The genesis and evolution of karstic conduit systems in the Chalk

The Upper Cretaceous Chalk Group is renowned as a major aquifer, but the development of secondary porosity due to karstic conduits is poorly understood. Hydrogeological data and evidence from boreholes, sections, and tracer tests indicate that dissolutional conduits occur throughout the Chalk aquifer. Here, we assess the evidence for Chalk karst, and combine it with theoretical models of dissolution and cave formation to produce a conceptual model for the development of karstic conduits. Dissolution due to the mixing of saturated waters of contrasting chemistry along key lithostratigraphical inception horizons form extensive but isolated conduit networks. These form a significant proportion of the secondary porosity and enhance permeability. They prime the aquifer for the development of more integrated conduit networks formed by focussed recharge of unsaturated surface derived water. However, the porous, well-fractured nature of the Chalk means that the time needed to form large integrated cave systems is often longer than timescales of landscape change. Continued landscape evolution and water table lowering halts conduit development before they can enlarge into cave systems except where geological and geomorphological settings are favourable. Groundwater models need to consider the formation of secondary karst permeability as this has a major influence on groundwater flow.

A physically-based distributed karst hydrological model (QMG model-V1.0) for flood simulations

Karst trough valleys are prone to flooding, primarily because of the unique hydrogeological features of karst landform, which are conducive to the spread of rapid runoff. Hydrological models that represent the complicated hydrological processes in karst regions are effective for predicting karst flooding, but their application has been hampered by their complex model structures and associated parameter set, especially so for distributed hydrological models, which require large amounts of hydrogeological data. Distributed hydrological models for predicting the Karst flooding is highly dependent on distributed structrues modeling, complicated boundary parameters setting, and tremendous hydrogeological data processing that is both time and computational power consuming. Proposed here is a distributed physically-based karst hydrological model, known as the QMG (Qingmuguan) model. The structural design of this model is relatively simple, and it is generally divided into surface and underground double-layered structures. The parameters that represent the structural functions of each layer have clear physical meanings, and the parameters are less than those of the current distributed models. This allows modeling in karst areas with only a small amount of necessary hydrogeological data. 18 flood processes across the karst underground river in the Qingmuguan karst trough valley are simulated by the QMG model, and the simulated values agree well with observations, for which the average value of Nash–Sutcliffe coefficient was 0.92. A sensitivity analysis shows that the infiltration coefficient, permeability coefficient, and rock porosity are the parameters that require the most attention in model calibration and optimization. The improved predictability of karst flooding by the proposed QMG model promotes a better mechanistic depicting of runoff generation and confluence in karst trough valleys.

3D Modelling of a Hydrothermal System in a Densely Populated Urban Area – the Alfama Springs Case-Study (Lisbon, Portugal)

In the XIX th century, the Alfama thermal and non-thermal springs were qualified as “mineral water” by the governmental authorities. But after a few years of legal usage in balneotherapy, all of them knew a constant and progressive definitive decay, and the last balneotherapic facility was abandoned and sealed more than 40 years ago. Despite their significant influence in Lisbon life along the History, their exact location is now only approximate. Nowadays, they are all buried below the city buildings, squares and streets. Since some of the Alfama springs reached temperatures up to 34 °C, groundwater from these springs can be used in a new modern spa or in district heating facilities in the heart of the city of Lisbon, if adequately recovered. But priorly, to carry out this task, a global understanding of the conceptual hydrogeological model is needed. However, the springs are located in a densely urbanized and touristic area, where geological outcrops are no longer visible and old springs’ location is unknown; therefore, a review of geological and hydrogeological data and geotechnical reports was carried out to plan further research works. Adding to this exhaustive bibliographic review and data integration, new seismic reflection data were acquired, and brought some new insights on the groundwater circulation system. All these data interpretations contributed significantly to achieve a better knowledge on the main and secondary faults that control the occurrence of Alfama springs and framed them into the complex regional tectonic framework. The entire set of historical hydrogeological data, geotechnical information, and newly acquired data lead to a reasonably accurate and data supported 3D geological and hydrogeological conceptual model of the deep groundwater flow circuit. This paper describes the research work that led to the conception of the local and complex 3D hydrogeological model of the Alfama springs system. With this 3D model, the best location for a dipped well can now be envisaged, keeping in mind the narrow local urban constraints, possible future users, and stakeholders.

