Hydro-sedimentology development is a great challenge in Peru due to limited data as well as sparse and confidential information. This study aimed to quantify and to understand the suspended sediment yield from the west-central Andes Mountains and to identify the main erosion-control factors and their relevance. The Tablachaca River (3132 km2) and the Santa River (6815 km²), located in two adjacent Andes catchments, showed similar statistical daily rainfall and discharge variability but large differences in specific suspended-sediment yield (SSY). In order to investigate the main erosion factors, daily water discharge and suspended sediment concentration (SSC) datasets of the Santa and Tablachaca rivers were analysed. Mining activity in specific lithologies was identified as the major factor that controls the high SSY of the Tablachaca (2204 t km² yr⁻¹), which is four times greater t...

This work provides an initial overview of climate features and their related hydrological impacts during the recent extreme droughts (1995, 1998, 2005 and 2010) in the upper Solimes River (western Amazon), using comprehensive in situ discharge and rainfall datasets. The droughts are generally associated with positive SST anomalies in the tropical North Atlantic and weak trade winds and water vapor transport toward the upper Solimes, which, in association with increased subsidence over central and southern Amazon, explain the lack of rainfall and very low discharge values. But in 1998, toward the end of the 1997-98 El Nio event, the drought is more likely related to an anomalous divergence of water vapor in the western Amazon that is characteristic of a warm event in the Pacific. During the austral spring and winter of 2010, the most severe drought since the seventies has been registered ...

The use of satellite imagery to assess river sediment discharge is discussed in the context of poorly monitored basins. For more than three decades, the Peruvian hydrological service SENAMHI has been maintaining several gauging stations in the lower part of the Amazon River catchment. This network has been recently supplemented by the Hydro-geodynamics of the Amazon Basin (HYBAM) program, which has a water quality monitoring network distributed over five locations and allows the assessment of river discharge and surface suspended sediment (SSS) concentration. In this paper, the three stations that are located near the confluence of the Marañon and Ucayali Rivers, which form the Amazon River, are reviewed in detail. Two of the stations provide a complete time series of 10-day SSS samples over the studied period. The third station, along the Ucayali River, failed to provide valid estimate...

Este trabajo ofrece un panorama inicial de las características climáticas y los impactos hidrológicos afines durante las recientes sequías extremas (1995, 1998, 2005 y 2010) en el río Amazonas peruano. Para ello se empleó una base de datos in situ de caudales y precipitaciones. Las sequías generalmente se asocian a anomalías positivas de temperatura superficial del mar (TSM) en el Atlántico tropical norte, vientos alisios y transporte de vapor de agua débiles hacia el oeste de la cuenca amazónica, que acompañados de un aumento en la subsidencia sobre la parte central y sur de la cuenca, explican la falta de lluvias y los muy bajos valores de caudales. Sin embargo, en 1998 hacia el final del evento El Niño de 1997/1998 la sequía estuvo más relacionada con una divergencia anómala de vapor de agua en el oeste de la amazonia, que es característica de un evento cálido en el ...

La variabilidad de las precipitaciones en la cuenca amazónica (CA) es analizada para el período 1964-2003. Este análisis está basado en 756 estaciones pluviométricas distribuidas en todos los países de la cuenca incluyendo datos de Bolivia, Perú, Ecuador y Colombia. En particular, la reciente disponibilidad de datos de precipitación de los países andinos hace posible completar estudios anteriores. Se subraya el impacto de la cordillera de los Andes sobre las lluvias. La mayor precipitación en la CA es observada en regiones bajas expuestas a los vientos húmedos del este, y menor lluvia es registrada en las estaciones de altura y protegidas por las primeras montañas de los Andes de los vientos húmedos del este. Además, los regímenes de las precipitaciones son más diversificados en las regiones andinas que en el llano amazónico. La variabilidad espacio-temporal de las preci...

Rainfall variability in the Amazon basin (AB) is analysed for the 1964-2003 period. It is based on 756 pluviometric stations distributed throughout the AB countries. For the first time it includes data from Bolivia, Peru, Ecuador, and Colombia. In particular, the recent availability of rainfall data from the Andean countries makes it possible to complete previous studies. The impact of mountain ranges on rainfall is pointed out. The highest rainfall in the AB is observed in low windward regions, and low rainfall is measured in leeward and elevated stations. Additionally, rainfall regimes are more diversified in the Andean regions than in the lowlands. Rainfall spatio-temporal variability is studied based on a varimax-rotated principal component analysis (PCA). Long-term variability with a decreasing rainfall since the 1980s prevails in June-July-August (JJA) and September-October-Novembe...

