Simulation of groundwater table dynamics based on Feflow in the Minqin Basin,China

As groundwater table declination is an important factor resulting in degradation of eco-environment in the Minqin Basin, China, it is significant to investigate and understand the groundwater table dynamics in this area. According to the physical and geographical conditions of the Minqin Basin, a hydrogeological conceptual model and a mathematical model were established, and the mathematical model was figured out by using Finite Element subsurface Flow system （Feflow）. Accurate hydrogeological parameters were acquired, and the spatio-temporal distribution dynamics of groundwater table for 1983-2001 were also simulated. The model performed well with a correlation coefficient of 0.977 and a mean error of 0.9768 m. The inflow and outflow of the groundwater system were predicted by time series analysis, and the groundwater table dynamics for 2011 were further acquired. Gen- erally the groundwater table in the Minqin Basin would continue to decline. The groundwater table would decline during spring and summer irrigation, while it would rise during autumn-winter irrigation. The groundwater depression cones would expand with the increase of center depths. Therefore, regulatory measures should be taken to prevent the declination of groundwater table and improve the eco-environment of this area.

Physiological responses of Populus euphratica Oliv. to groundwater table variations in the lower reaches of Heihe River, Northwest China

Riparian vegetation in the lower reaches of Heihe River serves important ecological functions. However, the riparian ecosystems have been constantly deteriorating in the past 30 years simply due to water interception for oasis agricultural irrigation in the middle reaches of the river. This study pays a particular attention to Populus eu- phratica Oily. forest because it is a dominant component of the riparian ecosystem in the lower reaches of Heihe River where the depth of groundwater table is the controlling factor in sustaining riparian ecosystems. To reveal leaf-related physiological responses of Populus euphratica Oliv. forest to groundwater table variations, we analyzed the relationships between the depth of groundwater table （DG） and three leaf-related parameters, i.e. leaf stomatal density （SD）, specific leaf area （SLA）, and stable carbon isotopic composition （6~SC）. Our results show that the relationship between DG and leaf SD is a bi-mode one shaped by both salt stress and water stress. That is, salt stress appeared in shallow groundwater conditions and water stress happened in deep groundwater conditions, and the thin layer around 2.7 m of DG is a stress-free layer. Leaf SD fluctuated according to the DG variation, first de- creased with increasing DG, then increased at depths ranging 2.7-3.7 m, and after a relatively stable plateau of SD at depths ranging 3.7-5.2 m, decreased again with increasing DG. Our results also show that SLA decreased ex- ponentially with increasing DG and foliar 6130 values are also strongly dependent on DG, further demonstrating that these two parameters are sensitive indicators of water stress. The exponential curve suggests that SLA is more sensitive to DG when groundwater table is shallow and 3 m seems to be a threshold beyond which SLA becomes less sensitive to DG. Foliar 613C becomes more sensitive when the groundwater table is deep and 7 m seems to be a threshold below which the 6130 signature becomes more sensitive to DG. These findings should be helpful in monitoring the growth and development of Populus euphratica Oliv. forests and also in providing protection measures （i.e. DG related） for Heihe River riparian forests.

Understanding groundwater table using a statistical model

In this study, a statistical model was established to estimate the groundwater table using precipitation, evaporation, the river stage of the Liangduo River, and the tide level of the Yellow Sea, as well as to predict the groundwater table with easily measurable climate data in a coastal plain in eastern China. To achieve these objectives, groundwater table data from twelve wells in a farmland covering an area of 50 m ~ 150 m were measured over a 12-month period in 2013 in Dongtai City, Jiangsu Province. Trend analysis and correlation analysis were conducted to study the patterns of changes in the groundwater table. In addition, a linear regression model was established and regression analysis was conducted to understand the relationships between precipitation, evaporation, river stage, tide level, and groundwater table. The results are as follows： （1） The groundwater table was strongly affected by climate factors （e.g., precipitation and evaporation）, and river stage was also a significant factor affecting the groundwater table in the study area （p 〈 0.01, where p is the probability value）. （2） The groundwater table was especially sensitive to precipitation. The significance of the factors of the groundwater table were ranked in the following descending order： precipitation, evaporation, and river stage. （3） A triple linear regression model of the groundwater table, precipitation, evaporation, and river stage was established. The linear relationship between the groundwater table and the main factors was satisfied by the actual values versus the simulated values of the groundwater table （R^2 = 0.841, where R^2 is the coefficient of determination）.

