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Response of hydrogeological processes in a regional groundwater system to environmental changes: A modeling study of Yinchuan Basin, China
Abstract
The sustainable development of groundwater resources in arid and semi-arid regions is a challenging task hindered by climate change and human activities. The rational utilization and management of groundwater resources is, therefore, dependent on an understanding of the influences of human and climatic factors on the spatial distribution of groundwater resources and their change over time. The thick Quaternary aquifers in the Yinchuan Basin, China were used herein as an example of how to quantitatively assess spatial and temporal trends in groundwater resources in response to human activities and climate change. A 3D transient groundwater flow model was constructed and used to simulate the evolution and spatial variability of hydrogeological processes from 1990 to 2020. By subsequently applying regime shift detection and correlation analysis to the simulation results, we found that: 1) groundwater storage was continuously depleted over the 30-year period, reaching a cumulative depletion of 1.89×10⁹ m³; 2) Human activities were mainly responsible for variations in regional hydrogeological processes for a period of up to 30 years. Climate only affected short-term interannual fluctuations in groundwater storage; 3) Human activities (e.g., river water diversion and groundwater abstractions) were the decisive factors causing a continuous reduction of groundwater resources. A policy-driven reduction in water diversion from the Yellow River directly led to a significant drop in groundwater storage, which had a consequent effect on surface water and groundwater interactions and altered agricultural irrigation patterns (crop patterns and irrigation methods); 4) The amount of groundwater recharge from the Yellow River and local lakes increased from 1990 to 2020, whereas the discharge of groundwater to the Yellow River and lakes decreased.
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Seepage flux from disconnected streams can be a main source of groundwater recharge in arid and semiarid regions. The seepage into the streambed will respond to a change in stream stage; however, the relationship between seepage flux and stream stage is uncertain due to a lack of in situ observations. This study investigated the change in seepage flow regime with stream stage in a natural streambed through field measurements along a 50.1 km long disconnected stream. Seepage fluxes were quantified using a seepage meter method involving the measurement and simulation of the variable stream stages in a seasonal stream. Flow regimes in the streambed were then evaluated using a developed model. Two seepage flow regimes were observed, the Darcy flow regime and the non‐Darcy flow regime, with the change of the stream stage in the streambed. Our analysis of the mechanisms of seepage flow indicates that drainable porosity and particle size of streambed media are the key factors controlling non‐Darcy seepage flow behavior. We demonstrated that the Reynolds number based on the particle diameter d30 instead of d50 can provide a more accurate criterion for non‐Darcy flow in natural heterogeneous streambeds. Model evaluation showed that predicted streambed seepage regimes and fluxes were consistent with field observations. Together, these results provide new insights into the seepage mechanisms, which have significant implications for the establishment of a better seepage model and the joint development of regional surface water and groundwater.
Groundwater contamination risk assessment is a useful tool for groundwater pollution prevention and control. Previous study has evaluated groundwater contamination risk at Yinchuan Plain, China, according to aquifer vulnerability. The present study enriches the assessment of contamination risk by adding pollution loading, which represents the hazard from human activities, and groundwater value, which represents the economic loss as a result of groundwater pollution. An approach that combines toxicity, release possibility, and the potential release quantity of pollutants on the ground surface was used to estimate the pollution loading. An integrated approach that considered both the in situ and extractive values was used to estimate groundwater value. In addition, a basic risk map was constructed by overlying the vulnerability and pollution loading maps showing the potential probability of pollution, while a value-weighted risk map was produced by overlying the basic risk and value map indicating the urgency of protection. The validation by specific contaminants shows the reliability of the basic risk assessment. Both the basic and value-weighted risk maps indicate a very high groundwater contamination risk in Yinchuan City, and the southern part of Yinchuan Plain exhibited a relatively high contamination risk. As a result of not only high vulnerability but also very high pollution loading and groundwater value, Yinchuan City is the most urgent area requiring groundwater protection. The produced maps provide effective information for decision-making regarding the optimization of monitoring network, preferential treatment, and allocating future potentially hazardous.
In recent years, the amount of water diverted from the Yellow River has been decreasing year by year, which is the biggest problem for the development and utilization of water resources in Yinchuan Oasis (YCO). Through the implementation of the Agricultural Water-saving Transformation Project (AWSTP), water resource shortage in the YCO has been alleviated greatly, and ecological degradation problems, such as soil salinization, have also been effectively addressed. However, how the shallow groundwater in YCO has changed after the AWSTP remains unclear. This paper, based on a lot of statistical data and measured data, and by using statistical and geostatistical methods, reveals the evolution of shallow groundwater in YCO in the past 18 years (2000–2017), since the implementation of the AWSTP and its driving factors, from two aspects: groundwater dynamics and groundwater quality. The results show that compared with the initial stage of AWSTP, the amount of water diverted from the Yellow River for the YCO reduced by 36%, and accordingly, the average groundwater depth in the irrigation period increased from 0.98 m to 2.01 m, representing an increase of 1.03 m, and an average annual increase of 6cm. Moreover, the depth increase in the irrigation period is higher than that in the non-irrigation period, and that in the Northern Irrigation Area (NIA) is higher than that in the Southern Irrigation Area (SIA). Furthermore, the groundwater storage is decreasing at a rate of 855.6 × 104 m3·a−1, and the cumulative storage has reduced by nearly 1.54 × 108 m3, indicating that it is in a long-term negative equilibrium. In terms of temporal and spatial distribution of total dissolved solids (TDS) in groundwater, the TDS in SIA and NIA decreased from 1.41 g·L−1 and 1.84 g·L−1 to 1.15 g·L−1 and 1.77 g·L−1, respectively. The saline water area with a TDS above 5 g·L−1 and the freshwater area with a TDS below 1 g·L−1 decreased by 16.6 km2 and 334.4 km2, respectively, while the brackish water area with a TDS of 1~3 g·L−1 increased by 492 km2. The spatial and temporal distribution heterogeneity of TDS in groundwater is reduced and is in a slight desalinized trend overall. However, the groundwater in some areas, such as the Xingqing District, Jinfeng District, Xixia District, Yongning County, Helan County and Huinong District of Yinchuan Oasis, is at risk of further salinization. Due to the agricultural water-saving caused by the reduction of water amount diverted from the Yellow River, the groundwater recharge in YCO was reduced by 36.3%, which, together with measures such as drainage, groundwater exploitation, and industrial restructuring, drives the groundwater circulation in the YCO to a new equilibrium. This study can help us to understand the influencing process and mechanism of agricultural water-saving on groundwater systems in YCO and provide reference for efficient use and optimal allocation and management of agricultural water resources.
