This contribution was supported by the Great Lakes Protection Fundand the University of Minnesota, College of Natural Resources, ExtensionService, and Agricultural Experiment Station under Project MN 42-42.

TABLE OF CONTENTS

Page

Introduction ....................................................................................... 1Stream and Wetland Crossing Considerations..................................... 4 Abutments and Geotextiles .............................................................. 4 Erosion Control Measures ............................................................... 6Temporary Stream Crossing Options .................................................. 9 Fords .............................................................................................. 9 Permanently constructed fords ................................................... 10 Temporarily constructed fords .................................................... 11 Culverts ........................................................................................ 12 PVC and HDPE Pipe Bundles ......................................................... 13 Bridges .......................................................................................... 15 Ice bridges .................................................................................. 16 Timber bridges ........................................................................... 17 Used railroad cars and flatbed truck trailers ............................... 20 Steel bridges............................................................................... 20 Pre-stressed concrete bridges ..................................................... 21Temporary Wetland Crossing Options ............................................... 21 Wood Mats .................................................................................... 22 Wood Panels .................................................................................. 23 Wood Pallets .................................................................................. 24 Bridge Decking .............................................................................. 24 Expanded Metal Grating ................................................................ 24 PVC and HDPE Pipe Mats or Plastic Road ...................................... 25 Tire Mats....................................................................................... 26 Corduroy ....................................................................................... 27 Pole Rails ...................................................................................... 27 Wood Aggregate ............................................................................. 28 Low Ground Pressure Equipment .................................................. 29 Equipment with wide tires, duals, bogies, and/or tire tracks ...... 30 Equipment with tracks ............................................................... 31 Lightweight equipment ............................................................... 32 Equipment with central tire inflation .......................................... 32Economic Considerations for Crossing Options ................................. 32Environmental Impacts Associated with Crossings ........................... 33 Background................................................................................... 33 Studies of Stream Crossings .......................................................... 35 Studies of Wetland Crossings......................................................... 39Summary of Some Stream and Wetland Crossing Statutes ................ 40 Michigan ....................................................................................... 40 Minnesota ..................................................................................... 40 New York ....................................................................................... 42 Pennsylvania ................................................................................. 42 Wisconsin ...................................................................................... 43 Ontario.......................................................................................... 44 Quebec .......................................................................................... 44Research and Education Needs......................................................... 45Summary ......................................................................................... 46Selected Pertinent Literature ............................................................ 46

Appendices ....................................................................................... 56 Appendix 1.—Partial List of Commercial Vendors for Temporary Crossing Options ..................................................................... 56 Appendix 2.—Specifications for Some Temporary Stream Crossing Options ..................................................................... 62 Appendix 3.—Specifications for Some Temporary Wetland Crossing Options ..................................................................... 74 Appendix 4.—Informational Summaries for Temporary Stream Crossing Options ..................................................................... 79 Appendix 5.—Informational Summaries for Temporary Wetland Crossing Options ................................................................... 101

List of TablesTable 1.—Criteria to consider when selecting a stream or wetland crossing option ......................................................................... 3

Table 2.—Informational categories summarized in Appendices 4 and 5 for each stream and wetland crossing option ......................... 4

Table 3.—Properties of some geotextiles used in stabilization and separation applications ............................................................ 6

Table 4.—Minimum ice thickness required to support a given load above a flowing river or stream or on a lake ............................. 18

Table 5.—Central office contact information for water regulatory authorities in Michigan, Minnesota, New York, Pennsylvania, Wisconsin, Ontario, and Quebec.............................................. 41

List of IllustrationsFigure 1. —Stream that may need to be crossed by an access road or trail .......................................................................................... 2Figure 2.—Wetland area that may need to be crossed by an access road or trail .............................................................................. 2Figure 3.—Rutting that can occur when crossing soft, wet soils ......... 2Figure 4.—Anchoring of a bridge to a nearby tree .............................. 5Figure 5.—Abutment logs below a log stringer bridge (approach yet to be constructed) ..................................................................... 5Figure 6.—Non-woven geotextile ......................................................... 5Figure 7.—Woven geotextile ............................................................... 5Figure 8.—Installation of hay or straw bale barriers ........................... 7Figure 9.—Installation of silt fencing.................................................. 7Figure 10.—Mulched surface ............................................................. 8Figure 11.—Erosion blanket samples ................................................. 8Figure 12.—Riprap slope ................................................................... 8Figure 13.—Seeding an area with a hand seeder ................................ 9Figure 14.—Ford crossing .................................................................. 9Figure 15.—A geotextile used in a ford .............................................. 11Figure 16.—A tire mat used to provide support in a temporary ford .. 11Figure 17.—Culvert .......................................................................... 12Figure 18.—Packing earth around a culvert during installation......... 13Figure 19.—PVC or HDPE pipe bundle.............................................. 13Figure 20.—Installation of a geotextile under a pipe bundle .............. 14Figure 21.—Pipe bundle crossing layered to the desired height ......... 14Figure 22.—Temporary bridge spanning a stream ............................. 15Figure 23.—Ice bridge ....................................................................... 17Figure 24.—Log stringer bridge ......................................................... 18

Figure 25.—Cabled logs in a log stringer bridge ................................ 18Figure 26.—Solid sawn stringer bridge ............................................. 18Figure 27.—Stress-laminated timber bridge panel ............................ 19Figure 28.—Bridge made from a used railroad car ............................ 20Figure 29.—Steel bridge ................................................................... 20Figure 30.—Pre-stressed concrete bridge .......................................... 21Figure 31.—Wet area in a haul road.................................................. 21Figure 32.—Applying a geotextile under a temporary wetland crossing .................................................................................. 22Figure 33.—Wood mat ...................................................................... 22Figure 34.—Cable loop at the end of a wood mat............................... 23Figure 35.—Wood panel .................................................................... 23Figure 36.—Wood pallet .................................................................... 24Figure 37.—Expanded metal grating over a geotextile ....................... 25Figure 38.—PVC or HDPE pipe mat in a road.................................... 25Figure 39.—PVC or HDPE pipe mat .................................................. 25Figure 40.—Plastic road mat ............................................................ 26Figure 41.—Tire mat ........................................................................ 26Figure 42.—Another tire mat design ................................................. 27Figure 43.—Corduroy ....................................................................... 27Figure 44.—Pole rails ....................................................................... 28Figure 45.—Wood aggregate .............................................................. 28Figure 46.—Use of a geotextile under wood aggregate ....................... 29Figure 47.—Wide tires ...................................................................... 30Figure 48.—Dual tires ...................................................................... 30Figure 49.—Tire tracks ..................................................................... 30Figure 50.—Bogie system ................................................................. 31Figure 51.—Tire tracks on a bogie .................................................... 31Figure 52.—Tracked machine ........................................................... 31Figure 53.—Central Tire Inflation (CTI) system ................................. 32Figure 54.—Tire footprint at two pressures ....................................... 32

Charles Blinn is a Professor/Extension Spe-cialist, Department of Forest Resources,University of Minnesota, St. Paul, MN.

Rick Dahlman is a Utilization and MarketingSpecialist, Minnesota Department of NaturalResources, Division of Forestry, St. Paul, MN.

Lola Hislop is a General Research Engineer,with the U.S. Department of Agriculture,Forest Service, Madison, WI.

Michael Thompson is a General Engineer,U.S. Department of Agriculture, Forest Ser-vice, Houghton, MI.

Temporary Stream and Wetland Crossing Optionsfor Forest Management

Charles R. Blinn, Rick Dahlman, Lola Hislop,and Michael A. Thompson

INTRODUCTION

Expansion of economies and populationsworldwide has increased the demand for forestproducts and other uses of forests. Removingwood products from the forest requires accesssystems, such as truck roads and skid trails.Roads and trails must often cross streams (fig.1) and wetlands1 (fig. 2). The construction anduse of these access roads and trails has thepotential to negatively impact streams andwetlands directly by soil compaction, rutting,or the placement of fill (fig. 3). Streams andwetlands can also be impacted indirectly byfunneling the movement of sediment, debris,and nutrients into the water body or by caus-ing changes in hydrologic flows across thearea.

The best way to protect streams and wetlandsis to avoid crossing them. If this is not fea-sible, it is important to minimize and mitigateimpacts while using the crossing. For anyparticular application, selecting a crossingoption that is cost-effective for the contractorand/or landowner, that adequately addressesthe environmental concerns of society, andthat satisfies the wide range of regulatoryconstraints is becoming increasingly difficult.

In many areas, fords, culverts, and ice bridgesare the types of stream crossings most com-monly used, although use of portable bridgesis rapidly increasing. Corduroy, permanentfill, and frozen soil are the most commonchoices for crossing wetlands. While there arenumerous other options, lack of informationhas been an obstacle to expanding the range ofoptions that landowners, land managers,contractors, and regulatory agencies are willingto consider.

The purpose of this paper is to help reduce thisobstacle by providing detailed informationabout a broad range of reusable temporary2

stream and wetland crossing options. Toaccomplish this, we have:

• Summarized information about many of thetemporary stream and wetland crossingoptions,

• Reviewed some of the reported environmen-tal impacts associated with using theseoptions,

• Highlighted some of the key points fromstatutes that regulate stream and wetlandcrossings in Michigan, Minnesota, New York,Pennsylvania, Wisconsin, Ontario, andQuebec, and

• Identified some research and educationneeds.

1 For the purpose of this report, wetlands are areasthat contain soil with poor load-bearing capacity andhigh moisture content or standing water that areoften affected by seasonal fluctuations in water level.Examples include peat, muck, wet mineral soils, orunstable sections of access roads and trails.

2 For the purpose of this report, a temporary cross-ing is one that is used for a maximum of 3 yearsbefore it is removed or rendered unusable.

Information was compiled through contactswith individual loggers, staff in several forestproducts companies and land managementand regulatory agencies, and through a reviewof published literature.

The options discussed in this report includeboth commercial and homemade devices thatare either transported to the site or built on-site. Increased use of these options can helpminimize the cost of protecting water re-sources. While the initial price of a reusabletemporary option may exceed the cost of acurrently used alternative (e.g., a culvert for astream crossing or fill for a wetland crossing),the fact that it is reusable and that it may beeasier to install may make it the lowest costoption in the long-term. Also, some of thetemporary options reduce environmental

Figure 1.—Stream that may need to be crossedby an access road or trail.

Figure 2.—Wetland area that may need to becrossed by an access road or trail.

Figure 3.—Rutting that can occur when crossingsoft, wet soils.

impacts and can be installed and removedmore rapidly than the options most frequentlyused today.

It is likely there are additional excellent cross-ing options not identified in this paper. It wasnot possible to identify all available options,and new ideas for crossings and new applica-tions of existing technologies are constantlybeing developed. We recommend that youcontact vendors, contractors, and othersources for more detailed information on localexperience regarding costs, installation andremoval, the availability of specific options inyour area, and additional options not coveredin this report.

We also recommend that you compare eachvendor’s recommendations and specificationsto your long-term needs and applications.Seek the advice of a licensed engineer whenpurchasing a stream crossing product thatlacks engineering specifications, when using aproduct in an application for which it was not

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designed, or when constructing a crossingyourself. Inspect all products before eachinstallation. Some criteria to consider whenevaluating which option(s) to select for yourparticular application are noted in table 1.Before deciding to install a crossing, be sure toweigh the potential value(s) of the resourcewithin the accessed area against the costs andpotential negative environmental impacts.

Additional details and quick reference tablesare provided in the Appendices. Appendix 1contains a list of commercial vendors. Tablessummarizing specifications, approximate cost,installation and removal time, and equipmentneeds are provided in Appendices 2 (stream

crossings) and 3 (wetland crossings). All costsand prices presented in this report are in $USunless specified. Arnold (1994) and Mason(1990) also provide excellent overviews of manyproducts, including design specifications,drawings, and photographs. Copstead et al.(1997) have also prepared an extensive anno-tated bibliography of published literature onwater/road interaction technologies andassociated environmental effects. Appendices4 (stream crossings) and 5 (wetland crossings)contain additional information for each optionaccording to the categories listed in table 2.Although we recognize that there is someredundancy built into this report, we chose todo this to make it more useful for a number ofdifferent applications and users.

Effectiveness for reducing potential impacts

Relative safety of the option

Compliance with safety regulations

Compliance with other applicable non-safetyregulations, including permitting requirements

Potential conflicts with insurance coverage

Season(s) of use

Length of time the crossing will be needed

Ability to handle anticipated traffic loads and speeds

Purchase price or construction cost

Maximum distance of crossing

Bridge abutment requirements (stream crossingoptions only)

Availability of engineering specifications, especiallyfor bridging options (stream crossing options only)

Ease of transport, installation, and removal withavailable labor and equipment

Local availability

Installation and removal time and costs

Number of reuses possible

Anticipated future need for a particular option

Maintenance requirements

Driving surface traction under anticipated operatingconditions

Potential costs avoided, such as the purchase andplacement of fill or the need to divert stream flowduring a culvert installation or removal

Anticipated fluctuation in water level during use

Site conditions (e.g., soil type, hydrology, amount ofrock present, stream width and depth, volume ofwater in the stream, types of aquatic life in thestream, permitting requirements, etc.)

Potential value(s) of the resource within the area tobe accessed

Landowner’s management objectives

Rehabilitation requirements following removal

Table 1.—Criteria to consider when selecting a stream or wetland crossing option. Unless otherwisenoted, all criteria are appropriate for both stream and wetland crossing options.

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STREAM AND WETLAND CROSSINGCONSIDERATIONS

There are several considerations that apply tonearly all stream and wetland crossings. Donot cross unless absolutely necessary. If it isnecessary to cross a stream or wetland, thenumber of crossings should be limited to asfew as possible and the location(s) should becarefully selected. Existing crossings shouldbe used whenever possible, unless theirrehabilitation and use would be more damag-ing than establishing a new one.

The crossing should be as short as possible.Stream crossings should be perpendicular tothe direction of water flow to the degree practi-cal. Wetland crossings should be parallel tothe direction of water flow to the degree practi-cal. Approaches to crossings should be directand have a low grade. Water diversion struc-tures, such as a broad-based dip or waterbars, should be constructed to direct waterflowing down the road or skid trail into avegetated area before it reaches the crossing.This will help minimize the movement ofsediment into the water body.

Stream crossings should be located on astraight segment of the stream channel thathas low banks (except for bridge crossingswhere higher banks are preferred to supportthe abutments). This will minimize the need todisturb the bank or to alter the natural shapeof the channel. It will also reduce the impactof turbulent water action against the crossingstructure itself or against any portions of thebank that need to be disturbed to permit

installation of the structure. Where there is arisk of flooding, structures should be anchoredat one end to allow them to swing out of themain channel without washing downstream orobstructing water flow (fig. 4).

Proper installation, maintenance, and siterehabilitation are essential for any crossingoption to be fully effective. All necessarypermits should be obtained in advance andterms communicated clearly to the employeesor contractors working on the crossing. Thecrossing structure should be carefully in-spected before each installation and appropri-ate repairs made. If the crossing structurebecomes damaged, a licensed engineer shouldbe consulted to certify that it is still safe forthe anticipated loads. Structures that areinstalled either in or over open water shouldbe cleaned (away from the water body) beforeeach installation to remove accumulateddebris, such as mud and branches. Streamcrossing options that are placed in the water(e.g., culverts, pipe bundles) need to be fre-quently checked for blockage to avoid dam-ming the stream.

Abutments and Geotextiles

Many of the structures are most effective whena proper foundation is provided. Bridges needa log, railroad tie, or similar abutment to reston to help level the structure, to minimizedisturbance to the stream bank, and to makeremoval easier (fig. 5).

Some stream crossing options and mostwetland crossing options function best with ageotextile under them. Geotextile, also called

Table 2.—Informational categories summarized in Appendices 4 and 5 for each stream and wetlandcrossing option.

Description of option

Area of application

Advantages

Disadvantages

Source(s)

Recommended supplemental material

Approximate price of materials (March 1998)

Construction directions and/or diagram and timerequired

Equipment needed for construction, installation,and/or removal

Installation approach and time required

Patent protection of product design

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Figure 4.—Anchoring of a bridge to a nearbytree.

Figure 5.—Abutment logs below a log stringerbridge (approach yet to be constructed).

filter fabric, is a fabric mat used to prevent anew layer of material from mixing with thematerial below (usually native soil when usedwith crossing structures). Geotextiles allowwater to drain through them, provide addi-tional support for a crossing, and make re-moval of the crossing easier. A non-wovenfabric is recommended for use with temporaryinstallations because it is less slippery thanwoven fabrics, reducing movement of thestructure during use (fig. 6). Also, non-wovengeotextiles exclude fine particles while allowingwater to flow through from above and below. A

needle-punched non-woven polypropylene orhigh-density polyethylene (HDPE) geotextile oflow (3 oz/yd2 [100 g/m2]) to medium (6 oz/yd2

[200 g/m2]) weight has been used in mosttrials of temporary crossings.

Another type of geotextile is a woven geotextile(fig. 7). It is mainly used in applications thatrequire high tensile strength and low elonga-tion of the fabric, such as permanent roadbuilding. The woven fabrics tend to allow morefine particles to flow through. Some propertiesof a few representative non-woven and wovengeotextiles are compared in table 3.

A non-woven fabric will not continue to tear asa woven fabric may if it becomes punctured.Despite this, it is important to limit the num-ber of high spots (e.g., rocks, stumps) toreduce the potential of punctures during use ofthe crossing. At the same time, care should betaken to avoid damaging the root or slash mat

Figure 6.—Non-woven geotextile.

Figure 7.—Woven geotextile.

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to the degree possible. This mat will provideadditional support during use, lessen themovement of sediment, and can speed reveg-etation of the site after the structure is re-moved.

The geotextile should be removed at the sametime as the crossing option. Sometimes, thegeotextile may be too heavy with soil and waterto be easily recovered in a reusable condition.For this reason, it may be beneficial to useshorter lengths with the ends overlapped (e.g.,25-ft [7.6-m] lengths with 2 ft [0.6 m] of over-lap) or sewn (e.g., leave about 3 in. [7.5 cm] ofoverlap in the sewn seam). On very soft soilwhere the geotextile sinks when it is steppedon, it is best to sew the overlapped area to-gether. If it is not possible to remove thegeotextile, a biodegradable fabric should beused. Fiber options for biobased geotextilesinclude coir, jute, kenaf, flax, sisal, hemp,cotton, and wood fiber (English 1994).

Paper machine felt may be a low-cost alterna-tive to geotextile (Bridge 1989). Used carpetand other materials may also be viable alterna-tives to geotextile. However, some materials

may contain toxic substances that could leachinto the water. Therefore, the appropriateregulatory agencies should be contacted beforeany substitute materials are used.

Erosion Control Measures

The installation, use, and removal of streamand wetland crossing structures frequentlyresults in movement and exposure of soil. Useof temporary erosion control measures isstrongly recommended to prevent movement ofsediment into water bodies while these soilsare being adequately stabilized by vegetation orarmoring. Adamson and Harris (1992) recom-mend development of a sediment control planto reduce sediment concerns at water cross-ings. The four broad categories they recom-mend that need to be considered in formulat-ing a plan for a particular water crossing arenoted below. Not all measures will apply for allcrossings.

• Administrative measures (e.g., purchase ofadequate pipe length, training and instruc-tion of workers, timing of the construction toavoid fish spawning periods, inspectionfrequency, contingency plan to follow in caseof change).

• Protection (e.g., protecting the existingground cover, limiting the area of distur-bance to reduce the area requiring stabiliza-tion).

Table 3.—Properties of some geotextiles used in stabilization and separation applicationsa (metricunits are reported in brackets).

