Subsurface Water System Research Articles

Groundwater dynamics on small carbonate islands: Insights from radiocarbon and stable isotopes in Kikai Island, Southwest Japan

Groundwater, the world's largest freshwater resource, faces significant challenges due to the overexploitation and depletion of aquifers in the 21st century. Small island groundwater aquifers are particularly valuable, and a scientific understanding of the behavior of subsurface water systems is vital. A comprehensive study using radiocarbon, stable oxygen isotopes, stable hydrogen isotopes, and hardness analysis (Δ14C, δ18O, δD, Ca, Mg) of groundwater was conducted in Kikai Island, a southern island in the Amami archipelago, Japan. The geological features and small size of the island make it an ideal location for assessing groundwater recharge and discharge relationships. Groundwater dynamics were investigated using samples collected seasonally from 15 points around the island (wells, springs, and an underground dam). Δ14C results indicated that despite considerable differences in precipitation, spatial variations were more prominent than seasonal variations, suggesting the presence of a large groundwater reservoir. The stable isotopes and hardness values, commonly used to detect groundwater dynamics, did not provide clear evidence to support this trend for the study site, a low-lying small island. However, the combination of deuterium excess (d-excess) values with radiocarbon analysis has the potential to provide a better understanding of groundwater flow. This study further illustrates that a combined approach utilizing Δ14C, δ18O, δD, and hardness levels can yield invaluable insights into groundwater dynamics. Considering geomorphic and geological features, groundwater in Kikai Island was categorized into five groups, providing insights into spatial groundwater flow. Results of this study indicate that the use of 14C allows the detection of groundwater movement with a high dynamic range and increased sensitivity, deepening our understanding of the diverse carbon sources that influence the groundwater system. Insights from this study are especially important for the efficient water management in comparable small carbonate islands and for tackling issues associated to overexploitation, pollution, and water scarcity.

Application of remote sensing and gis to identify the vulnerability of ground-water pollution in topograhic karst

Karst or limestone is a landscape in the form of unique. Karst or limestone has sensitive properties and is easily dissolved in water so that the karst topography has a subsurface water system in the form of holes that are susceptible to degradation due to the very fast flow of water so that it is easy to pass water underground. The purpose of this study was to determine the level of vulnerability of karst underground water pollution based on remote sensing data and GIS in the Rengel-Tuban Indonesia karst region. This type of research is quantitative research. Data analysis techniques in this study used image interpretation and logistic regression tests. The researched result is known that Remote sensing imagery and GIS as a tool to identify the level of vulnerability of underground water pollution in the karst region. Utilization of remote sensing imagery and GIS is presented as information of vulnerability of underground water pollution, and the study showed that the average area of karst Rengel was classified as vulnerable to pollution. In conclusion that the average area study was classified as vulnerable to pollution, and the Rengel karst hills are in line with local levels of vulnerability and pollution

Mapping Groundwater Potential Zone and Flood Risk Zone in the Visakhapatnam District, India.

Groundwater is a vital resource that significantly contributes to the annual supply. On the other hand, Overexploitation has resulted in a significant reduction in groundwater supplies and, in some cases, soil sinking. Therefore, it’s critical to assess the possible zone of groundwater rejuvenation to safeguard water quality and manage subsurface water systems. Potential groundwater zones are detected using RS and GIS technologies. GIS technologies were used to build the composite map. Accurate data is required to determine the criteria used to estimate the potential groundwater zone. DEM, soil, Rainfall, and LULC data are all generated by the satellites, and, at a scale of 1:50000, topo sheets are collected from the Survey of India (SOI). All the input data is combined with a weighted overlay in ArcGIS. Each of these criteria is given an appropriate ranking. The ability of various geomorphic units to store groundwater is assigned weight values. This procedure is repeated for each of the remaining layers, with the resulting layers being categorized. Extremely poor, poor, moderate, good, and exceptional are the five categories of potential groundwater zones. The method is used in a particular research area in the Visakhapatnam district. This data will help you figure out where you can get water, where water can be recharged, and where groundwater is limited.

