English: Llallagua Dam - Hydro-Electric Plant at a Bolivian Tin Mine (The Engineering & Mining Journal, 2 Jan 1915)

Fifteen kilometers from the Llallagua mine, the Catavi River runs through a narrow gorge in the mountain for a distance of 500 m., and the narrowest point in this cut makes an almost right-angle bend. At this point the cut is only 2 m. wide for a height of 20 m. From this point it opens out. and at 6O m, the width is 30 m.

Further up the gorge widens out to 180 m. The Catavi, Uncia, Zauta and Challanta rivers, together with various branches, run out to this cut. The amount of water varies a great deal, and the dry season of the high plateau of Bolivia, which is in November, is succeeded by the heavy rainfall of the spring, from December to April. In the dry season the total flow of the above rivers does not exceed 200 litres per second, while during the rainy season the flow has rised as much as 70 m³ per second. The water is from a shed of 8000 to 10,000 hectares. Several measurements of a rainfall of 20 liters per sqare mile during an hour have been obtained. This irregular flow makes it necessary to impound all of the water which falls during the rainy season, in order to have a constant supply of power, but the dry-season flow would not be sufficient for requirements.

In order to have sufficient fall and water for the turbines during all the year, it was necessary to have a head of at least 30 m, it being figured that an average head of 42 m would be obtained. The dam was designed for a height of 58 m, with a waste weir which would maintain a water level of 55 m during the rainy season. At this level it was estimated that enough water would be stored to supply power during the entire year. The lake so formed is 6500 m long, with a width which varies between 50 and 300 m, and there is capacity for 18,000,000 to 20,000,000 m³ of water. The dam is built en arco. both horizontally and vertically. The horizontal arch has a 1-ft. 10-in. versed sine, which was considered advisable for resisting the hydraulic pressure.

Construction of the Dam

The dam is built of cut stone laid in river sand and gravel, hydraulic lime and Alsen cement. The work is reinforced with I- and T-beams, ami steel cable- at three different levels. The dam foundation is 5 m below the level of the river and 58 m above the river at the crest. The base of the dam is 38 m. thick. At 55 m. the dam is three meters thick, with a crown 3 m high and 1,5 m. thick. The water reaches the turbines through a 65-m tunnel, through which it flows by a Mannesmann 0,70 m pipe 70 m long. The turbine house is built for four turbines, direct-connected to their respective generators, of which three are already installed. The turbines are of the horizontal type, built by Escher Wyss & Co. Each turbine passes 180 to 300 liters of water per second, depending upon the water level, and developing 200 to 320 hp. The waste weir is in a depression of a hill, which is at the center of the sharp turn of a river, and located about a kilometer above the dam, discharging to the river bed below the dam. The generators run 750 r.p.m. and generate a 3000-volt current, which is transformed to 10,000 volts for transmission to the mine. The line loss is 150 volts over the 15 km. The line passes over ground from 3500 to gOOO in. high. The dam has demonstrated its resistance and strength since completion, having successfully withstood an overflow a meter deep on the crest before the waste channel was completed.

The work has been particularly difficult due to its great distance from the coast. The railway haul is 900 km. to Cahllapata, and from there five days' journey in two-wheeled carts to the mine. From the mill there is a day of cart haul to the head of the inclined plain, from the foot of the plain the material was transported on a small Decauville railway to the dam site. The cement Was carried from the railway to the works on llama-. and the most of it was lost on the way. The llamas required seven days lor the trip, and sometimes were weeks on the way.

It is a curious commentary on human affairs that three years were laboriously -spent in building this dam, and it had just begun to furnish cheap power to the Llallagua Tin Mining Co., when the company bumped up against a war and has market lor the tin. Although the United States consumes the majority of the world's production, there is no one in America who will buy and smelt tin concentrates. Americans are talking loudly supplying the needs of South America, but they forget that the first need is a market for nitrates, tin, copper, silver, rubber, cotton, and all the various products of South American countries.