Assessment of village-wise groundwater draft for irrigation: a field-based study in hard-rock aquifers of central India

Extracted groundwater, 90% of which is used for irrigated agriculture, is central to the socio-economic development of India. A lack of regulation or implementation of regulations, alongside unrecorded extraction, often leads to over exploitation of large-scale common-pool resources like groundwater. Inevitably, management of groundwater extraction (draft) for irrigation is critical for sustainability of aquifers and the society at large. However, existing assessments of groundwater draft, which are mostly available at large spatial scales, are inadequate for managing groundwater resources that are primarily exploited by stakeholders at much finer scales. This study presents an estimate, projection and analysis of fine-scale groundwater draft in the Seonath-Kharun interfluve of central India. Using field surveys of instantaneous discharge from irrigation wells and boreholes, annual groundwater draft for irrigation in this area is estimated to be 212 × 10⁶ m³, most of which (89%) is withdrawn during non-monsoon season. However, the density of wells/boreholes, and consequent extraction of groundwater, is controlled by the existing hydrogeological conditions. Based on trends in the number of abstraction structures (1982–2011), groundwater draft for the year 2020 is projected to be approximately 307 × 10⁶ m³; hence, groundwater draft for irrigation in the study area is predicted to increase by ～44% within a span of 8 years. Central to the work presented here is the approach for estimation and prediction of groundwater draft at finer scales, which can be extended to critical groundwater zones of the country.     

PAHs contamination in groundwater from a part of metropolitan city,India: a study based on sampling over a 10-year period

Presence of polycyclic aromatic hydrocarbons (PAHs) in the soil and water is of serious environmental concern as they are carcinogenic in nature. The present study was carried out with an aim to identify the presence of PAHs in groundwater of Chennai, Tamil Nadu, India. This is an industrialised area where petrochemical storage tanks are located. Groundwater sampling was carried out in the years 2001, 2011 and 2012 to understand the variation in PAHs content in this area. Concentration of major ions, pH and EC were measured during the year 2001. Of the 24 groundwater samples collected in the year 2001, most of them were alkaline and 62.5 % were not permissible for drinking based on pH and EC, respectively. Influence of seawater was the major reason for the Na–Cl dominant nature of groundwater. TPH and PAHs analysis of groundwater carried out in 2001 and 2011, and physical examination of groundwater in 2012 indicate the increased level of contamination in the eastern part of the study area. The contamination in the eastern part persists because of the fact that groundwater is flowing towards the east and also due to the presence of petrochemical storage tanks near the coast. Thus this area is affected by PAHs pollution which has endured over the past 50 years. An underground storage tank that was functioning in this area was closed about 50 years ago and leakage of PAHs from this tank was reported in the year 1993. However, the present study indicates the decrease in the area of zone of pollution, possibly due to natural flushing of groundwater zone.     

Evaluating the impact of artificial groundwater recharge structures using geo-spatial techniques in the hard-rock terrain of Rajasthan,India