Seasonal patterns in water uptake for Medicago sativa grown along an elevation gradient with shallow groundwater table in Yanchi county of Ningxia,Northwest China

Lucerne （Medicago sativa L.） is a deep-rooted perennial leguminous forage with high evapo-transpiration rate exceeding the annual precipitation in semi-arid areas of Northwest China. Groundwater might be the potential water sources of lucerne in the area with shallow groundwater table. In this study, stable isotopic compositions of oxygen and hydrogen （6180 and 8D） of different water sources and xylem sap were analyzed to determine the seasonal （April, June, July and August） and topographic （three slope positions） variations in water sources for lucerne growing in Ningxia eastern semi-arid area adjacent to Mu Us Desert characterized by shallow groundwater table. IsoSource software was used to calculate the probable contribution of different water sources to the total plant water uptake. Stomatal conductance, stem water potential, carbon isotope discrimination （A13C） of whole plant were also determined for evaluating the water status of lucerne growing at different slope positions. The results showed that soil water content increased as the elevation decreased. Oxygen compositions of soil water in the 0-40 cm profile fluctuated considerably. Soil water 8180 values in deep profile （〉3.5 m） were similar to those in groundwater, implying the recharge of groundwater to this soil layer. Highest water utilization rate from deep soil profile （below 350 cm） was recorded for lucerne grown at the slope position 1 （groundwater table depth of 3.5-3.9 m） in April, June and July. The lucernes at slope position 2 （groundwater table depth of 5.8-6.4 m） and slope position 3 （groundwater table depth 7.1-8.3 m） mostly used water from deep soil layers （below 350 cm） during dry period, and turned to use water from superficial soil layer in wet period. Higher yield, A13C value of whole plant and stomatal conductance were observed for lucerne grown at the slope position 1 than those at other slope positions. These results indicated that groundwater is a significant water source for transpiration of lucerne grown in Ningxia semi-arid area with shallow groundwater table where lucerne grassland is suggested to be established so as to obtain better yield performance.

Decline of groundwater table in Beijing and recognition of seismic precursory information

This paper quantitatively analyzed groundwater table fluctuations caused by groundwater overdraft, and probed into the possibility of drawing earthquake precursory information from groundwater table variations on the background of groundwater overdraft. Main effect factors of groundwater regime in Beijing region include groundwater extraction and rainfall. The decline of groundwater table was directly related to regional groundwater overdraft. Using the method of correlation analysis, the paper analyzed the relation between groundwater overdraft and groundwater level variations, with the aim of evaluating the effect of groundwater overdraft on water levels in observation wells and providing scientific basis for identifying seismic precursory information. The results indicate that the variations of groundwater level in slightly-affected zones of groundwater overdraft can contain some seismic precursory information, and it is possible to extract seismic precursory anomalies if proper mathematical methods are adopted to remove the trend component and annual period changes.

The variation in soil moisture and the appropriate groundwater table for desert riparian forest along the Lower Tarim River

Based on data collected over five years of monitoring the Lower Tarim River,we analyzed the variability of soil moisture content （SMC） and the relationship between SMC,groundwater table depth （GWD） and vegetation by using the methods of coefficient of variation （Cv）,Pearson correlation and regression. The results of the variability of SMC indicate that it rose with increase in depth of soil layer -SMC in the soil layer of 0-60 cm was relatively small compared to SMC in the soil layer of 100-260 cm which showed a significant increase in variability. SMC and GWD before and after ecological water diversions exhibited significant differences at the site of the Yingsu transect and its vicinity of the watercourse,especially SMC in the soil layer of 100-260 cm increased significantly with a significant rise of GWD and reached maximum values at a GWD of about 4 m. Plant coverage and species diversity significantly improved with increases in SMC in the soil layer of 100-260 cm,both of them approached the maximum values and 92.3% of major plant species were able to grow when SMC was 〉 10%. To restore the ecosystem of desert riparian forest along the Lower Tarim River,the GWD must be maintained at 〈 4 m in the vicinity of the watercourse and at about 4 m for the rest of this arid region.

