracks help to trap water and provide seed niches for a variety of vegetation.
Use a variety of plants, shrubs, and trees that are native to the area and require little maintenance. Identify plants that have deep roots that will stabilize the slopes. Avoid shallow rooted grasses and weak colonizer tree species.
Hardy trees can permanently stabilize roadbanks and are especially beneficial on steep slopes.
Figure 7.2—Trying to grow grass on a smooth bank made of subsoil and rock is not a good strategy.
Figure 7.3—Tree roots are Mother Nature’s rebar.
Downed wood and stumps are often removed from the site and burned or chipped. A better use is to place woody debris perpendicular to the slope of the bank to disrupt flow paths and foster diverse bank habitat. Naturalize slopes by embedding stumps and snags into cutslopes (figures 7.4 and 7.5). Stumps bring their own seed base that adds to the diversity of vegetation on the bank.
Figure 7.4—All of the woody debris and stumps in this picture were placed there to naturalize the bank shape.
Figure 7.5—The same bank as pictured in figure 7.4, 4 years later.
The soil in cutslopes often is unfertile subsoil that cannot support vegetation. During new road construction, stockpile topsoil and reapply it over the newly constructed cutslope. In areas where cutslopes are reshaped to establish a more stable angle, import topsoil and spread on sites without topsoil to help reestablish vegetation.
Use compost berms or socks (a mesh tube stuffed with compost) to control run-on from upland areas. A compost berm reduces erosion, retains soil moisture, and increases site fertility. Compost berms are trenchless and stake free. Place compost berms on the hillslope contour at varying intervals depending on the hillslope gradient.
RETAINING WALLS AND ROCK BUTTRESS
Retaining walls are used for unstable cutslopes and come in many sizes and shapes. Retaining walls are designed to prevent sloughing material (soil and rocks) from entering the traveled way and disrupting the road drainage design.
Criteria for Use
Benefits of Retaining Walls and Rock Buttress
Figure 7.6—Crib wall stabilizes this steep cutslope ensuring appropriate road width and drainage function.
Figure 7.7—Retaining walls come in an assortment of materials and can often be constructed from large boulders onsite.
BENCHES AND INTERCEPTOR SWALES
A bench is a step or terrace built into the cutslope to slow and divert runoff before reaching the road.
An interceptor swale is a drainage channel built parallel above a roadway and above the cutslope to intercept overland flow and direct it to a stable outlet.
Figure 7.8—A bank bench has a flatter profile than an interceptor swale, similar to an insloped terrace.
Figure 7.9—An interceptor swale is designed to carry more water than a bank bench.
While benches and interceptor swales are similar in form and function, there are subtle differences. Benches are slightly
insloped steps designed to slow water down and carry minimal flow. They are especially useful on steeper slopes and often can be built within existing road right-of-ways. Interceptor swales usually are used above banks with larger flow volumes, and require landowner approval if located outside the road right-of-way. These structures should outlet water into a stable filter area.
Bank Benches Criteria for Use
Interceptor Swale Criteria for Use
Benefits of Benches and Interceptor Swales
Bank Bench Considerations
Interceptor Swale Considerations
Figure 7.10—The slightly insloped bench in this image takes water around the hill and away from the road.
Figure 7.11—The interceptor swale pictured here catches the runoff from a large field before it enters the road.
OFF RIGHT-OF-WAY (ROW) ISSUES
There are several strategies for addressing impacts to the road from off right-of-way or offsite sources. Practices can be used to lower traffic impacts as well as reduce the volume of water managed in the road drainage system at locations where driveways, lanes, trails, etc, intersect the roadway.
Off-ROW refers to anywhere roadside accesses either intersect or send water to the road. Farm lanes, driveways, utility
ROWs, trails, developments are all potential off-ROW impacts to public roads. These access points act as tributaries to the public road drainage system, reaching out into the landscape and funneling water to the road area. The key to handling this water is to address it on the access road, BEFORE it ever reaches the public road.
