Thesis advisor: Noah Snyder / Increasing attention has been drawn to the need for reliable streamflow estimates at ungaged locations under a range of climatic and hydrologic conditions. Climate projections for the northeastern United States over the 21st century--which include significant increases in temperature and precipitation--could have broad impacts on streamflows, potentially reducing the accuracies of existing streamflow models for the region. This thesis investigates recent changes in daily flow-durations in southern New England, and examines their influence on the reliability of the low-flow models for Massachusetts presented by Ries and Friesz (2000). An analysis of discharge data collected at gaging sites through water year 2012 revealed increases in nearly all flow durations at sites across southern New England since the mid-20th century, whereas very low flows (quantiles at or above the 95-percent exceedance probability) generally showed decreases, especially since the 1990s. Twenty-year moving streamflow quantiles at each of ten selected exceedance probabilities were examined for the periods of record of 16 streamflow-gaging stations in southern New England. The beginning of water year 1992 appeared to mark an inflection point in low-flow quantiles, before which very low flows were steady or increasing, and after which these flows showed near-universal decreases. While the observed peak in 20-year low-flow quantiles around 1992 may be due to the statistical method used to calculate the quantile trends, the inflection point could also be an indicator of when increasing evapotranspiration surpassed increasing precipitation as the principal climatic driver of changes in low flows in southern New England. The general upward translation of the flow-duration curve observed over the last 60 years is very likely linked to increases in annual precipitation during this period, while the decreases in very low flows are likely due to changes in climatic variables (increasing summer temperatures and evapotranspiration rates), and amplified by anthropogenic factors (greater areas of impervious surfaces and increasing rates of surface- and ground-water withdrawal). The data suggest that increasing precipitation rates have already caused the Ries and Friesz (2000) equations for the median low flows (Q50 to Q75) to become biased towards underestimation, and decreases in very low flows threaten to render the models for these flows biased towards overestimation in the coming decades. The streamflow quantile trends (for both the entire period of record of the gaging stations and just the post-1992 period) for each of the ten flow-durations of interest were extended into the future to the point where the corresponding Ries and Friesz (2000) model would fail (when actual flow durations would be outside the 90-percent prediction intervals for the estimated flows for greater than 10% of sites). The models for the lowest streamflows are estimated to lose validity by as early as 2018. Climate change is predicted to have significant effects on streamflow characteristics in southern New England over the 21st century, and the results of this study indicate that the Ries and Freisz (2000) low-flow models should be reformulated using more recent streamflow data within the next decade, and validated every 20 years thereafter to ensure their accuracies are maintained despite the effects of regional nonstationarity. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

The purpose of this study is to analyze how estimates of an important geomorphic parameter, effective discharge, are impacted by the choice of bed material load equations and flow duration curves (FDCs). The Yang (1979), Brownlie (1981), and Pagosa equations developed by Rosgen (2006) were compared for predicting bed material load. To calculate the bed material load using the Pagosa equations, the bedload and suspended load are calculated separately and the results are added together. To compare the effectiveness of the equations, measured bed material load data from the USGS Open-File Report 89-67 were used. Following the calculations, the equation results were compared to the measured data. It was determined that the Pagosa equations performed the best overall, followed by Brownlie and then Yang. The superior performance of the Pagosa equations is likely due to the equations being calibrated. USGS regression equations for FDCs were compared to a method developed by Dr. David Rosgen in which a dimensionless FDC (DFDC) is developed. Weminuche Creek in southwestern Colorado was used as the study site. Rosgen's DFDC method requires the selection of a streamgage for a stream that exhibits the same hydro-physiographic characteristics as the site of interest. An FDC is developed for the gaged site and made dimensionless by dividing the discharges by the bankfull discharge of the gaged site. The DFDC is then made dimensional by multiplying by the bankfull discharge of the site of interest and the resulting dimensional FDC is taken as the FDC of the ungaged site. The USGS regression equations underpredicted the discharges while Rosgen's DFDC method overpredicted them. Rosgen's DFDC method produced more accurate results than the USGS regression equations for Weminuche Creek. To calculate the effective discharge, the FDC was used to develop a flow frequency curve which was then multiplied by the sediment rating curve. Effective discharge calculations were performed for Weminuche Creek using several combinations of bed material load prediction equations and FDCs. The USGS regression equations, Rosgen's DFDC method, and streamgage data were all used in conjunction with the Yang and Pagosa equations. The Brownlie equation predicted zero bed material load for Weminuche Creek, and was thus not used to calculate the effective discharge. When the USGS regression equations were used with the Yang and Pagosa equations, the calculated effective discharge was approximately 4.5 cms for both bed material load prediction equations. When Rosgen's DFDC method and streamgage data were used with the Yang and Pagosa equations, the effective discharge was approximately 13.5 cms. From these results, it was determined that the bed material load prediction equations had little impact on the effective discharge for Weminuche Creek while the FDCs did influence the results.

