Background

Roads, skid trails, and landings are all part of a forest transportation system.  (Skid-trail and landing BMPs are covered in Timber Harvesting).  Roads connect the forest land to existing public roads.  They provide forest access for such activities as managing timber, improving fish and wildlife habitat, fighting fires, and recreation.

Forest roads that are poorly located, constructed or maintained are the largest source of nonpoint source pollution from forest management activities.  Roads over steep slopes, erodible soils or stream crossings hold the greatest potential for degrading water quality.

There are three types of forest roads.  Identify the type of road system you need during your planning phase.

Temporary roads.  These are the most common type of forest road, designed and constructed for short-term use during a specific project such as timber harvesting.  These roads are used only when the ground is frozen or firm.  When the project is done, the temporary road is closed, all stream crossing structures are removed, and the road is naturally revegetated or replanted.  Waterbars are constructed and maintained where needed, and should be retained after the road is retired.

Permanent seasonal roads.  These are maintained as part of the permanent road system but are designed for use only when the ground is frozen or firm.  These roads are generally narrower than permanent all-season roads, are built to lower engineering standards, and have minimal surface gravel.  Waterbars are constructed and maintained where needed.

Permanent all-season forest roads.  These roads usually have gravel surfaces and are designed for year-round use.  However, there may be some limitations on use at various times of the year.

For specific information on roads in wetlands, see Wetlands.

Planning, Location, and Design

Decisions made at the planning stage will affect a road's construction costs, long-term maintenance needs, service life, and the amount of nonpoint source pollution it causes.  Loggers and landowners should plan, locate, and design the road system together.  This plan should be completed prior to the beginning of any construction or harvest activities.

Plan road systems that minimize the number, width, and length of roads to limit the total area of site disturbance.  Remember to consider future uses of the road system and coordinate development with adjoining landowners when possible.

Use existing roads when they provide the best long-term access.  Consider relocating existing roads if doing so improves access and reduces environmental impacts.  Reconstruct existing roads to the extent necessary to provide adequate drainage and safety.  Do not disturb stable road surfaces.

Select road locations that allow for drainage away from the road and road ditches.

Minimize the number of stream crossings, and make crossings at right angles to stream channels.

Identify the best stream-crossing locations before locating the road.  The best locations include straight and narrow stream channels with low banks and firm rocky soil.  Roads should approach streams at the lowest slope possible.

Where possible, locate roads on well drained soils.

Locate roads outside streamside management zones except at stream crossings.  For more information see Streamside Management Zones.

Road grades should not exceed 10% (Figure 5-1).  If road grades greater than 10% are necessary, limit grade length to minimize erosion, or break the grade using drainage structures.  See the Drainage Structures section further on this page.  Graveling the road surface on steep grades can also help maintain stability.  Note:  Road grades should be less than 5%.  Long steep slopes should be avoided.  If unavoidable, they should be broken into short segments of grade separated by segments of reverse grade.

Locate roads to follow natural contours and to minimize cut and fills.  Balance cut and fills to minimize the need for fill or removing excess materials (Figure 5-2).

Stream Crossing Design and Construction

Operating equipment in or near perennial or intermittent stream channels may add sediment directly to streams.  Stream crossings that are poorly located or constructed may erode streambanks.  Explore all alternatives before deciding to cross a stream.

As roads approach a stream crossing, proper drainage is critical to avoid sedimentation in streams.  Three common stream crossing structures are culverts, bridges, and fords.

Stream crossings must be designed, constructed, and maintained to safely handle expected vehicle loads and to minimize disturbance of streambanks, channels and, ultimately, aquatic organisms.  Consider streambed material, stream size, storm frequency, flow rates, intensity of use (permanent or temporary), and the passage of fish when planning crossings.