Groundwater levels in hard-rock areas in India have shown very large declines in the recent past. The situation is becoming more critical due to a paucity of rainfall, limited surface water resources and an increasing pattern of groundwater extraction in these areas. Consequently, the Ground Water Department with the aid of World Bank has implemented the water structuring programme to mitigate groundwater scarcity and to develop a viable solution for sustainable development in the region. The present study has been undertaken to assess the impact of artificial groundwater recharge structures in the hard-rock area of Rajasthan, India. In this study groundwater level data (pre-monsoon and post-monsoon) of 85 dug-wells are used, spread over an area of 413.59 km². The weathered and fractured gneissic basement rocks act as major aquifer in the area. Spatial maps for pre- and post-monsoon groundwater levels were prepared using the kriging interpolation technique with best fitted semi-variogram models (Spherical, Exponential and Gaussian). The groundwater recharge is calculated spatially using the water level fluctuation method. The entire study period (2004–2011) is divided into pre- (2004–2008) and post-intervention (2009–2011) periods. Based on the identical nature of total monsoon rainfall, two combinations of average (2007 and 2009) and more than average (2006 and 2010) rainfall years are selected from the pre- and post-intervention periods for further comparisons. All of the water harvesting structures are grouped into the following categories: as anicuts (masonry overflow structure); percolation tanks; subsurface barriers; and renovation of earthen ponds/nadis. A buffer of 100 m around the intervention site is taken for assessing the influence of these structures on groundwater recharge. The relationship between the monsoon rainfall and groundwater recharge is fitted by power and exponential functions for the periods of 2004–2008 and 2008–2011 with R ² values of 0.95 and 0.98, respectively. The average groundwater recharge is found to be 18% of total monsoon rainfall prior to intervention and it became 28% during the post-intervention period. About 70.9% (293.43 km²) of the area during average rainfall and more than 95% (396.26 km²) of the area during above-average rainfalls show an increase in groundwater recharge after construction of water harvesting structures. The groundwater recharge pattern indicates a positive impact within the vicinity of intervention sites during both average and above-average rainfall. The anicuts are found to be the most effective recharge structures during periods of above-average rainfall, while subsurface barriers are responded well during average rainfall periods. In the hard-rock terrain, water harvesting structures produce significant increases in groundwater recharge. The geo-spatial techniques that are used are effective for evaluating the response of different artificial groundwater recharge techniques.     

GIS-based spatial and temporal investigation of groundwater level fluctuations under rice-wheat ecosystem over Haryana

Groundwater irrigation is the most predominant method used across India and about 50% of the total irrigated area is dependent on it. The state of Haryana has witnessed a spectacular increase in agricultural production in the last few decades, and is largely dependent on groundwater for irrigation. Groundwater mining for irrigation has become a reality in the state over the years as the number of tube wells has increased from 0.02 million in 1966 to 0.73 million in 2012, showing alarming signs of over-exploitation. The impact of increased groundwater irrigation on groundwater levels has not been studied both spatially and temporally. Therefore, this study has been undertaken to investigate the groundwater level fluctuations in the state using geographical information system (GIS) from the groundwater level data of 893 observation wells obtained from Groundwater Cell, Department of Agriculture, Government of Haryana, Panchkula, for the period 2004-12. Many researchers have applied GIS to reveal the spatial and temporal structure of groundwater level fluctuation and as a management and decision tool. The analysis of results indicated a mix of negative and positive trends in the groundwater levels. However, the negative trends were much more pronounced than positive ones. Groundwater level in the state ranged between 0.16 to 65.97 m from the ground surface and per cent area with groundwater level depth more than 10 meter (critical category) was about 56% in 2004 and has increased to 64% by 2012. The average annual decline in groundwater level was observed to be above 32 cm/year, with the strongest decline (108.9 cm/year) in Kurukshetra district.     

Statistical analysis of groundwater level variability across KwaZulu-Natal Province,South Africa

This paper reports the results of analysis of groundwater level changes and its relationship with rainfall across KwaZulu-Natal (KZN) Province of South Africa. The study used 32 groundwater level monitoring sites and 15 selected rainfall stations located across the province. The Mann–Kendall test was used to explore the presence of trends in groundwater level and rainfall data at 10% significance level. The slope of the trend was estimated using Sen’s slope estimator. To understand the cause–effect relationship between rainfall and groundwater level changes, the cumulative rainfall departure (CRD) was computed at the respective rainfall stations influencing the groundwater monitoring site. The results show variable but a general decreasing trend. The variability of the groundwater level trends was analyzed based on water management areas (WMA): (1) both groundwater level and rainfall have a decreasing trend for the entire record period in the Usuthu–Mhlathuzi WMA. Groundwater level around Tembe and Mbazwana areas declined by 0.7 and 2.7 m, respectively. Areas around Richards Bay experienced a reduction between 0.7 and 6.3 m from 2004 to 2015. During the same period, the rainfall within the WMA decreased by 26, 6 and 18% from the mean around Tembe, Mbazwana and Richards Bay, respectively; (2) The northern sector of the uThukela WMA, around Dundee and Newcastle exhibited groundwater level increase by about 1.5 m between 2004 and 2010 but later declined by 1.2 m from 2014 to 2015. The rainfall increased by 8% from 2004 to 2010, and decreased by 22% at the end of 2015. The central part of the uThukela WMA, around Tugela Ferry and Greytown, experienced groundwater level and rainfall reductions of 3.2 m and 15%, respectively, during the entire record period; (3) Within the Mvoti–uMzimkulu WMA in the vicinity of Maphumulo, groundwater level decline by 11 m from 2005 to 2011. However, it recovered by 8 m between 2012 and 2013 following an increase in rainfall by 21%. Areas around Durban exhibited increasing trend from 2005 to 2008 in response to an increasing rainfall amount by about 13% for the same period. The reduction in rainfall by 21% from 2012 to 2015 resulted in a decline of groundwater level by 0.4 m. The steady decline in groundwater levels across the province appears to be a response to prolonged reduction in rainfall, which consequently reduced the amount of groundwater recharge reaching the aquifer. The general response of groundwater levels to changes in rainfall across the province has a lag time from 1 to 4 months.     

