Existing knowledge of the flow in a river past a groyne is inadequate to explain fully the siltation and scour that take place around such a structure. A survey of published material reveals controversy over the choice of pertinent flow parameters affecting the maximum scour depth.

There is a need to predict the river flow conditions necessary to support instream (and river corridor) biota. Many rivers have their flow regulated in some way and the field of 'habitat hydraulics' (or 'ecohydraulics') has grown up to encourage classification and characterisation of lotic physical environments. This thesis, based on field measurements at eleven sites in Northeast England (which are nationally representative), presents the data nonnally collected for the calibration of the PHABSIM model in alternative ways, to identify and characterise 'physical biotopcs'. These are segregated on the basis of subjectively (visually)-defined flow types. Statistical validation of biotopes as hydraulically discrete units shows them to be defined by a characteristic range of hydraulic variables, especially the Froude number. An investigation of the spatial and temporal variability of biotopes in different channel types and at different flows was carried out (1993-1995), which included the most extreme floods and droughts on record at some sites. The 'biotope approach' is shown to have potential as a reconnaissance approach to the assessment of habitat quality. Despite the success of the biotope approach e.g. in River Habitat Surveys, methodological improvement is still required, notably in the area of hydraulic characterisation by velocity measurements. Hydraulically rough channels and those with substantial macrophyte growth present problems; a logarithmic velocity profile cannot be assumed. A relationship between biotope diversity and stream ecosystem health is suggested; biological surveys are required to determine the direct relationship. This thesis represents a shift from the geomorphological riffle-pool theory to a broader classification of instream hydraulic units. It provides a framework for testing the debate in ecological theory regarding the role of patch dynamics within the continuum of the river environment. The study indicates that an 'environmentally acceptable flow regime' is one which creates a range of biotopes and maintains 'critical biotopes' at periods coinciding with key lifestage events. Flood events are beneficial for their role in 'resetting' the system.

No description available.

A program of <u>in situ</u> and laboratory studies was conducted to elucidate the role of the deposited sediments of the Niagara Reservoir in affecting the quality of the flow of the Roanoke River above the headwaters of Smith Mountain Lake. Agronomic analysis techniques were adapted and applied to provide quantitative analysis capability for the sediments. The superficial sediments were observed to constitute a considerable reservoir of nitrogen and phosphorus, which, during the anoxic bottom conditions occurring during the summer months, caused an enhancement of concentrations in the water column. Conversely, during the winter months, the superficial sediments acted as a phosphorus and nitrogen sink, removing both materials from the water column. Laboratory batch and microcosm studies made it possible to quantify the release and removal of nitrogen and phosphorus under aerobic and anaerobic conditions, and to elucidate the factors upon which the exchanges depended. The phosphorus interactions were found to be governed principally by sediment iron and organic matter content. Under aerobic conditions, phosphorus adsorption could be described by the Langmuir Isotherm. The most important nitrogen release mechanism was found to be a cation exchange phenomenon under reducing conditions. Aithough the effective zone of exchange was found to extend only about 2 mm into the sediment surface, the analysis of cores showed the existing profile to be rich in both phosphorus and nitrogen forms, which could be exposed to the water column with sufficient mixing. The deposited sediments of Niagara Impoundment showed a capacity to redistribute the impoundment influent nutrient load, causing an enhance~ ment of the quantities released during the summer months, thus magnifying the impact on the waters of Smith Mountain Lake. The maintenance of aerobic benthic conditions could, at a tremendous energy cost, prevent the sediment releases from occurring. In the long term, sediment nutrients deposited in the past, without proper control, could provide a continuing source of N and P to the waters of Smith Mountain Lake, thereby reducing the effectiveness of upstream control of point and diffuse sources. / Ph. D.

