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Many engineering construction projects entail excavations into water bearing substrates. The authors explain the drainage techniques required to lower groundwater sufficiently to allow projects to be undertaken with confidence.

Predictions of groundwater fluctuations in space and time are important for sustainable water resource management. Infiltration variability on monthly to decadal timescales leads to fluctuations in the water tables and thus groundwater resources. However, connections between global‐scale climate variability and infiltration patterns and groundwater are often poorly understood because the relationships between groundwater conditions and infiltration tend to be highly nonlinear. In addition, understanding is further hampered because many groundwater records are incomplete and groundwater tables are often anthropogenically influenced, which makes identifying the effects of infiltration variability difficult. Previous studies that have evaluated how infiltration variability controls groundwater are based on a limited number of point measurements. Here, we present a global assessment of how infiltration variability is expected to affect groundwater tables. We use an analytical solution derived from Richards' equation to model water level responses to idealized periodic infiltration variability with periods that range from months to decades, to approximate both the effects of short‐term and long‐term climate variability and thus infiltration patterns. Our global‐scale assessment reveals why infiltration variability would lead to periodicity in groundwater recharge in particular regions. The vadose zone strongly dampens short‐term (seasonal and shorter) variations in infiltration fluxes throughout most of Earth's land surface, while infiltration cycles exceeding 1 year would yield transient recharge, except in more arid regions. Our results may help forecasting long‐term groundwater tables and could support improving groundwater resource management. Plain Language Summary Understanding how climate patterns affect groundwater is challenging because infiltration processes are complex and groundwater records are scarce and often incomplete. We use an analytical groundwater model to study the impact of infiltration variability on groundwater tables globally. Our analysis thereby quantifies how strongly groundwater recharge varies as the result of climate and infiltration variability at different timescales, ranging from seasonal fluctuations to multi‐year climate phenomena with characteristic lengths similar to the El Niño/Southern oscillation and Pacific decadal oscillation. Our results show that periodic variations in climate and infiltration often have minimal influence on water tables in arid to semi‐arid areas with deep groundwater tables, while, while wetter regions (and/or with shallower groundwater) have more strongly time‐varying groundwater conditions. These findings may help to predict future groundwater tables and enhance the management of groundwater resources. Key Points The vadose zone globally dampens short‐term infiltration fluctuations which stabilizes groundwater level variations Infiltration cycles longer than a year cause transient recharge variation, except in semi‐arid and arid regions Soil characteristics impact short‐term infiltration fluctuations but have a small effect on recharge dampening at longer infiltration cycles

Air–water interfacial adsorption represents a major source of retention for many per‐ and poly‐fluoroalkyl substances (PFAS). Therefore, transient hydrological fluxes that dynamically change the amount of air–water interfaces are expected to strongly influence PFAS retention in their source zones in the vadose zone. We employ mathematical modeling to study how seasonal groundwater table (GWT) fluctuations affect PFAS source‐zone leaching. The results suggest that, by periodically collapsing air–water interfaces, seasonal GWT fluctuations can lead to strong temporal variations in groundwater concentration and significantly enhance PFAS leaching in the vadose zone. The enhanced leaching is more pronounced for longer‐chain PFAS, coarser‐textured porous media, drier climates, and greater amplitudes of fluctuations. GWT fluctuations and lateral migration above the GWT introduce a downgradient persistent secondary source zone for longer‐chain PFAS. However, the enhanced leaching and the secondary source zone are greatly reduced when subsurface heterogeneity is present. In highly heterogeneous source zones, GWT fluctuations may even lead to overall slower leaching due to lateral flow (in the GWT fluctuation zone and above the GWT) moving PFAS into local regions with greater retention capacities. Model simplification analyses suggest that the enhanced source‐zone leaching due to GWT fluctuations may be approximated using a static but shallower GWT. Additionally, while vertical 1D models underestimate source‐zone leaching due to not representing lateral migration, they can be revised to account for lateral migration and provide lower‐ and upper‐bound estimates of PFAS source‐zone leaching under GWT fluctuations. Overall, our study suggests that representing GWT fluctuations is critical for quantifying source‐zone leaching of PFAS, especially the more interfacially active longer‐chain compounds. Plain Language Summary Per‐ and poly‐fluoroalkyl substances (PFAS) are contaminants that are now widespread in the environment. Many PFAS are interfacially active and tend to accumulate at solid surfaces and air–water interfaces. A growing body of field data at PFAS‐contaminated sites has shown that significant amounts of PFAS have accumulated in soils, posing great risks to the groundwater underneath. Because the accumulation at air–water interfaces is a primary mechanism that retains PFAS in soils, any transient water fluxes that dynamically collapse air–water interfaces may accelerate the downward movement of PFAS. One important type of temporal change to air–water interfaces can be caused by the fluctuation of groundwater, such as seasonal groundwater table fluctuations (GWT). We use mathematical models to study the impact of GWT on enhancing the downward movement of PFAS from soils to groundwater. Our analyses suggest that seasonal GWT fluctuations can significantly enhance PFAS downward movement by periodically collapsing air–water interfaces in soils. They also lead to seasonal variations in groundwater PFAS concentrations that may have important implications for groundwater sampling and risk assessment. Overall, representing groundwater table fluctuations is critical for quantifying groundwater contamination risks of PFAS, especially the more interfacially active compounds with longer carbon chains. Key Points Groundwater table (GWT) fluctuations enhance source‐zone poly‐fluoroalkyl substances (PFAS) leaching, but the enhanced leaching is reduced in heterogeneous source zones GWT fluctuations and lateral migration above the GWT lead to a downgradient persistent secondary source zone for longer‐chain PFAS Develop simplified modeling strategies to estimate the lower‐ and upper‐bounds of PFAS source‐zone leaching under GWT fluctuations