General BMPs for Stream Crossings

Before installing or constructing a ford, culvert, or bridge across any intermittent or perennial stream contact the Illinois Department of Natural Resources, Office of Water Resources.  A permit is required for construction in a floodway of any stream if the drainage area exceeds 1 square mile in an urban area or 10 square miles in a rural area.  IDNR-Office of Water Resources, Army Corp of Engineers, and EPA have a joint application form for this permit in Illinois.  To receive a application form contact the IDNR-Office of Water Resources for the 96 downstate counties 217/782-3863, for the northeastern 6 counties 847/705-4341.

For temporary stream crossings for skid trails, see the Stream Crossings for Skidding section in Timber Harvesting.

Use soil stabilization practices at stream crossings.  Use seed and mulch and install temporary sediment control structures, such as straw bales or silt fences, immediately following construction to minimize erosion into streams.  Maintain these practices until the soil is permanently stabilized.  Refer to the Soil Stabilization section.

Design, construct, and maintain stream crossings to avoid disrupting the migration or movement of fish and other aquatic life.  Bridges or arch culverts that retain the natural stream bottom and slope are preferred for this reason.

Install stream crossings using materials that are clean, non-erodible and not-toxic to aquatic life.

Install stream crossing structures at right angles to the stream channel.

Minimize channel changes and the amount of excavation or fill needed at the crossing.

Limit construction activity in the water to periods of low or normal flow.  Keep use of equipment in the stream to a minimum.

Construct a bridge or place fill directly over a culvert higher than the road approach to prevent surface runoff from draining onto the crossing structure and into the stream (Figure 5-3).

Divert road drainage into undisturbed vegetation, preferable outside the SMZ so that the drainage does not directly enter the stream (Figure 5-4).  See Diversion Structures.

Stabilize approaches to bridge, culvert, and ford crossings with gravel or other suitable material to reduce sediment entering the stream.

Anchor temporary structures on one end with a cable or other device so they do not float away during high water.  Install them so that they can be easily removed when no longer used, regardless of the season.

Pipe Culverts for Stream Crossings

Install pipe culverts long enough so that road fill does not extend beyond the ends of a culvert.

Install permanent culverts that are large enough to pass flood flows and are a minimum of 12 inches in diameter.  Culverts that are too small can plug up with debris and result in the road washing out or in flooding upstream.  See Appendices for culvert sizing table.

Install culverts so there is no change in the stream bottom elevation (Figure 5-5).  Culverts should not cause damming or pooling.

Firmly compact fill material around culverts, particularly around the bottom half.  Cover the top of culverts with fill to a depth of one-third of the pipe diameter or at least 12 inches, whichever is greater, to prevent crushing (Figure 5-6).

Use riprap around the inlet of culverts to prevent water from eroding and undercutting the culvert (Figure 5-7).  For permanent installations, use filter fabric under the riprap.  In addition, consider using flared-end culvert sections for inlets.

Keep culverts clear and free of debris so that water can pass at all times.  This is especially important in areas where beaver are present.

Fords

Use fords for crossing dry streambeds or where fording would cause minimal water quality impacts.

Locate fords where streambanks are low.

Streambed should have a firm rock or gravel base.  Otherwise, install stabilizing material such as reinforced concrete planks, crushed rock, riprap or rubber mats on streambeds.


Road Construction

The most effective method to control erosion on forest roads is to keep water from accumulating on the road surface.  Fast-moving water can easily erode soil from road surfaces and ditches, but road erosion can be controlled when water drains off the road surface and is dispersed into vegetation and ground litter.

Design and construct roads to remove water from road surfaces to keep the road dry and structurally sound.  Figure 5-8 shows three common road designs: crowned, outsloped, and insloped.  Install insloped roads with ditches and adequate cross drainage.  Outsloped roads (usually outsloped 2-4%) are less expensive to construct and maintain; use them on roads with moderate gradients and stable soils.

Construct stable cut-and-fill slopes that will revegetate easily, either naturally or artificially.

Do not bury debris in the road base.  It causes uneven settling that can lead to erosion and frost-heaving that creates mud holes.

Compact the road base material or allow it to settle before using the road to reduce the amount of water that soaks into it.  This will increase the road's carrying capacity, reduce road maintenance and reduce erosion.