Impact of urbanization in groundwater of south Chennai City, Tamil Nadu, India

Chennai is one of the four major metropolitan cities in India, and is located in the southeastern part of the country. The average rate of population growth of the city is 25 % per decade and this is recurrently reducing the green-covered area in the city. Exceptionally, during the post-economic liberalization period (i.e., between the years 1997 and 2007), the city lost up to 99 % of its green-covered areas at some parts. Subsequently, the Chennai City started to experience wide range of environmental issues, including groundwater pollution and the effects of groundwater depletion. As a consequence of these factors, a study was undertaken to determine the impact of urbanization on the groundwater quality. In the present study, groundwater samples were collected from 54 stations from the study area during the premonsoon and postmonsoon seasons for the year 2011–2012 and were analyzed for physico-chemical parameters and trace elements. The type of water that predominated in the study area was assessed based on hydrochemical facies. The study of the hydrochemical characteristics of the major ions in these waters shows that in premonsoon, the alkalis and the alkaline earth metals are found to be balanced by chlorides and bicarbonates and sulphates, respectively. Reverse ion exchange study illustrates that Ca, Mg and Na concentrations are interrelated through reverse ion exchange. Box and whisker plots illustrate the seasonal effect on the chemical parameters of the groundwater. Gibbs’ diagram reveals that the chemical composition of the groundwater in the study area is predominated by rock–water interaction. Besides, suitability of groundwater for irrigation was evaluated based on sodium adsorption ratio, Kelley’s ratio, magnesium ratio, Wilcox and USSL diagrams.     

An approximate projection of availability of the fresh groundwater resources in the South West district of NCT Delhi, India: a case study

The future availability and sustainability of fresh groundwater resources in the South West district of the national capital territory (NCT) Delhi, India, have been projected. Due to a rapid decline in groundwater level and quality, the district has been required by the Government of India to regulate development of groundwater resources. Shallow groundwater is mostly saline and water resources in the area are limited. The methodology applied here involves microzonation of the district in terms of thickness of fresh groundwater and then quantification of present and future availability of freshwater in different freshwater zones, including tentative timescales. The calculation method has been aided by data on historic trends in water level at representative groundwater monitoring stations, located either in fresh groundwater zones or near to them. It is estimated that the presently available 481 million m³ of resources will be reduced to 374 million m³ by year 2007 and to 303 million m³ by the year 2012, and by the year 2022 the district will have only 176 million m³ of available fresh groundwater resources.     

Groundwater recharge in natural dune systems and agricultural ecosystems in the Thar Desert region, Rajasthan, India

Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO₃ and PO₄) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7–5.6 mm/year (2–3% of precipitation, 165 mm/year). In contrast, recharge rates in rain-fed agriculture in the Jaipur study area are 61–94 mm/year (10–16% of precipitation, 600 mm/year). Minimum recharge rates under current freshwater irrigated sites are 50–120 mm/year (8–20% of precipitation). Nitrate concentrations are low at most sites. Similarity in recharge rates based on SO₄ with those based on Cl is attributed to a meteoric origin of SO₄ and generally conservative chemical behavior in these sandy soils. Modeling results increased confidence in tracer-based recharge estimates. Recharge rates under rain-fed agriculture indicate that irrigation of 20–40% of cultivated land with 300 mm/year should be sustainable.     