Scarcity of groundwater is a severe problem in this region due to over exploitation of groundwater from unconfined hard rock aquifers. The main objectives of this study are to analyse the spatiotemporal variability and fluctuation of groundwater table and to predict the location of groundwater depression pockets. Total 21 consecutive years (1996–2017) groundwater monitoring well data (pre- and post-monsoon) have been collected from CGWB, Government of India. The nonparametric Mann–Kendall trend analysis and standardized precipitation index (SPI) have been applied to detect the trend of groundwater level and rainfall variability, respectively. Exponential smoothing has also been fitted for future prediction. The pre- and post-monsoon results (1996–2017) showed that around 77% (22 stations) and 78% (23) monitoring stations were indicating declining trend of groundwater table at the rate of −0.006 to −0.205 m/year and −0.005 to −0.192 m/year, respectively. Similarly, future (2040) groundwater depression result predicted that around 75% (21) stations, the groundwater table will be depleted above 5 m during pre-monsoon while about 53% (16 stations) monitoring wells, the groundwater table will be fallen above 5 m during post-monsoon. Consequently, around 52% (15) and 50% (14) stations are being faced groundwater drought in the recurrent interval of above 2 years during pre-monsoon and post-monsoon, respectively. Driving factors of water table depletion are huge withdrawal of groundwater for dry farming and reduction of recharge areas due to rapid land use modification. The uniqueness of this study exhibits the nature of declining trend of groundwater table and identification of depression pockets.

Land-use practices can alter shallow groundwater and salinity, further impacting greenhouse gas (GHG) emissions, particularly in the hydrologically dynamic riparian zones of wetlands. Emissions of CO₂, CH₄, and N₂O were estimated in soil cores collected from two prairie pothole region (PPR) sites with three adjacent land-use practices (i. e., annual crop = AC, pasture = PA, and short rotation willow = SRW) and treated with declining water table depths (2 to 26 cm), and salinity (S0 = control, S1 = 6 mS cm⁻¹, and S2 = 12 mS cm⁻¹) in a microcosm experiment. Land-use practices significantly (p < 0.001) affected GHG emissions in soils from both sites in the order of PA > AC = SRW. Compared to the control, emissions of CO₂ and CH₄ were significantly lower under higher salinity treatments (i.e., S1 and S2), while N₂O was significantly higher (p < 0.05). Emissions under declining groundwater table depths were significantly (p < 0.001) variable and specific to each gas, indicating the impacts of shifted soil moisture regime. Overall, the CO₂ and CH₄ emissions increased up to week four and then decreased with declining water table depths, whereas N₂O emission increased up to a maximum at week six. The soils from SRW had considerably lower global warming potential compared to AC and PA. Groundwater salinity in soils from contrasting land-use in the PPR has significant impacts on GHG emissions with potential for crucial climate feedback; however, the magnitude and direction of the impacts depend on hydrology.

In the present study, a new hybridization strategy for predicting the groundwater table (GWT) and drought analysis is presented. Therefore, a hybrid of the bi-directional long short-term model (BLSTM) and the Harris hawk optimization (HHO) algorithm, namely the BLSTM–HHO algorithm, is applied. In this algorithm, the lagged data of the GWT are used as the input, whereas the current GWT data are used as the output. Additionally, the standalone BLSTM, the long short-term model (LSTM), artificial neural networks (ANN), Seasonal Autoregressive Integrated Moving Average (SARIMA), and the Autoregressive Integrated Moving Average (ARIMA) are employed as benchmark simulating algorithms. The results show that the BLSTM–HHO algorithm has more accuracy than the other investigated simulating algorithms based on the different evaluation criteria such as relative root mean squared error (RRMSE), Nash–Sutcliffe coefficient (NSE), and refined Willmott index (dr). The prediction results (from 2018 to 2022) in all three investigated aquifers show the decline of the GWT (−5.40 m for Brojen aquifer, −7.23 m for Javanmardi aquifer, and −5.81 m for Shahrekord aquifer). Accordingly, the drought analysis by the ground resource index (GRI) in the investigated areas shows that drought is expected to be continued for the next 5 years with an increasing magnitude of severity.

