Overview
Timor-Leste has over 100 rivers arising in its highlands and discharging into its coastal zone. The country also has 29 main river systems – 12 in its north and 17 in its south. As the island of Timor is small and Timor-Leste's topography is steep, the rivers are short and drain quickly, with fast flowing discharges. [1] : 21 [2] : xvi, 3, 75
Almost all of Timor-Leste's creeks and rivers originate in its central mountain range or ridge, which dominates the country. The mountain range extends from Tatamailau, or Tata Mailau, sometimes referred as Mount Ramelau (2,963 m (9,721 ft)) in the west to the Fuiloro Plateau in the east, and includes Ira Lalaro (318 m (1,043 ft)), the country's largest lake. [3] A drainage divide trends along it, approximately from southwest to northeast; [4] rain falling north of the divide flows northwards, and that falling to its south drains southwards. [3] [5]
The country's rainfall has distinct seasonal variability affected by the West Pacific Monsoon (WPM). Maximum precipitation occurs only in the high elevations of the mountain range. The northern coast is drier than its southern counterpart. [3]
Very few of Timor-Leste's rivers flow perennially, because the country is narrow from north to south, and has steep terrain and infrequent rain. Most of the rivers have short courses, are dry most of the year, and are not navigable. In the dry season, the ephemeral rivers often form pools of stagnant water. [2] : xvi, 3, 75 [5] The south has more perennial rivers than the north because of its larger catchment areas, longer rainy season, greater rainfall and prevailing winds. [1] : 21 [2] : 75 According to a Timor-Leste Water Sector Assessment and Roadmap published by The World Bank in 2018:
"The monsoon climate results in highly variable river flows from wet season peaks and flash floods to low or no dry season flows. Along the northern coastline are many of the smaller river catchments that are either semi-permanent or ephemeral, flowing for short periods in the wet season after heavy rainfall events. This contrasts with the south coast where the bimodal wet seasons and higher rainfall has resulted in many large permanent rivers that have high peak flows in the wet season, which are reduced to the base flow during the dry season. At all times, subsurface flows occur below the gravel and cobblestone riverbeds of most rivers, and in the dry season, this can represent the primary flows within a river, particularly in lowland areas." [6]
During periods of greater precipitation, the rivers in the south cannot accommodate the whole of their flow, and therefore overspill into coastal swamps and lagoons known as coilões. [1] : 21–22
On the north coast, most rivers are choked with nearshore gravel, and there are few deltas. The reason is that the offshore gradient, into either Ombai Strait or Wetar Strait, is very steep, with the consequence that sediment that flows offshore is deposited in deep water. On the south coast, where the offshore gradient into the Timor Sea is much gentler, deltas are common. [7] : 6–7 [8] : 35
Many of Timor-Leste's rivers are polluted by sewage released from homes and light industrial premises, due to a lack of basic sanitation. Additionally, the majority of the population uses river water for washing clothes, bathing and other domestic uses, and thus promotes the spread of diseases. [1] : 23
The country has been broadly divided into twelve 'hydrologic units', groupings of climatologically and physiographically similar and adjacent river catchments, drainage basins or watersheds. Each hydrologic unit is made up of a number of rivers. In total, there are 29 main river systems in Timor-Leste – 12 in the north and 17 in the south. [9] : 2, 52 [10]
Timor-Leste's longest river is the North Laclo, at about 80 km (50 mi) long; [1] : 22 [5] [11] its largest catchment is that of the Loes, [1] : 22 which has a total area of 2,184 km2 (843 sq mi) (almost 15% of the whole country), about 9% of which lies in Indonesia. [12]
The people of Timor-Leste often have no single common name for, or any single spelling of any name allocated to, a particular river. Further, an East Timorese river may change its name several times between its source and its mouth. [13] The names set out below are therefore not necessarily authoritative, either as to the name of a river, or as to the spelling of any particular name.