Petroleum potential of the Riphean of the Siberian on hydrogeological data (on the example of the Kuyumbinskoe structure)

In the article, when considering the prospects of oil and gas potential of the Riphean strata in Siberia as indicators of oil content, special attention is paid to hydrocarbon gases in sorbed form. Sorbed hydrocarbon gases are still poorly used as indicators of oil content, although they have significant prerequisites for this. Some of them can be understood by reading this article.

Construction of 3D Discrete Fracture Network Model using Structural and Hydrogeological Data

<p>The presence of fractures and discontinuities in the intact rock affects the hydraulic, thermal, chemical and mechanical behavior of the underground structures. Various techniques have been developed to provide information on the spatial distribution of these complex features. LIDAR, for instance, could provide a 2D fracture network model of the outcrop, Geophysical borehole logs such as OPTV and ATV can be used to investigate 1D geometrical data (i.e. dip and dip direction, aperture) of the intersected fractures, and seismic survey can mainly offer a large structure distribution of the deep structures. The ability to combine all the existing data collected from various resources and different scales to construct a 3D discrete fracture network (DFN) model of the rock mass allows to adequately represent the physical behavior of the interested subsurface structure.</p><p>In this study, an effort on the construction of such a 3D DFN model is carried out via combination of various structural and hydrogeological data collected in fractured crystalline rock. During the pre-characterization phase of the In-situ Stimulation and Circulation (ISC) experiment [Amann et al., 2018] at the Grimsel Test Site (GTS) in central Switzerland, a comprehensive characterization campaign was carried out to better understand the hydromechanical characteristics of the existing structures. The collected multiscale and multidisciplinary data such as OPTV, ATV, hydraulic packer testing and solute tracer tests [Jalali et al., 2018; Krietsch et al., 2018] are combined, analyzed and interpreted to form a combined stochastic and deterministic DFN model using the FracMan software [Golder Associates, 2017]. For further validation of the model, the results from in-situ hydraulic tests are used to compare the simulated and measured hydraulic responses, allowing to evaluate whether the simulated model could reasonably represent the characteristics of the fracture network in the ISC experiment.</p><p> </p><p><strong>References</strong></p><ul><li>Amann, F., Gischig, V., Evans, K., Doetsch, J., Jalali, M., Valley, B., Krietsch, H., Dutler, N., Villiger, L., Brixel, B., Klepikova, M., Kittilä, A., Madonna, C., Wiemer, S., Saar, M.O., Loew, S., Driesner, T., Maurer, H., Giardini, D., 2018. The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment. Solid Earth 9, 115–137.</li> <li>Golder Associates, 2017. FracMan User Documentation.  Golder Associates Inc, Redmond WA.</li> <li>Krietsch, H., Doetsch, J., Dutler, N., Jalali, M., Gischig, V., Loew, S., Amann, F., 2018. Comprehensive geological dataset describing a crystalline rock mass for hydraulic stimulation experiments. Scientific Data 5, 180269.</li> <li>Jalali, M., Klepikova, M., Doetsch, J., Krietsch, H., Brixel, B., Dutler, N., Gischig, V., Amann, F., 2018. A Multi-Scale Approach to Identify and Characterize the Preferential Flow Paths of a Fractured Crystalline Rock. Presented at the 2<sup>nd</sup> International Discrete Fracture Network Engineering Conference, American Rock Mechanics Association.</li> </ul>

Hydrodynamic and hydrochemical evolution of the Bajo Guadalhorce Valley alluvial aquifer (Málaga, S Spain) in the last 40 years