Climate change and human activities have profound effects on the characteristics of groundwater in arid oases. Analyzing the change of groundwater level and quantifying the contributions of influencing factors are essential for mastering the groundwater dynamic variation and providing scientific guidance for the rational utilization and management of groundwater resources. In this study, the characteristics and causes of groundwater level in an arid oasis of Northwest China were explored using the Mann–Kendall trend test, Morlet wavelet analysis, and principal component analysis. Results showed that the groundwater level every year exhibited tremendous regular characteristics with the seasonal exploitation. Meanwhile, the inter-annual groundwater level dropped continuously from 1982 to 2018, with a cumulative decline depth that exceeded 12 m, thereby causing the cone of depression. In addition, the monthly groundwater level had an evident cyclical variation on the two time scales of 17–35 and 7–15 months, and the main periodicity of monthly level was 12 months. Analysis results of the climatic factors from 1954 to 2018 observed a significant warming trend in temperature, an indistinctive increase in rainfall, an inconspicuous decrease in evaporation, and an insignificant reduction in relative humidity. The human factors such as exploitation amount, irrigated area, and population quantity rose substantially since the development of the oasis in the 1970s. In accordance with the quantitative calculation, human activities were decisive factors on groundwater level reduction, accounting for 87.79%. However, climate change, including rainfall and evaporation, which contributed to 12.21%, still had the driving force to change the groundwater level in the study area. The groundwater level of Yaoba Oasis has been greatly diminished and the ecological environment has deteriorated further due to the combined effect of climate change and human activities.
In this paper, we present an assessment of the sensitivity of groundwater-surface water interactions to climate change in an alluvial aquifer, located in the Ljubljansko polje, Slovenia. The investigation is motivated by a recent assessment of climate change pressures on the water balance in the Sava River Basin (Gampe et al., 2016). The assessment was performed using a comprehensive hydrological modelling approach, which is based on the direct/indirect communication between FEFLOW and WaSiM/MIKE 11. This modelling framework provides a precise simulation of the critical processes in the study domain, which are the main drivers influencing the interactions between precipitation, river water and groundwater under different future climate scenarios. Climate projections were based on the results of the three regional climate models SMHI-RCA4, KNMI-RACMO22E and CLMcom-CCLM4. The results show that there will be higher levels of local precipitation during 2036–2065, the projected river discharge will be larger in the future compared to 2000–2014, and it is unlikely that the Ljubljansko polje will suffer from water scarcity. In addition, amongst the various sections of the Sava River the section between Črnuče and Šentjakob is the one most sensitive to climate change. By running the models under different climate scenarios a deeper insight into aquifer system functioning was obtained. Investigating impacts of climate change on groundwater and interactions between surface water and groundwater on the local scale is a basis for applying such a study on the global scale, which was still not very well investigated.
Existing studies on the impacts of climate change on groundwater recharge are either global or basin/location-specific. The global studies lack the specificity to inform decision making, while the local studies do little to clarify potential changes over large regions (major river basins, states, or groups of states), a scale often important in the development of water policy. An analysis of the potential impact of climate change on groundwater recharge across the western United States (west of 100° longitude) is presented synthesizing existing studies and applying current knowledge of recharge processes and amounts. Eight representative aquifers located across the region were evaluated. For each aquifer published recharge budget components were converted into four standard recharge mechanisms: diffuse, focused, irrigation, and mountain-systems recharge. Future changes in individual recharge mechanisms and total recharge were then estimated for each aquifer. Model-based studies of projected climate-change effects on recharge were available and utilized for half of the aquifers. For the remainder, forecasted changes in temperature and precipitation were logically propagated through each recharge mechanism producing qualitative estimates of direction of changes in recharge only (not magnitude). Several key patterns emerge from the analysis. First, the available estimates indicate average declines of 10-20% in total recharge across the southern aquifers, but with a wide range of uncertainty that includes no change. Second, the northern set of aquifers will likely incur little change to slight increases in total recharge. Third, mountain system recharge is expected to decline across much of the region due to decreased snowpack, with that impact lessening with higher elevation and latitude. Factors contributing the greatest uncertainty in the estimates include: (1) limited studies quantitatively coupling climate projections to recharge estimation methods using detailed, process-based numerical models; (2) a generally poor understanding of hydrologic flowpaths and processes in mountain systems; (3) difficulty predicting the response of focused recharge to potential changes in the frequency and intensity of extreme precipitation events; and (4) unconstrained feedbacks between climate, irrigation practices, and recharge in highly developed aquifer systems.
Climate and land use change (global change) impacts on groundwater systems cannot be studied in isolation. Land use and land cover (LULC) changes have a great impact on the water cycle and contaminant production and transport. Groundwater flow and storage are changing in response not only to climatic changes but also to human impacts on land uses and demands, which will alter the hydrologic cycle and subsequently impact the quantity and quality of regional water systems. Predicting groundwater recharge and discharge conditions under future climate and land use changes is essential for integrated water management and adaptation. In the Mancha Oriental system (MOS), one of the largest groundwater bodies in Spain, the transformation from dry to irrigated lands during the last decades has led to a significant drop of the groundwater table, with the consequent effect on stream–aquifer interaction in the connected Jucar River. Understanding the spatial and temporal distribution of water quantity and water quality is essential for a proper management of the system. On the one hand, streamflow depletion is compromising the dependent ecosystems and the supply to the downstream demands, provoking a complex management issue. On the other hand, the intense use of fertilizer in agriculture is leading to locally high groundwater nitrate concentrations. In this paper we analyze the potential impacts of climate and land use change in the system by using an integrated modeling framework that consists in sequentially coupling a watershed agriculturally based hydrological model (Soil and Water Assessment Tool, SWAT) with a groundwater flow model developed in MODFLOW, and with a nitrate mass-transport model in MT3DMS. SWAT model outputs (mainly groundwater recharge and pumping, considering new irrigation needs under changing evapotranspiration (ET) and precipitation) are used as MODFLOW inputs to simulate changes in groundwater flow and storage and impacts on stream–aquifer interaction. SWAT and MODFLOW outputs (nitrate loads from SWAT, groundwater velocity field from MODFLOW) are used as MT3DMS inputs for assessing the fate and transport of nitrate leached from the topsoil. Three climate change scenarios have been considered, corresponding to three different general circulation models (GCMs) for emission scenario A1B that covers the control period, and short-, medium- and long-term future periods. A multi-temporal analysis of LULC change was carried out, helped by the study of historical trends (from remote-sensing images) and key driving forces to explain LULC transitions. Markov chains and European scenarios and projections were used to quantify trends in the future. The cellular automata technique was applied for stochastic modeling future LULC maps. Simulated values of river discharge, crop yields, groundwater levels and nitrate concentrations fit well to the observed ones. The results show the response of groundwater quantity and quality (nitrate pollution) to climate and land use changes, with decreasing groundwater recharge and an increase in nitrate concentrations. The sequential modeling chain has been proven to be a valuable assessment tool for supporting the development of sustainable management strategies.