Property Non-woven geotextiles Typical woven4546 4551 4553 geotextile 2002

PhysicalWeight (oz/yd2) [g/m2] 4.6 [156] 7.0 [237] 9.2 [312] 5.0 [170]Grab tensile strength (lbs) [kN] 100 [0.44] 150 [0.67] 203 [0.90] 200 [0.89]Grab tensile elongation (%) 50 50 50 15Packaging and priceRoll width(s) (ft) [m] 15 [4.6] 15 [4.6] 15 [4.6] 12.5 [3.8] or 18 [5.5]Roll length(s) (ft) [m] 300 [91] 300 [91] 240 [73] 504 [154] or 351 [107]Gross weight/roll (lbs) [kg] 145 [66] 220 [98] 229 [104] 220 [100]Area/roll (yd2) [m2] 500 [418] 500 [418] 400 [334] 700 [585]Priceb ($/yd2) [$/m2] 0.56 [0.47] 0.84 [0.70] 0.95 [0.82] 0.60 [0.50]

aThe geotextiles shown here are produced by Amoco Fabrics and Fibers Company3.bThe reported 1998 price (FOB) assumes the purchase of one roll of geotextile. Prices may vary betweenvendors and according to the amount of fabric purchased.

3 The use of trade, firm, or corporation names in thispublication is for the information and convenience ofthe reader. It does not constitute an official endorse-ment or approval of any product or service by theUniversity of Minnesota, the Minnesota Departmentof Natural Resources, or the USDA Forest Service tothe exclusion of others that may be suitable.

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• Strategic planning of the sequence of opera-tions to manage the factors affecting sedi-ment entering the water body (e.g., stormwater flowing toward the water body, flowagewithin the water body during construction).

• Structural controls that will be used indi-vidually or in combination for reducingsediment (e.g., silt fencing, hay or strawbales, mulch, erosion blankets, diversionditches, water bars).

Options that may be used for reducing sedi-ment include silt fencing, hay or straw bales,mulch, and erosion blankets. Silt fencing andhay bales are installed as barriers across theslope of exposed soils to intercept and slow themovement of water down the slope. They trapthe sediment the water is carrying and releasethe water slowly. To be most effective, theyshould be placed at spacings similar to thatrecommended for water bars on long slopes(refer to the Best Management Practices [BMP]guidelines in your State or Province). Thebarrier closest to the water or wetland is mostcritical. Proper installation and maintenanceis essential for these barriers to work effec-tively.

To properly install hay or straw bale barriers(fig. 8):

• Set the bales in a shallow trench to preventwater from flowing under the barrier. Ifdigging is impractical due to frost, packsnow against the uphill side of the bales.

• Overlap the bales to avoid leaving gapsbetween them.

• Drive stakes or lath through the bales sothat the stakes are buried 6 to 10 in. (15 to25 cm) into the soil to firmly anchor them inplace.

To properly install silt fencing (fig. 9):

• Drive wooden stakes or lath spaced 4 to 6 ft(1.2 to 1.8 m) apart into the ground to holdthe geotextile or other permeable fabric siltfencing in place.

• Cut the fabric in long strips that are 2 to 3 ft(0.6 to 0.9 m) wide.

• Attach a continuous length of the fabric tothe uphill side of the stakes so that pressurefrom water and sediment will not pull thefabric loose. The lower 6 in. (15 cm) of thefabric should form an “L” facing uphill. Thisshould be buried, preferably in a shallowtrench, or covered with soil to prevent waterfrom running under the barrier. Pack thesoil firmly over this part of the fabric.

Silt fence and hay bale barriers should beinspected periodically and maintained asnecessary to make sure they remain func-tional. They may fill with sediment or becomedamaged, rendering them ineffective. Once thesite is effectively stabilized by revegetation, thebarriers should be removed.

In some situations, additional erosion protec-tion may be needed. The force of raindrops onexposed surfaces can loosen and wash awaysubstantial amounts of soil. In most cases, a

Figure 8.—Installation of hay or straw balebarriers.

Figure 9.—Installation of silt fencing.

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layer of mulch or an erosion blanket over theexposed soil will provide good protection.Mulch or erosion blankets shield the soil andhelp disperse and slow the surface flow ofwater. Mulching with loose straw or hay (fig.10) on level or moderate slopes can work well.On steeper slopes, it may be necessary tolightly disk the mulch into the soil to keep it inplace. Where the risk of erosion is high orwhere concentrated flows of water are antici-pated, such as the bottom of a ditch, an ero-sion blanket may be needed. These blankets(fig. 11) are mats made of shredded wood orother fibers. They are commercially marketedby several manufacturers and should beavailable through suppliers that sell culvertsand geotextiles.

Steep excavated cuts, particularly on the bankof a stream, may require permanent protec-tion, such as heavy rock riprap (fig. 12). Infor-mation on this and several other possibletreatments for slope failure prone areas can befound in Moll (1996) and Mohoney (1994).Moll (1996) also discusses techniques used toclose and obliterate access routes after use.The level of restoration required for a particu-lar access corridor will depend on many site,management, and political factors.

Figure 10.—Mulched surface.

Figure 11.—Erosion blanket samples.

Figure 12.—Riprap slope.

In any case, speeding the revegetation ofdisturbed soil surfaces is always a good idea.Vegetation provides a root mass that holds soilin place and soaks up water, reducing runoff.Fertilizing and seeding disturbed soil facilitatesand speeds revegetation, minimizing erosionpotential (fig. 13). Care should be taken to usenative seed sources to avoid introducing non-native species to the ecosystem unless theyhave been proven to be innocuous. Fertilizerand seed mixture recommendations for ex-posed soil are generally available from mostlocal land management organizations.

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Figure 14.—Ford crossing.

Figure 13.—Seeding an area with a hand seeder.

TEMPORARY STREAM CROSSING OPTIONS

Crossing streams is often perceived to be oneof the most controversial, time consuming,and expensive parts of any forest managementoperation. Properly designed, installed, andmaintained temporary stream crossing struc-tures can greatly reduce costs and help meetthe concerns of regulatory agencies. Thetypes of temporary stream crossing optionsdiscussed below include fords, culverts,polyvinyl chloride (PVC) and high-densitypolyethylene (HDPE) pipe bundles, and por-table or on-site constructed bridges.

It is important to follow the proper permittingprocess when installing and using a streamcrossing. A local hydrologist should be con-tacted to determine whether a permit isrequired. The permit may specify what type ofcrossing as well as when it can be installedand/or used.

As noted previously, engineering input from alicensed engineer into the design of manystream crossing options is recommended.However, engineering design information forsome of the alternatives is limited, and theadditional costs for an engineered design maybe considered exorbitant for a temporarycrossing. Caution is necessary when usingany crossing that has not been engineeredand/or that has not been inspected duringand between uses.

The condition of any crossing should bemonitored as long as it exists. Regular main-tenance may be needed to keep the crossing

functional. Maintenance is especially impor-tant for culvert and pipe bundle crossings tomake sure that they are clear and free ofdebris. Weak soils on the approach to acrossing can be stabilized by placing one ormore of the temporary wetland crossingoptions (e.g., corduroy, wood mats, woodpanels, expanded metal grating, tire mats,etc.) on top of a non-woven geotextile.

Appendix 1 contains a list of commercialvendors for several stream crossing options.Appendix 2 presents a summary of productspecifications and approximate costs for someof the options discussed. Additional informa-tion can be found on the Internet. The Log-ging and Sawmilling Journal has a World WideWeb page (http://www.forestnet.com/log&saw/stream/introstr.htm) that includesinformation on a variety of stream crossingoptions, planning tips, and suggestions forprotecting aquatic resources and rehabilitat-ing the site.

Fords

A ford or low-water crossing uses the streambed as part of the road or access trail (fig. 14).They are best suited for short-term, limitedtraffic. Use should be limited to periods of lowflow when the water is less than 2 ft (0.6 m)deep. Because the spawning beds of manyfish species occur within the same areas thatmake a good ford crossing, fords should notbe constructed or used during periods of fishspawning. Also, construction should notoccur during fish migration periods. Fordsshould maintain the natural shape andelevation of the stream channel to avoidcreating obstructions to the movement of fishand other aquatic organisms.

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Because equipment will be directly in thestream channel when using a ford, it is espe-cially important to keep vehicles clean andwell-maintained. Mud and debris dragged inon skid loads or on tracks and tires, as well asoil and fuel leaks, contribute to polluting thewater. Protecting the approaches to a fordwith clean gravel, corduroy, wood mats, woodpanels, expanded metal grating, or othertemporary surfacing material is recommendedfor this reason. (See the section on wetlandcrossing options for a description of corduroy,wood mats, wood panels, expanded metalgrating, tire mats, etc.)

Existing crossings should be used wheneverpractical unless rehabilitating and using thecrossing would be more damaging than estab-lishing a new one. New fords should be lo-cated where the banks are low, less than 4 ft(1.2 m) high, and gently sloping; where thegrade of the approach to the stream does notexceed 5:1 (horizontal to vertical); and wherethe stream bed is firm rock or gravel. Suchlocations require little or no modification toaccommodate traffic. More often some grad-ing, excavating, and placement of road basematerial is needed.

To facilitate construction of a ford where thestream bed is not dry, it may be desirable totemporarily divert the main flow of the streamaround the work site using ditches, berms,dikes, piping, high capacity pumps, or anexisting alternate channel crossing. Thismakes placement and compaction of fill mucheasier and minimizes sediment movement inthe stream. It may also be desirable to placelarge rocks or logs or to construct a sedimenttrap below a ford to catch sediment introducedby use of the ford. However, excavation ofmaterial within the stream bed should only bedone with the advice of a qualified hydrologistor licensed engineer and approval of the appro-priate regulatory authorities.

A mucky or weak stream bed is not acceptableas a base for a ford unless it is frozen. Whenthe soil within the stream bed is weak, it willbe necessary to cover or to replace it withmaterials that will support traffic. There areseveral alternative materials for creating a firmbase for a ford. Those applicable to normalforestry operations include:

• Permanently constructed fords using cleangravel or rock with or without geotextile or a

plastic cell webbing known as a cellularconfinement system.4 A ford constructedwith the cellular confinement system issometimes known as a plastic ford.

• Temporarily constructed fords using matsmade of wood, tires, expanded metal grating,logs or poles, or a floating rubber mat.

Use of a geotextile below any material (e.g.,clean gravel, rock, wood, or tire mats) in eithera permanently or temporarily constructed fordcan provide additional support to the crossingwhile separating the material from weak nativesoil. However, use of the geotextile should beapproved by the appropriate regulatory au-thorities because of concerns about impacts ifany downstream movement of the geotextileoccurs.

Permanently constructed fords

Constructing a firm crossing using gravel orrock is common when the existing bed of anintermittent or perennial stream is too weak tosupport traffic. When using clean gravel orrock fill to construct a ford, the existing weakmaterial in the stream bed should be exca-vated first. This allows the natural shape ofthe stream channel to be maintained andreduces the problem of the gravel mixing withthe mud, making the fill ineffective. A mini-mum of 6 in. of gravel or rock fill should beused unless it is not possible to excavate deepenough to accommodate this much fill. Thegravel or rock fill should not raise the crossinghigher than the original stream bed level.

We recommend that a geotextile be laid downbefore placing gravel or rock fill (fig. 15), aslong as it is approved by the appropriateregulatory authorities. This keeps the fillseparated from the weak native materials andprovides added support to the crossing. Al-though fords that are constructed with gravelor rock fill are intended as temporary cross-ings, the gravel or rock fill is not removed whenthe crossing becomes inactive.

4 A cellular confinement system is an expandablehoneycomb plastic panel into which different types offill material can be added. The panels confine the fillinto small compartments, holding them in place.

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Pence (1987) and Tufts et al. (1994) describeplastic fords that were constructed to helpkeep the gravel or rock fill in place. Withoutthe cellular confinement system, the fill can bepushed aside by heavy vehicles or frequenttraffic over a crossing. Also, the cellularconfinement system reduces the chance thatfast currents will wash the gravel downstream.

A vented ford or emergency spillway can beformed by providing culverts to handle theday-to-day flow and by partially lowering theroad grades for passing floods (Adamson andRacey 1989). This type of ford is suitablewhere the normal flow may exceed a fordabledepth either seasonally or following stormevents. A wall must be provided along thedownstream edge of the spillway to keep thegravel fill from eroding under the action of theflowing water. Various wall types includegabions and precast concrete sections. Ripraperosion protection is required downstream ofthe wall. Coarse granular fill is required tomake the vented ford erosion resistant.

Temporarily constructed fords

A firm base for a ford can be temporarilyestablished by using materials such as matsmade of wood or tires, or by using expandedmetal grating, logs, or floating rubber mats.(See the section on wetland crossing optionsfor a description of wood mats, tire mats, andexpanded metal grating.) Wood or tire mats orexpanded metal grating, in combination with anon-woven geotextile, can be placed directlyacross a stream to create a firm base for theford (fig. 16). Installation is quick and easy.Removal is also simple, but may require re-turning at a later date if the site is frozen whenthe operation is finished. In some instances,

Figure 15.—A geotextile used in a ford.

Figure 16.—A tire mat used to provide supportin a temporary ford.

the stream bed or bank may be too weak forthe geotextile and mats or expanded metalgrating to provide sufficient support for traffic.Supplemental corduroy, gravel, or rock fill maybe needed in the weakest portions of thecrossing to create a firm base for the ford.

In some jurisdictions, a pole or log ford may beestablished for crossing small streams. Forthis type of ford, the stream channel is filledwith logs laid parallel to the direction of streamflow. This works well for crossings that will beused only a few times and where the logs canbe easily removed as soon as the work iscompleted. It is best suited for dry ditches andintermittent stream channels because of therisk of blocking stream flow, particularlyduring spring breakup or following a heavyrain. Placement of two or more steel cableslaid bank-to-bank below the pole ford willfacilitate removal of the logs. To minimize therisk of blocking stream flow, polyvinyl chloride(PVC) pipe bundles can be used in place oflogs. (See the section on PVC pipe bundlesbelow for a description of this option.)

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A “dam bridge” or “rubber mat bridge” can alsobe used to provide a temporary ford (Arnold1994, Looney 1981). It is constructed fromstrips of rubber conveyor belting joined side-by-side. Looney (1981) describes a dam bridgeconstructed of 0.5-in.- (1.3-cm)-thick strips ofrubber conveyor belt that was cemented andbolted together. Support cables hold the sidesupright so the mat floats on the water when novehicles are in the crossing. When a vehicleenters the dam bridge the mat is pushed downto the stream bottom, momentarily dammingthe stream. Once the vehicle is across thestream, the mat floats up again, allowing thestream to flow normally. Looney (1981) recom-mends placing rock on the approaches to thedam bridge to assist vehicles in climbing out,particularly for skidders with chains.

Culverts

A culvert is a structure that conveys waterunder a road or access trail (fig. 17). It is oneof the most common methods of crossingintermittent and perennial streams. Manufac-tured culverts come in many shapes (round,oblong, or arched), lengths, and diameters,and may be made of corrugated steel, concrete,or polyethylene. An arch culvert is an open-bottom arch with appropriate footings intowhich the arch is fitted. New culverts areavailable from a variety of suppliers. Usedculverts suitable for temporary installationsmay be available from state, provincial, or localroad authorities or from construction, pipeline,or drilling companies.

Although corrugated steel culverts are usedmost frequently, the use of polyethylene pipesis increasing for temporary installations and

Figure 17.—Culvert.

low standard roads. Polyethylene pipes haveseveral limitations that should be considered(Stjernberg 1987); however, proper installationcan overcome most problems. Other materialsare often used as substitutes for manufacturedculverts on temporary forest roads and skidtrails. Some examples are hollow steel piling,well casings, gas pipeline, wooden box culverts,and hollow logs. Small culverts can be in-stalled and removed with a bulldozer or back-hoe. An excavator may be needed to installand remove larger culverts. Low-cost culverttransportation systems have been developed(Ewing 1992).

Proper sizing and installation of culverts arecritical to constructing a successful crossing.Both culvert diameter and length need to beconsidered when determining culvert sizerequirements. The recommended minimumdiameter for any culvert is generally 12 in. (30cm). Smaller sizes are difficult or impossible toclean out if they become clogged. Temporaryinstallations that are removed seasonally mayonly need to accommodate estimated peak flowfor the season of use. Year-round installationsneed to consider peak flows of longer termevents (e.g., 10-, 25-, 50-, or 100-year floods).In all cases, it is important to confirm sizingrequirements with a hydrologist or licensedengineer and the appropriate permittingauthority.

A single large-diameter culvert is better thantwo or more smaller culverts. A commonmistake is to assume that two 12-in. (30-cm)culverts equal the capacity of a single 24-in.(60-cm) culvert. However, it takes at leastthree 12-in. (30-cm) culverts to equal thecapacity of one 24-in. (60-cm) culvert. Thegreater surface area of the three smallerculverts will also cause more turbulence,reducing the flow rate through each culvert.The pipe must also be long enough to extend toat least the toe of the fill slope. Placement ofthe culvert should follow the same grade as theexisting stream channel and should be placeddeep enough to avoid washing out from below.If the upstream end of the culvert becomes tooelevated, the water may move through theculvert too fast and impede the migration ofaquatic organisms. Culverts should not beinstalled during fish spawning and migration.

The pipe should be placed in line with thedirection of stream flow. Attempting to use the

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culvert to redirect the stream may violate theterms of a permit and can result in the culvertbeing washed out. The side slope of the fillshould be no steeper than 2 to 1 (horizontal tovertical) to ensure it is stable. The culvertshould be covered with fill to a depth of 12 in.(30 cm), or one-half the diameter of the pipe,whichever is greater. This protects the pipefrom being crushed and avoids damage to thepipe during grading of the road surface. Whenearth fill is used, it should be compacted inlayers (fig. 18). This is especially important forthe bottom half of the culvert, which may bewashed out if the earth fill is not properlycompacted. Compaction of the road surfaceover the culvert will help ensure that thedriving surface sheds water rather thanturning to mud.

Figure 18.—Packing earth around a culvertduring installation.

Some jurisdictions may permit logs or brush tobe used as fill around a temporary culvert toavoid placement of soil that would need to bedisturbed when the pipe is removed. A hy-drologist or the appropriate permitting author-ity should be consulted before using logs orbrush. There may be concerns about the logsor brush washing away during use of thecrossing, or that the fill material will not beremoved from the stream when the culvert isremoved. In either case, downstream move-ment of the logs and/or brush may dam thestream.

To facilitate installation and/or removal of aculvert where the stream bed is not dry, it maybe desirable to temporarily divert the main flowof the stream around the work site usingditches, berms, dikes, piping, high capacity

pumps, or an existing alternate channel cross-ing. This makes placement, compaction, and/or removal of fill much easier and minimizessediment movement in the stream. It may alsobe desirable to place large rocks or logs or toconstruct a sediment trap below a culvert tocatch sediment introduced by use of thecrossing. However, this should only be donewith the advice of a qualified hydrologist orlicensed engineer and approval of the appropri-ate regulatory authorities.

Periodic maintenance of culverts is importantto ensure proper function. Both ends of theculvert should be checked and cleared ofdebris to allow an unimpeded flow of water.This is especially important in areas subject tobeaver activity. Problems with unnaturalerosion around the culvert should be correctedto minimize the chance of washout of theculvert and sedimentation of the stream.

PVC and HDPE Pipe Bundles

A pipe bundle crossing is constructed using 4-in.- (10-cm)-diameter Schedule 40 PVC orSDR11 HDPE pipes that are cabled togetherforming loose mats that can be formed intobundles. The bundle provides mechanicalsupport for the vehicle while allowing water topass through the pipes unimpeded (fig. 19).Streams with a U-shaped channel to containthe pipes are most appropriate for this option.

Because standard PVC pipe is light-sensitiveand will lose strength when exposed to sun-light, using PVC pipe that has been exposed tothe sun should be avoided. Strength of thecrossing can be maintained by covering or

Figure 19.—PVC or HDPE pipe bundle.

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painting PVC pipe or by using an ultraviolet-resistant type of pipe, such as HDPE. HDPEpipe also tolerates temperature extremes of-40° F (-40° C) better than PVC without becom-ing brittle or losing shock resistance and willreturn to its original shape after being de-formed (Légère 1997). No published studieshave evaluated the use of PVC or HDPE pipebundles for stream crossings during winter inan environment where temperatures areconsistently below freezing.

