Water management techniques for resource roads

Water management techniques
for resource roads in wetlands
A state of practice review
Contract Report CR-652
Clayton Gillies, RPF, RPBio
FPInnovations
Prepared for: Ducks Unlimited Canada
May 2011
Table of contents
Introduction ............................................................................................................................................................. 5
Objective ................................................................................................................................................................. 6
Methods................................................................................................................................................................... 6
Impacts to wetlands ................................................................................................................................................. 7
Water management: planning ................................................................................................................................. 9
Road-location tools ......................................................................................................................................... 9
Positioning and fill requirments ...................................................................................................................... 9
Avoiding wetlands ........................................................................................................................................ 10
Winter construction....................................................................................................................................... 10
Understanding wetlands and their hydrologic function ................................................................................ 11
Water management: construction .......................................................................................................................... 12
Culverts ......................................................................................................................................................... 12
Size and spacing/location ..................................................................................................................... 13
Maintenance.......................................................................................................................................... 15
Bedding................................................................................................................................................. 16
Inlet control........................................................................................................................................... 16
Beaver activity and blockage ................................................................................................................ 17
Bridges .......................................................................................................................................................... 18
Abutments and bearing requirements ................................................................................................... 18
Approaches ........................................................................................................................................... 19
Corduroy and brush mats .............................................................................................................................. 20
Materials and design ............................................................................................................................. 20
Flow considerations .............................................................................................................................. 21
Subsurface drainage considerations .............................................................................................................. 23
Road decommissioning ......................................................................................................................................... 25
Winter ................................................................................................................................................... 25
Summer ................................................................................................................................................. 25
Summary ............................................................................................................................................................... 27
References ............................................................................................................................................................. 30
Suggested reading ................................................................................................................................................. 33
Acknowledgements ............................................................................................................................................... 33
Appendix I............................................................................................................................................................. 34
Appendix II ........................................................................................................................................................... 42
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Introduction
Various industries develop resource access roads in Canada’s northern forested landscapes. Often
these resource roads pass through wetlands, such as fens, bogs, and swamps, and thus present
numerous environmental and operational challenges for road managers. In addition, the effects of
these resource roads on the many ecological functions of wetlands are of increasing concern to
Canada’s forest industry, other resource-based industries, governments, and conservation
organisations.
Forest access roads used for harvesting operations are considered the largest contributors of sediment
entering watercourses (Decker 2003, Gillies 2007), and they can have critical effects on water and the
environment (Forestry Corp. 2004). Understanding and promoting good water management techniques
for resource roads in wetlands may conceivably address many environmental and operational
challenges. When developing and implementing industry best management practices (BMP), the intent
is to minimize negative impacts caused by operations; when operators are trained in using proper
BMPs, the end result can be cost effective and ecologically sensitive (Rummer 2004). Sheehy (1993),
in his review of wetland conservation in managed forests, suggests that wetland conservation measures
do not need to unduly restrict forestry operations, and they are not likely to add significantly to costs.
When a resource road is built through a wetland, the wetland’s hydrologic functions may be
compromised, resulting in various negative outcomes. Resource roads can alter the hydrology of a
wetland by interfering or blocking surface flow, and possibly subsurface flow (Graf 2009). Drainage
structures that underperform due to the lack of adequate bearing capacity, or due to the sinking/settling
of a road, may need to be replaced or maintained on an ongoing basis. With careful planning,
knowledge of the various wetlands and associated wetland functions, and the development and use of
BMPs for water management, it is anticipated that both wetlands and resource roads can function as
anticipated (Partington and Gillies 2010).
This document describes knowledge gained through a state-of-practice review, with a focus on water
management, of road development in and around wetland systems. This document describes numerous
BMPs available to practitioners who may be looking for practical guidance concerning water
management when constructing resource roads through wetlands. It may also help bring attention to
areas where there is a need for further development of practical tools to help practitioners understand
and identify the environment they are working in.
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Objective
The objective of this document is to provide an overview of the current state of practice for
constructing resource roads in wetlands, particularly in boreal environments. The focus is on water
management and the maintenance of hydrology in wetland systems in forested environments.
Methods
In order to document the state of practice for water management as it pertains to resource roads in
wetlands, various techniques were used to gain information. The four primary methods were:
 Literature review of papers and manuals pertinent to the state of practice for water
management.
 Development of a survey (Appendix I) to help reach numerous practitioners and road builders
in Canada and the United States, and internationally. Approximately 120 surveys were sent
out. The 31 responses (Canada 19, United States 7, and international 5) are in Appendix II.
 Telephone contact was also made with individuals who have road-building, academic, or
research knowledge of wetlands pertaining to resource roads, and these responses were
incorporated in the findings.
 Four days were spent in the field to view and discuss wetland crossings. The field visits were
conducted during late August and early September 2010 near Peace River, Boyle, and Cold
Lake, Alberta. Techniques used and lessons learned from these field days were included in
the findings.
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Impacts to wetlands
In wetlands, effects on vegetation and surface conditions immediately next to a resource road have
been noted during field visits and discussions by many forest management and road development
practitioners. The presence of dead and dying trees is the most common visible clue that the hydrology
of the site may have been altered. Ponded water on one side of the road also supports the concept that
the hydrologic function of the site has been altered. Dead trees tend to be on one side of the road, and
it has been suggested that flooded conditions on the high side cause the dieback. The wetter conditions
on the upstream site cause vegetation to die off and be replaced by species that are better suited to the
wetter conditions (Ducks Unlimited Canada and University of Alberta 2006). One practitioner
interviewed suggested that bulrush or ―cattails‖ start to move in and grow on the high side. It may take
up to 10 years to see any effects on tree species (standing dead), but grasses and forbs (sedge spp.)
may react more quickly. Dead and dying trees in a flooded area of a wetland have been noted in areas
where beaver dams are the cause of the flooding. The downstream site will have a lowered water table,
thus potentially allowing for the growth of vigorous plant species (Ducks Unlimited Canada and
University of Alberta 2006). One survey respondent suggested that sage can move in if the area
becomes too dry.
In northern Alberta it was noted that large areas of dieback occurred in places where no resource road
was present (Figure 1). This may be in part due to beaver activity, or possibly it is related to
precipitation (drought) and weather patterns. It was suggested that the natural succession of a wetland
includes cyclical dieback of the trees, but not necessarily the understory vegetation. As trees die and
fall to the ground, slightly higher and hummocky micro-habitats form.
Figure 1. Large areas of tree dieback have been observed in northern Alberta
in places with no road access. Note the presence of seismic lines.
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Although the incidence of altered conditions would be expected to increase with crossing length,
particularly as some of the crossings are fairly long (up to 3 km), some areas of Saskatchewan and
Manitoba have not seen much dieback of trees or the ponding of water next to the road. Many
practitioners have suggested that declines and changes in vegetation have not been consistent across
the landscape. This may indicate how different wetland systems (i.e., those with flow and those
without flow) are affected.
During the field visits, FPInnovations observed one area to have dead and dying trees on one side of
the road, yet a few kilometres further along the road the dead and dying stand was on the opposite side
of the road. This may indicate the meandering nature of the surface and/or subsurface flows of the
wetland and the complexity of boreal hydrology. During the same field visit and where the same roadbuilding practices were not associated with dead and dying stands of trees, it may indicate that the
road was not dissecting and altering the flow but rather was built parallel to it. Building roads parallel
to a wetland flow direction may be a difficult BMP to implement given it would entail understanding
and knowing the flow direction of the wetland, and, by paralleling the flow, the road may not reach the
desired destination.
One survey respondent noted that along an older road where a cross drain was not installed or was
installed at the wrong elevation, a small wetland was inadvertently created on the upstream side where
none existed before. This same practitioner noted that the area is now seen as very valuable wetland
habitat and practitioners would be reluctant to destroy them by installing proper drainage structures.
Sheehy (1993) describes an example of cooperative wetland conservation between a forest company
(Corner Brook Pulp and Paper) in eastern Canada, Ducks Unlimited Canada, and a federal department
(Fisheries and Oceans Canada). The company built a road bed to purposefully act as a dam, resulting
in higher water levels to one side and an increased aquatic habitat at the site. A fish passage structure
was incorporated through the road, which presumably allowed some flow while maintaining the newly
established water level/habitat. It should be noted that such intentional creation of wetlands by roads
acting as dams is not a current practice and that where there is an abundance of wetlands and wetland
types (i.e., western Canada) that the creation of additional wetlands is not seen as necessary.
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Water management: planning
In constructing any resource road, one of the main objectives is to ensure the road will safely support
the anticipated vehicular traffic. In constructing roads across wetlands in the boreal forest it is
necessary to increase bearing capacity, therefore particular attention is given to constructing a
subgrade that will not fail. The development of resource roads in boreal wetlands has taken on a dual
focus such that the need to establish a road must be fulfilled, but only while addressing water
management requirements, and thus the characteristics of a wetland require careful attention which
may result in modifications to traditional forestry operational approaches. Alternative methods should
be considered for constructing roads on mineral soil wetlands, shallow peat wetlands, and deep peat
wetlands (Watertight Solutions Ltd. 2009). Further, planning for surface flows may be different than
planning for subsurface flows.
It has been noted that a well-designed road will not interfere with the hydrology of a site; roads should
be designed to allow water to move as if no road was present (South Carolina Forestry Commission
2011). In areas of low topographic relief, it can be difficult to know which way the water flows;
however, it is imperative to plan for water movement and not impede flows in order to prevent
negative impacts to the wetland function (Ducks Unlimited Canada and University of Alberta 2006).
The planning of a crossing should also take into account that wetland hydrology can occur laterally
and/or vertically.
Road-location tools
During the initial planning stages the use of tools such as the following can help minimize the number
of stream or wetland crossings (Decker 2003): wetland maps (where available), topographic maps,
forest cover maps, aerial photographs, digital photography, bedrock and surficial geology maps,
LiDAR (light detection and ranging is an optical remote sensing technology), Wet Areas Mapping,
RoadEng flow predictions (application within a road engineering software package), channel
assessments, Google Earth, and fish inventory information. These tools can also be used to locate the
shortest route across a wetland, with some consideration given to crossing the wetland at one of its
narrowest points. Other factors are: (1) realizing the position of the proposed road within a catchment,
and (2) understanding whether the road is located in a localized wetland basin/complex or in an
interconnected wetland complex.
One survey respondent noted the use of a probe to help find a shallow area of a muskeg in order to
locate a road crossing. It has also been suggested that vegetation can give an indication of the depth of
a wetland. Ground reconnaissance is also a valuable effort with respect to planning and accuracy and
is often used as the final confirmation of a road’s location.
Positioning and fill requirments
Positioning a wetland road on higher ground and on ridges where it travels into and out of a wetland
(which are typically drier due to the increased drainage associated with the height of land), has been
advocated by many practitioners and is a component of many BMPs (Nebraska Forest Service 1998,
Moesswild 2004). By placing the road on the ridge, a source of fill would be available from the road
cut across the ridge. As well, borrow pits can be planned and placed along the drier ridge area to gain
additional fill material for use through the wetland crossing. It is not recommended to borrow road fill
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or embankment material from the wetland itself; such practices would damage the fragile surface, may
lower the water table, or damage hydric soils (Zeedyk 1996).
One practitioner noted that his company often positions a crossing below a beaver dam or a series of
beaver dams because this positioning provides a slightly drier environment than the expanded wetland
above the beaver dam(s).
It is widely suggested to construct fill roads (where fill is delivered and built up) in forested wetlands
only when alternative access routes do not exist. This is especially important in wetlands with flowing
water (i.e., fens) because fill roads have the potential to hinder or restrict natural flow patterns; roads
constructed at natural ground level have less potential to restrict flowing water (Mississippi Forestry
Commission 2008). Culverts, bridges, or other means of conveying water through the road must be
used to prevent any restriction of water movement. The sizing and spacing of culverts and bridges
need to be planned with high-flow events in mind, which may happen only periodically. Properly
planned and constructed temporary roads will have fewer effects on the hydrology of forested
wetlands than permanent roads (Baker 1991). This is partly due to the length of time that the road will
be in use before being decommissioned.
Avoiding wetlands
Avoiding the construction of resource roads in boreal wetlands wherever possible is something that
was well supported by survey respondents, and the literature supports this too. Cox and Cullington
(2009) suggest that the construction of roads through wetlands should be avoided unless there is no
reasonable alternative; building roads in or near wetlands is difficult and expensive. Road managers
often avoid wetlands by planning longer roads that circumvent these sites (Légère and Blond 2002).
Special attention should be paid to identifying wetland locations, types, and sensitivities prior to
beginning road construction operations. The incentive to build resource a road across a wetland arises
when the distance associated with avoiding the wetland becomes too great. In various locations in
Canada, avoiding wetlands all together is not a realistic option due to the vastness of the wetlands on
the landscape. Given that resource roads are necessary, negative impacts can be minimized through the
use of properly utilized BMPs (Graf 2009).
Winter construction
If a wetland is planned to be crossed, it is beneficial to construct the road during frozen conditions
(Illinois Department of Forest Resources 2000). Frozen ground offers a greater bearing capacity, and
there are well-known techniques for promoting early and deep freezing of the soils. Snow will often be
cleared away to remove any insulating effect, and tracked machines will be walked along the road to
help drive in the frost. At some operations the road construction process starts with smaller machines
and then when the bearing capacity is appropriate, larger road-construction machines come in to finish
the construction phase. Eventually the frost will penetrate to a depth where the frozen ground will be
able to support the weight of a loaded logging truck.
Many road-building practitioners believe that during frozen conditions the wetland is not overly
affected and that during non-frozen periods the subsurface flows should function as intended.
Although this is a common prediction, road builders have some uncertainties and questions regarding
the actual effects of building frozen roads on surface and subsurface flows during non-frozen periods.