The major benefit of geo-referenced exposure modelling tools is the provision of spatially distributed information on expected environmental concentrations. This allows for identifying local and regional concentration differences in the environment which facilitates the development of efficient mitigation strategies. Predicted substance concentrations in the environment are governed by emission rates and representation of the substances' transport and transformation processes on the one hand and by the description of the spatial environmental heterogeneity and temporal variability on the other hand. The shape of river basins and streamflow variability within them is a product of physiographic and climatic factors like e. g. topography, land use, precipitation, or evapotranspiration. These factors are very variable in space and time. This heterogeneity in river basins may have an impact on surface water concentrations of various substances. In this work a hydrological framework for geo-referenced exposure assessment in river networks has been developed which predominantly addresses spatial heterogeneity of river basins. The theoretical background for parameterising a river network for the application of GREAT-ER (Geo-referenced Regional Exposure Assessment Tool for European Rivers) is elaborated and implemented. Quantity of discharge, flow velocity of river water and depth of river bed have to be determined at any location in a river network for the representation of substance dilution, transport and degradation. Temporal variability is handled by a probabilistic approach which demands choice and parameterisation of probability distribution functions to describe the river network characteristics. It is substantiated that discharge and its variation can be described by a lognormal probability distribution. This distribution can be parameterised by spatially distributed information on effective precipitation and specific low flow discharge from the German Hydrological Atlas. Geoprocessing methods are applied to couple information from these maps and the river network. Evaluation of discharge probability distributions by means of gauging data demonstrates good agreement. River depth and flow velocity are estimated on the basis of spatially distributed river structure data and therefore account for actual river morphology more than former approaches do. A comparison with hitherto used flow velocity and depth estimation shows significant differences which trigger perceivable differences in surface water concentration estimates. Identification of the sensitivity of hydrological parameters in terms of chemical fate estimation attaches importance to spatial explicit consideration of river networks. The main benefit of the presented methods is comprehensive incorporation of geo-referenced river basin characteristics into the data basis for the GREAT-ER model because this provides the basis for successful prediction of surface water concentrations by GREAT-ER.

Vários trabalhos relacionados ao tema produção de água estão sendo realizados, tendo em comum a associação da cobertura florestal com o escoamento em bacias hidrográficas. Entretanto, não existem estudos onde foram verificados os locais onde esta cobertura tem efeito ótimo, pois, este é dependente das condições edafoclimáticas de cada bacia. O objetivo deste trabalho é avaliar as alterações na produção de água ocasionadas pela posição das áreas com cobertura florestal em relação às de solos rasos em uma bacia hidrográfica. Os estudos foram realizados na Bacia Hidrográfica do Ribeirão dos Marins em Piracicaba, SP, Brasil, por meio da modelagem hidrológica utilizando o modelo distribuído GSSHA. Para a calibração foram utilizados dados meteorológicos, fluviométricos e pluviométricos dos anos de 1999 e 2000, além da obtenção, em laboratório, da condutividade hidráulica e da curva de retenção dos solos da bacia. Foram realizadas sondagens SPT e testes de infiltração de água no solo para determinar a espessura dos solos na bacia e a condutividade hidráulica da zona saturada (lençol freático) desta. A espessura dos solos foi representada por um modelo numérico, elaborado a partir das espessuras medidas e da utilização do modelo HAND. A profundidade do lençol freático foi representada por outro modelo numérico, elaborado a partir da espessura do solo e da profundidade deste lençol medida em campo. Uma nova metodologia que, a partir do coeficiente CN, estima o coeficiente de rugosidade de Manning foi utilizada, apresentando resultados satisfatórios. Nos processos de calibração e validação o modelo apresentou coeficientes de índices de correlação adequados. Foram feitas simulações hidrológicas para 15 anos em três cenários de uso e ocupação do solo, que foram elaborados de modo a comparar uma mesma área de cobertura florestal em diferentes posições da bacia, em função da presença de solos rasos nas proximidades dos cursos d\'água. Foram analisados, entre os cenários para todo o período simulado: o escoamento total e o de base; parâmetros dos hidrogramas (em eventos selecionados da série histórica); posição do lençol freático; umidade do solo; e, curva de permanência. Os resultados permitiram concluir que na área de estudo não há influência da posição da cobertura florestal em relação aos solos rasos para a produção de água. Devido à existência de poucos trabalhos a campo e, também, de modelagem que abordem o efeito da localização da cobertura florestal na produção de água, incentiva-se a realização de novas pesquisas, necessárias, entre outras razões, para a determinação dos locais prioritários a reflorestar ou manter florestado em programas de conservação ambiental. / Several works related to the theme of water production are being made, having in common the association of forest cover with runoff in watersheds. However, no studies were found where the places where this land cover has optimum effect, because it is dependent on climatic and physiographic conditions of each watershed. The objective of this study is to evaluate changes in water yield caused by the spatial distribution of forest cover in relation to the shallow soils in a watershed. The studies were conducted in the watershed \"Ribeirão dos Marins\" in Piracicaba, SP, Brazil, through the hydrologic modeling using the distributed model GSSHA. For calibration were used data of meteorological, rainfall and stream flow to the years 1999 and 2000, in addition of the hydraulic conductivity and soil water retention curve obtained in laboratory. SPT tests and water infiltration tests were conducted to determine the thickness of the soils and hydraulic conductivity of the saturated zone (water table) in the watershed. The thickness of the soil was represented by a numerical model, based on those thicknesses measures and the model HAND. The depth of the water table was represented by another numerical model, drawn from the soil thickness and depth of field measured. A new methodology that estimates the Manning coefficient from the CN coefficient was used with satisfactory results. In the processes of calibration and validation of the model, the coefficients showed adequate correlation indexes. Hydrological simulations were made for 15 years in three land cover and land use scenarios, which have been prepared in order to compare the same area of forest cover in different positions of the basin, due to the presence of shallow soils near watercourses. Were analyzed, among the scenarios simulated for the entire period: total flow and baseflow; parameters of hydrographs (in selected events of the series); position of the water table, available water content; and flow duration curves. The results showed that in the study area there is no influence of the position of forest cover in relation to shallow soils to the water yield. Because there are few studies that address the effect of the location of forest cover in water yield is encouraged to conduct further research, among other reasons, for the determination of the priority sites to the reforestation in environmental conservation programs.