Climate change impact on a groundwater-dependent small urban town has been investigated in the semiarid hard rock aquifer in southern India. A distributed groundwater model was used to simulate the groundwater levels in the study region for the projected future rainfall (2012-32) obtained from a general circulation model (GCM) to estimate the impacts of climate change and management practices on groundwater system. Management practices were based on the human-induced changes on the urban infrastructure such as reduced recharge from the lakes, reduced recharge from water and wastewater utility due to an operational and functioning underground drainage system, and additional water extracted by the water utility for domestic purposes. An assessment of impacts on the groundwater levels was carried out by calibrating a groundwater model using comprehensive data gathered during the period 2008-11 and then simulating the future groundwater level changes using rainfall from six GCMs [Institute of Numerical Mathematics Coupled Model, version 3.0 (INM-CM.3.0); L'Institut Pierre-Simon Laplace Coupled Model, version 4 (IPSL-CM4); Model for Interdisciplinary Research on Climate, version 3.2 (MIROC3.2); ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G); Hadley Centre Coupled Model, version 3 (HadCM3); and Hadley Centre Global Environment Model, version 1 (HadGEM1)] that were found to show good correlation to the historical rainfall in the study area. The model results for the present condition indicate that the annual average discharge (sum of pumping and natural groundwater outflow) was marginally or moderately higher at various locations than the recharge and further the recharge is aided from the recharge from the lakes. Model simulations showed that groundwater levels were vulnerable to the GCM rainfall and a scenario of moderate reduction in recharge from lakes. Hence, it is important to sustain the induced recharge from lakes by ensuring that sufficient runoff water flows to these lakes.
Available from:
http://dx.doi.org/10.1016/j.jhydrol.2014.11.062
Episodic streamflow events in the Upper Santa Cruz River recharge a shallow alluvial aquifer that is an essential water resource for the surrounding communities. The complex natural variability of the rainfall-driven streamflow events introduces a water resources management challenge for the region. In this study, we assessed the impact of projected climate change on regional water resources management. We analyzed climate change projections of precipitation for the Upper Santa Cruz River from eight dynamically downscaled Global Circulation Models (GCMs). Our analysis indicates an increase (decrease) in the frequency of occurrence of dry (wet) summers. The winter rainfall projections indicate an increased frequency of both dry and wet winter seasons, which implies lower chance for medium-precipitation winters. The climate analysis results were also compared with resampled coarse GCMs and bias adjusted and statistically downscaled CMIP3 and CMIP5 projections readily available for the contiguous U.S. The impact of the projected climatic change was assessed through a water resources management case study. The hydrologic framework utilized includes a rainfall generator of likely scenarios and a series of hydrologic models that estimate the groundwater recharge and the change in groundwater storage. We conclude that climatic change projections increase the uncertainty and further exacerbate the already complicated water resources management task. The ability to attain an annual water supply goal, the accrued annual water deficit and the potential for replenishment of the aquifer depend considerably on the selected management regime.
The Yinchuan Plain has more than 2000 years of history of irrigation by diverting water from the Yellow River. Currently, the amount of water diverted from the Yellow River is about 21.7 times the water formed on the plain as a result of precipitation and inflow of groundwater. Under the intensive influence of irrigation, the plain changed from a desert into a rich and populous area, earning its name as ‘South China Beyond the Great Wall’, with lakes scattered across the Yinchuan Plain just as stars in the sky. In this research, 17 representative lakes were sampled to analyze and study 2H and 18O content; the results showed that lakes on the plain have undergone obvious non-equilibrium evaporation. Recharges of the lakes can be divided into three types: recharge from the Yellow River, from groundwater and from both of these. The Craig–Gordon non-equilibrium evaporation model for isotope fractionation was used to estimate the evaporation proportion of each lake. The results showed that evaporation from lakes on Yinchuan Plain is generally extensive under the dry climatic conditions. Most lakes have an evaporation proportion of over 25%, with the largest originating from Shahu lake and Gaomiaohu lake in the northern part of the plain, at 42.5% and 42.8%, respectively. The evaporation proportions calculated on the basis of 18O and 2H are very close to each other. This shows that the method used in this paper is feasible for estimating the evaporation proportions of lakes in areas with a heavy anthropogenic influence. Copyright © 2013 John Wiley & Sons, Ltd.
As the world's largest distributed store of fresh water, ground water
plays a central part in sustaining ecosystems and enabling human
adaptation to climate variability and change. The strategic importance
of ground water for global water and food security will probably
intensify under climate change as more frequent and intense climate
extremes (droughts and floods) increase variability in precipitation,
soil moisture and surface water. Here we critically review recent
research assessing the impacts of climate on ground water through
natural and human-induced processes as well as through
groundwater-driven feedbacks on the climate system. Furthermore, we
examine the possible opportunities and challenges of using and
sustaining groundwater resources in climate adaptation strategies, and
highlight the lack of groundwater observations, which, at present,
limits our understanding of the dynamic relationship between ground
water and climate.
A common problem of existing methods for regime shift detection is their poor performance at the ends of time-series. Consequently,
shifts in environmental and biological indices are usually detected long after their actual appearance. A recently introduced
method based on sequential t-test analysis of regime shifts (STARS) treats all incoming data in real time, signals the possibility
of a regime shift as soon as possible, then monitors how perception of the magnitude of the shift changes over time. Results
of a STARS application to the eastern Bering Sea ecosystem show how the 1989 and 1998 regime shifts manifest themselves in
biotic and abiotic indices in comparison with the 1977 shift.