Benefits of Addressing Off-ROW Issues:
Figure 7.12—Unchecked off-ROW accesses, such as this logging road, lead to increased runoff, erosion, and maintenance cost to the receiving road.
Ordinances or Permits
Ordinances and permits can effectively control the way a new driveway or access road handles water, giving the road manager a tool to directly oversee the installation of the new interface. Simply creating an access permit that allows encroachment is not enough. The permit or ordinance must address the way access roads bring water to the public road, and the effectiveness of vehicle transitions at the intersections. This process will allow involvement in the planning and layout phase before the road is cut, instead of retrofitting solutions.
Access Interface and Drainage
Many practices in this guide can be applied effectively to new off-ROW interfaces; broad-based dips, grade brakes, and conveyor-belt diversions work well in redirecting surface flow from a driveway or lane. A change in the elevation of the access road can prevent surface water from flowing on to the public road. Smooth surface transitions at the access road interface will reduce traffic impacts on the road. The increase in elevation also will improve driver visibility.
Mixed Road Ownership Road Drainage Solutions
Run-on from a permanent or temporary road access can be disconnected using different practices.
Figure 7.13—This conveyor-belt diversion on a farm access lane prevents drainage from flowing on to the public road at the bottom of the hill.
Figure 7.14—The broad-based-dip on this driveway provides a good transition and keeps water off the public road.
CHAPTER 8: SURFACE AGGREGATE
Figure 8.1—Proper gradation of aggregate can prevent the raveling and pumping in this picture.
Surface aggregate is often the most visible and expensive component of unpaved road maintenance. Aggregates used for gravel road surfacing vary a great deal around the nation based on climate and available material.
Poor quality aggregates, or poor gradation of aggregates, will lead to excessive road surface erosion and degradation. This will lead to increased sediment runoff, increased maintenance costs, and poor traffic support.
The ideal surface aggregate should be designed with a range of particle sizes in order to achieve the highest possible dry density after compaction. This chapter is presented as an introduction to some important concepts in choosing a surface aggregate.
Figure 8.2—Rutting due to excess clay content.
Figure 8.3—3-year-old dense packed surface aggregate after 40,000 vehicles.
Surface aggregate is the unbound layer of graded rock and other material used as a driving surface for a roadway.
About Surface Aggregates
In many locations, the surface aggregate of choice is whatever is cheapest. Many road managers assume the gravel will erode away, and the road surface will need to be regraveled in a relatively short timeframe. However, some entities see a benefit from putting in a higher quality aggregate to resist erosion and stretch the life cycle of the road surface before regraveling is needed. There are two major factors that determine surface aggregate quality: material and gradation (size distribution).
WHAT QUALITIES MAKE A GOOD SURFACE AGGREGATE?
Space Material Properties
Figure 8.4—Loose aggregate will unravel and form windrows of material along the road center and edge.
AGGREGATE PLACEMENT CONSIDERATIONS
Base Preparation. It is important that a stable road base exists on which to place aggregate. Any failures in road base will be reflected in the new surface aggregate. Surface aggregate will also reflect any imperfections in the road base. Ensure that any ruts or potholes are graded out prior to placing aggregate. It is also important to establish adequate (4 to 6 percent) crown or cross slope in the existing road. Then place aggregate in a uniform layer to maintain this crown. When placing aggregate deeper than 4 inches, consider cutting a key along the edge of the road to support the edge of the aggregate. Otherwise, the noncompacted aggregate edge may create a traffic hazard and unravel more quickly than a supported edge.
Moisture. Optimum moisture is critical when placing a well-graded aggregate. A dry aggregate will segregate by size and will never achieve maximum compaction. The range of optimum moisture will depend on the aggregate type and gradation.
Optimum moisture should be determined by a lab before ordering, and verified in the field when possible.
Compaction. Maximum dry density must be achieved through compaction equipment, such as a vibratory roller. Maximum compaction has been achieved when the road surface no longer compacts under the roller, or when larger stones on the road surface begin to break apart. The exact degree of compaction can be measured in the field using a nuclear density meter.
