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Different aspects of management policies for shallow geothermal systems are currently under development. Although this technology has been used for a long time, doubts and concerns have been raised in the last years due to the massive implementation of new systems. To assess possible environmental impacts and manage subsurface energy resources, collecting data from operating shallow geothermal systems is becoming mandatory in Europe. This study presents novel advances in the upscaling of operation datasets obtained from open-loop geothermal energy systems for an optimal integration in hydrogeological models. The proposed procedure allows efficient numerical simulations to be performed at an urban scale. Specifically, this work proposes a novel methodology to optimize the data treatment of highly transient real exploitation regimes by integrating energy transfer in the environment to reduce more than 90% registered raw datasets. The proposed methodology is then applied to and validated on five different real optimization scenarios in which upscaling transformation of the injection temperature series of 15-min sampling frequency has been considered. The error derived from each approach was evaluated and compared for validation purposes. The results obtained from the upscaling procedures have proven the usefulness and transferability of the proposed method for achieving daily time functions to efficiently reproduce the exploitation regimes of these systems with an acceptable error in a sustainable resource management framework.

The shallow subsurface in urban areas is increasingly used by shallow geothermal energy systems as a renewable energy resource and as a cheap cooling medium, e.g. for building air conditioning. In combination with further anthropogenic activities, this results in altered thermal regimes in the subsurface and the so-called subsurface urban heat island effect. Successful thermal management of urban groundwater resources requires understanding the relative contributions of the different thermal parameters and boundary conditions that result in the “present thermal state” of individual urban groundwater bodies. To evaluate the “present thermal state” of urban groundwater bodies, good quality data are required to characterize the hydraulic and thermal aquifer parameters. This process also involved adequate monitoring systems which provide consistent subsurface temperature measurements and are the basis for parameterizing numerical heat-transport models. This study is based on previous work already published for two urban groundwater bodies in Basel (CH) and Zaragoza (ES), where comprehensive monitoring networks (hydraulics and temperature) as well as calibrated high-resolution numerical flow- and heat-transport models have been analyzed. The “present thermal state” and how it developed according to the different hydraulic and thermal boundary conditions is compared to a “potential natural state” in order to assess the anthropogenic thermal changes that have already occurred in the urban groundwater bodies we investigated. This comparison allows us to describe the various processes concerning groundwater flow and thermal regimes for the different urban settings. Furthermore, the results facilitate defining goals for specific aquifer regions, including future aquifer use and urbanization, as well as evaluating the thermal use potential for these regions. As one example for a more sustainable thermal use of subsurface water resources, we introduce the thermal management concept of the “relaxation factor”, which is a first approach to overcome the present policy of “first come, first served”. Remediation measures to regenerate overheated urban aquifers are also introduced. The transferability of the applied methods to other urban areas is discussed. It is shown that an appropriate selection of locations for monitoring hydraulic and thermal boundary conditions make it possible to implement representative interpretations of groundwater flow and thermal regimes as well as to set up high-resolution numerical flow- and heat-transport models. Those models are the basis for the sustainable management of thermal resources.

Shallow geothermal resource exploitation through the use of groundwater heat pump systems not only has hydraulic and thermal effects on the environment but also induces physicochemical changes that can compromise the operability of installations. This study focuses on chemical clogging and dissolution subsidence processes observed during the geothermal re-injection of pumped groundwater into an urban aquifer. To explain these phenomena, two transient reactive transport models of a groundwater heat pump installation in an alluvial aquifer were used to reproduce groundwater-solid matrix interactions occurring in a surrounding aquifer environment during system operation. The models couple groundwater flow, heat and solute transport together with chemical reactions. In these models, the permeability distribution in space changes with precipitation-dissolution reactions over time. The simulations allowed us to estimate the calcite precipitation rates and porosity variations over space and time as a function of existent hydraulic gradients in an aquifer as well as the intensity of CO2 exchanges with the atmosphere. The results obtained from the numerical model show how CO2 exolution processes that occur during groundwater reinjection into an aquifer and calcite precipitation are related to hydraulic efficiency losses in exploitation systems. Finally, the performance of reinjection wells was evaluated over time according to different scenarios until the systems were fully obstructed. Our simulations also show a reduction in hydraulic conductivity that forces re-injected water to flow downwards, thereby enhancing the dissolution of evaporitic bedrock and producing subsidence that can ultimately result in a dramatic collapse of the injection well infrastructure.

Summary A frequency analysis of rainfall and flow from the available data and applications in Spain takes place. In the case of streamflow, various methods that can be grouped into two categories are used, (1) the gauged method which consist in the analysis of maximum flow rate annual series, and (2) the hydro-meteorological method which take into account processes with rainfall–runoff transformation models. The results are compared with observed data in historical series. Finally, six episodes with actual rainfall and flow record are analyzed. These episodes are also classified according to their frequency domain and results obtained from models are contrasted. To make this work we have used two applications launched in the University of Zaragoza: the SHEE program, which provides a simple and flexible working environment which allows the simultaneous management of the most actual and important databases from a hydrological point of view, highlighting the digital terrain models, the rainfall coverage and the curve number coverage, and that is suitable for the application of hydro-meteorological models; and the EHVE software, which is a hydrological statistical program for analysis of time series of extreme values, suitable for application in models of gauged data.