HDPE pipes may be more expensive thanstandard PVC and may need to be purchasedthrough a vendor that specializes in plasticpipe. The thickness of many alternative plasticpipes is often specified using the term “stan-dard dimension ratio” (SDR), which is calcu-lated by dividing the average outside diameterof the pipe by its minimum wall thickness. Forany given outside diameter, SDR will increaseas wall thickness decreases.

It is important to make the crossing wideenough for the widest vehicle that will use it.Plastic pipe is generally sold in multiples of 10-ft (3-m) lengths; therefore, it may be necessaryto purchase 20-ft (6.1-m) sections that can becut to the desired length. Mason andGreenfield (1995) proposed using shorter pipesections, end-to-end, between full-length pipesmaking a 14-ft- (4.2-m)-wide crossing.

Constructing pipe bundles consists of drilling1/4-in.- (6.4-mm)-diameter holes at 1 ft (0.3m) and 4 ft (1.2 m) from each end of each pipe.Four 3/16-in.- (4.8-mm)-diameter galvanizedsteel cables are threaded through the holes toconnect the individual pieces. It is importantto drill round holes to avoid creating potentialstress points that could later facilitate pipeshattering. It may be necessary to controlcable end fray before stringing the cablethrough the sections. Loops should be madeat the end of each cable, extending beyond thelast pipe, and then secured using 3/16-in.-(4.8-mm)-diameter cable clamps to preventindividual pipes from rolling or moving in otherdirections.

Our experience has shown that it takes about1 hr for two people using two hand drills andone saw to cut, drill, and cable 4-in.- (10-cm)-diameter and 20-ft- (6.1-m)-long PVC into a10-ft x 12-ft (3-m x 3.7-m) section. The initialconstruction cost of this size section, including

materials and labor, is about $500. Two 10-ftx 12-ft (3-m x 3.7-m) sections are necessary tobuild a crossing for a 6-ft (1.8-m) wide x 2-ft(0.6-m) deep channel. Each cabled sectionshould be loose so the pipes can conform tothe stream channel. A tight connection isused for a single layer crossing.

The crossing is created by first laying down ageotextile fabric (fig. 20) to ensure separationfrom the stream bottom and to facilitateremoval (Mason and Greenfield 1995). A layerof connected pipes is then placed on top of thegeotextile along the stream bottom, parallel tothe stream flow. If necessary, loose or con-nected pipes are then layered to the desiredheight (fig. 21). A layer of connected pipesshould be placed as the top mat. Loops at theend of connecting cables should be covered sothat they don’t hook onto the underside of apassing vehicle. The top and bottom layers ofpipe should be long enough to go beyond thestream edge to protect the stream banks.

Figure 20.—Installation of a geotextile under apipe bundle.

Figure 21.—Pipe bundle crossing layered to thedesired height.

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Typically, a stiff surface such as expandedmetal grating, tire mats, or wood panels arelaid over the top mat to limit pipe movement(wave action) and to provide traction. Thecrossing surface needs to be sufficiently con-nected to the pipe to avoid flipping up under acrossing vehicle (Mason and Greenfield 1995).Wood mats or expanded metal grating can beplaced on top of a non-woven geotextile tostabilize the approaches to the crossing if theyare weak.

The time required to install the crossing de-pends on the crossing length, stream depth,water volume, equipment available, and theamount of room needed for the equipment tomaneuver. It took about 1.5 hr to place a PVCpipe bundle crossing with a wood pallet run-ning surface within a stream channel that was35 ft (11 m) wide (the bundles covered 25 ft[7.5 m] of that span). It took about 20 minutesto remove a PVC pipe bundle crossing consist-ing of a non-woven geotextile placed below two10-ft x 12-ft (3-m x 3.7-m) bundle sections, awood plank running surface, and one 10-ft x12-ft (3-m x 3.7-m) wood mat that was used oneach side of the stream to protect the banks.

Transportation equipment needed to bring thepipe or bundles to the crossing site depends onthe length and amount of pipe (Mason andGreenfield 1995). In some cases, the drilledindividual pipes may be transported by pickuptruck and constructed on-site. Preconstructedmats may be too heavy for a pickup truck,requiring a dump truck or lowboy. Front-endloaders or skidders are typically used to placethe mats.

Bridges

By spanning the stream, bridges keep fill andequipment out of the water body to the greatestdegree of any stream crossing option (fig. 22).For this reason, they have the least impact onstreams. Designs are available for a widerange of span lengths and load capacities (e.g.,pickup trucks, skidders and forwarders, orloaded semi-tractor trailers). Temporarybridges can be made from ice, timber, usedrailroad cars (flatcars and boxcars), usedflatbed truck trailers, steel, or pre-stressedconcrete.

Little site preparation is normally requiredwhen installing a temporary bridge. To provide

stable, level support for the structure, it isrecommended that bridges be installed onabutments on both sides of a stream. This willalso facilitate removal if the ground is frozen.Logs or large wooden beams are often used forabutments. Crossing permit requirements,local statutes, or specific site conditions mayrequire more extensive abutments. Also,crossing permit requirements or local statutesmay specify the minimum clearance betweenthe bridge and the stream to accommodatepeak flows and/or recreational use.

Ramps from the approaches up to the bridgetraffic surface often need to be created on-site.Soil, snow, and corduroy are usually adequate,but permit requirements and/or site condi-tions, such as weak soil, may require use ofother materials. Also, if the soils within theapproaches to the bridge are weak, or if theywill be significantly disturbed during installa-tion and use of the bridge, we recommendusing corduroy, wood mats, wood panels,expanded metal grating, or other temporarysurfacing material to strengthen the ap-proaches. (See the section on wetland crossingoptions for a description of corduroy, woodmats, wood panels, and expanded metalgrating.) This will reduce rutting or otherdamage that may inhibit use of the crossing. Itwill also minimize the potential for sedimentreaching the stream.

Bridges are generally designed to be a fixedlength. Unfortunately, a fixed-length bridge isnot applicable to all streams. Engineeredbridges have been evaluated and a load(weight) rating established for a maximumspan distance. If that maximum span distance

Figure 22.—Temporary bridge spanning astream.

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is lengthened and/or the maximum load isexceeded, the bridge may fail. It may befeasible to span longer distances; however, themaximum load will need to be decreased andshould be determined only by a licensedengineer.

Some bridge designs are open in the middle, orhave holes or gaps in the traffic surface. Thesedesigns may be less expensive or easier toinstall, but also allow dirt and debris to fallinto the stream. As a result, some jurisdic-tions may not permit use of these designs.Also, movement of individual bridge panelsmay occur during use if they are not ad-equately connected. For structures with a gapin the traffic surface, it is recommended that adecking material (e.g., plywood, lumber) beadded to close this space. Installation of curbsor guardrails is an important safety consider-ation for bridges designed for truck traffic.They help the driver position the vehicle safelyon the structure. The curbs or guardrails mayneed to be removed for skidder traffic if theskid loads will damage them.

Most temporary bridges can be installed andremoved with a knuckleboom loader, front-endloader, bulldozer, or skidder. Long spans forwide streams may require special equipment,such as a crane or excavator. Keliher et al.(1995) recommend that individual bridgesections weigh less than 5,000 lb (2,300 kg)and be under 30 ft (10 m) long if a grappleskidder is to lift the structure. Sections couldweigh as much as 11,000 lb (5,000 kg) if theskidder drags, winches, or pushes them. Thesize and weight of the bridge or its individualcomponents is also an important considerationfor loading, unloading, and transport from onelocation to another. In some circumstances,the machine installing the bridge may need tocross through or work in the stream channel toget the structure in place. This should beavoided whenever possible and may requireprior approval from the local permitting au-thority.

Prefabricated, portable bridges made of steel,treated or untreated lumber, and pre-stressedconcrete can be purchased from commercialmanufacturers. When they are retrofitted,used railroad cars and flatbed truck trailerscan also serve as a prefabricated crossing.Although they are generally more expensivethan a structure built of locally available

materials, prefabricated options offer twoimportant advantages. First, commerciallymanufactured bridges generally incorporateengineering input into their design. This willhelp reduce concerns about safety and liabil-ity. Second, they can be used many times overseveral years, considerably reducing the costper crossing. Prefabricated designs includesingle, rigid structures, and hinged or modularpanels. The hinged or modular panels facili-tate transport, installation, removal, andhandling. Prefabricated bridges can usually beinstalled or removed in less than 2 hr.

Bridges fabricated from locally available mate-rials also come in a wide variety of shapes andsizes. Some are built on-site for a single use;others are portable and can be used severaltimes. Examples of on-site constructedbridges include ice and log stringer bridges.Portable bridges may be constructed from solidsawn timbers and planking, flatbed trucktrailers, steel beams, pre-stressed concretepanels, or other materials. Because the initialcost of a bridge fabricated from locally avail-able materials is often much lower than that ofcommercially manufactured bridges, they are aviable alternative for many stream crossings.The installation and removal time may belonger for a bridge fabricated from locallyavailable materials than for a prefabricatedbridge.

We recommend that a licensed engineer reviewthe design of any bridge that is fabricated fromlocally available materials to ensure that thestructure will be safe and is adequate for theintended use. However, this review may bedifficult to obtain and the cost may be consid-ered too exorbitant in some cases. Construc-tion specifications have not been establishedfor some materials (i.e., hardwood lumber),and others may be converted to a use forwhich they were not originally designed (e.g.,flatbed truck trailers). Many materials orstructures have had substantial wear and tearbefore their use as a bridge structure (i.e.,railroad flat cars, flatbed truck trailers, con-crete panels), which may have significantlyreduced their strength or limited their remain-ing service life.

Ice bridges

Ice bridges are a common type of winter cross-ing over streams, lakes, and rivers in areas

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where there are extended periods of tempera-tures below freezing (fig. 23). In some areas,the ice may be thick enough that no construc-tion is needed. Where construction is neces-sary, ice bridges are made by packing snowand/or pumping water onto the existing ice.Some jurisdictions permit slash or brush to beplaced in the stream channel when there is noice to build on, but this is generally undesir-able because it is often difficult to remove thebrush. Because an ice bridge will take longerto melt than the stream, a new channel maybe cut around the blockage on streams withlarge or high velocity spring flows. Therefore,ice bridges may not be appropriate on thosestreams.

Figure 23.—Ice bridge.

On lakes, ice bridges are sometimes created byplowing snow off the path chosen for the road.Removing the snow enables the ice to growthicker faster, thereby increasing the loadbearing capacity. Because the plowed snow-banks represent concentrated loads on the ice,they should be spread over as large an area aspossible. When a vehicle crosses floating ice, adeflection bowl moves with it, generating wavesin the water (Haynes and Carey 1996). If thespeed of these waves is the same as the vehiclespeed, the deflection of the ice sheet is in-creased and will likely lead to failure of the ice.The problem is more serious for thin ice andshallow water depths. When in doubt, opera-tors should drive less than 15 miles (24 km)per hr.

The following formula was developed to esti-mate the minimum ice thickness required tosupport a given load above a flowing river orstream or on a lake (Haynes and Carey 1996).

h=4(P)1/2

Where: h = ice thickness in inches P = the load or gross weight of the vehicle plus its contents, in tons.

This equation can also be expressed in tabularformat, where the vehicle class equals the totalweight of the vehicle plus its load (table 4).

Timber bridges

Donnelly (1997) provides a good overview oftimber bridges. Engineering design guidelinesare available for many different types of timberbridges. Two popular designs for temporarystructures are log stringer bridges and solidsawn stringer bridges with or without a plankdeck. Log stringer bridges (fig. 24) are built bycabling logs together from trees felled in thearea of construction. It is especially importantto bundle stringers together with cable (fig. 25)when building a log stringer bridge to improveperformance. A narrow stream can sometimesbe crossed by bundling stringers together withchains or cable and placing them only in thewheel path. Several log stringer bridge optionsare discussed in Peterson (1987). Solid sawnstringer bridges (fig. 26) are built with newlumber, railroad ties, or demolition materials.Kittredge and Woodall (1997) describe a solidsawn stringer bridge made with 6-in. x 6-in.(15-cm x 15-cm) and 6-in. x 8-in. (15-cm x 20-cm) cants. This design provides an unevendriving surface for better traction.

Creating an ice bridge requires cold weather.Night temperatures below 0° F (-18° C) are best,with several days required to build up ice thickenough to safely support traffic. Once an icebridge is in use, the thickness and condition ofthe ice should be checked frequently to be sureit remains adequate. This may need to be doneas often as once or twice a day, or more, on fastmoving streams or large rivers and lakes and astemperatures warm up.

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Table 4.—Minimum ice thickness required to support a given load above a flowing river or stream oron a lake (Haynes and Carey 1996)a

Vehicle class b Minimum ice thickness Minimum distance between vehicles c

(tons) [tonnes] (in.) [cm] (ft) [m]

0.1 [0.1] 2 [5.1] 17 [5.2] 1 [1.1] 4 [10] 34 [10] 2 [2.2] 6 [15] 48 [15] 3 [3.3] 7 [18] 58 [18] 4 [4.4] 8 [20] 67 [20] 5 [5.5] 9 [23] 75 [23] 10 [11] 13 [33] 106 [32] 20 [22] 18 [46] 149 [45] 30 [33] 22 [56] 183 [56] 40 [44] 26 [66] 211 [64]

a Information in this table assumes clear, sound ice. If white, bubble-filled ice makes up part of the icethickness, count it only half as much as clear ice. If the air temperature has been above freezing for at least6 of the previous 24 hr, multiply the vehicle class by 1.3 to obtain a larger minimum thickness. If the airtemperature stays above freezing for 24 hr or more, the ice begins to lose strength and the table no longerrepresents safe conditions. Maximum recommended speed is 15 mi (24 km) per hr.b Vehicle class equals the gross weight of the vehicle plus the weight of its contents in tons.c At ice thicknesses greater than the minimum, the spacing between vehicles can be reduced on sound ice.

Figure 24.—Log stringer bridge. Figure 25.—Cabled logs in a log stringer bridge.

Figure 26.—Solid sawnstringer bridge.

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Plank decks provide a smooth running surface,decrease lateral movement of the structureduring use, and reduce the amount of dirt anddebris that may fall into the stream. If a plankdeck is to be installed on either of these bridgetypes, annularly threaded (ring-shank) orhelically threaded (spiral) spikes should beused to attach the surface deck. The spikesshould be at least 9 in. (23 cm) long to reducewithdrawal during use of the crossing. If careis used during installation, removal, andtransport, stringer bridges can be reusedseveral times.

The main concern with log stringer and solidsawn stringer designs is that there is limitedinformation on the engineering properties oflogs, railroad ties, and demolition materials.Thus, designs using these materials typicallyinclude little, if any, engineering input. Careshould be exercised when using these materi-als if they have not been evaluated to deter-mine their structural strength and engineersare not involved in the design or in accuratelyestimating their load ratings. Rot, decay,knots, and grain can greatly affect theirstrength properties. Some of these factorsbecome more important the longer a bridge isin use, especially if the species does not have ahigh decay resistance.

Muchmore (1976) presents basic design crite-ria to determine whether single lane logstringer bridges are designed and constructedto safely support specific loadings and to meetminimum safety criteria. Bradley and Krag(1990) present span designs for seven treespecies (white spruce [Picea glauca], easternwhite pine [Pinus strobus], jack pine [Pinusbanksiana], red pine [Pinus resinosa], easternhemlock [Tsuga canadensis], quaking aspen[Populus tremuloides], and balsam poplar[Populus balsamifera]) and two types of bridges(with and without needle beams5). Guidelinesare also available for evaluating the capacity ofsawn timber and log stringers in existingbridges (Ontario Ministry of Natural Resources1989). The USDA Forest Service is currentlydeveloping guidelines for different types ofportable timber bridges.

Other timber bridges have been constructedusing treated panels of stress-laminated,

glued-laminated (glulam), dowel-laminated, ornail-laminated materials. Stress-laminatedpanels consist of lumber placed edgewise andheld together with high-strength steel rods (fig.27) that are stressed in tension, up to 100 lb/in.2 [PSI] (7,000 g/cm2). There is a need toretension the steel rods periodically. Russell(1997) presents a review of stress-laminatedtechnology. Glulam panels consist of dimen-sion lumber glued together on the wide face.Dowel- and nail-laminated panels are similarto stress-laminated panels, except that dowelsor nails are used to connect each successivepiece of lumber. In all cases, the panels areplaced side-by-side across a stream.

One advantage of these designs, as well as asolid sawn stringer design using new lumber,is that the lumber is a known species andgrade. Thus, structural properties are knownand an engineer can properly design a safestructure. Also, because they are panelized,transportation to the site may be easier thanfor some other bridging options. Field perfor-mance for some of these engineered bridges

5 A needle beam distributes a live load to all string-ers and is positioned across the stringers at mid-span.

Figure 27.—Stress-laminated timber bridgepanel.

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installed for permanent use indicates that theirperformance is generally satisfactory (Ritter etal. 1995).

Behr et al. (1990) compared the initial costs oftimber, steel/concrete, and prestressed con-crete bridges. Five New England generalcontractors performed cost estimates on bridgedesigns spanning 20, 40, and 60 ft. Also,three timber bridge suppliers provided costestimates for nine bridge designs, three at eachspan length. Results from general contractorsindicated that timber was cost competitive withsteel/concrete and was less expensive thanprestressed concrete. Results from timberbridge suppliers showed a distinct initial costadvantage for timber over both steel/concreteand prestressed concrete.

The USDA Forest Service Wood in Transporta-tion Program has established the Wood inTransport National Information Center. TheCenter maintains a website at http://wit.fsl.wvnet.edu that describes the programand provides an on-line order form to obtainfree publications, design plans, cost informa-tion, etc. The Center can also be contacteddirectly at 304-285-1591 (voice) or 304-285-1505 (FAX). The Forest Products Lab also hasa website at http://www.fpl.fs.fed.us/wit/containing some of their publications on wood-in-transportation technology. The ForestService has also published an excellent refer-ence on timber bridge design, construction,inspection, and maintenance (Ritter 1992).

Used railroad cars and flatbed truck trailers

Railroad cars (flatcars and boxcars) and flatbedtruck trailers can be retrofitted for use asstream crossings (fig. 28). The retrofittingprovides additional reinforcing to the mainsupport beams so they will support vehicletraffic. Bradley and Pronker (1994) present astandard design for using railcars as tempo-rary bridges. Carraway (1997) indicated thatrailroad boxcars are much lighter than flat-cars, allowing a 50-ft- (15-m)-long x 10-ft- (3-m)-wide bridge to be transported on a lowboytrailer. A railroad boxcar bridge can be un-loaded with a knuckleboom loader and placedacross the stream with a skidder. A crane maybe needed to lift and install a railroad flatcarbridge. Individual railroad cars and flatbedtruck trailers tend to be narrow which may bea limitation for hauling applications.

Figure 28.—Bridge made from a used railroadcar.

Used railroad cars may be purchased fromthird-party vendors who purchase old railroadcars from railroad companies. Contact yourlocal railroad company or railroad car repairfacility to find out how to obtain one. Usedflatbed truck trailers are lighter and are morereadily available locally through trailer repairand salvage operations. While it is possible topurchase retrofitted used railroad cars for useas bridges, most used flatbed truck trailervendors do not provide the additional rein-forcement needed.

Steel bridges

Steel bridges include hinged portable bridgesand modular bridges (fig. 29). Where permit-ted, two or more bridge spans or bridge panels(multi-spans) may be connected across a pierto span wide crossings. Hinged bridges fold upfor transport. Modular steel bridges are de-signed as a series of individual panels thatinterlock, forming a bridge of variable length.

Figure 29.—Steel bridge.20

We are aware of a locally fabricated, non-engineered, steel bridge that is about 50 ft (15m) long and was constructed using I-beams.Also, catwalks with wood decking have beenused.