The three-dimensional geometry of fluvial channel bodies and valley fills has received much less attention than their internal structure, despite the fact that many subsurface analyses draw upon the geometry of suitable fluvial analogues. Although channel-body geometry has been widely linked to base-level change and accommodation, few studies have evaluated the influence of local geomorphic controls. To remedy these deficiencies, we review the terminology for describing channel-body geometry, and present a literature dataset that represents more than 1500 bedrock and Quaternary fluvial bodies for which width (W) and thickness (T) are recorded. Twelve types of channel bodies and valley fills are distinguished based on their geomorphic setting, geometry, and internal structure, and log-log plots of W against T are presented for each type. Narrow and broad ribbons (WIT < 5 and 5-15, respectively) and narrow, broad, and very broad sheets (W/T 15-100, 100-1000, and > 1000, respectively) are distinguished. The dataset allows an informed selection of analogues for subsurface applications, and spreadsheets and graphs can be downloaded from a data repository. Mobile-channel belts are mainly the deposits of braided and low-sinuosity rivers, which may exceed 1 km in composite thickness and 1300 kin in width. Their overwhelming dominance throughout geological time reflects their link to tectonic activity, exhumation events, and high sediment supply. Some deposits that rest on flat-lying bedrock unconformities cover areas > 70,000 km(2). In contrast, meandering river bodies in the dataset are < 38 m thick and < 15 km wide, and the organized flow conditions necessary for their development may have been unusual. They do not appear to have built basin-scale deposits. Fixed channels and poorly channelized systems are divided into distributary systems (channels on megafans, deltas, and distal alluvial fans, and in crevasse systems and avulsion deposits), through-going rivers, and channels in eolian settings. Because width/maximum depth of many modern alluvial channels is between 5 and 15, these bodies probably record an initial aspect ratio followed by modest widening prior to filling or avulsion. The narrow form (W/T typically < 15) commonly reflects bank resistance and rapid filling, although some are associated with base-level rise. Exceptionally narrow bodies (W/T locally < 1) may additionally reflect unusually deep incision, compactional thickening, filling by mass-flow deposits, balanced aggradation of natural levees and channels, thawing of frozen substrates, and channel reoccupation. Valley fills rest on older bedrock or represent a brief hiatus within marine and alluvial successions. Many bedrock valley fills have W/T < 20 due to deep incision along tectonic lineaments and stacking along faults. Within marine and alluvial strata, upper Paleozoic valley fills appear larger than Mesozoic examples, possibly reflecting the influence of large glacioeustatic fluctuations in the Paleozoic. Valley fills in sub-glacial and proglacial settings are relatively narrow (W/T as low as 2.5) due to incision from catastrophic meltwater flows. The overlap in dimensions between channel bodies and valley fills, as identified by the original authors, suggests that many braided and meandering channel bodies in the rock record occupy paleovalleys. Modeling has emphasized the importance of avulsion frequency, sedimentation rate, and the ratio of channel belt and floodplain width in determining channel-body connectedness. Although these controls strongly influence mobile channel belts, they are less effective in fixed-channel systems, for which many database examples testify to the influence of local geomorphic factors that include bank strength and channel aggradation. The dataset contains few examples of highly connected suites of fixed-channel bodies, despite their abundance in many formations. Whereas accommodation is paramount for preservation, its influence is mediated through geomorphic factors, thus complicating inferences about base-level controls.
An upscaling algorithm has been developed that generates an irregular coarse grid that preserves flow connectivity by applying a rule-based upscaling algorithm to a fine-scale facies distribution. The algorithm is demonstrated using stochastically generated paleo-fluvial facies distributions. First, an irregular grid honoring the channel facies is created, followed by computation of effective anisotropic parameters for all coarse-grid cells. For the apparent layer-cake geometry of overbank deposits seen in outcrop, two local upscaling methods are compared: (1) the layered system approximation and (2) the mode. To assess upscaling performance, flow simulations for the original and upscaled grids are compared. The horizontal layered approximation (arithmetic mean) performs poorly, over-predicting lateral connectivity where even infrequent disconnection becomes important. Performance of the mode as an upscaling algorithm depends on the probability that a coarse-grid cell will be dominated by a single facies, and it performs surprisingly well because the upscaled grid-generation algorithm honors the channels, informing the upscaling process. Lastly, the irregular coarse grid was compared to a uniform coarse grid, showing superior performance with the irregular grid. The reduction in grid size achieved by irregular-grid generation will be a function of the geometrical complexity of the geologic objects to be honored.
Groundwater vulnerability assessments provide a measure of the sensitivity of groundwater quality to an imposed contaminant load and are globally recognized as an essential element of all aquifer management and protection plans. In this paper, the vulnerability of groundwaters underlying the Yinchuan Plain of Northwest China is determined using OREADIC, a GIS-based assessment tool that incorporates the key characteristics of the universally popular DRASTIC approach to vulnerability assessment but has been modified to consider important additional hydrogeological factors that are specific to the region. The results show that areas of high vulnerability are distributed mainly around Qingtongxia City, Wuzhong City, Lingwu City, and Yongning County and are associated with high rates of aquifer recharge, shallow depths to the water table, and highly permeable aquifer materials. The presence of elevated NO
3− in the high vulnerability areas endorses the OREADIC approach. The vulnerability maps developed in this study have become valuable tools for environmental planning in the region and will be used for predictive management of the groundwater resource.
Intensive groundwater exploitation has depleted groundwater storage and led to a series of geo-environmental problems in Beijing Plain, China. Managed Aquifer Recharge (MAR) has been endorsed to mitigate the groundwater storage depletion and achieve groundwater sustainability. A pilot MAR has been tested in the Chaobai River catchment since 2015. An innovative large-scale MAR consisting of 9 cascade terraced infiltration ponds was proposed and its effectiveness was assessed in this study using an integrated modelling approach. The integrated model coupled the regional and local transient flow and transport processes. The transient regional flow model simulated historical groundwater level declines and storage depletion in the Beijing Plain from 1995 to 2018. The coupled regional and local flow model was used to simulate the pilot MAR test in the Chaobai River from 2015 to 2018. A significant groundwater level increase was observed nearby the pilot MAR since 2015. The transport model results indicate that approximately 40% of the infiltrated water was captured by pumping wells in the No.8 well field. The models were further used to assess the long-term effects of the large-scale MAR from 2020 to 2050. The simulation results show that the groundwater system will reach a new equilibrium state under the implementation of the large-scale MAR scheme. Almost 91% of the abstracted water in the No. 8 well field will come from the MAR infiltration. The proposed large-scale MAR is very effective in restoring the depleted aquifer storage and maintaining the groundwater abstraction in the No.8 well field. However, with the increase of the groundwater level, the infiltration rate of several ponds will decrease. Therefore, it is important to maintain a dynamic balance between artificial recharge and groundwater abstraction in order to achieve a sustainable long-term MAR operation in the region.