This is highlighted by Smith et al. (2007), who suggest that during winter road-building operations, the
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weight of the frost and the equipment compresses the peat and likely affects hydraulic conductivity. It
is further suggested in Graf (2009) that the function of compression may decrease hydraulic
conductivity by 75%. Where fill is used, the use of a lightweight fill (any material that is lighter than
the parent soil) may lessen the weight acting on weak wetland soils, thereby keeping them from
compressing and blocking subsurface flow (Wiest 1998).
As with any winter road, it is critical to stop the use of the road when the temperature at night stays
above freezing. Frost within the soil starts to disappear when night temperatures stay above freezing
for three or four consecutive nights (Illinois Department of Forest Resources 2000) (Figure 2).
Figure 2. A winter road built across a wetland.
Understanding wetlands and their hydrologic function
Paying attention to the type of wetland being crossed is an excellent suggestion, yet most practitioners
surveyed did not know the major divisions between wetland types or their unique attributes. Therefore,
there may be an opportunity for training or knowledge transfer to help practitioners identify wetland
types and to understand the main differences in how they function. As an example, understanding
surficial geology would allow practitioners to better plan for water management through the
expectation of vertical water movement compared to lateral. Compared to moraine with coarse
material where the water flow may be vertical, clay lowlands can be impermeable and therefore have
lateral flows. Relative to roads built in moraines or areas with known vertical flows, roads have the
potential to affect wetland function in clay lowlands due to the lateral flows (Ducks Unlimited Canada
and University of Alberta 2006). Similarly, the lateral flow within fens may be interrupted by road
development, which dissects the flow. Identifying a fen with such flows may be important with respect
to the chosen crossing location or construction technique.
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Water management: construction
Good road construction practices should include adequate provisions for drainage. Water management
can have a range of effects depending on the extent and intensity of the works; widespread (extensive)
drainage measures are likely to have less significant effects than concentrated (intensive) systems
(Sheehy 1993). The South Carolina Forestry Commission (1994) states in their BMP manual, which
describes forested wetland road construction, that a road fill shall be bridged, culverted, or otherwise
designed to prevent the restriction of expected flows; a sufficient number of culverts across the
wetland will help satisfy this requirement. It is also noted that where ditches are constructed, typically
to direct water to a culvert crossing, the ditches should not convert wetlands into uplands. Water
management techniques that address drainage are described in the following sections.
Culverts
The use of culverts along road sections crossing various types of wetlands (both treed and open) that
are built up with fill were seen at four field visit sites near the towns of Peace River, Boyle, and Cold
Lake, Alberta. Culverts are typically the main water management technique used to allow water to
flow from one side of the road to the other. Culverts are used for streams with well-defined channels
or for balancing water to either side of the road where there is no defined channel. The following
discussion is predominantly about balancing-type culverts unless otherwise noted.
Phillips (1997) suggests that when culverts are installed in peatlands, they should be embedded
(buried), with the upper portion catering to storm surface flow, and the lower portion catering to daily
subsurface flows. Where culverts are not embedded, subsurface flow may pond on the upstream side
and possibly promote the killing of any trees. During FPInnovations’ field visits in Alberta, nearly all
of the culverts examined contained water and appeared to be at or near similar elevations as when they
were installed (i.e., no obvious settlement or curving of the culvert had occurred). A few of the
culverts appeared to be purposefully embedded (partially buried) and a small number had ends
prepared with a step-bevel (Figure 3). Both techniques are considered good practice for promoting
flow through a culvert. Construction of a cambered culvert is a common technique to prepare for the
settlement of the centre.
Figure 3. A partially embedded culvert (left) and a culvert prepared with a
step-bevel (right). Both structures contained shallow, slow-flowing water.
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Size and spacing/location
Generally steel culverts used for wetland crossings range in diameter from 300 to 800 mm, whereas
the diameter of plastic (HDPE) culverts ranges from 230 to 450 mm. Culvert were commonly found to
be of lengths that allow water to exit at ground level. Therefore, the height of road fill has an influence
on culvert length. Culverts that are 12 m long are common.
It is considered good practice to place a culvert at each end of the wetland crossing where the
transition into and out of the crossing provides access to local inorganic materials (sand, silt, or clay),
which will help minimize culvert settlement (Muskeg Subcommittee 1969). In addition, a series of
culverts are typically spaced along the crossing, with spacing ranging from 15 m to 100 m. Illinois
Department of Forest Resources (2000) suggests installing culverts or bridges a minimum of 91 m
apart and at all natural drainages such as defined channels. The National Research Council of
Canada’s Muskeg Subcommittee (1969) suggested that for roads built through a fen muskeg with
horizontal flow, 600-mm-diameter culverts should be used and, if needed, spaced at 60-m intervals;
occasionally 1.5-m-diameter culverts may be needed. Some of the surveyed practitioners suggested
using culverts no smaller than 600-mm in order to help prevent any blockage due to fines settling
within the culvert. The greatest spacing suggested was three 600-mm diameter culverts per kilometre
of ―swamp road‖.
Installing a battery of culverts for wetland crossing at a spacing of 15 to 50 m is one practitioner’s cost
effective solution (Figure 4). In the Peace River area, where culverts were noted to be evenly and
relatively closely spaced across a wetland (at an approximate spacing of 60 m), there appeared to be
no roadside ponded water or obvious negative influence to the immediate wetland vegetation (i.e., no
dead or dying trees).
Figure 4. A battery of closely spaced culverts placed is one technique
for balancing flow on either side of a road through a wetland.
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Field visits and survey responses have shown that as a prudent practice, some practitioners will
periodically revisit a built road to asses if culverts were placed and spaced appropriately. If field
indicators, such as the presence of ponded water immediately adjacent to the road (Figure 5), show
that an additional culvert may be needed, the area will be marked in the field and an additional culvert
installed. Installing a culvert after a road is built adds to the cost of the water management aspect of
the road; the cost could be considerably reduced if the culvert is instead installed during initial road
construction. However, it is often difficult for roadbuilders to identify the right location and number of
culverts needed for a wetland road during its initial construction. Again, it would be valuable for
practitioners to have additional knowledge (possibly gained through targeted research) to help guide
them through these challenges. In the meantime it is a good practice to revisit the site periodically after
the completion of construction to prescribe and install additional culverts where required.
Figure 5. Ponded water next to a built road may indicate the need for additional culverts.
During the field visits, FPInnovations noted one company to be using survey equipment to help locate
the lowest areas along a road right-of-way in order to identify the best location for installing a culvert.
Although a culvert should be placed where water is flowing, and these areas are commonly found in
low lying areas, wetlands may function differently. It did not appear that the survey method was
entirely successful because ponded water was still noted next to the road at various locations.
Discussions on-site included placing culverts at set intervals (at an increased cost) and eliminating the
survey efforts to help offset any increased costs. Given that water may not flow laterally through all
wetland types (depending on connectivity) seasonal ponding may take place as a result of vertical
water dynamics. Having additional knowledge of the wetland types and their hydrologic function
(lateral versus vertical movement), and how best to address the hydrologic needs, would be valuable
for road building practitioners.
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Maintenance
During the field visits, FPInnovations noted that some culverts had sunk over time and become
submerged (Figure 6). The poor bearing capacity of a wetland can result in a culvert sinking below its
installed elevation. Sunken culverts may not function as intended. Having knowledge regarding
wetland characteristics may help practitioners develop alternative construction techniques. In some
cases an entire length of road can sink into the wetland; roads that are constructed from local material
such as sand and clay placed directly onto the wet soils will gradually settle downwards (South
Carolina Forestry Commission 1994). Increased maintenance costs result from the delivery of
additional material along the road to maintain a travel surface adequate for the anticipated traffic. One
surveyed practitioner suggested the increased maintenance associated with water management for
resource roads that cross wetlands was in the magnitude of an additional 20 to 30%. Increased
maintenance through wetlands is also associated with beaver activity.
Figure 6. Sunken culverts may not function as intended and lead to increased maintenance costs
because of the need to replace them.
Culverts are typically marked (staked), which helps in locating their inlet and outlet during routine
maintenance (cleaning or de-icing), and it helps identify the culvert to grader operators in order to
avoid damage during grading operations (Figure 7). Damaged culverts have a reduced capacity and
damage may shorten the life of the structure.
Figure 7. The use of stakes to mark culvert locations helps prevent damage to the culvert and
allows the culvert to be easily located during times of snow cover.
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Bedding
When installing culverts, one technique used to bed culverts on firm ground is to excavate down
through the peat (3 to 5 feet) in an attempt to find firm clay soil. If the firm soil is located, the
additional depth of excavation can be filled with granular fill (where available) and the culvert placed
on top at the desired elevation. If no firm soil is found, the culvert may be placed where firm soil can
be located. In exceptional cases it may be necessary to construct a basic log crib to help support the
culvert (Muskeg Subcommittee 1969). If aggregate is available (pit run) or can be located (seam of
gravel), then the culvert can be bedded and supported on delivered aggregate without undertaking
additional excavation to find firm clay. Depending on the road being built, this may allow the bedding
material to be placed directly on to the organic material or some other layer within the wetland which
can support the bedding material. In deep organic wetlands where corduroy is used, a culverts can be
placed in and amongst the corduroy (for description of corduroy see ―corduroy and brush mats‖
section).
Inlet control
One survey respondent noted that the use of inlet control devices (typically a rock weir) with culverts
can help control water levels on the upstream side of the crossing. An inlet control device is used to
back up water into the wetland and thus prevent a dramatic lowering of the water levels on the upper
side. Inlet control devices may also be well suited for use with large culverts on defined channels to
help maintain upstream water levels (Figure 8).
Figure 8. During the installation of a culvert on a wetland resource road (left), an unanticipated
drop in the water level occurred within the upstream area (right). Constructing an inlet control
device would help maintain defined water levels.
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Beaver activity and blockage
The presence of beavers and beaver dams should be investigated if ponded water is observed
immediately adjacent to the road edge. Culverts are susceptible to plugging and blockage by beavers
as well as by debris (Rummer 2004). Even if culverts are appropriately spaced for the anticipated
flows, or if balancing or equalizing is required, the presence of beaver dams may prevent the culverts
from functioning as intended. One site included in the field visits had ponded water next to the road
because a beaver dam kept water from flowing through an installed culvert, and another culvert had
beaver dam activity at the outlet. The presence of ponded water adjacent to the road does not
necessarily indicate the need for an additional culvert (Figure 9).
Figure 9. Inlet of culvert plugged by beaver activity (left), and outlet area of a culvert that
has a long perimeter dam holding water against the road (right).
There are products to help prevent the blockage of a culvert’s inlet or outlet by beaver activity. The
Beaver Proof Add On, the Beavercone, and the Beaver Stop are all extension type devices that attach
to an existing culvert and help prevent any blockage or damming occurring immediately adjacent to
the culvert, while providing space for flow through openings and grates (Figure 10). Additional
maintenance costs for managing the problems caused by beavers and beaver activity along wetland
road sections have been noted by one survey respondent to be in the magnitude of tens of thousands of
dollars every year.
Figure 10. The Beaver Proof Add On (left) and the Beavercone (right) are examples of
products that help prevent the damming or blockage of a culvert by beaver activity.
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Bridges
Typically, a bridge is used only to cross a well-defined channel within a wetland. A bridge is preferred
for spanning a large stream or where a water course is defined as a navigable water/route. Bridges are
a more expensive option than culverts, and for this reason they are not well suited for crossing small
streams. One survey respondent suggested a bridge or a wooden box culvert would be used when the
channel width approaches 6 m. The aperture below the bridge allows for debris to flow freely through
the channel without concern for blockage. In an area of high beaver activity, a bridge is often preferred
due to the perceived inability of beavers to build a dam at bridge crossings.
Abutments and bearing requirements
The abutments at either end of a bridge require adequate bearing capacity; the use of lightweight fill
may be especially useful in these locations (Figure 11). Geotextile and geogrid are used to help
prevent the settlement or the rotation of abutments. Aggregate is often used for armouring around the
abutments and channel banks but may be too heavy for use in a wetland. The use of geotextile or
geogrid can improve the bearing conditions of the site to a point.
Figure 11. Expanded polystyrene (geofoam) in block form is an example of lightweight fill.
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One innovative method observed was the use of a floating bridge (Figure 12). This technique alleviates
some of the load-bearing requirements associated with typical abutments. The road approaches to the
crossing were constructed on corduroy, which promotes flow opportunities due to the lineal voids along
the length of the logs. A floating bridge was chosen to cross this defined channel through a wetland
because the channel did not freeze to the bottom during the winter access, and seasonal timing was not
always conducive to the construction of an ice bridge. The bridge was removed during non-frozen
periods in order not to interfere with stream flow or navigation (canoe route).
Figure 12. Implementing a floating bridge with approach ramps helps alleviate the use of
weak wetland soils to provide bearing capacity to traditional bridge abutments.
The approaches of this bridge were built with corduroy.
Approaches
When a bridge is used to span a defined stream channel within a wetland, usually the approaches are
built up on either side (Figure 13). Practitioners should consider installing culverts, or other waterpassing options, within the approaches to address flow in these areas. Culverts could be positioned to
allow flows during periods of high water, otherwise subsurface flows might be addressed. A
permeable fill, designed and built to allow for water to pass through, may be well suited for this
application. The wetland outside of the defined channel may have a hydrologic function, such as
lateral flows, that should be considered when planning the crossing.
Figure 13. A bridge is used to cross a channel where a culvert is not well suited.
The road approaches can be designed and built to allow water to pass through;
for example, through the use of a permeable fill or open conduits (culverts).
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Corduroy and brush mats
The use of tree-length logs laid parallel to one another (corduroy) below the surface of a road was seen
at field sites near Peace River and Boyle, Alberta. The use of corduroy is one of the most costeffective methods of increasing a resource road’s bearing capacity. This is partially because the treelength logs are available from on-site and many practitioners are familiar with this technique.
