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Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Badain Jaran Desert (BJD) in China is a desert with impressive sand dunes and a groundwater situation that has attracted numerous researchers. This paper gives an overview of the mysteries of groundwater in the BJD that are exhibited as five key problems identified in previous studies. These problems relate to the origin of the groundwater, the hydrological connection between the BJD and the Heihe River Basin (HRB), the infiltration recharge, the lake-groundwater interactions, and the features of stable isotope analyses. The existing controversial analyses and hypotheses have caused debate and have hindered effective water resources management in the region. In recent years, these problems have been partly addressed by additional surveys. It has been revealed that the Quaternary sandy sediments and Neogene-Cretaceous sandstones form a thick aquifer system in the BJD. Groundwater flow at the regional scale is dominated by a significant difference in water levels between the surrounding mountains and lowlands at the western and northern edges. Discharge of groundwater from the BJD to the downstream HRB occurs according to the regional flow. Seasonal fluctuations of the water level in lakes are less than 0.5 m due to the quasi-steady groundwater discharge. The magnitude of infiltration recharge is still highly uncertain because significant limitations existed in previous studies. The evaporation effect may be the key to interpreting the anomalous negative deuterium-excess in the BJD groundwater. Further investigations are expected to reveal the hydrogeological conditions in more detail. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coal-floor water-inrush incidents account for a large proportion of coal mine disasters in northern China, and accurate risk assessment is crucial for safe coal production. A novel and promising assessment model for water inrush is proposed based on random forest (RF), which is a powerful intelligent machine-learning algorithm. RF has considerable advantages, including high classification accuracy and the capability to evaluate the importance of variables; in particularly, it is robust in dealing with the complicated and non-linear problems inherent in risk assessment. In this study, the proposed model is applied to Panjiayao Coal Mine, northern China. Eight factors were selected as evaluation indices according to systematic analysis of the geological conditions and a field survey of the study area. Risk assessment maps were generated based on RF, and the probabilistic neural network (PNN) model was also used for risk assessment as a comparison. The results demonstrate that the two methods are consistent in the risk assessment of water inrush at the mine, and RF shows a better performance compared to PNN with an overall accuracy higher by 6.67%. It is concluded that RF is more practicable to assess the water-inrush risk than PNN. The presented method will be helpful in avoiding water inrush and also can be extended to various engineering applications. [ABSTRACT FROM AUTHOR]

Inter-basin water transfer projects (IBWTPs) can involve basins as water donors and water receivers. In contrast to most studies on IBWTPs, which mainly impact the surface-water eco-environment, this study focuses on the impacts of an IBWTP on groundwater and its eco-environment in a water donor basin in an arid area, where surface water and groundwater are exchanged. Surface water is assumed to recharge groundwater and a groundwater numerical simulation model was constructed using MODFLOW. The model was used to quantitatively evaluate the impact of an IBWTP located in the upstream portion of Nalenggele River (the biggest river in the Qaidam basin, Northwest China). The impact involved decrease in spring flow, drawdown of groundwater, reduction in oasis area, and an increase in species replacement of oasis vegetation in the midstream and downstream of the river. Results show that the emergence sites of springs at the front of the oasis will move 2-5 km downstream, and the outflow of springs will decrease by 42 million m3/a. The maximum drawdown of groundwater level at the front of the oasis will be 3.6 m and the area across which groundwater drawdown exceeds 2.0 m will be about 59.02 km2, accounting for 2.71% of the total area of the oasis. Under such conditions, reeds will gradually be replaced by Tamarix, shrubs, and other alternative plant species. These findings have important implications for the optimization of water resource allocation and protection of the eco-environment in arid regions. [ABSTRACT FROM AUTHOR]