The suspended sediment yield and associated current denudation rates of eight large catchments located along the eastern range of the central Andes have been determined. The catchments have been chosen as mountainous and mainly denudational basins to avoid sediment sinks that could bias our analysis. Discharge data and suspended sediment concentrations measured at each catchment outlet have been combined to produce average annual sediment fluxes and thus yields and current denudation rates over time spans of 2–43 years. Denudation rates range between 0.25 and 1.20 mm yr−1 with a north to south gradient. Maximum values are observed in Bolivian catchments. A correlation analysis has been carried out to determine the main controlling factors of current denudation rates at the catchments spatial scale. Climatic, topographic and lithologic parameters have been studied. Our results suggest...

In Ecuador and Peru, geochemical information from Pacific coastal rivers is limited and scarce. Here, we present an unedited database of major element concentrations from five HYBAM observatory stations monitored monthly between 4 and 10 years, and the discrete sampling of 23 Andean rivers distributed along the climate gradient of the Ecuadorian and Peruvian Pacific coasts. Concentration (C) vs. discharge (Q) relationships of the five monitored basins exhibit a clear dilution behavior for evaporites and/or pyrite solutes, while the solute concentrations delivered by other endmembers are less variable. Spatially, the annual specific fluxes for total dissolved solids (TDS), Ca2+, HCO3 −, K+, Mg2+, and SiO2 are controlled on the first order by runoff variability, while Cl−, Na+ and SO4 2− are controlled by the occurrence of evaporites and/or pyrite. The entire Pacific basin in Ecuador...

Previos estudios describen de manera general la variabilidad anual de los caudales en el curso principal del Amazonas en Brasil, el cual sólo representa el estado general del sistema hidrológico de la cuenca. Por ello, este estudio utiliza una nueva serie de datos que incluye la descarga diaria de 18 subcuencas, con la finalidad de analizar la variabilidad de los extremos regionales en la cuenca del Amazonas. Luego de describir la diversidad de los ciclos hidrológicos anuales, diferentes pruebas estadísticas son aplicadas para detectar tendencias y rupturas de las series temporales. Este estudio muestra que durante el período 1974-2004, la estabilidad de caudales del río principal en Óbidos, se explica por cambios regionales opuestos que involucran principalmente a ríos Andinos: una disminución de la escorrentía en el periodo de estiage, particularmente importante en las region...

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget of the Ucayali River catchment, based on spatial ...

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget

Because increasing climatic variability and anthropic pressures have affected the sediment dynamics of large tropical rivers, long-term sediment concentration series have become crucial for understanding the related socioeconomic and environmental impacts. For operational and cost rationalization purposes, index concentrations are often sampled in the flow and used as a surrogate of the cross-sectional average concentration. However, in large rivers where suspended sands are responsible for vertical concentration gradients, this index method can induce large uncertainties in the matter fluxes. Assuming that physical laws describing the suspension of grains in turbulent flow are valid for large rivers, a simple formulation is derived to model the ratio (α) between the depth-averaged and index concentrations. The model is validated using an exceptional dataset (1330 water samples, 249 con...

The biodiversity and productivity of the Amazon floodplain depend on nutrients and organic matter transported with suspended sediments. Nevertheless, there are still fundamental unknowns about how hydrological and rainfall variability influence sediment flux in the Amazon River. To address this gap, we analyzed 3069 sediment samples collected every 10 days during 1995–2014 at five gauging stations located in the main rivers. We have two distinct fractions of suspended sediments, fine (clay and silt) and coarse (sand), which followed contrasting seasonal and long-term patterns. By taking these dynamics into account, it was estimated, for first time, in the Amazon plain, that the suspended sediment flux separately measured approximately 60% fine and 40% coarse sediment. We find that the fine suspended sediments flux is linked to rainfall and higher coarse suspended sediment flux is relat...

The aim of this study is to evaluate the ability of the ORCHIDEE land surface model to simulate streamflows over each sub-basin of the Amazon River basin. For this purpose, simulations are performed with a routing module including the influence of floodplains and swamps on river discharge and validated against on-site hydrological measurements collected within the HYBAM observatory over the 1980–2000 period. When forced by the NCC global meteorological dataset, the initial version of ORCHIDEE shows discrepancies with ORE HYBAM measurements with underestimation by 15 % of the annual mean streamflow at Obidos hydrological station. Consequently, several improvements are incrementally added to the initial simulation in order to reduce those discrepancies. First, values of NCC precipitation are substituted by ORE HYBAM daily in-situ rainfall observations from the meteorological services of ...

The aim of this study is to evaluate the ability of the ORCHIDEE land surface model to simulate streamflows over each sub-basin of the Amazon River basin. For this purpose, simulations are performed with a routing module including the influence of floodplains and swamps on river discharge and validated against on-site hydrological measurements collected within the HYBAM observatory over the 1980-2000 period. When forced by the NCC global meteorological dataset, the initial version of ORCHIDEE shows discrepancies with ORE HYBAM measurements with underestimation by 15% of the annual mean streamflow at Óbidos hydrological station. Consequently, several improvements are incrementally added to the initial simulation in order to reduce those discrepancies. First, values of NCC precipitation are substituted by ORE HYBAM daily in-situ rainfall observations from the meteorological services of Am...