Groundwater Level Changes Research Articles

Impact of artificial recharge on groundwater and springs: Jinan, China, case study

Baotu spring, known widely as the most famous spring in China, has experienced continuous water level drops, especially during the dry season. Artificial recharge (AR) to groundwater via the Yufu river has been conducted to maintain the required water level to keep regional springs flowing. The purpose of this study is to evaluate the effects of recharge on groundwater. A three-dimensional numerical model was built to simulate groundwater level changes after recharge was applied to the Yufu river. The model was calibrated using hydraulic heads measured at multiple monitoring wells. The results showed that AR is an effective way to maintain the groundwater level in a region where groundwater was excessively exploited for irrigation and industry use. In the studied region, the response of groundwater level to AR near the Yufu river was faster in the west than that in the east as a result of different hydrogeologic conditions. Furthermore, different springs responded differently to AR. For example, the water level increases at the Baotu and Heihu springs were 0.06 m and 0.04 m, respectively, whereas other springs experienced decreases. This implies that a more detailed hydrogeologic characterization is necessary to determine the preferential flow paths and low permeability layers in order to maximize the effect of AR for sustainable groundwater management.

Assessment of the impact of clear-cutting on groundwater regime in swampy habitats

The aim of the study was evaluation of clear-cutting effect on water regime in a tree harvesting area. The results were made based on the study carried out in the Rakowski Ditch catchment, in Wielkopolska lowland in Poland. It was found that a more useful method to establish the effects of clear-cutting is to compare the groundwater level (GWL) in the post-clear-cutting area with that in a control area than to analyse the GWL changes in the same area before and after the clear-cutting. Regression analysis is a particularly useful tool in groundwater regime analyses. The results obtained in this study indicated that the groundwater regime changes in the post-clear-cutting area that were manifested as an increase in the mean GWL. The major changes in the groundwater regime after clear-cutting were observed in the minimum levels, while the lowest changes took place in the maximum GWL. The variation in GWL was higher in the period after clear-cutting than in the period before it. The analysis of linear regression of GWL in the well located in the clear-cutting area and that in the control area confirmed the change in the groundwater regime in the post-clear-cutting area. Stronger relations in the period before clear-cutting were observed.
 Key words: clear-cutting, groundwater, forest catchment, swampy habitats

Comparing Q-Tree with Nested Grids for Simulating Managed River Recharge of Groundwater

The use of rivers to recharge groundwater is a key water resource management method. High-precision simulations of the groundwater level near rivers can be used to accurately assess the recharge effect. In this study, we used two unstructured grid refinement methods, namely, the quadtree (Q-tree) and nested grid refinement techniques, to simulate groundwater movement under river recharge. We comparatively analyzed the two refinement methods by considering the simulated groundwater level changes before and after the recharge at different distances from the river and by analyzing the groundwater flow and model computation efficiency. Compared to the unrefined model, the two unstructured grid refinement models significantly improve the simulation precision and more accurately describe groundwater level changes from river recharge. The unstructured grid refinement models have higher calculation efficiencies than the base model (the global refinement model) without compromising the simulation precision too much. The Q-tree model has a higher simulation precision and a lower computation time than the nested grid model. In summary, the Q-tree grid refinement method increases the computation efficiency while guaranteeing simulation precision at a certain extent. We therefore recommended the use of this grid refinement method in simulating river recharge to the aquifers.