Data on spatiotemporal variations in groundwater levels are crucial for understanding arsenic (As) behavior and dynamics in groundwater systems. Little is known about the influences of groundwater extraction on the transport and mobilization of As in the Hetao Basin, Inner Mongolia (China), so groundwater levels were recorded in five monitoring wells from 2011 to 2016 and in 57 irrigation wells and two multilevel wells in 2016. Results showed that groundwater level in the groundwater irrigation area had two troughs each year, induced by extensive groundwater extraction, while groundwater levels in the river-diverted (Yellow River) water irrigation area had two peaks each year, resulting from surface-water irrigation. From 2011 to 2016, groundwater levels in the groundwater irrigation area presented a decreasing trend due to the overextraction. Groundwater samples were taken for geochemical analysis each year in July from 2011 to 2016. Increasing trends were observed in groundwater total dissolved solids (TDS) and As. Owing to the reverse groundwater flow direction, the Shahai Lake acts as a new groundwater recharge source. Lake water had flushed the near-surface sediments, which contain abundant soluble components, and increased groundwater salinity. In addition, groundwater extraction induced strong downward hydraulic gradients, which led to leakage recharge from shallow high-TDS groundwater to the deep semiconfined aquifer. The most plausible explanation for similar variations among As, Fe(II) and total organic carbon (TOC) concentrations is the expected dissimilatory reduction of Fe(III) oxyhydroxides. [ABSTRACT FROM AUTHOR]

The modeling of changes in surface water and groundwater in the areas of inter-basin water diversion projects is quite difficult because surface water and groundwater models are run separately most of the time and the lack of sufficient data limits the application of complex surface-water/groundwater coupling models based on physical laws, especially for developing countries. In this study, a distributed surface-water and groundwater coupling model, named the distributed time variant gain model-groundwater model (DTVGM-GWM), was used to assess the influence of climate change and inter-basin water diversion on a watershed hydrological cycle. The DTVGM-GWM model can reflect the interaction processes of surface water and groundwater at basin scale. The model was applied to the Haihe River Basin (HRB) in eastern China. The possible influences of climate change and the South-to-North Water Diversion Project (SNWDP) on surface water and groundwater in the HRB were analyzed under various scenarios. The results showed that the newly constructed model DTVGM-GWM can reasonably simulate the surface and river runoff, and describe the spatiotemporal distribution characteristics of groundwater level, groundwater storage and phreatic recharge. The prediction results under different scenarios showed a decline in annual groundwater exploitation and also runoff in the HRB, while an increase of groundwater storage and groundwater level after the SNWDP’s operation. Additionally, as the project also addresses future scenarios, a slight increase is predicted in the actual evapotranspiration, soil water content and phreatic recharge. This study provides valuable insights for developing sustainable groundwater management options for the HRB. [ABSTRACT FROM AUTHOR]

Elevated fluoride (F) concentration in groundwater is posing a public health risk in the Manas River Basin (MRB), Northwest China. Based on the characterization of regional groundwater flow, 90 groundwater samples from aquifers were analyzed, along with top-soil leachate and pore-water samples from aquitards. Stable oxygen (δ18O) and hydrogen isotopes, radiocarbon and hydrochemical analyses of the groundwater and pore-water samples were conducted to trace groundwater hydrological and hydrochemical processes and thereby understand the distribution and migration mechanism of F. The groundwater is recharged by meteoric precipitation through vapor condensation processes in the Tianshan Mountains. The F concentration in groundwater samples from this basin ranged from 0.11 to 48.15 mg/L (mean 2.56 mg/L). In 37 of the 90 groundwater samples, the F concentrations were above the safe level for drinking water. The F concentrations progressively increased with the residence time and well depths in the northwest of the alluvial-fluvial plain, where groundwater is overexploited for agricultural and domestic use. Positive correlations between F and sodium (Na)/calcium (Ca) indicate that the enrichment and migration of F are influenced by cation exchange processes under high-Na and alkaline pH conditions. The relationships between δ18O and F and chloride (Cl) concentrations were nonlinear due to leaching and mixing processes. This shows that vertical leaching by irrigation return flow and mixing with pore water are the dominant processes driving the migration of F in the groundwater flow system of MRB, in addition to geochemical processes. [ABSTRACT FROM AUTHOR]

Sustainability has been one of the key criteria of effective water exploitation. Groundwater exploitation and water-table decline at Haolebaoji water source site in the Ordos basin in NW China has drawn public attention due to concerns about potential threats to ecosystems and grazing land in the area. To better investigate the impact of production wells at Haolebaoji on the water table, an adapted algorithm called the random walk on grid method (WOG) is applied to simulate the hydraulic head in the unconfined and confined aquifers. This is the first attempt to apply WOG to a real groundwater problem. The method can not only evaluate the head values but also the contributions made by each source/sink term. One is allowed to analyze the impact of source/sink terms just as if one had an analytical solution. The head values evaluated by WOG match the values derived from the software Groundwater Modeling System (GMS). It suggests that WOG is effective and applicable in a heterogeneous aquifer with respect to practical problems, and the resultant information is useful for groundwater management. [ABSTRACT FROM AUTHOR]

