Brunei Bay

Brunei Bay (Malay: Teluk Brunei) is the gateway to Brunei and Borneo. It is located 4°45'-5°02'N, 114°58'-115°10'E; east of Bandar Seri Begawan. The Brunei portion of the bay is in two sections separated by a finger of Sarawak (Limbang) about 6km wide at the coast. It is a deeply indented bay with an area of about 250,000 ha (c.50,ooo ha in Brunei territory), shared between Brunei Darussalam and the East Malaysian States of Sarawak and Sabah. A chain of islands including the large Malaysian island of Labuan forms the boundary between the bay and the South China Sea. Most of the east and south shores of the bay are covered in extensive mangrove forests with associated mudflats and sandflats at the mouths of the major estuaries. The mangrove forests form a continuous, intact forest within Bruneian territory, but those within the adjacent Sarawak territory have been largely clear-felled to supply the wood-chip industry. Freshwater flows into the bay via a labyrinth of interconnecting channels and waterways.

The major rivers entering the Brunei Estuary in the southwest are the Brunei, Limbang, Temburong, Bangar, Trusan, and Pandaruan. The Limbang and Temburong drain catchments which are predominantly primary rainforest, and carry high silt loads. The smaller Brunei River receives the drainage from the city of Bandar Seri Begawan and its environment, and is therefore subject to considerable urban pollution. Several smaller rivers drain the extensive peat swamp forests of Temburong District. These carry very small silt loads, but are rich in peat and woody debris.The outer bay varies in depth from about 20 to 40 metres; the inner bay is generally less than 5m deep. The massive inflow of freshwater reduces the salinity to only 2.6 p.p.t. in places, compared with a mean offshore salinity of 31.5 p.p.t. The retention time for water in the bay has been estimated at 2-4 weeks. The tides are diurnal for two or three days in each month and substantially diurnal for the remainder of the month. There is a secondary tide, however, which gradually increases and decreases in magnitude so that for a few days in each month there are semi-diurnal tides of similar amplitude. The tidal amplitude at Muara ranges from about 2.0m at spring tides to 0.9m at neap tides.