Land Subsidence Prediction Induced by Multiple Factors Using Machine Learning Method

In the Beijing Plain, land subsidence is one of the most prominent geological problems, which is affected by multiple factors. Groundwater exploitation, thickness of the Quaternary deposit and urban development and construction are important factors affecting the formation and development of land subsidence. Here we choose groundwater level change, thickness of the Quaternary deposit and index-based built-up index (IBI) as influencing factors, and we use the influence factors to predict the subsidence amount in the Beijing Plain. The Sentinel-1 radar images and the persistent scatters interferometry (PSI) were adopted to obtain the information of land subsidence. By using Google Earth Engine platform and Landsat8 optical images, IBI was extracted. Groundwater level change and thickness of the Quaternary deposit were obtained from hydrogeological data. Machine learning algorithms Linear Regression and Principal Component Analysis (PCA) were used to investigate the relationship between land subsidence and influencing factors. Based on the results obtained by Linear Regression and PCA, a suitable machine learning algorithm was selected to predict the subsidence amount in the Beijing Plain in 2018 through influencing factors. In this study, we found that the maximum subsidence rate in the Beijing Plain had reached 115.96 mm/y from 2016 to 2018. The land subsidence was serious in eastern Chaoyang and northwestern Tongzhou. In addition, the area where thickness of the Quaternary deposit reached 150–200 m was prone to more serious land subsidence in the Beijing Plain. In groundwater exploitation, the second confined aquifer had the greatest impact on land subsidence. Through Linear Regression and PCA, we found that the relationship between land subsidence and influencing factors was nonlinear. XGBoost was feasible to predict subsidence amount. The prediction accuracy of XGBoost on the subsidence amount reached 0.9431, and the mean square error was controlled at 15.97. By using XGBoost to predict the subsidence amount, our research provides a new idea for land subsidence prediction.

Evaluation of the spatial and temporal changes in groundwater level and mineralization in agricultural lands under climate change in the Syrdarya province, Uzbekistan

Salinization processes are taking place as a result of rising groundwater level and its mineralization rate due to inefficient and unsustainable use of water and land resources in Uzbekistan. This leads to a reduction of arable land productivity and a decrease in nationwide yield production. Especially, salinization is the case in the plain irrigated areas of Uzbekistan where the groundwater is closer to the surface. Salinization processes occur as a result of an increase in the level of groundwater and the degree of their mineralization due to inefficient and irrational use of water and land resources in Uzbekistan. This leads to a decrease in the productivity of irrigated land and a decrease in yields throughout the country. Principally, salinization takes place in irrigated plain areas like the Syrdarya province, where mineralized groundwater is closer to the surface. Considering the geo-location of Uzbekistan as an aridic zone, there is a massive stress on groundwater because of surface water shortage. Since the estimation of the salinization consequences on groundwater is critical, this research, therefore, was aimed to understand and evaluate the long-term changing behavior of groundwater level and its mineralization in the irrigated areas of the Syrdarya province of Uzbekistan from 2000 to 2015 by using traditional methods, and GIS-based methods for from 2016 to 2019.The level and mineralization of groundwater in each administrative district of the province were for the first time studied and assessed. Consequently, the dependence of the groundwater level and its mineralization on soil conditions and climatic factors were determined. Based on the results of the study, agricultural specialists and farmers of the province were highly advocated to take the following measures considering the actual condition of groundwater mineralization in the irrigated areas of the Syrdarya province: (1) targeted and economical use of irrigation water; (2) ensuring that existing drainage networks are in an adequate working condition and can operate with full-efficiency; and (3) to conduct annual monitoring of groundwater table and its mineralization of irrigated lands using traditional and GIS technologies.

Hydrogeochemical Evidence of Earthquake‐Induced Anomalies in Response to the 2017MW5.5 Pohang Earthquake in Korea

