The North Laclo River ( or , ) is the second longest river in Timor-Leste after Loes River, with a total length of . It flows northeast into Wetar Strait, reaching the coast near the city of Manatuto. It has no connection to the South Laclo River, which flows into the Timor Sea.
Toponymy The river takes its name from the town of , which is located on its left bank, about from its mouth.
English language sources conventionally refer to the river as the North Laclo River, as there is also another Laclo River, usually referred to in English as the South Laclo River, which discharges into the Timor Sea on the south coast of Timor-Leste.
The two rivers are not connected to each other; both rise in the uplands near Turiscai in Manufahi municipality, where a drainage divide causes them to flow northwards and southwards, respectively, in each case later augmented by several tributaries.
Course The headwaters of the river are in the portion of Timor-Leste's central mountains ranging from Aileu municipality southwest of Manatuto city to Manatuto municipality to the city's south. From the headwaters, the river and its tributaries flow for the most part in a northeasterly to northern direction through Aileu, Ainaro, Manufahi, and Manatuto municipalities, and eventually into Wetar Strait just to the west of Manatuto,. between the Ponta de Subaio and Lanessana Bay.
At around in length, the river is the longest in Timor-Leste. It is also one of the country's few perennial streams, and one of only three such watercourses in the northern part of the country that can potentially be inhabited by saltwater crocodiles all year round (the others being the Loes and the Seiçal). The river's water level varies between the rainy and dry seasons. Its channel width ranges from about to over in some sections. Near Laclo, the channel was about wide prior to 1960; it then became around wide, and difficult to cross during floods. In the second half of the twentieth century, the river's lower reaches widened by about . Its tributary the Sumasse River (see below) similarly became wider.
About upstream of the river's mouth is the Manatuto Bridge, a -long prestressed concrete girder structure that carries the Dili to Baucau highway over the river. The bridge was built in the late 2010s as part of a project to reconstruct the highway. It replaced an earlier bridge that had been funded by the Australian aid program, built by Indonesian public works engineers, and opened in 1984. The first bridge over the river, built in the 1960s, was washed away by floods, and its replacement collapsed a few years later. Between the opening of the 1984 bridge and 2005, the river bed at that location rose by about .
There is no delta at the river's mouth, presumably because the offshore slope is very steep (a near-constant grade over the from the mouth of about 1 in 5 or 20%), with the consequence that sediment has not been deposited sufficiently to break even the nearshore surface. In that respect, the river differs from some of the other rivers on the north coast and most on the south coast (such as the Caraulun River, where the grade over the same distance from the mouth is only about 1 in 20 or 5%, and the river has formed a delta, even though the wave climate is much more energetic).
During the rainy season, the middle and lower reaches of the river have increased sedimentation rates, due to flash flooding, which, typically, causes the otherwise braided channel to become submerged. When flooded, the river carries abundant sediments from parent rock in the upper catchment, and deposits them in the channel and on the floodplain. The river then runs freely through its mouth, and large flows create turbid plumes that head eastwards along Wetar Strait. During the dry season, a bar forms across the mouth, and the baseflow of the river is directed to a fast-flowing channel on the mouth's western side.
The river has eight tributaries, two of which have a major branch. Some of the tributaries are intermittent. In order of entrance, the tributaries are as follows:
Monofunihun River (or Manufonihun River): rises in central Aileu municipality; flows initially southwest past the town of Aileu, then eastwards to merge with the Daisoli River (see below) at the border between Aileu and Ainaro municipalities north of Turiscai in Manufahi municipality, to form the Eralibanaubere River (see below). Manotahe River (major branch of Monofunihun River): rises in western Aileu municipality; divided into the Liurai, Kulalan, and Malubui Rivers; flows approximately eastwards to enter the Monofunihun River south of the town of Aileu, and approximately upstream of where the latter river merges with the Daisoli River (see below). Daisoli River: rises in southwestern Aileu municipality near the AMSL peak of the North Laclo catchment; flows approximately eastwards, mainly along the border between Aileu and Ainaro municipalities, to merge with the Monofunihun River (see above) and form the Eralibanaubere River (see below). Eralibanaubere River: flows from the confluence of the Monofunihun and Daisoli Rivers initially southeast, and then northeast to where it merges with the Noru River (see below) to form the North Laclo River; main tributaries are the Malikan, Haru, Aibeli, Karama, Hatoarabau and Orlaquiric Rivers. Malikan River (major branch of Eralibanaubere River): rises in Ainaro municipality; flows approximately eastwards, mainly along the border between Ainaro and Manufahi municipalities, to enter the Eralibanaubere River near the tripoint between Aileu, Ainaro and Manufahi municipalities. Noru River: rises in central Aileu municipality near the suco of ; flows via two branches (Coimai and Hatomero, respectively) approximately eastwards, mainly along the border between the Remexio and Lequidoe administrative posts, to merge with the Eralibanaubere River (see above) and form the North Laclo River about upstream of its mouth. Lohun River: rises in eastern Aileu municipality near the suco of ; flows approximately eastwards, to enter the North Laclo River about upstream of its mouth. Lihubani River: rises in northern Aileu municipality near ; flows approximately eastwards, to enter the North Laclo River about upstream of its mouth. Ue Coi River: rises in central Manatuto municipality a short distance north of Laclubar; flows approximately northwards, to enter the North Laclo River about upstream of its mouth. Sumasse River (or Sumasi River): rises in central Manatuto municipality a short distance northeast of Laclubar; flows approximately northwards, to enter the North Laclo River in the southwest periphery of Manatuto city, about upstream of the latter river's mouth; in late October 1942, a group of Australian commandos carried out ambushes of Japanese troops at two sites nearby.