Vários trabalhos relacionados ao tema produção de água estão sendo realizados, tendo em comum a associação da cobertura florestal com o escoamento em bacias hidrográficas. Entretanto, não existem estudos onde foram verificados os locais onde esta cobertura tem efeito ótimo, pois, este é dependente das condições edafoclimáticas de cada bacia. O objetivo deste trabalho é avaliar as alterações na produção de água ocasionadas pela posição das áreas com cobertura florestal em relação às de solos rasos em uma bacia hidrográfica. Os estudos foram realizados na Bacia Hidrográfica do Ribeirão dos Marins em Piracicaba, SP, Brasil, por meio da modelagem hidrológica utilizando o modelo distribuído GSSHA. Para a calibração foram utilizados dados meteorológicos, fluviométricos e pluviométricos dos anos de 1999 e 2000, além da obtenção, em laboratório, da condutividade hidráulica e da curva de retenção dos solos da bacia. Foram realizadas sondagens SPT e testes de infiltração de água no solo para determinar a espessura dos solos na bacia e a condutividade hidráulica da zona saturada (lençol freático) desta. A espessura dos solos foi representada por um modelo numérico, elaborado a partir das espessuras medidas e da utilização do modelo HAND. A profundidade do lençol freático foi representada por outro modelo numérico, elaborado a partir da espessura do solo e da profundidade deste lençol medida em campo. Uma nova metodologia que, a partir do coeficiente CN, estima o coeficiente de rugosidade de Manning foi utilizada, apresentando resultados satisfatórios. Nos processos de calibração e validação o modelo apresentou coeficientes de índices de correlação adequados. Foram feitas simulações hidrológicas para 15 anos em três cenários de uso e ocupação do solo, que foram elaborados de modo a comparar uma mesma área de cobertura florestal em diferentes posições da bacia, em função da presença de solos rasos nas proximidades dos cursos d\'água. Foram analisados, entre os cenários para todo o período simulado: o escoamento total e o de base; parâmetros dos hidrogramas (em eventos selecionados da série histórica); posição do lençol freático; umidade do solo; e, curva de permanência. Os resultados permitiram concluir que na área de estudo não há influência da posição da cobertura florestal em relação aos solos rasos para a produção de água. Devido à existência de poucos trabalhos a campo e, também, de modelagem que abordem o efeito da localização da cobertura florestal na produção de água, incentiva-se a realização de novas pesquisas, necessárias, entre outras razões, para a determinação dos locais prioritários a reflorestar ou manter florestado em programas de conservação ambiental. / Several works related to the theme of water production are being made, having in common the association of forest cover with runoff in watersheds. However, no studies were found where the places where this land cover has optimum effect, because it is dependent on climatic and physiographic conditions of each watershed. The objective of this study is to evaluate changes in water yield caused by the spatial distribution of forest cover in relation to the shallow soils in a watershed. The studies were conducted in the watershed \"Ribeirão dos Marins\" in Piracicaba, SP, Brazil, through the hydrologic modeling using the distributed model GSSHA. For calibration were used data of meteorological, rainfall and stream flow to the years 1999 and 2000, in addition of the hydraulic conductivity and soil water retention curve obtained in laboratory. SPT tests and water infiltration tests were conducted to determine the thickness of the soils and hydraulic conductivity of the saturated zone (water table) in the watershed. The thickness of the soil was represented by a numerical model, based on those thicknesses measures and the model HAND. The depth of the water table was represented by another numerical model, drawn from the soil thickness and depth of field measured. A new methodology that estimates the Manning coefficient from the CN coefficient was used with satisfactory results. In the processes of calibration and validation of the model, the coefficients showed adequate correlation indexes. Hydrological simulations were made for 15 years in three land cover and land use scenarios, which have been prepared in order to compare the same area of forest cover in different positions of the basin, due to the presence of shallow soils near watercourses. Were analyzed, among the scenarios simulated for the entire period: total flow and baseflow; parameters of hydrographs (in selected events of the series); position of the water table, available water content; and flow duration curves. The results showed that in the study area there is no influence of the position of forest cover in relation to shallow soils to the water yield. Because there are few studies that address the effect of the location of forest cover in water yield is encouraged to conduct further research, among other reasons, for the determination of the priority sites to the reforestation in environmental conservation programs.