EXPERIMENTAL INVESTIGATION OF EFFECT OF TIDE ON COASTAL GROUNDWATER TABLE

In this article, a tide simulation system based on a two-way water pump technique is developed. Using this system and numerical simulations, the groundwater table fluctuation characteristics, relative over height of groundwater table, and influencing factors of over height are investigated. The experimental and numerical results indicate that the groundwater table fluctuation is of periodic, and of asymmetric. The amplitude of groundwater table fluctuations decreases with the increase of the onshore distances. There are phase lags of groundwater table fluctuations for different monitoring points. The tide can bring about remarkable over height of coastal groundwater table. The dominating factors bring about over height include the tide amplitude, aquifer thickness and tide frequency. Under experimental conditions, the relative tide amplitude over height may exceeded 50% of the maximal tide amplitude, and reach about 10% of aquifer thickness.

Experimental Study on the Utilization of Shallow Groundwater for Spring Wheat

[Objective]The paper aimed to study effect of shallow groundwater at different depths on crop water requirement and crop evaporation in spring wheat field.[Method]Five treatments of shallow groundwater table at different depth were designed to do evaporation experiment for spring wheat in 2008-2009.[Result]The groundwater at different depths had great impact on crop growth and field evaporation;its supply accounted for 0-52% of actual evapotranspiration.Atmospheric evaporation and crop rooting depth were the major factors to affect the uptake of groundwater at shallow table,and the supply of deep groundwater was controlled by groundwater table.[Conclusion]The study reveled the pattern of evapotranspiration of spring wheat and evaporation of shallow groundwater at different depth,in order to supply basis for the rational and effective utilization of shallow groundwater as well as optimization of the irrigation scheduling for spring wheat.

Groundwater regime and calculation of yield response in North China Plain: a case study of Luancheng County in Hebei Province

The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since large scale groundwater extraction carried out in the 1960s. The drop of precipitation, substantial increase in agricultural output, variations of crop planting structure and construction of water conservancy projects in the headwater area all tie up with the decline of the groundwater table. On the basis of analyzing the hydrogeological conditions and the water resources utilization of Luancheng County, a three-dimensional groundwater flow model was developed to simulate the county抯 groundwater flow through finite-difference method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition. Based on parameter calibration and adjustment using measured data, the hydraulic conductivity and specific yield were simulated. Using the calibrated model, we analyze the agricultural water saving potentiality and its influence on the groundwater. The results are as follows: (1) if we decrease the amount of water extracted by 0.14×108 m3, the average groundwater table of the five observation wells in December will rise by 0.33 m; (2) if we decrease the water by 0.29×108 m3, the average groundwater table of the five observation wells in December will rise by 0.64 m; and (3) if we increase the water by 0.29×108 m3, the average groundwater table of the five observation wells in December will decline by 0.45 m. So we can draw a conclusion that controlling the agricultural water use is an important way to prevent the decline of groundwater table.

Numerical simulation of groundwater and early warnings from the simulated dynamic evolution trend in the plain area of Shenyang,Liaoning Province(P.R. China)

