José Cândido Stevaux

Damming the rivers of the Amazon basin

More than a hundred hydropower dams have already been built in the Amazon basin and numerous proposals for further dam constructions are under consideration. The accumulated negative environmental effects of existing dams and proposed dams, if constructed, will trigger massive hydrophysical and biotic disturbances that will affect the Amazon basin’s floodplains, estuary and sediment plume. We introduce a Dam Environmental Vulnerability Index to quantify the current and potential impacts of dams in the basin. The scale of foreseeable environmental degradation indicates the need for collective action among nations and states to avoid cumulative, far-reaching impacts. We suggest institutional innovations to assess and avoid the likely impoverishment of Amazon rivers.

Avulsive Rivers in the Hydrology of the Pantanal Wetland

This chapter presents and discusses the avulsive nature of the Pantanal rivers and shows how the ever-changing drainage network influences the surface hydrology and ecology. Besides, the systemic portrait here outlined provides new insights concerning the Pantanal hydrodynamics, in its particularities and as a whole system. A simple model of the avulsion process is illustrated, and several realistic examples of the processes leading to river avulsions are shown and discussed. The north-to-south flood-pulse wave due to the presence of bottlenecks is further described in detail. This systemic approach allows identifying that the fluvial “avulsive and bottleneck” dynamics seasonally affects both local and regional ecohydrological processes. Moreover, it shows that avulsive processes are commonplace in Pantanal, and changes in land use, particularly in river headwaters in the highlands, accelerate the avulsions, making the sustainable use of the Pantanal lowland areas difficult.

Geochemistry of the Upper Paraná River floodplain: study of the Garças Pond and Patos Pond

Abstract The aim of this study was to investigate the temporal evolution of the supply of chemical elements to the Upper Paraná River floodplain and identify trends in the geochemistry of its drainage basin. The primary factor that regulates the supply of chemical elements of the Upper Paraná River floodplain is the flood pulse, which can be magnified by the El Niño—Southern Oscillation. Garças Pond is affected by agriculture, urbanization, discharge of industrial effluents and hydroelectric power production activities. Patos Pond is affected by sugarcane burning, gold mining, agriculture and urbanization.

Iguazu Falls: A history of differential fluvial incision

The Iguazu Falls are one of the most beautiful in the world because of the combination of a high and wide structural step across a fluvial system with large water discharge and the tropical environmental location that sustains an exuberant forest and high biodiversity. The geology of the area consists of three layers of basalts that give a staircase-type shape to the falls. The Iguazu River is about 1,500 m wide above the falls and forms many rapids between rock outcrops and small islands. The falls have a sinuous arch-like head 2.7 km long, and part of water volume enters a canyon 80–90 m wide and 70–80 m deep, forming the spectacular “Garganta do Diabo” (Devil’s Gorge). Part of river water enters the canyon by its left side and generates a front with 160–200 individual falls that form a unique wall of water during floods. Although no absolute ages exist on the evolution of the fluvial system, it has been suggested that the falls have been continuously wandering upstream to its present position by progressive headwater erosion at a rate of 1.4–2.1 cm/year in the last 1.5–2.0 million years. The falls are recognized as UNESCO World Heritage property and regarded as a Geomorphological Site by the Brazilian Commission of Geologic and Paleobiological Sites – SIGEP.

The Anavilhanas and Mariuá Archipelagos: Fluvial Wonders from the Negro River, Amazon Basin

With a mean annual discharge of ~29,000 m3 s−1, the Negro River ranks as the sixth in the world in terms of water discharge and is the second largest tributary of the Amazon. The Mariua and Anavilhanas are two huge, fascinating archipelagoes of the Negro River that sustain the largest flooded “igapo” forest systems in the world and rich fish diversity. This chapter presents how hydro-geomorphology and changes in environmental conditions controlled the formation and functioning of these two anabranching reaches in the Negro River. The present hydro-sedimentary dynamics is not compatible with the existing morphology, which is product of a Middle-Late Holocene history. The very low amount of suspended sediment transported by the Negro is not sufficient to construct the intricate islands and floodplain. This condition produces a permanent non-equilibrium stage that controls not only river geomorphology but also vegetation distribution. As a product of long history, the Negro River basin with its wonderful pristine fluvial archipelagos and the “igapo” forests faces their most dangerous enemy: The irrecoverable destruction of the Amazon Rivers by the environmentally irresponsible dam construction planned by the Brazilian government.