Sabe-se que a formação de reservatórios altera a qualidade e a quantidade da água de montante e jusante e que a direção e a magnitude das alterações dependem de suas características construtivas, operacionais, morfométricas, bem como do regime hidrológico e climático da região. Porém, a maior parte deste conhecimento foi fundamentada em pesquisas de reservatórios com grande capacidade de regularização, que fazem parte da realidade do Pantanal, uma região que vem sendo impactada por um número cada vez maior de reservatórios com pequena capacidade de regularização, levantando questionamentos sobre seus possíveis efeitos no funcionamento da planície de inundação. Sendo assim, este trabalho procurou (i) identificar qual o fator chave determinante no processo de estratificação e mistura vertical do reservatório e se este pode influenciar na qualidade da água; (ii) avaliar os efeitos da formação e operação do reservatório na alteração da qualidade da água de montante e jusante e (iii) avaliar os efeitos da operação do reservatório na alteração do regime hidrológico de jusante, além de propor os limites preventivos para a sustentabilidade. O estudo foi desenvolvido no reservatório de Ponte de Pedra, localizado no rio Correntes, divisa dos estados de Mato Grasso e Mato Grosso do Sul (Centro Oeste do Brail), na fronteira entre o Pantanal e o Planalto. O reservatório apresentou prolongado período de estratificação vertical (mistura no inverno) dos parâmetros físicos e químicos da água nas partes médias e profundas, mantendo-se homogêneo na parte superior, onde se encontra a captação, não alterando as características da água de jusante. Entre os fatores analisados, o vento foi o único fator que influenciou significativamente a estrutura vertical da qualidade da água sendo beneficiada pelas características morfométricas e construtivas do reservatório. Longitudinalmente, a formação do reservatório alterou significativamente quatro dos dez parâmetros analisados, com redução média de 38% da turbidez, 28% do fósforo total, 23% dos sólidos totais e 14% do nitrato. Destes, apenas a turbidez e o nitrato foram afetados pelo controle operacional do tempo de retenção hidráulica. Em relação à alteração dos parâmetros do regime hidrológico anual, dos 31 analisados, os parâmetros de vazões mínimas de curta duração (1, 3 e 7 dias), vazões máximas de 90 dias e o número de pulsos baixos e altos foram significativamente alterados pela operação do reservatório. Destes, a vazão máxima de 90 dias e o número de pulsos altos resumem os impactos, e podem ser utilizados como parâmetros alvos para restauração e conservação do regime hidrológico. As vazões sazonais também foram significativamente alteradas, com maior impacto na estação seca (inverno). Com base na variabilidade natural do rio, foram propostos os limites preventivos para a sustentabilidade, com alterações diárias permitidas de ±18% no inverno, ±24% na primavera e ±22% no verão e outono, aplicados sobre a vazão natural. De maneira geral, as alterações na qualidade da água e no regime hidrológico provocado pela formação e operação do reservatório foram consideradas baixas, tanto em número de parâmetros alterados quanto nas magnitudes das alterações, e estas foram atribuídas às baixas concentrações de partículas e nutrientes na bacia, ao sistema de captação superficial, o curto tempo de retenção hidráulica, pequena capacidade de regularização associadas à sazonalidade no regime de chuvas e ventos na região, que limitam manobras operacionais para a maximização da eficiência energética. / The formation of reservoirs changes the quality and quantity of water, both upstream and downstream, and the direction and magnitude of such changes depend on their characteristics of construction, operation, morphometry, as well as hydrological regime and climate of the region. However, much of this knowledge was based on large reservoirs, which is not the reality of the Pantanal, an area that is being impacted by a growing number of reservoirs with low capacity for regularization, raising questions about possible effects on the floodplain functioning. In this way, this study aimed (i) to identify the key factor in the process of stratification and vertical mixing of the reservoir, and whether this can influence the water quality, (ii) to evaluate the effects of the reservoir formation and operation on the quality of water upstream and downstream of the reservoir, and (iii) to examine the effects of the reservoir operation on the downstream hydrological regime, in addition to propose preventive limits for sustainability. The study was conducted at Ponte de Pedra Reservoir, located on the Correntes river, the motto between the states of Mato Grasso and Mato Grosso do Sul (Central West Brazil), on the border between the Plateau and the Pantanal. The reservoir had an extended period of vertical stratification (mixture in the winter) of physical and chemical water parameters in the medium and deep parts of the water column, being homogeneous in the upper part where the water is capitation, without changing the characteristics of the downstream water. Among the factors analyzed, the wind was the only factor that significantly influenced the vertical structure of the water quality, favored by morphometric and constructive characteristics of the reservoir. Along the longitudinal axis, the reservoir formation significantly altered the turbidity and concentrations of total phosphorus, total solids, and nitrate, with mean reduction of 38, 28, 23 and 14% of their values. Among these, only turbidity and nitrate were affected by the operational control of the hydraulic retention time. In relation to the change in parameters of the annual hydrological regime, parameters of short-term minimum flows (1, 3 and 7 days), maximum flows of 90 days and the number of low and high pulses were significantly modified by the reservoir operation. Of these, the maximum flow of 90 days and the number of high pulses have summarized the impacts, and can be used as target parameters for restoration and conservation of the hydrological regime. Seasonal flows were also significantly altered, with the greatest impact in the dry season (winter). Based on the natural variability of the river, it was proposed preventive limits for sustainability, with permitted daily changes of ±18% in winter, ±24% in spring and ±22% in summer and autumn applied on the natural flow. In general, changes in water quality and hydrological regime caused by the reservoir formation and operation were considered low, both in number of altered parameters as magnitudes of such changes, and these characteristics were ascribed to low concentrations of particles and nutrients in the basin, to the surface capitation system, short hydraulic retention time, low capacity of regularization associated with the seasonality of the regime of rainfall and wind in the region, limiting operational maneuvers for maximizing the energy efficiency.