Catchment
The river's catchment or drainage basin is the second largest in Timor-Leste after the Loes River catchment, and also one of the few with a perennial stream. It is about in length, and extends over four municipalities, namely Aileu, Ainaro, Manufahi, and Manatuto.
Excluding the portion downstream of the Laclo irrigation system's intake, the catchment is around or in area, with the eight tributaries.
Timor-Leste has been broadly divided into twelve 'hydrologic units', groupings of climatologically and physiographically similar and adjacent river catchments. The North Laclo River catchment is one of the two major catchments in the Laclo hydrologic unit, which is about in total area, and covers 13.6% of the country; the other one is the Comoro River catchment.
The major population centres in the Northern Laclo River catchment, from southwest to northeast, are Aileu, Lequidoe, Remexio, Laclo and Manatuto.
The elevation of the catchment ranges from AMSL at its southwestern edge to sea level at the river's mouth. Its topography is generally steep. About half the catchment is classified as being lands of between 15% and 40% slopes, and about one quarter has more than 40% slopes. There are small floodplains along the major rivers in the catchment; smaller river channels not flanked by floodplains are, in general, directly abutted by hillslopes.
The catchment has a mixture of dendritic () and parallel drainage networks. In the upper catchment, drainage is predominantly dendritic; in its middle reaches, some of the drainage is parallel. Almost all of the catchment's rivers have braided gravel beds, the widest of which, reaching a maximum of across, are on the North Laclo River.
In April 2005, the Ministry of Agriculture, Fisheries, and Forestry appointed the Japan International Cooperation Agency (JICA) to develop a community-based integrated watershed management plan for the Laclo and Comoro River catchments. JICA provided its report to the Ministry in March 2010.
The catchment's original vegetation was probably moist deciduous forest and semi-evergreen rainforest at high altitude, dry deciduous forest over the lower hills and valley floors, and thorn forest at the coast. However, large numbers of commercially valuable trees were removed during the Portuguese colonial era, and there was significant deforestation during the subsequent Indonesian occupation, when parts of the catchment, especially around military camps, were burned by the military in efforts to curtail and restrict the activities of armed Timorese resistance groups. Deliberate burning by local people also increased.
Over the last few decades of the twentieth century, the already degraded forest in the catchment became increasingly more degraded, due mainly to illegal cutting, firewood collection, wild fires and cattle grazing. The deforestation, in turn, caused tributaries in the upper reaches of the catchment to become intermittent, and is believed by local people to have led to the drying up of springs in those uplands. The catchment was also disturbed by cultivation, shifting agriculture, construction of roads, villages and towns, and Indonesian transmigration and relocation policies.
By contrast, in the early years of the twenty first century there was a reduction in local practices of deliberately burning grassland. In some parts of the catchment, burning was still used to flush out game for hunting, but in other areas, it was banned, in compliance with local rules.
A 2012 study concluded that erosion (denudation) of the catchment had become up to 20 times higher than over the last few thousand years. According to the report of the study, the most likely reason for the increased erosion was land use. In particular, the removal of vegetation from riverbanks (riparian zones) had caused widespread erosion, and its removal from hill slopes had promoted landslides. By increasing the river's sediment load, the greater catchment erosion had made the river shallower and wider, and thus increased the erosion of its riverbanks. The two forms of erosion, in turn, had combined to increase flooding in the river, and, by making its channels wider and braided, had caused its flows to become more erratic.
Another factor in the erosion of the catchment is that Timor is the deformed northern margin of the Australian continent, where Australia is colliding with the Banda Arc. Due to the collision, much of the catchment is undergoing rapid uplift, at several mm/annum, and as a result, the natural erosion rate of the catchment, involving downcutting by rivers and erosion of steep hillslopes, is very high. In such erosion systems, physical erosion processes (such as landslides, river downcutting, and sheet erosion) normally dominate over releases of fine sediment by erosion of weathered rocks.