This reprint focuses on the application of groundwater models developed with the aim of optimizing the management of water resources in urban environments, coastal areas, karst aquifers, and riparian ...zones, among other environments. The testing of innovative techniques applied to traditional models, including machine learning techniques, is of particular interest. Special attention is given to the application of tools for the evaluation of climate change effects on groundwater.
Science, society, and the coastal groundwater squeeze Michael, Holly A.; Post, Vincent E. A.; Wilson, Alicia M. ...
Water resources research,
April 2017, 2017-04-00, 20170401, Letnik:
53, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Coastal zones encompass the complex interface between land and sea. Understanding how water and solutes move within and across this interface is essential for managing resources for society. The ...increasingly dense human occupation of coastal zones disrupts natural groundwater flow patterns and degrades freshwater resources by both overuse and pollution. This pressure results in a “coastal groundwater squeeze,” where the thin veneers of potable freshwater are threatened by contaminant sources at the land surface and saline groundwater at depth. Scientific advances in the field of coastal hydrogeology have enabled responsible management of water resources and protection of important ecosystems. To address the problems of the future, we must continue to make scientific advances, and groundwater hydrology needs to be firmly embedded in integrated coastal zone management. This will require interdisciplinary scientific collaboration, open communication between scientists and the public, and strong partnerships with policymakers.
Key Points
Coastal hydrogeology addresses important societal problems
Scientific advances have created tangible societal benefits
Collaborations between scientists, policymakers, and the public are essential for coastal water resource sustainability
When simulating groundwater flow in unconfined and convertible aquifers using a groundwater model with the block‐centered finite‐difference approach, such as MODFLOW, it frequently encounters drying ...and rewetting of cells. Although many drying and rewetting simulation methods have been proposed in the past, balancing simulation accuracy and convergence capability all at once is difficult. MODFLOW‐2005, which has second‐order accuracy, employs a trial‐and‐error method, but it suffers from computational instability when large quantities of grid cells are dried. MODFLOW‐NWT adopts the upstream‐weighting approach and Newton iteration method to ensure the stability of the drying and rewetting simulations. However, the upstream‐weighting approach has only first‐order accuracy, and the Newton iteration method is complex to implement because it necessitates the establishment of an additional Jacobian matrix. The methods employed by MODFLOW‐NWT are also available in MODFLOW 6, therefore it inherits both the strengths and weaknesses of MODFLOW‐NWT. In this study, a new method, Picard iteration‐based always active cell (PAAC), is proposed. Similar to MODFLOW‐NWT, the PAAC method also uses dry cells as active cells. The PAAC method, however, does not use the upstream‐weighting approach and has second‐order accuracy. Moreover, it ensures good convergence stability even under the Picard iteration method. In addition to discussing the algorithm, five cases were used to comprehensively compare the simulation effects of the PAAC method with MODFLOW‐2005 and MODFLOW‐NWT, including an analytical solution, repeated drying‐rewetting of multi‐layer grids, pumping well problem, perched aquifer problem and a nearly dry single‐layer grid, which verified the practicability of the PACC method.
Key Points
A new physically‐based method to simulating the drying‐rewetting problems of groundwater model, Picard iteration‐based always active cell
The new method performed robust convergence even with the Picard iteration method and a general PCG solver
The new method achieved second‐order accuracy
This study explores the capability of Gravity Recovery and Climate Experiment (GRACE) to detect heterogeneous groundwater storage (GWS) variations in two subregions of the North China Plain: the ...Piedmont Plain (PP, ~54,000 km2, mainly exploiting shallow groundwater) and East Central Plain (ECP, ~86,000 km2, mainly exploiting deep groundwater). Results show that the GWS anomalies estimated from GRACE data (2003–2013) agree well with those estimated from in situ observations (2005–2010) for both PP (R2 = 0.91) and ECP (R2 = 0.75). The shallow GWS (2003–2013) in PP declines faster (−46.5 ± 6.8 mm/yr) than the deep GWS in ECP (−16.9 ± 1.9 mm/yr). However, the shallow GWS in PP recovered more quickly especially during the 2008–2011 drought period. Despite its lower magnitude, the GRACE‐derived GWS depletion in ECP reveals the overexploitation of deep GWS. This study demonstrated that the heterogeneous GWS variations can potentially be detected by GRACE at the subregional scale smaller than the typical GRACE footprint (200,000 km2).