Pre-stressed concrete bridges

Precast, pre-stressed concrete panels can belocally fabricated. Generally, two or morepanels are placed side-by-side to form thebridge (fig. 30). Although the initial cost of thisbridge may be low, they are usually heavy andrequire larger equipment to install and remove.It is important to make sure that the panelsare engineered to handle the anticipated loads.Highway departments or local road authoritiesmay be a source for used panels.

Figure 30.—Pre-stressed concrete bridge.

TEMPORARY WETLANDCROSSING OPTIONS

This overview of temporary wetland crossingoptions focuses on alternatives that can beapplied to the surface of a wetland soil, includ-ing a wet spot on a haul road, to stabilize it forshort crossing distances (fig. 31). While wedefine “short” as being less than 200 ft (61 m),the distance may depend on the initial cost topurchase or construct the selected option, thevalue of whatever is to be accessed, and thecosts associated with other travel routes.Although a very long distance could be crossedwhen the option is matched to site needs, thecost may be prohibitive. The ability to reuseoptions makes them more viable, especiallythose with a higher initial cost.

Temporary wetland crossing options includewood mats, wood panels, wood pallets, bridgedecking, expanded metal grating, PVC andHDPE pipe mats or plastic road, tire mats,

Figure 31.—Wet area in a haul road.

corduroy, pole rails, wood aggregate, and lowground pressure equipment. Low groundpressure equipment includes machines withwide tires, duals, tire tracks, bogies, tracks,light weight, and/or central tire inflation (CTI).We have chosen not to discuss road construc-tion activities or wetland dredging and fillingoperations that are associated with constructinga new road or crossing over long distances. Wehave also not included cable yarding systems,helicopters, or balloons. Although use of frozenground may be the most viable crossing optionin many areas, that option is also not dis-cussed.

Many of the options should not be placed onareas that have firm high spots (e.g., stumps,large rocks) to reduce bending stress andbreakage during use. Hislop and Moll (1996)recommend blading the surface as flat aspossible before installation. For sites with grassmounds or other uneven vegetation, bladingshould not disturb the root mat associated withthe vegetation. The performance of any wetlandcrossing option is enhanced if there is a root orslash mat to provide additional support to theequipment.

Maintaining the root mat can also speed reveg-etation of the site following removal of thecrossing. The performance of the crossing isalso enhanced by use of a geotextile (fig. 32),which helps segregate the crossing from theunderlying soil and provides additional flota-tion. Most of the options are best suited to beused in conjunction with hauling and forward-ing, but not during skidding. If used duringskidding operations, the options will wear fasterand may move out of position when trees aredragged over them. Also, if a geotextile is used,it may become torn and displaced by skidding.

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We are aware of a locally fabricated, non-engineered, steel bridge that is about 50 ft (15m) long and was constructed using I-beams.Also, catwalks with wood decking have beenused.

Pre-stressed concrete bridges

Precast, pre-stressed concrete panels can belocally fabricated. Generally, two or morepanels are placed side-by-side to form thebridge (fig. 30). Although the initial cost of thisbridge may be low, they are usually heavy andrequire larger equipment to install and remove.It is important to make sure that the panelsare engineered to handle the anticipated loads.Highway departments or local road authoritiesmay be a source for used panels.

Figure 30.—Pre-stressed concrete bridge.

TEMPORARY WETLANDCROSSING OPTIONS

This overview of temporary wetland crossingoptions focuses on alternatives that can beapplied to the surface of a wetland soil, includ-ing a wet spot on a haul road, to stabilize it forshort crossing distances (fig. 31). While wedefine “short” as being less than 200 ft (61 m),the distance may depend on the initial cost topurchase or construct the selected option, thevalue of whatever is to be accessed, and thecosts associated with other travel routes.Although a very long distance could be crossedwhen the option is matched to site needs, thecost may be prohibitive. The ability to reuseoptions makes them more viable, especiallythose with a higher initial cost.

Temporary wetland crossing options includewood mats, wood panels, wood pallets, bridgedecking, expanded metal grating, PVC andHDPE pipe mats or plastic road, tire mats,

Figure 31.—Wet area in a haul road.

corduroy, pole rails, wood aggregate, and lowground pressure equipment. Low groundpressure equipment includes machines withwide tires, duals, tire tracks, bogies, tracks,light weight, and/or central tire inflation (CTI).We have chosen not to discuss road construc-tion activities or wetland dredging and fillingoperations that are associated with constructinga new road or crossing over long distances. Wehave also not included cable yarding systems,helicopters, or balloons. Although use of frozenground may be the most viable crossing optionin many areas, that option is also not dis-cussed.

Many of the options should not be placed onareas that have firm high spots (e.g., stumps,large rocks) to reduce bending stress andbreakage during use. Hislop and Moll (1996)recommend blading the surface as flat aspossible before installation. For sites with grassmounds or other uneven vegetation, bladingshould not disturb the root mat associated withthe vegetation. The performance of any wetlandcrossing option is enhanced if there is a root orslash mat to provide additional support to theequipment.

Maintaining the root mat can also speed reveg-etation of the site following removal of thecrossing. The performance of the crossing isalso enhanced by use of a geotextile (fig. 32),which helps segregate the crossing from theunderlying soil and provides additional flota-tion. Most of the options are best suited to beused in conjunction with hauling and forward-ing, but not during skidding. If used duringskidding operations, the options will wear fasterand may move out of position when trees aredragged over them. Also, if a geotextile is used,it may become torn and displaced by skidding.

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The length and width of a crossing optionneeded to achieve a particular wetland cross-ing will vary according to the site characteris-tics, soil strength, anticipated loads, andinstallation equipment available. The crossingoption used should cover the entire length ofarea to be crossed so that ruts do not developbeyond the end of the option. Ruts may causedrivers to steer the vehicle out of a wheel pathon the crossing option and to rut outside theedge of the crossing. On very weak soils thathave a low bearing strength (e.g., muck, peat),the options may need to be wider than what isrequired on other soils. The additional widthis needed to spread the weight over a largerarea. Additional width may also be needed atroad intersections and curves to providenecessary maneuvering room for vehicles.

Most of the options are best applied on roadsections with straight alignments, grades up to4 percent, and no cross slope. Steeper grades,cross slope, or curves may result in loss oftraction or lateral movement of the optionoutside of the planned travel area. Tractionloss may occur between the tires and thesurface of the option, especially when thesurface is wet. Slippage can occur between thecrossing option and the geotextile below it.Because most wetland crossing options have arough surface, they require a reduction ofvehicle speed. They should be placed in areaswhere the speed is low or where there is goodvisibility and plenty of distance to slow thevehicle.

For the options constructed from wood (e.g.,wood mats, wood panels, wood pallets), theground surface should be fairly level before

Figure 32.—Applying a geotextile under atemporary wetland crossing.

installation to reduce breakage of the woodmembers. Use of a dense hardwood speciesand treated timbers may extend the life of thecrossing. However, use of treated timbers maynot be cost-effective if the anticipated life anduse of the panels do not require that applica-tion (e.g., only a short-term use is anticipated,skidding material over the option). Also, bestmanagement practices for the use of treatedwood in aquatic environments should be used(WWPI 1996).

Each temporary wetland crossing option isbriefly described below. Rummer and Stokes(1994) also discuss some of these options. Aswith stream crossings, there are several waysto accomplish each of the various options.Appendix 3 includes further information aboutmany of the temporary wetland crossingoptions, including information about dimen-sions, product weight, and approximate pur-chase price. A list of some vendors of tempo-rary wetland crossing options is presented inAppendix 1.

Wood Mats

Wood mats are individual cants or logs cabledtogether to make a single-layer crossing (fig.33). A 10-ft- (3-m)-long, 4-in. x 4-in. (10-cm x10-cm) cant or log is the recommended mini-mum size. Longer cants or logs may be neededto distribute the weight better on very weaksoils or under heavy loads. Mason andGreenfield (1995) tested both 4-in.- (10-cm)-and 6-in.- (15-cm)-square cants on a silty sandsoil within the Osceola National Forest inFlorida. They found that while both matsworked well, the smaller mats cost less andwere lighter weight, facilitating on-site installa-tion.

Figure 33.—Wood mat.22

Constructing wood mats consists of drillingholes 1/4-in. (6.4-mm) in diameter througheach cant or log about 1 to 2 ft (0.3 to 0.6 m)from each end. Two 3/16-in. (4.8-mm) galva-nized steel cables are then threaded throughthese holes to form the mat. Loops should bemade at the end of each cable, extendingbeyond the last cant, and then secured with3/16-in.- (4.8-mm)-diameter cable clamps (fig.34). These loops are used to handle the matduring installation and removal. The connec-tion between the cants should be tight toreduce any rippling or “wave” movement thatmight occur when vehicles pass. Improperlytightened cable clamps can lead to slip andloss of connectivity within the mat. We notedthat a 10-ft x 12-ft (3-m x 3.7-m) mat con-structed from 4-in. x 4-in. (10-cm x 10-cm)material over deep, organic, muck soil devel-oped a rippling motion in front of the tires of amoving flatbed truck. This was caused by themat sinking into the soil in the area immedi-ately below the tire. We speculated that awider mat with the cants more tightly con-nected may have avoided this problem.

Figure 34.—Cable loop at the end of a wood mat.

Hislop (1996a) reported that it took threepeople up to 3 hr to cut, drill, and cable to-gether a 20-ft- (6.1-m)-long x 10-ft- (3-m)-widemat. To reduce drilling time and errors inmarking, she recommends making one set ofdrilling marks on the ground and ensuringthat several hand drills are available. A weld-ing torch or some other means of controllingcable end fraying will increase threading speed.The cost to initially construct a 10-ft x 12-ft (3-m x 3.7-m) mat using 4-in. x 4-in. (10.2-cm x10.2-cm) cants is about $200 (including about$40 for labor) and the mat can be expected tolast several years under normal use.

Individual mats can be connected to oneanother on-site to form the complete crossing.Limiting mat length to about 10 ft (3 m) re-duces weight and facilitates installation.Shorter lengths may be needed if the mats arewider than about 12 ft (3.7 m). During instal-lation, it is important to tuck the ends of allcable loops under the mats to avoid their beingcaught by a passing vehicle. If the surface ofthe crossing becomes slick during use, ex-panded metal grating (as described later in thisreport) can be added as a running surface toprovide traction.

Wood Panels

Two-layer wood panels can be constructed bynailing parallel wood planks to several perpen-dicular wood planks where the vehicle’s tireswill pass (fig. 35). The actual running surfacemay be on either side of the panel, unless thenails have gone all the way through it. Theindividual panels can be either preconstructedor constructed on-site. We constructed panelsusing 3-in.- (7.6-cm)-thick x 8-in.- (20-cm)-wide planks. A gap of about 1 in. (2.5 cm) wasleft between each plank during assembly.Each finished panel was 8 ft x 12 ft (2.4 m x3.7 m).

Figure 35.—Wood panel.

Annularly threaded (ring-shank) or helicallythreaded (spiral) spikes can be used to attachthe planks. For ease of construction, starterholes should be pre-drilled into the top board.To reduce withdrawal, spikes should be placedat slight angles from vertical with one spikeangled toward the traffic and one away from it.To facilitate picking up the panels duringinstallation and removal, loops can be createdby attaching 3/16-in.- (4.8-mm)-diameter

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galvanized steel cables to each section using3/16-in.- (9.5-mm)-diameter cable clamps.The initial construction cost of an 8-ft x 12-ft(2.4-m x 3.7-m) wood panel is about $150(including about $40 for labor). Connectorsand non-woven geotextile are extra.

Interconnecting adjacent panels in a crossingwill help minimize the rocking that occurswhen vehicles drive over the panels and willimprove the overall flotation provided by thecrossing. However, interconnecting panels willalso increase the time required for installationand removal of the crossing. Adjacent panelscan be interconnected using eye hooks screwedinto the end of each panel with quick links orother heavy duty connectors through thehooks. If the panels won’t be interconnectedwhen installed, about 6 in. (15 cm) should beleft between the individual panels to facilitateinstallation and removal.

Wood Pallets

Wood pallets for crossings are sturdy, three-layered pallets similar to those used for ship-ping and storage but specifically designed tosupport traffic (fig. 36). They are a commer-cially available product generally made fromdense hardwood planks that are nailed to-gether. They are specially designed so thatthey can interconnect, so that they are revers-ible, so that broken planks can be easilyreplaced, and so that nail points won’t surface.Some pallets are designed so that the top andbottom pieces are already interconnectedsimilar to a traditional pallet, while others aredesigned so that the top and bottom pieces areseparate and interlock during installation toprevent longitudinal movement.

Figure 36.—Wood pallet.

Hislop and Moll (1996) indicated that the widthof some commercial wood pallets is a disad-vantage. Interconnection along their 8-ft (2.4-m) edge is too narrow for hauling roads. Itmay be necessary to cut commercial pallets inhalf to make two 4-ft- (1.2-m)-wide x 14-ft-(4.3-m)-long pallets. Each half-pallet wouldthen be placed in a wheel path. Because thehalf-pallets weigh less, they are also lesscumbersome to install. However, the smallerpallets may become too narrow to supportequipment on undisturbed peat or very weakmineral soils. Pallets can be custom-made sothat the interconnection is along the 12-ft-(3.7-m)- or 14-ft- (4.3-m)-wide edge.

Most commercial pallets are designed to bemoved with a forklift, which is not a commonpiece of equipment in the woods. A thinchoker cable can be run between the planksand hooked to lifting chains to facilitate instal-lation with a front-end loader or backhoe(Hislop and Moll 1996). Before installation, theground surface should be fairly level to reducebreakage.

Bridge Decking

The decking of a timber bridge can be used tocross a small wetland area. Bridge paneloptions that do not have steel or wood string-ers, such as prefabricated stress-laminated,glulam, dowel-laminated, and nail-laminatedbridges, may be most appropriate and avail-able. Individual panels would be placed acrossthe area with soft soil and approach ramps tothe decking built.

Expanded Metal Grating

Machine weight can be distributed over abroader area by placing a rock crusher screenor a commercially available metal grating ontop of a geotextile, parallel to the direction oftravel (fig. 37). The two types of commercialgrating that have been tested are expandedmetal and deck span safety grating (Mason1992). Of the two commercial products tested,only the expanded metal grating is recom-mended. It is made of regular (not flattened),non-galvanized (carbon) steel and comes in avariety of thicknesses with different openingsizes. The grating is relatively light, inexpen-sive, and the surface is rough enough toprovide some traction.

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Figure 37.—Expanded metal grating over ageotextile.

Expanded metal grating can be installed byhand once it is moved to the crossing area.Various amounts of steel are used in expandedmetal grating, and it is sold on the basis ofweight/square unit of area. Although thelighter weight steel can be placed by oneperson, it is more susceptible to movement asvehicles drive over it. The heavier weight steelcan be placed by two people. Gloves arerecommended during installation and removal.It takes about 1 hr for four people to install100 ft (30 m) of geotextile and grating. Duringremoval, a winch may be needed to removesections if they become covered by tracked soil.

The grating sections will move during use ifthey are not interconnected. Adjacent sectionscan be connected using heavy duty connectors,such as quick links that are 3/8 in. (9.5 mm)in diameter or larger. Because the gratingsections are likely to bend into the shape of alarge shallow rut during use, they may need tobe flipped periodically or when placed at a newsite. This deformation of the grating does notharm it. A connector that is larger than 3/8in. (9.5 mm) will be easier to install and re-move if the grating becomes deformed. Acrescent wrench may be needed during instal-lation or removal of the quick links becausesoil will make it more difficult to close andopen the link. Hislop (1996a) indicated thattheft of the metal grating was a problem duringtests in Florida.

PVC and HDPE Pipe Mats or Plastic Road

A portable, reusable, lightweight corduroy-typecrossing can be created with PVC or HDPEpipe mats (fig. 38). An important advantage of

Figure 38.—PVC or HDPE pipe mat in a road.

using pipes is they provide a conduit for waterto move through the crossing without furtherwetting the area. A pipe mat is constructedusing 4-in.- (10.2-cm)-diameter Schedule 40PVC or SDR11 HDPE pipes that are tightlyconnected using 3/16-in.- (4.8-mm)-diametergalvanized steel cables to form panels (fig. 39).A plastic road (fig. 40) is similar to pipe mats,except that pipe transition mats/panels arebuilt into the design to ease the transition oftires ramping up and then back down again onthe approach between the firm soil and themat. Also, the various pipes in a plastic roadare connected using 1-in.- (2.5-cm)-diameterSchedule 80 PVC. Complete instructions forconstructing a plastic road mat are presentedin Moll and Hiramoto (1996). It is important todrill round holes to avoid creating potentialstress points that could facilitate pipe shatter-ing.

Because standard PVC pipe is light-sensitiveand will lose strength when exposed to sun-light, using PVC pipe that has been exposed to

Figure 39.—PVC or HDPE pipe mat.

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the sun should be avoided. Strength of thecrossing can be maintained by covering orpainting PVC pipe or by using an ultraviolet-resistant type of pipe, such as HDPE. HDPEpipe also tolerates temperature extremes of-40° F (-40° C) better than PVC without becom-ing brittle or losing shock resistance and willreturn to its original shape after being de-formed (Légère 1997). No published studieshave evaluated the use of PVC or HDPE pipemats or the plastic road option for wetlandcrossings during the winter in an environmentwhere temperatures are consistently belowfreezing.

HDPE pipes may be more expensive thanstandard PVC and may need to be purchasedthrough a vendor that specializes in plasticpipe sales. The thickness of many alternativeplastic pipes is often specified using the term“standard dimension ratio” (SDR), which iscalculated by dividing the average outsidediameter of the pipe by its minimum wallthickness. For any given outside diameter,SDR will increase as wall thickness decreases.

Moll and Hiramoto (1996) reported that PVCplastic road panels and transition mats for an8-ft- (2.4-m)-wide x 40-ft- (12-m)-long crossingwere transported in a 3/4-ton pickup truckand assembled by two people in about 1 hr.Material costs for that crossing, including thenon-woven geotextile, were about $2,000. Thevarious panels in either the pipe mat or theplastic road crossing can be quickly hand-placed by two people. A tractive surface, suchas expanded metal grating or wood panels,may be necessary depending on the length ofthe crossing and the grade. Once installed, theplastic road can be moved from site to site by

Figure 40.—Plastic road mat.

attaching a chain to one end of the transitionmats and then towing it with a pickup truck orlogging equipment. The distance and surfaceover which the plastic road is dragged shouldbe evaluated to avoid excessive wear andbreakage. A prototype plastic road installationsupported over 400 loaded 18-wheel log truckpasses at two sites.

Tire Mats

A mat or panel of tires can be created byinterconnecting tire sidewalls and/or treadswith corrosion resistant fasteners (figs. 41 and42). Mats of varying length and width can bedeveloped. Consideration of the weight thatcan be handled by on-site equipment duringinstallation and removal is important whendeciding on mat length and width. Somedesigns include double layers of sidewalls,while others use a layer of treads topped bysidewalls. The mats conform to the area afterplacement. Anchoring may be needed toprevent lateral movement during use, espe-cially in areas with a grade over about 5 per-cent. The mats can be dragged into place witha skidder or installed using a knuckleboomloader. Tire mats can be placed on top ofgeotextile or corduroy to provide additionalflotation. However, if a skidder will be used todrag the tire mat into place, geotextile is notrecommended due to the likelihood of bunch-ing and tearing of the fabric. No runningsurface is needed over the mat, although gravelcan be added to improve traction (MacGregorand Provencher 1993).

Mason and Greenfield (1995) reported thatbecause the mats are heavy, large, and veryflexible, on-site installation time can take

Figure 41.—Tire mat.