冬小麦田咸水灌溉与土壤盐分调控试验

利用浅层咸水灌溉，可使浅层咸水分布区无效降水转化为有效水资源，缓解北方水资源紧缺的矛盾；通过王瞳试验场进行的咸水灌溉与土壤盐分调控试验表明，利用3g/L左右的微咸水连续灌溉5a，根层土壤溶液浓度未超过小麦的耐盐能力，且作物增产；多年盐分变化趋势为：1994－1997年1m深度内土壤总含盐量在一定范围内波动，总体变化不大，连续干旱的1997－1998年略呈上升趋势；麦秸覆盖和施有机肥能减少根层土壤盐分，对土壤盐分具有有利的调控作用，具有增产效果。     

Groundwater sustainability assessment in coastal aquifers

The present work investigates the response of shallow, coastal unconfined aquifers to anticipated overdraft conditions and climate change effect using numerical simulation. The groundwater flow model MODFLOW and variable density groundwater model SEAWAT are used for this investigation. The transmissivity and specific yield estimated from the existing database range from 10 to 810 m ²/day and 0.08% to 10.92% respectively. After successful calibration with Nash–Sutcliffe efficiency greater than 0.80, the values of horizontal hydraulic conductivity and specific yield of the unconfined aquifer were set in the range 1.85–61.90 m/day and 0.006–0.24 respectively. After validating the model, it is applied for forecasting the aquifer’s response to anticipated future scenarios of groundwater draft, recharge rate and sea level rise. The findings of the study illustrate that saltwater intrusion is intensified in the area adjoining the tidal rivers, rather than that due to the sea alone. Of all the scenarios simulated, the immense negative impact on groundwater quality emerges due to overdraft conditions and reduced recharge with the areal extent of seawater intrusion exceeding about 67% (TDS >1 kg/m ³). The study also arrives at the conclusion that, regional sea level rise of 1 mm/year has no impact on the groundwater dynamics of the aquifer.     

Assessment of vulnerability to seawater intrusion and potential remediation measures for coastal aquifers: a case study from eastern India

Seawater intrusion is a major threat to the rapidly depleting groundwater resources in the coastal areas of India. Groundwater-based irrigation, significant industrial development and rapid urbanization are some of the key contributors exacerbating the stress on groundwater resources. Vulnerability to seawater intrusion in the Ramanathapuram district of Eastern India is assessed here utilizing the GALDIT method, for a period of 10 years (2001–2010). Results revealed a drastic increase in percent area coverage under moderate vulnerability, from 19.5 to 53.88 %, between the years 2001 and 2010. On the contrary, areas classified as highly vulnerable underwent minor changes over the span of the study. Vulnerability of the study area was also analyzed for the year 2050 considering an average global mean sea level rise of 3.1 mm/year. Results from the analysis for the year 2050 showed that, almost, the entire study area (~97 %) was classified under moderate vulnerability. As a remedial measure to this imminent threat, favorable zones for artificial recharge were delineated on the basis of overlay analysis with weightage values for important controlling factors. Subsequently, the quantity of artificial recharge required to inhibit the intrusion of seawater, at specified favorable zones were estimated to be 674.87, 599.18 and 1,450.66 m³/year.     