River flow regime is fundamental in determining lotic fish communities and populations, and especially of salmonid fishes. Quantifying the effects of human induced flow alteration on salmonids is a key question for conservation and water resources management. While qualitative responses to flow alteration are well characterised, a more intractable problem is quantifying responses in a way that is practical for environmental management. Using data drawn from the Environment Agency national database, I fitted generalised linear mixed models (GLMMs) using Bayesian inference to quantify the response of salmonid populations to the effects of impounding rivers, flow loss from rivers due to water abstraction, and the mitigating effects of flow restoration. I showed that in upland rivers downstream of impounded lakes, the magnitude of antecedent summer low flows had an important effect on the late summer abundance of 0+ salmonids Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). In contrast, the abundance of 1+ salmon and brown trout appeared to be largely unresponsive to the same flows. I demonstrated that short-term flow cessation had a negative impact on the abundance of 1+ brown trout in the following spring, but that recovery was rapid with negligible longer-term consequences. I further established that flow restoration in upland streams impacted by water abstraction provided limited short-term benefits to salmonid abundance when compared with changes at control locations. However, while benefits to salmonid abundance were limited, I detected important benefits to the mean growth rates of 0+ and 1+ brown trout from flow restoration. I discuss the implications of my findings for salmonid management and conservation and propose a more evidence-based approach to fishery management based on robust quantitative evidence derived using appropriate statistical models. The current approach to flow management for salmonids requires revision and I recommend an alternative approach based on quantitative evidence.

Without improved water management the global population could be facing serious water shortages. River flow discharge rates are one factor that could contribute to improving water management, being able to predict a forecasted river flow value would provide support in the management of water resources. This research investigates the use of an artificial neural network (ANN) to create a model that predicts river flow gauge values. The Driel Barrage monitoring station on the Thukela river in South Africa was used as a case study. The research makes use of data from the Department of Water and Sanitation (DWS) and weather forecast data from the European Center For Medium- Range Forecasts (ECMWF) to train the predictive model. An evaluation of the ANN model identified that the model is highly sensitive to selected weather parameters and is sensitive to the initial weights used in the ANN. These were overcome using an ANN ensemble and selective scenarios to identify the best weather parameters to use as input into the ANN model. Five weather parameters and a correlation coefficient cut-off value produced the most accurate prediction by the ANN. The research found that ANNs can be used for predicting river flow gauge values but to improve the results a greater ensemble, additional data and different ANN structures may create a better performing model. For the ANN model to be used in practice the research needs to be extended to evaluate the whole catchment area and a range of rivers in South Africa. / Dissertation (MSc)--University of Pretoria, 2017. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

Os processos de arenização no sudoeste do Rio Grande do Sul têm sua explicação na relação entre a fragilidade do meio e a dinâmica hídrica, esta sustentada por eventos torrenciais de chuva. A presença de processos erosivos sob a forma de ravinamentos e de voçorocamentos e a exposição das formações superficiais nos areais atestam, nessa área, elevada mobilidade de sedimentos. Além disso, atividades agropecuárias sem o manejo adequado têm intensificado esses processos naturais, ampliando a interação hidrossedimentar entre as vertentes e os fundos de vale. Embora haja inúmeros trabalhos que abordam o processo de arenização e as dinâmicas do espaço geográfico no sudoeste do Rio Grande do Sul, há ainda uma lacuna em pesquisas que visam compreender suas inter-relações com a morfodinâmica fluvial. Tendo como recorte espacial a Bacia Hidrográfica do Arroio Miracatu (BHAM), esta pesquisa visa analisar, justamente, a importância de eventos hidrológicos extremos na morfodinâmica fluvial e a sua interação com os processos de arenização. Dados de chuva e vazão da BHAM foram analisados com vistas a identificar o regime pluvio-fluviométrico. Para tanto foram empregados parâmetros estatísticos com a finalidade de discriminar os eventos mais comuns daqueles mais raros. Como a ênfase do trabalho são os eventos hidrológicos extremos, estes foram observados a partir de diferentes escalas temporais (anual, mensal, pentadal e diário) e relacionados tanto ao excesso, como à escassez hídrica. Os resultados apontam para uma elevada variabilidade nas chuvas, que tendem a se concentrar em um número reduzido de dias, tanto anualmente, como mensalmente. Uma relação muito próxima entre a chuva e a vazão foi observada, de tal modo que os anos-padrão de chuva apresentaram correspondência com aqueles classificados pela Condição Hídrica da Bacia Hidrográfica (CHid). Isso decorre do fato de que tanto o El Niño Oscilação Sul (ENOS) como a Oscilação Decadal do Pacífico (ODP) modulam as chuvas