Depth. Aggregate must be placed at a sufficient depth to allow for compaction. As a general rule, the depth of compacted aggregate should be three times the largest stone diameter. For example, an aggregate with a 1.5-inch maximum stone size should be placed 3×1.5 inches = 4.5 inches deep. Thinner so-called skim coats of aggregate are often ineffective because the material cannot form a cohesive layer and is quickly raveled off by traffic.
Placement Method. A well-graded aggregate should be placed using methods that cause the least amount of size segregation. A motor paver, like those used to place asphalt, is the best way to ensure uniform aggregate distribution and coverage. Other devices, such as spreader boxes can be used to place aggregate. Tailgating (dump and spread) aggregate makes it much more difficult to avoid segregation and create a uniform surface. Every time the aggregate is handled or graded, it begins to segregate by size and becomes more likely to fail.
Figure 8.5—A well-graded aggregate is being placed through a paver at a noncompacted depth of 8 inches, and compacted to 6 inches. Notice the roller in the background for compaction.
SHOULD A SURFACE AGGREGATE INCLUDE CLAY?
NO CLAY. In regions with abundant precipitation, ground moisture, or freeze-thaw cycles, clay-laden aggregate can cause problems. In these regions, clay in surface aggregate can retain excessive moisture and cause rutting, especially during thaw cycles. The clay also will tend to pump to the surface of the aggregate in wet conditions, increasing the amount of sediment runoff during rain events, and increasing the amount of dust generated during dry conditions. Clay particles are more likely to become mobilized by traffic than crushed rock, and are more likely to travel long distances before settling out of the air because of their fine size and platy shape
YES CLAY. In arid regions where dust is not a major concern, a small amount of clay may be desirable in surface aggregates. The clay will retain moisture and help to bind the aggregate together during excessive dry periods. The amount of clay in the aggregate (approximated by the plasticity index) will vary depending on local climate and material being used.
Table 8.1 Other “Surface Aggregate” Specifications from around the United States: This table shows the variation in aggregates designated for an unbound wearing course from around the country.
2 Skorseth, K., and A. A. Selim. 2000. Gravel Roads Maintenance and Design Manual. SD LTAP, U.S. Department of Transportation, Fed Highway
Administration. Nov 2000. (http://www.epa.gov/owow/NPS/gravelman.pdf, page 39)
3 Foltz, R.B. and M. Truebe. 2003. Locally Available Aggregate and Sediment Production.. In Low-Volume Roads 8 proceedings. TRB, Washington,
D.C. (http://www.fs.fed.us/rm/pubs_other/rmrs_2003_foltz_r001.pdf. Pg 118)
4 Keller, G., and J. Sherar. 2003. Low-volume Roads Engineering Best Management Practices Field Guide. USDA Forest Service (http://ntl.bts.gov/
lib/24000/24600/24650/Chapters/N_Ch12_Roadway_Materials.pdf. Pg 120)
5 1996 FHWA Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-96) (http://www.efl.fhwa.dot.gov/design/manual/Fp96.pdf. Pg 686)
6 Ohio Dot Specification (http://www.dot.state.oh.us/Divisions/ConstructionMgt/OnlineDocs/Specifications/2005CMS/700/703.htm#a_703_18_ _
8 Iowa DOT: http://www.iowadot.gov/erl/archives/Apr_2005/GS/common/english_gradations.htm
Driving Surface Aggregate (DSA): DSA is an aggregate specification from Pennsylvania Department of
Transportation that was designed as a wearing course for unpaved roads. It was designed to achieve maximum packing density in order to resist wear and erosion.
Key Facts about DSA
Table 8.2 DSA size gradation.
CHAPTER 9: ROAD ASSESSMENT AND MONITORING
Figure 9.1—Road Assessment and monitoring.
Assessing road condition and monitoring post-treatment installation requires a systematic process to evaluate if treatments implemented have corrected the problem. The soil water road condition index serves as an assessment and monitoring tool, which is used to identify road condition relative to soil and water resource concerns. The form can be used on a single road or every road of concern. The index is a systematic process that first characterizes the road or road segment by identifying surface shape, location, road gradient, hillslope gradient, and surface material. Once the segment is characterized, the road is evaluated using the following eight key indicators.