The arid inland regions around the world are suffering from extreme water shortages and ecological crises due to the impacts of climate change and enhanced human activities. This study used multiple methods including trend and abrupt analysis, correlation analysis, water-balance analysis, and hydrochemical analysis to evaluate the hydrogeological processes and hydrochemical effects in 5 periods in the Manas River catchment, a typical arid inland catchment in China. The results show that groundwater storage in the catchment decreased by 5.45×10⁸ m³ over the past 60 years, while glacial melt, snowmelt, and precipitation showed an increasing trend since the 1980s. A drop in the groundwater level in the alluvial fan and a 28% reduction in spring discharge in the lower alluvial fan since 1959 were caused by reduced river infiltration owing to the water diversion projects. Meanwhile, the concentrations of SO4²⁻ and Cl⁻ in the alluvial fan groundwater have more than doubled over the period 1957-2018 as a result of the decrease of both groundwater level and flow rate. Long-term over-exploitation of groundwater associated with irrigation after 1978 strongly depleted the groundwater storage and altered the flow path of groundwater in the oasis zone. In addition, the expansion of arable land and increased temperatures enhanced evapotranspiration and salinization of shallow groundwater in the oasis and desert zones. Based on the results, we propose making full use of natural underground reservoirs to increase infiltration of river water and flood water in the alluvial fan zone, and reducing the arable land area to ensure the sustainability of water resources and ecology in the middle and lower reaches of the catchment. The results will provide reference for the sustainable development of water resources and environmental protection in arid inland regions and similar catchments worldwide.
The simulation of groundwater flow is widely used to understand dynamic groundwater processes and frequently serves as the basis for quantitative analysis and management of groundwater resources. Reliable groundwater flow simulations require a sound understanding of the hydrogeological structure of the subsurface materials. However, a detailed model of the hydrological structure of thick unconsolidated basin sediments is often limited by their inaccessible nature, especially in the deep domain. As a result, deep regional flow is generally neglected in traditional groundwater flow simulations. This study presents an integrated approach for developing a model of hydrogeological structures using multiple data sources, including audio-frequency magnetotelluric data (AMT), borehole data, and the interpreted lower boundary of Quaternary sediments. The approach overcomes the disadvantages of using the depth of boreholes as the lower boundary of the hydrogeological system and may be used to analyse the effects of hydrogeological structures on groundwater flow simulations. The model, which utilized Sequential Gaussian Simulation (SGS) and Natural Neighbor Interpolation (NNI), was evaluated by application to a typical cross-section through the Yinchuan Basin, China, to a depth of 1,700 m. The horizontal hydraulic conductivity (Kx) field was calibrated using observation wells and the PEST Pilot Points (PPP) method. The effects of the developed hydrogeological structure on groundwater flow simulations were evaluated for the entire thickness of Quaternary sediments (complete-domain model, CDM) as well as for sediments above the maximum depth of the boreholes (shallow-domain model, SDM). In addition, the sensitivity of the K field on groundwater flow patterns was analysed. The results show that the proposed approach can characterize the spatial distribution of lithologic units and the heterogeneity of hydrogeological parameters in the deep domain (>300 m), as well as avoid the multi-solution problem of inferring hydrogeological parameters from geophysical data. It can also improve the accuracy of the hydrogeological structure model and the reliability of groundwater flow simulations. The adjustment of the hydrogeological structure affects the flow budget as well as the pattern of the groundwater flow systems (including the type of system, and their number, location, and extent). Changes in the K field affect the local flow field, whereas adjustment of the hydrogeological structure model affects the global flow field.
The arid and semi-arid regions within China host 75% of the country’s cultivated lands. These regions heavily rely on groundwater for drinking, irrigation, industry and energy production. Understanding recharge and discharge processes is critical to managing sustainable use and development of groundwater resources. Recently, groundwater recharge and discharge have been altered by climate change (air temperature, rainfall) and human activities (e.g. irrigation, pumping, reforestation), resulting in significant changes in the quantity, quality, and spatiotemporal distribution of groundwater resources. This essay describes some examples of the associated issues, challenges and opportunities in the arid and semi-arid areas of China.
Three alternative groundwater flow models were evaluated for Beijing Plain, China. The first model (AM1) was constructed with the “thin layer approach” in which all 9 model layers, including five aquifers separated by four aquitards, are continuously present in the same model area. The second model (AM2) was constructed with the “quasi-3D approach” in which the hydrogeological formations were classified into five aquifer units consisting of mixed permeable and semi-permeable layers at different depth ranges. The third model (AM3) was constructed with the “true layer approach” in which aquifers and aquitards were defined according to hydrostratigraphic properties, and model layers are absent in the area where corresponding hydrogeological formations intersect bedrocks. All 3 models were calibrated with the parameter optimization method under the steady state flow condition with the same hydrological stresses and observation data. All three models fit to observations well with the similar calibration criteria values. Furthermore, AIC and BIC information criteria could not distinguish three alternative models. Only KIC could identify AM3 as the best model. Major differences of the three alternative models were identified from a hydrogeological perspective. The AM1 model depicted an illusion through contour maps that groundwater was present everywhere in the deep aquifers. The model computed larger vertical leakages because more abstraction rates were assigned improperly in deep aquifers. The AM2 model was able to compute regional groundwater balances and depicted spatial groundwater level variations. However, the AM2 model computed longer groundwater travel times around the wellfield and should not be used for the delineation of the well field protection zones and contaminant transport simulation. The AM3 model could not only compute the regional groundwater balances and describe spatial groundwater distribution in deep confined aquifers, but also delineate the capture zone of the wellfield. It can therefore be used for simulating contaminant transport. Furthermore, the AM3 model is suitable to construct a coupled regional and local flow model for simulating a managed aquifer recharge scheme.
In low-lying fluvial-lacustrine plain, anthropogenic activities and climatic variation could have a comprehensive influence on the interactions between surface water and groundwater (SW-GW) involving lake-river-aquifer. Quantification of the changes in SW-GW interaction in spatial and temporal scale causing by the two driving sources could help to the understanding of the regional water cycle mechanism and the adjustment of the decision making. However, it is usually difficult to distinguish the impact of anthropogenic activities from the climatic variation on a regional scale. Here, by using a regional three-dimensional groundwater numerical model with long term monitoring of the hydrological dynamic in Poyang Lake Basin (PLB), China, we found that groundwater storage variation in the bank storage districts can be used as an indicator to quantify each source and sink in the process of SW-GW interactions. And surface water infiltration plays a more dominant role in constructing bank storage which is meant to preserve groundwater storage. Our research in PLB demonstrates that the hydrological change caused by the operation of the Three Gorges Dam (TGD) since 2003 is mainly responsible for the autumn drought in PLB. The surface water recession due to the impoundment in TGD from September to October has an impact about 7 times stronger than the rainfall reduction. Moreover, the groundwater storage deficit caused by the insufficient recharge from the surface water infiltration would maintain the whole year, unlike the surface water system which would easily recover at the end of the year. The results demonstrate the chain interactions among lake-river-aquifer. Failing to distinguish the magnitude of each influence factor may lead to underestimating the impact on the whole water system. The results also highlight the function and the vulnerability of the groundwater system which might be vital to the riparian and estuarine-wetland ecosystem.