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Figure 42.—Another tire mat design.

about 15 minutes to more than 1 hr per mat.Maneuvering room and the type of equipmentused are critical to the amount of time requiredfor placement. Placement is easier without thegeotextile because the mats can be draggedinstead of lifted into place. However, this willresult in the loss of the separation and supportprovided by the geotextile. When installing themats with a clam loader, it is important thatthe clam not close on any of the fasteners (e.g.,bolts) used to connect the individual sectionswithin a mat. Once the bolts are bent, the matis more susceptible to coming apart, life ex-pectancy is reduced, and/or its strengthcharacteristics are diminished.

Overall site impacts will be reduced duringinstallation and removal by having the properequipment on-site to handle the mats andthrough the use of lighter mats. To the extentpossible, installation machinery should workparallel to the direction of the crossing insteadof perpendicular to it so that disturbance isminimized. However, depending on the con-figuration of the mats and the particular areawhere they are to be installed, they can beeither positioned in front of the installationequipment, laid from a perpendicular position,or dragged into place.

Corduroy

Corduroy is a crossing made of brush, smalllogs cut from low-value and noncommercialtrees on-site, or mill slabs that are laid perpen-dicular (most often) or parallel to the directionof travel (fig. 43). The effect of corduroy is tospread the load over the whole length of the logor slab, effectively increasing the load-bearingarea. Flotation increases with increasingsurface area, especially length, of the indi-vidual pieces of corduroy. Multiple layers ofcorduroy may be required in some crossings.Brush corduroy will provide less flotation thansmall logs or mill slabs (Arnold and Gaddum1995).

Figure 43.—Corduroy.

Corduroy is not normally covered with fill.During installation, application of a non-wovengeotextile is recommended to separate thebrush, logs, or mill slabs from the underlyingsoil. The use of geotextile should result in lesscorduroy being required to accomplish thecrossing. To facilitate removal of temporarycorduroy, two cables can be laid below andperpendicular to the corduroy before installingthe crossing. The ends of each cable wouldthen be joined with a cable clamp or similardevice forming two large cable loops. Theloops are then pulled out after use of thecrossing with available on-site machinery.Corduroy is usually not removed or reused,however.

Pole Rails

When attempting to support skidding or for-warding machinery equipped with high flota-tion or dual tires, one or more straight hard-wood poles cut from on-site trees can be laid

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parallel to the direction of travel below eachwheel (fig. 44). The poles can either be with orwithout limbs. If the poles are not delimbed,more flotation will be provided at the top ofthe tree where the diameter is smallest. Thediameter of the poles should not exceed about10 in. (25 cm) on the large end so that theypenetrate the wet area to a sufficient depththat the tires come in contact with the soil.Two or more poles may need to be laid parallelto each other if only small diameter material isavailable or if sufficient flotation is not pro-vided. If dense hardwood poles are used,large limbs facing upward may need to beremoved to minimize the chance of puncturesand other tire damage.

For a crossing that is longer than the length ofone pole, additional poles may need to be laidin a linear manner. The larger end of the pole,or the top of the tree for full-tree material,should be placed in the end of the crossingwith the weakest soil to maximize flotation.After placing the poles, it is important to driveacross them a few times without carrying aload to get them properly seated in the soil.Remove the poles when there is no furtherneed to cross the wet area. This option will

Figure 44.—Pole rails.

not work well if the machinery is equipped withconventional width tires because they are toonarrow and are operated at too high a pressureto stay on top of the poles. It takes about 15minutes to build a 40-ft- (12-m)-long pole railcrossing using two precut 40-ft- (12-m)-longpoles.

Wood Aggregate

Wood particles ranging in size from chips tochunks (fist-size and larger) can be used as afill material for crossing soft soils (fig. 45).There are several advantages to using woodaggregate in wetland crossings. Wood isrelatively light, giving it better natural flotationthan other materials, such as gravel. Lowgrade, unmerchantable wood that is normallyleft in the woods can be used. Low grade woodcan be easier and cheaper to obtain in areaswhere no gravel deposits exist. Also, wood willnaturally biodegrade over time, eliminating theneed to remove it from the crossing followinguse (wood aggregate is not considered reus-able). Finally, chunk-size wood aggregateallows water to flow freely through it, causingno changes to natural hydrologic flows. Al-though chunk-size particles are better for fillmaterial than chips, chips are more readilyavailable as chunking machines have not yetbeen commercialized.

Figure 45.—Wood aggregate.

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The depth of aggregate needed will depend onsoil conditions at the site. Saturated organicand mineral soils generally require at least 12in. (30 cm) of aggregate. Less is generallyneeded to stabilize soft sand. Wetzel (1997)describes the use of green wood fuel chips tostabilize haul roads on deep sand soils innorthwest Florida. The chips were spread to adepth of 6 in. (15 cm). The cost of stabilizingthis road with wood chips was about half thecost of using gravel.

Wood aggregate can be used with or withoutgeotextiles underneath (fig. 46). A layer ofgeotextile will improve performance on any softsoil, reducing the depth of aggregate needed.Provencher (1991) recommends the use ofgeotextile over organic soils. The use ofgeotextile is more critical over deep, saturated,organic soils where the root mat suppliesmuch of the support. In this case, a heavygeotextile with at least 24 in. (61 cm) of aggre-gate is recommended (Arola et al. 1991). Thiskeeps the aggregate from being forced downthrough the root mat. Another layer ofgeotextile should be placed over the aggregate(MN DNR 1995), creating a floating subgrade,with additional surfacing placed on top.Surfacing may also need to be added duringuse to maintain acceptable performance. Ifuse of the road is meant to be short-term,biodegradable geotextile should be used.

Mullis and Bowman (1995) evaluated severalsawmill-generated wood aggregate materialsfor rutting potential and road stiffness. Awoodwaste material depth of 18 in. (46 cm)was able to carry construction traffic in themuskeg areas but did not seem to provide a

Figure 46.—Use of a geotextile under woodaggregate.

significantly stable base for extended use.Depths of woodwaste material greater than 24in. (61 cm) performed well. It was noted thatsawdust tended to break down under trafficloading. When sawdust was predominant inthe section, deeper rutting tended to occur.Planer chips did not compact very well. Barkfibers tended to form a well-compacted layer.The woodwaste seemed to perform the bestwhen placed in a good mixture of sawdust,planer chips, and bark fibers. Mullis andBowman (1995) recommend frequent mainte-nance to repair the rutting and low-frequencywashboarding that developed on the testsections.

Low Ground Pressure Equipment

The pressure exerted by a machine on theground surface will affect trafficking abilityand site impacts. Low ground pressure equip-ment reduces this pressure by reducing overallmachine weight, or by increasing the contactarea between the equipment and soil, spread-ing the weight over a larger surface area. Byreducing ground pressure at each contactpoint, equipment flotation is enhanced, trac-tion is usually improved, and road mainte-nance requirements, such as grading, can bereduced. Low ground pressure equipment canalso reduce rut depth and compaction, andcan result in reduced fuel consumption.

Ground pressures of less than 5 or 6 PSI (34 or41 kPa) are often considered high flotation.For reference, a typical adult applies about 3PSI (28 kPa) to the ground when standing.Ground pressures lower than 4 PSI (28 kPa)may be needed to operate on wetland soilswithout significant impacts. The principaloptions for achieving low ground pressure onin-woods equipment include use of machineswith wide tires, duals, tire tracks, bogies,tracks, light weight, and/or central tire infla-tion (CTI). CTI is an option for use on haulingtrucks and may become available for in-woodsequipment in the future.

Clambunk skidders and tree-length forwarderscan move large loads while exerting a lowground pressure. A conventional cable skiddercan operate like low ground pressure equip-ment on ground with intermittent soft spots byreleasing its load, crossing to better ground,and winching the load back to the machine.Aerial systems that can either partially or fully

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lift logs off the ground, such as skyline cablesystems, helicopters, and balloons, may also bean option.

While reducing load size when skidding, for-warding, or hauling is an option that doesn’trequire additional equipment or the retrofittingof existing machinery, many operators arereluctant to do this because of the loss inproduction and the resulting higher productioncosts. Forwarders may be able to maintainacceptable productivity and costs under situa-tions where a reduced load is needed. Becausea specific volume of material may need to bemoved when skidding, forwarding, or hauling,more trips will be required to transport thatvolume under the reduced load scenario.Therefore, the net reduction in site impacts maybe minimal.

A potential problem with low ground pressureequipment is that operators may build largerloads, given their increased traction and flota-tion. In weak soil conditions, this could resultin impacts similar to traditional equipment.Therefore, the net positive environmental effectcould be minimal unless operators keep theirload size properly adjusted for soil conditions.Also, as machinery becomes bigger and heavieradditional ground contact area is required tomaintain the same ground pressure as smallerequipment with narrow tires. Therefore, asequipment gets bigger, the minimum size ofhigh flotation tires will need to be increased tocompensate for the added weight.

Equipment with wide tires, duals, bogies,and/or tire tracks

Wide tires, duals, bogies, and tire tracks im-prove flotation and mobility in soft ground byspreading the machine and load weight over alarger surface area. Wide (or high flotation)tires are wider than conventional tires (fig. 47).They are usually considered wide tires at about34 in. (0.9 m) and are available up to about 72in. (1.8 m) wide. Dual tires consist of twoconventional width tires mounted on each endof an axle (fig. 48). Dual tires may be used onone machine axle (e.g., front or back axle,usually the back) or on all axles. It is alsopossible to add wrap-around tracks to existing,individual, conventional width rubber tires tomake them wider (fig. 49). As an example,tracks can extend the width of a 30-in. (0.76-m)tire to either 42 in. (1.1 m) or 53 in. (1.3 m) andextend a 44-in. (1.1-m) tire to 65 in. (1.6 m).

Figure 47.—Wide tires.

Figure 48.—Dual tires.

Figure 49.—Tire tracks.

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Although flotation is improved with wide tiresand duals, these options have several disad-vantages. The cost of purchasing and usingwide tires and duals can be significantlygreater than the cost of conventional tires. Agood portion of this cost can be attributed tothe heavy duty axles and transmissions thatare usually required to carry the extra loadfrom these tires. Because these options taketime to install and remove, operators may keepthem on the machines longer than necessary,reducing useful life and increasing costs. It ismore difficult to transport machinery with widetires and duals over some roads becauseoversize permits may be required. It may alsobe difficult to move equipment with wide tiresdown narrow roads or roads that have gates onthem, unless the gate posts are wide enoughapart or unless the machinery can go off theroad around the gate. The turning radius ofequipment outfitted with wide tires or duals isnormally greater than that of conventionallyequipped machinery.

A bogie is an axle system in which two tandemwheels with independent axles are mounted ona rocker frame and axle (fig. 50). If the wheelsare driven, the bogie frame contains the appro-priate devices to drive each wheel on theassembly. The bogie functions in two ways toreduce impacts to the site. First, the extrawheel adds contact area, reducing staticground pressure. Second, the rocking actionof the bogie frame allows better contact withthe broken ground surface, improving tractionand lowering impacts. Further improvementsin traction can be made by installing tiretracks around the adjacent tires on the bogie(fig. 51). These tracks are usually made ofrubber with steel reinforcement. They arefairly easy to install and remove, especially

relative to wide tires and duals. Also, tiretracks can be used on bald, worn-out tires toimprove traction and extend their useful life.

Equipment with tracks

Tracked machines distribute the weight of themachine and load over steel or rubber tracks(fig. 52). These tracks are usually between 18and 36 in. (46 and 91 cm) wide and 8 to 14 ft(2.4 to 4.3 m) long on each side of the ma-chine. This provides a large area over which todistribute the weight of the machine and load,normally resulting in lower ground pressuresthan conventional equipment and betterflotation. A disadvantage of these machines inskidding is they often travel at slower speedsthan rubber-tired machines, which reducesproductivity, especially for long skiddingdistances. Tracks are more commonly foundon felling equipment where speed of movementis not as important, especially for designs thatreach out to the tree. These designs also lowerimpact by not having to traverse as much ofthe site to access the area.

Figure 50.—Bogie system.

Figure 51.—Tire tracks on a bogie.

Figure 52.—Tracked machine.31

Lightweight equipment

Lightweight equipment reduces ground pres-sure by reducing the weight of the machinery.In many cases, there is little change in contactarea with the soil surface as compared totraditional-size equipment. An added benefitof smaller equipment is better maneuverability,which results in less damage to the remainingvegetation. This is especially important inthinning and partial cutting, which is becom-ing more prevalent across the country due topublic concerns. By reducing the weight of themachinery, the machinery’s ability to movelarge loads is also reduced. As a result,smaller, lightweight equipment has not beenpopular with producers in the past becausethe smaller loads have resulted in lower pro-ductivity and profitability. This will probablychange in the future as land managers andlandowners begin specifying the use of light-weight equipment to lessen impacts on theirforests.

Equipment with central tire inflation

Central tire inflation (CTI) technology is a lowground pressure option for use on haulingvehicles equipped with radial tires (fig. 53).Most log trucks operate with very high tirepressure (around 100 PSI [690 kPa]) to allowheavy loads to be transported at highwayspeeds. However, problems such as damage tothe road surface (Bradley 1993 and Hodges etal. 1987) can develop on unpaved roads duringuse of these high pressure tires. CTI allows adriver to automatically and uniformly vary theinflation pressure of a truck’s tires while thevehicle is moving. With a CTI system, the tirepressure can be lowered to yield a tire with a

larger footprint area (fig. 54), which reducesthe vehicle pressures applied to the ground.As an example, the typical footprint length of atire with 100 PSI (689 kPa) is 8 in. (20.3 cm),whereas the footprint of a tire inflated to 43PSI (296 kPa) is 13 in. (33 cm) (Anonymous1993, Greenfield 1992). That larger footprinttranslates into better flotation, increasedtraction, and reduced rutting in wet areas(Bradley 1997). The cost to retrofit a vehicledepends on the number of axles that are to beretrofitted. For an 18-wheel log truck with athree-zone system, the cost will probablyexceed $16,000.

ECONOMIC CONSIDERATIONSFOR CROSSING OPTIONS

The temporary and portable crossing optionsidentified in this paper differ greatly in cost.Some can be assembled on-site using nativematerials, while others require more sophisti-cated design and assembly, available primarilyfrom commercial vendors. Each option has alimited range of conditions and applications

Figure 53.—Central Tire Inflation (CTI) system. Figure 54.—Tire footprint at two pressures.

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under which it is most effective. Severaloptions may be considered effective for anyparticular application. Selecting the option(s)that best fit the normal applications andoperating conditions for your company oragency requires careful consideration of manyshort-term and long-term factors. Investing incrossing options can control or reduce overalloperating costs.

For example, a log stringer bridge constructedon-site may have the lowest initial cost, but astress-laminated panel bridge that can be usedand reused for several years may be the cheap-est option over the long term. Internal factorsaffecting overall cost include initial cost;reusability; average time to replacement; time,labor, and equipment required for construc-tion, installation, and removal; safety; andoperational efficiency and effectiveness. Exter-nal factors driving these decisions includeproduct availability, public policy, regulatoryagency acceptance, market conditions, andother site specific conditions or considerations.All these factors must be weighed carefullyagainst actual out-of-pocket costs to determinethe best long-term choices.

Most organizations invest in the options theyanticipate using most often or that best meettheir immediate need. Some options are tooexpensive for many companies or agencies toinvest in, even though they may be the safestand most effective option for their needs. Thismay be because the initial cost is beyond theirfinancial resources, or because the frequencyof use is too limited to justify the major invest-ment. Investment in a portable steel bridgemay be one example. In these situations, itmay be desirable for larger forest productscompanies and land management agencies topurchase these items and make them availablefor loan or rent to smaller organizations.

ENVIRONMENTAL IMPACTS ASSOCIATEDWITH CROSSINGS

Environmental impacts associated with abroad range of forest management practices inareas near streams, and to a much lesserextent wetlands, have been extensively studied.These impacts can affect the aesthetics, biol-ogy (e.g., presence of plant and animal species,biomass), physical characteristics (width,depth, and shape of the stream or wetland,

stream channel stability), temperature, andchemical composition (e.g., pH, turbidity,6

conductivity7) of water bodies. Some of thereports that have summarized impacts frommany studies include Brown and Binkley(1994), Campbell and Doeg (1989), Kahl(1996), Marcus et al. (1990), Meehan (1991),Salo and Cundy (1987), and Ward (1992).

Unfortunately, little information exists thatfocuses specifically on the environmentalimpacts associated with stream or wetlandcrossings. Most of the literature relates to theuse of round culverts. Few studies haveaddressed the effect of stream crossings onstream quality other than from the standpointof sedimentation. Few studies have examinedimpacts associated with the removal of thetemporary crossings or have compared thelong-term impacts associated with using a fordversus a temporary bridge. Questions stillremain about what type of and how muchimpact is acceptable. The information thatfollows summarizes some of the studies thathave reported environmental impacts resultingfrom these crossings.

Background

Where a stream bank becomes destabilized asa part of constructing or removing a crossing,sedimentation can become a problem, espe-cially in lower gradient systems that respond toincreased flow by increasing stream width.Such problems will likely be more persistentthan those associated with just the roadcrossing itself (Everest et al. 1987, Sullivan etal. 1987). Sedimentation is a concern instreams because of the change in habitat forfisheries and benthic fauna, and because ofphosphorus input associated with soils andsediment. Establishing the crossing at an areawith a stable stream bank and providingadequate bank protection are critical.

When a culvert crossing fails, extensive localscouring occurs with deposition and additionalerosion downstream (Furniss et al. 1991).Culvert crossing failures that divert streamflowinto nonstream areas are particularly damag-ing (Weaver et al. 1987).

6 Volume of suspended solids.7 Electrical resistance due to dissolved solids.

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Sediment can have lethal impacts on fish inseveral ways (Ward 1992):

• Increased suspended sediment limitsphotosynthesis of algae and rooted aquaticplants by reducing sunlight penetration intothe water. This limits production of food foraquatic life.

• Spawning beds for many species (e.g.,walleye, whitefish, brook trout) consist ofcobble or gravel substrate where the eggsfall into the interstitial spaces betweenstone particles. In these spaces, the eggsare protected from predators while waterflow ensures the exchange of gases neededfor survival. Sediment from constructionsites can change the substrate by blockingthe spaces and reducing or destroyingproductivity.

• Suspended sediment can cause changes infish feeding behavior because prey is lessvisible.

• Suspended sediment can harm incubatingfish eggs or fry and reduce the abundanceof insect larvae, a food source for fish.Many fish eggs have an adhesive surface towhich suspended sediment can attach andblock gas exchange, causing the egg tosuffocate.

• High levels of suspended sediment lastingfor many days can cause direct fish mortal-ity.

In addition, all fish species do not spawn atthe same time. While some species spawn inthe spring, others spawn in the fall and theeggs then hatch during the following spring.Because fish spawn at different times andareas with cobble or gravel are a preferredspawning area for some species, any in-streamactivity can impact fish habitat and popula-tions.

Fish are particularly sensitive to changes inwater quality, temperature, and oxygen.Suspended sediments can abrade or clog gillfilaments and reduce visibility of insects, thusreducing feeding success. A comparative post-logging study of 10 moderate gradient (0.3 to 3percent) streams in New Brunswick and NovaScotia found a significant reduction in thebiomass of Atlantic salmon, brook trout, andbrown trout at stream crossings (Grant et al.

1986). It has been reported that a 17 parts permillion (ppm) increase in sand bedload resultsin a 10 lb per acre decline in trout populations(Alexander and Hansen 1983).

The immediate effects of in-stream disturbancefrequently cause fish populations to decline.Generally, these effects last less than 10 yearsand often only a year or two (Gregory et al.1987). Within a watershed, the cumulativeeffects of multiple crossings or other distur-bances may be more persistent. In contrast tomost authors, Everest et al. (1987) suggestthat some fine sediment may be beneficial totrout and salmon (salmonids) by contributingto increased invertebrate productivity, and thatthe adverse consequences of fine sedimentintroduction to trout streams have been over-stated.

