DOMINIQUE ANAK JIKIE

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 Centre.

Erosion
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. comm.).

Study Areas
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
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, 2000:8).

Crossboards
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.

Silt traps
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.

Crossboards
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 the crossboard.

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