Groundwater flow dynamics plays a crucial role in social development and ecosystem protection. This study investigated the impacts of long-term climate change on the regional groundwater flow in Alashan, China to reveal the spatial variability of groundwater flow response to climate change and the dynamic patterns of both deep and shallow groundwater flow velocity. To this end, the hydrogeologic conditions and climate evolution history were analyzed. Based on these, four future scenarios of long-term climate change were designed, including linearly varying and cyclic changes, and numerical groundwater flow modeling was then conducted to investigate the effects of long-term climate changes on groundwater flow dynamics (including groundwater level and flow velocity). It was found that groundwater level dynamics were notably influenced by climate changes; the time scale and initial change pattern of cyclic climate influenced the amplitude and mean level of groundwater level fluctuations. In addition, our results also revealed that, for a regional groundwater system, climate change impacts on groundwater level had obvious spatial variability. Groundwater level in recharge and discharge areas were sensitive to drying and wetting climates, respectively. Thus, the spatial variability of groundwater level dynamics reflected climate change information. Moreover, groundwater flow velocity dynamics were also affected by climate changes. However, linearly varying and cyclic climates had different influences. Linearly wetting climate generally increased the groundwater flow velocity in recharge and discharge areas, but decreased that in runoff area, whereas cyclic climate induced periodical fluctuation of groundwater flow velocity. The fluctuation period of shallow groundwater flow velocity matched the full climate cycle period, whereas of the deep groundwater flow velocity was only half. This unique behavior of deep groundwater flow velocity is caused by fluctuation of the vertical velocity alternating between positive (upward flow) and negative (downward flow) values. This finding of groundwater flow velocity dynamics contributes to deeper understanding of long-term climate change effects on groundwater flow dynamics.
Climate change and future abstraction regimes will influence the availability of groundwater resources. To alleviate any potential negative effects on aquifer systems and dependent industrial and human uses, it is important to develop long-term water management plans. This study evaluates the effect of climate change and future increased groundwater demand from a coastal aquifer located in Kwale County in southern Kenya. A previously calibrated numerical groundwater flow model has been used as an assessment tool to study how future climate (precipitation and temperature variation) and groundwater abstraction changes will affect the aquifer system. The groundwater flow model was built to simulate the period 2010 to 2017, and eight future model scenarios were developed that cover six hypothetical future years. Future groundwater abstraction has been based on current allocations and future estimates made by Kenya’s Water Resources Authority. Future rainfall scenarios have been constructed based on a long historical data series (from 1959 to 2017) and the Standard Precipitation Index. The main results show that future abstraction increases due to economic growth exerts a minimum impact compared with expected climate variability. Recharge depends on intense rain events with important implications for both dry periods and for an average rainfall year. A succession of extended dry seasons may affect all water users. However, the groundwater level decline in the local shallow aquifer can reach five meters, with important consequences for local community water supplies. The most significant groundwater decline in drought periods is observed in the area surrounding the pumping wellfields in the deep aquifers, where the effects of drought and significant abstraction are multiplied. However, the effect of increased abstraction on the shallow aquifer system is limited. Despite groundwater level decline observed during prolonged dry periods, a dry period followed by a humid period leads to the relatively swift recovery of the groundwater system.
The alluvial aquifer in the lower Durance valley, southern France, constitutes the main source of drinking water for the city of Avignon. This aquifer is amply recharged by both the Durance River water and irrigation return flows. In the context of diminishing area for cultivation and of climate change, preserving the water resources in this region is essential. Effective management requires adequate knowledge of the recharge sources and groundwater flow. For this purpose, a field study was conducted during the period 2010–2011. Samples of groundwater from the shallow aquifer, rainfall and surface water were analyzed for chemical and stable isotope composition—oxygen (δ¹⁸O) and hydrogen (δ²H)—to characterize the groundwater flow and major recharge sources. The results of the groundwater hydrochemical investigation indicate that the predominant geochemical processes taking place along the main groundwater flow path are highly affected by land cover and human activities. Spatial variation in the isotopic signature and total dissolved solids of the groundwater highlights different flow patterns and identifies the different recharge zones. Using the contrast in isotopic mixing proportions between irrigation water and regional precipitation, the relative contribution and spatiotemporal distribution of the different sources of recharge can be determined. By synthetizing all available data, a conceptual model is proposed, providing a basis for integrated modelling of the hydrosystem according to likely future scenarios of land-use and/or climate change.
Desert oases exist around the alluvial fans of inland river basins in arid areas, where the vegetation growth is wholly dependent on groundwater due to scanty rainfall and arid environment. Climate change and water resources exploitation may threaten the groundwater-dependent ecosystems (GDEs) in the arid areas; a case study was proposed to evaluate the vegetative growth state with the normalized difference vegetation index (NDVI), hydrometeorological data, and the exploitation of water resources of the Nalenggele alluvial fan in northwest China. Climate change, and increasing temperature and precipitation may be indispensable factors for vegetation growth; however, based on the results of a correlation analysis, it was found that climatic factors shared little direct correlation with the NDVIs of the Nalenggele alluvial fan. Also, the depth to groundwater table (DWT) and distribution of shallow groundwater (DSG) are the direct influencing factors of vegetation growth. DWT and DSG are mainly controlled by the groundwater recharge mechanism and the original water sources from snowmelt, which are directly correlated with climate change. Predictions for DWT and DSG were made considering water resource exploitation and different river discharges amid climate change. The results reveal that the distribution area of shallow groundwater with the ecological water level (DWT < 4 m) in 2020 will decrease to approximately 78–86% of that in the status quo year, which suggests vegetation may be at risk of degradation from the combined influence of climate change and human activities. Therefore, management strategy and legislation for protecting GDEs should be proactively initiated in other similar areas in China.
