Brunei Darussalam lies on the northwest coast of Borneo island Where it faces the South China Sea. With a land area of 5,765 square kilometres, it shares a common border with Sarawak, an east Malaysian state, which divides Brunei Darussalam into two, The eastern part is the Temburong District while the western portion consists of Brunei-Muara, Tutong and Belait districts.

The 570-sq.km. Brunei-Muara District, where the capital, Bandar Seri Begawan is located, is the smallest, but the most important and populous of the four districts. The 1166 sq. km. Tutong District, the third largest, is home to indigenous groups like the Tutong, the Kedayan, Dusun and Iban.

The Belait District, the centre of the oil and gas industries, is about 100 lcrns. From the capital. Hilly lowlands, swampy plains and alluvial valleys dominate the BruneiMuara, Tutong and Belait districts in the larger western portion of the sultanate. Mountainous terrain abound in the estern district of Temburong which has a land area of 1,288 sq.km.

Physical features

The land surface is developed on a bedrock of tertiary age, comprising sandstones, shales and clay. The terrain in the western part is hilly lowland, which rises in the hinterland to about three hundred metres. To the east, the wide coastal plain reaches up to 1,841 metres above sea level on Mount Pagon in the Temburong District.

Main Rivers

Four main river Systems irrigate the four districts of Temburong, Belait, Tutong and Brunei-Muara. Temburong, the smallest of the rivers, drains nearly the whole district.

The 2,700 sq. km. Belait basin has the largest area. The river narrows at the town of Kuala Belait. The upper catchment is mostly jungle and is sparsely populated. Some areas here have been cleared for agriculture. The lower catchment has an extensive area of peat swamp forests at its lower catchment area. Sandbars at the river mouth restricts shipping and water flow to the South China Sea.

The Tutong river covers the 1,300-square kilometre Tutong Basin. Sand-pits and sandbars make a complex estuary system at the Tutong river. Subject to fairly high tidal influence, its lower catchment area is a flood plain. Jungle with patches of agriculture covers its upper catchment. Near the upper part of Tutong River is Tasek Merimbun, Brunei's largest lake.

Dense mangroves and nipah palms, a rich breeding ground of coastal fisheries, cover the lower parts of rivers near estuaries. Pristine tropical jungles and valuable freshwater sources are the upper reaches of Brunei river. A high proportion of urban development borders in the Brunei river.

The Brunei River runs into the Brunei Bay beyond which is the Port of Muara. The upper reaches of the river are a major freshwater source particularly for the western part of the country.

Located by the principal rivers are all the district centres, including Bandar Seri Begawan, the capital, which is some distant inland, like Bangar in Temburong. Near respective estuaries are Tutong and Kuala Belait.

Islands

Within the Brunei border are 33 islands with a total area of 7,939 hectares or 1.4 per cent of the total land area. Offshore are two islands while others are in inner Brunei Bay and in the country's major rivers. Mostly jungle covered, their sandy beaches face the open sea and mangroves in areas facing inland.

Largely uninhabited, the islands are an undisturbed environment and breeding grounds for endangered species. Turtle nesting has been found on some islands with sandy beaches. Many islands have a big population of the proboscis monkeys, an endangered breed found only in Borneo.

The islands also are a natural habitat for birds, flying foxes (large fruit bats), and animals.