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Purpose Finer sediment particles (silt and clay) transported by rivers carry the major part of nutrient loads by absorption; thus, sediment settling can remove nutrients from the water column. The purpose of this paper is to analyze the relation between reservoir sedimentation and water quality by assessing the reservoir sedimentation process and the sediments’ characteristics. Design/methodology/approach Bathymetric surveys from 2004 to 2014 were analyzed to assess the sedimentation process. Core samples provided information on a layer-by-layer basis of the sediment deposits, and water samples near the surface and near the bottom provided information on sediment concentration, and adsorbed and dissolved nutrients. Findings The upstream region of a reservoir is already silted. From 2004 to 2014, the delta evoluted approximately 500 m downstream and the deposits were mainly composed of clay. An area of approximately 1,000 m between the delta and the dam should still be able to continue allowing sediment deposition in the coming years. Most of the nutrients were absorbed into the sediment particles, except for the nitrogen measured in the dry season. Research limitations/implications Although analyses of the full cycle of the nutrients were not carried out, the constant sediment trapping of finer sediments and the high rate of absorbed nutrients in the suspended sediment support the hypothesis that the reservoir has removed nutrients from aqueous media by adsorption into sediments. Practical implications In the studied case, reservoir sedimentation has led to better water quality downstream. Originality/value It is shown in this study that reservoir sedimentation may have positive effects on river water quality.

À Minha Lindinha que esteve ao meu lado nesta longa e conturbada jornada do Doutorado! Amo você! Agradecimentos A Deus, por toda força nos momentos difíceis, dons concedidos e por sempre colocar pessoas boas em meu caminho. Ao Prof. Assoc. Frederico F. Mauad, não somente pela orientação deste trabalho, mas pela grande amizade e companheirismo ao longo desses 10 anos de convivência. Obrigado pelos ensinamentos técnicos e da vida... pelos puxões de orelha, longas conversas, boas risadas, e acima de tudo pelas oportunidades e pela grande confiança depositada. À minha esposa Yukari pelo amor, carinho, cuidado, apoio e compreensão, em especial nos momentos finais da conclusão deste trabalho. Aos meus pais por todo amor incondicional, e apoio irrestrito. Ao Paulo e Dália Higashi por todo o carinho e ajuda. A Hatian pelo acolhimento, conversas, comidas, toda a ajuda, e etc.... é sério... muito obrigado!! A equipe na Northwest Hydraulic Consultants que me recebeu calorosamente no frio inverno canadense durante o período de intercâmbio, em especial ao Mr. Mike Okun, José "Pepe" Vasquez pela co-orientação desta pesquisa, Amber e o pessoal da "beer Friday" pelos ótimos momentos. A equipe brasileira da empresa, Guilherme de Lima e Silvana pelos ensinamentos e apoio nas minhas atividades profissionais e de pesquisa. Aos membros da minha "família" da República FURA ZOiO, pela amizade, apoio, boas risadas e momentos de diversão. Em especial, ao Julio "Pankada" Kuwajima, companheiro de moradia e de pesquisa, pelos mais de 10 peculiares anos de convivência. Aos companheiros de pesquisa do Núcleo de Hidrometria, especialmente ao Renato Billia de Miranda pela ajuda na execução deste trabalho e amizade desde o mestrado, Norvin pelas infinitas risadas. Ao técnico hidrometrista Waldomiro Antônio Filho não só pelo auxílio, mas também pela boa companhia durante os trabalhos em campo. Aos amigos e Funcionários do CRHEA. À FIPAI pelo apoio à apresentação de trabalhos e suporte das atividades de coleta de dados. A empresa AES Tietê S.A., em especial ao Odemberg Veronez, e ao Programa de P&D da ANEEL os quais financiaram esta pesquisa. À empresa BMT WBM Pty. pela parceria no projeto de P&D e em especial ao Daniel Botelho. Ao CNPq, à CAPES e ao programa PDSE, pelas bolsas concedidas, e pela oportunidade da realização de parte da pesquisa no exterior. "A bove majore discit arare minor" "O boi mais velho ensina o mais novo a arar"

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The debris flood created by the 5 November 2015 failure of the Fundão dam in Brazil injected a large amount of fine sediment in the Gualaxo do Norte River system. Although coarse and sand‐sized sediment injections in rivers have been studied in relative detail, little is known about river response to overloading of mud‐sized sediments (consisting of clay and silt). This paper presents an assessment of suspended sediment transport occurring in and along the Gualaxo do Norte River after the Fundão dam failure to contribute to the general understanding of how rivers recover following large inputs of mud‐sized sediments (consisting of clay and silt). The average total sediment removal estimated based on the last 2 rainy periods is 54 466 tonnes, ranging from 37 385 to 71 546 tonnes according to the uncertainty analysis. The sediment transport analysis suggests that the Gualaxo do Norte River is returning to its pre‐event morphological character in terms of sediment transport. However, the morphologic recovery of the system has been constrained in recent years by decreased stream power, the result of moderate wet seasons and limited large flood events. We anticipate that future larger flood events will transport most of the remaining available in‐channel tailings, speeding up the physical morphologic recovery of the Gualaxo do Norte River, which is a key component of improving water quality and eventually the river ecology. Although the proposed approach for the sediment budget is simplified and has limitations and uncertainties, it provides a scientific basis to explain the natural fluvial processes that have been occurring in the river system. The approach used for the sediment budget presented in this paper could be applied to similar cases with limited data. Integr Environ Assess Manag 2020;16:572–582. © 2020 SETAC