e, consequentemente, as vazões na BHAM. Adicionalmente, foram identificados períodos ora mais secos (ODP-), ora mais chuvosos (ODP+). Esses períodos foram fundamentais para a compreensão da morfodinâmica fluvial, que é moldada por uma sucessão de regimes dominados por estiagem ou por inundação. Com a finalidade de avaliar esses processos de ajustamento foi selecionado um segmento localizado no médio curso da sanga da Areia. Nesse local a rede de drenagem é influenciada pelos processos de arenização, havendo conexão entre as vertentes e o fundo de vale, com intenso aporte de sedimentos. Com base em imagens de sensoriamento remoto (fotos aéreas e satélite) foi possível identificar a posição do canal em dez ocasiões diferentes, no período que se insere entre 1948-2013. Os ajustamentos que se processaram nesse segmento permitiram dividi-lo em dois trechos distintos (a montante e a jusante), com evolução diferenciada. Além dos ajustamentos na morfologia de canal, foram observados ainda variações na largura do canal, demonstrando ora um padrão entrelaçado (mais largo), ora meandrante (mais estreito). Concomitantemente a esses ajustamentos, a incisão fluvial promoveu a esculturação de diferentes feições, sendo possível delimitar dois níveis de terraços e um nível de planície de inundação. Na intenção de compreender os processos erosivo-deposicionais, procedeu-se ao monitoramento de nove seções transversais no trecho a montante do segmento estudado na sanga da Areia. O canal fluvial, inicialmente meandrante com calha estreita e profunda, passou para um padrão entrelaçado, com leito muito mais largo e raso ao fim do levantamento. Esses ajustamentos não se processaram de modo contínuo, mas bruscamente, em decorrência de pulso excepcional de cheia por ocasião de chuva pentadal extrema. Esse pulso promoveu um aumento brusco da carga sedimentar esculturando um canal entrelaçado (raso e largo) pela estocagem intracanal do material. Ajustamentos dessa natureza moldam a morfologia do canal e sugerem ocorrer de modo periódico na sanga da Areia. / The sandization processes in the southwestern of Rio Grande do Sul State have their explanation on the relationship between environment fragility and water dynamics, and this, supported by torrential rain event. The presence of erosive processes in the form of ravines and gullies and the exposure of soil surface in the sand deposits attest, in this area, high sediment mobility. In addition, agricultural activities without appropriate management have intensified these natural processes, expanding water-sediment interaction between the slopes and valley bottoms. Although there are numerous studies that discuss the sandization process and the dynamics of the geographic space in the southwestern of Rio Grande do Sul, there is still, a gap in research aimed at understanding their interrelations with the fluvial morphodynamics. The Miracatu arroyo watershed was defined as the study area of this research, which aims to analyze the importance of extreme hydrological events in the river morphodynamics and their interaction with sandization processes. Rainfall and river-flow were analyzed in order to identify the rain-flow regime. For this purpose, statistical parameters were used in order to discriminate the most common of those rare events. The extreme hydrological events were observed from different time scales (annual, monthly, daily and pentad) and related either to excess, as the water scarcity. The results indicate a high variability in rainfall that tend to occur in a few days both annual as monthly. Was observed a relationship between rainfall and river-flow and it happens due the influence of El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) that modulate the rains and therefore the flow in Miracatu Arroyo. Furthermore, was identified a succession of drier (PDO-) and rainiest periods (PDO+). These periods were fundamental to the understanding of fluvial morphodynamics, once it allow characterize alternating drought- and flood dominated regimes. In order, to evaluate the fluvial adjustment processes were selected a segment-river located in the Areia Creek. In this place, the drainage network is influenced by sandization processes, with connection between the slopes and the valley bottom, with strong input of sediments. Based on remote sensing images (air photo and satellite) was identified the channel position in ten occasions in the period of 1948-2013. The fluvial adjustments that were processed in this segment allowed to divide it into two distinct reaches (upstream and downstream reaches), with different evolution. It was also observed variations in the width and channel pattern, sometimes showing a braided channel (wider) while in others a meandering course (narrower). Concurrently with these adjustments, the fluvial incision promoted the sculpturing of different features and it is possible define two levels of terraces and a flood plain level. The intention to understand the erosive-depositional processes proceeded to monitoring nine cross sections in the upstream reach of the segment-river studied in Areia Creek. The river channel, initially meandering with narrow and deep channel, passed for a braided pattern with bed wider and shallower at the end of the survey. These fluvial adjustments are not processed in a continuous manner, but abruptly, due to exceptional flood-pulse during extreme pentadal rain. This event promoted an abrupt increase in load-bed forming a braided channel (shallow and wide) by in-channel sediment storage. Adjustments of this nature shape the channel morphology and occur periodically in Areia Creek.

