Recharge Rates Research Articles

Experimental Study on Groundwater Dewatering and Recharge of Deep Foundation Pit of a Subway Station in Jinan Water-Rich Area

A large amount of groundwater dewatering is beneficial to the foundation pit construction, but it will cause surface collapse, waste groundwater resources and damage the groundwater environment. In order to maintain the stability of groundwater level and the safety of surrounding buildings in the construction of deep foundation pit, the combination of dewatering and recharge is adopted. Taking the construction of deep foundation pit of a subway station in Jinan water-rich area as an example, the theoretical model of recharge quantity, stratum parameters and groundwater level was obtained through the backward derivation of the precipitation calculation model. 78 dewatering wells and 78 recharge wells were designed, and the on-site dewatering and recharge teat was carried out. The test results show that the water level of a single dewatering well decreases sharply in the initial stage of precipitation, and then the depth drops gradually to a stable level, and finally maintains a fixed value. The water inflow of a single well ranges from 34.54~57.07 m³/d, and the groundwater level can be lowered to 1.53~2.79 m below the foundation pit floor. The recharge volume of a single well in the natural recharge state is 146.88~ 241.44 m3/d, and the higher the recharge pressure, the stronger the recharge capacity of the recharge well. Through field test research, it is found that the recharge capacity of single well of recharge well is much greater than the pumping capacity of single well of dewatering well, and 56 recharge wells can make the recharge rate reach 100%, which optimizes the dewatering and recharge design of deep foundation pit.

Quantifying seasonal, depression focused recharge in the context of public supply well vulnerability

AbstractDepression focused recharge (DFR) may be a hydrologically important process that impacts the vulnerability of public supply wells, specifically related to pathogenic contaminants. The nature of DFR in glacial moraine environments, such as those located in northern latitudes within North America and Europe, is less well established than in other regions such as the Prairie Pothole Region (Northern United States, Western Canada) and the High Plains Aquifer (Central United States). The objectives of this study were to quantify seasonal infiltration flux beneath a topographically‐closed depression within 50 m of a public supply well and to interpret the impact of this DFR process on well vulnerability. Field instruments including groundwater monitoring wells, pressure transducers, soil moisture sensors and temperature sensors were installed in vertical clusters to capture the dynamics of infiltration, drainage and recharge within the depression feature. Continuous weather data were recorded by a meteorological station at the site. Transient infiltration was quantified during two contrasting hydrological events. The first event (~2 days) was an intense rainfall (>50 mm) on a melting snowpack during the fall season when the soils were unfrozen. The second was a longer (35 day) period during the spring freshet when the surficial soils were initially frozen and subject to diurnal freezing and thawing and occasional precipitation events. The water table fluctuation method augmented by Darcy flux contributions, in addition to numerical modelling using the HYDRUS‐1D model, were used to quantify recharge rates beneath the depression. Numerical DFR estimates and analytical results differed by ±8%. Results indicate that recharge rates on the order of the annual regional average can occur beneath localized features in response to extreme events associated with snowmelt and intense rainfall. Such events may represent a microbial threat to groundwater quality if public supply wells are located nearby.

Variation of some Water Quality Parameters with Fluctuation of Groundwater Table in Wana Sub-District Northern Iraq

This study aims to investigate the effect of groundwater fluctuation on some water quality characteristics in the Wana region of Northern Iraq. The fluctuations in water table levels in 18 tube wells were monitored to find out if there is a relationship between water table levels with some water quality factors. Groundwater samples were collected monthly from September 2020 to April 2021. Electric conductivity (EC), temperature, pH, water table level, total hardness (TH), sulfate and nitrate concentrations were all measured monthly for eight months. The results showed a wide range of water salinity variation ranging from 715 to 4420 µmohs/cm, with more than half of the examined samples exceeding 3000 µmohs/cm. Even in the same wells, water salinity varied during the monthly monitoring. The depth to the water table ranged from 3.39 to 37.56 m, depending on the topography, recharge rate, and aquifer conditions in the area. All of the wells produced very hard water as a result of the dissolution of gypsum and anhydrite bedrock, with about 84% having high sulphate concentrations of over 250 mg/l. More than a quarter of the samples tested showed pollution with nitrate at concentrations extremely close to or over 50 mg/l. It was found that there is no obvious correlation between groundwater quality properties and the fluctuation of the water table.

