- North Carolina Forestry Library

W
hen permanent access to a logging
site is not needed, temporary
bridging should be considered.
Dragline (bridge) mats can be installed and
used during logging operations, then removed
after operations are finished, and moved to
another location. In the past, relatively lower
cost approaches to temporary stream crossings, such as log crossings, fords, and culverts,
were preferred to portable bridges because of
the relatively high initial cost of bridges.
However, these low cost techniques frequently
involved the use of large quantities of earthen
fill in the stream crossing, which resulted in
excessive erosion and stream sedimentation.
Since dragline mats can be installed and used
with minimal sediment impacts on water
quality, they have become a preferred alternative for temporary stream crossings.
Using Dragline Mats for Stream
Crossings
Planning*
Ð Avoid stream crossings where possible.
Ð Minimize the number of stream crossings.
Ð Where a stream crossing is required, select a
crossing site with these features:
1. Straight and narrow stream channel with
high banks;
2. Stable stream banks that provide solid
foundation for mats and a minimum threefoot clearance between the bottom of the
installed mats and water surface;
3. Minimal elevation changes (0-10%) on
road/skid trail leading to crossing.
*Contact the NCFS for on-site assistance in
selection of a proper stream crossing location.
Installation
Ð Keep heavy equipment out of stream.
Ð Use a skidder, knuckleboom loader, or
bulldozer to install and remove dragline mats.
Ð Install mats between “bumper trees” to direct
skidded logs across mats.
Ð Install water diversion devices (water bars,
turnouts, broad-based dips, etc.) on both sides
of the crossing.
Ð Stabilize exposed soil with tree tops or brush
during mat installation, and seed or mulch
after mat removal.
Ð Install mats to create a minimum ten (10) foot
bridge width.
Maintenance
Ð Keep mat surface free of soil and logging
debris that could enter stream.
Ð Periodically check mat hardware; retighten
nuts and cable clamps as necessary to maintain mat strength and integrity.
Ð Remove any debris which enters the stream at
the crossing locations.
Please contact your local County Ranger
for further details on dragline mat use. You can
obtain additional dragline mat information on
the Internet at http://www.dfr.state.nc.us,
including a list of mat vendors. An on-line loan
request form can also be completed at this site.
Funding for this brochure was provided by
the N.C. Division of Forest Resources (otherwise known as the North Carolina Forest
Service) and the U.S. Environmental Protection Agency through a federal grant under
Section 319 of the Clean Water Act.
NCFS Dragline Mat Loan Program
Since 1996, the NCFS has provided an
EPA-funded dragline mat loan program. If
you have never participated in this program
and would like more information on the benefits
of dragline mats, call your local District or
County office for participation information.
Dragline mat used at a stream crossing.
Removal
Ð Clean off mat surface; Keep debris out of
stream channel.
Ð Remove mats by lifting rather than dragging
across the stream channel.
Ð Permanently stabilize disturbed portions of
stream bank and approaches with perennial
grasses/mulch.
Ð Leave appropriate water diversion structures
in place on both sides of stream.
The North Carolina Division
of
Forest Resources
The following steps are recommended
for dragline (bridge) mat installation:
nClear trees and underbrush where the
access road/skid trail stream crossing will
be installed,while minimizing disturbance
to the forest floor (duff). Remember to
leave “bumper trees” to guide skidded logs
across the mats. Some stream crossings may
require upstream “anchor trees” and chain/
cable to prevent mat washout during storm
flow events (Figure 1).
n Use grapple, cable skidder, or bulldozer to
n Installation may require some minor site
transport (Figure 2) dragline mats to the
crossing site and install the mats one at a
time. The mats can be placed in position
with a skidder (Figures 3 and 4), bulldozer,
or knuckleboom loader; the use of a loader
will quicken the installation and minimize
damage to the stream bank.
work with a bulldozer or excavator. Try to
get the dragline mats as level as possible.
n
To complete the installation, the skid trail
should be built up to the same elevation as
the mats. Some surfacing material such as
crushed rock should be applied to the trail
surface to reduce the potential for sediment
being washed into the stream. Water
diversion devices such as waterbars, turnouts, etc., should be installed on the skid
trail on either side of the stream crossing.
Figure 3: Dragline mat installation using a cable
skidder.
n After the crossing is no longer needed,
the mats can be removed in reverse order of
installation. Some stabilization of the stream
banks may be required after the mats have
been removed. Revegetation combined with
mulch will usually prevent sediment from
entering the stream (Figure 5).
Figure 2: Dragline mat transported to stream
crossing by skidder.
n
Place dragline mats at least 3 feet
above the high water mark of the stream.
In locations where the mats will be installed
for a short period of time, it may be possible
to place the mats closer to the stream channel.
Figure 1: Dragline mat anchored on stream bank and
bumper trees to guide logs.
Figure 4: Dragline mat installation using a grapple
skidder.
Figure 5: Stream crossing after dragline mat removal.