Maximizing the management of groundwater resources in the Paris–Abu Bayan reclaimed area,Western Desert,Egypt

The Paris–Abu Bayan area located along the Darb El Arbaein road is involved in the New Valley Project in the Egyptian Western Desert (EWD) as part of ongoing efforts since the 1960s. In this dryland area, groundwater stored in the Nubian Sandstone Aquifer System (NSAS) serves as the only water resource for a number of different uses. A major concern is the significant groundwater withdrawals from 74 pumped wells since the beginning of agricultural activities in 2000. The recent rapid expansion of agricultural activity and the lack of sufficient groundwater recharge as a result of unplanned groundwater development have led to severe stress on the aquifer. Field measurements have shown a rapid decline in groundwater levels, creating a crisis situation for this sole source of water in the area. In this study, mathematical modeling of the groundwater system (single aquifer layer) of the Paris–Abu Bayan reclaimed area was implemented using MODFLOW to devise a new strategy for the sustainable use of groundwater, by applying a number of scenarios in a finite-difference program. The conceptual model and calibration were developed by generating and studying the hydrogeological records, NSA parameters, production wells, and water level measurements for 2005 and 2012. Three management scenarios were applied on the calibrated model to display the present and future stresses on this aquifer over a 30-year period (2012–2042). The results clearly show a high decline in the heads of the NSA, by about 13.8 m, due to the continuous withdrawal of water (first scenario: present conditions, 102,473 m³/day). In the second scenario, the water level is expected to decrease significantly, by about 16 m, in most of the reclamation area by increasing the pumping rates by about 25% (over-pumping) to meet the continuous need for more cultivation land in the area. To reduce the large decline in water levels, the third plan tests the aquifer after reducing the water withdrawal by approximately 25%, applying modern irrigation systems, and suggesting two new reclaimed areas in the northeastern and northwestern parts (areas 1 and 2), with 20 new wells, at 500 m³/day/well. The results in this case show that groundwater levels are slightly decreased, by about 9.5 m, while many wells (especially the new wells in the northern part) show a slight decrease in groundwater levels (0.8 m). The results comparison shows that the groundwater level in the modeled area is lowered by 0.3 m/year with an increase in the number of wells to 94 and increased cultivation area by about 18% (third scenario), versus 0.45 m/year and 0.60 m/year recorded for the first and second scenarios, respectively. Therefore, based on the results, the third scenario is recommended as a new strategy for improving groundwater resource sustainability in the region.     

Performance evaluation and parameters sensitivity of a distributed hydrological model for a semi-arid catchment in India

In present study, a distributed physics based hydrological model, MIKE SHE coupled with MIKE 11, is calibrated using multi-objective approach, i.e., minimization of error in prediction of stream flows and groundwater levels, using the data of eight years from 1991 to 1998 of Yerli sub-catchment \((\hbox {area} = 15{,}881\,\hbox {km}^{2})\) of upper Tapi basin in India. The sensitivity analyses of thirteen model parameters related with overland flow, unsaturated and saturated zones have been undertaken while simulating the runoff volume, peak runoff at catchment outlet and groundwater levels within the catchment with wide variations \((\pm 50\%)\) in the model parameters. The calibrated model has also been validated for prediction of stream flow and groundwater levels within the Yerli sub-catchment for period 1999–2004. The simulated results revealed that calibrated model is able to simulate hydrographs satisfactorily for Yerli sub-catchment (NSE \(=\) 0.65–0.89, \(r=0.80{-}0.95\)) at daily and monthly time scales. The ground water levels are predicted reasonably satisfactorily for the plain area (RMSE \(=\) 0.50–6.50 m) in the study area. The results of total water balance indicated that about 78% of water is lost from the system through evapotranspiration, out of which about 3.5% is contributed from the groundwater zone.     

A hydrological simulation of the water regime in two playa lakes located in southern Spain

The subject of this paper is the detailed hydrological simulation of two playa lakes located in southern Spain from January 2011 to March 2012 on a daily basis. These playas are placed over a 400-km ² shallow aquifer, which is exposed to an increasing stress caused by agricultural activities, mainly olive grove plantations. The objective of the paper is to elaborate a detailed numeric model that simulates the water regime of each playa lake on a daily scale. The simulation is compared to measured water level (WL) data of the playas in order to characterize the groundwater–surface interactions. The ultimate objective of this paper is to assess the environmental impact of the increasing anthropogenic water consumption within the area of research. The results of the GW–surface interaction were very consistent with previous works. One of the playa lakes is groundwater-dependent and the other one is presumably a perched playa lake. The GW discharge of the former playa (214 mm) during the research period stands in sharp contrast to no regional GW discharge in the latter. Water level data prove that the hydrological year (2011–2012) had a very negative water budget. The evapotranspiration estimation was almost as high as double the sum of the precipitation, the run-off, and the groundwater discharge. The simulation of an anthropologically altered water regime proves that water retrieval has a harmful impact on the WL of the playa lakes as well as on the aquifer.     