Soil surface evaporation is a significant component of the hydrological cycle, occurring at the interface between the atmosphere and vadose zone, but it is affected by factors such as groundwater level, soil properties, solar radiation and others. In order to understand the soil evaporation characteristics in arid regions, a field experiment was conducted in the Ordos Basin, central China, and high accuracy sensors of soil moisture, moisture potential and temperature were installed in three field soil profiles with water-table depths (WTDs) of about 0.4, 1.4 and 2.2 m. Soil-surface-evaporation values were estimated by observed data combined with Darcy’s law. Results showed that: (1) soil-surface-evaporation rate is linked to moisture content and it is also affected by air temperature. When there is sufficient moisture in the soil profile, soil evaporation increases with rising air temperature. For a WTD larger than the height of capillary rise, the soil evaporation is related to soil moisture content, and when air temperature is above 25 °C, the soil moisture content reduces quickly and the evaporation rate lowers; (2) phreatic water contributes to soil surface evaporation under conditions in which the WTD is within the capillary fringe. This indicates that phreatic water would not participate in soil evaporation for a WTD larger than the height of capillary rise. This finding developed further the understanding of phreatic evaporation, and this study provides valuable information on recognized soil evaporation processes in the arid environment. [ABSTRACT FROM AUTHOR]

The Guanzhong Basin in central China features a booming economy and has suffered severe drought, resulting in serious groundwater depletion in the last 30 years. As a major water resource, groundwater plays a significant role in water supply. The combined impact of climate change and intensive human activities has caused a substantial decline in groundwater recharge and groundwater levels, as well as degradation of groundwater quality and associated changes in the ecosystems. Based on observational data, an integrated approach was used to assess the impact of climate change and human activities on the groundwater system and the base flow of the river basin. Methods included: river runoff records and a multivariate statistical analysis of data including historical groundwater levels and climate; hydro-chemical investigation and trend analysis of the historical hydro-chemical data; wavelet analysis of climate data; and the base flow index. The analyses indicate a clear warming trend and a decreasing trend in rainfall since the 1960s, in addition to increased human activities since the 1970s. The reduction of groundwater recharge in the past 30 years has led to a continuous depletion of groundwater levels, complex changes of the hydro-chemical environment, localized salinization, and a strong decline of the base flow to the river. It is expected that the results will contribute to a more comprehensive management plan for groundwater and the related eco-environment in the face of growing pressures from intensive human activities superimposed on climate change in this region. [ABSTRACT FROM AUTHOR]

The Dunhuang Basin, a typical inland basin in northwestern China, suffers a net loss of groundwater and the occasional disappearance of the Crescent Lake. Within this region, the groundwater/surface-water interactions are important for the sustainability of the groundwater resources. A three-dimensional transient groundwater flow model was established and calibrated using MODFLOW 2000, which was used to predict changes to these interactions once a water diversion project is completed. The simulated results indicate that introducing water from outside of the basin into the Shule and Danghe rivers could reverse the negative groundwater balance in the Basin. River-water/groundwater interactions control the groundwater hydrology, where river leakage to the groundwater in the Basin will increase from 3,114 × 104 m3/year in 2017 to 11,875 × 104 m3/year in 2021, and to 17,039 × 104 m3/year in 2036. In comparison, groundwater discharge to the rivers will decrease from 3277 × 104 m3/year in 2017 to 1857 × 104 m3/year in 2021, and to 510 × 104 m3/year by 2036; thus, the hydrology will switch from groundwater discharge to groundwater recharge after implementing the water diversion project. The simulation indicates that the increased net river infiltration due to the water diversion project will raise the water table and then effectively increasing the water level of the Crescent Lake, as the lake level is contiguous with the water table. However, the regional phreatic evaporation will be enhanced, which may intensify soil salinization in the Dunhuang Basin. These results can guide the water allocation scheme for the water diversion project to alleviate groundwater depletion and mitigate geo-environmental problem. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)