Desaguadero River (Titicaca)

The Desaguadero River is a river shared between Bolivia and Peru, the main river in the endorheic basin of Lake Titicaca, where it originates, discharging excess water to Lake Poopó, where it is evacuated mainly to through a strong evaporation process. Its basin represents 21% of the area of the TDPS System. Like the Titicaca basin, the Desaguadero basin is framed by the Eastern and Western mountain ranges, with the highlands in its central part.

History

This river was known in pre-Columbian times by the names of Aullagas or Chacamarca.

Geography

The Desaguadero River rises in Lake Titicaca, discharging excess water. In the part closest to the mouth of Lake Titicaca, forming the 96 km² Aguallamaya lagoon, there is a first and short section of 14 km that forms the natural border between Peru and Bolivia. It then runs southeast, crossing the department of La Paz and then the department of Oruro, where it flows into Lake Poopó, after a journey of 436 km. The river passes near the towns of Calacoto, Ulloma and Puerto Japonés.

On its banks, in Bolivian territory, its waters are used for irrigation, despite the high content of mineral salts.

The following stretches can be identified along the Desaguadero River:

• From kilometer 0 to km 63: Wide plains (from the International Bridge to Nazacara);
• From km 63 to km 226: Mountain area (from Nazacara to Chilahuala); and
• From km 226 at km 398: Flood plains (from Chilahuala to Lake Poopó),

The average slope is 0.45 per thousand (45 cm per km).

Variations in Lake Titicaca

The river valley is geologically unstable, and the sliding of its slopes, in the first part of the river, in the vicinity of Lake Titicaca, is responsible for the variations in the lake level. Indeed, in the 1990s, pre-Columbian ruins have been found on the banks of the lake islands, at a level below the current average level, which clearly indicates that in earlier times the lake level was lower.

The last major event that raised the level of Lake Titicaca occurred in the early 1980s. As a result of this event, the two countries, Bolivia and Peru, have prepared, with the support of the European Union, a Master Plan for management of water resources throughout the basin. As a result of this international effort, the following actions have been carried out:

• Waru-Waru Program;
• Coastal defence construction programme;
• Desaguadero River Dredging Program;
• Construction of gates in the mouth of the river for the management of the lake levels.

Flow rate

Lake Titicaca is not the only source of the Desaguadero River. In fact, along its journey to Lake Poopó, it receives a series of tributaries from the Andes mountain range that belong to its basin and increase the river's water flow, the largest being the Mauri River. Measurements from 1960 to 1990 gave the following flows:

• at the exit of Lake Titicaca: 35 m3/s;
• in Calacoto (before the confluence with the river Mauri): 52 m3/s;
• in Ulloma: 77 m3/s;
• in Chuquiña: 89 m3/s;

A measurement in March 2017 gave the following flows:

• At the exit of Lake Titicaca: 2.34 m3/s;
• After the confluence with the Mauri River: 7.72 m3/s;
• In Eucaliptus: 4.40 m3/s (decrease of flow for unknown reasons)

[2]

In August 2016, the peasants in the region of the river warned that the flow of the river was gradually decreasing, and they were alarmed when they saw a much lower flow than was customary in previous years or decades. [3]

Taking into account the fact that, throughout its course, the important flow consisting of the large quantities necessary for irrigation must be considered, it is estimated that only a third of the waters of the Desaguadero River that reach the lake Poopó come from Lake Titicaca.

The continuous supply of water through its own tributaries allows the Desaguadero River, as it advances, to become more regular. Thus, at its birth, it can even have a null or negative flow, which means a reversal of the upper course. In cases of extreme decrease in the waters of Titicaca (in an exceptional drought), since the slope in this first section is equal to zero, the course is reversed and the Desaguadero River feeds the lake instead of being fed by it.

The Floods

The flooding of the Desaguadero River at the International Bridge is obviously determined by the maximum levels of Lake Titicaca. These, moreover, undergo a first lamination in the Laguna de Aguallamaya, located immediately downstream of the bridge.

The contribution of the Alto Desaguadero (interbasin Calacoto-Puente Internacional) to the flooding of the Desaguadero River is significantly higher than that of the Mauri River, despite the fact that the latter's basin is larger. In the inter-basin it is worth mentioning especially the Callaccame, Llinqui and Jacha Mauri rivers, whose floods can be particularly violent, of the order of 500 m³/s for a return period of 50 years and 1,000 m³/s for 1,000 years. In fact, in the historical series of 18 years they have already produced a maximum flow event greater than 400 m³/s. In this regard, it should be remembered that, since the floods of these rivers generally occur in the months of January to March, when Lake Titicaca has not yet reached its maximum levels, a part of said flows can penetrate the lake itself, producing flows negatives that have exceeded 70 m³/s. However, this possibility can be controlled since the gates have been built in proximity to the International Bridge.

The extreme floods of Bajo Desaguadero are also produced by its tributaries. However, given the great extension of the Poopó and Uru Uru lakes, these floods do not provide the volume of water required to bring these lakes to certain limit levels, an effect that is achieved with sustained discharges from Titicaca in the period of high water..