Hydrological changes in the northern Pantanal caused by the Manso dam: Impact analysis and suggestions for mitigation

Since 1999, the Manso hydropower plant has been regulating the Cuiabá River, which is one of the two main affluents of the northern Pantanal of Mato Grosso, responsible for the flooding of at least 20,000 km 2 of the world's greatest floodplain. Since the initiation of regular reservoir operation in 2002, discharge at the beginning of the wet season (November–December) has been reduced by about 20%. Current power plant operation increases dry-season discharges from about 100 m 3/s to 150 m 3/s, resulting in water levels approximately 1 m above those recorded before regulation. Rainy season runoff higher than 400 m 3/s is retained in about 6 weeks and the period of drying up is anticipated. Hydrograph analysis in conjunction with a planialtimetric field survey determined that discharge of 240 m 3/s is the minimum required to initiate flooding in the Pantanal in the northern Cuiabá River floodplain, while runoff of 355 m 3/s is necessary to guarantee consistent flooding of the same. Constrained by positive linear trends in precipitation and discharge, which were detected through a time series analysis of a 68-year period, two reoperation alternatives are proposed, which would not reduce mass balance of power generation, but can guarantee river overflow during the months November through May, minimizing the impact on ecological functions of the floodplain.