For each of the eight indicators the reviewers identify if the road design, structure, or stream crossing is functioning. If the structure and design is operating in the proper or expected manner the road condition evaluation for that indicator is functional. If the structure or design is not operating as expected and is blocked, eroded, or has the chance of damaging resources (soil and water) in its present condition, the road condition evaluation is at-risk.
To determine the overall condition index for a road or segment, the reviewers evaluate each indicator for functionality and track each score to determine the percentage. Road segments with greater than 25 percent of the surface drainage structures at-risk receive an overall impaired condition rating. If less than 25 percent of the segment’s surface drainage is not operating or functioning in the proper or expected manner, the overall rating is at-risk. The sample form and rule set shows how the tool is used.
STEPS TO DETERMINE OVERALL CONDITION INDEX:
1. Drive the entire road or road segment to review the road and identify potential road segments. Road segments can be delineated from U.S. Geological Survey quadrangles or routed linear Arc/Info coverage. Without any preidentified segment breaks, look for the following when segmenting a road:
The amount of segmentation may vary depending on resource objectives.
2. Characterize each segment by closely examining the indicators on the form. Return to the first road segment and before driving the segment; identify the road surface shape, location, gradient, hillslope gradient, and surface material. Together with a coworker identify the following:
3. Drive the remainder of the segment. Identify the number of drainage structures that are functional. Often if one culvert is plugged, many culverts on the road also will be plugged. The record keeper tracks the ratings to determine the overall road segment rating.
4. Complete a form for each segment. Circle functional, at-risk, or N/A for each of the eight indicators. Add the circled rating for each category. Determine the percentage of functioning indicators for each indicator. Follow the rule set to obtain an overall rating. Turn the form over and answer the questions on the back related to maintenance or improvement considerations, potential causes of sediment, and site-specific concerns.
5. Repeat the process and drive to a typical location within the next segment. Identify the segment (2) of FS road (x) and complete the form. Identify the segment breaks on quadrangle maps or with a global positioning system waypoint.
Photograph a representative segment of the road.
Figure 9.2—Road assessment and monitoring form.
CHAPTER 10: REFERENCES AND ADDITIONAL RESOURCES
1. Water-Roads Field Guide <http://www.fs.fed.us/eng/php/library_card.phpp_num=0077%201803P>.
Road Surface Drainage
1. Riparian Restoration: Roads Field Guide <http://www.fs.fed.us/eng/php/library_card.php?p_num=0577%201801P>.
1. Water Roads Interaction: Introduction to Surface Cross Drains
1. Low-Water Crossings: Geomorphic, Biological and Engineering Design Considerations <http://www.fs.fed.us/eng/php/library_card.php?p_num=0625%201808P>.
2. Stream Simulation: An Ecological Approach to Providing Passage to Aquatic Organism at Road-stream Crossings.
3. Culvert Design for Aquatic Organism Passage, Hydraulic Engineering Circular No. 26. First Edition.
Fillslopes and Cutslopes
1. Soil Bioengineering: An Alternative to Roadside Management <http://www.fs.fed.us/eng/php/library_card.php?p_num=0077%201801>.
2. Roadside Revegetation. An Integrated Approach to Establishing Native Plants
1. Driving Surface Aggregate <www.dirtandgravelroads.org>.
2. Stabilization Selection Guide for Aggregate and Native-Surfaced Low-Volume Roads <http://www.fs.fed.us/eng/php/library_card.php?p_num=0877%201805P>.
Road Assessment and Monitoring
1. Soil and Water Road Condition Index – Field Guide <http://www.fs.fed.us/eng/php/library_card.php?p_num=0877%201806P>.
2. Soil and Water Road Condition Index – Desk Reference <http://www.fs.fed.us/eng/php/library_card.php?p_num=0877%201807P>.