The increasing global air temperature will trigger changes in the global mean water vapor, precipitation patterns and evapotranspiration, which further leads to changes, for instance, instream flow, groundwater flow and soil moisture. Projections of future changes in thehydrological regime of the Aral Sea Drainage Basin (ASDB) in Central Asia are however highlyuncertain, due to complexities of natural and engineered water systems of the basin. The AmuDarya River Delta (ADRD) is vital to the water budget of the Large Aral Sea, the livelihood inUzbekistan and Turkmenistan, as well as the surrounding riparian ecosystem. This study attemptsto investigate responses of river flow in the Aral Sea Drainage Basin and key riparian vegetationspecies (of the so-called Tugai community) in the Amu Darya River Delta to projected futureclimate change. Results from hydrological model and outputs from multi-GCM predictions providea basis for conducting more robust quantitative analysis of possible future hydro-climatic changesin the Amu Darya River Basin. A qualitative synthesis of the suitability of Tugai is furthermoreperformed in order to increase the knowledge of the riparian vegetation status under thechanging hydro-climatic conditions. The results show that the averaged temperature in the ASDBis likely to continuously increase and yield a total increase of about 2 °C ~ 5°C by 2100. Thechange trend of the annual regional precipitation of 2100 is relatively unclear, with estimatesranging from 50 mm lower than today to 75 mm higher than today. Modeled ensemble means (EM)river flow, obtained from hydrological modeling of climate output from multi-GCM projections,converge on showing future decreases in river runoff (R). Projected absolute R may decrease tozero around 2100, implying no surface flow and a dry out near the river outlet. The relationship ofwater flux between upstream and downstream will be changed dramatically due to climatechange. More specifically, R of the upstream region will decrease, and it is likely to becomeinsufficient for feeding downstream river reaches as it used to. The decreased river flow in thedelta may accelerate the desertification and salinization processes. Consequently, speciestransitions may occur, along with degradations of the existing Tugai communities. Theuncertainties of hydro-climatic change projections to some extent hinder the understanding of thedynamic hydrological-climatic-ecological system. However, the detailed responses of the delta toclimate change based on multiple qualitative and quantitative analyses provide an important basisfor the formulation of more robust forecasts on the future ecological development in the ADRD, and further for recommendations of measures to mitigate the ecosystem’s deterioration under achanging climate.