Sabe-se que a formação de reservatórios altera a qualidade e a quantidade da água de montante e jusante e que a direção e a magnitude das alterações dependem de suas características construtivas, operacionais, morfométricas, bem como do regime hidrológico e climático da região. Porém, a maior parte deste conhecimento foi fundamentada em pesquisas de reservatórios com grande capacidade de regularização, que fazem parte da realidade do Pantanal, uma região que vem sendo impactada por um número cada vez maior de reservatórios com pequena capacidade de regularização, levantando questionamentos sobre seus possíveis efeitos no funcionamento da planície de inundação. Sendo assim, este trabalho procurou (i) identificar qual o fator chave determinante no processo de estratificação e mistura vertical do reservatório e se este pode influenciar na qualidade da água; (ii) avaliar os efeitos da formação e operação do reservatório na alteração da qualidade da água de montante e jusante e (iii) avaliar os efeitos da operação do reservatório na alteração do regime hidrológico de jusante, além de propor os limites preventivos para a sustentabilidade. O estudo foi desenvolvido no reservatório de Ponte de Pedra, localizado no rio Correntes, divisa dos estados de Mato Grasso e Mato Grosso do Sul (Centro Oeste do Brail), na fronteira entre o Pantanal e o Planalto. O reservatório apresentou prolongado período de estratificação vertical (mistura no inverno) dos parâmetros físicos e químicos da água nas partes médias e profundas, mantendo-se homogêneo na parte superior, onde se encontra a captação, não alterando as características da água de jusante. Entre os fatores analisados, o vento foi o único fator que influenciou significativamente a estrutura vertical da qualidade da água sendo beneficiada pelas características morfométricas e construtivas do reservatório. Longitudinalmente, a formação do reservatório alterou significativamente quatro dos dez parâmetros analisados, com redução média de 38% da turbidez, 28% do fósforo total, 23% dos sólidos totais e 14% do nitrato. Destes, apenas a turbidez e o nitrato foram afetados pelo controle operacional do tempo de retenção hidráulica. Em relação à alteração dos parâmetros do regime hidrológico anual, dos 31 analisados, os parâmetros de vazões mínimas de curta duração (1, 3 e 7 dias), vazões máximas de 90 dias e o número de pulsos baixos e altos foram significativamente alterados pela operação do reservatório. Destes, a vazão máxima de 90 dias e o número de pulsos altos resumem os impactos, e podem ser utilizados como parâmetros alvos para restauração e conservação do regime hidrológico. As vazões sazonais também foram significativamente alteradas, com maior impacto na estação seca (inverno). Com base na variabilidade natural do rio, foram propostos os limites preventivos para a sustentabilidade, com alterações diárias permitidas de ±18% no inverno, ±24% na primavera e ±22% no verão e outono, aplicados sobre a vazão natural. De maneira geral, as alterações na qualidade da água e no regime hidrológico provocado pela formação e operação do reservatório foram consideradas baixas, tanto em número de parâmetros alterados quanto nas magnitudes das alterações, e estas foram atribuídas às baixas concentrações de partículas e nutrientes na bacia, ao sistema de captação superficial, o curto tempo de retenção hidráulica, pequena capacidade de regularização associadas à sazonalidade no regime de chuvas e ventos na região, que limitam manobras operacionais para a maximização da eficiência energética. / The formation of reservoirs changes the quality and quantity of water, both upstream and downstream, and the direction and magnitude of such changes depend on their characteristics of construction, operation, morphometry, as well as hydrological regime and climate of the region. However, much of this knowledge was based on large reservoirs, which is not the reality of the Pantanal, an area that is being impacted by a growing number of reservoirs with low capacity for regularization, raising questions about possible effects on the floodplain functioning. In this way, this study aimed (i) to identify the key factor in the process of stratification and vertical mixing of the reservoir, and whether this can influence the water quality, (ii) to evaluate the effects of the reservoir formation and operation on the quality of water upstream and downstream of the reservoir, and (iii) to examine the effects of the reservoir operation on the downstream hydrological regime, in addition to propose preventive limits for sustainability. The study was conducted at Ponte de Pedra Reservoir, located on the Correntes river, the motto between the states of Mato Grasso and Mato Grosso do Sul (Central West Brazil), on the border between the Plateau and the Pantanal. The reservoir had an extended period of vertical stratification (mixture in the winter) of physical and chemical water parameters in the medium and deep parts of the water column, being homogeneous in the upper part where the water is capitation, without changing the characteristics of the downstream water. Among the factors analyzed, the wind was the only factor that significantly influenced the vertical structure of the water quality, favored by morphometric and constructive characteristics of the reservoir. Along the longitudinal axis, the reservoir formation significantly altered the turbidity and concentrations of total phosphorus, total solids, and nitrate, with mean reduction of 38, 28, 23 and 14% of their values. Among these, only turbidity and nitrate were affected by the operational control of the hydraulic retention time. In relation to the change in parameters of the annual hydrological regime, parameters of short-term minimum flows (1, 3 and 7 days), maximum flows of 90 days and the number of low and high pulses were significantly modified by the reservoir operation. Of these, the maximum flow of 90 days and the number of high pulses have summarized the impacts, and can be used as target parameters for restoration and conservation of the hydrological regime. Seasonal flows were also significantly altered, with the greatest impact in the dry season (winter). Based on the natural variability of the river, it was proposed preventive limits for sustainability, with permitted daily changes of ±18% in winter, ±24% in spring and ±22% in summer and autumn applied on the natural flow. In general, changes in water quality and hydrological regime caused by the reservoir formation and operation were considered low, both in number of altered parameters as magnitudes of such changes, and these characteristics were ascribed to low concentrations of particles and nutrients in the basin, to the surface capitation system, short hydraulic retention time, low capacity of regularization associated with the seasonality of the regime of rainfall and wind in the region, limiting operational maneuvers for maximizing the energy efficiency.