Summary Shallow aquifers have an important role in reducing greenhouse gases through helping manage the temperature of urban environments. Nevertheless, the uncontrolled rapid use of shallow groundwater resources to heat or cool urban environments can cause thermal pollution that will limit the long term sustainability of the resource. Therefore, there is a need for appropriate mitigation/remediation strategies capable of recovering energetically overexploited aquifers. In this work, a novel remediation strategy based on surface water recharge into aquifers is presented. To evaluate the capabilities of such measures for effective remediation, this strategy is optimized for a management problem raised in the overheated “Urban Alluvial Aquifer of Zaragoza” (Spain). The application of a transient groundwater flow and heat transport model under 512 different mitigation scenarios has enabled to quantify and discuss the magnitude of the remediation effect as a respond to injection rates of surface water, seasonal schedule of the injection and location of injection. The quantification of the relationship between these variables together with the evaluation of the amount of surface water injected per year in each scenario proposed have provided a better understanding of the system processes and an optimal management alternative. This work also makes awareness of the magnitude of the remediation procedure which is in an order of magnitude of tenths of years.

Summary The extraordinary rise of piezometric surface in aquifers may induce an unexpected interaction of groundwater with anthropogenic elements known as groundwater inundation phenomena. This could result in several damage processes, including building foundation destabilization, groundwater infiltration and pollutant remobilization, which are responsible for considerable economic losses worldwide. To improve our knowledge concerning flood-induced head wavefront propagation and groundwater inundation phenomena, the reconstructed kinematics of the head wavefronts obtained from a calibrated groundwater model simulating 12 ordinary flood events have been statistically analyzed. The correlation between kinematic variables of a flood-induced head wavefront, flood event characteristics and aquifer properties was the basis for the study of the aquifer response to river flood events along four different trajectories, i.e. the identification of river level rise rate, absolute–relative height of the maximum rise stage, hydraulic parameter variability, river–aquifer exchange rates, pre-event state of the aquifer and distance to the aquifer boundary as the key-influencing factors in groundwater inundation. Finally, model and scenario results were used to develop two synthetic models for groundwater inundation as novel decision-support tools for assessing both ordinary and extraordinary flood events in groundwater flood risk management and in urban development planning. These synthetic models gives the technical criteria to predict extraordinary rise of piezometric surface and therefore allows increasing the confidence of stakeholders in the risk assessment and improving the subsurface infrastructure design to mitigate damage processes derived from groundwater interaction.

Summary A methodology based on Parallel Linear Reservoir (PLR) models is presented. To carry it out has been implemented within the software SHEE (Simulation of Hydrological Extreme Events), which is a tool for the analysis of hydrological processes in catchments with the management and display of DEM and datasets. The algorithms of the models pass throughout the cells and drainage network, by means of the Watershed Traversal Algorithm (WTA) that runs the entire drainage network of a basin in both directions, upwards and downwards, which is ideal for incorporating the models of the hydrological processes of the basins into its structure. The WTA methodology is combined with another one based on models of Parallel Linear Reservoirs (PLR) whose main qualities include: (1) the models are defined by observing the recession curves of actual hydrographs, i.e., the watershed actual responses; (2) the models serve as a way to simulate the routing through the watershed and its different reservoirs; and (3) the models allow calculating the water balance, which is essential to the study of actual events in the watershed. A complete hydrometeorological event needs the combination of several models, each one of which represents a hydrological process. The PLR model is a routing model, but it also contributes to the adjustment of other models (e.g., the rainfall–runoff model) and allows establishing a distributed model of effective rainfall for an actual event occurred in a basin. On the other hand, the proposed formulation solves the rainfall distribution problem for each deposit in the reservoir combination models.

The skin effect is an important issue associated with a loss of hydraulic efficiency in pumping systems. In this paper, a comprehensive study is conducted to determine how the evolution of the skin effect over time affects the productivity and functionality of brine exploitation systems in a crystalline halite aquifer. Several double-packer system tests have been interpreted via groundwater modeling to hydrogeologically characterize the investigated aquifer. A numerical groundwater flow model that accounts for the heterogeneity of the multilayer halite aquifer and the transient well skin effect on the brine exploitation system is presented to explain the continuous drawdown during three months of constant-rate brine extractions. Numerical results obtained suggested that an exponential decay function of permeability over time was required in a wellbore skin zone to reproduce numerically experimental observations during brine exploitation. The empirical exponential function obtained specifically for this case study was generalized, and coefficients considered were discussed to infer their physical and geochemical dimensions related to the mixing process triggering heterogenous reactions responsible for the hydraulic loses. Our results will be useful for predicting the spatial and temporal losses of hydraulic efficiency and for evaluating the lifetimes of brine exploitation infrastructure. © 2019 Elsevier B.V., Personnel of the Sociedad Química y Minera de Chile (SQM) generously provided access to data, accommodations and logistical support in the field. The authors would like to extend gratitude to the associate editor and two anonymous reviewers for their valuable and constructive comments that led us to an improvement of the work.