Surface the road with gravel where steep grades, erodible soils, or high traffic volume make the potential for surface erosion significant.

Drainage Structures

Road drainage structures include cross drains (pipe culverts, open-top culverts, broad-based dips, and water bars) and water-diverting structures.  Cross drains allow water from roadside ditches to move from one side of the road to the other.

Where necessary to protect water quality, install road drainage structures to remove storm water or seepage from the road surface and ditches.  Space these structures at intervals close enough to minimize water flow volume and speed, avoiding ditch erosion.  As road grades increase, use drainage structures more often.  See Table 5-1 below.

Where necessary, provide erosion protection for outflows from road drainage structures to minimize erosion and disperse the water, allowing it to soak into the soil.  Riprap, mulch and/or seeding may be necessary.

Table 5-1. Recommended distances between drainage structures on forest roads and skid trails

Road grade                     Distance between                                     Distance between broad-
        %                             waterbars (feet)                             based dips and cross-drain culverts (feet)
        1                                    400                                                                       500
        2                                    250                                                                       300
        5                                    130                                                                       180
       10                                     80                                                                       150
       15                                     50                                                                       130
       20                                     45                                                                       120
       25+                                   40                                                                       110                             

Pipe Culverts for Cross Drains

Install pipe culverts to provide cross drainage on road grades at regular intervals immediately above steep grades, below bank seepages, and where water will run onto log landings or forest roads.

Install pipe culverts long enough so that road fill does not extend beyond the end of a culvert.

Install cross drain pipe culverts at grades at least 2% more than the ditch grade and angled 30 to 45 degrees to improve inlet efficiency (Figure 5-9).

Select the size of cross-drain culverts according to the size of the road and area drained by the ditch.  To avoid clogging, permanent culverts should be at least 12 inches in diameter.

Install pipe culverts on a surface of compacted granular material.  Firmly compact fill material around culverts, particularly around the bottom half.  Cover the top of the culvert with fill to a depth of one-third of the pipe diameter, or at least 12 inches (whichever is greater) to prevent crushing (Figure 5-6).

Use riprap around the inlet of culverts to prevent water from eroding and undercutting the culvert.

Open-Top Culverts

Open-top culverts provide cross drainage and road surface drainage (Figure 5-10) and are usually installed on seasonal or temporary roads.

Install open-top culverts to provide cross drainage immediately above steep grades, below bank seepages, where water will run onto log landings or forest roads, and on road grades at regular intervals.

Clean open-top culverts frequently since they easily fill with debris.

Broad-Based Dips

Broad-based dips can provide cross drainage and road-surface drainage for roads and skid trails with a gradient of 15% or less (Figure 5-11).  Broad based dips can be used instead of culverts, usually at lower cost and with lower maintenance.  Dips are not used for draining seeps, or for intermittent or permanent streams.

Broad-based dips are often used in conjunction with outsloped roads.  That eliminates the need for ditching the upslope side of the road, thus eliminating costly road maintenance.

Construct broad-based dips deep enough to provide adequate drainage and wide enough to allow trucks and equipment to pass safely.

Place a surface of crushed stone or gravel on the dip and mound for soils and conditions where rutting may occur.

Water Bars

A water bar is a shallow trench with a mound (or berm) which provides cross drainage and intercepts runoff from skid trails, recreational trails, firebreaks, or inactive or closed roads (Figure 5-12).  Constructing a water bar will minimize erosion and provide conditions for natural or artificial revegetation.

Place water bars at a 30 to 45 degree angle with a cross drainage grade of 2%.

Diversion Structures

Diversion ditches, or berms, divert water away from roads and side ditches, and channel it into vegetation (Figure 5-4).  These structures are often used before stream crossings to ensure that water will be diverted into vegetation and not directly into a stream, lake, or wetland.

Construct diversion ditches so they intersect the roadside ditch at the same depth and are outsloped 1% to 3% (Figure 5-4).