Sabe-se que a formação de reservatórios altera a qualidade e a quantidade da água de montante e jusante e que a direção e a magnitude das alterações dependem de suas características construtivas, operacionais, morfométricas, bem como do regime hidrológico e climático da região. Porém, a maior parte deste conhecimento foi fundamentada em pesquisas de reservatórios com grande capacidade de regularização, que fazem parte da realidade do Pantanal, uma região que vem sendo impactada por um número cada vez maior de reservatórios com pequena capacidade de regularização, levantando questionamentos sobre seus possíveis efeitos no funcionamento da planície de inundação. Sendo assim, este trabalho procurou (i) identificar qual o fator chave determinante no processo de estratificação e mistura vertical do reservatório e se este pode influenciar na qualidade da água; (ii) avaliar os efeitos da formação e operação do reservatório na alteração da qualidade da água de montante e jusante e (iii) avaliar os efeitos da operação do reservatório na alteração do regime hidrológico de jusante, além de propor os limites preventivos para a sustentabilidade. O estudo foi desenvolvido no reservatório de Ponte de Pedra, localizado no rio Correntes, divisa dos estados de Mato Grasso e Mato Grosso do Sul (Centro Oeste do Brail), na fronteira entre o Pantanal e o Planalto. O reservatório apresentou prolongado período de estratificação vertical (mistura no inverno) dos parâmetros físicos e químicos da água nas partes médias e profundas, mantendo-se homogêneo na parte superior, onde se encontra a captação, não alterando as características da água de jusante. Entre os fatores analisados, o vento foi o único fator que influenciou significativamente a estrutura vertical da qualidade da água sendo beneficiada pelas características morfométricas e construtivas do reservatório. Longitudinalmente, a formação do reservatório alterou significativamente quatro dos dez parâmetros analisados, com redução média de 38% da turbidez, 28% do fósforo total, 23% dos sólidos totais e 14% do nitrato. Destes, apenas a turbidez e o nitrato foram afetados pelo controle operacional do tempo de retenção hidráulica. Em relação à alteração dos parâmetros do regime hidrológico anual, dos 31 analisados, os parâmetros de vazões mínimas de curta duração (1, 3 e 7 dias), vazões máximas de 90 dias e o número de pulsos baixos e altos foram significativamente alterados pela operação do reservatório. Destes, a vazão máxima de 90 dias e o número de pulsos altos resumem os impactos, e podem ser utilizados como parâmetros alvos para restauração e conservação do regime hidrológico. As vazões sazonais também foram significativamente alteradas, com maior impacto na estação seca (inverno). Com base na variabilidade natural do rio, foram propostos os limites preventivos para a sustentabilidade, com alterações diárias permitidas de ±18% no inverno, ±24% na primavera e ±22% no verão e outono, aplicados sobre a vazão natural. De maneira geral, as alterações na qualidade da água e no regime hidrológico provocado pela formação e operação do reservatório foram consideradas baixas, tanto em número de parâmetros alterados quanto nas magnitudes das alterações, e estas foram atribuídas às baixas concentrações de partículas e nutrientes na bacia, ao sistema de captação superficial, o curto tempo de retenção hidráulica, pequena capacidade de regularização associadas à sazonalidade no regime de chuvas e ventos na região, que limitam manobras operacionais para a maximização da eficiência energética. / The formation of reservoirs changes the quality and quantity of water, both upstream and downstream, and the direction and magnitude of such changes depend on their characteristics of construction, operation, morphometry, as well as hydrological regime and climate of the region. However, much of this knowledge was based on large reservoirs, which is not the reality of the Pantanal, an area that is being impacted by a growing number of reservoirs with low capacity for regularization, raising questions about possible effects on the floodplain functioning. In this way, this study aimed (i) to identify the key factor in the process of stratification and vertical mixing of the reservoir, and whether this can influence the water quality, (ii) to evaluate the effects of the reservoir formation and operation on the quality of water upstream and downstream of the reservoir, and (iii) to examine the effects of the reservoir operation on the downstream hydrological regime, in addition to propose preventive limits for sustainability. The study was conducted at Ponte de Pedra Reservoir, located on the Correntes river, the motto between the states of Mato Grasso and Mato Grosso do Sul (Central West Brazil), on the border between the Plateau and the Pantanal. The reservoir had an extended period of vertical stratification (mixture in the winter) of physical and chemical water parameters in the medium and deep parts of the water column, being homogeneous in the upper part where the water is capitation, without changing the characteristics of the downstream water. Among the factors analyzed, the wind was the only factor that significantly influenced the vertical structure of the water quality, favored by morphometric and constructive characteristics of the reservoir. Along the longitudinal axis, the reservoir formation significantly altered the turbidity and concentrations of total phosphorus, total solids, and nitrate, with mean reduction of 38, 28, 23 and 14% of their values. Among these, only turbidity and nitrate were affected by the operational control of the hydraulic retention time. In relation to the change in parameters of the annual hydrological regime, parameters of short-term minimum flows (1, 3 and 7 days), maximum flows of 90 days and the number of low and high pulses were significantly modified by the reservoir operation. Of these, the maximum flow of 90 days and the number of high pulses have summarized the impacts, and can be used as target parameters for restoration and conservation of the hydrological regime. Seasonal flows were also significantly altered, with the greatest impact in the dry season (winter). Based on the natural variability of the river, it was proposed preventive limits for sustainability, with permitted daily changes of ±18% in winter, ±24% in spring and ±22% in summer and autumn applied on the natural flow. In general, changes in water quality and hydrological regime caused by the reservoir formation and operation were considered low, both in number of altered parameters as magnitudes of such changes, and these characteristics were ascribed to low concentrations of particles and nutrients in the basin, to the surface capitation system, short hydraulic retention time, low capacity of regularization associated with the seasonality of the regime of rainfall and wind in the region, limiting operational maneuvers for maximizing the energy efficiency.

