Isluga River is a river in Chile and Bolivia, and is also known as Sitani or Arabilla. It starts at the confluence of the rivers Chaguane and Huinchuta and flows for before reaching the Laguna Mucalliri of the Salar de Coipasa. It receives water from the volcanoes Isluga, Cabaray and Quimsachata as well as the Sierra Uscana.
The watershed of the river lies mainly in Chile and has a dry climate, resulting in a small river discharge of about . There are a number of towns and hamlets in the catchment, as well as wetlands with a number of animal and plant species.
Course
The Isluga River (also known as Sitani or Arabilla) begins at the southern foot of the high Cerro Alpajeres west of the town of Chaguane at the confluence of the Chaguane and Huinchuta. In its upper parts the Isluga River is also known as the Arabilla River. The Chaguane is long and receives water from the Laguna Parinacota, which in turn is nourished from two creeks that join it from the west and north. The Huinchuta (also known as Pasijro) is also long but comes from the northwest and turns south before joining the Chaguane.
After the confluence, the Isluga River proceeds in southeast-eastward direction save for a brief turn northeast, past the towns of Chaguane and Arabilla; between the two the Quebrada Taipicollo joins from the northwest. After Arabilla it turns more eastward and receives waters from the Laguna Arabilla farther south; the Isluga River here passes through wetland territory. It flows past the towns of Chapicollo, Enquelca and Coraguane before turning sharply to the south. After this turn the river continues first southeast-east, then due east between Cachaguano and Isluga where it has a slight northeasterly tilt, and finally southeastward towards Sitani and Cotasaya. The penultimate part of the river runs irregularly eastward towards Colchani and Pisigua. After a total course of before ending into the Laguna Mucalliri, which is part of a system of wetlands at Salar de Coipasa. The Cariquima River ends into the same general area and is sometimes considered to be part of the Rio Isluga. From that area, the Sitani River continues into the Salar de Coipasa proper.
The Isluga River is entrenched between river terraces. It receives several tributaries that drain the Quimsachata, Isluga and Cabaray from the north; the Alsare from Cabaray is a major tributary. From the south it receives tributaries from the Sierra Uscana, including the long Mauque which joins the Isluga River in the Fisica Choque/Chaque wetland.
Watershed
The Isluga River drains of Chile's Tarapaca Region and a further of Bolivia, and lies at an average elevation of elevation. The catchment of Isluga is more gentle than Pacific-draining catchments, resulting in the formation of wetlands.
The region has an arid climate. Most precipitation arrives from the Amazon and falls mainly during the summer months. This results in the region having a steppe vegetation above elevation with about precipitation. Above elevation lies a montane desert climate with precipitation amounting to . During the Quaternary, the Altiplano was at times wetter than today, resulting in the formation of lakes.
Much of the watershed is dominated by Oligocene to Quaternary age volcanic rocks formed by basalt, basaltic andesite, andesite and dacite. In the central and eastern parts there are also sedimentary formations of Pleistocene to Holocene, including alluvial and lacustrine deposits; these sedimentary formations are concentrated in the central parts of the catchment high Isluga volcano is still active, with eruptions in 1900 and 1963; other important mountains are the high Cabaray and the high Cerro El Fraile.
During the Pliocene-Pleistocene, tectonic uplift raised the Altiplano to heights of over . A number of endorheic systems such as the Lauca River and the Isluga River drain the Altiplano. Part of the Isluga catchment was covered by lakes, which have left wetlands and small lakes.
Discharge
Water temperatures at Ríos Arabilla at elevation range . The salinity is dominated by chloride, sodium and sulfate owing to high evaporation and the dissolution of salts in the catchment. The waters are eutrophic.
A stream gauge was active at Bocatoma (between the towns of Isluga and Sitani) between 1995 and 2001, and at Puente in 1998. At Bocatoma discharge is fairly constant with the exception of the spring months; average runoff is about but can increase to over or decrease to less than . A more recent report indicated a discharge of at the Bocatoma station.