Manso Dam

The dam impounds the Manso River in the upper Paraguay sub-basin of the Paraná basin. The reservoir is in the municipalities of Chapada dos Guimarães and Rosário Oeste in the midwest region of Mato Grosso.[2] It is the largest in the Paraopeba system.[3] The dam is 86 kilometres (53 mi) from Cuiabá, the state capital, along good roads. It is about 360 metres (1,180 ft) above sea level. The lake has become a tourist attraction.[4]

The dam project was launched in 1974, when a flood of the Cuiabá River left more than 20% of the population of the state capital homeless. The objective was to control flooding while generating electricity, developing tourism and supporting irrigation. Construction began in 1988 and was completed in 1999.[5] The dam has a height of 72 metres (236 ft).[6] 200,000 cubic metres (7,100,000 cu ft) of concrete were used in construction.[7] Total cost was R$340 million.[2] The reservoir covers an area of 427 square kilometres (165 sq mi).[6] It was full in 2001.[5]

The operating contract is 70% owned by Eletrobras Furnas.[2] Installed capacity is 212 MW, with guaranteed output of 92 MW.[6] It can meet the power demands of 300,000 people.[8] After an extended drought, in December 2015 the water level had fallen to 28.7% of capacity. However, record rainfall raised it to 76% by June 2016.[3] At 70% capacity the water line is 6.59 metres (21.6 ft) above the minimum operating level.[8]

Relatively little information was provided about the dam to the affected people in Mato Grosso.[9] 109 properties were requisitioned for the project, and between 652 and 1,065 families were displaced.[6] The displaced families were settled in areas with sandy soil, unsuitable for agriculture, and given insanitary straw shacks as homes.[9]

The reservoir submerged a significant quantity of biomass, which was not cleared before construction started. This reduces dissolved oxygen levels as it decays and encourages proliferation of water weeds. Rather than use a surface-level channel to divert excess water downstream, the design uses a drain from the reservoir bottom, feeding the worst-quality water downstream. This has had a negative effect on edible fish stocks in the Cuiabá River.[9] By reducing flooding the dam affects the Mato Grosso Pantanal environment, which depends on seasonal floods, but does not fully protect Cuiabá from floods when the reservoir is full.[7]