Geotextile, which is a manufactured fabric, is often used as a separation layer during construction. The
geotextile, which is placed either below the corduroy, above it or both, prevents fine road building
material from entering the wetland or depositing amongst the logs (Figure 14).
During the winter, building a corduroy section of road on frozen ground gives the soil additional
strength, which helps prevent any damage by or sinking of heavy equipment. The use of corduroy also
allows the road base to be more widely built, thus providing additional load-bearing capacity.
Figure 14. Construction of a corduroy section of road with geotextile being placed below the
logs (left); and the final road surface, which was built from delivered material (right).
Materials and design
Across the western provinces, corduroy is a common technique for crossing wetlands. Brush mat is a
term used extensively within certain areas and the use of brush mats is similar to that of corduroy but
with an emphasis on retaining the limbs and tops on the stems. Brush mats can be up to 20 m wide and
depth can vary from 0.5 to 1 m.
It is good practice to build a wide subgrade that can accommodate two lanes of traffic because it can
be difficult to reconstruct and widen a subgrade through a wetland at a later time, i.e., if additional
running surface width is subsequently required (Muskeg Subcommittee 1969). Stakes can be used to
mark the centre line and edges of a road, and logs (with branches and tops intact) can be skidded into
place. Any portion of a log extending past the edge of a width stake can be cut with a chainsaw and the
excess portion positioned back onto the brush mat. Geotextile is used on top of the brush mat to keep
fines from migrating amongst the mat; loss of road material would be costly, could increase
maintenance costs, and may impede water flow through the mat.
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The mechanical properties of geotextile include grab tensile strength, elongation strength, trapezoidal
tear strength, mullen burst test, and puncture strength. Hydraulic specifications include water flow
rate, permittivity, coefficient of permeability, and apparent opening size. Understanding the various
attributes of geotextile is important. If geotextile is to be placed on top of a brush mat, additional
strength is required so that the material is not punctured by limbs and chunks of wood. If future roadreclamation plans include rolling back the geotextile, even greater strength may be required. Where
water movement is a concern, hydraulics need to be taken into account.
FPInnovations researchers have noted a varied use of corduroy in the eastern provinces of Canada. In
some locations it is not a common construction technique in part due to the perception that the cost of
using timber as corduroy is too high relative to geogrid (Figure 15) or geotextile. As well, most roads
are built to be permanent (very few roads are decommissioned) and wood within a road might be
susceptible to rotting and deterioration over time. However, one survey respondent felt the opposite,
i.e., that it was more cost effective to use corduroy than geotextile. In some areas of eastern Canada,
when a site is not too wet (i.e., machines can still operate), thick moss and stumps have been used
below the road subgrade as a means of giving additional bearing capacity. In such cases, without the
lineal voids being present, open conduits such as culverts would be needed to allow water passage
through the road. Overlanding construction techniques using inverted stumps to cross wet areas have
been used in British Columbia (BCMOF 2002).
Figure 15. Geogrid is sometimes used to provide additional bearing capacity across wetlands.
Flow considerations
It is unclear if many corduroyed sections of road are attempting to also promote water flow or if they
are attempting to address only the traditional bearing capacity improvements. The opportunities to use
this technique to promote water flow need to be explored further. Because of voids left between logs
and the lineal nature of a log, this construction technique could be the starting point for an improved
method of addressing both bearing and hydrologic function of a wetland. Given that corduroy should
be laid parallel to the direction of flow to promote drainage, understanding wetland function and the
direction of flow is critical to the success of the design (Forestry Corp. 2004).
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One site visited by FPInnovations was unique in that corduroy used was approximately 2 m thick
(Figure 16). This is not a common thickness for corduroy to be built up to; based on field visits
corduroy is typically built one or two logs thick. A 2-m thickness of corduroy may help alleviate the
need for additional fill in an area that is transitioning from hummocky terrain to a flatter, low lying
wetland. The use of logs can be favourable given that logs help prevent the fill material from settling
into the wetland, which may otherwise cause a blockage (South Carolina Forestry Commission, 1994).
Building up corduroy to a thickness greater than 1 m may help address increased seasonal flows when
the water table rises.
Figure 16. A thicker layer of corduroy may be especially cost effective at locations where the
road transitions from a high, dry, hummocky site (left) towards a lower wetland (right).
Placing culverts in and amongst the corduroy may help promote flow through the structure. At one field
site, a plastic pipe was used for this purpose (Figure 17). The site also used geotextile as a separation
layer to prevent the road surface material from migrating downwards and potentially blocking any flow
through the corduroy. The geotextile was also wrapped around ―curb‖ logs on either side of the road to
make subsequent reclamation easier. The geotextile wrapped around the ―curb‖ logs also doubled as a
containment barrier, preventing the road fill from spilling into the adjacent wetland.
Figure 17. A plastic culvert allows water to pass through a corduroy section of road. The stakes
help locate the culvert, and aid in preventing damage to the culvert, e.g., by grading machines.
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Subsurface drainage considerations
Where bearing capacity permits, it is possible to construct a road base that allows water to move
through it, i.e., by the use of angular aggregate within the base level. Many terms are used to describe
this construction technique, including permeable rock fill, rock embankment, rock fill embankment,
French drain, and stabilized natural drainage (Zeedyk 1996). In order to keep fines from migrating into
the aggregate and plugging the permeable mass voids, geotextile can be used as a separation layer
between the aggregate material and the road-surfacing material. A combination of techniques can be
used to allow water to flow freely through a length of roadbed (Watertight Solutions Ltd. 2009).
Zeedyk (1996) points out that these structures are well suited for areas where groundwater discharges
are relatively constant and where there is a need to maintain well-dispersed flows; having a slight
angle to the structure towards the lower side will help maintain positive flow. Zeedyk (1996) also
suggests that the permeable seam should be constructed with 5- to 15-cm rock spread to a depth of
30 cm, and that a flood-relief culvert should be incorporated within the structure. A source of
aggregate is needed for this design, which may be difficult to find / purchase in many areas of the
Boreal Plains.
As an example, a permeable rock subgrade built with flood-relief culverts was observed on Vancouver
Island, where the bearing capacity allowed for the use of large aggregate (Figure 18). The successful
movement of water through the base suggested that the macro pores were not filled with fines and the
design was valid.
Figure 18. A permeable rock fill subgrade constructed to allow for the passage of water.
Note the settlement area on the uphill side (left), which requires periodic cleaning to remove
accumulated sediments. Two culverts have been placed higher within the road to provide
additional conduits for water during periods of high flow. Note that on the downhill side (right),
water has passed successfully through the causeway.
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Cox and Cullington (2009) in British Columbia have suggested that subsurface drainage structures be
built with large, clean gravel or crushed rock placed on top of geotextile fabric to allow unrestricted
water movement from one side of the road to the other. The use of geotextile may provide additional
bearing capacity to help support the gravel and keep it from sinking. The design of this technique can
also include a second layer of geotextile at the top of the aggregate seam (aggregate mattress) to act as a
separation layer and to prevent road surface material from migrating into the seam designed for water
movement. The lower level of geotextile can be positioned on undisturbed vegetation (Figure 19).
Figure 19. An example of geotextile being placed on top of undisturbed wetland vegetation.
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Road decommissioning
Many forest companies are establishing programs for restoring temporary forest roads to productive
forest land after harvesting; generally, rehabilitation addresses soil compaction and includes the
retrieval of displaced topsoil, organic material, and woody debris (Sutherland and Gillies 2001).
Compacted soils result in higher soil bulk density leading to lower porosity, reduced aeration, and
slower infiltration rates (Sutton 1991). Paramount within this practice is the re-establishment of any
natural drainage within stream channels or draws, which is typically achieved by the removal of any
conduits such as culverts or log structures. Any work conducted in and around streams needs to be
done carefully for the protection of stream features (riparian, bank, and channel) and the aquatic
environment, including the prevention of sediment delivery.
Winter
For winter access roads, where road use is restricted to frozen periods, it is common to promote stream
or drainage flow paths through the road during the spring melt. Where a known stream or flow area is
located, a crawler-tractor can use a ripper shank to rip a path through the snow-covered road and snow
fill to promote flow and drainage. Once the water has worked away at this ripped path, the path
becomes wider and more pronounced. This technique helps prevent flows from spreading out over the
entire road, which can cause erosion and other damage.
Many operations have moved to the use of clean snow to build stream crossings along winter roads
that cross wetlands. The use of log bundles to cross streams has decreased, partially because the
bundles are difficult to remove without causing bank or channel disturbance. The disturbance caused
by removing the frozen-in log bundles can be avoided by using clean, compacted snow. Because the
snow is relatively clean and free of aggregate, a chainsaw can be used to cut a trench /seam into the
road at the stream crossing to help train and promote flows during the spring melt. Some practitioners
still use log bundles for crossings along winter roads, but careful attention must be given to the timing
and the technique of removing the bundles, including leaving the bottom logs in place in order not to
disturb the stream channel.
Summer
As practitioners move towards using more geotextile for separation and partial bearing improvements,
working with the right strength of material may be important. Choosing the proper strength of
geotextile could help prevent the material from being ripped as it is being retrieved during road
decommissioning. The geotextile can be prepared in such a way as to enhance its retrieval; i.e., it can
be attached to a log or piece of dimension lumber before being covered with fill material (Figure 20).
This will allow the equipment (such as an excavator with live thumb) to grasp and pull on the piece of
lumber and thus spread the forces along a greater length of geotextile. This may be very practical
during decommissioning activities at locations such as stream crossings where it is common to remove
any crossing structures and re-establish the natural channel.
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Figure 20. Geotextile is wrapped around dimensional lumber which is then nailed to
a log in preparation for easier retrieval during road decommissioning.
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Summary
The construction of forest and resource access roads through wetlands can create numerous
environmental and operational challenges for road managers. Understanding and promoting good
water management techniques for resource roads in wetlands may help address many of these
challenges.
Addressing the hydrologic function of a given wetland during construction is of paramount concern.
Best management practices (BMPs) are used to minimize negative operational impacts, and when
operators are trained and provided with the knowledge of BMPs for their worksite, the results can be
cost effective, ecologically sensitive, and not necessarily excessively restrictive to forestry operations.
With careful planning, by having knowledge of the various wetlands and associated wetland functions,
and by developing and using BMPs for water management, it is anticipated that both wetlands and
resource roads can function as anticipated (Partington and Gillies 2010).
Effects on wetlands have been noted by many practitioners. Dead and dying trees, and ponded water,
are the most common visual clue that the hydrology of a site may have been affected by a road. Dead
trees tend to be on one side of the road, and it is assumed that flooded conditions cause the dieback.
However, the presence of dead and dying trees has not been consistent on the landscape, which may
indicate how the different wetland systems (with flow and without flow) are affected. Impacts may
also occur due to beaver activity or weather patterns such as drought.
Planning for water management where roads cross wetlands has become an additional focus among
practitioners who have historically been concerned with issues regarding the bearing capacity of the
site. The characteristics of a wetland require careful attention, and modifications to traditional forestry
operational approaches are needed. A well planned and designed road should not interfere with the
hydrology of a site; roads should be designed to allow water to move as if no road was present (South
Carolina Forestry Commission 2011). There are many crossing location tools that can help minimize
the number of wetland/stream crossings, as well as aid in positioning the crossing in a desired location
such as a narrow area. Planning for fill requirements will also have an influence on road location.
Avoiding the building of roads through wetlands by building longer roads that circumvent these areas
should be considered when planning a road network. Road construction through wetlands can be
difficult and expensive. If a wetland is planned to be crossed, it is beneficial to undertake the
construction during frozen conditions (Illinois Department of Forest Resources 2000). The frozen
ground provides greater bearing capacity and there are well-known techniques for promoting early and
deep freezing of the soil. There are some uncertainties and questions regarding the actual effects of
building frozen roads on surface and subsurface flows during non-frozen periods.
Road-planning and road-building practitioners need to understand wetlands and their hydrologic
functions in order to better manage for water movement. This may require training and knowledge
transfer. Many practitioners do not know the major divisions between wetland types or their unique
attributes. Understanding the need for both vertical and lateral water movement, and understanding
seasonal influences, may lead to better water management and minimized impacts to the wetland
being crossed.
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During construction a common technique for managing water is by the use of culverts. Culverts can be
used for streams with well-defined channels or for balancing water to either side of the road where
there is no well-defined channel. Culverts can be partially embedded during construction to allow the
upper portion to cater to surface flows, with the lower portion catering to daily subsurface flows
(Phillips 1997). A range of culvert diameters are used for these purposes (300 to 800 mm for metal
pipe), and both metal and plastic culverts are used. The spacing of culverts used to balance water on
either side of a road varies, from as close as every 15 m to as far apart as 335 m. Installing a battery of
culverts, or placing culverts at a set spacing may be cost effective. During road construction, culverts
need to be bedded and supported to maintain their vertical positioning. Excavating down to a firm
ground or the construction of a log crib may be required to help support the culvert. Revisiting a newly
built road to assess if culverts were placed and/or spaced adequately is considered a prudent practice.
Unexpected maintenance may be needed when culverts do not perform as intended. Additional costs
would be incurred if sunken or deformed culverts have to be replaced. There are also increased
maintenance costs associated with monitoring and preventing beaver activity at culverts.
Bridges are typically used within a wetland for crossing a well-defined channel. The bridge abutments
require an adequate bearing capacity, which can be accomplished by the use of a lightweight fill. The
use of concrete abutments and aggregate armouring may prove to be too heavy for use in a wetland. A
floating bridge would not require the same load-bearing capacity from its abutments, which function
more like ramps. The approaches on either side of a bridge within a wetland can be planned and
designed to have a water-passing capability.