Groundwater level is the most direct factor reflecting whether groundwater is in a virtuous cycle. It is the most important benchmark for deciding whether a balance can be struck between groundwater discharge and recharge and whether groundwater exploitation will trigger problems pertinent to environment, ecology and environmental geology. According to the borehole and long-term monitoring wells data in the plain area of Shenyang, a numerical groundwater model is established and used to identify and verify the hydrogeological parameters and balanced items of groundwater. Then the concept of red line levels, the control levels of groundwater is proposed, the dynamic evolution trend of groundwater under different scenarios is analyzed and predicted and groundwater alerts are given when groundwater tables are not between the lower limit and the upper limit. Results indicated:(1) The results of identification and verification period fitted well, and the calculation accuracy of balanced items was high;(2) with the implementation of shutting wells, groundwater levels in urban areas of Shenyang would exceed the upper limit water level after 2020 and incur some secondary disasters;(3) under the recommended scenario of water resources allocation, early-warnings for groundwater tables outside the range would occur in the year of 2020, 2023, 2025 respectively for successive wet, normal and dry years. It was imperative to reopen some groundwater sources and enhance real-time supervision and early-warning to prevent the occurrence of potential problems.

Limiting drainage criterion for groundwater of mountain tunnel

Large amount of groundwater discharging from tunnel is likely to cause destruction of the ecological environment in the vicinity of the tunnel, thus an appropriate drainage criterion should be established to balance the tunnel construction and groundwater.To assess the related problems, an limiting drainage standard ranging from 0.5 to 2.0 m3/(m·d) was suggested for mountain tunnels based on survey and comparative analysis. After that, for the purpose of verifying the rationality of the standard, a calculated formula for dewatering funnel volume caused by drainage was deduced on the basis of the groundwater dynamics and experience method.Furthermore, the equation about the relationship between water discharge and drawdown of groundwater table was presented. The permeability coefficient, specific yield and groundwater table value were introduced, and then combined with the above equation, the drawdown of groundwater table under the proposed limiting drainage criterion was calculated. It is shown that the proposed drainage standard can reach the purpose of protecting ecological environment under the following two conditions. One is the permeability coefficient ranges from 10-4 to 10-5 m/s and the specific yield ranges from 0.1 to 0.001. The other is the permeability coefficient varies from 10-6 to 10-8 m/s and the specific yield varies from 0.1 to 0.01. In addition, a majority of common geotechnical layers are involved in the above ranges. Thus, the proposed limiting drainage standard which ranges from 0.5 to 2.0 m3/(m·d) for mountain tunnel is reasonable.

Water Environmental Degradation of the Source Area of the Yellow River on Northeast Qinghai-Tibet Plateau

The issue on water environmental degradation in the source area of the Yellow River has been one of very serious ecological and socially economic problems. The temporal-spatial changes of water environment led to the decreasing of land capacity and river disconnecting. The status of water environmental degradation in this paper was analyzed based on the data and field investigation. The results indicated that the surface water area in the region has obviously decreased owing to the climate changes and human irrational use of water resources and the continuous lowering of the regional groundwater table and the steadily decreasing tendency of the flow rate in the source areas of the Yellow River.

Balance of Irrigation Water in Jinghui Canal Irrigation District of China

Jinghuiqu Canal Irrigation District is an old irrigation area with a long history.Due to natural and man-made factors,the inflow and rainfall of the irrigation area are decreasing,which seriously affects agricultural production water in the irrigation area and constantly threatens the safety of irrigation water in irrigation area.In this paper,natural and man-made factors of affecting irrigation water in irrigation area are analyzed,and it is proposed that main channels of solving safety of irrigation water are enhancing the utilization of canal water and optimizing the allocation of canals and wells.

Engineering Geological and Geotechnical Studies of Taprang Landslide, West-central Nepal: An Approach for Slope Stability Analysis

Detailed investigation of Taprang landslide was carried out in order tounderstand the surface, subsurface lithological information and physicalproperties of soil by using multi-disciplinary methods such as engineeringgeological, geophysical and geotechnical studies for the determinationof factor of safety for slope stability analysis. Geological study wascarried out by detail mapping of surface geology, soil condition, propertiesof bedrock and its discontinuities. The geophysical survey (ElectricalResistivity Tomography-ERT) were carried out to know the electricalresistivity of soil for identifying the groundwater table and slip surface ofthe landslide. Geotechnical analysis such as grain size analysis, liquid limitand direct shear test were carried out in order to evaluate soil classification,moisture content, cohesion and the angle of internal friction of soil forknowing the strength the soil. These soil parameters indicate the soil is verylow strength. The combination of these results were used for calculatingthe factor of safety (FoS) by Limit Equilibrium Method (LEM) proposedby Bishop and Janbu methods. The result of factor of safety in the Tapranglandslide demonstrates that the slope become stable in drained (dry)condition, remain ultimate stage in undrained (wet) condition and finallyfailure occurs if applied the seismic load in both drained and undrainedconditions.

