Northern Laclo River

The headwaters of the river are in the portion of East Timor's central mountains ranging from southwest to south of Manatuto. From the headwaters, the river and its tributaries flow in a northeasterly to northern direction, and eventually into Wetar Strait just to the west of Manatuto.[2]^{: LM, S-5, 3-6, F-7}

The river has eight tributaries, two of which have a major branch. In order of entrance, the tributaries are as follows:[2]^{: LM, F-7}

• Manotahe River (major branch of Monofunin River)

• Monofunihun River

• Daisoli River

• Malikan River (major branch of Eralibanauber River)

• Eralibanaubere River

• Noru River

• Lohun River

• Lihubani River

• Ue Coi River

• Sumasse River

The river's catchment or drainage basin is one of the 10 major catchments in East Timor.[3] It extends over five municipalities, namely Manatuto, Aileu, Manufahi, Ermera and Dili.[2]^{: LM, S-1} Excluding the portion downstream of the Laclo irrigation system's intake, it is approximately 138,600 ha (342,000 acres) or 1,386 km² (535 sq mi) in area, with the eight tributaries in the river system.[2]^{: S-1, S-4}

The elevation of the catchment ranges from 2,512 m (8,241 ft) AMSL at its southwestern edge to sea level at the river's mouth. About half the catchment is classified as being lands of between 15% and 40% slopes, and about one quarter has more than 40% slopes.[2]^: S-5

There has been forest degradation in the catchment, due mainly to illegal cutting, firewood collection, wild fires and cattle grazing.[2]^: S-1

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 latter erosion, in turn, had led to bridge collapse and road damage. Additionally, the two forms of erosion had combined to increase flooding in the river, and, by making its channels wider and braided, had caused its flows to become more erratic.[4]^: 5

All of East Timor's catchments are exposed to a monsoon type climate, with a clear distinction between just two seasons, wet and dry. The southwestern edges of the upper Northern Laclo catchment have an annual precipitation of around 2,000–2,500 mm (79–98 in); the coastal part has a lower precipitation (500–1,000 mm (20–39 in) annually), and the river mouth has the longest dry season (7–9 months).[2]^{: S-4, 3-1}

Based on records from 1952 to 1974, the average monthly discharge of the river as a whole is 29.3 m³/s (62,000 cu ft/min), with the lowest one being 8.1 m³/s (17,000 cu ft/min) in September, and the highest being 69.8 m³/s (148,000 cu ft/min) in March.[2]^{: S-4, S-5}

The catchment's parent materials are limestone in its southern portion, and phyllite in its upper reaches. The phyllite materials in the catchment (between the central mountains at an elevation of about 1,000 m (3,300 ft) AMSL and the river mouth at sea level) are somewhat geologically fragile, and are easily eroded on being exposed to air after surface soil removal.[2]^{: S-5, 3-6}

• List of rivers of East Timor