Corduroy and/or brush mats are used to cross wetlands. Corduroy allows for the construction of a twolane road. Sections up to 20 m wide have been constructed and the typical thickness varies from 0.5 to
1.0 m. Geotextile is used as a separation layer, which prevents fines from migrating into the wetland or
amongst the logs; migration of fines could impeded flow and result in lost road material, thus
increasing maintenance costs. Constructing sections of corduroy during frozen conditions provides
greater bearing capacity for heavy equipment. Many practitioners feel the use of corduroy is costeffective while others opt to use geotextile/geogrid. How well water flows through corduroy may need
to be further assessed. Corduroy needs to be orientated appropriately to promote flow between the
logs. Culverts can be placed amongst the logs to help promote flow.
Where bearing capacity permits, it is possible to construct a permeable road base to allow for water
movement through the road by the use of large aggregate within the base level. The voids created by
the aggregate allow for the passage of water. Geotextile is used as a separation layer to keep fines
from migrating and filling the voids. Flood relief culverts can be positioned to accommodate high flow
events. A combination of subsurface drainage techniques can be used along a section of road,
including seams of aggregate and French drains.
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Road decommissioning includes re-establishing any natural drainage within stream channels or draws
by removing structures such as culverts. These works need to be done carefully to protect the stream
and aquatic environment, including preventing the delivery of sediment. Along winter access roads,
channels may be filled with clean snow, or log bundles with snow. These crossing areas need to be
carefully decommissioned in order not to cause bank or channel damage. To promote flows in a
known channel or flow area during the spring melt, a path can be formed by the use of a ripper shank
attached to a crawler-tractor, or by the use of a chainsaw (providing it is cutting into clean snow only).
All-season or summer access roads may also be decommissioned. Stream-crossing structures are
usually removed in order to re-establish the natural channel. These stream crossings/channels can be
built in ways that facilitate the decommissioning process, such as by choosing and preparing any
geotextile separation layer to be more easily retrieved.
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References
Baker, E. 1991. Mississippi’s best management practices for wetlands. Mississippi Forestry
Commission, Jackson, Mississippi.
http://www.deq.state.ms.us/mdeq.nsf/pdf/NPS_Mississippis_BMP_for_Wetlands/$File/Mis
sissippis%20Best%20Management%20Practices%20for%20Wetlands.pdf?OpenElement
British Columbia Ministry of Forests. 2002. Forest Practices Code of British Columbia—forest road
engineering guidebook. Second edition. For. Prac. Br., B.C. Min. For., Victoria, B.C. Forest
Practices Code of British Columbia Guidebook.
http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/Road/fre.pdf
Cox, R.K.; Cullington, J. 2009. Wetland guidelines for forestry. Chapter 5 in Wetland ways: interim
guidelines for wetland protection and conservation in British Columbia. Wetland
Stewardship Partnership and B.C. Min. Env., Victoria, B.C.
http://www.env.gov.bc.ca/wld/documents/bmp/wetlandways2009/Wetland%20Ways%20Ch
%205%20Forests.pdf
Decker, R.C. 2003. Current regulations, guidelines and best management practices concerning forest
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tices%20Concerning%20Forest%20Harvesting%20and%20Riparian%20Zone%20Manage
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Ducks Unlimited Canada and University of Alberta. 2006. Wetlands in the boreal plains of the
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University of Alberta, Western Hydrology Group, Edmonton, Alberta. Internal Report.
The Forestry Corp.; Watertight Solutions Ltd. 2004. Review of forest management practices for
protection of water related resources in the boreal and taiga plain western Canada. Ducks
Unlimited Canada, Western Boreal Office, Edmonton, Alberta. Internal Report.
Gillies, C. 2007. Erosion and sediment control practices for forest roads and stream crossings.
FPInnovations, Vancouver, B.C. Advantage Report Vol. 9 No. 5.
Graf, M.D. 2009. Literature review on the restoration of Alberta’s boreal wetlands affected by oil, gas
and in situ oil sands development. Ducks Unlimited Canada, Edmonton, Alberta. Internal
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Illinois Department of Forest Resources. 2000. Forestry best management practices for Illinois.
Springfield, Ill.
http://web.extension.illinois.edu/forestry/publications/pdf/timber_harvesting/Illinois_BMPs.pdf
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Légère, G.; Blond, E. 2002. Applicability of geosynthetics for the reinforcement of forest roads in
muskeg bogs. Forest Engineering Research Institute of Canada (FERIC), Vancouver, B.C.
Advantage Report Vol. 3 No. 25.
Mississippi Forestry Commission. 2008. Mississipi’s BMPs, best management practices for forestry
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Moesswild, M. 2004. Best management practices for forestry: protecting Maine’s water quality.
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I.C. MacFarlane, editor. University of Toronto Press.
Nebraska Forest Service. 1998. Forestry best management practices for Nebraska: a reference guide
for loggers, landowners and managers. Nebraska Forest Service and University of Nebraska
Institute of Agriculture and Natural Resources, Lincoln, Nebr.
http://www.nfs.unl.edu/documents/ruralforestry/Forestry%20BMPs%20for%20Neb
raska.pdf
Partington, M.; Gillies, C. 2010. Resource roads and wetlands: opportunities to maintain
hydrologic function. FPInnovations, Pointe-Claire, Quebec. Internal Report IR-2010-11-01.
Phillips, M.J. 1997. Chapter 28, forestry best management practices for wetlands in Minnesota. Pages
403–409 in C.C. Trettin, M.F. Jurgensen, D.F. Grigal, M.R. Gale, and J.K. Jeglum, editors.
Northern forested wetlands: ecology and management. Lewis Publishers, New York, N.Y.
http://www.srs.fs.usda.gov/pubs/ja/ja_phillips001.pdf
Rummer, Bob. 2004. Managing water quality in wetlands with forestry BMPs. Water, Air, & Soil
Pollution: Focus 4(1):55–66.
Sheehy, Gregg. 1993. Conserving wetlands in managed forests. North American Wetlands
Conservation Council (Canada). Ottawa, Ontario. Issue Paper No. 1993-2.
Smith, C.; Morisette, J.; Forest, S.; Falk, D.; Butterworth, E. 2007. Synthesis of technical
information on forest wetlands in Canada. National Council for Air and Stream
Improvement, Inc. Research Triangle Park, N.C. Technical Bulletin No. 938.
South Carolina Forestry Commission. 1994. Best management practices, forested wetland road
construction. Pages 26–29 in South Carolina’s best management practices for forestry.
Columbia, S.C. http://www.state.sc.us/forest/bmpmanual.pdf
South Carolina Forestry Commission. 2011. Best management practices for braided stream systems: a
supplement to the 1994 BMP manual. Columbia, S.C.
http://www.state.sc.us/forest/braid.htm
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Sutherland, B.; Gillies, C. 2001. Rehabilitation of temporary forest roads in Alberta and
Saskatchewan. Forest Engineering Research Institute of Canada (FERIC), Vancouver, B.C.
Advantage Report Vol. 2 No. 6.
Sutton, R.F. 1991. Soil properties and root development in forest trees: a review. Forestry Canada,
Great Lakes Forestry Centre, Sault Ste. Marie, Ont. Forestry Canada Information Report OX-413.
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Wiest, R.L. 1998. A landowner’s guide to building forest access roads. USDA Forest Service,
Northeastern Area, State and Private Forestry, Radnor, Penn. Technical Publication NA-TP06-98. http://www.na.fs.fed.us/spfo/pubs/stewardship/accessroads/accessroads.htm
Zeedyk, W.D. 1996. Managing roads for wet meadow ecosystem recovery. USDA, Forest Service,
Southwest Region, Albuquerque, N.M. Publication no. FHWA-FLP-96-016.
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Suggested reading
Holaday S.; Martin, J. 1995. Wisconsin’s forestry best management practices for water quality—
wetlands. Dept. of Forest Ecology, School of Nat. Res., University of Wisconsin, Madison, Wis.
Forestry Facts No. 11. http://basineducation.uwex.edu/woodland/OWW/Pubs/FEM/FEM_011.pdf
Government of New Brunswick. 2002. New Brunswick wetlands conservation policy. Dept. of Nat.
Res. and Ener., Frederiction, N.B. http://www.gnb.ca/0078/publications/wetlands.pdf
Government of Nova Scotia. 2009. Nova Scotia wetland conservation policy–draft for consultation.
Dept. of Env., Halifax, N.S.
http://www.gov.ns.ca/nse/wetland/docs/Nova.Scotia.Wetland.Conservation.Policy.pdf
Minnesota Forest Resources Council. 2005. Sustaining Minnesota forest resources:
voluntary site-level forest management guidelines for landowners, loggers and resource managers.
State of Minn., St. Paul, Minn. http://www.mlep.org/documents/completefmgbook2009.pdf
Ontario Ministry of Natural Resources. 1990. Environmental guidelines for access roads
and water crossings. Govt. of Ont., Toronto, Ont.
Tiner, R.W. 1999. Wetland indicators: a guide to wetland identification, delineation, classification,
and mapping. CRC Press, Inc., Boca Raton, Fl.
Welsch, D.J.; Smart, D.L.; Boyer, J.N.; Minkin, P., Smith, H.C.; McCandless, T.L. 1995. Forested
wetlands: functions, benefits and the use of best management practices. USDA Forest Service,
Northeastern Area, Radnor, Penn. Publication no. NA-PR-01-95.
Acknowledgements
The author expresses his appreciation to the following individuals for their cooperation and for
reviewing this paper: Chris Smith, Julienne Morissette, Al Richard, and Kevin Smith of Ducks
Unlimited Canada; Donna Kopecky and the planning/operations staff of Louisiana-Pacific Canada
Ltd.; and Doug Bennett, Séverine Lavoie, and Judith Pothier of FPInnovations. The author also
gratefully acknowledges funding provided by Sustainable Forestry Initiative (SFI) and by Natural
Resources Canada under the NRCan / FPInnovations CFS Contribution Agreement.
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Appendix I
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Appendix II
1. When planning a new road location through a wetland, do you use specific
techniques, or have specific reasons for locating the road with respect to
anticipated water managements?
Canadian Responses
a. We are a winter log and haul company so all of our logging and hauling
activities are on frozen ground. That does not exclude us from ensuring that
we cross watercourses appropriately. We try to ensure that watercourse
crossings are in the most appropriate locations taking into consideration items
such as: new cut or existing trail, bank development, channel definition and
depth. Questions to ask: Is crossing perpendicular to road or at an angle, Is
the area flat or is there a valley to deal with, Difficulty of reclamation.
b. When I am planning an access through a wetland you need to first look at if
there are any wildlife restrictions or timings, water body class and types. Then
find the most suitable and stable crossings and the distance from the required
objective. Costs are a big driving factor so you try to balance the distance and
or quality of the crossing.
c. Location is the best combination of road alignment and stream crossing
variables to minimize stream crossing lengths, impact to stream morphology,
and sensitive wetland habitat. Initial location must also allow for habitat
considerations for species at risk, SFM objectives, etc. – this information
needs to be required up-front prior to layout and usually requires field recee.
d. Usually we try to avoid going through a wetland but if there is no choice we
cross at the narrowest point. If there is a stream in the wetland we will cross
at the straightest location.
e. Most of our roads are located along and over top of seismic lines. It’s mostly
this specific reason for location, usually the disturbance is already there.
f. Yes. We have operating ground rules with ASRD. Our company also has a
matrix for summer or winter operations depending on the size and shape of
the wetlands. We tend to build winter roads on wetlands. Construction varies
depending on how the area freezes.
g. Normal practice is to find the narrowest area to cross, which is usually also
the area that has the best defined channel. In the boreal, we often end up
aiming for a crossing just below a beaver dam or a series of beaver dams.
There are occasions that we have “probed” a muskeg to find the shallower
area to cross. Vegetation cover will also be of some help in indicating the
depth of the wetland.
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h. Assess for: Soil type & stability, General topography & slope, Surrounding
vegetation, Crossing alignment, Channel characteristics and Ease of removal.
i. We try to avoid road crossings of wetlands. If unavoidable we try to minimize
crossing width and do it in the winter with a temporary crossing. If summer
access is required we install cross drains and channel crossings. In a few
cases we use geotextile corduroy or similar to support the road grade,
otherwise we use sub grade / gravel on top of wetland soils or if the wet soil
isn’t too deep, excavate and fill.
j. The Alberta Government Timber Harvest Planning and Operating Ground
Rules specify how values associated with “wetlands” are planned for and
protected. Jamie Bruha (Jamie.bruha@gov.ab.ca) is the Provincial Ground
Rules negotiator (780-415-8561) ex wetlands and habitat for swans.
http://www.srd.alberta.ca/ManagingPrograms/ForestManagement/documents/
Annex_4_draft_Jan_15_08Final.pdf
k. We try to avoid wetlands when designing all season roads. Wetlands will be
crossed to maintain road alignment. Our preference would be to stay away
from defined channels as the crossings tend to be more difficult to construct
and more expensive.
l.
Finding a narrow section of the wetland is preferred from a geotechnical
perspective. Using wood to construct the fill helps to lighten the embankment
loading, reduce settlement and encourage water flow through the
embankment. In one instance, we pile support the embankment. The
embankment fills consisted of clean (very low fines content) sand and gravel
used to build a GRS load transfer platform.
m. On the rare cases that we plan on locating road through wetlands, generally
the shortest rout through would be taken. Crossing perpendicular has been
done on most occasions where roads cross narrow wetlands surrounding
rivers or floodplains.
n. I would say no. More important is trying to locate the road close to sources of
potential aggregate so you have some to put on top of your swamp road that
is cost effective. That being said when crossing well defined drainages, at
least you know which way the water will go. In extremely flat swampland
areas sometimes it is trial and error with an excavator to try and determine
which way the water drains.
o. We usually pick a spot that minimizes the need for a structure. If we do need
to install a structure we try to pick a spot where the structure size would be
minimized. To sum it up we try to corduroy versus installing a structure.