Crossings can cause loss of fish habitat within,above, or below the crossing (Marcus et al.1990). Improperly designed and installedculvert crossings can block fish migrationroutes. Common problems include outfalldrops that are too great, lack of resting poolsbelow culverts, excessive water velocities, orinsufficient water depth within culverts.Anderson and Bryant (1980) published anannotated bibliography of fish passage at roadcrossings. A number of considerations neces-sary to minimize potential effects of culvertcrossings on salmonids have been suggested(Yee and Roelofs 1980). Culvert and bridgeinstallers also need to consider whether theyare creating an obstruction of a navigablewaterway.

A stream adjusts its geometry to accommodatethe water and sediment it carries. When theamount of water or sediment a stream mustcarry increases, channel geometry mustchange to accommodate the increase. Whenchannel geometry is artificially changed, suchas by an incorrect stream crossing, the streamwill adjust by altering its geometry upstream ordownstream of the change (Furniss et al.1991). Road crossings that modify and restrictstream geometry least, such as bridges or low-water fords, are likely to have the least adverseeffects on channel geometry.

Using treated wood products in and aroundwater bodies can cause toxic substances toleach into the water. Best Management Prac-tices for the use of treated wood near waterhave been developed (WWPI 1996). These

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practices should be followed when usingtreated wood in temporary crossings.

Studies of Stream Crossings

Thompson et al. (1996) evaluated sedimentproduction from two gravel-bottom fordslocated on third-order streams in the TalladegaNational Forest in Alabama. Both permanentfords were being used for occasional adminis-trative traffic before being cleaned out andgravel added in preparation for a timber har-vest. Results from background samples takenbefore the sites were disturbed indicated thatthe old existing fords produced little sedimentat base flow rates. The base flow rate duringwinter months ranged from 0.0038 m3/sec to0.051 m3/sec for Ford 1 and from 0.0018 m3/sec to 0.049 m3/sec for Ford 2. During therenovation of the fords, the peak sedimentconcentration increases were 2,810 mg/l and1,355 mg/l for Fords 1 and 2, respectively.Mean sediment concentration increases were359 mg/l and 353 mg/l for Fords 1 and 2,respectively. The total sediment produced was116.8 lb (53 kg) for Ford 1 versus 35.3 lb (16kg) for Ford 2. The difference in sediment loadwas due to differences in stream flow rates.

Thompson et al. (1996) reported that the firststorm after renovation of the two fords pro-duced higher sediment loads than duringconstruction. The rainfall, which measured12.78 cm over a 50-hr period, resulted in peaksediment concentration increases of 585 mg/land 745 mg/l for Fords 1 and 2, respectively.Total sediment produced at Fords 1 and 2during the storm event was 2,107 lb (956 kg)and 374.7 lb (170 kg), respectively.

Tests showed that when a pickup truck drovethrough Ford 1 at base flow rate conditions,sediment concentrations increased by as muchas 255 mg/l (10 minutes after the vehiclespassed through the ford) and 110 mg/l (25minutes after the vehicles passed through theford) at sampling points that were 148 ft (45 m)and 302 ft (92 m) downstream, respectively,from the lower edge of the ford (Thompson etal. 1996). Sediment concentration levelsreturned to normal within 1 hr after the ve-hicles passed through the fords. It was pro-jected that heavier vehicles with more wheels,such as log trucks, might generate moresediment load than the light vehicles used inthe tests.

Water quality was monitored while installing aford with a bulldozer in a stream with a moder-ate current (2.3 ft/s) [0.7 m/s] and a hardbottom (limestone bedrock, limestone cobble,and gravel) in Michigan (White Water Associ-ates, Inc. 1996). Sampling stations were setup 66 ft (20 m) upstream of the ford (control)and 33 ft (10 m), 82 ft (25 m), and 164 ft (50m) downstream. A total of 33 samples werecollected at each station. The control stationhad significantly lower sediment load than theother stations (p<0.001). The total sedimentloads produced by the ford installation at thestations 33 ft (10 m) and 82 ft (25 m) down-stream were about 1,570 lb (710 kg) and 1,030lb (470 kg), respectively. The total suspendedsediments returned to near zero soon afterdiscrete disturbance events occurred. Theinterval between disturbance and return tonear background level took about 18 minutesfor the two disturbances that had sufficienttime between them and the next disturbance.

Water quality was monitored while installing aculvert on a stream that was 7.2 ft (2.2 m)wide, 9.3 in. (24 cm) deep, flowing 0.63 ft/s(0.19 m/s), and discharging 3.5 ft3 (0.1 m3) ofwater per second (White Water Associates, Inc.1997). Monitoring stations were established atpoints 66 ft (20 m) upstream of the culvert(control) and at 33 ft (10 m), 82 ft (25 m), 144ft (45 m), 331 ft (100 m), and 427 ft (130 m)downstream. Highly significant increases insediment load were noted for each stationexcept the one that was 427 ft (130 m) down-stream, which had sediment loads that wereequivalent to the upstream control. It wasestimated that 482 lb (220 kg) of sedimentwere deposited between the stations 33 ft (10m) and 427 ft (130 m) downstream of theculvert installation.

In a study conducted on Horse Creek in Idaho,12.3 lb (5.6 kg) of sediment were contributed toa stream when right-of-way timber and debriswere cleared from the stream channel and atemporary culvert was installed (USDA ForestService 1981). When a permanent culvert wasinstalled after the stream was diverted aroundthe construction site, 0.2 lb (0.1 kg) of sedi-ment were contributed to the stream as com-pared to 46 lb (20.9 kg) for a similar culvertinstallation where the water was not diverted.

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Hornbeck et al. (1986) reported turbidity levelsof 2,200 and 3,300 Jackson TurbidimeterUnits (JTU) for a skid road culvert crossing inNew Hampshire. A value of 10 JTU or lessusually is considered desirable for drinkingwater. The high values, which occurred duringsummer harvesting activities, resulted fromfailure of the culvert.

Mason and Greenfield (1995) provide observa-tional information about potential impacts dueto PVC pipe bundle crossings. They indicatethat soil may be picked up and later depositedinto the stream if the crossing materials werestored on the ground before installation. Also,small fragments of pipe from cutting anddrilling may remain inside the pipes and bedeposited in the stream. During removal of aPVC pipe bundle crossing, sediment that hadsettled on the surface of the pipes can enterthe stream. Removal of the geotextile causeddisturbance. Indentations of about 0.5 in. (12mm) were noticeable at the stream edges uponremoval of a 25-ft- (7.5-m)-wide PVC pipebundle crossing that was crossed once with aloaded 80,000 lb (36,230 kg) lowboy.

During two demonstrations that we conducted,depressions of about 0.5 in. (12 mm) werecaused by a PVC pipe bundle crossing afterabout 20 passes with a loaded forwarder.When we used wood mats on the approaches,maximum rutting was about 0.5 in. (12 mm)as compared to areas beyond the approacheswhere maximum rut depth was about 8 in. (20cm). No sediment was observed being stirredup while the pipes were being removed. How-ever, removal of the geotextile did stir up asmall amount of deposited sediment. Fisheriesand waters biologists were impressed by theminimal impact caused by the crossing.Légère (1997) reported similar findings for twocrossings where HDPE pipe bundles wereinstalled. In one test, 70 passes were made bya forwarder. In the second test, 40 passeswere made with a cable skidder.

Hassler et al. (1990) reported that there wereno statistically significant differences betweenturbidity, pH, and conductivity samples takenabove and below a stress-laminated timberbridge crossing. Thompson et al. (1994, 1995)reported that culverts contributed more sedi-ment to the stream during installation andremoval than the bridge crossings, which didnot contribute any sediment. Pierce et al.(1993) noted that bridges usually are preferred

because culvert installation and removalcauses channel disturbance and producessediment and turbidity.

Taylor et al. (1996) reported that the installa-tion and removal of several glulam bridges wasaccomplished without operating any equip-ment in the stream or disturbing the streamchannel or banks. Based on a visual ap-praisal, the authors reported no adverseimpacts on water quality. Keliher et al. (1995)reported that some debris fell into the streamduring skidding over a glulam bridge thatconsisted of two separate longitudinal panels.The 2-ft (0.6-m) gap between the bridge panelswas partially filled with logs to reduce theamount of soil and vegetation dragged into thestream during skidding.

Without specifying the type of crossing thatwas constructed, Swift (1988) reported thatroad crossings over streams are the mostcritical points on a road because fills arelarger, the road drains directly into the streamsystem, and opportunities for mitigatingpractices are limited. As an example, theauthor refers to three roads built in one water-shed within the Coweeta Hydrologic Laboratoryin western North Carolina during 1976 at adensity of 1.26 mi/100 ac (5 km/100 ha).During the first year, all sediment collected ina stream weir originated from the roads, mostof it from eight stream crossings during thefirst 2 months after construction began. Sedi-ment measurements immediately below onecrossing showed a cumulative total of 267.7tons of soil entering the stream from each acre(600 metric tons of soil from each hectare) ofroadway during those 2 months and 357 tonsfrom each acre (800 metric tons from eachhectare) of roadway in the first 2.5 yearsfollowing construction of the crossing. About80 percent of the soil washed into the streamremained in the channel and had not reachedthe weir located 2,362 ft (720 m) downstreamafter 2.5 years. However, portions of thosedeposits were still being transported out of thestream system 8 years later.

A series of 1-day post-harvest assessments of78 recently completed timber harvesting siteswas conducted in Vermont to evaluate Accept-able Management Practice compliance, soilerosion extent, and water quality impacts(Brynn and Clausen 1991). The crossings wereaccomplished with either a metal or woodenculvert, ford, bridge, or brush. Some of the

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crossings were permanent. Comparisons ofimpacts between crossing types were notconducted. Over 60 percent of the crossingswere made by a ford. Stream crossing sedi-mentation and debris were above backgroundlevels on 57 and 55 percent of the sites, re-spectively. The impacts of increased woodydebris were judged not to be major.

Brynn and Clausen (1991) reported thatstream crossings for trucks on perennialstreams had adequately sized bridges orculverts 60 percent of the time. Also, 60percent of the fords had stable approaches andstream beds. Stream crossings were made atright angles 81 percent of the time. Temporarystream crossing structures were removed andthe channel restored 77 percent of the time.The study recommended that stream crossingsover brush or pole fords8 should not be allowedbecause the brush was infrequently removedand restoration may result in increased sedi-mentation. The seeding and mulching of thestream crossing approaches was completed ononly 2 percent of the sites. Newton et al.(1990) recommended that fords of perennialstreams should not be allowed except underunusual circumstances (e.g., the crossing istoo wide for any other option).

Suspended solids and turbidity were evaluatedfor several stream crossing options on haulroads and skid trails at two locations in Penn-sylvania (Tornatore 1995, Tornatore et al.1996). At one site, four skidder crossings wereinstalled: a culvert with shale fill, a culvertwith log fill,9 a portable hinged steel bridge,and a plastic ford that was constructed using aGEOWEB® cellular confinement system with

shale fill underlain by geotextile fabric. Anunmitigated crossing was also evaluated atthat site by having a bulldozer pass directlythrough the stream at an area with a rockybottom and a gradual approach. At the secondsite, three hauling crossings were installed: aculvert with gravel fill, a bedrock-based gravelford, and a wooden cross-tie bridge that usedrejected railroad ties as the cross supports andoak lumber spaced 2 in. (5 cm) apart for thedecking. Stream samples were taken at sitesabove and below each crossing before, during,and after installation, during the use of thecrossings, and during high flows due to snowmelt.

Tornatore (1995) and Tornatore et al. (1996)reported that installation of all skidder cross-ings at the first site caused significant in-creases in suspended solids and turbidity. Thelevel of impact to the stream was less severeduring installation of the portable bridgeversus the culvert. Installation impacts werereduced to insignificant levels within 24 hrfollowing bridge installation versus 96 hrfollowing installation of the culvert with the logfill.

Increases in suspended solids occurred down-stream from all skidder crossings at the firstsite (Tornatore 1995, Tornatore et al. 1996).Increases below the portable bridge appearedto be a result of debris (leaves, twigs, and bark)falling through gaps in the bridge planking.Despite this, the portable steel bridge showedlower increases in suspended solids thaneither the culvert with shale fill or the culvertwith log fill. To reduce debris, it was recom-mended that the bridge deck be kept reason-ably clean. The culvert with shale fill per-formed better than the culvert with log fill.Suspended solids below the culvert with log fillresulted primarily from increased inorganicsediment that may be related to the stability ofthe approach area and stream bank. Twoskidder passes made within 15 minutes ofeach other at the unmitigated ford crossingincreased sediment solids by 350 times.

The ford with the GEOWEB® cellular confine-ment system protected and supported whatotherwise would have been a wet, muddydepression in the haul road (Tornatore 1995,Tornatore et al. 1996). Use of the gravel-basedford resulted in greater increases in suspendedsolids and turbidity on haul roads than the

8 The poled ford (also known as corduroy) wasinstalled by filling the stream with logs or poles thatwere longer than the width of the equipment usingthe crossing. The poles were laid parallel to the flowof the stream with sufficient space between logs toallow the stream to pass through. To improve streamflow through the ford, two 10-ft- (3-m)-long sections of16-in.- (41-cm)-wide ductile iron pipe (a high-carbonpipe designed to withstand pressurized gas) wereplaced in the poled ford without backfill.

9 The culvert with log fill was “filled” with 4 to 5 in.(10 to 13 cm) diameter pole-size timber taken from theimmediate vicinity of the crossing. The poles werelaid parallel to the culvert until both the culvert andthe area 2 to 3 ft (0.6 to 0.9 m) on either side werecovered by a 8 to 12 in.- (20 to 30 cm)-deep log fillbuffer.

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culvert with shale fill and the cross-tie bridgecrossings. Approach stability was importantfor all skidder and haul road crossings.

Tornatore (1995) recommended constructingcrossings during dry or low flow periods toreduce downstream impacts. Also, the studyconcluded that culvert use for both skid trailsand haul roads is a viable means of crossingstreams if care is taken to minimize installa-tion time, if approaches and stream bank areasare adequately protected, and if the culvertsare properly maintained. The study alsosuggested that if sufficient care is taken toprevent the accumulation of mud and debrison top of portable bridges and wooden cross-tiebridges, those crossing options would outper-form culverts in protecting streams.

Miller et al. (1997) evaluated environmentalconditions above and below 70 forest roadcrossings (40 culvert, 21 bridge, and 9 ford) inPennsylvania. Only crossings 2 years old orolder were evaluated. The study reported thatonly 35 of the 814 comparisons of meanenvironmental conditions above and below thecrossings were found to be significantly differ-ent (p<0.05). Significant differences foundwere related to increased levels of fine sedi-ment, reduced basal area, and increasedherbaceous vegetation in the immediate vicin-ity of the road crossings. Successional- anddisturbance-related factors seemed to beresponsible for the vegetation changes typicallyfound in the crossing area. Based on themeasurements made in their study, the au-thors suggested that severe long-term impactsdue to crossings are not common.

Thompson and Kyker-Snowman (1989) evalu-ated both short- and long-term impacts at anunmitigated stream crossing as well as miti-gated crossings constructed with a portablebridge, a poled ford with a ductile iron culvert,and concrete slabs with hay bales. The un-mitigated crossings provided no protectionfrom disturbance of the stream or its banks.No clear effect of season (flow level) or equip-ment type (rubber-tire cable skidder vs. dualrear axle forwarder) on turbidity levels wasdocumented. The effect of mitigation wasdramatic. Unmitigated crossings generallycaused large increases in turbidity at 15 and100 ft (4.6 and 30.5 m) downstream of thecrossing. No significant differences betweenbefore- and after-crossing values were found

for pH, specific conductivity, or nitrate levels.Nitrate levels were negligible and in no case didthey come near the allowable drinking waterlimit. For both unmitigated and mitigatedcrossings, there were no significant differencesbetween turbidity values measured at 1,000,2,200, 2,640, or 5,280 ft (305, 671, 805, or1,609 m) below the crossings from samplestaken at upstream locations.

Of the mitigated crossings, Thompson andKyker-Snowman (1989) reported that thebridge was the most effective and the concreteslabs with hay bales the least effective atreducing crossing impacts. Measurable im-pacts with a portable bridge extended less than100 ft (30.5 m) downstream. Measurableeffects with other crossing options rarelyextended as far as 1,000 ft (305 m) down-stream. Although a natural ford was notincluded as a mitigated crossing in the study,the authors concluded that this option wouldbe an acceptable mitigation from observationalevidence of active and inactive harvesting sites.The study concluded that the largest impactsoccurred as a result of unmitigated crossings,crossings that did not meet Best ManagementPractices (BMP) standards, and unstableapproach areas adjacent to some of the cross-ings.

Thompson and Kyker-Snowman (1989) notedthat poled fords used in winter can become aproblem if they freeze into the stream andbecome difficult to remove. The temporarilyabandoned ford can act as a dam duringspring runoff, possibly causing the stream tooverflow its banks and increase erosion. Theysuggested that ductile iron pipes might carrythe spring floods through the ford and facili-tate earlier removal.

Looney (1981) compared the use of a rubbermat dam bridge to a ford and a culvert cross-ing. While whole-tree skidding, the rubber matdam bridge yielded a significant reduction inthe amount of suspended solids being carrieddownstream, as compared to a ford crossing.During 1.33 hr of use at one site (5 one-waycrossings with the first, third, and fifth cross-ings being loaded), the ford crossing resultedin 155 lb (52.7 kg) of sediment as compared to92 lb (31.2 kg) of sediment for the dam bridge.During 2 hr of use at a second site (8 one-waycrossings, every other one being loaded), theford crossing resulted in 613 lb (208 kg) ofsediment as compared to 242 lb (82.3 kg) for

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the dam bridge. The author also noted thatthe dam bridge provided considerable flotationto the skidder as compared to the ford cross-ing. Installation and removal of a culvertcrossing added 583 lb (198 kg) of sediment tothe stream. Water quality protection was givenparamount importance during the culvertinstallation. To accomplish that goal, sand-bags were used to divert the water flow into theculvert during backfilling around the culvertand the fill material was of superior quality.The author indicated that a dam bridge fallssomewhere between a ford and a culvert interms of stream protection.

Studies of Wetland Crossings

Mason and Greenfield (1995) compared theimpacts associated with using or not usingwood pallets over a silty sand soil in theOsceola National Forest in Florida. The soilmoisture content in the area that did not havewood pallets was typically 5 to 10 percent lessthan in the area that contained the pallets.After 150 passes with a loaded log truck thathad a gross vehicle weight of 80,000 lb (36,300kg), the rutting that occurred at the non-palletcrossing was 6 to 10 in. (15.3 to 25.4 cm) deep.The wood pallets had settled about 0.5 in. (12mm). The authors reported that the use ofwood pallets left no specific areas to hold andchannelize water or specific areas of highcompaction or rutting.

Hislop (1996b) tested wood pallets, wood mats,and an expanded metal grating on a silty sandsoil within the Osceola National Forest inFlorida. A non-woven, needle-punchedgeotextile was placed beneath each option.After 240 passes with a loaded log truck thathad a gross vehicle weight of 80,000 lb (36,300kg), the maximum rut depth was 8 in. (20 cm)on a control section and 1.5 in. (3.8 cm) on thewood pallet and wood mat section. After 75passes, the maximum depth was 15 in. (38 cm)on a control section versus 5 in. (13 cm) for theexpanded metal grating.

On a silty sand soil within the Osceola Na-tional Forest, areas with geotextile underexpanded metal and deck-span safety gratingshowed less soil rutting as compared to areaswith no grating (Mason and Greenfield 1995).After about 130 round trips with loaded logtrucks that had a gross vehicle weight of80,000 lb (36,300 kg), rutting in the area with

grating was about 0.5 to 1 in. (1.3 to 2.5 cm)as compared with up to 1 ft (0.3 m) in areaswithout grating.

