Northern Laclo River
The Northern Laclo River (, ) is the longest river in East Timor. It flows northeast into the Wetar Strait, reaching the coast near Manatuto. It has no connection to the Southern Laclo, which flows into the Timor Sea. Course. 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. The river has eight tributaries, two of which have a major  branch. In order of entrance, the tributaries are as follows: Catchment. The river's catchment or drainage basin is one of the 10 major catchments in East Timor. It extends over five municipalities, namely Manatuto, Aileu, Manufahi, Ermera and Dili. Excluding the portion downstream of the Laclo irrigation system's intake, it is approximately or in area, with the eight tributaries in the river system. The elevation of the catchment ranges from 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. There has been forest degradation in the catchment, due mainly to illegal cutting, firewood collection, wild fires and cattle grazing. 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. 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 ; the coastal part has a lower precipitation ( annually), and the river mouth has the longest dry season (7–9 months). Based on records from 1952 to 1974, the average monthly discharge of the river as a whole is , with the lowest one being in September, and the highest being in March. Geology. 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 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.