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p. I use aerial photography to direct me to areas that have the least amount of
impact to the wetland and the water. I also use wet area mapping to direct
myself to the fewest crossings.
q. Choose preferred corridor based on shortest possible wetland crossing,
without compromising long term costs. Test the depth of the peat or depth to
mineral soil. I take advantage of mineral soil ridges above and below the
surface. Then keep alignment in areas of heavier vegetation or thicker root
mat areas to assist in floatation of grade. Locate channels, run a drainage
analysis of basin and target right angle crossings if possible. Install cross
drains intermittently even if no channels are evident, approximately every
200m.
r. Yes, we have specific techniques for roads and crossings.
s. Planning uses depth-to-water table and wetland GIS layers to avoid wetlands
where possible.
USA Responses
a. The answers I provide are based on the South Carolina Forestry Best
Management Practices manual and braided stream system supplement.
These guides are being followed on over 90% of the forestry operations in the
state. Road plans are made to parallel the direction of water flow except when
a crossing is necessary.
b. Do everything possible to avoid routing a new road through a wetland. Use
remote sensing of all kinds available to help find alternative routes and, if
absolutely necessary, locate the road to minimize length in the wetland.
c. Identify stream crossing locations, stream crossings needs, microtopography,
soil types.
d. Try to avoid locating roads in the wetlands first. My experience is with
California Sierra Nevada forest where meadows can sometimes be avoided.
Not like the picture below. However when a road is already in meadow or new
construction must go through the meadow we have used permeable fills with
culvert arrays, and lowered road profiles to allow for controlled overtopping.
As far as location is concerned I look for the shortest path across, higher in
the channel as opposed to lower. Location with respect to channel form,
locate in a riffle, or a straight stretch. Not in a channel bend, or at a pool.
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e. The first question to consider is can one get to the other side without crossing
the wetland or a stream. If possible and practicable, don’t cross the wetland
or stream. BMPs would suggest crossing at the narrowest point. In the case
of a stream crossing, look for a location where the crossing distance can be
minimized, where banks are firm and approaches shallow (low), at a 90
degree angle to the stream, where one can easily divert water from the road
crossing surface before it reaches the crossing area. All of this, and many
other considerations, are part of our BMPs.
f. First we would try hard to avoid crossing a wetland area, particularly if it is a
designated wetland. If we did have to cross it, it may be that we would have to
get a Corps of Engineers permit. If we crossed such an area, we would
typically try to do it with a raised rock fill with a battery of culverts to maintain
any natural surface or subsurface flow.
g. Roads across wetlands in Minnesota must conform to the state’s Wetland
Conservation Act and related Federal Clean Water Act requirements top avoid
impact to the extent practical, and minimize any unavoidable impacts. This
involves planning to select the shortest crossing location, using temporary
crossing options whenever possible, and utilizing construction methods that
limit the area impacted and maintain the hydrologic flow in the wetland. Most of
this is to be done by the landowner or contractor on their own. Limited staffing
and funding results in limited oversight by the regulatory agencies.
International Responses
a. At first we try to avoid wetlands but because we have lots of them we have to
pass through them. The detailed design with measurements to find the best
locations is important. If we are allowed and can drain away the water from
the road we will do that. If we can get rid of the water we then have to build it
through the wetland. We always try to build where the maintenance will be as
easy as possible. Nowadays life cycle thinking is important.
b. In the UK, wetlands, are hyper-protected, there being so few, that it’s almost
impossible to build through them for environmental reasons. In a few
extensive peat bogs (Scotland and Ireland) there have been roads built
across wetlands, but I don’t believe water management has been the key
issue, except to ensure that the road isn’t damming up near surface water
flows across the line of the road. Peat settlement or displacement issues are
usually more important.
c. I am not aware that in Finland such techniques have been used. But in
general not too many new roads are currently being built. The main criteria
has been the peat thickness. This info is collected for geotechnical design
and has been surveyed with ground penetrating radar.
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d. I am a few years out of date on the practical design issues concerning the
construction of roads on peat in Scotland but what follow will hopefully not be
too far from what is done in northern Scotland.
The new European environmental regulations are having an effect,
particularly the requirement to adhere to the new European Water
Framework Directive. This came into force in December 2000 and became
part of UK law in December 2003. It focuses on delivering better water
environment and local ecology. For these reasons new roads are generally
planned and located with statutory consultees - the Scottish Environmental
Protection Agency (SEPA) and Scottish Natural Heritage (SNH).
Additionally, the Water Environment (Controlled Activities) (Scotland)
Regulations 2005 enables the Scottish Environmental Protection Agency to
control activities which may have an impact on the water environment.
e. We try to avoid wetland as much as possible. But when we have to cross
wetland, it’s mostly aesthetic and biological consideration we look at. And of
course crossing creeks at the right places is important. Right place is often
defined as the cheapest crossing.
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2. Do you use planning tools when locating a road through a wetland?
What are they?
Canadian Responses
a. Maps, air photos, ground reconnaissance.
b. We first start out with a table top study where we use Aerial imager with Lidar
to narrow down our choice. We then field scout and ground truth from what
we have found from the table top study and make a final decision.
c. Resource overlays, orthophotos.
d. Maps and orthos.
e. No.
f. Yes. We have Lidar bare earth, wet areas mapping, current vegetative
inventory and excellent photography to evaluate the sites. These are major
enhancement tools we have used within the last year.
g. We normally use a number of tools for our location work, including forest
cover, aerial photos and now Wet Areas Mapping and Lidar, but it still
requires on site inspections to confirm the final site.
h. Considerations: General overview – fly over, aerial view, water flow etc. Haul
safety – straightness, grades etc. Environmental concerns – cuts etc. Soil
stability sub-surface water flow, etc. Minimize number of crossings summer or
winter standards structure requirements.
i. Digital photography Lidar wet areas mapping (supplied by ASRD) RoadEng
Flow predictions channel assessment fish inventory.
j. Alberta Vegetation Layer (AVI) – forest inventory cover layer Provincial
hydrography layer Wet Areas Mapping (WAM) data layer Lidar data (if
available) Digital ortho coverage.
k. We do view the entire landscape using aerial photos to determine where
culverts are required. We also survey the centre line to determine low spots
for drainage across the road.
l. Aerial photographs, Google Earth, topographic maps, bedrock and surficial
geology maps.
m. Yes aerial photos or orthophotos are always a great tool to utilize when
determining the best road location.
n. No. The goal is to minimize costly water crossings and keep the road
relatively straight.
o. No.
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p. Yes. Wet areas mapping, i.e.: flow grids topographic maps, Aerial
photography, and Sat imagery.
q. Air photos, topo and forest inventory maps. Probes or drills to test depth to
mineral soil. Helicopter recon.
r. Yes, we have planning tools. GIS Hydrography layers, Hydrologically
Sensitive Areas Map, digital orthophotography, DEM.
s. Depth-to-water table and wetland GIS layer.
USA Responses
a. Topographic and soil maps and aerial photographs are used. The South
Carolina DNR has a GIS site where all of these are available online for the
entire state.
b. Ordinary and infrared aerial photos and orthophotos; soil, vegetation, wetland
maps.
c. Topomaps, Soil Surveys, Aerial Photos, Soil Auger, Field Recon.
d. Yes, aerial photos and GIS. But you really need to assess the condition of the
stream / wetland (i.e., stability of the stream) well above and below the
proposed crossing with direct observation.
e. Air photos, topography maps, plat book maps, protected waters maps, and
soils information. I would also ask the landowner or resource manager if they
knew of any existing crossings and then look at those as possible locations
for the planned crossing. All of this information would be collected from office
sources to better inform the forester when walking the ground during the
design of the timber sale.
f. We would look at route alternatives using our resource tools including air
photos, topographic maps, and GIS data on the area.
g. Planning tools are available. Large projects often involve extensive planning
by engineers, but on most forest management projects individual landowner,
managers, and contractors use their own judgment and may nay utilize any
other resources.
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International Responses
a. This is part of the building process. First we have forest studies, feasibility
studies and then detailed designs to find the best location for the road. In the
building process the most important thing to consider is environmental impact.
b. Not enough wetlands to use special tools. General road planning tools in
use.
c. See previous question. In addition to GPR some drilling can be used.
d. The usual environmental impact analysis and statement, site and ground
investigation, but increasingly bringing in professional hydrologists and
ecologists for their inputs.
Aerial surveys, geophysical mapping are common on larger schemes. Peat
thickness identified by probing, and sometimes GPR.
e. Map in scale 1:5000 and orthophoto And map in scale 1:50000 to get an
overview.
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3. Is the use of corduroy part of your wetland crossings, and if so please
describe how?
Canadian Responses
a. Sometimes, but not very often. It is difficult to reclaim when the ground is
frozen. We do use log fills for watercourse crossings.
b. It can be if it’s an option. We first talk to the Forest officer and FMA holder to
get there thoughts. If everyone agrees, we then pre cut the trees to length so
they don’t hang out of the shoulder of the road. Then we install the tree’s
leaving caps where our culverts will be placed, then role the filter cloth over
top. Then we cover with dirt and you now have a very good road.
c. Yes. As it is part of an over landing technique. It looks exactly like the
example below.
d. Corduroy with felt is laid down to cross the wetland. Normally we only cross in
the winter.
e. We don’t encounter too many roads where we do this in the summer months;
it is mostly freeze in and go. Where we do encounter it in the summer,
corduroy with local tree species is the preferred method.
f. Generally, for non frozen activities, we use corduroy and / or matting. If dirt
caps are required we have a separation layer of geotextile.
g. We use some long “log fills” with filter fabric as shown for temporary seasonal
crossings, but for any long term structure we are not allowed to use corduroy.
h. Corduroy used when: Wet area can not be avoided. Wet areas where
adequate frost conditions don’t exist. Protection of soils in soft soils improve
the integrity of road grade or surface.
i. Corduroy is used mainly as part of log fills. Layer of logs with geotextile on top
and soil cap, similar to your photo below. Rarely extends very far though – too
expensive for long stretches. Usually only use these for temporary crossings
with removal afterward. In some cases the corduroy becomes permanent
component of the road.
j. Corduroy can be used as a temporary crossing measure (winter access) but
must be removed as part of the reclamation effort (OGR 11.3 Road
Construction, Maintenance and Reclamation).
k. Corduroy crossings are used in short term roads (less than 2 years of use).
For longer term roads we use geotextile and dirt to cross wetlands. Corduroy
crossings are built by placing timber with a loader side by side then covering
with dirt.
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l. Yes. Both conventional corduroy and fore and aft log construction. However, in
most cases geotextiles are used in conjunction with the corduroy to increase
permeability by limiting the infilling of the voids with organics or road fill.
m. I have not witnessed corduroy roads crossing wetlands in my field
experience.
n. Yes, in extremely wet areas where tracked equipment has a high probability
of getting stuck, otherwise we use primarily thick moss and stumps. In areas
of non-merchantable wood the buncher does not harvest the ROW and the
excavator places all material in the road for brush mat. It is cheaper to make
use of corduroy and good brush mat material than to use rolls and rolls of
geotech.
o. Dirt over logs, sometimes we use geotech.
p. Not a practice that I recommend for the long term, unless materials such as
GEOGRID is used. Wood tends to rot.
q. Yes. Will email BMP.
r. Yes, but not used very often and only on specific situations. Corduroy is
mainly used during skidding operations when crossing dry channels.
Corduroy is removed following operations. It has been used with and without
geotextile.
s. Corduroy often used to provide a base (similar to photograph shown).
However, geo-textile is rarely used.
USA Responses
a. Few wetlands in South Carolina have deep organic soils so there is little
corduroy construction when used consists of logs covered with sand and clay
obtained from upland sources.
b. No answer provided.
c. Pole crossings, slashing to close approaches, mats, crane mats, etc.
d. Only as a temporary measure.
e. Corduroy can be an excellent tool for crossing a wetland, especially when
placed on top of or sandwiched between geotextile and adequately sized to
support the anticipated loads. Corduroy can remain in the wetland crossing if it
originated from within the wetland. If the material originated from an upland
location, it must be removed at the end of the activity (otherwise it becomes fill).
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f. Yes, we do periodically use corduroy to cross wetland areas, but only for
temporary roads. Our purchasers are much more likely to use it than us
design a corduroy crossing. Where used we would put down geotextile, logs,
more geotextile, and a gravel or soil surface to drive upon.
g. Corduroy is one option for constructing roads in wetland. When used it may be
installed in a variety of ways, such by itself with not geotextile or gravel, with
gravel but no geotextile, or as shown in your example. There is no standard
approach required.
International Responses
a. For temporary roads used for building a bigger road or roads with lesser
traffic we often use geotextile or geogrid. Crisscrossing timber is seldom used
nowadays but in older roads we often can find it. Geogrid is often used to
strengthen roads and also used when widening the road. For roads with more
traffic, reinforcements or excavations have to be done.
b. Forest roads often use brash (as opposed to logs that they want to sell). Most
forest roads will only be used for short periods (months) while a forest block
is cut and the brash won’t deteriorate in that period. it might be 40 years
before heavy traffic uses that route again, so it’s not economic to use log
based corduroy.
c. This was earlier used but not any more. Maybe in some forest roads.
d. Corduroys are not currently used on public roads but they have been used in
the past, so many floating roads on peat built in the 50’s, 60’s & 70’s still sit
on corduroys.
e. Corduroys are however regularly being used on upland wind farm
developments and forest roads where timber is cheaply available. Usually
laid directly on the surface of the peat or on a mat of brash. Crushed local
aggregates and geogrid(s) above.
f. http://www.roadex.org/index.php/services/partner-knowledgebank/scotland/floating-roads-on-peat-report has background and
descriptions.
g. Very seldom. But always geotextiles, and often GeoNet. First we lay out the
geotextiles, and then the GeoNet if necessary, and the base course upon that.
We have guidelines for how thick the base course should be, depending on the
construction material
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4. Construction across wetlands is often done during frozen conditions. Do you use
any specific construction techniques to address the anticipated flows during the
spring thaw and summer months?