Groundwater resources management through flow modeling in lower part of Bhagirathi — Jalangi interfluve,Nadia, West Bengal

Groundwater utilization in Nadia district, West Bengal has been subjected to rapid exploitation in the wake of increasing urbanization and production of agricultural commodities. It is, therefore, necessary to evaluate the existing trend and availability of groundwater in time and space and its movement for proper planning in future. In the present study, an attempt has been made develop a groundwater management model using Visual MODFLOW software. The groundwater flow model for the study area was formulated by using input hydrogeological data and appropriate boundary conditions. The groundwater flow pattern of the study area indicates the occurrence of base flow which feed both the Rivers Bhagirathi and Jalangi throughout the year. The computed hydraulic heads were calibrated by comparing with observed groundwater level data for years 2004 to 2006 and were verified with the data of 2007. The outcome of modeling shows that this model can be used for prediction purpose in the future by updating input boundary conditions and hydrologic stresses during the preceding year. The model optimized unit draft for deep tube well as 556.5 m³/day and the same for shallow tube well as 41 m³/day keeping the existing tube well structures in running condition and maintaining the present and recent past trends of groundwater level. The model can be further improved if more spatial and temporal input parameters are available and can be incorporated into the model for more realistic characterization of groundwater flow.     

Multi-method assessment of connectivity between surface water and shallow groundwater: the case of Limarí River basin,north-central Chile

A study that tests the applicability and consistency of independent but complementary approaches in the assessment of interactions between surface water and shallow groundwater within a water-stressed basin is described. The mostly agricultural Limarí basin in arid north-central Chile was chosen as a suitable case study. The analyses involved: (1) a connectivity index method, (2) hydrochemistry, and (3) water isotopic geochemistry. Chemical and isotopic data were obtained from two sampling campaigns conducted in April (fall) and December (summer) of 2011 in 22 sampling locations, which included surface water and groundwater. The results obtained by each of the methodologies were mutually consistent and indicate high connectivity conditions. Additionally, the relative contribution by different sources was assessed through end-member mixing analysis, and for reaches of the river that showed gaining conditions, the contribution of groundwater inflow to stream discharge was estimated. It is suggested that this multi-method approach is useful for the characterization of surface-water–groundwater interactions, since it at least represents a suitable starting point for obtaining basic information on these relationships. Thus, it may become the base for further studies in arid and semi-arid basins facing water management challenges.     

Groundwater recharge dams in arid areas as tools for aquifer replenishment and mitigating seawater intrusion: example of AlKhod, Oman

Groundwater depletion and seawater intrusion constitute major challenges along coastal aquifers in arid areas. This paper assesses the role of groundwater recharge dams constructed to replenish aquifers and fight seawater intrusion with reference to AlKhod dam, Oman, sited 7 km from the coast on a gravely unconfined aquifer. Water table rise in piezometers located downstream from the dam shows regular patterns correlating with magnitude of wadi flow, whereas upstream piezometers show irregular patterns. Controlled release of water captured by the dam optimizes water percolation and enhances artificial recharge which was estimated in the wet years 1997, 2003 and 2005 as 15, 22 and 27 Mm³, respectively, using water table fluctuation method. Recharge contributed 40–60 % of the total annual abstraction. Groundwater salinity increased in the 1980s and 1990s and the saline/freshwater interface advanced inland, but has receded partially after 1997 (highest rainfall) and completely after 2005 indicated by reduction in electrical conductivity and thickening of freshwater lens. The recession is attributed to the dam’s induced recharge and reduction of pumping in 2004 following the commissioning of Barka desalination plant. Integrating artificial recharge with groundwater resources management is therefore an effective measure to replenish aquifers in arid areas and mitigate seawater intrusion along the coasts.     

