The hydrological aspects of the Amazon and the La Plata basins are interconnected through southward moisture transport performed by the Low‐Level Jet east of the Andes and the South Atlantic Convergence Zone. Remote effects of sea surface temperature variability in the Pacific and the Atlantic are of varied periodicities, from multi‐decadal to inter‐annual time scales. Major oscillations thus far detected are Atlantic Multi‐decadal Oscillation, Pacific Multi‐decadal Oscillation, North Atlantic Oscillation, Atlantic Dipole, Antarctic Oscillation, and the El Niño Southern Oscillation. In the multi‐decadal, inter‐decadal and decadal time scales, the effects of climate variability over the hydrological processes that interconnect the Amazon and La Plata watersheds are felt predominantly in the South American Monsoon season, while on the inter‐annual scale the effects vary along the year. The hydrological memory in Amazonian soils is also responsible for the inter‐annual variability of hydrology of the Amazon Basin. Due to the effects of soil water on evapotranspiration, the hydrological memory can affect the supply of moisture to the La Plata Basin, influencing the inter‐annual variability of this basin. The implications of the observed oscillations to the hydrological and climatological variability in the two basins are discussed and synthesized in this article. Hypotheses for future research are formulated.

Many articles on the subjects of moisture transport, precipitation and surface hydrology of the two largest watersheds of South America, the Amazon and the La Plata basins, are stitched together to obtain an overview of the aspects related to the hydrological processes interconnecting them on time scales ranging from seasonal to intra‐monthly. In the mean, moisture from the tropical Atlantic Ocean is transported by the trade winds into the Amazon Basin. A good part of it precipitates over the Amazon Basin and the other part reaches the La Plata Basin by northerly winds east of the Andes. Besides the moisture transported from the Atlantic, there is evapotranspiration in the Amazon and La Plata basins. A part of the evapotranspiration of the Amazon Basin precipitates over the same basin, contributing with about 1/3 of annual precipitation this basin, and a part joins the aerial stream into the La Plata Basin, contributing with about 1/4 of its annual precipitation. Semi‐permanent and transient meteorological systems such as Inter‐Tropical Convergence Zone, South Atlantic Convergence Zone, Low‐Level Jet (LLJ) east of the Andes, Madden–Julian Oscillation, cold fronts and cyclones play an important role in the seasonal and intra‐seasonal variations of precipitation, evapotranspiration and river discharge. The hydrological memory in Amazonian soils and the LLJ constitute an inter‐seasonal coupling between the water balances of the two basins. All these aspects are succinctly described and discussed in this review article. Hypotheses for future research are formulated.

Calibration and validation of hydrosedimentological models, usually performed at the outlet of a single basin, does not always correctly represent the hydrosedimentological processes in the different subdivisions of dammed river systems. The aim of this study was to evaluate simple calibration techniques (watershed outlet) and multi-site calibration (watershed outlet and internal reservoirs) with the Soil and Water Assessment Tool - SWAT model, using two nested basins in the southern region of Brazil. Three modeling procedures were analyzed, adjusting the hydrological and sedimentological parameters of the watershed and the reservoirs. It was found that (a) the simplest calibration does not correctly represent the processes in reservoirs; (b) the multi-site calibration provided a better simulation of the hydrosedimentological dynamics of the nested basins; and (c) parameterizations of the SWAT reservoir module have limitations in the context of the study area. The results showed that the multi-site calibration in watershed with reservoirs is more appropriate.

O represamento hídrico altera a hidrodinâmica do escoamento fluvial e dos processos de transporte e deposição de sedimentos. O presente trabalho tem por objetivo amostrar e analisar o comportamento de sedimentos suspensos em uma bacia hidrográfica de 5ª ordem fluvial, que possui um reservatório d'água em seu exutório. Foram realizadas 20 campanhas de amostragem de sedimentos em suspensão, de 2 a 3 metros a montante da barragem, em quatro profundidades da coluna d´água. Para amostrar a mistura água-sedimentos da descarga do reservatório foi utilizado um novo amostrador de sedimentos em suspensão, assim como um novo método de amostragem, dimensionalisados para esta represa. Os resultados do monitoramento mostraram que a concentração de sedimentos suspensos perto do fundo do reservatório é maior do que na superfície do mesmo, sendo que a amostragem do dia 05/09/14 indicou a ocorrência de correntes de turbidez de fundo. A análise estatística dos dados mostra que o sedimento em suspensão não responde rápidamente aos eventos de precipitação, havendo um retardo entre o pico da vazão e os valores máximos da descarga de sedimentos do reservatório. Com esta análise foram identificados dois processos hidrossedimentológicos reponsáveis pela descarga sólida desta represa. No entanto, somente um destes processos foi totalmente caracterizado, o qual é desencadeado pela chuva diária ocorrida entre o atraso temporal de 1 a 2 dias, gerando incremento de água e sedimentos na vazão com atraso de 1 dia, determinando parte da concentração de sedimentos na vazão do dia da amostragem. Já o outro processo, referente a vazão com atraso de 2 dias, que possui maior determinação nos sedimentos suspensos do dia da amostragem, ainda carece de uma maior amostragem espaço/temporal de precipitação e sedimentos suspensos para caracterização de sua gênese, podendo ser devido ao fenômeno de histerese.

The evolution of the fluvial landscape is the result of controls and processes that can be observed by the adjustments a river makes to its hydrological regime. The Negro River is the sixth-largest river in the world by water volume and contains two complex anabranching systems, the Anavilhanas and Mariuá archipelagos, and despite its importance, there is a lack of hydrological survey data on its multichannel reaches.The objective of this study was to analyse the fluvial dynamics of the lower Negro River and the morphodynamics of the Anavilhanas Archipelago channels in the Amazon basin. The analysed set of fluviometric surveys and cartographic data indicated that the average water velocity and depth of the channels were the most sensitive variables for water discharge variability. In addition, the reduction in the width/depth ratio of the channels in the Anavilhanas region is associated with an increased number of islands, but not with a fluvial transport capacity increase. These landforms play an important role in modulating flood wave dynamics in the lower reach of the Negro River. Seasonal water storage occurs in the channels and lakes of the archipelago due to the backwater effect caused by the Amazon River, which is the main control in the spatiotemporal variation of water discharge along the Anavilhanas Archipelago.