AbstractSignificant changes in groundwater systems were observed after the 2017Mw5.5 Pohang earthquake. Groundwater level changes cannot be explained solely by poroelastic responses to the earthquake. In this study, we analyzed hydrogeochemical data, including environmental isotopes (18O,2H,87Sr/86Sr, and222Rn) of water samples as well as time‐series data of groundwater level, temperature, and electrical conductivity. Principal component analysis (PCA) and physical modeling of pore pressure changes were also used. Some anomalies in time‐series data could be explained by the distributions of pore pressure changes based on modeling. However, the other wells, which did not have the correlation between time‐series data and modeling results, exhibited abnormal patterns in hydrogeochemical and isotope data. Stiff diagrams showed differing patterns of temporal change among groundwater wells. These diagrams and isotopic anomalies revealed possible mechanisms underlying the aftereffects of earthquakes, including saline water mixing, water‐rock interactions, deep fluid upwelling, and bedrock fracture opening. These anomalous phenomena were related to the clusters derived by PCA and depended on the distance to the epicenter, faults, and sea water. This study highlights that a single measurement is insufficient to reliably interpret groundwater responses, whereas a combined hydrogeochemical and physical interpretation may provide critical information for clarifying anomalies related to earthquakes.

Numerical modeling of groundwater flow system in the Modjo River catchment, Central Ethiopia

In recent years, groundwater pumping has increased for domestic, industrial, and irrigation use in the Modjo River catchment. Understanding changes in groundwater levels is crucial for the sustainable use and management of aquifer. This study investigates the groundwater flow system and aquifer response to increased groundwater pumping and reduced recharge using the calibrated steady-state groundwater level and budget as a baseline. The groundwater flow corresponds to the direction of the Modjo River flow, following the topographic gradient. The simulated groundwater budget indicates that recharge from precipitation and surface water (crater lakes and river) are the main inflow to the aquifer, while the outflow from the aquifer is due to groundwater pumping, natural subsurface flow to downstream area, and base flow. Analysis of the different scenarios reveals that both an increase in well pumping and a decline in recharge resulted in a decrease of the base flow to Bishoftu crater lakes and Mojo River, and to the downstream subsurface flow. In conclusion, increasing human demand for groundwater and variability in recharge will affect groundwater contribution to surface water and ultimately will be a source of concern in the future for both environmental flows and groundwater management.

Investigating sea-level change on the coastal aquifer, case study: Jafakendeh aquifer

Do the sea-level changes affect the quantity and quality of groundwater on the coastal Jafakendeh aquifer? More than half of the world's population now lives near the coastline. Surface water in the coastal basin and the island interacts with adjacent groundwater. This interaction affects the quantity and quality of water in surface and subsurface waters. In this study, the relationship between the Jafakendeh aquifer and groundwater of the Caspian Sea in northern Iran has been investigated. Therefore, this study aimed to examine the trend, changes in surface groundwater level, and groundwater quality variables of the groundwater aquifer by the Mann–Kendall nonparametric method and detect point change by the Pettitt method. Four piezometer wells were measured, where is only one piezometer located at the artificial recharge site and piezometer one near the Caspian Sea. In the present study, the statistics were used to find a sudden change in groundwater data quantity and quality. The analysis shows that sea-level changes and wells near the sea do not affect the amount and quality of coastal aquifer and adjacent wells' significance.

An assessment of the effects of excessive groundwater abstraction on the quality of groundwater resources of the Zanjan Plain, Iran

In the present study, the quality of groundwater and the effects of pumping on the phreatic surface beneath the Zanjan Plain located in northwestern Iran were investigated by measuring water levels in 81 observation wells as well as various physicochemical parameters including electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH) and pH. In addition, the results of the chemical analysis of major anions and cations from 53 boreholes that were sampled during the period 2004–2018 were evaluated. The water level measurements indicated that the elevation of the phreatic surface had declined by up to about 8 m during the studied period, indicating an average decrease of about 0.57 m per year. A comparison of the measured physicochemical parameters with WHO, ISIRI, and EPA standards for drinking water quality showed that some parameters including EC, TDS, TH, SO4, and Cl in the northwestern and central parts of the plain exceeded the allowable level. An assessment of water quality index (WQI) values showed that most parts of the Zanjan Plain lie in the “good” quality class, although in some parts, the water quality of “poor” quality class, most likely due to the effects of urban activities. A comparison of the results from a Schoeller diagram assessment with WQI values showed some differences between the results of the qualitative classification of some parts of the Zanjan Plain groundwater based on the two mentioned methods. The results of the present study showed that groundwater of some areas of the Zanjan Plain is not suitable to be used for irrigation of agricultural lands with limited drainage. The Piper diagram also indicated that the dominant groundwater quality facies on the Zanjan Plain were Ca–Na–HCO3 and Ca–HCO3 water types. The results of the Spearman correlation analysis also showed a high correlation of most anions with cations. Analysis of the volume changes versus qualitative changes in groundwater also showed a general decreasing trend of water quality with decreases in the volume of groundwater in storage in the aquifer, although in some conditions due to changes in solubility of water-soluble materials because of the changes in groundwater level, other trends were also observed.