Vegetation dynamics induced by groundwater fluctuations in the lower Heihe River Basin,northwestern China

Aims Since 2000,the environmental flow controls project has been implemented in the lower Heihe River Basin,a typical arid inland river basin in northwest China,to restore the deteriorated ecological environment in this region.The aim of this study was to explore the impacts of groundwater fluctuations on vegetation dynamics.Our results can be used as a reference for water resources planning and management to maintain proper environmental flows in arid areas.Methods The location(by Global Positioning System)and depth of the monitoring wells,as well as groundwater table depth and salinity were measured in situ at each site from July to August 2009.Based on the measurements of the groundwater table depth and salinity following the implementation of environmental flow controls project(EFCP)in the lower Heihe River Basin,the groundwater fluctuations during the period from 2001 to 2009 were analyzed.Descriptive statistics and Pearson’s correlation were used to analyze the relationship between vegetation changes and groundwater table fluctuations.Additionally,the spatial distributions of the groundwater table depth and salinity were interpolated using the simple kriging method.Trend analysis was applied to the time series of integrated Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to identify interannual vegetation dynamics.The relationship between vegetation status and groundwater environment was investigated at different spatial scales by analyzing and comparing the time series and trends.Important Findings(i)The groundwater table and salinity increased significantly in most of the study area with spatial heterogeneity.On average,the groundwater table rose;0.5 and 1.5 m in the upper and lower Ejina Basin,respectively,and the groundwater salinity increased across the study area by 0–4%.(ii)A notable correlation between the vegetation status and the groundwater table was revealed when the groundwater table depth fluctuated between 1.8 and 3.5 m,whereas the vegetation did not show an obvious response to groundwater table changes when the groundwater table depth was more than 5–6 m.(iii)Vegetation restoration mainly occurred in riparian areas within 500–1000 m of from natural rivers,where the groundwater table depth varied from 2 to 4 m,and salinity was<5%,whereas vegetation degradation appeared at some locations where groundwater environment had deteriorated.

Effects of Long-Term Groundwater Management and Straw Application on Aggregation of Paddy Soils in Subtropical China

Soil organic carbon （SOC） and iron （Fe）-oxides are important contributors of aggregate stability in highly weathered soils, and they are influenced by groundwater management and straw application. A 30-year plot experiment with early rice （Oryza sativa L.）-late rice-winter fallow rotations was conducted using a upland clay soil in cement pools under shallow groundwater table at a depth of 20 am （SGT） aud deep groundwater table at a depth of 80 cm （DGT） to simulate the groundwater tables of two types of important paddy soils, gleyed paddy soils and hydromorphic paddy soils, respectively, in subtropical China. Soil redox potential （Eh） was measured in situ, and 0-20 cm soil samples were collected for the analyses of soil Fe-oxides, SOC, and aggregates under SGT or DGT with different straw application treatments, in order to evaluate the interaction of groundwater management and straw application on paddy soil aggregation and the relative importance of SOC or Fe-oxides on soil aggregation. The results showed that soil Eh was restricted by irrigation, and its variation was more significant under DGT than under SGT. The decreased soil Eh or reduced drying and wetting cycles under SGT resulted in more SOC accumulation with the straw application, had no effect on soil free Fe-oxides （Fed）, significantly increased the amorphous Fe-oxide （Feo） and complex Fe-oxide contents, but decreased the crystalline Fe-oxide content （Fed-Feo）. The soils under DGT had more macroaggregates than those under SGT, but the difference decreased with the straw application. It could be concluded that soil Fe-oxides were the principal contributing factor to the aggregation of paddy soils in subtropical China and SOC was also an important contributing factor.