Key Points
GRACE has the potential to detect subregional heterogeneous GWS depletion in NCP
Shallow GWS in the Piedmont Plain declines faster but also recovers more quickly
GRACE data reveal the overexploitation of deep GWS in the East Central Plain
Groundwater is an important water source for agricultural irrigation in Penyang County. Some traditional methods such as irrigation coefficient, sodium adsorption ratio, total alkalinity, total ...salinity and total dissolved solids were employed to assess groundwater quality in this area. In addition, an improved technique for order preference by similarity to ideal solution model was applied for comprehensive assessment. The origin of major ions and groundwater hydrogeochemical evolution was also discussed. Groundwater in Penyang County contains relative concentrations of dominant constituents in the following order: Na
+
> Ca
2+
> Mg
2+
> K
+
for cations and HCO
3
−
> SO
4
2−
> Cl
−
> CO
3
2−
for anions. Groundwater quality is largely excellent and/or good, suggesting general suitability for agricultural use. Calcite and dolomite are found saturated in groundwater and thus tend to precipitate out, while halite, fluorite and gypsum are unsaturated and will dissolve into groundwater during flow. Groundwater in the study area is weathering-dominated, and mineral weathering (carbonate and silicate minerals) and ion exchange are the most important factors controlling groundwater chemistry.
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•Groundwater related research papers from 1978 to 2017 were collected.•The number of published studies increased by >10% per year on average.•Institutions based in developed countries ...have led groundwater research output.•China and India have experienced strong growth in output in recent years.•Depletion and sustainability have increased as a percentage of groundwater studies.
Long-term over-exploitation and unsustainable practices have caused severe groundwater depletion and deterioration across many regions throughout the world. This has triggered a series of negative impacts on human populations and the natural environment. To understand groundwater-related processes and explore ways to mitigate pertaining issues, large numbers of groundwater-related studies have been performed by the research community. In this study, all research papers published between 1978 and 2017 incorporating “groundwater” in the title, keywords, or abstract, were retrieved from the Web of Science Core Collection (WSCC). Of these, a total of 80,763 papers were identified as being groundwater-related publications. Our analysis revealed that groundwater research output increased significantly during this period, at average annual rate of 10.1%, exceeding the general trend for the WSCC (3.4%). Institutions based in developed countries have held predominance in publishing groundwater research, however, research output from developing countries, such as China and India, experienced much growth in recent years. Development trends were assessed among the research topics of groundwater depletion, contamination, remediation technology, and sustainable management, all of which experienced increased research output. Among sub-topics, groundwater depletion and sustainable management research have increased as a percentage of total groundwater studies, while studies of arsenic, chlorinated solvents, BTEX, bioremediation, and natural attenuation have dropped off in recent years. Additionally, as groundwater-related research output has increased rapidly, robust secondary analyses and meta-analyses are called for in order to make sense of the rapidly expanding body of groundwater research literature. Moreover, owing to the many complexities surround groundwater issues, greater interdisciplinary collaboration is also called for.
How topography controls topography‐driven groundwater flow is investigated with varying rainfall and topography using a two‐dimensional groundwater‐surface water coupled model. Results show that the ...penetration depths of local flow systems present a good relation with capture zone size (Cl) and topography rise (Hl) of local flow systems, but poor and opposite relation with the two topographic indices of the surface water watershed. The stagnant zones are formed due to the movement of stagnation points, whose velocity magnitude is almost zero. The area and depth of stagnant zones below the mountains have a good or no relation with the mountain size, depending on the hydraulic conductivity. The fractal behavior of penetration depth variations with rainfall presents a good or no relation with Cl and Hl, depending on the rainfall rate and hydraulic conductivity. The topography control may be less important when rainfall rate or hydraulic conductivity is significantly reduced.
