9:00am - 9:15am
Measurement of Diffuse Submarine Groundwater Discharge at intertidal puddles at the Königshafen - Sylt
1ZMT, Germany; 2UFZ, Germany; 3CAU Kiel, Germany
Coastal regions represent a transition between land and sea. From the hydro(geo)logical point of view freshwater and saltwater are coming together here. The groundwater discharge which discharges directly into the sea is called submarine groundwater discharge (SGD). At the regional scale, SGD is often measured indirectly based on tracers. At the local scale, SGD flux over time can be measured directly, e.g. using seepage meters. However, this method only represents the punctual source of discharge. Especially to record the diffusive discharge locations, a new method which focuses on the puddles in intertidal areas as potential diffusive discharge locations was developed. There, the salinity and water depth were observed at different puddle locations over time. Moreover, photos were taken in order to get information about the changing area of the puddle. From these data we calculated a water budget to show how much submarine groundwater discharges at the measured puddle. The results show a geographically and temporal variability of the SGD in the mudflat of the south of Königshafen on Sylt. The diffusive discharge locations were primarily located at the beginning of the intertidal zone. In order to support the new method, two additional pore water measurements were conducted at each puddle. The salinity of the pore waters were freshening with increasing depth here. The presented method can help to transfer the observed data of SGD to a regional scale.
9:15am - 9:30am
Towards identifying scale-dependent impacts on groundwater level dynamics with Deep Learning
1Climate Service Center Germany (GERICS), Helmholtz-Zentrum Hereon, Hamburg, Germany; 2Universität Hamburg, Institute of Geology, Hamburg, Germany
Detailed process-understanding of climatic and non-climatic drivers is generally required to estimate future groundwater availability under climate change. Groundwater level (GWL) dynamics are very sensitive to groundwater pumping, but information on their local effects and magnitude – especially in combination with natural fluctuations – is often missing or inaccurate. It has been shown by previous studies that complex hydrogeological processes can be learned from neural networks, whereby Deep Learning (DL) demonstrates its strengths particularly in combination with large data sets. However, there are limitations in the interpretability of the predictions and the transferability with such methods. Furthermore, most groundwater data are not yet ready for data-driven applications. This study aims at improving GWL predictions with DL by combining big data elements from a newly constructed global groundwater database with long-term short-term memory (LSTM) networks. Our underlying hypothesis is that scale-dependent processes can be learned for groundwater dynamics, similar to streamflow data. For our experiments we use continuous groundwater level observations from basins worldwide and basin attributes – spatially heterogeneous but temporally static catchment attributes (e.g. topography) and continuous observations of the meteorological forcing (precipitation and temperature). The initial results are consistent with previous studies in that GWL prediction performance is good with LSTM models trained with climate input on single wells. It is now being tested whether the LSTM model trained on many wells simultaneously is able to represent the climatic effects - but not the anthropogenic effects, e.g. with wells that are considered to be anthropogenically unaffected.
9:30am - 9:45am
Optimized coverage of potash tailings piles
Forschungsinstitut für Bergbaufolgelandschaften e.V. Finsterwalde; Humboldt-Universität zu Berlin, Germany
Saline contaminants from potash mining endanger aquatic ecosystems. Uncovered potash tailings piles release high amounts of chloride and sodium. Conventional coverage systems with a transpiration-intensive vegetation on a soil layer reduce percolation water only to some extent and does not protect the surrounding environment sufficiently. Powerful sealing layers are used to cover other mining deposits, but are still uncommon for potash tailings piles. In this paper, I study how to complement conventional coverage with additional sealings to minimize the release of contaminants effectively. I investigate a yet uncovered potash tailings pile in Germany. I model water balance parameters and calculate percolation rates for 44 different coverage systems. The results show that sealings always outperforms (max. 24.8 % of P) conventional coverage without an additional sealing (26.5 % of P). Site-specific coverage reduces percolation water more than uniform coverage and requires less layer material. A sealing works best on slopes with a northern orientation, soil cover systems perform better on southern slopes. I conclude that site-specific coverage systems are most effective to improve water quality in post-mining landscapes.