Canadian Responses
a. Activities are usually completed and reclamation is complete prior to spring thaw.
b. The only things we do is notch the snow fill, without disturbing the banks to
maintain positive water flow through breakup.
c. Removal of some of the corduroy to provide cross-drainage, cross-ditching,
removal of any low-clearance structures.
d. Our practice is to remove logs in wet areas to avoid water issues.
e. Not really, sometimes log bundles in heavy known flow areas or seepages.
f. Our company has an erosion control document that outlines criteria for
reclamation. Slopes have more parameter as erosion potential increase. It is the
intent to leave the area with minimal disturbance. All crossings are removed. In
many cases crossings use snow fills to minimize disturbance.
g. If it is a seasonal crossing we will use smaller equipment to freeze in the
crossing to a depth that a larger machine can cross up to the point that loaded
trucks can then cross. Any defined channel will have a crossing built of natural
snow, man-made snow, logs or a temporary bridge. Log and snow fills should
have culverts installed in case warm weather or springs create water flow during
the life of the crossing.
h. Choice of crossing structures that allow water flow: Bridges, timber bridges,
arches, culverts, snow fill ice bridges, log fills on ephemeral notches in log
corduroy.
i. Logfills and snowfills or temporary bridge decks are the common crossing
structures on winter roads across wetlands. Logfills are removed prior to
breakup. Snowfills melt on their own and bridge decks provide flow paths. We
are always careful to ensure flow continuity.
j. Typically all logs used for corduroy are removed prior to break up. If using fill
then separation layers are required.
k. Typically when crossing channels in the winter we will build ice bridges or use
temporary bridges. Ice bridges are built with clean snow and flooding. We do not
use logs or branches in crossings. Ice bridges are notched in the spring to help
with the spring melt.
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l. Laying geotextiles into the gullies before placing logs helps to limit disturbance of
the ground during log removal.
m. Generally we would wait till a wet area would be totally frozen before any activity
takes place. When totally frozen the road could be graded or located on top of
the wet area with minimal ground disturbance.
n. No.
o. No.
p. We do not build winter roads.
q. Prefer to use snow and ice only, but can use metal or plastic culverts, cabled
logs or portable bridges. Usually dig out or scarify snow fill prior to breakup.
r. Snow and ice crossings are typically used with small round culverts (either steel
or plastic). Culvert and snow and ice are removed prior to spring melt or a trench
is constructed through the snow and ice to allow for flow during spring melt.
s. No difference between winter and summer road construction specifications.
Winters in our operating area lack sufficient cold weather to allow for “winter
roads”.
USA Responses
a. No answer provided.
b. No answer provided.
c. Not applicable in southeastern US.
d. No winter construction where I come from. Snow is either too deep or ambient
temps not cold enough.
e. Place corduroy above and below the corduroy. This reduces sinkage into the
weak soil beneath as well as the movement of fines and fill between the
pieces of corduroy. We discourage the use of corduroy in streams as
operators will neglect to remove it at the end of operations and because it is
difficult to completely remove when applied during the winter.
f. I have not worked with this! You might send this to Maureen Kestler who
works with cold region issues.
g. Use of corduroy and/or installation of crossdrain culverts is recommended,
but compliance is uneven.
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International Responses
a. We try to schedule projects to allow work throughout all seasons. This means
that the winter season can be used for the “groundwork” and we can then
finish the rest in the summer. Often the work will be stopped for a couple of
weeks when the spring thaw is too difficult to manage.
b. We don’t experience seasonally frozen conditions in the UK.
c. Not that I am aware of.
d. No. This is not a problem in Scotland.
e. A shallow ditch 4-5 meter away from the road edge, and culvert across/under
the road where the water naturally drain away.
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5. Are culverts used to cross well defined main channels of a wetland stream?
If so please describe typical culvert type, size, length, and installation techniques.
Canadian Responses
a. This is not typical for us.
b. They are in most cases or in cases where flash fluids are not anticipated. The
particular size is based on anticipated volumes of water. As far as the length is,
so the culvert sticks out from the shoulder of the road no more and no less than
a foot. Then a marker is installed on the end so it’s not damaged with a grader.
c. Depends on the size of the stream, fish-bearing status, beaver activity, etc. In
general, larger is better for fish and beaver applications. Multiple large
openings also work to allow for seasonal changes to the channel location
(i.e., Toe of alluvial fans).
d. Since we rarely cross them and if we do it’s usually in winter time, we rarely
use culverts. If it’s a fish bearing stream we would put a temp bridge across it.
If it’s non-fish we may stick an appropriately sized pipe for the channel or if it
requires a large pipe >1000 mm we may put a smaller 500-600 pipe in and
remove it before freshet.
e. Yes, usually a 500 mm or better pipe with logs on either side to facilitate
recovery and better re-use.
f. Crossing types (culverts, bridges) are determined by channel width and peak
flows as well as fish barriers. If we are in beaver country we may choose to
install beaver-ad-ons to prevent damming.
g. Culverts are used in most instances, but if they require more then perhaps
two 1.0 meter culverts. We prefer to put in single span bridges if possible. The
culverts are often installed in the late winter, when water flows are low. This
also allows easier access to both sides of the site. The site has to be
undercut to solid natural material and then back filled with proper materialgenerally pit-run gravel in the center with clay ends to seal out water. If done
in freezing conditions the project must be continuous to avoid freezing the
material before it is properly placed.
h. Use normal galvanized steel culverts length must extend beyond fill with
overburden back sloped and stabilized size & installation techniques are
dependant on design road life – minimum size 500 mm. Special conditions
followed on fish bearing streams (depth, slope, grade, etc).
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i. We are moving away from round culverts as crossings of channels. In most
cases we feel GRS and bridges are better options. When using culverts we
typically use D or oval shapes embedded to maintain natural bottom on fishbearing streams, but may still use round non-embedded on non-fish-bearing.
Culverts always installed in the dry with water bypassed in alternate structure
while construction is in progress. In-stream work in timing window or by
special permission.
j. Yes culverts are used. Q50 specification used for sizing is the industry
practice.
k. Depending on the circumstance, bridges may be utilized to cross channels.
We have installed culverts in channels utilizing standard procedures for
culvert sizing. We also use standard installation processes to cross channels.
l. Culverts are problematic due to differential settlement and hydraulic uplift
forces. Currently we prefer open bottom arches and have several plans out to
install these arches on corduroy running perpendicular to the arch (parallel to
the road).
m. Yes I have witnessed large culverts such as these. Mainly on all season
roads that cross wetlands. Generally it is a large engineered project and
incorporates careful planning and construction.
n. Standard technique is used when solid bottom creek is within 5-6 feet of
reach with an excavator, 3-6 diameter culverts, round steel, embedded with
compaction and erosion control. The biggest challenge here is to make sure
you keep the center of your culvert a little higher during installation to account
for downward pressure from logging trucks over time. The harder installation
is where you have no bottom. We pile in conifer to solidify the bottom of the
creek area as best as possible, lay geotech, 2-3 layers wide and tie it into the
road on each side of the creek so it supports the pipe when you set the pipe
in the creek. Then complete the culvert installation as you would normally
from here on. You are never sure if your pipe will not bend or deflect when
done though. Stream diversions around work areas are the norm when
dealing with water flow during this work. Dirty water is pumped from the area
of work into the forest to filter back towards the creek. When working on
swamps or soft organic areas be sure not to concentrate the traffic of
equipment in local areas as there is the potential to punch through organic
mat and then you will need to corduroy to close up any holes. Keep your
footprint of your working area as wide as possible to displace weight of
working equipment, work slow and smoothly with equipment, and avoid jerky
movements.
o. Yes but we are trying to go with temporary bridges more often.
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p. Previously we used open bottom arch culverts; however do to the
environmental standards now required when installing open bottom arches
we now use bridges 12’ to 20’ in length.
q. Yes. Size will vary pending stream flow and flood analysis. Always install in
dry conditions by diverting, damning or pumping. See BMP.
r. A variety of crossing types are used based on specific conditions and timing
of construction. Culverts are used on streams and wetland features, in
addition to portable bridges and snow and ice crossings. Geotextile may be
used as an additional means of strengthening crossing and road bed in low
lying areas (conducive to high water tables and moist soil conditions).
s. Yes. Use watershed area calculation for minimum culvert size. Length
dependent upon fill depth. Installation techniques same as recognized
watercourse.
USA Responses
a. Culvert sizes are based on drainage area and physiographic province. For
example if the upstream water shed is 10 acres 24” culvert in the lower
coastal plain and 30” for piedmont and mountains for permanent roads, for
temporary roads 12” and 18” respectively. Lengths should be long enough
that culverts extend well beyond road fill on both upstream and downstream
sides. Fill material is to be stabilized with specified grass or herbaceous
material with recommended seeding rates.
b. Designed for specific site and channel: sized, sloped, and backfilled to permit
passage of all endemic aquatic species / life stages.
c. Common. 12 inches to 68 inches, multiple pipes possible. 20 to 100 feet long.
Put in with skidders, dozers, excavators, frontend loaders.
d. Yes, we use culverts. From question one, culvert arrays can help to distribute
water across the meadow more naturally. Permeable fills help to maintain
subsurface flows. Install techniques would entail adequate dewatering to
prevent sedimentation. Geotextiles helps keep the permeable mass voids
clear and free flowing. Also part of the foundation in wetland bedding. Again,
capacities for culverts, whatever you are comfortable with and can afford but
always provide for overflow.
e. Typically a steel culvert. It must be at least 12 inches in diameter, or half the
distance between the streambed and the road surface, whichever is greater.
Culvert length is highly variable as many operators don’t have a selection of
culverts to choose from. Installation could be with an excavator or a cat.
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f. If a well defined channel, we would install a culvert, and we typically use CMP
metal pipe. Length would be dictated by road width and fill slope to have a
projecting pipe. Size would be based on some hydrologic analysis using local
Hydro techniques, regression Equations, rational Formula, or local gauging
data. For very minor flows, a minimum diameter 24-inch pipe would be used.
g. Culverts are used. Bridges are preferred. Recommended culvert size is
dependent on the drainage area above the crossing and the width of the
channel. The culvert should be installed with approximately 1/4 of the
diameter below the stream bed or use an arch culvert. Any state protected
water will require a permit. Major crossings will involve licensed engineers.
International Responses
1. Yes. A typical culvert is made of steel or plastic and has a minimum diameter
of 800 mm, but most culverts are sized with regard to the flow of the
watercourse.
2. Yes. I’m not close enough to answer this accurately. Small (<600 mm) might
be corrugated pipe like your picture. In the forest, larger ones are often made
on site - e.g., with gabion faced abutments and concrete planks. Some are
even made of forest derived timber . . . because the forest is seen as
recreation area so shouldn’t be too “industrial” in appearance. On public
roads more substantial concrete pipes or concrete box culverts would usually
be used.
3. All culvert types have been used. In most of case their foundation is made to
“solid” ground and the problem after that is the fact that the rest of the road is
settled and culvert sections are higher. That is avoided by long transition
wedges.
4. Yes. All types. A good open-source reference for this is
http://vikingenergyfiles.opendebate.co.uk/files/Appendix-14.3-StreamCrossing-Guidance(4).pdf.
This shows examples of the types of “ecology culvert” now being required by
the Water Framework Directive.
5. Yes. Plastic culvert up to 800 mm, then treated steel culverts. We often put
geotextiles, GeoNet or logs beneath the pipe. The length is often 8-9 meter
long
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6. Are bridges used to cross well defined main channels of a wetland stream? If so
please describe any aspects of the design and construction related to water
management.
Canadian Responses
a. This is not typical for us
b. We use bridges where the water courses are classified as navigable waters,
or sees flow rate changes. The bridge design around the 100 flood and the
width of the channel.
c. Yes. Footing material may be questionable, consider pipe piling for
permanent structures. Winter applications can rely on frozen soils for bearing
capacity, and structure can be lower (may make it shorter) with less clearance
but must be removed prior to the freshet. Have to consider future access
concerns if this approach is utilized.
d. Yes they are used. They generally tend to be longer than normal to try to
span most of the wetland (our wetland crossings don’t tend to be huge).
Usually we try to avoid wetland crossings.
e. Yes, usually temporary in nature on sill logs in the winter and a more solid
base on the summer. We would have a P. Eng prepare a design, bring in a L75 to L-100 portable and set it in place.
f. We use bridges, some are temporary versus permanent including abutments.
This varies per site. We also use snow / ice bridges to minimize cost and site
disturbance.
g. A lot of wet areas that have defined channels that require a single span bridge
also require further cross-drain culvert installations. The weight of the fill for the
bridge approaches will act as a dam to subtle drainages in the wet area, and
the fills may displace native material up and out into the wet area and later the
natural drainage further. The single span bridge itself will help avoid beaver
interference compared to culverts and generally allow more natural water flow.
The bridge bearing piles have to be to a depth to meet refusal and the wing
walls have to be properly installed to avoid movement in the soft soils of the
site. Bridges are often designed somewhat short for financial considerations.
h. Maximum timber bridge life is 5 years. Portable steel span: Totally enclosed
with curbs clean – free from dirt, debris, etc. Proper foundation length spans
entire channel all disturbed soils are stabilized adjacent water flow managed
to protect stream straight road approach all approvals in place structure
certified to planned traffic loads.
