Edgardo M. Latrubesse

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.

Coral reefs chronically exposed to river sediment plumes in the southwestern Caribbean: Rosario Islands, Colombia

Politicians do not acknowledge the devastating impacts riverine sediments can have on healthy coral reef ecosystems during environmental debates in Caribbean countries. Therefore, regional and/or local decision makers do not implement the necessary measures to reduce fluvial sediment fluxes on coral reefs. The Magdalena River, the main contributor of continental fluxes into the Caribbean Sea, delivers water and sediment fluxes into the Rosario Islands National Park, an important marine protected area in the southwestern Caribbean. Until now, there is no scientific consensus on the presence of sediment fluxes from the Magdalena River in the coral reefs of the Rosario Islands. Our hypothesis is that high sediment and freshwater inputs from the Magdalena have been present at higher acute levels during the last decade than previously thought, and that these runoff pulses are not flashy. We use in-situ calibrated MODIS satellite images to capture the spatiotemporal variability of the distribution of suspended sediment over the coral reefs. Furthermore, geochemical data are analyzed to detect associated sedimentation rates and pollutant dispersion into the coastal zone. Results confirm that turbidity levels have been much higher than previous values presented by national environmental authorities on coral reefs off Colombia over the last decade. During the 2003-2013-period most of the Total Suspended Sediments (TSS) values witnessed in the sampled regions were above 10mg/l, a threshold value of turbidity for healthy coral reef waters. TSS concentrations throughout the analyzed time were up to 62.3mg/l. Plume pulses were more pronounced during wet seasons of La Niña events in 2002-2003, 2007-2008, and 2009-2010. Reconstructed time series of MODIS TSS indicates that coral reef waters were exposed to river plumes between 19.6 and 47.8% of the entire period of analysis (2000-2013). Further analyses of time series of water discharge and sediment load into the coastal zone during the last two decades show temporal increases in water discharge and sediment load of 28% and 48%, respectively. (210)Pb dating results from two cores indicate sedimentation rates of ~0.75 cm/y of continentally exported clastic muddy sediments that are being deposited on the carbonatic shelf. The cores contain sediments with heavy metals and their concentrations are frequently above the ecologically accepted standards. Overall, the last decade has witnessed stronger magnitudes in fluvial fluxes to the coastal region, which probably coincide with associated declines in healthy coral cover and water quality. Our results emphasize the importance of local stressors, such as runoff and dispersion of turbid plumes, as opposed to ocean warming, disease and hurricanes, which have played a larger role on other coral reefs in the Caribbean. Coral reef management across the southwestern Caribbean, a coastal region influenced by continental fluxes of numerous rivers flowing from the Andes, may only be effective when land and marine-based stressors are simultaneously mitigated.

Surface water types and sediment distribution patterns at the confluence of mega rivers: The Solimões‐Amazon and Negro rivers junction

Large river channel confluences are recognized as critical fluvial features because both intensive and extensive hydrophysical and geoecological processes take place at this interface. However, identifications of suspended sediment routing patterns through channel junctions and the roles of tributaries on downstream sediment transport in large rivers are still poorly explored. In this paper, we propose a remote sensing-based approach to characterize the spatiotemporal patterns of the postconfluence suspended sediment transport by mapping the surface water distribution in the ultimate example of large river confluence on Earth where distinct water types meet: The Solimoes-Amazon (white water) and Negro (black water) rivers. The surface water types distribution was modeled for three different years: average hydrological condition (2007) and 2 years when extreme events occurred (drought-2005 and flood-2009). Amazonian surface water domination along the main channel is highest during the water discharge rising season. Surface water mixing along the main channel depends on the hydrological seasons with the highest mixed-homogenized area observed during water discharge peak season and the lowest during discharge rising season. Water mixture also depends on the yearly hydrological regime with the highest rates of water mixing in 2009, followed by 2005 and 2007. We conclude that the dominant mixing patterns observed in this study have been persistent over a decadal scale and the anabranching patterns contribute to avoid a faster mixing in a shorter distance. Our proposed approach can be applied to a variety of morphodynamic and environmental analyses in confluences of large rivers around the world.