Deep-learning-based workflow for boundary and small target segmentation in digital rock images using UNet++ and IK-EBM

Three-dimensional (3D) X-ray micro-computed tomography (μCT) has been widely used in petroleum engineering because it can provide detailed pore structural information for a reservoir rock, which can be imported into a pore-scale numerical model to simulate the transport and distribution of multiple fluids in the pore space. The partial volume blurring (PVB) problem is a major challenge in segmenting raw μCT images of rock samples, which impacts boundaries and small targets near the resolution limit. We developed a deep-learning (DL)-based workflow for accurate and fast partial volume segmentation. The DL model's performance depends primarily on the training data quality and model architecture. This study employed the entropy-based-masking indicator kriging (IK-EBM) to segment 3D Berea sandstone images as training datasets. The comparison between IK-EBM and manual segmentation using a 3D synthetic sphere pack, which had a known ground truth, showed that IK-EBM had higher accuracy on partial volume segmentation. We then trained and tested the UNet++ model, a state-of-the-art supervised encoder-decoder model, for binary (i.e., void and solid) and four-class segmentation. We compared the UNet++ with the commonly used U-Net and wide U-Net models and showed that the UNet++ had the best performance in terms of pixel-wise and physics-based evaluation metrics. Specifically, boundary-scaled accuracy demonstrated that the UNet++ architecture outperformed the regular U-Net architecture in the segmentation of pixels near boundaries and small targets, which were subjected to the PVB effect. Feature map visualization illustrated that the UNet++ bridged the semantic gaps between the feature maps extracted at different depths of the network, thereby enabling faster convergence and more accurate extraction of fine-scale features. The developed workflow significantly enhances the performance of supervised encoder-decoder models in partial volume segmentation, which has extensive applications in fundamental studies of subsurface energy, water, and environmental systems.

Spatial variation of saturated hydraulic conductivity in a riparian zone: A case study of the Baoan Lake in Hubei Province, China

Saturated hydraulic conductivity (Ks, [L T−1]) is an important physical property of soil in riparian zones that influences water and solutes exchange between surface and subsurface water systems. Spatial variation of Ks should be considered in the assessment of its effects on the interaction of surface and subsurface waters in riparian zones. In this study, 133 disturbed and 399 undisturbed soil samples were collected from the riparian zones of the Baoan Lake in Hubei Province, China. Spatial distribution patterns of Ks in rural riparian zones were determined, and their variabilities were analyzed to understand the influences of soil, land use, vegetation, hydrological, and geological factors. The spatial variations of Ks indicated the following: (1) the mean Ks value decreased with soil depth in the riparian zone; (2) Ks values showed increasing and fluctuating patterns in the lateral direction of the lakeshore; (3) the study region was divided into high-, medium-, and low-permeability areas; and (4) Ks values of influent tributaries decreased from upstream to downstream reaches in the periodic inundation zone (Zone 1), whereas the effluent tributary exhibited the opposite trend. Permeabilities were low at the confluences of the lake and its tributaries compared to that of the other reaches of the same tributaries. Riparian soil displayed fast to slow infiltration patterns between 0–20 cm and 20–40 cm soil layers. The degree of vertical variation caused by the periodic inundation of water was smaller. Permeability based on land use decreased in the order of farmland, forests, and fishponds. Studying the permeation of riparian zones and associated ecosystems provides a scientific basis for their comprehensive management and efficient utilization, and this work provides a framework for the same through a case study.

Modeling Unsaturated Zone Water Movement in the Floodplain Wetlands of the Volta Basin

The unsaturated zone of floodplain wetlands in the White Volta River basin provides an inextricable link between basin hydrology and the sustenance of plant growth. The HYDRUS-1D model was used to derive water budgets and to estimate fluxes to understand the hydrological complexities of these wetland systems. The model result indicates Spatio-temporal variation in the volume of vertical fluxes. In 2005, the estimate for average simulated flux was 0.29 cm/month in June and 1.23 cm/month in July. Consequently, the hydraulic head increased from 138.94 m to 139.30 m for the period from June to July 2005. For all sample sites, the increase in hydraulic head occurs within July and October, coinciding with high surface water fluxes. From the calculated water balance, the average monthly estimate of bottom flux was 0.01 cm/month for 2004 and 1.1 cm/month for 2005. The flow through the unsaturated zone and discharging into the subsurface water system has a high dependency on both the soil structure and the volume of water infiltrating through the surface; the highest discharge is within the period of highest water input.

The “badland trilogy” of the Desierto de la Tatacoa, upper Magdalena Valley, Colombia, a result of geodynamics and climate: With a review of badland landscapes