Estimating the effect of shallow groundwater on diurnal heat transport in a vadose zone

The influence of shallow groundwater on the diurnal heat transport of the soil profile was analyzed using a soil sensor automatic monitoring system that continu- ously measures temperature and water content of soil profiles to simulate heat transport based on the Philip and de Vries （PDV） model. Three experiments were conducted to measure soil properties at depths of 5 cm, 10 cm, 20 cm, and 30 cm when groundwater tables reached l0 cm, 30 cm, and 60 cm （Experiments I, II, and III）. Results show that both the soil temperature near shallow groundwater and the soil water content were effectively simulated by the PDV model. The root mean square errors of the temperature at depths of 5 cm, 10 cm, and 20 cm were 1.018℃, 0.909℃, and 0.255℃, respectively. The total heat flux generated the convergent and divergent planes in space-time fields with valley values of-161.5 W-m 2 at 7：30 and -234.6 W.m2 at 11：10 in Experiments II and III, respectively. The diurnal heat transport of the saturated soil occurred in five stages, while that of saturated-unsaturated and unsaturated soil profiles occurred in four stages because high moisture content led to high thermal conductivity, which hastened the heat transport.

Drainage design combining drain holes and pinholes for tunnel boring machine segments subject to high water pressure

Balance of the groundwater and ecology is crucial for controlled discharge.However,regarding the segments of tunnel boring machines(TBMs)under high water pressure,the stability of the lining structure is often reduced by excessive drain holes required to achieve this balance.The large discharge of pinholes can easily have severe consequences,such as the lowering of the groundwater table,drying of springs,and vegetation wilting.Thus,in this study,according to the fluid-structure coupling theory,a new drainage design for TBM segments was developed by considering a mountain tunnel subject to a high water pressure as a case study.The evolution characteristics,including the external water pressure of the lining,discharge volume of the segment,and groundwater-table drawdown,were investigated via numerical modeling with drain holes and pinholes.The results indicated that the optimal design parameters of drainage segments for the project case were as follows:a circumferential spacing angle and longitudinal number on one side of a single ring of 51°and 2,respectively,for the drain holes and an inclination angle and length of 46.41°and 0.25 times the grouting thickness,respectively,for the pin holes.

Spatio-Temporal Variability of Soil Salinity in Alluvial Plain of the Lower Reaches of the Yellow River——A Case Study

Soil salinity and hydrologic datasets were assembled to analyze the spatio-temporal variability of salinization in Fengqiu County, Henan Province, China, in the alluvial plain of the lower reaches of the Yellow River. The saline soil and groundwater depth data of the county in 1981 were obtained to serve as a historical reference. Electrical conductivity （EC） of 293 surface soil samples taken from 2 kin x 2 km grids in 2007 and 4{） soil profiles acquired in 2（108 was analyzed and used for comparative mapping. Ordinary kriging was applied to predict EC at unobserved locations to derive the horizontal and vertical distribution patterns and variation of soil salinity. Groundwater table data from 22 observation wells in 2008 were collected and used as input for regression kriging to predict the maximum groundwater depth of the county in 2008. Changes in the groundwater level of Fengqiu County in 27 years from 1981 to 2008 was calculated. Two quantitative criteria, the mean error or bias （ME） and the mean squared error （MSE）, were computed to assess the estimation accuracy of the kriging predictions. The results demonstrated that the soil salinity in the upper soil layers decreased dramatically and the taxonomically defined saline soils were present only in a few micro-landscapes after 27 years. Presently, the soils with relatively elevated salt content were mainly distributed in depressions along the Yellow River bed. The reduction in surface soil salinity corresponded to the locations with deepened maximum groundwater depth. It could be concluded that groundwater table recession allowed water to move deeper into the soil profile, transporting salts with it, and thus played an important role in reducing soil salinity in this region. Accumulation of salts in the soil profiles at various depths below the surface indicated that secondary soil salinization would occur when the groundwater was not controlled at a safe depth.