Floods in Argentina

Argentina is a country strongly affected by floods; the main areas affected and the disasters produced by such floods are discussed herein. The fluvial systems of Argentina can be classified into three main groups: large tropical rivers, torrential rivers with headwaters in mountain areas, and flat-plain rivers with insufficient drainage efficiency. The torrential rivers group can be subdivided into two categories: (a) Rivers fed by torrential rains, and (b) rivers fed by rain and snow. Agriculture and cattle farming have been the main activities of the national economy since the origin of the nation, and these activities are concentrated in the Chaco-Pampean region, an extremely flat area with very productive land but poor drainage capacity. Floods in rivers such as the Salado (Buenos Aires Province) and local floods in the Sub-Mmeridional lowlands of Santa Fe affect thousands of inhabitants and millions of hectares of productive land, causing huge economic losses of up to more than US

Floods in Urban Areas of Brazil

500 million. The Parana River is the country’s largest tropical river and its main waterway. Several important cities are located along its banks. Some of the largest floods on the Parana River have been related to El Nino-ENSO events. During the 1982-1983 El Nino-Enso event, more than 234,000 people had to be evacuated, and damage caused losses of more than US

The Late Pleistocene in Amazonia: A Paleoclimatic Approach

2,600 million. The floods of the 1991-1992 El Nino-ENSO event were also catastrophic, causing estimated losses of US

Geomorphology of Natural Hazards and Human-induced Disasters in Bolivia

513 million and affecting more than 122,000 inhabitants.. Floods also affect some of the inhabitants of Patagonia and urban centers in the Piedmont areas of the Andes in the northwest region of the country, although the number of people affected and economic losses are lower that those in the Pampa and Parana River regions because of their low population densities and less developed regional economies. One particular case, the flood of the city of Santa Fe in 2003, one of the most dramatic natural catastrophes in Argentina, is also analyzed. The disaster was produced by a combination of intense rain in the lower basin of the Salado River (Santa Fe) and the negligence of the local government. Nearly 140,000 inhabitants were affected, and the flood caused an economic loss of around US

Considerations about the land use and conversion trends in the savanna environments of Central Brazil under a geomorphological perspective

1,000 million. It is argued that two main factors have contributed to generating the worst scenario for disasters in Argentina: a climatic trend, since approximately 1970, of increasing rainfall, and the political instability of the country throughout practically the whole of the second half of the twentieth century until the present day.

Iguazu Falls: A history of differential fluvial incision

Abstract Floods in three very different urban areas of Brazil are presented in this chapter: Sao Paulo, the largest city of South America; the mountain basins of Santa Catarina State, southeastern Brazil; and the city of Rio Branco (Acre State), a typical medium-sized city of the southwestern Brazilian Amazonia. Sao Paulo represents a case of uncontrolled and disorganized urban growth, typical of many cities of southeastern Brazil where the infrastructure and production systems (railroads, roads, and industries) have been settled on the alluvial plains. Santa Catarina disasters are produced because of a combination of tropical storms in a region of mountain fluvial basins that are characterized by flash floods, slope instability (landslides), and urban occupation of the valleys. The Amazonian city of Rio Branco suffered similar fast population growth and because of the cultural Amazonian tradition of “living near the river” suffered many consequences from flooding. The intensive urbanization in both Sao Paulo and Rio Branco around and within the floodplains has introduced many problems involving rain-water drainage. Urban interference in the drainage system is strong in Sao Paulo. The city’s flat topography, associated with channel rectification and the pluvial drainage system, improves surface runoff and consequently water concentration in the lowest areas. On the other hand, obstructed and underfitted sweepers are responsible for many of the small but frequent localized floods. In both cities, floods are more a planning than a natural problem, and the number of deaths and affected people related directly to floods is very small when compared with countries like Bangladesh, India, or China. Nonetheless, the number of persons affected is high, and the diseases and urban problems brought by floods are significant.

Climate and Geomorphologic-related Disasters in Latin America

The Amazon rainforest at the time of the last glaciation, during the late Pleistocene, suffered strong changes in its biogeography and landscape. The review of multidisciplinary data (geology, palynology, vertebrate paleontology) permits one to obtain some palaeoenvironmental pictures. The best information that we have about Pleistocene chronology, paleoecology and geology is related to the time before 24 000 yr BP, possibly corresponding to the middle Pleniglacial (isotopes stage 3 and early stage 2). During that period the climate was apparently influenced by high precipitation at the Andes and a continuing change towards dry conditions in the lowlands. The Amazonian rivers were characterized by alluvial sedimentation, associated with the changing climate. The aridity reached its climax during the upper Pleniglacial. The resulting eolian sedimentation extended over parts of the central and north Amazonia. At the same time, the savanna vegetation reached its maximum extension. The trade winds were more intense and dry than today. Beginning at about 14 000 yr BP, the sedimentation in the alluvial belts was influenced by the deglaciation. Probably this sedimentation phase culminated with the marine transgression of the Middle Holocene.