A dificuldade que se tem em promover uma adequada gestão da qualidade dos recursos hídricos tem como uma das causas a escassez de dados, seja espacial ou temporalmente. Os programas de monitoramento da qualidade da água convencionais possuem uma taxa de amostragem baixa, que em muitos casos se resume a algumas amostras por ano. Na busca por tornar as séries históricas de qualidade da água mais densas e representativas, desenvolvem-se técnicas de monitoramento automatizado, com equipamentos fixos em campo, coleta de dados automática e envio em tempo real. Embora estas técnicas tornem as séries históricas muito mais representativas e possibilitem uma tomada de decisão em tempo hábil para o gestor, elas ainda não estão consolidadas e possuem uma série de obstáculos na sua utilização, como o alto custo, as dificuldades de instalação dos equipamentos em campo, e a manutenção e calibração dispendiosas. Uma alternativa seria o chamado monitoramento da qualidade da água em tempo quase real (MQATQR), no qual um operador vai até o curso d’água portando o sensor, que pode ser uma sonda multiparamétrica, faz as leituras com uma frequência maior que o monitoramento convencional, e vai até uma base onde possa enviar esta informação. Com um mesmo aparelho pode ser feita a cobertura de um grande número de pontos e o equipamento pode ter sua calibração controlada em laboratório. Nesse contexto, o objetivo desta tese é avaliar a efetividade e o impacto econômico da utilização de uma estratégia de MQATQR como ferramenta de geração de dados de qualidade da água em um cenário de escassez de dados. Para isso foram utilizadas séries históricas de pontos de monitoramento da qualidade da água em tempo real no Brasil, Canadá e EUA. Estas séries foram submetidas à análise espectral para identificação das frequências mais densas e da representatividade delas dentro das séries. Os valores das frequências obtidos foram relacionados com atributos físicos e hidrológicos das bacias hidrográficas dos pontos de monitoramento. Para obtenção dos intervalos de amostragem foi aplicado o teorema de Nyquist-Shannon. A avaliação da viabilidade econômica da estratégia foi feita com dois estudos de caso, um é a aplicação na Rede Hidrometeorológica Nacional de Referência e o outro a aplicação no âmbito dos empreendimentos hidrelétricos sujeitos à resolução conjunta ANA/ANEEL nº 03/2010. Foi possível observar uma boa relação entre as frequências de amostragem e a área das bacias, possibilitando a prescrição de diferentes tipos de MQATQR para diferentes tipos de bacia. Os intervalos de amostragem obtidos por meio das frequências características em geral se mostraram executáveis nos moldes do MQATQR até a permanência de frequência de 90%. Para as permanências maiores que 90% os intervalos se aproximam do diário, sendo mais aconselhável a utilização de estratégias em tempo real. A estratégia de MQATQR se mostrou com melhor custo-efetividade para a maioria dos programas de monitoramento quando se utilizam permanências de frequências inferiores a 65%. Para permanências maiores que 65% a estratégia se mostrou economicamente viável para programas de monitoramento cujos pontos de amostragem estão próximos à base de operação. A estratégia de MQATQR se mostra como alternativa efetiva para o aumento da densidade temporal dos dados para diversos tipos de programas de monitoramento, com exceção daqueles que exigem o acompanhamento das variações bruscas na qualidade da água, como sistemas de alerta de qualidade da água. | The difficulty in promoting an adequate water quality management is mainly because data scarcity, either spatially or temporally. Conventional water quality monitoring programs have a low sampling rate, in many cases only few samples per year. By using appropriated equipment in field for data collection and real time sending, it is possible to develop some automated monitoring techniques to make the water quality series denser and representative. Although these techniques make the series more representative and allow a time decision-making for the manager, there are some barriers in their application such as higher costs, difficulties of installing the equipment and expensive maintenance and calibration. An alternative is the near-real-time water quality monitoring (NRTWQM), in which an operator goes to the river carrying the sensor, as a multi-parametric probe for example, to obtain a higher sampling frequency than monitoring conventional. In sequence the operator goes to a base where the information can be sent. By using the same sensor, it is possible to cover a large number of points. The equipment can also be calibrated in the laboratory. In this context, the objective of this work is to evaluate the effectiveness and economic impact in using a NRTWQM strategy as a tool to generate water quality data in a data scarcity scenario. For this purpose, water quality series are considered in real time at monitoring points in Brazil, Canada and the USA. The series were submitted to the spectral analysis to identify dense frequencies and their representativeness within the series. The frequencies values were related to the physical and hydrological attributes of the hydrographic basins. The Nyquist-Shannon theorem was applied to obtain the sampling intervals. The economic viability of the strategy is evaluated in two study cases. The National Hydrometeorological Reference Network is applied in the first, whilst the second is based on the application in the scope of hydroelectric projects subject to ANA / ANEEL nº 03/2010 normative resolution. It is observed a good relationship between the sampling frequencies and the basin area, which makes possible to prescribe different types of NRTWQM for different types of basin. In general, the sampling intervals obtained by means of the characteristic frequencies were shown to be executable in the NRTWQM models up to the 90% of cumulative frequency. For cumulative frequency higher than 90% the intervals approach the diary, consequently it is more advisable to use real-time strategies. The NRTWQM strategy proved to be the most cost-effective for mainly monitoring programs when using cumulative frequencies less than 65%. For cumulative frequency higher than 65%, the strategy proved to be economically viable for monitoring programs where sampling points are close to the base of operation. The NRTWQM strategy is an effective alternative to increase the temporal density of data for several types of monitoring programs, except for those that require the monitoring, of sudden changes in water quality, such as water quality warning systems.

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.

Correct understanding of groundwater/surface-water (GW–SW) interaction in karst systems is of greatest importance for managing the water resources. A typical karst region, Fangshan in northern China, was selected as a case study. Groundwater levels and hydrochemistry analyses, together with isotope data based on hydrogeological field investigations, were used to assess the GW–SW interaction. Chemistry data reveal that water type and the concentration of cations in the groundwater are consistent with those of the surface water. Stable isotope ratios of all samples are close to the local meteoric water line, and the ³H concentrations of surface water and groundwater samples are close to that of rainfall, so isotopes also confirm that karst groundwater is recharged by rainfall. Cross-correlation analysis reveals that rainfall leads to a rise in groundwater level with a lag time of 2 months and groundwater exploitation leads to a fall within 1 month. Spectral analysis also reveals that groundwater level, groundwater exploitation and rainfall have significantly similar response periods, indicating their possible inter-relationship. Furthermore, a multiple nonlinear regression model indicates that groundwater level can be negatively correlated with groundwater exploitation, and positively correlated with rainfall. The overall results revealed that groundwater level has a close correlation with groundwater exploitation and rainfall, and they are indicative of a close hydraulic connection and interaction between surface water and groundwater in this karst system.