Tropical rivers

Abstract

This paper presents an overview of tropical river systems around the world and identifies major knowledge gaps. We focus particularly on the rivers draining the wet and wet-dry tropics with annual rainfall of more than 700 mm/year. The size of the analyzed river basins varies from 10 4 to 6 Â 10 6 km 2 . The tropical rivers across the globe drain a variety of geologicgeomorphologic settings: (a) orogenic mountains belts, (b) sedimentary and basaltic plateau/platforms, (c) cratonic areas, (d) lowland plains in sedimentary basins and (e) mixed terrain. All of them show clearly high but variable peak discharges during the rainy season and a period of low flow when rainfall decreases. Some tropical rivers show two flood peaks, a principal and a secondary one, during the year. We computed the intensity of floods and discharge variability in tropical rivers. The relationship between sediment yield and average water discharge for orogenic continental rivers of South America and Asia was also plotted. Insular Asian rivers show lower values of sediment yield related to mean annual discharge than continental orogenic rivers of Asia and South America. Rivers draining platforms or cratonic areas in savanna and wet tropical climates are characterized by low sediment yields. Tropical rivers exhibit a large variety of channel form. In most cases, and particularly in large basins, rivers exhibit a transition from one form to another so that traditional definitions of straight, meandering and braided may be difficult to apply. In general, it is more useful to apply the terminology of single and multi-channel systems or complex anabranching systems at least for selected regional segments.Present-day knowledge of tropical systems and its potential application to improve interpretation of older alluvial sequences and facies models are briefly discussed. Human impact and river management issues including land use changes, mining, dams, interbasin water transference as well as flood hazards are some of the daunting problems in tropical river basins today. D

Damming the rivers of the Amazon basin

“…The river basin discharges ~16 to 18% of the planet's fresh water flow to its large estuary and the nearshore Atlantic 12,13 . Four of the world's ten largest rivers are in the Amazon basin (the Amazon, Negro, Madeira and Japurá), and twenty of the 34 largest tropical rivers are Amazonian tributaries 14 . The Amazon is also the largest and most complex river system that transfers sediments and solutes across continental distances, constructing and sustaining Earth's largest continuous belt of floodplain and a mosaic of wetlands encompassing more than 1,000,000 km 2 .…”

The dependence of meteoric 10Be concentrations on particle size in Amazon River bed sediment and the extraction of reactive 10Be/9Be ratios

“…At the Óbidos gauging station, the Amazon basin covers an area of more than 6×10 6 km 2 , thus being the world´s largest river basin in terms of water discharge (Q of 209,000 m 3 /s, Latrubesse et al, 2005), and being one of the largest in terms of sediment discharge (an average denudation rate from in situ-10 Be yielded ca. 650 t/km 2 /yr by Wittmann et al, 2011).…”

Flood pulse and spatial dynamics of mercury in sediments in Puruzinho lake, Brazilian Amazon

“…Thus, the Madeira river and its tributaries act as the principal route in exporting Hg to their associated aquatic systems . Approximately 25% of the sediment stored in the lower Amazon river originates from the Madeira river basin (Filizola-Junior 1999;Latrubesse et al 2005).…”