Os processos de arenização no sudoeste do Rio Grande do Sul têm sua explicação na relação entre a fragilidade do meio e a dinâmica hídrica, esta sustentada por eventos torrenciais de chuva. A presença de processos erosivos sob a forma de ravinamentos e de voçorocamentos e a exposição das formações superficiais nos areais atestam, nessa área, elevada mobilidade de sedimentos. Além disso, atividades agropecuárias sem o manejo adequado têm intensificado esses processos naturais, ampliando a interação hidrossedimentar entre as vertentes e os fundos de vale. Embora haja inúmeros trabalhos que abordam o processo de arenização e as dinâmicas do espaço geográfico no sudoeste do Rio Grande do Sul, há ainda uma lacuna em pesquisas que visam compreender suas inter-relações com a morfodinâmica fluvial. Tendo como recorte espacial a Bacia Hidrográfica do Arroio Miracatu (BHAM), esta pesquisa visa analisar, justamente, a importância de eventos hidrológicos extremos na morfodinâmica fluvial e a sua interação com os processos de arenização. Dados de chuva e vazão da BHAM foram analisados com vistas a identificar o regime pluvio-fluviométrico. Para tanto foram empregados parâmetros estatísticos com a finalidade de discriminar os eventos mais comuns daqueles mais raros. Como a ênfase do trabalho são os eventos hidrológicos extremos, estes foram observados a partir de diferentes escalas temporais (anual, mensal, pentadal e diário) e relacionados tanto ao excesso, como à escassez hídrica. Os resultados apontam para uma elevada variabilidade nas chuvas, que tendem a se concentrar em um número reduzido de dias, tanto anualmente, como mensalmente. Uma relação muito próxima entre a chuva e a vazão foi observada, de tal modo que os anos-padrão de chuva apresentaram correspondência com aqueles classificados pela Condição Hídrica da Bacia Hidrográfica (CHid). Isso decorre do fato de que tanto o El Niño Oscilação Sul (ENOS) como a Oscilação Decadal do Pacífico (ODP) modulam as chuvas e, consequentemente, as vazões na BHAM. Adicionalmente, foram identificados períodos ora mais secos (ODP-), ora mais chuvosos (ODP+). Esses períodos foram fundamentais para a compreensão da morfodinâmica fluvial, que é moldada por uma sucessão de regimes dominados por estiagem ou por inundação. Com a finalidade de avaliar esses processos de ajustamento foi selecionado um segmento localizado no médio curso da sanga da Areia. Nesse local a rede de drenagem é influenciada pelos processos de arenização, havendo conexão entre as vertentes e o fundo de vale, com intenso aporte de sedimentos. Com base em imagens de sensoriamento remoto (fotos aéreas e satélite) foi possível identificar a posição do canal em dez ocasiões diferentes, no período que se insere entre 1948-2013. Os ajustamentos que se processaram nesse segmento permitiram dividi-lo em dois trechos distintos (a montante e a jusante), com evolução diferenciada. Além dos ajustamentos na morfologia de canal, foram observados ainda variações na largura do canal, demonstrando ora um padrão entrelaçado (mais largo), ora meandrante (mais estreito). Concomitantemente a esses ajustamentos, a incisão fluvial promoveu a esculturação de diferentes feições, sendo possível delimitar dois níveis de terraços e um nível de planície de inundação. Na intenção de compreender os processos erosivo-deposicionais, procedeu-se ao monitoramento de nove seções transversais no trecho a montante do segmento estudado na sanga da Areia. O canal fluvial, inicialmente meandrante com calha estreita e profunda, passou para um padrão entrelaçado, com leito muito mais largo e raso ao fim do levantamento. Esses ajustamentos não se processaram de modo contínuo, mas bruscamente, em decorrência de pulso excepcional de cheia por ocasião de chuva pentadal extrema. Esse pulso promoveu um aumento brusco da carga sedimentar esculturando um canal entrelaçado (raso e largo) pela estocagem intracanal do material. Ajustamentos dessa natureza moldam a morfologia do canal e sugerem ocorrer de modo periódico na sanga da Areia. / The sandization processes in the southwestern of Rio Grande do Sul State have their explanation on the relationship between environment fragility and water dynamics, and this, supported by torrential rain event. The presence of erosive processes in the form of ravines and gullies and the exposure of soil surface in the sand deposits attest, in this area, high sediment mobility. In addition, agricultural activities without appropriate management have intensified these natural processes, expanding water-sediment interaction between the slopes and valley bottoms. Although there are numerous studies that discuss the sandization process and the dynamics of the geographic space in the southwestern of Rio Grande do Sul, there is still, a gap in research aimed at understanding their interrelations with the fluvial morphodynamics. The Miracatu arroyo watershed was defined as the study area of this research, which aims to analyze the importance of extreme hydrological events in the river morphodynamics and their interaction with sandization