Plain Language Summary
This study explains which topographic indices control topography‐driven groundwater flow. Our study demonstrates that the groundwater subsystems are not controlled by the size and topography rise of a surface water watershed, but by the size and topography rise of each groundwater subsystem. In previous studies, identifying surface water divide was usually thought to be important before setting up a model to investigate groundwater flow patterns, but this study indicates that groundwater divide is totally independent of surface water divide. And it comes to an opposite conclusion when we base on capture zone size of groundwater subsystems. Our research also indicates that the control of topography on stagnant zones and variations of groundwater flow system can become weakened when the hydraulic conductivity or rainfall rate is reduced. The combined effect of topography, climate, and geology on groundwater flow patterns should be considered to fully understand the dominant factors on topography‐driven groundwater flow.
Key Points
Stagnant zones are formed due to the movement of stagnant points with rainfall fluctuation
Penetration depth of local flow systems is controlled by the capture zone size and topography rise of local flow systems
When the rainfall or hydraulic conductivity is reduced, climate or geology may control groundwater flow systems much more than topography
In Africa, groundwater is the major source of drinking water and its use for irrigation is forecast to increase substantially to combat growing food insecurity. Despite this, there is little ...quantitative information on groundwater resources in Africa, and groundwater storage is consequently omitted from assessments of freshwater availability. Here we present the first quantitative continent-wide maps of aquifer storage and potential borehole yields in Africa based on an extensive review of available maps, publications and data. We estimate total groundwater storage in Africa to be 0.66 million km3 (0.36-1.75 million km3). Not all of this groundwater storage is available for abstraction, but the estimated volume is more than 100 times estimates of annual renewable freshwater resources on Africa. Groundwater resources are unevenly distributed: the largest groundwater volumes are found in the large sedimentary aquifers in the North African countries Libya, Algeria, Egypt and Sudan. Nevertheless, for many African countries appropriately sited and constructed boreholes can support handpump abstraction (yields of 0.1-0.3 l s−1), and contain sufficient storage to sustain abstraction through inter-annual variations in recharge. The maps show further that the potential for higher yielding boreholes ( > 5 l s−1) is much more limited. Therefore, strategies for increasing irrigation or supplying water to rapidly urbanizing cities that are predicated on the widespread drilling of high yielding boreholes are likely to be unsuccessful. As groundwater is the largest and most widely distributed store of freshwater in Africa, the quantitative maps are intended to lead to more realistic assessments of water security and water stress, and to promote a more quantitative approach to mapping of groundwater resources at national and regional level.
Managing fragile island freshwater resources requires identifying pumping strategies that trade off the financial cost of groundwater supply against controlling the seawater intrusion (SWI) ...associated with aquifer pumping. In this work, these tradeoffs are investigated through a sensitivity analysis conducted in the context of an optimization formulation of the groundwater management problem, which aims at minimizing the groundwater supply operation cost associated with groundwater pumping and desalination treatment, subject to constraints on SWI control, as quantified by the water table drawdown over the well (∆s), the reduction in freshwater volume (∆FV) in the aquifer, or the salt mass increase (∆SM) in the aquifer. This study focuses on a simplified two‐dimensional model of the San Salvador Island aquifer (Bahamas). Pumping strategies are characterized by the distance of the pumping system from the shoreline (WL), the ion screen depth (D) and overall pumping rate (Q), constituting the decision variables of the optimization problem. We investigate the impacts of pumping strategies on the operation cost, ∆s, ∆FV and ∆SM. Findings indicate increasing D or decreasing WL reduces ∆s, ∆FV and ∆SM, thus preserving the aquifer hydrogeologic stability, but also leads to extracting saltier groundwater, thus increasing the water treatment requirements, which have a strong impact on the overall groundwater supply cost. From a financial perspective, groundwater ion near the island center and at shallow depths seems the most convenient strategy. However, the analysis of the optimization constraints reveals that strategies where the pumping system approaches the island center tend to cause more severe SWI, highlighting the need to trade off groundwater supply cost against SWI control.
Key Points
Effects of pumping patterns (pump depth, rate and well location) on island groundwater supply cost and seawater intrusion (SWI) are studied
Shallow pumping near the island center is cost‐effective but causes more severe SWI, that is, a conflict between economic cost and SWI control
Controlling SWI by limiting water table drawdown usually leads to selecting more expensive groundwater supply strategies
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