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i. Yes. Design for flow interval applicable to class of road. May use cross drains
or French drains for additional water movement but try to avoid situations
where that is needed.
j. Bridges used. See OGRs.
k. Yes bridges are used to cross well defined main channels, especially if there
is fish present. Some of the construction techniques we use to help with water
management is to use shot rock for sub grade material close to bridges,
bridges are usually placed on piles such that we are not narrowing the creek
channel.
l. We have constructed bridges across wetlands using a light weight log fill
abutment design where the log fills are retained by a series of short, log
pilings pushed into the ground with the excavator. The front and back pilings
are cabled together to provide fixity to the pile tops.
m. Yes of course.
n. Make sure abutments have solid supports through use of geotech or grids in
order to avoid rotation of cribs or settlement.
o. Yes, use MNR portable bridge design.
p. These are pre built during the winter months. We install either gabion baskets
filled with 4 to 8 inch stone as an abutment or concrete blocks that are often
used as barricades depending on the height required. This is all done in
respect to the watercourse alteration course required when crossing any
watercourse.
q. Yes. The key is to prepare solid approaches and ensure adequate span. We
use mostly portable single span and ensure 10-12 feet of overlap with
approach each end of bridge, to provide the extra support and guard against
failure.
r. Yes, portable bridges are used. During construction, footings are placed
outside of high water mark during summer / fall operations. In the winter,
bridges can be placed on top of frozen stream banks and removed before
spring melt. Wing walls are constructed and wrapped with geotextile to
prevent road material from eroding and depositing into channels.
s. Bridge design and construction conform to provincial requirements that
include sizing to accommodate peak flows (1:100 year flood).
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USA Responses
a. Most forest roads use culverts.
b. Span longer than bankfull width of channel so that piers do not encroach on
streambanks.
c. Common. Headwalls, intermediate supports, footers, approach, overflows,
height above floods, etc.
d. Stream simulation; An Ecological Approach to Providing Passage for Aquatic
Organisms at road stream Crossings.
http://www.fs.fed.us/eng/pubs/pdf/StreamSimulation/index.shtml
Consider the geomorphic approach to crossing design for culverts and
bridges. Water management is intertwined with aquatic organism
management.
e. We recommend use of the MESBOA approach. Match culvert width to
bankfull stream width. Extend culvert length through the toe of the side slope.
Set the culvert at the same slope as the stream slope. Bury the culvert 4 to
12 inches into the stream bottom. For culverts 2 to 6 feet in diameter, dig 10
to 18 inches below the stream bottom. Offset multiple culverts, with culvert in
the deepest part of the channel cross section buried according to permit
requirements and centered on that deepest part. Set other culvert(s) one foot
higher. Align the culvert with the stream channel.
f. If a span is over around 20 feet a small bridge is most likely used, or a large
box culvert. We try to not constrict the natural channel. Abutment work would
be done in an area either dewatered or in a confined area out of the main
channel flow.
Most common footings are shallow spread footing, below the depth of
anticipated scour. In very soft soils a raft foundation may be used using layers
of geotextile. For a main permanent bridge, a deeper foundation would likely
be used, either with caissons or piles.
g. Many bridges for temporary crossing will be built or provided by the logger.
Larger projects will involve licensed engineers.
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International Responses
a. Maybe more environmental and geohydrological questions are necessary in
order to make a decision as to which method to use for a main channel? For
permanent roads, the bridges are designed according to the national and
European standards.
b. Yes. Irish bridges might be built if a shallow founding depth is possible. If not
a piled abutment might be built with small (<600-mm) pipes under approach
embankments. I wouldn’t expect any training works.
c. If there is a stream then a bridge is built according to standard design
principles.
d. As in 6.
e. We rather use half culverts, especially when we are crossing creeks with fish
living there
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7. In wetlands without a defined stream channel, are culverts used to help “balance”
water through a resource road?
Canadian Responses
a. Yes, but it is difficult to get it right.
b. First we see if there is a lowest point to the wetland or where a defined
channel runs in for culvert placement. If neither of those exists we put in
equalizer culverts which are counter sunk into the wetland so water can travel
back and forth with no restrictions.
c. Yes.
d. Yes.
e. No.
f. Yes, or crossings removed for non frozen times and reinstalled in winter.
g. “Equalizer” culverts are required in all wet area crossings, and generally a
number of culverts are required. Often, later inspections may show the need
for further culverts, as the “channels” will not be apparent to normal sight or
survey tools. These installations will have to be properly bedded and set at
the proper grade.
h. Culverts, various types of French drains and corduroy are used to ensure
water flow when dealing with sub-surface water movement. The degree of
excavation, base prep, installation, backfilling, and finishing is directly related
to the type and tenure of the road and associated site specific factors.
i. Yes. Also use French drains and logfills.
j. Culverts typically used with defined channels; winter roads through wetlands
have used ice or snow fills without separation layers.
k. Yes, we install at least 1 culvert on every wetland to maintain water flow on
either side of the road.
l. We have mixed culvert in with a corduroy approach. In addition, it is possible
to use multiple culverts such as the Megaflow culvert system installed on the
Doris Road.
m. Yes.
n. Yes, rule of thumb for us is a minimum of 3-600 mm cross drains per
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kilometre of swamp road. You are literally draining a swamp when you build
roads through these areas and not enough cross drains forces water further
down the ditch lines eroding the fine clays and filling what culverts you have
with sediment. This is why we don’t use anything smaller than 600 mm
culverts.
o. Yes, usually use a 450-mm plastic.
p. Yes, typically we will install 450 to 600-mm culverts to balance the water if a
better location for the road could not be found.
q. Yes.
r. Yes.
s. Yes. Culverts installed as deemed necessary by Operations Coordinator.
USA Responses
a. Yes. The goal is to convey water under the road so that the wetland flows as
if the road was not there. South Carolina wetlands often receive groundwater
flow from surrounding uplands so that the edges are wetter. A culvert should
be placed just as it enters the wetland to allow this water to move within the
wetland.
b. Yes.
c. Sometimes.
d. Ok, however this could concentrate and accelerate water and possibly cause
headcuts upstream or scour below.
http://www.fsl.orst.edu/geowater/RRR/
Some presentations in here address these issues.
We have tried inlet control devices to back up water in a meadow and prevent
headcuts.
e. Yes, spaced no more than 300 feet apart.
f. Yes, often a battery of culverts spread across the wetland area, and
particularly in any location where it appears that there is a distinct flow.
Otherwise culvert spacing seems to vary from 15 to 50 meters apart.
g. They are recommended, but implementation is spotty.
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International Responses
a. Yes. It is important to keep the balance with the water pressure on the banks.
This is important because of the stability and also to prevent bank material to
move in one direction, which can give settlements.
b. Yes, small one (<600-mm), sometimes with a spreader ditch running parallel
with the embankment so as to de-localize the ingress and egress from/to the
wetland.
c. Not that I know.
d. Yes, both in excavated roads and floating roads on peat.
e. Yes
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8. If culverts are used to “balance” water, do you have a method for spacing the culverts?
If there is no method of spacing, how do you decide culvert spacing?
Canadian Responses
a. See #7
b. There is no specific guideline to the spacing other than visually making an
assessment appropriate to the wetland.
c. Initial placement at dry channels, then modify as required where water pools.
d. No method necessarily. More based on experience and knowledge of the
wetland and lay of the land.
e. No.
f. Varies per site depending on how much water movement potential there is.
We monitor and adjust if more are required. Water yield varies from year to
year.
g. There may not be a correct formula for culvert spacing, but on any area over
say 200 meters you will find that you will need one in the apparent drainage
channel and one near each side of the wet area. It seems the weight of the fill
tends to lift the deeper part of the area and deflect drainage to the shallower
sides of the area.
h. Place in all slight depressions where water flow could be managed. Additional
structures installed if water flow is obstructed.
i. Not generally a problem for us as we are usually able to avoid extensive
wetland crossings. If needed spacing is subjective. We do have older roads
where a cross drain was not installed or installed at the wrong elevation and a
small wetland was created on the upstream side where none existed before.
Many of these are now very valuable wetland habitat and we would be
reluctant to destroy them by installing a proper drainage structures.
j. Culvert spacing have referenced water yield models built on drainage sizes
and topography but this subject area is not included currently in our OGRs.
k. No we do not have a spacing method. We install culverts based on our
previous experience and looking at the vegetation in the lowland.
l. Frequent (10 to 20m spacing), small diameter (300 to 400-mm) culverts. Field
judgment.
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m. In a situation such as this generally a contractor would place extra culverts in
the ground during road construction. I’m not sure what the spacing would be.
n. Where the water pools after you have constructed the brush mat road.
o. No answer provided.
p. I would say that depending on the amount of water in the wetland a culvert
should be placed at least every 20m. Where possible avoiding crossing a
wetland of this nature is done at all costs.
q. Rule of thumb is 200m apart or as deemed necessary.
r. Spacing is not required in the situations that exist in our area.
s. No specification used – at discretion of Operations Coordinator. Would be
good to have a simple method to calculate this though.
USA Responses
a. At least 24” culverts are placed at all apparent low spots and regularly
between. Spacing is dependent on the expected flow. Roads are often made
by digging ditches on each side of the road and using spoil for the road
surface, most wetlands do not have very deep organic surfaces, and several
culverts connecting upstream to down stream ditches. The ditches are not
connected to any surface water course and end such that any flow will
disperse on the forest floor. Ideally the upstream ditch collects groundwater
accumulating upstream of the road, the water passes through the culverts
and downstream ditch disperses the water back into the soil.
b. Generally, place them in natural side channels and swales.
c. Sufficient to allow water movement.
d. Use the permeable fill.
e. Yes, no more than 300 feet apart.
f. See comment in #7. I think this arbitrary spacing is based purely on
experience and how “wet” the area seems.
g. The recommended spacing is placement of culverts near the entry point to
the wetland and every 300 feet across the wetland. Culverts should be a
minimum of 24 inches in diameter, with 1/2 the diameter below the surface of
the wetland. In deep peat (4 feet or more) collection ditches on both sides and
parallel to the road should be considered with lead ditches from them to the
crossing culverts to facilitate flow across the road prism.
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International Responses
a. This is a geohydrological question.
b. None that I know of. I suspect that they are designed for flood purposes to
prevent excessive flows under any main bridge, not dimensioned particularly
for the benefit of the wetland.
c. Not that I know.
d. No, apart from visual inspection of “flushes” and “springs”, and onsite
estimation of likely water flows. It is also important that any existing stream
crossings and underground peat pipes are retained in place.
e. Not a described instruction. The road planner comes up with a suggestion in
the road plan, but the road builder (contractor) might see some more needs
during the construction. We try to have a good teamwork between the
planner and the constructor.
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9. Have subsurface structures been built through the resource road to address water
movement at depth?
Canadian Responses
a. Not typical for us.
b. I use the French drain technique when springs develop in or beside the
access. We find the source of the water, and ditch it out so it will drain. Then
we line the ditch with filter cloth, install weeping tile, cover the weeping tile
with screened out rock and cover over with filter cloth and back fill.
c. Not utilized here.
d. French drains have been used in some areas but not on any wetland
crossings that I have been involved in.
e. No.
f. Generally no for wetlands. We tend to use French drains in areas where there
are springs that lead to soil displacement.
g. While these substructures would have some merit to maintaining the natural
water flow, frost and the interaction of traffic and frost in the north are very
unforgiving on delicate structures. About the only way to avoid frost damage
in our area is to keep water away which of course can’t be done in this case.
h. French drains are used primarily to deal with sub-surface water movement to
stabilize road grade or slopes. Various designs: Geotextile wrapped clean
gravel specially built geotextile drains wrapped perforated pipe wrapped log
fill combination of above ensure exit portion is open.
i. Yes. French drains, but not commonly.
j. Not that I am aware of as government regulator.
k. Sorry, don’t know what a French drain is?
l. I have not tried a buried drain approach. However it should work provided the
inlet end can be kept clear of organic build up plugging. It could be a
maintenance problem.
m. No answer provided.
n. No.
o. No.
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p. No.
q. No, but some of the brush mat ends up being embedded below the surface
and allows seepage.
r. No subsurface structures have ever been used.
s. No.
USA Responses
a. Only ditches as described in the previous section.
b. I have heard of these in Arizona / New Mexico but have never seen them.
c. Seldom.
d. Yes, French drains or mattress work well.
e. Not generally.
f. Only minor over excavation and placement of geotextile, and backfill with
coarse, permeable rock.
g. See previous response.
International Responses
a. Yes. We have sometimes built with crushed rock, which help to give balance
to each side of the bank. To prevent fast movements of water through the
crushed rock along the road, small “dams” can be built with moraine.
b. A coarse aggregate blanket (120-mm stone size perhaps) might be used
between geosynthetic sheets on public roads, but more as a construction
expedient and consolidation drain and only incidentally as a link between the
wetlands each side of the road.
c. No instructions that I know.
d. Not that I am aware of - apart from preserving flows through existing peat
pipes using culverts below the road.
e. Yes. Crushed rock are often used as base course, and the water can flow
slowly through there.
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10. Have you noticed any changes or impacts to the wetland ecosystem immediately to
the wetland ecosystem immediately adjacent to the resource road?
Canadian Responses
a. Your example of dead and dying trees on 1 side of the road is accurate.
b. Never, unless water flow was blocked or route altered.
c. No impacts here, limited size of wetlands.
d. No.
e. No.
f. Yes. This may be due to the road and sometimes uncontrolled beaver activity.
I’ve also noticed large areas on primary highways.
g. There is ample evidence of ecosystem alteration when there is inadequate or
improper cross drainage at a wetlands site. Beyond water dammed on the
high side next to the road grade, there may be vegetation species change,
with most common evidence being “cat-tails” on the high side. There may be
flooding of black spruce or other tree species on the high side and even die
back from lack of moisture on the low side. In extreme cases the native
material and tree cover in the area may be visibly pushed up at the side of the
grade, dramatically impacting the wet land and the drainage.
h. Ensure water doesn’t puddle. Vegetation isn’t dying or showing signs of
stress soil stability.
i. Generally no for our own roads. But we see evidence of impacts in the area,
especially provincial highways and energy sector roads that cross larger
wetlands. Example: trees die on wet side of the road. Note the previous
comment about inadvertent creation of wetlands on uphill side or road where
none existed before.
j. Yes when subsurface drainage has been impeded. This is on a case by case
basis. Quite difficult to assess on a landscape scale (SOFTCOPY interpreted
images may assist with this question).
k. No.
l. I have seen trees flooded (killed) by embankment construction.
m. Not that I am aware of but then I have not consciously looked for a difference.
n. Lack of drainage will flood out and kill adjacent stands of trees similar to what
beavers dams do.
o. No.