Modeling assessment of groundwater vulnerability to contamination risk in a typical basement terrain using TOPSIS-entropy developed vulnerability data mining technique

This study involved a comparative analysis in the groundwater vulnerability domain, which is a crucial component of groundwater management decision support systems (DSS). This was achieved by creating models that covered the range of algorithms from the subjective to the data-driven. The study was conducted in a basement complex area. Databases of climatic, remote sensing, and geophysical datasets were created using varieties of data acquisition techniques. The datasets included in this assessment were: rainfall (R), land use (LU), bedrock topography (BT), recharge rate (Re), and slope (S). The slope and rainfall were determined to have the highest (0.78) and lowest (0.01) weighted factors, respectively, using the entropy method. For the development of the TOPSIS-Entropy model algorithm, the weights results were combined with the TOPSIS outranking method. To generate the Groundwater Vulnerability Model map of the study area, the hybrid model was applied to griddled raster layers of the factors. Also, the TOPSIS and Entropy-WLA model algorithms were also explored and used to generate groundwater vulnerability maps. The TOPSIS-Entropy algorithms produced an accuracy of 70%, while TOPSIS and Entropy-WLA produced accuracy of 50 and 47%, respectively. The resulting model maps were validated by using correlation technique on the produced map and the longitudinal conductance map of the study area. The TOPSIS-Entropy, which followed an object-oriented model pattern, demonstrates greater accuracy and has the potential to provide appropriate insights and alternatives to decision-making in the field of groundwater hydrology in the study area and other regions of the world with comparable geology.

Application of mass-balance method to evaluate recharge rate patterns in a Quaternary aquifer in northern Mexico

This study deals with the application of mass-balance method to evaluate spatial changes in recharge-discharge rates patterns. MODFLOW was used to generate two finite-difference steady-state groundwater models for an alluvial aquifer at the Lagunera Region in northern Mexico. Additionally, a spreadsheet program was developed to generate recharge-discharge patterns distribution corresponding to 2002 and 2014 years. Inverse numerical modeling was used to calibrate the steady-state groundwater models applying a universal parameter estimation code. A root-mean square error between observed and simulated heads was used as statistical control to evaluate model calibration. Results show that recharge values are predominant at surrounding areas whereas discharge values are dominant at central zones coinciding with agricultural areas. Furthermore, alternative-hypothesis from sign test suggests that a change has occurred in recharge patterns distribution for the studied period.

Effects of groundwater depth on groundwater recharge and soybean growth dynamics in Northeast China Plain.

To explore the groundwater recharge rate and soybean growth dynamics under different groundwater depths, we conducted a field experiment with four groundwater depth treatments (1 m, D1; 2 m, D2; 3 m, D3; 4 m, D4) through the groundwater simulation system in 2021 and 2022 and explored the relationships between groundwater depth and groundwater recharge, irrigation, growth dynamics of soybean plants, and yield. We used the Logistic regression model to simulate the dynamics of soybean growth indices, including plant height, leaf area index, and dry matter accumulation. The results showed that compared with D1 treatment, the amount of groundwater recharge under D2, D3, and D4 treatments decreased by 81.1%, 96.8%, 97.5% and 80.7%, 96.7%, 97.3% in the two years, respectively. The groundwater in D1 treatment could meet water needs of soybean throughout the whole growth period, except that irrigation was needed in the sowing stage. The amount of irrigation under D1 treatment was decreased by 91.7%, 93.0%, 94.2%, and 90.9%, 92.9%, 94.0% in the two years, respectively, compared with D2, D3, D4 treatments. Among the four treatments, D1 treatment took the shortest time for entering the rapid growth stage and reach the maximum growth rate, which had the highest maximum growth rate. At the mature stage of soybean, the dry matter distribution ratio of stem in D1 treatment was the highest. D1 treatment promoted the translocation of post-flowering assimilates in soybean, and its post-flowering assimilate contribution to seeds increased by 15.5%, 16.2%, 32.6% and 45.5%, 48.7%, 63.3% in the two years, respectively, compared with D2, D3, D4 treatments. D1 treatment had the highest plant height, leaf area index, and dry matter accumulation, follo-wed by D4 treatment, while D3 treatment had the lowest. Soybean yield, number of pods per plant, number of grains per plant, and 100-grain weight all decreased and then increased with increasing groundwater depth, following an order of D1>D4>D2>D3. Soybean yield was significantly positively correlated with groundwater recharge, which was positively correlated with plant height, leaf area index, and dry matter accumulation. Our results indicated that the D1 treatment with adequate groundwater recharge increased plant height, leaf area index, and dry matter accumulation, coordinated the distribution and translocation of dry matter among all plant parts in the late soybean growth period, and ultimately achieved the highest yield. When groundwater depth was deep (D4), groundwater recharge was small. In such case, the growth and development status and yield of soybean could also reach a high level if there was sufficient water supply.

