|Dominique J (2001) Use of silt traps and crossboards to reduce erosion
on walking tracks at Matang Wildlife Centre, Malaysia, Hornbill
USE OF SILT TRAPS AND CROSSBOARDS TO REDUCE EROSION ON
WALKING TRACKS AT MATANG WILDLIFE CENTRE, MALAYSIA
DOMINIQUE ANAK JIKIE
Erosion has been seen as a major problem on visitor
trails in National Parks and Nature Reserves throughout Sarawak.
Trampling, weather and vegetation removal are the main factors causing
this problem. Silt traps and crossboards have been used to reduce
erosion. The traps collect sediment and forest litter brought by runoff
flowing down a trail, while crossboards divert runoff into the bushes
away from the trail. This research project looked at the effectiveness
of these methods at two areas, one heavily and the other lightly used,
at Matang Wildlife Centre.
Due to the increasing number of visitors patronising
the centre (59,418 in 1998, 62,398 in 1999 and 66,476 in 2000), some of
the walking tracks and the picnic area are exposed to heavy foot
traffic, causing heavy degradation to some parts of these areas. The
objective of this study is to look at the effectiveness of silt traps
and crossboards in reducing erosion on visitor trails at Matang Wildlife
In a tropical environment, "soil is moved primarily by runoff
associated with rainfall, thus, erosion is defined as the movement of
soil particles either individually or as aggregates, downslope as a
result of the waterflow" (Crighton and Tomkins, 2000). Crighton and
Tomkins (2000) set up six silt traps in Bako National Park in October
2000, two of which did not work well and were removed during subsequent
trail maintenance; only two were full by February 2002 (Meredith, pers.
Two areas which have different soil, terrain and forest types were
chosen for the construction of these traps and crossboards.
- Heavy use : Picnic Area. This area is located at the edge of
Rayu river and has seen a heavy erosion problem since the centre was
opened for public use. During the monsoon season, the river overflows
its banks and the whole picnic area is covered with fast-flowing
water, bringing away all forest litter and leaving the ground exposed
to weather and foot traffic. Thus, runoff and trampling combine
together to increase the rate of erosion which, if not mitigated, will
result in degradation.
- Little-used trail: Senduk Waterfall Trail. Visitors who
frequent this route are mostly foreigners who want to see wildlife,
plants and the waterfall at the end of the trail. This trail passes
through different terrain types with different soil textures. Erosion
is mainly heavy in hilly areas, which have sandy clay soil, with very
loose particles. Steps and plankwalks were constructed in previous
years to reduce erosion but they do not seem to be effective during
heavy rain when runoff is very swift.
Silt traps are constructed using pieces of wood (preferably
rot-resistant ironwood) measuring 8"wide and 1"thick, the
length depending on the width of the trail. The timber is placed across
the trail and held by several stakes on the down-slope side which are
fixed by stainless steel nails. It must be dug deep enough into the
ground (2"-3") and extended far enough to the sides of the
track so that water cannot flow around the edges, bringing sediment and
forest litter away. "Sediment brought along by runoff will be
trapped by the board which will fill up over time, forming a step.
Another one will be constructed farther up when the first one is full
and this process will go on and on until the whole eroded area is
covered, forming hard and easily used steps" (Crighton and Tomkins,
Crossboards are constructed using pieces of timbers (rot-resistant
ironwood) 6" wide and 1" thick, the length depending on the
width of the trail. The timber is placed across the trail at an angle of
45 degrees (Agate and Roper, 1983) and held by several stakes on the
down-slope side which are fixed by stainless steel nails. The board is
dug halfway into the ground, so that the visible part does not form an
obstacle to trail users.
In the frequently used area, one silt trap leaked and did not fill
up, perhaps because maintenance works removed dead leaves and twigs
which might have plugged the leak. The other two filled slowly from June
to August 2001 (gaining 22 to 25 mm of silt), but were completely full
after flooding in early January 2002.
In the less used area, one trap filled rapidly in the
first two months (48 mm of silt) and was also full after the flood. The
other collected only 11mm of fine mud, leaves and twigs.
Inspection of the crossboards after the wet season, seven months
after installation, showed that mud had collected at the down-slope end
of the board, together with forest litter among the bushes, which shows
that water is being diverted. No gullying was developing at the end of
One silt trap was poorly constructed and one
collected only a little mud, but the rest began to collect sediment and
were full after the following wet season. More silt traps uphill of the
full ones should now be installed to make a series of steps.
A problem encountered in the frequently used area was
that weekly maintenance involved removal of dead leaves from the trail
with a blower, which also removed sand and sediment.
As for the crossboards, observation suggests that
they are effective in diverting water. Long term monitoring is needed to
check on gullying at the down-slope end of the board and reduced erosion
on the trail below the board.
From the research and studies conducted both at
Matang Wildlife Centre and Bako National Park (Crighton and Tomkins,
2000), silt traps seem to be a good way to prevent gullying along trails
and to create a flight of steps. Crossboards are effective in removing
water and thus reducing erosion along visitor trails. Both are cheap and
easy to construct, with little maintenance needed provided rot-
resistant ironwood and stainless steel nails are used.
Obviously, silt traps will be more effective if loose
sediment and forest litter are not removed from the trail, but allowed
to accumulate at the traps.
Agate E and Roper A (1983) Footpaths: A Practical
Conservation Handbook. British Trust for Conservation Volunteers.
Crighton P. and Tomkins J. (2000) Current
condition and suggested management for the walking tracks at Bako
National Park. Unpublished report to Sarawak forest Department