Trends and Non-Stationarity in Groundwater Level Changes in Rapidly Developing Indian Cities

In most of the Indian cities, around half of the urban water requirement is fulfilled by groundwater. Recently, seasonal urban droughts have been frequently witnessed globally, which adds more stress to groundwater systems. Excessive pumping and increasing demands in several Indian cities impose a high risk of running out of groundwater storage, which could potentially affect millions of lives in the future. In this paper, groundwater level changes have been comprehensively assessed for seven densely populated and rapidly growing secondary cities across India. Several statistical analyses were performed to detect the trends and non-stationarity in the groundwater level (GWL). Also, the influence of rainfall and land use/land cover changes (LULC) on the GWL was explored. The results suggest that overall, the groundwater level was found to vary between ±10 cm/year in the majority of the wells. Further, the non-stationarity analysis revealed a high impact of rainfall and LULC due to climate variability and anthropogenic activities respectively on the GWL change dynamics. Statistical correlation analysis showed evidence supporting that climate variability could potentially be a major component affecting the rainfall and groundwater recharge relationship. Additionally, from the LULC analysis, a decrease in the green cover area (R = 0.93) was found to have a higher correlation with decreasing groundwater level than that of urban area growth across seven rapidly developing cities.

Spatial-Temporal Evolution of Land Subsidence and Rebound over Xi’an in Western China Revealed by SBAS-InSAR Analysis

Land subsidence is one of the major urban geological hazards, which seriously restricts the development of many cities in the world. As one of the major cities in China, Xi’an has also been experiencing a large area of land subsidence due to excessive exploitation of groundwater. Since the Heihe Water Transfer Project (HWTP) became fully operational in late 2003, the problem of subsidence has been restrained, but other issues, such as ground rebounds, have appeared, and the effect of the underground space utilization on land subsidence remains unsolved. The spatial-temporal pattern of land subsidence and rebound in Xi’an after HWTP and their possible cause have so far not been well understood. In this study, the evolutionary characteristics of land subsidence and rebound in Xi’an city from 2007–2019 was investigated using Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-SAR) technology to process the Advanced Land Observing Satellite (ALOS) and Sentinel-1A SAR datasets, and their cause and the correlation with groundwater level changes and the underground space utilization were discussed. We found that the land subsidence rate in the study area slowed from 2007–2019, and the subsidence area shrank and gradually developed into three relatively independent and isolated subsidence areas primarily. Significant local rebound deformation up to 22 mm/y commenced in the groundwater recharge region during 2015–2019. The magnitude of local rebound was dominated by the rise in groundwater level due to HWTP, whereas tectonic faults and ground fissures control the range of subsidence and the uplift area. The influence of building load on surface deformation became increasingly evident and primarily manifested by slowing the subsidence reduction trend. Additionally, land subsidence caused by the disturbances during the subway construction period was stronger than that in the operational stage. Future land subsidence in Xi’an is predicted to be alleviated overall, and the areas of rebound deformation will continue increasing for a limited time. However, uneven settlement range may extend to the Qujiang and Xixian New District due to the rapid urban construction. Our results could provide a scientific basis for land subsidence hazard mitigation, underground space planning, and groundwater management in Xi’an or similar regions where severe ground subsidence was induced by rapid urbanization.