After about 20 passes with an unloaded flatbedtruck with a loader on a deep black muck soilin Michigan, we noted the following maximumrutting depths: wood mat—12.5 in. (32 cm),expanded metal grating—8 in. (20 cm), tiremat—6.5 in. (17 cm), and wood plank—4.5 in.(11 cm). A single pass in a control area pro-duced ruts 11.5 in. (29 cm) deep. On anupland area at that site, the flatbed truckbecame stuck and had to be pushed with abulldozer. Once it was pushed onto the firsttest section of expanded metal grating that ledfrom the upland area to the wetland, tractionwas regained and the vehicle was able to driveup and back down the slope without anytrouble.

After about 20 passes with a loaded forwarderon a ponded histosol soil in Minnesota, wenoted the following maximum rutting depths:tire mat—21 in. (53 cm), wood plank—6.8 in.(17 cm), wood mat—5.1 in. (13 cm), expandedmetal grating—4.8 in. (12 cm), and PVC pipemat—1.3 in. (3.3 cm). A non-woven geotextilewas placed below all options. Soil penetrom-eter readings at both sites did not show anydifferences in soil strength.

Wolanek (1995) monitored downslope waterquality for 25 months after constructing a roadusing mill-generated bark and wood fiber asprimary fill material on the Tongass NationalForest in Alaska. Overall, the study foundminimal effects on stream water quality. Theparameter most effected was pH, increasingsignificantly by 0.2 to 1.5 pH units in thenaturally acidic streams. Dissolved oxygen inthe streams remained unaffected. All observedeffects were within the limits of Alaska waterquality standards.

Goudey and Taylor (1992) and Taylor (1994)examined the toxicity of aspen wood leachateto aquatic organisms. They reported thatleachate from aspen wood chips and woodpiles was very toxic to aquatic life. Aspen woodleachate can be produced in any season whenthe wood is exposed to water and the tempera-ture is above freezing. Karsky (1993) reportedthat the short-term potential leaching of tannicacid from cedar and some other species mustbe considered when constructing a chunkwood

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road close to a stream. No studies have re-ported leachate toxicity in wetlandroadbuilding using chunkwood.

Bradley (1995) and Foltz (1994) reported thatcentral tire inflation can reduce sedimentrunoff from unpaved roads. In a 3-year studythat evaluated CTI on test loops, sedimentrunoff was reduced by as much as 80 percenton road sections that were used by CTI-equipped vehicles (70 PSI [480 kPa] on thesteering axle and 30 PSI [210 kPa] on the otheraxles), as compared to vehicles using 90 PSI(620 kPa) in all tires. Little rut developmentoccurred after 1,205 passes with a CTI-equipped loaded log truck.

SUMMARY OF SOME STREAM ANDWETLAND CROSSING STATUTES

Each State and Province has enacted statutesto reduce nonpoint source pollution and toprotect wetlands. As a result, there is nouniformity in regulations across the GreatLakes basin. In addition, many local jurisdic-tions (e.g., county, shoreland zoning ordi-nances) within a State or Province have imple-mented additional statutes to further regulatenonpoint pollution sources. A summary ofsome of the key State/Provincial statutoryregulations on stream and wetland crossingsin Michigan, Minnesota, New York, Pennsylva-nia, Wisconsin, Ontario, and Quebec is pre-sented below. This information was gleanedfrom a review of the statutes as well as fromcontact with individuals in the appropriateregulatory organization in each State or Prov-ince. Regulators from each State or Provincereviewed draft copies of the summary for theirjurisdiction, and their revisions were thenincorporated. If you are interested in addi-tional information, contact the appropriateregulating body in that State or Province.Contact information for each State and Prov-ince is provided in table 5.

Michigan

Stream quality, cost, and season of use areevaluated when deciding what type of crossingto allow. Bridges are the preferred crossingmethod for streams, especially designatedtrout streams and their tributaries. Duringwinter, it is acceptable to place native materialor an ice/snow bridge across the stream whena frozen water crossing is not practical. When

determining culvert size and the minimumclearance height for bridges, the height of the100-year flooding frequency is considered.

A permit is required anytime a stream is to becrossed. The minimum permit fee is $50 andthe maximum $2,000. Most permits cost $50.Permits may be granted or denied within 60days after an acceptable application has beenreceived. No permits are required for wetlandcrossings. However, the operator should followvoluntary BMP’s.

Areas that have high-quality fish spawningbeds or that contain threatened and endan-gered species should be avoided for crossings.Waterbars may be required on the approachesof stream crossings to divert water off the roadbefore it reaches the stream.

Minnesota

The type of crossing is determined based onsite-specific needs. Crossings of protectedwaterbasins or wetlands are allowed onlywhere there is no feasible and practical alter-native. It is more difficult to obtain a permit tocross a designated wild and scenic river, adesignated trout stream or one of its tributar-ies, or a protected wetland. Ice bridges do notrequire a permit. Other crossings that do notrequire a permit are described below.

Provided that all conditions are met, a permitis not required for a low water ford crossing ona stream when the site is not an officiallydesignated trout stream, wild, scenic, orrecreational river, or officially designated canoeor boating route; no special site preparation isnecessary; normal summer flow does notexceed 2 ft (0.6 m) in depth; normal low flow isnot restricted or reduced; the crossing con-forms to the shape of the natural streamchannel; the original stream bank is no higherthan 4 ft (1.2 m); the ford is constructed ofgravel, natural rock, concrete, steel matting orother durable, inorganic material not morethan 1 ft (0.3 m) thick; the graded finishedslope is not steeper than 5:1 (horizontal tovertical); and graded banks are re-seeded ormulched.

A permit is not required for a temporary bridgeon a stream when the crossing is consistentwith floodplain, shoreland, and wild, scenic, orrecreational river ordinances; the stream bank

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Table 5.—Central office contact information for water regulatory authorities in Michigan, Minnesota,New York, Pennsylvania, Wisconsin, Ontario, and Quebec

State or Province Organization and address Telephone number

Michigan Department of Environmental QualityLand and Water Management Division (517) 373-1170P.O. Box 30458Lansing, MI 48909-7958

Minnesota Department of Natural ResourcesDivision of Waters (651) 296-4800500 Lafayette Rd.St. Paul, MN 55155-4032

New York Department of Environmental ConservationDivision of Regulatory Services (518) 457-222450 Wolf RoadAlbany, NY 12233-1750

Adirondack Park AgencyP.O. Box 99 (518) 891-4050Ray Brook, NY 12977

Pennsylvania Department of Environmental ResourcesBureau of Dams, Waterways and Wetlands (717) 783-1384P.O. Box 8554Harrisburg, PA 17105-8554

Wisconsin Department of Natural ResourcesBureau of Water Regulation and Zoning (608) 266-8034Box 7921Madison, WI 53707-7921

Ontario Director, Forest Management BranchMinistry of Natural Resources (705) 945-6660Suite 400, Roberta Bonda Place70 Foster DriveSault Ste. Marie, ON Canada P6A 6V5

Quebec Ministere des Ressources NaturellesDirection de l’environnement forestier (418) 643-2922880 Chemin Sainte-Foy, 5e étage PQCanada G1S 4X4

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can support the bridge without pilings, founda-tions, culverts, excavation, or other special sitepreparation; nothing is placed in the bed of thestream; the bridge can be removed for mainte-nance and flood prevention, the bridge is firmlyanchored at one end and can swing awayduring flooding; and there is a minimum 3 ft(0.9 m) of clearance between the lowest portionof the bridge and normal summer stream flow.

All other crossings require permits. Theapplication fee for a permit ranges from $75 to$500, depending on the size or cost of theproject. Once an application is declared to becomplete, the average turnaround time beforea decision is made concerning a permit is 45 to60 calendar days.

New York

The New York Department of EnvironmentalConservation (DEC) has jurisdiction overstream crossings throughout the State. Withinthe Adirondack Park, wetlands are regulatedby the Adirondack Park Agency. Outside of thePark, the DEC regulates wetlands. Crossingsare determined on a case-by-case basis byevaluating factors such as season, cost, andlocal conditions. The Talbot formula (Merritt1983) is used to size culvert and bridge open-ings for temporary stream crossings that willbe in place during periods other than lowsummer flow. A 2 in./hr (5 cm/hr) rainfall isassumed, unless conditions warrant consider-ation of a larger rainfall. Multi-span bridgesmay be acceptable. Skidding or winching oflogs or trees in or along the axis of tributarychannels or across wild rivers is prohibited.

Outside of the Adirondack Park, permits arerequired for all protected stream crossingswhere disturbance will occur to the streambank or stream bed or within 100 ft (30 m) ofwetland crossings in regulated wetlands thatare 12.4 acres (5 ha) or larger in size. A wet-land smaller than 12.4 acres (5 ha) in areamay be regulated if it is determined to haveunusual local importance. For some smallstream crossings, permits may be issued on-site. There is no cost for filing any permitapplication.

Stream and wetland crossing applications areclassified as either minor or major using reviewcriteria contained in the Freshwater WetlandsPermit Requirements Regulations. Review time

frames, procedures, and requirements forpublic notice of applications differ for minorand major projects. For stream crossings, aminor permit application is one where thelength of the stream bed or bank to be im-pacted does not exceed 50 ft (15.2 m). Thereare many other criteria in these regulationsthat are used to assess whether a wetlandcrossing is minor or major.

Minor permit applications require up to 45calendar days for a decision on the permit afterthe application is declared to be complete. Adecision on a major crossing permit applica-tion can take up to 90 calendar days if nopublic hearing is held. Major permit applica-tions require publication in the New YorkDepartment of Environmental Conservation’sEnvironmental Notice Bulletin and a desig-nated local newspaper to solicit public reviewand comments.

Within the Adirondack Park, the DEC rulesspecified above apply to stream crossings. Anywetland within the Park that is 1 acre (0.4 ha)in size or larger, or any size wetland adjoiningan open water body that has a free interchangeof water at the surface, falls under the jurisdic-tion of the Adirondack Park Agency. Skidtrails and other roads may be constructedwithout a permit within a wetland if they donot involve a material disturbance to thewetland (e.g., cut and fill). Permits are re-quired for all other activities within a wetland.Before a permit is denied, a public hearingmust be held.

Pennsylvania

Two different types of crossings, minor roadcrossings (GP-7) and temporary road crossings(GP-8), are recognized. A minor road crossingis a road constructed across a wetland wherethe length of the crossing is less than 100 ft(30 m) and the total wetland area disturbed isless than 0.1 acre (0.04 ha), or a road con-structed across a stream and an adjacentwetland using a bridge, culvert, or ford cross-ing where the watershed drainage area is 1.0mi2 (259 ha) or less and the total wetland areadisturbed is less than 0.1 acre (0.04 ha). Atemporary road crossing would consist of aroad installed for a period of time not to exceed1 year across a wetland or along a stream thatuses a pipe culvert or a series of culverts, abridge, a causeway, or a ford.

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If the crossing of a wetland cannot be avoidedunder a minor road crossing, the crossingmust be undertaken at the narrowest point ofthe wetland and shall not exceed 100 ft (30 m)in length and 0.1 acre (0.04 ha) in disturbance.The total wetland impact for all minor roadcrossings installed on an individual property orproject, including phased projects, cannotexceed 0.25 acre (0.10 ha).

For a temporary road crossing, skidding acrossfords and multiple-span bridges is prohibited.Also, temporary fords are prohibited within2,000 ft (610 m) upstream of all high qualityand exceptional value watersheds and water-sheds tributary to drinking water intakes orpublic water supply reservoirs. Within atemporary road crossing, culverts must beinstalled with a depressed roadway embank-ment so that overtopping of the roadway willoccur within the stream channel. If a tempo-rary road crossing across a wetland cannot beavoided, the crossing is permissible if it islocated at the narrowest practicable point ofthe wetland and the length of the crossingwithin the wetland does not exceed 200 ft (61m). Temporary road wetland crossing surfacesmust be stabilized by appropriate means, suchas removable, temporary mats, pads, or othersimilar devices.

Instead of using a specified flooding frequencywhen sizing culverts, knowledge of local condi-tions and season(s) of operation are consid-ered. A permit is required for all minor roadand temporary road crossings, unless thedrainage area is less than 100 acres (40 ha).Within wetlands, the regulations specifiedabove apply. There are two different types ofpermits: a general permit and a joint permit.For forest management activities, an applica-tion for a joint permit would be filed only whenthe general permit is not applicable. Whilejoint permits may offer an alternative to adenied general permit, the detailed environ-mental assessment requirements make themunattractive for most forest managementpractices. If neither a general permit for aminor road (GP-7) nor a temporary road cross-ing (GP-8) is applicable to a certain location,the only option is to apply for the joint permitapplication.

For both minor road and temporary roadcrossings, a general permit would not begranted under a number of situations. As an

example, for both crossing types, a generalpermit would not be usable where any of thefollowing conditions were present: historic,cultural, or archaeological sites were identified;stocked trout streams from March 1 to June15, wild trout streams from October 1 toDecember 31, and Lake Erie tributaries fromSeptember 1 to December 1 unless writtenapproval is obtained from the FishCommission’s Division of EnvironmentalServices. During these periods, the generalpermits for minor road and temporary roadcrossings and a joint permit can be used.However, no in-stream work can occur duringthose dates.

Minor road crossings of wetlands both underthe general permit (GP-7) and the joint permitapplication require a wetland delineation and areplacement plan. If the permanent impact tothe wetland is less than 0.05 acre (0.02 ha), noreplacement is required under the State’sdeminimus policy. There is no application feefor a general permit, unless the crossing is tobe established across submerged water landsof the Commonwealth. In that case, thelicense fee for occupying submerged lands is$50/0.10 acre ($50/0.04 ha) of disturbancewith a minimum charge of $250/year.

Wisconsin

Culvert crossings on navigable waterways10

must be designed to pass a 100-year floodfrequency without causing an increase of 0.01ft (1 cm) or greater in the regional flood eleva-tion if flooding easements are not obtainedfrom affected upstream property owners beforea permit will be issued. Gravel or concreteplank fords and clearspan bridges are pre-ferred over culverts. For multi-span bridges,bridge piers may be permitted, as long as theydon’t create upstream flooding on propertywhere an easement cannot be obtained. Icebridges can be used on a case-by-case basis.A clearance of 5 ft (1.5 m) or more may berequired for bridge and culvert clearance onwaterways that may be used by other thanlightweight craft (e.g., powerboats). Clearanceon other navigable waterways is evaluated on acase-by-case basis.

10 A waterway is navigable if it has beds andbanks, and if it is possible to float a canoe or othersmall craft in the waterway on a regular recurringbasis, even if only during spring runoff.

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Permits are required whenever crossing anavigable waterway or grading and/or remov-ing top soil from the bank of any navigablewaterway where the area exposed will exceed10,000 ft2. The minimum cost for a permit,$30, is applicable to ford crossings. Culvertand bridge crossings and grading or removal oftop soil from the bank of a waterway for anarea more than 10,000 ft2 require an applica-tion fee of $100. The permit cost for crossing astream wider than 35 ft (10.7 m) is $300. Apermit is required to remove or dredge materialfrom navigable and non-navigable streams.The permit costs $100 if less than 3,000 yd3

are removed and $300 for larger removals.

After receiving a complete application, the DNRWater Regulation and Zoning staff will providethe applicant with language for a public noticeof intent that the applicant must have pub-lished in local newspapers. After a 30-calen-dar day comment period, the crossing could beapproved if objections were not filed against it.If objections are filed, it may take 6 months orlonger before the permit might be approvedthrough a hearing process.

Ontario

Every 5 years, a forest management plan mustbe prepared or renewed for approval by theprovincial government. This plan identifiesactivities (e.g., access, harvest, renewal, andmaintenance) that will take place over the next20 years, although specific plans are requiredonly for the upcoming 5-year period. As a partof the planning process, public input is solic-ited at three different times. Once a plan isapproved by the government, a company mustannually submit a work schedule showingspecific locations and a time frame for activi-ties that will occur within the next 12 months.All of those activities must fall within the scopeof the 5-year plan. An approval to beginoperations is issued when the annual workschedule is approved. As part of the approval,specific stream and wetland crossings areauthorized. There is not a separate applicationprocess or cost associated with securingpermission to make a crossing.

In lieu of developing statutes, Ontario hasproduced several different sets of guidelinesthat must be followed as a part of timbermanagement. Each set of guidelines is de-signed to establish standards and to provide

practical advice for ensuring minimum distur-bance to the natural environment. Most of thedecisions about what to apply in a specificinstance are left for the professionals andoperators to make on-site. Operators muststay within the guidelines, unless an exceptionis granted. Areas where the approach deviatesfrom the guidelines are to be clearly noted onthe plan. If the variances are approved, theymust be closely monitored by the contractor.The Ministry of Natural Resources also moni-tors variances on-site and/or through anextensive reporting process.

No crossing options are excluded by the guide-lines. All water crossings must be sized usinghydrological analysis techniques approved byMinistry of Natural Resources engineers.Design flows on access roads are typically for a10- to 50-year flooding frequency, with thelower frequency for culverts and the higher formajor bridges. All bridges must be designed bya qualified professional engineer to meet bridgedesign codes and Ministry standards. Bridgeproposals must be reviewed and approved bythe Ministry engineer. The Ministry providesdesign aids and training for in-house staff andthe forest industry.

Quebec

Before harvesting within a publicly ownedforest, a company must submit a 25- and 5-year plan to the provincial government forapproval. Public consultation is also manda-tory during the development of these plans.Annual plans delineating areas to be harvestedwithin the upcoming year must also be sub-mitted. The 25-year, 5-year, and annual plansmust be approved by a forest engineer. Roadsmust be indicated on the plan (only accessroads are usually shown). Except for cross-ings, any road that is to come within 197 ft (60m) of a stream or lake must be clearly indi-cated, justified, and protection measuresidentified. The location of bridges, along withtheir size, must appear on the annual plan. Allbridge designs must be approved by a civilengineer, although they can be constructed bya forest engineer.

Logs can be used on each side of the stream tostabilize the approach. If logs are used for thispurpose, they must remain in place after use.A goal is to achieve zero particles depositedinto streams. Therefore, the use of geotextile is

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mandatory for permanent stream crossingsand strongly suggested for temporary streamcrossings.

Fording a stream is not allowed, even in winter.Bridging or ice bridges are acceptable onwinter roads. Logs can be incorporated intothe ice bridge, as long as they are securelycabled to a tree or other nearby secure struc-ture. Both types of structures must be re-moved at the end of the work, except for thelog mats used to stabilize the banks on eitherside of the stream.

Culverts are sized on a 10-year flood fre-quency, if the watershed is less than 14,830acres (6,000 ha). On larger watersheds, cul-verts are sized on a 20-year flood frequency.The smallest culvert that can be used in astream is 18 in. (45 cm) diameter. Prescribedor equivalent stabilization techniques must beused during the installation and removal of theculvert. Wooden culverts are acceptable only iftheir span does not exceed 3.3 ft (1 m) wide.Stream enlargement is prohibited. Whenconstructing either a culvert or bridge cross-ing, the width of the stream can be reduced byup to 20 percent or, if calculations based onflood frequency allow it, by up to 50 percent.Only bridges are acceptable when crossing alake or bay within a lake.

A stream crossing (bridge or culvert) cannot beconstructed in or within 164 ft (50 m) up-stream from a spawning ground indicated onthe annual plan. When designing a crossing ina stream where fish migrate, installation of astructural plate culvert or construction orimprovement of a bridge cannot be conductedduring the upstream migration of fish, asdetermined by the Ministry of Environment.

RESEARCH AND EDUCATION NEEDS

The growing worldwide demand for forestproducts will increase the probability of har-vesting in areas that are adjacent to or thatcontain streams and wetlands. Appropriatecrossing options are needed to avoid negativeimpacts to these water bodies. Unfortunately,little research is currently available that hasevaluated and compared the various crossingoptions. Also, little information has beencompiled to make people aware of how to bestuse each option so that it meets their opera-tional requirements and provides adequate

environmental protection. As a result, we haveidentified the following research and educationneeds:

• Relatively few studies have evaluated theimpacts of different stream and wetlandcrossing options. Further examination ofthe impacts associated with stream andwetland crossings, especially those thatresult from the removal of a temporarycrossing, is needed.