9:45am - 10:00am
China’s future as a low carbon economy: The Chinese hard coal industry & renewable energies in perspective
Technische Hochschule Georg Agricola University, Germany
With the recently announced climate neutrality for the year 2060, there are plenty of questions in China about the future and the existence of the hard coal mining industry. With an annual production of 4 billion tons of hard coal, China remains the biggest producer of this resource. The consequences for the environment are tremendous. Climate neutrality poses new challenges for this country with its abundance of resources: hard coal is still the easiest and safest way to guarantee the supply of energy to its citizens, whereby energy security is a high priority. The switch to and the integration of renewable energies has already started and, according to the latest 14th five-year plan, should become the main driver of growth in the coming years. The transition to green development with a low carbon economy as one of the most important objectives is imminent. These developments will have a decisive impact on the next few years and will drive structural change forward. Since China also has large reserves of rare earths, which are required in particular for the construction of regenerative energy options. But here, too, only one environmental problem is shifted to the next, since the recycling of rare earths has not yet been developed and the sustainability factor is a big question mark. What impact this will have in terms of sustainability and environmental protection is identified in the research project.
10:00am - 10:15am
Numerical modeling of the stress state around the Enguri power tunnel
1Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences, Technical Petrophysics, Germany; 2Piewak & Partner GmbH, Germany; 3Georgian Technical University, Hydraulic Department, Georgia
The Enguri Dam in NW Georgia is one of the highest arch dams in the world. The 15 km power tunnel was initially flooded in 1978. During the rehabilitation project from January - April 2021, an 40 m long open construction-joint was observed. The construction-joints are located on both sides in the lower third of the tunnel, but only the construction-joint on the valley side showed an opening character.
The research question of the paper was whether the preferential opening of this joint can be explained by rock stresses.
The approach is based on the comparison of a numerical calculation of the stress-state with the observed cracks (recorded in April 2021) in the tunnel section at km 13.7, using a static, linear elastic 2D model with homogeneous material (limestone) with a variable FE-mesh. The initial stress-state is created via a lateral shortening at the valley side of the model in combination with gravitation.
The results show a symmetrical distribution of tensile and compressive stresses around the power tunnel, with the axis of symmetry tilted by about 30°. This results in tangential tensile stresses on the downslope side in the region of the construction-joint, while compressive stresses are expected in the section of the upslope construction-joint.
It has been shown that the initial stress-state is an important parameter for the positioning and design of the power tunnel. Furthermore, the topography can result in tilting of the stress field, which must be considered in the interpretation of observed fractures in the tunnel.
10:15am - 10:30am
Hydrothermal Synthesis of Low Layer Charge Trioctahedral Smectite
1Competence Center for Material Moisture (IMB-CMM), Karlsruhe Institute of Technology; 2Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology
Smectites are widely used in (geo-) technical applications and are important components of soils. A definition gap exists between the uncharged non-swellable pyrophyllite and talc (ξ = 0) and the low charged swellable clay minerals (smectites) with 0.2 ≤ ξ ≤ 0.6. Furthermore, no reliable measurement method exists for ξ < 0.2. A recent theoretical study on the hydration of smectites (Emmerich et al. 2018) based on the density functional theory (DFT) indicates the existence of stable dioctahedral 2:1 layer silicates with ξ < 0.2 and substitutions either in the tetrahedral or octahedral sheet that are swellable. Therefore, our focus is to synthesize low charged smectites.
The Na2O-MgO-Al2O3-SiO2-H2O system was reacted for triocthedral smectite synthesis at 200℃, for 72 h, and with stoichiometric composition corresponding to ideal layer charge of 0.18. The XRD results showed that the synthesis of trioctahedral smectite was successful with a small particle size. Particle size will be confirmed by AFM measurements. The CEC indicates a low charge in the envisaged range. According to the principle of AAM method (Lagaly. 1981), under ideal assumptions, when the layer charge value is less than 0.2, the long-chain alkylammonium ions will only form a monolayer structure (basal spacing <17.7 Å) after being intercalated into the smectite layer, which can also be proved by measuring the d001 value of synthetic smectite. Similar results obtained through our experiments.
Emmerich et al. (2018) The Journal of Physical Chemistry C 122, 7484−7493.
Lagaly. (1981) Clay Minerals. 16, 1-21.