Soil Stabilization

Soil stabilization practices are used where soil is exposed and natural revegetation in inadequate to prevent soil erosion and subsequent sedimentation into streams, lakes and wetlands.  This occurs during road construction and when the road system is being used (active) or is closed (inactive).  Practices include mulching, seeding, and installing sediment control structures. 

It is always more efficient and cost effective to prevent erosion than it is to repair damage after the fact.

Mulching and Seeding

Use mulch and/or seed where necessary to minimize soil erosion into streams, lakes, and wetlands.

Mulch, such as straw, woodchips or bark, retains soil moisture, important for seed germination, and protects the soil surface from erosion due to runoff and raindrop impact.  Mulch can be used to promote natural revegetation and protect a seeded area.  If you seed, apply mulch immediately afterward.  Netting may be necessary to hold mulch in place on steep slopes or on areas where water flow concentrates.

Seed mixtures should include fast growing species for quick soil protection plus perennial species for longer soil protection until native vegetation returns to the site.  Recommendations for seed mixes that are best for specific regions in Illinois are available at your local Illinois Department of Natural Resource office and USDA Natural Resources Conservation Service (NRCS) office.  See Appendix E for NRCS recommended Critical Area Planting seeding rates. 

Wildlife Enhancement

To ensure immediate vegetative cover, a generic "shotgun" wildlife mix is often recommended to account for differences in pH levels, soil types, and seasons of the year.  Apply the mixture at approximately 14 lbs. of seed/acre.

Minimum seed combination rates:

Orchard grass              3 lbs./acre
Medium red clover      4 lbs./acre
Ladino clover              1 lbs./acre
Timothy                       2 lbs./acre
Korean lespedeza        4 lbs./acre

Use a cover crop of Winter Wheat at 40 lbs./acre or Annual Rye at 10 lbs./acre to 12 lbs./acre.  The time of the year will determine which seed is used.  Use wheat in the fall only and rye throughout the summer months.  Then use combined seed mixture in the spring.

A soil test is recommended for fertilizer and lime amounts needed.

Alternative wildlife seed mixture:

Red Top                      2 lbs./acre
Timothy                       2 lbs./acre
Korean Lespedeza or  5 lbs./acre
Ladino Clover           3/4 lbs./acre

A soil test is recommended for fertilizer and lime amounts needed.

Sediment Control Structures

Install sediment control structures where necessary to slow the flow of runoff and to trap sediment until vegetation is established at the sediment source.  Sediment control structures include straw bales, fencing, silt fencing, and sediment traps (Figure 5-13).

Maintain, clean, or replace sediment-control structures until areas of exposed soil are stabilized.

Road Maintenance

Roads must be well maintained or water quality protection structures quickly degrade.  For both active and inactive roads, follow BMPs in the Soil Stabilization section.

Active Roads

Inspect the road system at regular intervals, especially after heavy rainfall, to detect problems and to schedule repairs.

Clear debris from culverts, ditches, dips and other drainage structures to decrease clogging that can lead to washouts.  Place debris where it cannot be washed back into these structures or into open water.

Keep traffic to a minimum during wet periods to reduce maintenance needs.

Shape road surfaces periodically to maintain proper surface drainage.  Fill in ruts and holes with gravel or compacted fill as soon as possible to reduce erosion potential.

Remove berms along the edge of the road if they will trap water on the road.

Inactive Roads

When forest roads are inactive for extended periods, closing the system will help to protect the road surface and the water quality protection structures.  Consider erecting a barrier to traffic such as a gate or berm, and post "Closed" signs at the entrance of temporarily closed roads.  Stating the length of time and/or reason for closure, and inviting acceptable uses may be helpful to assure compliance.

Remove all temporary drainage and stream crossing structures.

Shape all road system surfaces to maintain proper surface drainage, if necessary.

Install water bars where necessary.  See the Water Bars section and follow recommendations in Table 5-1.

Inspect and maintain road surfaces, permanent drainage and stream-crossing structures (ditches, culverts, bridges, etc.) to minimize erosion.