Eric C.F. Bird (ed.), Encyclopedia of the World’s Coastal Landforms, DOI 10.1007/ 978-1-4020-8639-7_19.4, © Springer Science+Business Media B.V. 2010 (Dordrecht) 19.4 Brunei (Negara Brunei Darussalam) Gabriel Yong 1. Introduction Brunei occupies a 130 km stretch of the northwestern coast of Borneo between longitudes 114°4' E and 115°9' E, which includes parts of the Baram Delta in its western sec- tion and the Brunei Bay in its eastern section. Te conti- nental shelf is 50–80 km wide and contains submerged sand shoals, rocky outcrops and patch reefs (> Fig. 19.4.1). Te main sources of information on Brunei’s coast include the works of Wilford (1961), Tate (1970, 1971), James (1984), Chua et al. (1987), Goh (1981) and Sandal (1996). Brunei has a consistently warm climate (mean monthly temperature range 27–28°C) and is wet (annual rainfall range 2,500–4,500 mm) throughout the year because of its geographic location (4–5° N of the Equator). Fluctuation of the Inter-Tropical Convergence Zone (ITCZ) gives rise to two seasons, the northeast and southwest monsoons. Although there is high spatial and temporal variability in rainfall distribution, it is generally wetter during the northeast monsoon from November to January. Climatic conditions are also afected by cyclones in the South China Sea, which produces squally weather, as well as the El Nino Southern Oscillation (ENSO), which bring about dry spells (El Nino) and foods (La Nina). Te coastal environment is controlled largely by the interaction of the country’s geology, climate and wave regimes. Increasingly, however, As over 80% of the coun- try’s population lives along the coast, human activities have modifed, and will continue to alter, Brunei’s coastal landscape through mining and development. 2. Coastal Environment From November to January, the northeast monsoon gen- erates storm waves that arrive at the coast from the north and northeast with wave heights and periods typically of 1–3 m and 4–6 s respectively. Storms in the South China Sea generate destructive swell waves that scour the beach face and backshore and produce ofshore sand bars. Along the Brunei-Muara coast rip currents and undertows are common, while in the Tutong-Belait coasts to the west large waves generate strong longshore currents and a west- ward longshore drif. Te sea is mostly calm during April and May. Te wave regime during the southwest monsoon is generally con- structive. Low-energy swell waves (height <1 m, period ~4s) that arrive from the north-west build berms and beach ridges. During this period sea level is about 40 cm lower, and the beach higher by 20–30 cm and wider by 20–40 m. Longshore currents are strong (reaching 1 m/s), producing an eastward drif. Occasional storms associated with cyclonic activities result in scouring of the beach face and backshore. Longshore drif is evident from the diverted mounts of streams and rivers and the narrow sandy beaches and spits found along the coast. Estimates of longshore drif rates range from 50,000 to 70,000 m 3 /yr on the 8 km long Pelumpong Spit in Brunei Bay to 20,000 m 3 /yr on the Tutong spit and 12,000 m 3 /yr in Kuala Belait. Longshore drifing is eastward during the southwest monsoon and westward during the northeast monsoon, but varies with coastal aspect, so that there is a divergence of net long- shore drifing eastward and westward from the Penanjong- Tungku area. Te position of the mouths of small rivers, such as Sg. Pemburongan near Tg Batu, fuctuates by about lh 200 m between the two monsoons during the course of the year because of the change in drif direction. Te tidal regime is mixed, with a dominant diurnal component becoming semi-diurnal for a few days during neap tides. Tidal currents are generally weak (0.6 m/s), particularly during rising tides, which occur for 70% of each tidal cycle. Ebb currents can exceed 1 m/s and are rapid in channels in the Brunei Bay, especially around large islands, such as Tg Sapo on Pulau Muara Besar. Tide ranges are small, generally 1–2 m, reaching a maximum of 2.7 m in Brunei Bay. Tidal regime and river discharge are more prominent in the sheltered Brunei Bay. Te main sources of sediment for beaches, bars and spits are the eroding blufs of weakly consolidated sand, sandstone and clay strata between Penanjong and Berakas and submerged sand shoals, particularly the submerged delta of Jerudong. Rivers in Brunei carry high silt, clay and organic sediment with a low sandy load. It is possible