Prediction of land subsidence caused by groundwater exploitation in Hanoi, Vietnam, using multifactorial correlation analysis

Multifactorial correlation analysis is a new method used to predict the land subsidence caused by groundwater exploitation This article introduces and applies the method to establish the function of the surface settlement rate （Vs） and the function of the time-dependent surface settlement （St） caused by groundwater exploitation, based on data acquired at three land subsidence monitoring stations in the Hanoi area of Vietnam. Comparison with actual monitoring data indicates that the prediction results are relatively close to the monitoring data. From this, we conclude that multifactorial correlation analysis is a reliable method and can be used to predict future land subsidence caused by groundwater exploitation in Hanoi.

The Damaging Effects of Abstracting the Deep Aquifers’Groundwater in Jordan-Quality Constraints

The deep aquifers in Jordan contain non-renewable and fossil groundwater and their extraction is quasi a mining process, which ends in the depletion of these resources. Although aquifers in the majority of groundwater basins in Jordan are vertically and horizontally interconnected stratification in different water quality horizons with generally increasing water salinity with the depth is observed. Many officials and planners advocate the extraction of deep salty and brackish water to be desalinated and used in household, industrial, and agricultural uses. In this article, the quality of the groundwater in the different deep aquifers and areas in Jordan is discussed. The results of this study show that the consequences of the deep groundwater exploitation are not restricted to depletion of the deep aquifers but also that the overlying fresh groundwater will, due to vertical and horizontal interconnectedness of the different aquifers, percolate down to replace the extracted deep groundwater. This will cause the down-percolating fresh groundwater to become salinized in the deep saline aquifers, which means that extracting the deep brackish and saline groundwater is not only an emptying process of the deep groundwater but also it is an emptying process of the fresh groundwater overlying them. The results allow to conclude that any extraction of the deep groundwater in areas lying to the north of Ras en Naqab Escarpment will have damaging impacts on the fresh groundwater in the overlying fresh groundwater aquifers. This article strongly advises not to extract the deep brackish and saline groundwater, but to conserve that groundwater as a base supporting the overlying fresh groundwater resources, and that will help in protecting the thermal mineralized water springs used in spas originating from these deep aquifers. The increasing water needs of the country can be covered by the desalination of seawater at Aqaba, which is the only viable option for Jordan at present and in the coming decades.

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.

An assessment of the carrying capacity of groundwater resources in North China Plain region–Analysis of potential for development

Over-exploitation of groundwater in North China Plain(NCP) has resulted in a series of eco-environment problems. Sustainable use of groundwater resources in NCP, in particular management of groundwater resource carrying capacity(GRCC), faces an unprecedented challenge. Here we define GRCC, and a new assessment method is tentatively proposed and applied to evaluate GRCC based on the whole NCP, city administrative units and county administrative units. Our study divided the NCP into three zones, i.e. non-overexploited non-overloaded zone(NNZ), overexploited but non-overloaded zone(ONZ), and overexploited overloaded zone(OOZ). Results confirmed 27.6% of counties belonged to NNZ. However, 58.9% of counties and NCP as a whole belonged to ONZ, and 13.5% of counties belonged to OOZ. Spatially, NNZs were mainly distributed in Beijing, parts of eastern coastal cities and Henan Province. OOZs were mostly distributed in middle-eastern part of Cangzhou, parts of Dezhou, Tianjin and Binzhou, and the remaining areas belonged to ONZs. We suggest two approaches for enhancing GRCC, i) increasing the amount of available groundwater and ii) improving the water use efficiency. An increase of 11.0 billion cubic meters to the available groundwater levels combined with water use efficiency improvements up to 479 CNY per cubic meter of the world mean, the gross domestic product(GDP) sustained by groundwater in the NCP could reach 11.1 trillion CNY and maintain a 20 years of GDP development assuming the current rate of growth.

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.

Multivariate statistical analysis of chemical and stable isotopic data as indicative of groundwater evolution with reduced exploitation

Groundwater resources in the North China Plain(NCP)are undergoing tremendous changes in response to the operation of groundwater exploitation reduction(GWER)project.To identify groundwater evolution in this complex context,hierarchical cluster analysis(HCA)and principal component analysis(PCA)were combined to interpret an integrated dataset of stable isotopes and chemical data from four sampling campaigns in a pilot area of groundwater control.We proposed a novel HCA approach integrating stable isotopes and chemical signals,which successfully partitioned the groundwater samples into the unconfined and the confined water samples.Stable isotopic evidence showed that the lateral inflow and the surface water may contribute more to groundwater recharge in this region than local modern precipitation.The unconfined water's main hydrochemical types were Na type with mixed anions,and Na-Cl-SO_(4)type,while the confined water was mainly Na-Cl and Na-SO_(4)types.Geochemical processes mainly involved the dissolution/precipitation of halite,gypsum,Glauber's salt,feldspar,calcite and dolomite,as well as the cation exchange.PCA results showed that water-rock interaction(i.e.,salinity-based and alkalinity-based processes)predominated the hydrochemical evolution,along with local nitrate contamination resulting from fertilizers and domestic sewage.The GWER project regulated the natural evolution of unconfined water chemistry,and significantly reduced the unconfined water's salinity(mainly Na^(+),Mg^(2+),SO_(4)^(2-)).This may be attributed to upward leakage from low-salinity confined water at some parts of the aquifer.Additionally,insignificant changes in the confined water's salinity reflected that the impact of GWER on the confined aquifer was negligible.This study facilitates the groundwater classification effectively in the areas lack of geological data,and enhances the knowledge of groundwater chemical evolution in such a region where groundwater restoration is in progress,with important implications for groundwater sustainable management in similar basins worldwide.