An analysis of the influences of groundwater level changes on the frost heave and mechanical properties of trapezoidal channels

Abstract In this research study, platforms with different heights were established for the purpose of simulating the different groundwater level conditions. Combined with the prototype channel, the influences of the groundwater level changes on the frost heave deformations in the foundation soil and on the frost heave force of the channel, as well as on the bending moment of the channel section and water content migration of the foundation soil, were studied by the method of mechanical analysis. The research results show that, after a comparative analysis of the ground temperatures in the same layer had been completed, the difference value was found to have been less than 5%. The frost heave of the foundation soil had decreased by 0.15 cm for every 1 cm reduction in the groundwater level. In addition, the maximum frost heave force of the channel was shown to have varied with the change of groundwater level. This study's theoretical calculations determined that the most unsafe groundwater level of a typical channel was 2.61 m. It was concluded that the increase of groundwater level can reduce the amount of soil moisture transfer, while the influence of groundwater level on frost heave of foundation soil can be effectively reduced by laying polystyrene boards.

Assessment of Causes and Effects of Groundwater Level Change in an Urban Area (Warsaw, Poland)

Monitoring the data of groundwater level in long-term measurement series has allowed for assessment of the impact of natural and anthropogenic factors on groundwater recharge. It allows for assessing the actual groundwater quantity, which constitutes the basis for balanced and sustainable groundwater planning and management in an urban area. Groundwater levels in three aquifers were studied: the shallow and deeper Quaternary aquifers and the Oligocene aquifer in Warsaw (Poland). Statistical analysis was performed on a 27-year (1993–2019) cycle of daily measurements of groundwater levels. The studies focused on determining the range and causes of groundwater level changes in urban-area aquifers. The groundwater table position in the Quaternary aquifer pointed to variable long-term recharge and allowed for the identification of homogenous intervals with identification of water table fluctuation trends. A decrease in the water table was observed within the Quaternary aquifers. The Oligocene aquifer displayed an opposite trend.

Prediction of landslide sharp increase displacement by SVM with considering hysteresis of groundwater change

The displacement-time curves of reservoir landslide mostly show step-by-step growth characteristics. The sharp increase of the displacement plays a significant role in the evolution process of the step-like landslide, so it is extremely important to accurately predict the suddenly change displacement of landslide. In order to overcome the shortcomings existed in the current displacement monitoring methods and prediction models for the mutation displacement of landslide, this paper proposed a hybrid machine learning displacement prediction model based on Support Vector Machine, including Support Vector Classification(SVC) and Support Vector Regression(SVR), optimized by Particle Swarm Optimization (SVC-PSO-SVR) and considering the hysteresis of groundwater level change. The Majiagou No. 1 Landslide in the Three Gorges Reservoir (TGR) Area, whose deformation shows typical step-by-step tendency, was illustrated. Base on the deep displacement data of Majiagou landslide from January 2016 to December 2017, the landslide deformation pattern can be divided into two states: stability and acceleration. Firstly, the SVC model was adopted to predict the time range of acceleration state. Then, considering the lag fluctuation of groundwater level, the concept of “equivalent reservoir level” was proposed. Finally, based on SVC model, the sharp increase displacement of landslide was predicted using PSO-SVR model. The proposed SVC-PSO-SVR model yielded the root mean square error (RMSE) of 0.08827 mm and the mean absolute percentage error (MAPE) of 0.02105 mm. Besides, the prediction accuracy of SVC can attain 96.49% (55 / 57). The results show that the model can accurately predict the time range and displacement of acceleration deformation section of Majiagou landslide. The proposed model is of great significance for landslide prediction and early warning.

