The upper basin of the Baram, Tinjar and Rajang Rivers
Location:
1°52'-4°01'N, 113°33'-115°38'E; the northern interior of Sarawak, Fourth and Seventh Divisions.
Area:
Approximately 1,700,000 ha.
Altitude:
Mainly 150-300m, with peaks up to 1 ,800m.
Biogeographical Province:
4.25.12.
Wetland type:
12, 15, 19 & 22.
Description of site:
A vast area of upland terrain in the upper catchment areas of the Batang Baram, Batang Tinjar and Batang Rajang rivers. The terrain is predominantly a valley-ridge complex with some small dissected alluvial valley floors, very steeply sloping, and some flat valley floors. Most of the area is about 300m above sea-level, but some peaks rise to about 1,800m. The area encompasses the Usun Apau plateau, a large volcanic mass at 1,100-1,400m with a topography varying from moderately dissected to gently undulating. Its soils are generally deep, well drained clays, with local poorly drained, saturated, organic (peat) soils of the Unor and possibly Bareo families in channels and basinal depressions. The original vegetation was mixed dipterocarp, hill dipterocarp and montane forest, but there is much shifting cultivation and logging in parts of the area. The site includes two main regions: the upper Baram and Tinjar catchments (Fourth Division), and the upper Rajang catchment (Seventh Division). The area has imperfect to good drainage, with rapid run-off from ridge systems. There is a good subterranean water supply during the dry season. Water samples from a bubbling spring near Long Aton in Ulu Tinjar had a pH of 8.1-8.2, and were strongly saline. A pH of 5.1 was recorded in a stream on the Usun Apau plateau. Flash-flooding occurs in some of the alluvial valleys, with resultant large fluctuations in river level, e.g. I 1.40m in the Batang Baram at Lio Matu and lO.64m at Long Pilah; 6.60m in the Batang Rajang/Baloi at Giam Pasang; 16.87m in the Batang Tinjar at Long Jegan and 13.00m at Long Terawan.
Climatic conditions:
Humid tropical climate. The average annual rainfall at Long Anap is 5,027 mm, and at Long Sobing on the Tinjar, 7,087 mm. The upper Dapoi, a tributary of the Tinjar, has a mean monthly rainfall approaching 800 mm during the wet (landas) season. This area is distinctly cooler and wetter than comparable areas elsewhere in Sarawak. The Long Akah and Long Pilah area is the wettest region in Sarawak, with the rainfall more or less evenly distributed throughout the year. The average daily maximum temperature (at 1400 hrs) is 37°C, and the average daily minimum (at 0600 hrs), 23°C.
Principal vegetation:
Mixed dipterocarp forest, hill dipterocarp forest, montane forest, shifting cultivation, plantations of rubber and pepper, and rice paddies.
Land tenure:
No information.
Conservation measures taken:
None.
Conservation measures proposed:
A proposal has been made for the establishment of a National Park (the Usun Apau National Park) and World Heritage Site within the system. The southern and eastern boundaries of the proposed Pulong Tau National Park overlap the site. It is essential that proper environmental impact assessments be carried out for the planning and management of the Bakun, Pelagus, Baleh and Murum hydro-electric schemes. An environmental impact assessment should also be carried out for the proposed intensive logging operation in the Bakun impoundment area, to guard against possible adverse downstream effects and to consider the loss of the biological material involved. This should be assessed in the context of the need to protect the proposed machinery at Bakun. The Bakun catchment should probably not be logged at all, and certainly not without a prior environmental assessment. Further research is urgently needed in view of the rapid decline of some of the important species of fish such as Semah Tor tambroides, Empurau T. doureusis, Kulung Labeobarbus sp, Tengadak Puntius schwanenfeldii and Tapah Wallago sp, with the rapid changes in water quality. Co-operation between State Governmental departments such as the Department of Agriculture and non-governmental conservation bodies would facilitate implementation of such research.
Land use:
Fishing and hunting; an extensive trade in wild meat has been established throughout the Rajang Basin. In 1984, the value of the trade in wild pig and deer meat exceeded M$4 million. The trade is organized in a number of private businesses based in Belaga, Kapit and Sibu. Shifting cultivation and logging occur in adjacent areas. Although the land has only marginal to poor agricultural potential because of shallow soils and steep slopes, large areas have been cleared for rubber and pepper plantations, and terraced rice paddies. Extensive areas of primary forest are uninhabited.
Possible Changes in Land use:
The proposed Bakun Dam Hydro Project involves the construction of a dam on the Balui River, 37 km upstream from Belaga. The reservoir created by this dam will flood 71,000 ha (4.7%) of the catchment area of the Balui River above the dam. The hydro-electric station will generate 2,400 megawatts for supply to Sabah, Sarawak and Peninsular Malaysia. Three other major hydro-electric projects have been identified for possible commissioning between 1995 and 2010: the Murum (900 megawatts), Pelagus (770 megawatts) and Baleh (950 megawatts), all in the upper Rajang River Basin. Logging is very likely in the future. The proposed development of the Baran River Club may involve clearance of forest on the Usun Apau plateau and replacement with grassland stocked with exotic animals.
Disturbances and threats:
The principal threats at present include excessive logging, erosion from forest clearance on very steep terrain, over-fishing, siltation of the river system and heavy hunting pressure. In 1984, about 10,200 Bearded Pig Sus barbatus, 1,400 Sambar Deer Cervus unicolor and a few Muntjak Muntiacus muntjak were sent to Sibu, while another 6,400 pigs and 200-300 deer were bought and consumed locally along the way. At this rate, it is uncertain how long this trade in wild meat can be maintained. Mining may pose a threat to the area in the future.
Economic and social values:
The river basin supports a locally important fishery. The forested water catchment area minimizes flooding in the middle Baram, Tinjar and Rajang Rivers and maintains water quality. The region has considerable potential for scientific research and conservation education. According to the Department of Agriculture (1980), the area has no agricultural potential.
Fauna:
Most if not all wildlife species typical of lowland, submontane and montane forests in Sarawak probably occur in the basin, but little information is available. Hose's Langur Presbytis hosei is known to occur.
Special floral values:
The localized upland peat bogs almost certainly support a highly specialized flora of considerable botanical interest, but these areas have yet to be investigated.
Research and facilities:
The Department of Agriculture has surveyed the soils of the region, and carried out a fisheries and aquatic ecology survey in Ulu Rejang from 1979-1982. The Inland Fisheries Branch of the Department is currently conducting a survey on fishery resources in the Baleh River system, with a view to formulating proposals for the conservation of riverine fish of economic, social, ecological and recreational value.
References:
Caldecott (1986); Department of Agriculture (1980); DID Sarawak (1979/80); Eilers & Loi (1982); National Parks and Wildlife Office (1984); Sarawak Electricity Supply Corporation (1984); WWF Malaysia & State Planning Unit of Sarawak (1985).
Criteria for Inclusion:
1a, 1b, 1e, 2a, 2b.
Source:
Kumbang Juggang.