TITULO VIGESIMO PRIMERO

Geologically, the Balui lies in an area called the Sibu zone of the Rajang Group, characterised by ‘highly deformed steeply dipping low-grade metamorphic flysch’. The immediate area is called the Pelagus Member of the Rajang Group, made up predominantly of argillite, with extremely strong greywacke beds 15 to 90m thick. The Pelagus member is intensively folded and tectonic disruption is evident (Osman, 2008; Hutchison, 2005). The Bakun dam is named after the Bakun rapids, over which the dam was built.

The entire area that is left after inundation consists mostly of steep, rugged, and slippery slopes. The seasons vary the heights of the dam as well. These factors affect the availability and access to locations for trapping and transect sites. There is actually little primary forest around the Balui area, due to the long history of various human activities, from shifting cultivation to logging. Much of the area is fragmented to some degree which can be caused by a combination of inundation, rivers and streams, walking trails, logging tracks and camps. Although the earlier EIA (Ekran Berhad, 1994) described there to be virgin mixed dipterocarp forest above 200m, large-scale logging activities had entered these higher altitudes since the construction of the dam. It is not uncommon to see log barges plying the lake. The second EIA recognised that the various plant species play important roles culturally and ecologically, and rescued 34,000 tree (mostly dipterocarp) seeds and 1188 saplings of non-tree species for cultivation at a nursery and replanting. However, due to the rescue team miscalculating the final inundation height, 82% of all the seedlings were planted too low and were lost to the rising water level (SFC, 2013).

4.2.1.1 Hydrology and Climatology

The Batang Balui is a tributary of the Batang Rajang. The Batang Rajang is Sarawak’s longest river, the associated watershed, the state’s largest, covering an estimated 1.5 million hectares. The Balui itself has three major tributaries: the Murum, which was also being dammed and slated to go online in 2013 with a 944MW capacity, the Linau, which may have a 290 MW dam planned, and the Bahau (Kadikon, 2006; Ekran Berhad, 1994). More than 1,500 permanent streams also feed into the Balui. The topography of the land immediately surrounding the Balui River is steep, and as such the Bakun Lake, although covering more than 700km2_{, does not spread out radially. Instead, a 160 km}

65 long lake with a 2000km perimeter that follows the valleys is formed, averaging 2km across (Ekran Berhad, 1994). Within the area of the lake, hilltops have become islands. Some islands would be transient. In December 2011, when the height of the reservoir level was at 219m above sea level (a.s.l.), there were more than 20 major islands in the lake. When the water level finally reaches the target elevation of 228m a.s.l., which is also the maximum operating level of the dam, it is expected that more than 10 major islands would still be left (Sibon, 2011b; Figure 4.2). It is possible that the state authorities may try to develop these islands into ecotourism destinations. The land surrounding the lake is rugged with steep slopes, with much of the land above 500m a.s.l. and the highest peak rising to 2040m (Samad and Abdul Patah, 1997; Figure 4.3).

The region around Balui and Sarawak, in general, is remarkable for its abundance of rainfall, even by tropical standards. More than 4000mm of rain falls annually on average around the Balui from as many as four rainy seasons (Sovacool and Bulan, 2011a; Kadikon, 2006; Samad and Abdul Patah, 1997; Ekran Berhad, 1994), which is high in comparison to other nearby areas. For example, annual rainfall in Singapore averages about 2,360mm, while the Danum Valley Field Centre in Sabah receives about 2822mm (Hu et al, 2003; Marsh and Greer, 1992). The heaviest rains come during the Landas season, which occurs under the influence of the northeast monsoon from October till February, and there is no distinct dry season (Sovacool and Bulan, 2012; Kadikon, 2006; Morrison, 1993). Of the rainfall in the Bakun catchment area (located between latitudes 1.5°N and 3.0°N and longitudes 113.5°E and 115.3°E), about 70% - 75% becomes run-off (Kadikon, 2006; Samad and Abdul Patah, 1997; Ekran Berhad, 1994). Mean annual evapotranspiration is also high at 1300mm (Samad and Abdul Patah, 1997). Depending on land use, microclimatic variables, such as temperature and humidity, fluctuate. Overall, temperatures range from 220_{C - 36}0_{C, while humidity ranges from 35%-88%} (Kadikon, 2006). It is likely, however, that with the rest of Southeast Asia and Sarawak, Balui is experiencing, or will experience, rising temperatures as vegetation is lost from logging.

66 Figure 4.2: Map showing inundated areas forming Bakun Lake and the islands in it.

67 Figure 4.3: Terrain map of the region around the Bakun rapids preinundation, which is indicated by the placemark ‘A’. The terrain is generally steep and rugged. The flat plains opening to

68 Figure 4.4: Landsat 8 image mosaic of the Bakun Dam from 16th June 2016. The small water body on the right is the reservoir of the newer Murum Dam (Source: Landsat 8, United States Geological Service Products).

69 4.2.1.2 Camera Traps

Camera traps were deployed in six different locations at various times over 18 months. The traps were checked every three months where it is possible. The models used were Bushnell Trophy Cam, Bushnell Trophy Cam HD and Bushnell Aggressor. Locations were marked with a Garmin GPSmap 62s set.

Between three to five camera traps were used on each trap line, at heights of 0.5 m above the ground in small openings or wildlife trails. The traps all faced in the same direction, and the distance between each trap was 25m, creating surveillance belts of 50m (three traps) to 100m long (5 traps). The traps were not baited and continuously set for at least three months until it was time to check the traps and remove the memory cards. As there could be an issue with the same animal returning to particular cameras or walking along the trap line, it was taken that unless the individuals were clearly identifiable, the species will not be counted if it reappears in the same trap or adjacent traps within two hours. Camera traps might also sometimes produce unclear images, due to fog or long shutter speeds under poor light conditions. When this happened, the images were discarded.