Water is essential for human well-being and healthy ecosystems, but population growth and changes in climate and land-use are putting increased stress on water resources in many regions. To ensure water security, knowledge about the spatiotemporal distribution of these resources is of great importance. However, estimates of global water resources are constrained by limitations in availability and quality of data. This thesis explores the quality of both observational and modelled data, gives an overview of models used for large-scale hydrological modelling, and explores the possibilities to deal with the scarcity of data by prediction of flow-duration curves. The evaluation of the quality of observational data for large-scale hydrological modelling was based on both hydrographic data, and model forcing and evaluation data for basins worldwide. The results showed that a GIS polygon dataset outperformed all gridded hydrographic products analysed in terms of representation of basin areas. Through a screening methodology based on the long-term water-balance equation it was shown that as many as 8–43% of the basins analysed displayed inconsistencies between forcing (precipitation and potential evaporation) and evaluation (discharge) data depending on how datasets were combined. These data could prove disinformative in hydrological model inference and analysis. The quality of key hydrological variables from a numerical weather prediction model was assessed by benchmarking against observational datasets and by analysis of the internal land-surface water budgets of several different model setups. Long-term imbalances were found between precipitation and evaporation on the global scale and between precipitation, evaporation and runoff on both cell and basin scales. These imbalances were mainly attributed to the data assimilation system in which soil moisture is used as a nudge factor to improve weather forecasts. Regionalisation, i.e. transfer of information from data-rich areas to data-sparse areas, is a necessity in hydrology because of a lack of observed data in many areas. In this thesis, the possibility to predict flow-duration curves in ungauged basins was explored by testing several different methodologies including machine learning. The results were mixed, with some well predicted curves, but many predicted curves exhibited large biases and several methods resulted in unrealistic curves. / Vatten är en förutsättning för människors och ekosystems hälsa, men befolkningsökning och förändringar av klimat och markanvändning förväntas öka trycket på vattenresurserna i många regioner i världen. För att kunna säkerställa en god tillgång till vatten krävs kunskap om hur dessa resurser varierar i tid och rum. Tillförlitligheten hos skattningar av globala vattenresurser begränsas dock både av begränsad tillgänglighet av och kvalitet hos observerade data. Denna avhandling utforskar kvaliteten av såväl observations- som modellbaserade data, ger en överblick över modeller som används för storskalig hydrologisk modellering och utforskar möjligheterna att förutsäga varaktighetskurvor som ett sätt att hantera bristen på data i många områden. Utvärderingen av observationsbaserade datas kvalitet baserades på hydrografiska data och driv- och utvärderingsdata för storskaliga hydrologiska modeller. Resultaten visade att en uppsättning data över hydrografin baserad på GIS-polygoner representerade avrinningsområdesareorna bättre än alla de som byggde på rutor. En metod baserad på långtidsvattenbalansen identifierade att kombinationen av drivdata (nederbörd och potentiell avdunstning) och utvärderingsdata (vattenföring) var fysiskt orimlig för så många som 8–43 % av de analyserade avrinningsområdena beroende på hur olika datauppsättningar kombinerades. Sådana data kan vara desinformativa för slutsatser som dras av resultat från hydrologiska modeller och analyser. Kvaliteten hos hydrologiskt viktiga variabler från en numerisk väderprognosmodell utvärderades dels genom jämförelser med observationsdata och dels genom analys av landytans vattenbudget för ett flertal olika modellvarianter. Resultaten visade obalanser mellan långtidsvärden av nederbörd och avdunstning i global skala och mellan långtidsvärden av nederbörd, avdunstning och avrinning i både modellrute- och avrinningsområdesskala. Dessa obalanser skulle till stor del kunna förklaras av den data assimilering som görs, i vilken markvattenlagret används som en justeringsfaktor för att förbättra väderprognoserna. Regionalisering, som innebär en överföring av information från områden med god tillgång på mätdata till områden med otillräcklig tillgång, är i många fall nödvändig för hydrologisk analys på grund av att mätdata saknas i många områden. I denna avhandling utforskades möjligheten att förutsäga varaktighetskurvor för avrinningsområden utan vattenföringsdata genom flera metoder inklusive maskininlärning. Resultaten var blandade med en del kurvor som förutsas väl, och andra kurvor som visade stora systematiska avvikelser. Flera metoder resulterade i orealistiska kurvor (ickemonotona eller med negativa värden).