Ground Subsidence in Areas of Loose Porous Aquifers

Groundwater is one of the important water resources in northern China's plain areas. Many severe geological hazards have occurred in these areas due to ground subsidence which is caused by over exploitation of groundwater. This paper introduces and analyses the ground subsidence caused by groundwater exploitation and its mechanism in the northern China's plains. A ground subsidence prediction model has been developed based on the consolidation theory. The authors have tested this model in a case study of Fuyang City, Anhui Province, where ground subsidence is a severe environmental problem. In the case study, the model results match very well with those of the actual measurement. Two schemes of groundwater exploitation are assessed. The conclusion from the study could be used in the long-term water and economical management planning. The strategies for the control of ground subsidence are discussed.

3-D VARIABLE PARAMETER NUMERICAL MODEL FOR EVALUATION OF THE PLANNED EXPLOITABLE GROUNDWATER RESOURCE IN RE-GIONAL UNCONSOLIDATED SEDIMENTS

In order to correctly evaluate the exploitable groundwater resottrce in regional complex, thick Quaternary unconsolidated sediments, the whole Quaternary unconsolidated sediments are considered as a unified hydrogeological unit and a 3-D unsteady groundwater flow numerical model is adopted. Meanwhile, with the consideration of the dynamic changes of the porosity, the hydraulic conductivity and the specific storage with the groundwater level dropping during the exploitation process, an improved composite element seepage matrix adjustment method is applied to solve the unsteady flow problem of free surface. In order to eva- luate the exploitable groundwater resource in Cangzhou, Hebei Province, the hydrogeological conceptual model of Cangzhou is generalized to establish, a 3-D variable parameter numerical model of Cangzhou. Based on the prediction of the present groundwater exploitation, and by adjusting the groundwater exploitation layout, the exploitable groundwater resource is predicted. The model enjoys features like good convergence, good stability and high precision.

Impacts of Human Activities on the Occurrence of Groundwater Nitrate in an Alluvial Plain: A Multiple Isotopic Tracers Approach

Nitrate pollution is a severe problem in areas with intensive agricultural activities. This study focuses on nitrate occurrence and its constraints in a selected alluvial fan using chemical data combined with environmental isotopic tracers （180, 3H, and lSN）. Results show that groundwater nitrate in the study area is as high as 258.0 mg/L （hereafter NO3） with an average of 86.8 mg/L against national drinking water limit of 45 mg/L and a regional baseline value of 14.4 mg/L. Outside of the riparian zone, nitrate occurrence is closely related to groundwater circulation and application of chemical fertilizer.High groundwater nitrate is found in the re- charge area, where nitrate enters into ground- water through vertical infiltration, correspond- ing to high 3H and enriched 1SO in the water. In the riparian zone, on the contrary, the fate of groundwater nitrate is strongly affected by groundwater level. Based on two sampling tran- sects perpendicular to the riverbank, we found that the high level of nitrate corresponds to the deeper water table （25 m） near the urban center, where groundwater is heavily extracted.Groundwater nitrate is much lower （〈12.4 mg/L） at localities with a shallow water table （5 m）, which is likely caused by denitrification in the aquifer.

Sustainability of Intensively Exploited Aquifer Systems in the North China Plain: Insights from Multiple Environmental Tracers

Environmental tracers are proving to be a unique tool for assessing groundwater sustainability, such as characterization of recharge, identification of pathways and sources of contaminants, and prediction of groundwater change in response to excessive abstraction. This paper helps to better understand the groundwater sustainability in the Quaternary aquifer from the tracer data in the North China Plain. Relatively modern ground waters occur in the piedmont plain with 3H-3He age less than 40 a within a depth 100 m. These ground waters are mainly recharged from the local precipitation and irrigation return. The recharge rate estimated by tracers is in the range of 0.24 to 0.32 m/a. Paleowater which is dated from 10 000 a B.P. to more than 35 000 a B.P. by radiocarbon dating is found in highly-confined portions of Quaternary aquifer systems. This indicates that water recharge took place during the past glacial period. The tracers have suggested a slow natural replenishment rates to the central plain. The aquifer has been overexploited currently. Some strategies that can be implemented to promote a sustainable groundwater supply are needed to implement in future.

Environmental deterioration of farmlands caused by the irrational use of agricultural technologies

Without considering the ecosystem-depen- dence of agricultural production, irrational use of agricultural technologies could bring only short-term economic benefits but leave long-term environmental deterioration. If some agricultural lands have to be abandoned because of these technologies such as chemical films or groundwater depletion, it will aggravate the burden of remaining lands for maintaining or enhancing production. Thus, agricultural production should be a part of public services, requiring the consideration of interests of different stakeholders and sustainability.