This paper demonstrated the benefits of statistical methods when investigating the climatic and non-climatic drivers responsible for variations in groundwater recharge with a series of up to 43 years of annual recharge for 426 bores in South-East South Australia. We identified the factors influencing groundwater recharge based on 71 climatic metrics and 17 non-climatic metrics (including groundwater abstraction). The results showed: (1) Rainfall during April to October was the most important variable influencing recharge temporal variation, with its decline identified as the most significant factor related to recharge reduction; (2) In contrast, a negative correlation between rainfall during December to February (DJF) and annual groundwater recharge was found. This suggests that a seasonal shift in rainfall (such as decreasing rainfall during April to October and an increase during DJF) can result in a decline in recharge even when the annual rainfall remains unchanged; (3) The length of wet spells (consecutive rain days) and increasing potential evapotranspiration (PET) were additional significant predictors for recharge temporal variation. It demonstrated that a simple empirical relationship (such as recharge as a fixed percentage of rainfall) is not a reliable estimation of renewable groundwater resources under changing climatic conditions; (4) There is a statistically significant correlation between mean groundwater depth and recharge, which implies that if groundwater level fall due to rainfall declines then a positive feedback loop can lead to further recharge declines; (5) Spatially the most statistically significant factors influencing groundwater recharge were soil types and land attributes. The findings of this study can identify which stressors should be included when investigating the impact of climate change on groundwater recharge.
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.
Water resources in coastal areas can be profoundly influenced by both climate change and human activities. These climatic and human impacts are usually intertwined and difficult to isolate. This study developed an integrated model-based approach for detection and attribution of climatic and human impacts and applied this approach to the Luanhe Plain, a typical coastal area in northern China. An integrated surface water-groundwater model was developed for the study area using GSFLOW (coupled groundwater and surface-water flow). Model calibration and validation were performed for background years between 1975 and 2000. The variation in water resources between the 1980s and 1990s was then quantitatively attributed to climate variability, groundwater pumping and changes in upstream inflow. Climate scenarios for future years (2075–2100) were also developed by downscaling the projections in CMIP5. Potential water resource responses to climate change, as well as their uncertainty, were then investigated through integrated modeling. The study results demonstrated the feasibility and value of the integrated modeling-based analysis for water resource management in areas with complex surface water-groundwater interaction. Specific findings for the Luanhe Plain included the following: (1) During the historical period, upstream inflow had the most significant impact on river outflow to the sea, followed by climate variability, whereas groundwater pumping was the least influential. (2) The increase in groundwater pumping had a dominant influence on the decline in groundwater change, followed by climate variability. (3) Synergetic and counteractive effects among different impacting factors, while identified, were not significant, which implied that the interaction among different factors was not very strong in this case. (4) It is highly probable that future climate change will accelerate groundwater depletion in the study area, implying that strict regulations for groundwater pumping are imperative for adaptation.
The supply of irrigation water often overcomes crop evapotranspiration, and the resulting return flow may infiltrate and significantly contribute to an aquifer water budget. Despite its crucial importance for water resource management, the proportion of irrigation water that contributes to groundwater recharge, namely the return flow coefficient, often remains difficult to assess. Here, a chloride mass balance is combined with an isotopic mixing model (δ¹⁸O and δD) to quantify return flow coefficients, in the Crau alluvial-type aquifer (Southern France), characterized by a long-term traditional practice of flood irrigation. Local groundwater compositions are interpreted in terms of average recharge along different flow paths. The high isotopic contrast between irrigation water and regional precipitation allows the partitioning of recharge between rainfall infiltration and irrigation return flows. Isotopic mixing proportions are then used to decipher the chloride concentration of groundwater purely recharged by return flow. This allows an original application of the chloride mass balance approach to estimate return flow coefficients, which doesn't rely on any atmospheric chloride survey. Values around 0.53 ± 0.16 were found for well defined stream lines averaging the functioning of the upstream aquifer, which leads to a return flow rate of 1190 ± 140 mm yr⁻¹. These results are consistent with a local daily time series of recharge fluxes derived from the water-table fluctuation method over the 2003-2009 period, and in line with the spatial average previously quantified over the whole aquifer. This study confirms the ability of geochemical tracers to provide recharge rates fully independent from flux measurements. They can be further used to assess the irrigation efficiency in other similar systems, or to monitor the variations of irrigation return flow, which will result from the future modifications of land use, irrigation practices and climate.
In recent years, the Xitiaoxi river basin in China has experienced intensified human activity, including city expansion and increased water demand. Climate change also has influenced streamflow. Assessing the impact of climate variability and human activity on hydrological processes is important for water resources planning and management and for the sustainable development of eco-environmental systems. The non-parametric Mann–Kendall test was employed to detect the trends of climatic and hydrological variables. The Mann–Kendall–Sneyers test and the moving t-test were used to locate any abrupt change of annual streamflow. A runoff model, driven by precipitation and potential evapotranspiration, was employed to assess the impact of climate change on streamflow. A significant downward trend was detected for annual streamflow from 1975 to 2009, and an abrupt change occurred in 1999, which was consistent with the change detected by the double mass curve test between streamflow and precipitation. The annual precipitation decreased slightly, but upward trends of annual mean temperature and potential evapotranspiration were significant. The annual streamflow during the period 1999–2009 decreased by 26.19% compared with the reference stage, 1975–1998. Climate change was estimated to be responsible for 42.8% of the total reduction in annual streamflow, and human activity accounted for 57.2%. Copyright © 2012 John Wiley & Sons, Ltd.
Groundwater is a strategic resource in Yinchuan Plain, with deep groundwater increasingly used for drinking water supply to reduce arsenic exposure of rural villagers who have relied on shallow tube wells for drinking. To understand the sources and mobilization processes for arsenic enrichment in groundwater, a well water and sediment geochemistry study was carried out. Considerable spatial variability of groundwater arsenic exists. Arsenic concentration in deeper groundwater (40–250 m) was generally less than 10 μg/L (n = 26) except for seven wells, with a mean of 7.0 μg/L (n = 33). For shallower depths (4–40 m), As concentration increased from < 1 μg/L in the alluvial plain at higher elevation to 177 μg/L near the center of alluvial lacustrine plain at lower elevation. Two clusters of high arsenic, shallow groundwater run nearly parallel to the Yellow River present day and ancient courses as two narrow strips where groundwater flow is sluggish. Arsenic content in sediments ranged from 3.7 μg/g to 49.8 μg/g with an average of 9.2 μg/g, and was positively correlated with concentrations of sediment Cu, Fe2O3, Mn, Ba, Zn, F and organic C. Concentrations of arsenic between Dec. 2007 to Aug. 2011 in groundwater samples collected monthly vary more for the shallower depths (8 m: 76 ± 29 μg/L; 12 m: 116 ± 27 μg/L; 15 m: 88 ± 26 μg/L; 20 m: 164 ± 14 μg/L) than for the deeper depths (30 m: 35 ± 4 μg/L; 80 m: 33 ± 5 μg/L). Temporal variability of As concentrations in shallow groundwater correlates with water levels, driven by irrigation to a large extent.