The badlands of the “Desierto de la Tatacoa” (DDT) form part of the alluvial-fluvial system and are characterized by a landform trilogy: (1) gully zone, (2) wadi zone, (3) hillwash plain/mesa zone. This facies differentiation is controlled by the fluvial regimes and their degree of sinuosity of channels. The hydraulic and hydrographic systems of the badland trilogy depend on the geodynamic setting and climate (1st order) and on the bedrock lithology and tectonics (2nd order). Allogenic heavy minerals attest to two counteracting palaeogradients which interdigitate where the badlands evolved and authigenic heavy and light minerals furnish evidence of the physical-chemical regime to be governed by alkaline meteoric solutions and oxidizing conditions driven by the climate and the parent rocks. It is the high solubility of sulfates and chlorides and the differential expandability of smectite which impacted on the development of the individual badland zones. Large 1st order synclines plunging to the W and 2nd order fold structures account for the traps and conduits of the subsurface water system. The key to the hydraulic evolution of the badland lies within the hinterland hampering surface alteration and favoring the subsurface hydrogeological system to corrode the gully zone from below. The binary genetic model of the badlands in the DDT reveals, on a local scale, a “fight for dominance” of different fluvial drainage systems at the edge of the badlands as a hydrological consequence of neotectonics while, on a regional scale, badland formation is an upstream expression of a eustatic sea level oscillation in the Caribbean Sea. A review of true, false and pseudo-badlands concludes the study and underscores the reference character of the DDT badlands among the true badland series.

Quantifying fate and transport of nitrate in saturated soil systems using fractional derivative model

Natural soil systems usually exhibit complex properties such as fractal geometry, resulting in complex dynamics for the movement of solutes and colloids in soils, such as the well-documented non-Fickian or anomalous diffusion for contaminant transport in saturated soils. The development of robust mathematical models to simulate anomalous diffusion for reactive contaminants at all relevant scales presents a contemporary problem in computational hydrology. This study aims to develop and validate a novel fractional derivative, advection-dispersion-reaction equation (fADRE) with first order decay to quantify nitrate contaminants transport in various soil systems. As an essential nutrient for crop growth, nitrogen in various forms (i.e., fertilizers) is typically applied to agricultural plots but a certain fraction or excess that is converted to nitrate or nitrite will serve as a critical pollutant to surface-water and groundwater. Applications show that the fADRE model can consider both hydrological and biogeochemical processes describing the fate and transport of nitrate in saturated soil. Here “fate” is a commonly used terminology in hydrology to describe the transformation and destination of pollutants in surface and subsurface water systems. The model is tested and validated using the results from three independent studies including: (1) nitrate transport in natural soil columns collected from the North China Plain agricultural pollution zone, (2) nitrate leaching from aridisols and entisols soil columns, and (3) two bacteria (Escherichia coli and Klebsiella sp.) transport through saturated soil columns. The qualitative relationship between model parameters and the target system properties (including soil physical properties, experimental conditions, and nitrate/bacteria physical and chemical properties) is also explored in detail, as well as the impact of chemical reactions on nitrate transport and fate dynamics. Results show that the fADRE can be a reliable mathematical model to quantify non-Fickian and reactive transport of chemicals in various soil systems, and it can also be used to describe other biological degradation and decay processes in soil. Hence, the mathematical model proposed by this study may help provide valuable insight on the quantification of various biogeochemical dynamics in complex soil systems, but needs to be tested in real-world applications in the future.

Using tritium and 222Rn to estimate groundwater discharge and thawing permafrost contributing to surface water in permafrost regions on Qinghai-Tibet Plateau

On the Qinghai-Tibet Plateau, permafrost degradation and associated release of permafrost meltwater has undoubtedly modified the annual and seasonal streamflow patterns and influenced groundwater conditions. However, it is still unclear how extensively permafrost degradation has influenced surface and subsurface water systems due to very sparse observations. Isotope mass models combining tritium and 222Rn measurements are developed here to quantify the contributions of groundwater discharge and thawing permafrost to rivers and lakes in the Source Area of the Yellow River. Results demonstrate the spatial variability of permafrost thaw impacts and confirm significant influence on surface and subsurface runoff processes including effects on water yield capacity and water drainage connectivity. While results to date are conclusive, further work to refine the method and extend observations is warranted.

Hydrological insights from hydrogen and oxygen isotopes in Source Area of the Yellow River, east-northern part of Qinghai–Tibet Plateau

Analyses of stable (D and 18O) and radioactive (T) isotopes of different waters were applied to obtain the hydrological information in watersheds with different frozen ground types in the Source Area of the Yellow River, northeastern of Qinghai–Tibet Plateau in 2014 and 2016. Variations of oxygen and hydrogen isotope ratios, statistically higher tritium concentrations and lower water yields in thaw lakes confirm disparate sources of recharges to thaw lakes and other lakes. Thaw lakes at various stages of evolution influence the surface and subsurface water systems differently.