Calculation of the SPI, SPEI, and GRDI Indices for Historical Climatic Data from Doñana National Park: Forecasting Climatic Series (2030–2059) Using Two Climatic Scenarios RCP 4.5 and RCP 8.5 by IPCC

In this study, we utilized three different indices to assess drought conditions in the Doñana National Park (DNP) located in southern Spain. These indices included the Standardized Precipitation Index (SPI), which is based on precipitation statistics, the Standardized Precipitation Evapotranspiration Index (SPEI), which incorporates both precipitation and air temperature data, and the Groundwater Recharge Drought Index (GRDI), a newly developed index specifically designed to evaluate groundwater drought. The analysis covered the time period from 1985 to 2015, and future projections were made for the years 2030–2060 under different climate scenarios (RCP 4.5 and RCP 8.5). Our findings revealed a significant decrease in total precipitation of approximately 13–14% compared to historical records (1985–2015). Moreover, severely to extremely wet periods exhibited a reduction ranging from 25% to 38%. A key contribution of this study is the application of the GRDI index, which allowed us to assess groundwater recharge rates. We observed a decline in the simulated mean recharge rates during the 21st century when compared to the historical period spanning from 1950 to 2009. This decline can be attributed to increased evapotranspiration. The results of this research provide valuable insights for the Spanish water resources administration. The observed reductions in precipitation and groundwater recharge rates emphasize the need for appropriate mitigation measures. The findings will aid the administration in formulating an integrated water resources management strategy in the Doñana National Park and its surrounding basin. By understanding the projected changes in drought conditions, the administration can make informed decisions to ensure sustainable water resource management in the region.

Changes in widespread aquifer properties caused by a magnitude 6-class earthquake evaluated using InSAR analyses

Correlations between surface displacements and groundwater level changes have been widely used to understand aquifer properties and their site characteristics; however, the underlying mechanisms of various correlation types and the influence of earthquakes have not been fully investigated. In this study, we examine correlations between surface displacements from interferometric synthetic aperture radar analyses and groundwater level monitoring data in Osaka and Kyoto, Japan, over 4 years, a period including the 18 June 2018 Mw 5.6 northern Osaka earthquake. Both positive and negative correlations between the seasonal groundwater level changes and the seasonal surface displacements are identified. Based on the observations of the effects of the earthquake, a new conceptual aquifer dynamical model driving the relationship between the surface displacements and the groundwater level changes is proposed. We further reveal that sites with negative correlations increased after the earthquake, suggesting that the earthquake increased the groundwater recharge rate as a result of increases in aquifer transportation properties such as permeability and porosity.

Redox-zoning in high-energy subterranean estuaries as a function of storm floods, temperatures, seasonal groundwater recharge and morphodynamics

Redox conditions are a major control for the concentrations and mass fluxes of water constituents, e.g., nutrients, metals and organic molecules within subterranean estuaries (STE). Due to the transient flow and transport processes in STEs as well as the variable temperatures and input of redox reactants, redox zoning in the STE is believed to be highly dynamic. In the present study we analyzed the individual and combined effects of storm floods, seasonal changes of temperatures and groundwater recharge rates, as well as beach morphodynamics on the redox zoning in the STE. For this purpose, a 2D cross-shore density-dependent flow and reactive transport model was set up representing a beach aquifer exposed to high-mesotidal and medium-to high-energy wave conditions, as well as to storm floods. The simulation results show that under the given conditions, redox dynamics may occur down to a depth of 20 m. Morphodynamics appear to be the most important factor for the transience of redox zones compared to the other factors. Seasonal changes in meteoric groundwater recharge rates appear to be least relevant for the redox dynamics in STEs.