processes. Rainfall and river-flow were analyzed in order to identify the rain-flow regime. For this purpose, statistical parameters were used in order to discriminate the most common of those rare events. The extreme hydrological events were observed from different time scales (annual, monthly, daily and pentad) and related either to excess, as the water scarcity. The results indicate a high variability in rainfall that tend to occur in a few days both annual as monthly. Was observed a relationship between rainfall and river-flow and it happens due the influence of El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) that modulate the rains and therefore the flow in Miracatu Arroyo. Furthermore, was identified a succession of drier (PDO-) and rainiest periods (PDO+). These periods were fundamental to the understanding of fluvial morphodynamics, once it allow characterize alternating drought- and flood dominated regimes. In order, to evaluate the fluvial adjustment processes were selected a segment-river located in the Areia Creek. In this place, the drainage network is influenced by sandization processes, with connection between the slopes and the valley bottom, with strong input of sediments. Based on remote sensing images (air photo and satellite) was identified the channel position in ten occasions in the period of 1948-2013. The fluvial adjustments that were processed in this segment allowed to divide it into two distinct reaches (upstream and downstream reaches), with different evolution. It was also observed variations in the width and channel pattern, sometimes showing a braided channel (wider) while in others a meandering course (narrower). Concurrently with these adjustments, the fluvial incision promoted the sculpturing of different features and it is possible define two levels of terraces and a flood plain level. The intention to understand the erosive-depositional processes proceeded to monitoring nine cross sections in the upstream reach of the segment-river studied in Areia Creek. The river channel, initially meandering with narrow and deep channel, passed for a braided pattern with bed wider and shallower at the end of the survey. These fluvial adjustments are not processed in a continuous manner, but abruptly, due to exceptional flood-pulse during extreme pentadal rain. This event promoted an abrupt increase in load-bed forming a braided channel (shallow and wide) by in-channel sediment storage. Adjustments of this nature shape the channel morphology and occur periodically in Areia Creek.

Os processos de arenização no sudoeste do Rio Grande do Sul têm sua explicação na relação entre a fragilidade do meio e a dinâmica hídrica, esta sustentada por eventos torrenciais de chuva. A presença de processos erosivos sob a forma de ravinamentos e de voçorocamentos e a exposição das formações superficiais nos areais atestam, nessa área, elevada mobilidade de sedimentos. Além disso, atividades agropecuárias sem o manejo adequado têm intensificado esses processos naturais, ampliando a interação hidrossedimentar entre as vertentes e os fundos de vale. Embora haja inúmeros trabalhos que abordam o processo de arenização e as dinâmicas do espaço geográfico no sudoeste do Rio Grande do Sul, há ainda uma lacuna em pesquisas que visam compreender suas inter-relações com a morfodinâmica fluvial. Tendo como recorte espacial a Bacia Hidrográfica do Arroio Miracatu (BHAM), esta pesquisa visa analisar, justamente, a importância de eventos hidrológicos extremos na morfodinâmica fluvial e a sua interação com os processos de arenização. Dados de chuva e vazão da BHAM foram analisados com vistas a identificar o regime pluvio-fluviométrico. Para tanto foram empregados parâmetros estatísticos com a finalidade de discriminar os eventos mais comuns daqueles mais raros. Como a ênfase do trabalho são os eventos hidrológicos extremos, estes foram observados a partir de diferentes escalas temporais (anual, mensal, pentadal e diário) e relacionados tanto ao excesso, como à escassez hídrica. Os resultados apontam para uma elevada variabilidade nas chuvas, que tendem a se concentrar em um número reduzido de dias, tanto anualmente, como mensalmente. Uma relação muito próxima entre a chuva e a vazão foi observada, de tal modo que os anos-padrão de chuva apresentaram correspondência com aqueles classificados pela Condição Hídrica da Bacia Hidrográfica (CHid). Isso decorre do fato de que tanto o El Niño Oscilação Sul (ENOS) como a Oscilação Decadal do Pacífico (ODP) modulam as chuvas e, consequentemente, as vazões na BHAM. Adicionalmente, foram identificados períodos ora mais secos (ODP-), ora mais chuvosos (ODP+). Esses períodos foram fundamentais para a compreensão da morfodinâmica fluvial, que é moldada por uma sucessão de regimes dominados por estiagem ou por inundação. Com a finalidade de avaliar esses processos de ajustamento foi selecionado um segmento localizado no médio curso da sanga da Areia. Nesse local a rede de drenagem é influenciada pelos processos de arenização, havendo conexão entre as vertentes e o fundo de vale, com