Spatiotemporal variation of groundwater quality in an arid area experiencing long-term paper wastewater irrigation,northwest China

Groundwater is crucial for multiple uses over the world, especially in arid and semiarid regions. However, human activities significantly decreased groundwater quality. In this study, the spatiotemporal variation of groundwater quality was evaluated in an arid area where long-term paper wastewater irrigation has been implemented. For this study, seven wells were regularly monitored for physicochemical parameters over a period of 1 year. Statistical and graphical approaches were applied to interpret the spatiotemporal variation of groundwater quality parameters in the wastewater irrigation zone. Correlation analysis was also carried out to reveal the sources of some major ions. The results indicate that the groundwater type in the study area is dominated by the Cl–Na, followed by the HCO₃–Na, the HCO₃–Ca·Mg, and the SO₄·Cl–Ca·Mg types. Groundwater in the area is significantly contaminated locally with fluoride, nitrite and ammonia, and the chemical oxygen demand levels were increased in some groundwater monitoring wells. Most contaminants showed an increasing trend from the Yellow River water irrigation zone toward the wastewater irrigation zone. Rock weathering, mineral dissolution, and cation exchange are important processes controlling groundwater quality, but human activities, such as wastewater irrigation, play an undeniable role in affecting groundwater quality in this area. The results of this study contribute to the understanding of the formation and circulation of groundwater under human activities and provide a scientific basis for regional water quality evaluation, water quality improvement, and protection.     

利用GRACE重力卫星数据反演黑河流域地下水变化

干旱区地表水资源有限, 地下水资源被超采利用, 黑河流域是西北干旱区典型内陆河流域, 有同样的地下水资源利用问题. 然而由于监测地下水变化的测井数目有限且分布不均, 难以从流域尺度上把握地下水资源的时空变化. 利用GRACE重力测量卫星数据反演黑河流域2003-2008年间的地下水时空变化, 为合理分配利用水资源提供科学依据, 为掌握无资料区域地下水水资源及其变化趋势提供了计算方法. 为验证GRACE反演结果的可靠性, 首先将计算出的黑河中上游地下水的变化, 与该区域实测地下水变化数据进行对比分析, 结果显示二者之间相关性较好, 在一定程度上表明GRACE数据具备反演整个黑河流域水储量变化及其各个组分的能力. 此后, 利用GRACE数据反演了全黑河流域的地下水变化, 对其时空变化进行了分析和讨论. 结果表明: 黑河流域2003-2004年间地下水减少的幅度越来越少, 2005年夏季期间地下水资源量增加量最多, 自此地下水增加幅度逐渐减少, 至2008年趋于平衡. 空间上流域局部变化波动较大, 2003-2004年间黑河上游地下水资源量处于减少状态, 2005年相对于6 a地下水平均含量有轻微增加趋势, 2006年处于6 a平均值状态, 2007-2008年有稍微上升趋势; 中游在2005年有略微的上升, 之后3 a下降; 下游地下水含量在6 a中整体呈上升趋势.     

A comparative study of shallow groundwater level simulation with WA–ANN and ITS model in a coastal island of south China

Accurate and reliable prediction of shallow groundwater level is a critical component in water resources management. Two nonlinear models, WA–ANN method based on discrete wavelet transform (WA) and artificial neural network (ANN) and integrated time series (ITS) model, were developed to predict groundwater level fluctuations of a shallow coastal aquifer (Fujian Province, China). The two models were testified with the monitored groundwater level from 2000 to 2011. Two representative wells are selected with different locations within the study area. The error criteria were estimated using the coefficient of determination (R ²), Nash–Sutcliffe model efficiency coefficient (E), and root-mean-square error (RMSE). The best model was determined based on the RMSE of prediction using independent test data set. The WA–ANN models were found to provide more accurate monthly average groundwater level forecasts compared to the ITS models. The results of the study indicate the potential of WA–ANN models in forecasting groundwater levels. It is recommended that additional studies explore this proposed method, which can be used in turn to facilitate the development and implementation of more effective and sustainable groundwater management strategies.