Long-term groundwater level changes and land subsidence in Tianjin, China

A large volume of groundwater is withdrawn annually in Tianjin Municipality, China, to meet agricultural, industrial, and municipal water uses. Groundwater overdraft in the urban districts and the Binhai New District in Tianjin Municipality has caused land subsidence. A series of field observation wells were installed to monitor the long-term groundwater level (GWL). The hydrostratigraphy of the aquifer system underlying Tianjin consists of four aquifer layers. The middle two aquifer layers are the main layers for groundwater withdrawal. The GWL of the top two aquifer layers responded rapidly to recharge from precipitation and seawater intrusion. The GWLs of the bottom two aquifer layers have been dropping steadily over the past 50 years. The aquifer sediments underlying Tianjin Municipality consist mainly of fine sand, silt, and clayey soil. The decline of the GWL has induced substantial land subsidence and led to overconsolidated compressible sediments.

Water repellency in eucalyptus and pine plantation forest soils and its relation to groundwater levels estimated with multi-temporal modeling

Abstract Water repellency makes soils capable of resisting to the penetration of water applied on the surface and inflict various influences on groundwater. The objectives of the present study were to identify the water repellency under pine and eucalyptus plantations, to determine social impacts of water level changes, to find possible changes in groundwater levels in the surrounding areas during the past four decades, and to relate water repellent characteristics of soils with the groundwater level changes. The study was conducted in eucalyptus (Eucalyptus grandis) and pine (Pinus caribaea) plantation forests located in Upcountry intermediate zone, Sri Lanka. Each land was separated into three blocks (B1, B2, B3) based on the slope. Water repellency was measured with water drop penetration time (WDPT) and contact angle. The water entry value was estimated with the pressure head method. Interconnected social impacts was examined using a questionnaire based survey. Groundwater levels from 1980 to present were modeled with remotely sensed information. Both eucalyptus and pine forest soils showed water repellency, which decreased with increasing soil depth. Eucalyptus soils showed highly hydrophobic conditions on the surface (WDPT>7200 s). Ponding depths required for entry of water into the soil in eucalyptus soils was 4.6–5.3 cm, whereas that of pine soils was 1.5–4.0 cm, although achieving these levels would be difficult considering the steep slopes. Contact angle showed positive logarithmic correlation with water entry value. The people living in the surrounding areas expressed less water availability for their domestic purposes, decreased water level in household wells, and drying up of natural water resources at present compared with 1980s. Modelling with remotely sensed thematic maps confirmed that the groundwater levels in both areas has decreased over the time. It indicated that the eucalyptus and pine vegetation have created unfavorable conditions in regard with water entry and groundwater recharge. Proper attention from the responsible authorities will be essential to prevent the adverse impacts of on groundwater resources.

Spatiotemporal Characterization of Land Subsidence in Guandu (China) Revealed by Multisensor InSAR Observations

Excessive groundwater exploitation has brought about severe ground subsidence in Guandu (China), threatening the stability of urban infrastructure. Mapping of the spatiotemporal variations of ground deformation is urgently needed for disaster prevention and mitigation. In this study, multisensor interferometric synthetic aperture radar (InSAR) observations were applied to Guandu to derive the time series deformation from 2007 to 2019. The annual deformation velocity revealed three severe subsiding regions in Guandu. Based on the ascending and descending Sentinel-1 images with overlapping temporal and spatial coverage, two-dimensional vertical and horizontal east–west deformation was calculated and indicated that the deformation in Guandu was dominated by vertical direction. After connecting the multisensor results, long-term ground deformation spanning from January 9, 2007, to September 1, 2019, was produced and showed that the north subsiding region experienced fast followed by slow subsidence, whereas the south subsiding region experienced slow followed by fast subsidence. This difference was due to the changes of groundwater pumping centers and rates. The cumulative maximum subsidence reached 400 mm during the period of 2007–2019. The similar variations in temporal domain between the change of groundwater level and ground deformation suggested that groundwater exploitation accounted for the severe subsidence in Guandu. Our results may provide scientific evidence regarding the sound management of groundwater exploitation to mitigate potential damage to infrastructure and the environment.