<p>Groundwater flowing through coastal aquifers is increasingly impacted by human pressures as consequence of a growing demand on drinking water, tourism and agriculture, among others. Thus, groundwater availability very often depend on its quality since water salinization and pollution are the main challenges for water management because of seawater and freshwater interaction. Therefore, it is crucial to monitor the availability of groundwater and its quality under changing scenarios where this water resource can be specially threatened.</p><p>This study aims to assess the spatial distribution and time evolution of groundwater levels and hydrochemistry of the alluvial aquifer of the Bajo Guadalhorce Valley (Málaga, S Spain) for the evaluation of its quantitative and qualitative status. To that, groundwater level, electrical conductivity and Cl<sup>-</sup> and SO<sub>4</sub><sup>2-</sup> concentrations of water have been measured in a field sampling campaign carried out in the alluvial aquifer of the Bajo Guadalhorce Valley (Málaga, S Spain) in April 2017. Additionally, historical data from the last 40 years have been compiled.</p><p>Results show that groundwater generally flow towards the Guadalhorce River, where gaining relationship remains more patent in its lower river stretch, and the Mediterranean Sea. Some negative groundwater elevations close to the coastal fringe are observed in several piezometers because of pumping during the study period. Electrical conductivity values were, generally, lower than 4 mS/cm in all samples and the major changes in groundwater mineralization were determined in the Guadalhorce River Mouth. In this aquifer sector, substantial increases in groundwater mineralization were identified, up to 50% in some observation points. Cl<sup>-</sup> and SO<sub>4</sub><sup>2-</sup>concentrations in groundwater (the more concentrated solutes of all) evolve similarly in time to that of electrical conductivity, with maximum recorded values up to 10000 mg/l and 2000 mg/l, respectively, the coastal area in 2017.</p><p>Changes in EC and Cl<sup>-</sup> and SO<sub>4</sub><sup>2-</sup> concentrations in the river mouth area could be related to the land use changes that took place here between 1997 and 2003, where channelization works resulted in the splitting of the river in two branches. This could have affected to the aquifer hydrodynamics, due to the reduced groundwater discharge to the river mouth area between both branches. This could have favored the mixing among surface water, sea water and groundwater. Also, the urbanized area has increased over the years, reducing the recharge area of this part of the aquifer, but also flowing groundwater has increased because of pumping reduction (up to 7 hm<sup>3</sup>/year). The presence of Cl<sup>- </sup>in the aquifer, as well as SO<sub>4</sub><sup>2-</sup>, is due to evaporite dissolution and the interaction with the Mediterranean Sea in the coastal area. An extra input of SO<sub>4</sub><sup>2-</sup> comes from of the fertilizers used in agriculture.</p><p>The availability of long-term hydrogeological data in a coastal aquifer (1976-2017) has allowed to check a remarkable salinization in the coastal area, caused by land use modifications. So, the monitoring of hydrogeological data is a very important tool to be used by land managers in coastal aquifers, where groundwater can be seriously endangered by human activities.</p>

KARST ROCKY DESERTIFICATION ANALYSIS BASED ON HISTORICAL DISP DATA TAKE TWO REGIONS FOR EXAMPLE

Karst rocky desertification (KRD) is used to characterize the processes that transform a karst area covered by vegetation and soil into a rocky landscape almost devoid of soil and vegetation. This situation seriously affects and threatens the living environment and standards of local people, which results in a series of social problems. In view of the importance and harmfulness of KRD, many scholars have studied the spatial and temporal evolution of KRD and its driving forces. In this paper, the Visual Interpretation Marks of Rocky Desertification in Southwest China in 1960s are constructed by using the DISP image of the United States, combined with DEM data and Hydrogeological data. The area of rocky desertification in Guangnan and Funing counties, where rocky desertification is more serious, is about 2457.729 km2. The area of rocky desertification can be used as the basic data for studying the historical changes in southwestern China by researchers.