• The various studies that have evaluatedimpacts to streams and wetlands from useof different crossings have applied differentmethodologies and evaluated differentparameters to derive their results. There isa need to develop and apply a standardapproach so that results can be more easilycompared.

• Maintaining the hydrologic function of awetland is key to sustaining its integrity.Severe rutting may impede subsurface flowof water across a wetland. There is a needto evaluate the impacts to subsurface watermovement across a wetland that result fromapplication of different crossing options.

• From the operator’s perspective, there arecosts and benefits associated with using anycrossing option. Costs can include theinstallation, maintenance, and removal ofan option. Benefits may include improvedaccess, shorter roads and skid trails, ex-tended time of operability, increased pro-ductivity, reuse, and reduced maintenance.The limited available research is largelyfocused on quantifying the installation andremoval costs associated with use of cul-verts in streams without considering anybenefits that may be derived. There is aneed to quantify the net costs (total costsminus total benefits) to the operator associ-ated with the variety of different optionsthat are available for use in streams andwetlands. That analysis needs to considerthe life cycle costs and benefits.

• While each crossing option may accomplishits intent, different options may performbetter in some instances and worse inothers. There is a need to identify theoptimal range of site and operating condi-tions for each option. As a part of thatprocess, the temporal dimension of “tempo-rary” needs to be addressed.

45

• There are costs and benefits to the operator,to the landowner, and to society associatedwith using the various options. Individualswho make on-the-ground decisions aboutwhat crossing option(s) to allow need betterinformation about these costs and benefitsto make sure that their prescription isappropriate to each particular crossing.

• An economic analysis (that includes pay-back analysis) comparing non-reusableoptions with reusable options needs to bedone. The analysis should consider allcosts associated with each option, includinglabor and materials, over the expected life ofthe crossing option.

• Several options are available to crossstreams and wetlands. Most operators areeither unaware of the variety of optionsavailable or lack sufficient information tocorrectly install, maintain, and remove theoptions or rehabilitate the site followingremoval. Training materials are needed tohelp them properly accomplish these tasks.

• Appropriate institutional arrangementsbetween organizations need to be identifiedto assist with the purchase of some options.Many large landowners may have a con-tinual need for reusable options on theirland, but many operators may not be able toafford the initial investment for some ofthese. If these larger landowners obtainedthe options outright, they could then makethem available to operators through avariety of mechanisms, to be reimbursed forthe investment. Owners could also sharetheir crossing options through other ar-rangements.

SUMMARY

Streams and wetlands are broadly recognizedas valuable ecosystems. Timber harvest andforest management activities have the potentialto adversely impact these systems. A variety ofreusable temporary stream and wetland cross-ing options are available that can reduceimpacts to water bodies while providing long-term cost advantages and day-to-day opera-tional benefits. Before implementing any of theoptions, be sure to compare their capabilitiesand costs to actual needs. We highly recom-mend using a non-woven geotextile fabricbelow most temporary wetland crossing op-tions. We also recommend using a geotextile

fabric with some stream crossing optionsplaced within the stream as well as beneathany temporary materials used to protect theapproaches on the stream banks. However,the use of geotextile with a stream crossingoption should be approved by the appropriateregulatory authorities because there may beconcerns about impacts if the geotextile movesdownstream. Various studies have reportedthat bridge crossings contribute less sedimentto the stream than culvert crossings duringinstallation. Various studies have reportedthat the options were effective in improvingtrafficability and reducing rut depth. Contactus for additional information about any of theoptions or to inform us of others that are notidentified in this publication. The e-mailaddress for the first author iscblinn@forestry.umn.edu.

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Adamson, R.B.; Racey, G. 1989. Low watercrossings: an inexpensive alternative forlow volume roads in Northern Ontario.Tech. Notes TN-02. Ontario, Canada:Ontario Ministry of Natural Resources,Northwestern Ontario Boreal Forest Man-agement. 4 p.

Alexander, G.R.; Hansen, E.A. 1983. Effects ofsand bedload sediment on a brook troutpopulation. Res. Rep. 1906. Ann Arbor, MI:Michigan Department of Natural Resources.50 p.

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APPENDIX 1

PARTIAL LIST OF COMMERCIAL VENDORS FOR TEMPORARY CROSSING OPTIONS

This is not a complete list and some information provided may be inaccurate or out-of-date. Manyvendors provide a variety of products but are listed under only one category. Although the listingfor a company may not be from your area, there may be a local distributor who can supply infor-mation and materials.

Geotextiles

Amoco Fabrics and Fibers Company Belton Industries900 Circle 75 Parkway, Suite 550 8613 Roswell Rd.Atlanta, GA 30339 Atlanta, GA 30350Voice: (800) 445-7732 Voice: (800) 225-4099

(770) 984-4444 (770) 587-0257Fax: (770) 956-2430 Fax: (770) 992-6361

Cascade Distribution Ltd. Fireflex Division, SEI Industries15620 - 121A Ave. 7400 Wilson Ave.Edmonton, AB Canada T5V 1B5 Delta, BC Canada V4G 1E5Voice: (800) 565-6130 Voice: (604) 946-3131

(403) 454-2400 Fax: (604) 940-9566Fax: (403) 451-0911

Linq Industrial Fabrics, Inc.Layfield Plastic Geotextile Division14604-115A Ave. 2550 West 5th North St.Edmonton, AB Canada T5M 3C5 Summerville, SC 29843-9669Voice: (403) 453-6731 Voice: (800) 543-9966Fax: (403) 455-5218 (803) 875-8277

Fax: (803) 875-8276Synthetic Industries, Inc.4019 Industry Dr. TC MirafiChattanooga, TN 37416 365 S. Holland Dr.Voice: (800) 621-0444 Pendergrass, GA 30567

(423) 899-0444 Voice: (800) 234-0484Fax: (423) 899-7619 Fax: (800) 333-6205

Cellular confinement systems

A. G. H. Industries, Inc. GeoCHEM, Inc.4600 Post Oak Place 106 Lake Ave. S.Suite 111 Seattle, WA 98055Houston, TX 77027 Voice: (425) 227-9312Voice: (713) 552-1749Fax: (713) 552-1147

Nilex Corporation Presto ProductsCompany6810 South Jordan Rd. P.O. Box 2399Englewood, CO 80112 Appleton, WI 54913-2399Voice: (800) 537-4241 Voice: (800) 548-3424

(303) 766-2000 (920) 738-1118Fax: (303) 766-1110 Fax: (920) 738-1432

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Tenax Corporation4800 East Monument St.Baltimore, MD 21205Voice: (410) 522-7000Fax: (410) 522-7015

Erosion control products

American Excelsior Company BonTerra America, Inc.P.O. Box 5067, 850 Ave. H East 355 West Chestnut St.Arlington, TX 76005-5067 Genesee, ID 83832Voice: (800) 777-SOIL Voice: (800) 882-9489

(817) 640-1555 Fax: (208) 285-0201Fax: (817) 649-7816

Canadian Forest Products, Ltd. Conwed FibersPanel and Fibre Division 219 Simpson St.430 Canfor Ave. Conover, NC 28613New Westminister, BC Canada V3L 5G2 Voice: (800) 366 1180Voice: (800) 363-8873 Fax: (704) 328-9826

Erosion Control Systems, Inc. Finn Corporation1800 McFarland Blvd., Suite 180 9281 LeSaint Dr.Tuscaloosa, AL 35406 Fairfield, OH 45014Voice: (800) 943-1986 Voice: (800) 543-7166

(513) 874-2818Fax: (513)874-2914

Greenfix AmericaP.O. Box 62, 604 E. Mead Rd. Nedia EnterprisesBrawley, CA 92227 89-66 217th St.Voice: (800) GREENFX Jamaica, NY 11427

(800) 929-2184 Voice: (888) 725-6999(760) 344-6700 (718) 740-5171

Fax: (760) 344-4305 Fax: (718) 740-1049

North American Green, Inc. RoLanka International, Inc.14649 Highway 41 North 365 Toccoa PlaceEvansville, IN 47711 Jonesboro, GA 30236Voice: (800) 772-2040 Voice: (800) 760-3215

(812) 867-6632 (770) 506-8211Fax: (812) 867-0247 Fax: (770) 506-0391

PPS Packaging Company Verydol Alabama, Inc.204 N. Seventh St. P.O. Box 605P.O. Box 56 Pell City, AL 35125Fowler, CA 93625 Voice: (205) 338-4411Voice: (209) 834-2011

Steel/aluminum culverts

Atlantic Industries Limited Contech Construction Products, Inc.Dorchester, NB, Canada 1001 Grove St.Voice: (506) 379-2455 Middletown, OH 45044Fax: (506) 379-2290 Voice: (800) 338-1122

(800) 363-3873

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Culverts and Industrial Supply Co. Johnston Fargo Culverts, Inc.7242 W. Yellowstone 3575 85th. Ave. NECasper, WY 82644 St. Paul, MN 55126-1186Voice: (307) 472-7121 Voice: (651) 780-1760Fax: (307) 577-4914 Fax: (651) 780-1763

Polyethylene culverts

Advanced Drainage Systems Crumpler Plastic Pipe3300 Riverside Dr. P.O. Box 2068, Highway 24 WestColumbus, OH 43221 Roseboro, NC 28382Voice: (800) 733-7473 Voice: (800) 334-5071

(614) 457-3051 Fax: (800) CPP-PIPEFax: (614) 459-0169

Hancor, Inc. Soleno SPD, Inc.401 Olive St. 1160 Rt. 133, C.P. 147Findlay, OH 45839 Iberville, PQ, Canada J2X 4J5Voice: (800) 537-9520 Voice: (800) 363-1471

(419) 423-6913 (514) 347-8315Fax: (419) 424-8337 Fax: (514) 347-3372

High density polyethylene pipe

CSR Polypipe Fluid ControlsP.O. Box 390 3435 Stanwood Blvd. NEGainesville, TX 76241-0390 Huntsville, AL 35811Voice: (800) 433-5632 Voice: (800) 462-0860

(817) 665-1721 (205) 851-6000Fax: (817) 668-8612 Fax: (205) 852-6005

Forrer Supply Harvel PlasticsP.O. Box 220 P.O. Box 757Germantown, WI 53022-0220 Easton, PA 18044-0757Voice: (800) 255-1030 Voice: (610) 252-7355

(414) 255-3030 Fax: (610) 253-4436Fax: (414) 255-4064

Plastic Pipe and Supply Plexco Performance Pipe Division100 Glen Rd. Chevron Chemical CompanyP.O. Box 8066 1050 IL Route 83 - Suite 200Cranston, RI 02920 Bensenville, IL 60106-1048Voice: (401) 467-9370 Voice: (630) 350-3700Fax: (401) 461-9520 Fax: (630) 350-2704

Stress-laminated bridges

Forestry and Wildlife Consult. Serv., Inc. Hughes BrothersRt. 1, Box 531 210 N. 13th St.Gretna, VA 24557 Seward, NE 68434Voice: (804) 656-6684 Voice: (402) 643-2991

Fax: (402) 643-2149

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Dowel-laminated bridges

Wheeler Lumber, LLC.P.O. Box 26100St. Louis Park, MN 55426Voice: (800) 328-3986

(612) 929-7854Fax: (612) 929-2909

Glued-laminated bridges

Structural Wood Systems, Inc.P.O. Box 250Greenville, AL 36037Voice: (334) 382-6534Fax: (334) 382-9860

Modular steel bridges

Acrow Corporation of America Big R ManufacturingP.O. Box 812 P.O. Box 1290Carlstadt, NJ 07072-0812 Greeley, CO 80632Voice: (800) 524-1363 Voice: (800) 234-0734

(201) 933-0450 (970) 356-9600Fax: (201) 933-3961 Fax: (970) 356-9621

Hamilton Construction Company Modular Bridge SystemsP.O. Box 659 8035 Alexander Rd.Springfield, OR 97477-0121 Delta, BC Canada V4G 1C6Voice: (541) 746-2426 Voice: (604) 946-1524Fax: (541) 746-7635 Fax: (604) 946-1514

Van Straten and Sons ManufacturingRFD #1, US 41 NorthBaraga, MI 49908Voice: (906) 353-8177

(906) 353-6490Fax: (906) 353-7115

Hinged bridges

ADM Welding and FabricationPennsylvania Ave. West Ext., RearWarren, PA 16365Voice: (814) 723-7227Fax: (814) 723-7227

Concrete decked steel bridges

SureSpan BridgeSuite 216545 Clyde Ave.West Vancouver, BC Canada V7T 1C5Voice: (604) 925-3377Fax: (604) 925-3394

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Railroad flatcar bridges

Rick Franklin Corporation101 Industrial WayP. O. Box 365Lebanon, OR 97355Voice: (800) 428-1516

(541) 451-1275Fax: (541) 258-6444

Expanded metal grating

Alabama Metal Industries, Inc. Brown-Campbell Steel Co.P.O. Box 3928 14290 Goddard St.Birmingham, AL 35208 Detroit, MI 48212Voice: (800) 366-2642 Voice: (800) 521-4512Fax: (205) 780-7838 (313) 891-2390

Fax: (313) 891-2903McNichols Co.1951 Lively Blvd.Elk Grove, IL 60007Voice: (800) 237-3820Fax: (847) 640-8388

Wood mats/panels

Carolina Mat Company Clemons Forest ProductsP.O. Box 339 P.O. Box 982Plymouth, NC 27962 Amite, LA 70422Voice: (800) 624-6027 Voice: (504) 748-9079

(919) 793-4045 Fax: (504) 748-9719Fax: (919) 793-5187

Wood pallets

Uni-Mat International503 Martin St.Houston, TX 77018Voice: (800) 445-7850

(713) 697-3585Fax: (713) 697-1227

Tire mats

Terra Mat Corporation Unique Tire Recycling, Inc.462 Arbor Circle 155 LaFarge Rd.Youngstown, OH 44505 Kamloops, BC Canada V2C 6T5Voice: (330) 759-9412 Voice: (800) 446-5955Fax: (330) 759-7679 Fax: (604) 573-3492

High flotation tires

Ardco-Traverse Lift, LLC. Continental General Tire Co.322 Riley Rd. 1800 Continental Blvd.Houston, TX 77047 Charlotte, NC 28273Voice: (713) 433-6751 Voice: (704) 583-3900Fax: (713) 433-5655 Fax: (704) 583-8540

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Firestone Agricultural Tire Co. OTR Wheel Engineering730 E. Second St. Box 5811Des Moines, IA 50309 Rome, GA 30162-5811Voice: (515) 242-2306 Voice: (706) 235-9781Fax: (515) 242-2329 Fax: (706) 234-8137

Rolligon Corporation Toyo Tire USA Corporation10635 Brighton Lane 300 W. Artesia Blvd.Stafford, TX 77477 Compton, CA 90220Voice: (281) 495-1140 Voice: (310) 537-2820Fax: (281) 495-1145 Fax: (310) 604-1519

United Tire & Rubber Company275 Belfield Rd.Rexdale, ON Canada M9W 5C6Voice: (416) 675-3077Fax: (416) 675-4337

Single and bogie tire tracks

Hultdins, Inc. Pedno Tracks, Inc.22 Morton Ave. East 3641 rue des ForgesBrantford, ON Canada N3T 5T3 Laterriere, PQ Canada G0V 1K0Voice: (519) 754-0044 Voice: (418) 678-1506Fax: (519) 754-1569 Fax: (418) 678-9748

Central tire inflation equipment

Eaton Air Control Products1303 Durham Rd.P.O. Box 241Roxboro, NC 27573-0241Voice: (910) 503-6411Fax: (910) 503-6425

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PVC Pipe Bundles

Description of option:

Four-inch (10.2-cm) diameter Schedule 40 polyvinyl chloride (PVC) or SDR11 high-densitypolyethylene (HDPE) pipes are cabled together using 3/16-inch- (4.8-mm)-dlameter galva-ntzed steel cable to form mats of varying length. A non-woven geotextile is used under themats to provide added support to the crossing and separate it from the underlying soil.

Area of application:Small streams or stream channels with confining banks (U-shaped channel) that are less than

10 feet (3 m) wide, 4 feet (1.2 m) deep, slow moving water, straight channel, and little, ifany, cross slope of the stream bottom. Pipe bundles should not be used in a stream that•has a lot of woody debris because this material can get lodged at the inlet of the pipes.Durability of the pipes during periods of extended frozen conditions is unknown.

admmagMaterial is lightweight and readily available.Easy to construct, install, remove, and repair.Can be constructed by the operator.No fill required.Can be easily adapted to different stream channel shapes and sizes.Low cost

Reasonably durable

Requires maintenance to keep pipes from becoming plugged.Surface moves and is slick during use without stiff surfacing (e.g., frozen ice/snow or non-

woven geotextile with wood plank, wood mat, expanded metal grating) to provide traction.May inhibit migration of aquatic organisms.Requires cleaning between uses to remove soil.Standard pipe is sensitive to ultraviolet (UV) light and will degrade. Need to cover the pipe or

use an ultraviolet-resistant type of pipe. Pipe should be stored out of the sun.Use during extended frozen conditions has not been evaluated.

Sourcefs}:

Local hardware or plumbing supply store.

Recommended supplemental material:Non-woven geotextile placed both below to protect stream bed and facflltate removal, and above

to prevent soil from dropping into the stream and reduce UV exposure of the pipes.Running surface material (e.g., wood planking, wood mat, expanded metal grating) to provide

traction.

Cable attached to upstream tree or other fixed object to anchor one end of the structure.Material to protect the approaches to the crossing if the soil is weak (e.g., wood mats, wood

planks, corduroy, or expanded metal grating with non-woven geotextile).A welding torch or some other means of controlling cable end fraying will increase threading

speed when constructing the pipe bundle.

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Tire Mats

Description of option:A tire mat is a mat or panel of tires created by interconnecting tire sidewalls with corrosion-

resistant fasteners. Tire treads are also used in some designs. Mats of varying length andwidth can be developed.

Area of application:Most wet mineral soils with different designs for distinct soils and situations. Tire mats require

a relatively level surface with grades up to 5 percent, a fairly straight alignment, and nocross slope. Steeper grades, cross slope, or curves may result in loss of traction or thelateral movement of the mats outside of the planned travel area. Tire mats are most appro-priate for use during hauling or forwarding operations. Performance is enhanced in areaswhere there is an adequate root or slash mat to provide additional support.

Relatively low maintenance.Some designs may not require non-woven geotextlle.With appropriate care, tire mats may have a long life.

Product is very heavy and flexible, making it difficult to Install and remove.Not recommended for use when skidding material.If the individual mats are dragged lnto place, It is difficult to use a non-woven geotextlle below

the mats.

Use of a clam loader to install or remove the mats may damage the fasteners (e.g., bolts} thathold the mats together.

Operators may not install product correctly.

Source{sl:Commercial vendor.

Homemade from waste tires and fasteners {e.g., cables, bolts}.

Recommended supplemental material:Non-woven geotextlle to place below the mats, unless they are dragged into place.

Approximate purchase price:Moderate. About $300 for a 5-foot x 10-foot (1.5-m x 3-m) mat.

Construction directions and/or diagram and time required:Not applicable.

Equipment needed for construction, installation, and/or removal:Skidder {ifmats are dragged}, forwarder, or a truck with a loader.

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Tire Mats (continued)

Installation approach and time:

Before installing the geotextile fabric, smooth out any high spots and fill in any ruts to reducethe potential of the geotextile tearing during use. For sites with grass mounds or otheruneven vegetation, blading should not disturb the root mat associated with that vegetation.Roll out the geotextile fabric across the area where the crossing is to be placedl Dependingon the configuration of the mats and the strength of the soil where the mats are to beinstalled, they can be either positioned in front.of the installation equipment, laid from aperpendicular position, or dragged into place.

About 30 minutes are needed to install two 5-foot x 10-foot (1.5-m x 3-m) sections, including anon-woven geotextile.

Patent protection of product design;Commercial designs are patented.

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