Groundwater is a vital factor affecting the stability of water-rich slope of open-pit mine, and the distribution of groundwater inside water-rich slope is always uncertain. To investigate the uncertainty of groundwater distribution inside the water-rich slope, based on the engineering background of DEZIWA open-pit mine, this paper adopts the research method of field investigation and test (single and multiple borehole pumping tests), numerical simulation (Visual MODFOW), and theoretical analysis (nonlinear fitting theory, distribution fitting theory, and one-sample Kolmogorov–Smirnov test) to study the uncertainty of the distribution of groundwater table line within the water-rich slope of open-pit mine. Results obtained from the above research indicate that, Visual MODFLOW is an effective tool for obtaining groundwater distribution information inside the water-rich slope of open-pit mine. When the open-pit mine excavated to the final boundary, it is found that within multiple cross-sections of the southern and western regions of water-rich slope of the open-pit mine, groundwater table line can all be delineated by a series of 3-term Fourier equations, which can be characterized by identical equation forms but varying fitting coefficients. Furthermore, based on the findings of distribution fitting and one-sample Kolmogorov–Smirnov test, it becomes evident that the probability distribution of the fitting coefficients of the aforementioned 3-term Fourier equations can all be described by the normal distribution models. Use the established normal distribution models in this paper, uncertainty of the groundwater distribution within the water-rich slope of DEZIWA open-pit mine can be described indirectly and quantitatively, and the research methods of this paper can provide a meaningful reference to the slope engineering with similar conditions.

Saline water resources are more abundant than freshwater. Bringing these resources into sustainable, productive use will ofer opportunities to reduce competition for freshwater resources, especially in arid and semi-arid areas where freshwater is scarce. Hence, the primary objective of this study was to elucidate the dynamics of salt ions in saline profiles of various soil types (sandy Clovelly and sandy loam Bainsvlei) under malt barley cultivation across 2 seasons where no leaching between the seasons took place. Results of this lysimeter study investigating increasing irrigation salinity (ECi) set at 1.5, 4.5, 6, 9, and 12 dS·m−1 over 2 seasons were used to explore ion dynamics of a saline environment. The lysimeter set-up included a saline constant (1.2 m) groundwater table with its salinity corresponding to ECi. Findings showed that ion concentrations are higher closer to the water source only in the Bainsvlei soil and remain variable in the Clovelly soil. Salt dynamics were more predictable in sandy loam soil than in sandy soil, making management of saline sandy soils far more challenging when leaching is not possible. Therefore, our hypothesis that the absence of leaching between seasons will lead to a diferentiated progressive accumulation of salt ions in the soil profile, with variable efects on the soil depending on soil texture, was true. We conclude that the desalinized zone, which we determined to be at a depth of 600 mm, should be used to guide crop selection. Furthermore, in addition to the apparent provision for leaching of saline profiles, fertilization should target restoring ion balances, especially provisioning for calcium deficiencies. Both soils were prone to nutritional disorders, most especially calcium deficiency. Therefore, in addition to provision for leaching saline profiles, fertilization should target calcium provisioning for crop production in arid saline environments.

This paper presents a numerical study of dynamic compaction (DC) on ground improvement in foundation with a high groundwater table, based on a dynamic fluid–solid coupled finite element method with a cap model. Firstly, an analysis of dry ground was carried out to evaluate the effective improvement range, with the proposal of a normalized formula capturing the improvement effect. Then, the parametric studies include the effect of groundwater table, the permeability coefficient, drop energy, and soil type have been carried out to not only find that the groundwater table has a dominant influence on soil improvement by DC but also clarify densification mechanisms of ground improvement by DC on the soil nearby groundwater table, which is through analyzing the contours of effective mean stress. Finally, a relative enhancement index, RD, based on a total of 52 calculations is derived to evaluate the depth of improvement below the groundwater table for different scenarios. These relationships provide a valuable reference for the evaluation of ground improvement by DC for a foundation with high groundwater table and the applicability of the proposed procedure is illustrated by comparing its prediction with three cases of DC in the field.

Exploitation of groundwater has greatly increased since the 1970s to meet the increased water demand due to fast economic development in China. Correspondingly, the regional groundwater level has declined substantially in many areas of China. Water sources are scarce in northern and northwestern China, and the anthropogenic pollution of groundwater has worsened the situation. Groundwater containing high concentrations of geogenic arsenic, fluoride, iodine, and salinity is widely distributed across China, which has negatively affected safe supply of water for drinking and other purposes. In addition to anthropogenic contamination, the interactions between surface water and groundwater, including seawater intrusion, have caused deterioration of groundwater quality. The ecosystem and geo-environment have been severely affected by the depletion of groundwater resources. Land subsidence due to excessive groundwater withdrawal has been observed in more than 50 cities in China, with a maximum accumulated subsidence of 2–3 m. Groundwater-dependent ecosystems are being degraded due to changes in the water table or poor groundwater quality. This paper reviews these changes in China, which have occurred under the impact of rapid economic development. The effects of economic growth on groundwater systems should be monitored, understood and predicted to better protect and manage groundwater resources for the future.