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p. Some of the burrow pits fill with water and actually become small wetlands
over time.
q. In isolated cases there have been ponding and damage to vegetation
because of it.
r. Yes, impacts have been observed but at a smaller scale, localized effects.
s. Have observed occasional decline in vegetation health, no consistent trend
though (i.e., sometimes health decline occurs / sometimes it does not).
USA Responses
a. Roads without the proper number of culverts may kill upstream tees or
hamper natural regeneration.
b. The situation you describe below is common. Also if there are not enough
floodplain drainage culverts, so that they concentrate flow. Scour can occur
downstream of the road in the floodplain channels.
c. Tree death due to flooding, beaver increases, species shift, open water, lack
of regenerations, etc.
d. I have seen small meadows dry up below a road because we intercepted
subsurface flows with the road prism. Tried to use French drain to correct this.
e. Where adequate drainage isn’t provided to facilitate the flow of water through
the road, water build up upstream, flooding new areas and killing timber
“upstream”.
f. if not properly done, or where only a fill has been used in the past, we have
blocked the flow and dried up areas of the wetlands. If too dry, sage moves in
rather than wetlands species (in the west). In other areas the lodgepole pine
or other tree species start dying. In some marine coastal areas we see the
mangroves die.
g. Responses vary widely, but in most cases there is little or no apparent
hydrologic impact. Often there are invasive species that seed in
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International Responses
a. Drainage through the road can give a dried out condition which can affect the
ecosystem. The opposite effects are as the example down.
b. No. But this doesn’t mean it hasn’t happened. it’s one reason the
environmentalists stop most construction over wetlands because they do
believe they’ll be a deleterious impact.
c. Our peat bogs are relatively small in areal size and road designer try to avoid
in crossing them. But still there are many roads in Finland crossing wetlands
and no major problems in ecosystem has been reported.
d. Some vegetation changes due to the effects of the new material and
associated road drainage. Deep roadside ditches can have an effect by
locally lowering the water table.
De-icing salts on public roads has locally affected trees but this is not a
problem on forest roads.
e. Some other type of vegetation might come into being, but is not consider to be
a “problem”.
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11. Are there increased, decreased, or unique maintenance costs associated with water
management and road sections which cross wetlands?
Canadian Responses
a. Your example is accurate.
b. Increased because they do have to be inspected more regular bases and
deal with minor issues before they become a major issue.
c. Beaver activity is the biggest issue! Constant cleaning and we have yet to find
a truly effective beaver fence. The odd pipe that gets heaved up due to frost
action.
d. Generally increase maintenance depending on beaver activity and how often
the culverts plug up. Often on old ones there may not be enough culverts so
we have to add more culverts to the road.
e. Not really.
f. Not for winter, but yes for summer. This is why we avoid these areas
whenever possible and operate seasonally. Some wetlands are shallow and
we have built good roads with low disturbance to the environment, while
others seem bottomless and should not have roads through them.
g. Depending on the depth of the wet area and the amount of non-frozen traffic
there may be efforts required up to and including rebuilding the grade as it
“sinks” into the wet area. The equalizing culverts will have to be replaced or at
least augmented by further drainage. If the fill material was not substantial
enough and if filter fabric was not used under the grade, native material may
be “pumped” up through the grade, creating a soft area that will be very
difficult to repair.
h. Management plans to address: Beaver activity water flow management soil
stability & erosion – ditch blocks, ditch outs, rip rap, erosion blankets, etc.
Road stability especially shoulders. Additional use of engineered products for
road reinforcement – geotextiles, etc. Vegetation cover. Structure
maintenance – repairs, thawing when frozen, etc. Unique drainage structures.
i. Beaver plugging of cross drain culverts is a fairly common problem. One of
the reasons we are trying to avoid using culverts. Another is that the culvert
may float or sink from original installation elevation, causing maintenance
problems.
j. I would argue that there are added costs of NOT managing water movement /
flow on a cut block / landscape scale… including flooding & reforestation
failures for example.
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k. When crossing wetlands there is always increased maintenance costs.
l. Culvert damage due to settlement increases maintenance and the need for
drainage repairs / replacement. It is also understood that the amplification of
the sound of running water caused by the installation of a culvert is what
attracts beaver to culvert sites. This further increase maintenance cost and
the potential for flood death of trees. This encourages us to look more at
frequent, cost effective, open bottom structures to cross wetlands
m. Yes. Inspections need to be done to make sure that the water is free flowing
from one side to the other. Plugged culverts can wash out roads. Beavers
may need to be removed or trapped to dissuade this from happening.
Generally there would be more care and attention in these places because
the risk of something happening is much higher.
n. Typically less beaver problems. Sometimes culvert sizing is too small so we
add an overflow pipe just to make sure during periods of high spring melting.
o. We spend tens of thousands of dollars every year on managing beavers.
p. All crossings have to be checked and repaired if damaged. The main cause of
repairs is due to beavers.
q. Yes. My guess is 20-30% higher due to more frequent failures.
r. There are increased and unique situations where maintenance costs are
variable. The most significant issue we face with culvert maintenance deals
with ice build-up within a culvert causing water to flow overtop of the road.
s. Increase in first year due to the sinking of road surface.
USA Responses
a. The roads are more expensive to build and maintenance can become an
issue. The US has specific regulations about activities in wetlands and road
construction and maintenance must comply with those regulations.
b. No answer provided.
c. Culvert maintenance, Beaver control, periodic crowning and gravel.
d. Increased maintenance if proper structures have not been put in place. As far
as the sinking road, use geotextile to reinforce the foundation and you should
be ok.
e. Definitely. Properly building the crossing takes time and money, as does
maintaining it. Appropriate paperwork has to be completed and filed with the
proper authorities.
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f. Wetlands often have beaver so they tend to plug up the culverts. We either
have to keep them cleaned out or use some sort of Beaver relief techniques.
If we have not used good rocky fill materials, or in deeper soil deposits we get
roadway settlement and have to live with an uneven road or refill the road
surface.
g. The quality of the construction and adequacy of crossdrainage are major
factors in maintenance. Also beaver, ATV traffic, and traffic volume affect costs.
Access control is important, but can be very difficult.
International Responses
a. Yes. Often there will be large settlements, which means that the road section
can be too low and you will have to build it up higher. Each time you fill up the
bank new settlements will come. This problem will not stop until the bank
stands on solid earth or reinforcements can be done. Culverts only work to
balance the water between both sides of the road.
b. Increased costs c.f. normal roads are inevitable - culverts and bridges need
regular safety checks and consequent maintenance (unblocking. e.g.).
Settlement is an issue. greater flexibility also leads to more rapid
deterioration of the pavement - thus need for re-gravelling (unbound) or
reinforcement / thickening if construction if sealed.
c. Drainage management is a big problem and in many places road are
deteriorating faster because drainage (like outlet ditches) cannot be improved
in these areas because of environmental reasons.
d. Increased costs. The Scottish government accept that public roads on peat
cost more to maintain by factoring in the length of roads on peat in each area
in their budget distributions. Older public roads are suffering due to higher
traffic volume and heavier axle loads.
Unique costs: Monitoring the settlement of floating roads. Keeping the local
hydrology in balance. Protecting the existing water table - new deep drainage
can trigger new settlement.
e. If decent built after our road guidelines, there is often less costs to maintain a
road over wet land than generally. Exceptions might arise!
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12. During the decommissioning of a road which crosses through a wetland,
what techniques are used to address the water management challenges?
Canadian Responses
a. Usually, complete reclamation is required.
b. The most common one is to remove the culverts slope back the banks off the
road and leave it that way through very wet areas. We are now trying to
remove the culverts and the clay up to the water or ground level. Then
covering it back with top soil and letting it naturally re-vegetate.
c. Leave the existing structures in place and create shallow, lined (rock) crossdrains to handle overflow.
d. On a recent removal of 2 culverts on a wetland crossing, various techniques
were used to dewater the area so that minimal sediment was released. They
had to be removed in order to be replaced with a bridge. Lots of pumping and
diverting of water occurred. We also leave them in if we feel we will do less
damage by leaving them in and we can clear them with a bridge.
e. Pull any imbedded structures and place water bars along the surface. I would
consider it temporary deactivation.
f. Remove all grade and crossings to its pre-road state and monitor. There should
be no barriers impeding flow after reclamation. For instance, corduroy removal.
Again, we have soil disturbance and erosion control program and re-vegetate
surrounding areas to prevent erosion from neighbouring areas. This may
include coarse woody debris, water bars, silt fences, diversion ditches, etc.
g. Normal decommissioning does involve removing the drainage structures. In
the Boreal, beaver activity would normally dictate that removal. Without
regular maintenance the beavers will make use of what is provided. Most of
our wetlands are slow draining and have natural filters, which are those
beaver dams.
h. Determine the type of decommissioning – temporary, total, etc. Restoration
and stabilization requirements. Salvage requirements. Removal of all water
course crossings. Removal of all cross-drains. Decompaction. Contouring
stabilization – spreading of striping’s, etc. Provide historical access. Establish
vegetation, provide erosion control measures and access control.
i. Use same methods for removal as for installation. Recently AB allows lowest
layer of logfill to be left in place. Remove soil and geo and leave logs.
Rationale is more damage / sedimentation is created than by leaving logs in
place to decompose naturally.
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j. Ultimately want to restore natural drainage patterns that existed prior to the
road building activity. Remove any possible obstruction to flow / prevent
sediment from being deposited into a channel (if it exists) and prevent
compaction of surface soils by not operating during non-frozen conditions or
at breakup.
k. Typically, any structures within a channel are removed. Based on the type of
flood plain, we remove the road bed as well.
l. Have not decommissioned any permanent wetland crossings. However, we
did wrap geotextiles around logs to facilitate mineral soil removal from a
stream crossing. In addition, typically we do not support any vegetation
stripping prior to construction and place geotextiles over the vegetation.
m. No answer provided.
n. Pull aggregate material back to edge of tree line, creek water bars so rainfall
or spring melt does not lead to sedimentation in the creek and use organic
(moss) to cover exposed slopes near creek.
o. No answer provided.
p. We do not decommission roads as a rule. This is why we try at all cost to
avoid these areas.
q. Ensure all grade and matting is removed to allow adequate drainage. Likely
every 200 meters or less.
r. Removal of fill and crossing structures is completed and typically seeded to
grass. If required further stabilization measures are employed e.g.: straw
mulch and slash debris.
s. Culverts are removed. Slopes are contoured and stabilized to prevent
erosion. Road grade is scarified and seeded or planted.
USA Responses
a. Road beds are seeded to minimize sedimentation. In wetlands the road is
breached in several places to allow movement of water. Breaches are placed
similar to the frequency of culverts in and active road.
b. No answer provided.
c. Pull out culverts and leave open channels.
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d. I would not leave a culvert that might interfere with natural flow paths and
cause more destabilizing consequences as a result. Culverts you expect to
function need to be maintained. This does not fit the definition of a
decommissioned road. Install a portable dike and pump the water away from
the active stream.
e. Remove the culverts and open the area enough so that water will continue to
flow through those openings. Seed the approaches to the crossing. Consider
closing the crossing area to future traffic. Place geotextile fabric to serve as a
filter fabric for sediment flowing toward the crossing.
f. I believe we try to remove any imported material and re-establish a natural
condition as much as possible. We might put up temporary silt fences around
the area as we remove materials to localize and contain any sediment!
g. Removal of permanent structures is difficult, particularly on long crossings.
Restoration of the wetland is encouraged, and can be used as a credit, if
done properly, to mitigate for other wetland impacts.
International Responses
a. No answer provided.
b. Can’t answer. I don’t know of any decommissioning.
c. No answer provided.
d. Engineers in the Scottish Forestry Commission use a backfall on roadside
ditches, and a settlement pit, at the pint that ditches discharge into water
courses. This slows down the water flow in the ditch and causes sediment to
settle out before entering the watercourse. I am not aware of this being done
on public roads.
e. This is not a relevant question for us.
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List of Respondents: (listed alphabetically)
Canadian Responses
Allan Dumouchel – Daishowa Marubeni International Ltd.
Andre Savaria - ASRD
Bernie Morin – Canfor
Calvin VanBuskirk - Terratech Consulting Ltd.
Darnell Sedlar – Shell
Dennis Boulet – New Page Corp
Donna Kopecky – Louisiana-Pacific
Kenny Johnston – Tembec
Lane Doucette – Louisiana-Pacific
Len Parsons – Weyerhaeuser
Mel Cadrain – Weyerhaeuser
Michael Van Arem – Canfor
Paul Leroux - Weyerhaeuser
Rebecca Werner – Canfor
Rick Bonar – West Fraser
Rod Badcock – Abitibi Bowater
Rod Brooks – Louisiana-Pacific
Steve Blanton – Manning Diversified Forest Products
Wally Quiring - Tolko
USA Responses
Charlie Blinn – University of Minnesota – Dept. of Forest Resources
Gordon Keller – USDA Forest Service, Plumas National Forest
Greg Napper – USDA, Forest Service, San Dimas Technology and Development
Kim Clarkin – USDA, Forest Service, San Dimas Technology and Development
Mike Aust – Virginia Tech
Rick Dahl man – Minnesota Dept of Natural Resources, Forestry (Retired)
Tom Williams – Clemson University
International Responses
Andrew Dawson – Nottingham Transportation Engineering Centre - UK
Niklas Thun – Trafikverket - Sweden
Nils Olaf Kyllo – Skog Landskap - Norway
Ron Munro – Munroconsult Ltd. - Scotland
Timo Saarenketo – Roadscanners - Finland
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