Driven in part by the need for better information about fluvial systems for the purpose of nonmarine reservoir evaluation and development, much valuable work is now being conducted on modern rivers and their deposits, aided by such techniques as ground-penetrating radar. However, studies of modern and recent systems cannot address the question of the long-term preservability of the present-day deposits. Only studies of the rock record itself can explore this issue. Two separate studies of ancient fluvial systems illustrate some of the problems. A study of the Hawkesbury Sandstone (Triassic, Sydney Basin, Australia), highlighted the difficulty in interpreting the dimensions of large sand bodies from comparisons with a modern analog, even when very large outcrops are available. A seismic time-slice study of Pliocene-Pleistocene fluvial systems in the Gulf of Thailand revealed major changes in channel size and fluvial style over short vertical intervals. Braided and meandering systems (meander-belt widths 4 to > 10 krn [2.5 to > 6 mi]) are separated by a few tens of meters of section, or less, and are interbedded with the deposits of much smaller rivers, showing straight, meandering, and anastomosed patterns. Incised valleys and underfit streams are also present. These variations can be interpreted in terms of a sequence model, but they indicate the problems that could arise from the use of a single suite of dimensional variables as input into numerical reservoir heterogeneity and flow models. Most numerical simulation models make use of sets of equations relating such parameters as channel width, depth, and sinuosity, but most such equations are generalized across the whole spectrum of fluvial styles and can be conditioned to the reality of individual reservoirs only with difficulty. The application of the principles of sequence stratigraphy to fluvial deposits is rendered difficult by the complex response to allogenic forcing that characterizes fluvial systems. Episodes of aggradation and degradation that may be used to define sequences, and their bounding unconformities in the stratigraphic record may be the result of the complex interplay of several allogenic mechanisms governing varying stream power and sediment supply, mechanisms that may be operating at different time scales and may be out of phase with each other. In developing practical solutions for reservoir development, numerical modeling and simulation may provide generalized starting points for the analysis. History matching commonly demonstrates inaccuracies in many initial models. Further progress may be made by direct study of the reservoir itself, using three-dimensional (3-D) seismic and surveillance techniques. There is a continuing role for the study of ancient analogs as providing a realistic database on the long-term preservation styles of fluvial reservoir deposits.
For semi-arid regions, methods of assessing aquifer recharge usually consider the potential evapotranspiration. Actual evapotranspiration rates can be below potential rates for long periods of time, even in irrigated systems. Accurate estimations of aquifer recharge in semi-arid areas under irrigated agriculture are essential for sustainable water-resources management. A method to estimate aquifer recharge from irrigated farmland has been tested. The water-balance-modelling approach was based on VisualBALAN v. 2.0, a computer code that simulates water balance in the soil, vadose zone and aquifer. The study was carried out in the Campo de Cartagena (SE Spain) in the period 1999-2008 for three different groups of crops: annual row crops (lettuce and melon), perennial vegetables (artichoke) and fruit trees (citrus). Computed mean-annual-recharge values (from irrigation+precipitation) during the study period were 397 mm for annual row crops, 201 mm for perennial vegetables and 194 mm for fruit trees: 31.4, 20.7 and 20.5% of the total applied water, respectively. The effects of rainfall events on the final recharge were clearly observed, due to the continuously high water content in soil which facilitated the infiltration process. A sensitivity analysis to assess the reliability and uncertainty of recharge estimations was carried out.
Understanding the process of groundwater recharge is fundamental to the management of groundwater resources. Quantifying the future evolution of recharge over time requires not only the reliable forecasting of changes in key climatic variables, but also modelling their impact on the spatially varying recharge process.This paper presents a physically based methodology that can be used to characterize both the temporal and spatial effect of climate change on groundwater recharge. The method, based on the hydrologic model HELP3, can be used to estimate potential groundwater recharge at the regional scale with high spatial and temporal resolution. In this study, the method is used to simulate the past conditions, with 40 years of actual weather data, and future changes in the hydrologic cycle of the Grand River watershed. The impact of climate change is modelled by perturbing the model input parameters using predicted changes in the regions climate.The results of the study indicate that the overall rate of groundwater recharge is predicted to increase as a result of climate change. The higher intensity and frequency of precipitation will also contribute significantly to surface runoff, while global warming may result in increased evapotranspiration rates. Warmer winter temperatures will reduce the extent of ground frost and shift the spring melt from spring toward winter, allowing more water to infiltrate into the ground. While many previous climate change impact studies have focused on the temporal changes in groundwater recharge, our results suggest that the impacts can also have high spatial variability.
The management of groundwater resources is paramount in semi-arid regions experiencing urban development. In the southwestern United States, enhancing recharge of urban storm runoff has been identified as a strategy for augmenting groundwater resources. An understanding of how urbanization may impact the timing of groundwater recharge and its quality is a prerequisite for mitigating water scarcity and identifying vulnerability to contamination. We sampled groundwater wells along the Rillito Creek in southern Arizona that had been previously analyzed for tritium in the late 1980s to early 1990s and analyzed samples for tritium (3H) and helium-3 (3H/3He) to evaluate changes in 3H and age date groundwaters. Groundwater samples were also analyzed for chlorofluorocarbons (CFCs) and basic water quality metrics. Substantial changes in 3H values from waters sampled in the early 1990s compared to 2009 were identified after accounting for radioactive decay and indicate areas of rapid recharge. 3H–3He groundwater ages ranged from 22 years before 2009 to modern recharge. CFC-11, -12 and -113 concentrations were anomalously high across the basin, and non-point source pollution in runoff and/or leaky infrastructure was identified as the most plausible source of this contamination. CFCs were strongly and positively correlated to nitrate (r2 = 0.77) and a mobile trace metal, nickel (r2 = 0.71), suggesting that solutes were derived from a similar source. Findings from this study suggest new waters from urban non-point sources are contributing to groundwater recharge and adversely affecting water quality. Reducing delivery of contaminants to areas of focused recharge will be critical to protect future groundwater resources.
Present models of river sedimentation are based largely on a classification of the geomorphology of present-day river channel patterns. The classes are difficult to apply with confidence to ancient sediments and their use should be restricted. A broad transport-mode classification can be useful, based on grain-size and distinguishing 'mainly bed-transport', 'mainly suspension', and 'bed-transport and suspension'. A descriptive classification of 2- or 3-D exposures is proposed, which is based on the shape and interrelations of distinctive sediment bodies. Environmental classification tends to concentrate on the degree and mobility of channelization during deposition. Useful classes are: 1) sheet flood, 2) fixed channel, 3) mobile channel. Terms such as meandering or braided may then be suffixed to any of these classes, and some estimation of indices of sinuosity or braiding may locally be possible.-from Author
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