Remote Sensing, as a driver for water management decisions, needs further integration with monitoring water quality programs, especially in developing countries. Moreover, usage of remote sensing approaches has not been broadly applied in monitoring routines. Therefore, it is necessary to assess the efficacy of available sensors to complement the often limited field measurements from such programs and build models that support monitoring tasks. Here, we integrate field measurements (2013–2019) from the Mexican national water quality monitoring system (RNMCA) with data from Landsat-8 OLI, Sentinel-3 OLCI, and Sentinel-2 MSI to train an extreme learning machine (ELM), a support vector regression (SVR) and a linear regression (LR) for estimating Chlorophyll-a (Chl-a), Turbidity, Total Suspended Matter (TSM) and Secchi Disk Depth (SDD). Additionally, OLCI Level-2 Products for Chl-a and TSM are compared against the RNMCA data. We observed that OLCI Level-2 Products are poorly correlated with the RNMCA data and it is not feasible to rely only on them to support monitoring operations. However, OLCI atmospherically corrected data is useful to develop accurate models using an ELM, particularly for Turbidity (R² = 0.7). We conclude that remote sensing is useful to support monitoring systems tasks, and its progressive integration will improve the quality of water quality monitoring programs.

This study presents high‐resolution flow‐through experiments investigating transport processes in a laboratory setup mimicking an aquifer affected by hydropeaking (i.e., abrupt fluctuations in the river stage by the release or storage of water in reservoirs). Highly transient flow conditions were experimentally generated by sudden changes of the water level in two rivers in hydraulic contact with an unconfined aquifer. High‐resolution image analysis and depth‐resolved, high‐frequency sampling at the outlet allowed monitoring of the spatio‐temporal evolution and the breakthrough of a dye tracer plume in the porous medium. The plume spreading and mixing were quantified by moment analysis and entropy‐based metrics of the scalar field. We show that hydropeaking strongly enhances spreading and mixing in the subsurface (up to 249.5% and 41.8% in these experiments) and demonstrate the relevance of considering highly transient flow regimes to properly capture transport and mixing‐controlled biogeochemical reactions at the surface water ‐ groundwater interface.

Management of hydropower plants strongly influences streamflow dynamics and hence the interaction between surface water and groundwater. As dam operations cause variations in river stages, these can result in changes in the groundwater level at multiple temporal scales. In this work, we study the case of an Alpine aquifer, where weekly fluctuations are particularly pronounced. We consider an area with four river reaches differently impacted by reservoir operations and investigate the influence of these rivers on the common aquifer. Using continuous wavelet transform and wavelet coherence analysis, we show that weekly fluctuations in the groundwater table are particularly pronounced in dry years, in particular in the winter season, although the area of the aquifer impacted by dam operations remains almost unchanged. We thus observe that in Alpine catchments, surface water‐groundwater interaction is sensitive to the conditions determined by a specific hydrological year. We also investigate the influences of the river‐aquifer water fluxes and show that under dry conditions hydropeaking mainly affects their temporal dynamics. Our observations have significant consequences for predicting nutrient and temperature dynamics/regimes in river‐aquifer systems impacted by hydropower plant management.

Transport processes in porous media are controlled by the characteristics of the flow field which are determined by the porous material properties and the boundary conditions of the system. This work provides experimental evidence of the relation between mixing and flow field topology in porous media at the continuum scale. The setup consists of a homogeneously packed quasi-two-dimensional flow-through chamber in which transient flow conditions, dynamically controlled by two external reservoirs, impact the transport of a dissolved tracer. The experiments were performed at two different flow velocities, corresponding to Péclet numbers of 191 and 565, respectively. The model-based interpretation of the experimental results shows that high values of the effective Okubo-Weiss parameter, driven by the changes of the boundary conditions, lead to high rates of increase of the Shannon entropy of the tracer distribution and, thus, to enhanced mixing. The comparison between a hydrodynamic dispersion model and an equivalent pore diffusion model demonstrates that despite the spatial and temporal variability in the hydrodynamic dispersion coefficients, the Shannon entropy remains almost unchanged because it is controlled by the Okubo-Weiss parameter. Overall, our work demonstrates that under highly transient boundary conditions, mixing dynamics in homogeneous porous media can also display complex patterns and is controlled by the flow topology.

Effective remediation of contaminated aquifers is often limited by the mixing among reaction partners. An effective method to enhance mixing and reach a faster groundwater remediation is engineered injection extraction (EIE). This technology consists of a sequence of 12-steps of injection and extraction of water through a system of four wells. In this work, we investigate, using Morris sensitivity analysis, which are the most relevant design parameters of EIE among the location of four injection-extraction wells and their pumping rate, in a two-dimensional domain. Moreover, we consider the effect of heterogeneous hydraulic conductivity fields in scenarios of increasing complexity. Our results show that the first steps of the remediation process are the most important ones. The value of the hydraulic conductivity is relevant in case of heterogeneous fields within the treated area, as it generates flow focusing, enhancing plume spreading and mixing. In the case of instantaneous, complete mixing-limited reactions, the sensitivity of the model parameters also depends on the critical mixing ratio, which controls the time needed for the complete degradation of a treatment solution injected in the middle of the EIE system.

The operation of hydropower plants leads to sudden changes in river stage and to a flow regime known as hydropeaking. Hydropeaking alters the morphology of the riverbed and water quality, and ultimately poses a risk to riverine ecosystems. While many indicators are available to quantitatively assess this problem in rivers, the impact of hydropeaking on aquifers is largely unknown and lacks of quantitative indicators. We analyze with wavelet techniques the spatial and temporal dynamics of surface water‐groundwater interaction in an aquifer impacted by two differently regulated rivers. We propose four indicators to study the aquifer stress produced by hydropeaking and classify the observed groundwater head time series into weakly, moderately and highly impacted. This study opens the possibility for a quantitative assessment of the impact of hydropeaking on the groundwater ecosystem.