intenso aporte de sedimentos. Com base em imagens de sensoriamento remoto (fotos aéreas e satélite) foi possível identificar a posição do canal em dez ocasiões diferentes, no período que se insere entre 1948-2013. Os ajustamentos que se processaram nesse segmento permitiram dividi-lo em dois trechos distintos (a montante e a jusante), com evolução diferenciada. Além dos ajustamentos na morfologia de canal, foram observados ainda variações na largura do canal, demonstrando ora um padrão entrelaçado (mais largo), ora meandrante (mais estreito). Concomitantemente a esses ajustamentos, a incisão fluvial promoveu a esculturação de diferentes feições, sendo possível delimitar dois níveis de terraços e um nível de planície de inundação. Na intenção de compreender os processos erosivo-deposicionais, procedeu-se ao monitoramento de nove seções transversais no trecho a montante do segmento estudado na sanga da Areia. O canal fluvial, inicialmente meandrante com calha estreita e profunda, passou para um padrão entrelaçado, com leito muito mais largo e raso ao fim do levantamento. Esses ajustamentos não se processaram de modo contínuo, mas bruscamente, em decorrência de pulso excepcional de cheia por ocasião de chuva pentadal extrema. Esse pulso promoveu um aumento brusco da carga sedimentar esculturando um canal entrelaçado (raso e largo) pela estocagem intracanal do material. Ajustamentos dessa natureza moldam a morfologia do canal e sugerem ocorrer de modo periódico na sanga da Areia. / The sandization processes in the southwestern of Rio Grande do Sul State have their explanation on the relationship between environment fragility and water dynamics, and this, supported by torrential rain event. The presence of erosive processes in the form of ravines and gullies and the exposure of soil surface in the sand deposits attest, in this area, high sediment mobility. In addition, agricultural activities without appropriate management have intensified these natural processes, expanding water-sediment interaction between the slopes and valley bottoms. Although there are numerous studies that discuss the sandization process and the dynamics of the geographic space in the southwestern of Rio Grande do Sul, there is still, a gap in research aimed at understanding their interrelations with the fluvial morphodynamics. The Miracatu arroyo watershed was defined as the study area of this research, which aims to analyze the importance of extreme hydrological events in the river morphodynamics and their interaction with sandization processes. Rainfall and river-flow were analyzed in order to identify the rain-flow regime. For this purpose, statistical parameters were used in order to discriminate the most common of those rare events. The extreme hydrological events were observed from different time scales (annual, monthly, daily and pentad) and related either to excess, as the water scarcity. The results indicate a high variability in rainfall that tend to occur in a few days both annual as monthly. Was observed a relationship between rainfall and river-flow and it happens due the influence of El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) that modulate the rains and therefore the flow in Miracatu Arroyo. Furthermore, was identified a succession of drier (PDO-) and rainiest periods (PDO+). These periods were fundamental to the understanding of fluvial morphodynamics, once it allow characterize alternating drought- and flood dominated regimes. In order, to evaluate the fluvial adjustment processes were selected a segment-river located in the Areia Creek. In this place, the drainage network is influenced by sandization processes, with connection between the slopes and the valley bottom, with strong input of sediments. Based on remote sensing images (air photo and satellite) was identified the channel position in ten occasions in the period of 1948-2013. The fluvial adjustments that were processed in this segment allowed to divide it into two distinct reaches (upstream and downstream reaches), with different evolution. It was also observed variations in the width and channel pattern, sometimes showing a braided channel (wider) while in others a meandering course (narrower). Concurrently with these adjustments, the fluvial incision promoted the sculpturing of different features and it is possible define two levels of terraces and a flood plain level. The intention to understand the erosive-depositional processes proceeded to monitoring nine cross sections in the upstream reach of the segment-river studied in Areia Creek. The river channel, initially meandering with narrow and deep channel, passed for a braided pattern with bed wider and shallower at the end of the survey. These fluvial adjustments are not processed in a continuous manner, but abruptly, due to exceptional flood-pulse during extreme pentadal rain. This event promoted an abrupt increase in load-bed forming a braided channel (shallow and wide) by in-channel sediment storage. Adjustments of this nature shape the channel morphology and occur periodically in Areia Creek.