Understanding the water balance paradox in the Athabasca River Basin, Canada

AbstractThis study demonstrates the importance of the including and appropriately parameterizing peatlands and forestlands for basin‐scale integrated surface–subsurface models in the northern boreal forest, with particular emphasis on the Athabasca River Basin (ARB). With a long‐term water balance approach to the ARB, we investigate reasons why downstream mean annual stream flow rates are consistently higher than upstream, despite the subhumid water deficit conditions in the downstream regimes. A high‐resolution 3D variably saturated subsurface and surface water flow and evapotranspiration model of the ARB is constructed based on the bedrock and surficial geology and the spatial distribution of peatlands and their corresponding eco‐regions. Historical climate data were used to drive the model for calibration against 40‐year long‐term average surface flow and groundwater observations during the historic instrumental period. The simulation results demonstrate that at the basin‐scale, peatlands and forestlands can have a strong influence on the surface–subsurface hydrologic systems. In particular, peatlands in the midstream and downstream regimes of the ARB increase the water availability to the surface–subsurface water systems by reducing water loss through evapotranspiration. Based on the comparison of forestland evapotranspiration between observation and simulation, the overall spatial average evapotranspiration in downstream forestlands is larger than that in peatlands and thus the water contribution to the stream flow in downstream areas is relatively minor. Therefore, appropriate representation of peatlands and forestlands within the basin‐scale hydrologic model is critical to reproduce the water balance of the ARB.

Groundwater Modeling Under Variable Operating Conditions Using SWAT, MODFLOW and MT3DMS: a Catchment Scale Approach to Water Resources Management

This paper presents an integrated modeling approach by linking soil and water application tool (SWAT), modular finite difference groundwater flow (MODFLOW) and modular 3-dimensional multi-species transport (MT3DMS) models capable of predicting a groundwater system response, in terms of flow and salt concentrations, to current and future development conditions. SWAT, a semi-distributed hydrologic model, estimates the spatio-temporal distribution of groundwater recharge rates. These rates are then input to MODFLOW using an interface module developed that maps the HRU-based spatial resolution of SWAT outflows into the cell-based spatial structure of inputs to MODFLOW and MT3DMS. The integrated SWAT-MODFLOW-MT3DMS model is used in modeling Dehloran aquifer system located in the arid western region of Iran, experiencing changes in land-use, irrigation system and pumping locations and loads. The results illustrate the significance of the developed integrated modeling tool in quantifying the impact of changes in land and surface water resources on its subsurface water system.

Lateral hydraulic performance of subsurface drip irrigation based on spatial variability of soil: Simulation

Soil physical properties (initial water content, bulk density, and mass fractal dimension) have a major influence on subsurface drip capillary water systems. The spatial distribution of lateral hydraulic performance varies along with the spatial variability of soil and is thus highly complex. In this paper, initial soil water content, soil bulk density, and mass fractal dimension generated according to a Gaussian distribution were used as input variables to a nonlinear lateral hydraulic mathematical model of subsurface drip irrigation. The numerical simulation indicated the following. 1) The greater the initial moisture content, soil bulk density and mass fractal dimension, the smaller was the lateral distribution of emitter discharge, and the smaller was the deviation rate of lateral flow. 2) The greater the standard deviation of initial moisture content, soil bulk density, and mass fractal dimension, the higher was the deviation rate of lateral flow, and the more laterally dispersed was the emitter discharge. 3) The greater the initial moisture content, soil bulk density, mass fractal dimension, and inner lateral diameter, the greater was the uniformity of lateral flow; The higher the inlet lateral pressure and emitter spacing, the lower was the uniformity of lateral flow; The uniformity of lateral flow increased with slope in the range −0.0003 to 1 and decreased with the increase of slope in the range 0–0.0005. The improved lateral hydraulic model by taking into account the influence of soil physical properties on subsurface drip capillary water systems, which permits identification of the critical points of the irrigation lateral

Spatial Optimization of Monitoring Networkson the Examples of a River, a Lake-Wetland System and a Sub-Surface Water System

Monitoring systems in general have to meet numerous requirements, the most important of which are representativeness and cost efficiency. The aim of the study, therefore, was to present the spatial optimization of the monitoring networks of a river (the Danube), a wetland-lake system (Kis-Balaton & Lake Balaton), and a sub-surface water system in the watershed of Lake Neusiedl/Fertő over a period of approximately two decades using a novel method, Combined cluster and discriminant analysis (CCDA). In the case of the river the results show that the monitoring network yields redundant information on certain sections, so that of 12 sampling sites 3 can be discarded. It was not, however, enough to consider just the tributaries when it comes to optimization. In the case of the wetland (Kis-Balaton) one pair of sampling sites out of 12, while in the case of Lake Balaton 5 out of 10 can be abandoned. For the sub-surface water system, however, all the 50 sites contained exclusive information; hence, all of these were shown to be necessary. In addition, neighboring sampling sites were compared pairwise using CCDA and the corresponding results were visualized in diagrams or so called “difference maps” indicating the location of the biggest differences. This approach also indicates the researcher where to place new sampling sites should the possibility arise. The discussed methodology proved to be highly useful in the optimization of the monitoring networks of the presented water systems.