The Relationship between Surface Displacement and Groundwater Level Change and Its Hydrogeological Implications in an Alluvial Fan: Case Study of the Choshui River, Taiwan

Balancing the demand of groundwater resources and the mitigation of land subsidence is particularly important, yet challenging, in populated alluvial fan areas. In this study, we combine multiple monitoring data derived from Multi-Temporal InSAR (MTI), GNSS (Global Navigation Satellite System), precise leveling, groundwater level, and compaction monitoring wells, in order to analyze the relationship between surface displacement and groundwater level change within the alluvial fan of the Choshui River in Taiwan. Our combined time-series analyses suggest, in a yearly time scale, that groundwater level increases with the vertical surface displacement when the effect of pore water pressure dominates. Conversely, this relationship is negative when the effect of water-mass loading predominates over pore water pressure. However, the correlation between the vertical surface displacement and the groundwater level change is consistently positive over the time scale of two decades. It is interpreted that the alluvial fan sequence in the subsurface is not fully elastic, and compaction is greater than rebound in this process. These findings were not well reported and discussed by previous studies because of insufficient monitoring data and analyses. Understanding the combined effect of groundwater level change and vertical surface displacement is very helpful for management of land subsidence and usage of groundwater resources. The spatial and temporal integration of multi-sensors can be applied to overcome the limitations associated with the single technique and provides further insights into land surface changes, particularly in highly populated alluvial fan areas.

Seasonal and transient surface displacements in the Kumamoto area, Japan, associated with the 2016 Kumamoto earthquake: implications for seismic-induced groundwater level change

The 2016 Kumamoto earthquake sequence on April 14 (Mw 6.2) and April 16 (Mw 7.0) altered the regional groundwater level. To better understand the relationship between groundwater level change and surface displacement, we estimated surface displacement in the Kumamoto area (Japan) using persistent scatterer interferometry from 19 ALOS/PALSAR images acquired between January 7, 2007 and March 5, 2011, 28 ALOS-2/PALSAR-2 images acquired between April 17, 2016 and December 10, 2018, and 113 Sentinel-1 images acquired between May 26, 2016 and December 30, 2018. Our estimation shows that transient surface displacement occurred following the 2016 Kumamoto earthquake sequence, together with seasonal surface displacement that was not detected from the 2007–2011 images. We suggest that a portion of the transient displacement occurred via groundwater drawdown through new ruptures that formed owing to the 2016 Kumamoto earthquake sequence and sediment compaction. Seasonal surface displacements detected after the 2016 Kumamoto earthquake sequence are linked to groundwater level variations.

Numerical analysis of subsurface deformation induced by groundwater level changes in the Bangkok aquifer system

Subsurface deformation due to long terms of groundwater drawdown from 1960 to 1997 and groundwater recovery from 1997 to 2016 in the upper part of the Bangkok multi-aquifer system and their possible effects on substructure stability were analyzed. The updated groundwater monitoring data show a linear recovery trend with a full recovery by 2031 in the study aquifer. Subsurface deformation was calculated using FEM transient coupled pore pressure/effective stress analysis by Abaqus. It was found that the groundwater drawdown from 1960 to 1997 caused a subsidence of 51, 62, and 76 cm, while the following groundwater recovery from 1997 to 2016 could pull back a rebound of 9.8, 9.7, and 5.3% at the three study sites, respectively. The effects of the change in pore pressure and undrained shear strength of the clay layers on the ultimate pile capacity were studied for cases of high-rise and low-rise buildings at a selected site. It was found that the groundwater drawdown from 1960 to 1997 could cause an increasing rate of ultimate pile capacity of about 1.0–1.5% per year, while the groundwater recovery from 1997 to 2031 can cause a similar reduction rate of ultimate pile capacity.