Knowledge about spatial and temporal variability of hydrological processes is central for sustainable water-resources management, and such knowledge is created from observational data. Hydrologic models are necessary for prediction for time periods and areas lacking data, but are affected by observational uncertainties. Methods for estimating and accounting for such uncertainties in water-resources modelling are of high importance, especially in regions such as Central America. Observational uncertainties were addressed in three ways in this thesis; quality control, quantitative estimation and development of model-evaluation techniques that addressed unquantifiable uncertainties. A first step in any modelling study should be the quality control and concurrent analysis of the representativeness of the observational data. In the characterisation of the precipitation regime in the Choluteca River basin in Honduras, four different quality problems were identified and 22% of the daily data had to be rejected. The monitoring network was found to be insufficient for a comprehensive characterisation of the high spatiotemporal variability of the precipitation regime. Quantitative estimations of data uncertainties can be made when sufficient information is available. Discharge-data uncertainties were estimated with a fuzzy regression for time-variable rating curves and from official rating curves for 35 stations in Honduras. The uncertainties were largest for low flows, as a result of measurement uncertainties and natural variability. A method for calibration with flow-duration curves was developed which enabled calibration to the whole flow range, accounting for discharge uncertainty and calibration with non-overlapping time periods for model input and evaluation data. The method compared favourably to traditional calibration in a test using two models applied in basins with different runoff-generation processes. A post-hoc analysis made it possible to identify potential model-structure errors and periods of disinformative data. Flow-duration curves were regionalised and used for calibration of a Central-American water-balance model. The initial model uncertainty for the ungauged basins was reduced by 70%. Non-representative precipitation data were found to be the main obstacle to comprehensive regional water-resources modelling in Central America. These methods bridged several problems related to observational uncertainties in water-balance modelling. Estimates of prediction uncertainty are an important basis for all types of decisions related to water-resources management. / Kännedom om hur hydrologiska processer varierar i tid och rum är grundläggande för hållbar vattenresursförvaltning och skapas utifrån observerade data. Hydrologiska modeller är nödvändiga för att förutsäga vattenbalansen för tidsperioder och områden utan data, men påverkas av observationsosäkerheter. Metoder för att hantera sådana osäkerheter i vattenresursmodellering är av stor betydelse i regioner såsom Centralamerika. Observationsosäkerheter hanterades på tre olika sätt i denna avhandling; kvalitetskontroll, kvantitativ uppskattning och utveckling av modellutvärderingsmetoder för beaktande av icke kvantifierbara osäkerheter. Ett viktigt första steg är kvalitetskontroll och samtidig analys av datas representativitet. Vid karaktäriseringen av nederbördsregimen i Cholutecaflodens avrinningsområde i Honduras identifierades fyra olika kvalitetsproblem och 22 % av data sorterades bort. Stationsnätet var otillräckligt för en fullödig karaktärisering av nederbördsregimens variationer i tid och rum. Dessa var mycket stora som ett resultat av komplexiteten hos de nederbördsgenererande mekanismerna. Kvantitativ uppskattning av observerade datas osäkerhet kan göras när tillräcklig information är tillgänglig. Osäkerheter i vattenföringsdata uppskattades dels vid beräkning av vattenföring med en oskarp regression för en tidsvariabel avbördningskurva, dels från en analys av officiella avbördningskurvor från 35 stationer i Honduras. Osäkerheten var i båda fallen högst vid låga flöden som ett resultat av högre mätosäkerheter samt större naturlig variabilitet än vid höga flöden. En metod för modellkalibrering med varaktighetskurvor utvecklades och gjorde det möjligt att kalibrera för hela flödesintervallet samtidigt, ta hänsyn till osäkerheter i vattenföringsdata samt kalibrera med icke överlappande driv- och utvärderingsdata. Metoden testades med två olika modeller i två avrinningsområden med olika avrinningsbildningsprocesser, och visade goda resultat jämfört med traditionell modellkalibrering. En post hoc-analys gjorde det möjligt att identifiera troliga modellstrukturfel och perioder med disinformativa data. Varaktighetskurvor regionaliserades och användes för kalibrering av en regional vattenbalansmodell för Centralamerika, varvid den initiala modellosäkerheten minskades med 70 %. Icke representativa nederbördsdata identifierades som det största hindret för regional vattenresursmodellering i Centralamerika. De metoder som utvecklades i detta arbete gör det möjligt att överbrygga ett flertal problem orsakade av bristfällig tillgänglighet och kvalitet av data och leder därmed till en förbättrad uppskattning av osäkerheten i vattenbalanssimuleringar. Sådana osäkerhetsskattningar är ett viktigt underlag vid alla typer av förvaltningsbeslut som rör vattenresurser.