Improved simulation of river water and groundwater exchange in an alluvial plain using the SWAT model

Hydrological interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The soil and water assessment tool (SWAT) model is a semi-distributed model that has been successfully applied around the world. However, it has not been able to simulate the two-way exchanges between surface water and groundwater. In this study, the SWAT-landscape unit (LU) model – based on a catena method that routes flow across three LUs (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT-LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water-level simulation during flooding periods was modified, and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT-LUD was compared with the output of a two-dimensional distributed model, surface–subsurface water exchange model. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT-LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface–groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river; water that flowed in this direction accounted for 65% of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the surface–subsurface water exchange process; it accounted for 69% of total water that flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale.

Impact of longwall mining on groundwater above the longwall panel in shallow coal seams

Since longwall mining causes subsidence through the overlying strata to the ground surface, the surface water and groundwater above the longwall panels may be affected and drained into the lower levels. Therefore, loss or interruption of streams and overburden aquifers is a common concern in coal industry. This paper analyzed the potential effects of longwall mining on subsurface water system in shallow coal seam. In order to monitor different water level fluctuations throughout the mining period, three water wells were drilled down to the proposed deformation zone above the longwall panel. A GGU-SS-FLOW3D model was used to predict water table contours for the periods of pre- and post-mining conditions. The field data from the three water wells were utilized to calibrate the model. The field test and numerical model can help to better understand the dewatering of shallow aquifers and surface waters related to ground subsidence from longwall mining in shallow coal seam.

A Fuzzy Inference System for the Conjunctive Use of Surface and Subsurface Water

This study develops the water resources management model for conjunctive use of surface and subsurface water using a fuzzy inference system (FIS). The study applies the FIS to allocate the demands of surface and subsurface water. Subsequently, water allocations in the surface water system are simulated by using linear programming techniques, and the responses of subsurface water system with respect to pumping are forecasted by using artificial neural networks. The operating rule for the water systems is that the more abundant water system supplies more water. By using the fuzzy rule, the FIS conjunctive use model easily incorporates expert knowledge and operational polices into water resources management. The result indicates that the FIS model is more effective and efficient when compared with the decoupled conjunctive use and simulation-optimization models. Furthermore, the FIS model is an alternative way to obtain the conjunctive use policies between surface and subsurface water.

An Integrating Approach for Conjunctive-Use Planning of Surface and Subsurface Water System

This study proposes an integrated approach to assess the performance of a conjunctive-use surface and subsurface water system. System dynamics serves as the main framework of the proposed conjunctive-use model, simulating the interaction between surface and subsurface water and the impact of various conjunctive-use alternatives on the system as a whole. This study assumes natural groundwater recharge as a water source to the system, and estimates its volume using geographic information system (GIS) tools, a groundwater simulation model (MODFLOW), and a parameter identification model (UCODE). This study assesses various conjunctive-use alternatives and analyzes the frequency of water shortage to illustrate how the recharge rate affects water supply reliability under the conjunctive-use framework. Simulation results indicate that conjunctive-use with artificial recharge indeed reduces the frequency of extreme water shortages. Results also reveal that artificial recharge is necessary to maintain groundwater conservation without overusing river flow. Although this study focuses on southern Taiwan, the proposed concepts and procedure are applicable to other areas with a similar conjunctive-use framework.

Biogeochemistry of subsurface geothermal water system in the Hishikari gold mine

Biogeochemistry of subsurface geothermal water system in the Hishikari gold mine

Long‐term development of phosphorus and nitrogen loads through the subsurface and surface water systems of drainage basins

We analyze and compare simulations and controlling processes of the past 60 years and possible future short‐ and long‐term development of phosphorus and nitrogen loading from the Swedish Norrström drainage basin to the Baltic Sea under different inland source management scenarios. Results indicate that both point and agricultural source inputs may need to be decreased by at least 40% in order to reach a long‐term sustainable 30% reduction of anthropogenic coastal nitrogen loading, as required by national environmental goals. A corresponding 20% anthropogenic phosphorus load reduction goal may be reached in the short term by analogous combined 40% source input reduction, but appears impossible to maintain as a long‐term achievement by inland source abatement only. In general, realistic quantification of the slow subsurface nutrient transport and accumulation‐release dynamics may be essential for accurately predicting and managing nutrient loading to surface and coastal waters.