A new insight into the molecular rearrangement of sulfurized polyacrylonitrile cathode in ether electrolyte

Sulfurized polyacrylonitrile (SPAN) is one of the most promising cathode materials with high energy density. However, irreversible shuttling effect is easily triggered by formation of soluble polysulfides (Li2Sn, 2< n ≤8) in ether electrolytes. The major challenge relies in the control of molecular rearrangement of SPAN to avoid spontaneous generation of Li2Sn. This work reveals the morphological and structural roles that responsible for the compatibility of SPAN with ether electrolytes. Besides the length of the covalently bonded –Sx– chains in the pyrolyzed PAN backbone, the protection of SPAN fragments from robust interactions with solvents enables a stable cycling of electrodes. The freestanding SPAN cathode with a continuous fibrous network exhibits a much higher electrochemical stability than its powder counterparts. The single-phase solid-solid reaction of SPAN with Li+ can be realized with Li2S as the sole discharge product. Nevertheless, the reversible reaction is kinetically dominated by the activation of the produced Li2S. The recharge ability and rate capability can be improved by rationally controlling the molecular rearrangement of SPAN. The trace amount of in-situ generated Li2Sn acting as a chemical mediator can promote the reversible decomposition of Li2S, offering a new insight into cathode design of Li–S batteries.

DETERMINATION OF PARAMETERS OF WATER EXCHANGE AND MODELLING OF GROUNDWATER FLOW PROCESS FOR URANIUM MILL TAILINGS “ZAHIDNE” OF THE PRYDNIPROVSKY CHEMICAL PLANT

Results are presented of field hydrogeological studies aimed at determining the parameters of water exchange and modelling predictions of groundwater flow processes in the zone of influence of the “Zahidne” uranium mill tailing situated at the Prydniprovsky Chemical Plant, Kamianske. Hydrogeological observations allowed to estimate the infiltration recharge rate to groundwater at the study site within the first terrace (200 mm/year) and within the second terrace (150 mm/year) of the Dnipro River. According to tracer test the real groundwater flow velocity in the unconfined aquifer in sandy alluvial deposits in the zone of influence of the tailing is estimated at 0.26–0.52 m/day. Determined water exchange parameters and groundwater level monitoring data were used to develop using Visual Modflow software and calibrate the groundwater flow model for the area between the “Zahidne” uranium mill tailing and Konoplyanka River. Groundwater travel time in the unconfined aquifer from uranium mill tailing to Konoplyanka River estimated using calibrated model is 13 years, which is significantly less than the previous estimates on regional groundwater flow model (20 years). Several remediation scenarios were modelled, which allowed to develop recommendations on improving the protection of groundwater and surface water from radioactive contamination

Spatiotemporal estimation of fresh submarine groundwater discharge across the coastal shorelines of Oahu Island, Hawaii

Abstract The integrated hydrological model is a powerful tool that is used to assess the temporal distribution of fresh groundwater discharge especially in coastal areas. The coastal regions of Hawaii are examples of crucial natural resources for the Hawaiian economy and general ecological health. To fully comprehend the intricate interactions between coastal hydrology processes and ecosystems, it is necessary to evaluate the fresh submarine groundwater discharge (FSGD) at the Heeia shoreline using an integrated hydrological modeling technique. Under steady-state settings, the results showed that the present daily average of FSGD is around 0.43 m3/days across 1 m of the shoreline. However, we showed that the FSGD values were considerably impacted by climate change, groundwater head of the coastal aquifer, recharge rate, and sea level rise, particularly by the end of the 21st century. The post-development FSGD fluxes were 1.5–3.5 times greater than the freshwater transported by the Heeia stream, demonstrating the considerable contribution of the FSGD to the coastal zones of Heeia. The results also showed an exponential association between the FSGD and the groundwater level for the coastal unconfined aquifer.

Effects of grazing on soil water recharge of rehabilitated grassland under natural rainfall on the Loess Pla-teau, Northwest China.

Rainfall is critical to the regulation of slope runoff and soil water recharge. Grazing affects land cover and soil structure, with consequence on slope runoff generation and soil water recharge. Little attention has been paid to the effects of rainfall on soil water recharge caused by grazing. In this study, we examined land covers and soil water contents under different grazing intensities (G1-G5: 2.2, 3.0, 4.2, 6.7, 16.7 sheep·hm-2) and no grazing sites (NG), aiming to analyze soil water recharge under natural rainfall conditions after grazing. The results showed that grazing exerted significant effects on vegetation and biocrust coverage. The vegetation coverage was decreased by 8.3%-16.4% under G1-G5 grazing, while the biocrust coverage was increased by 106.9% under G2 grazing compared to NG. The soil surface roughness under G1-G5 grazing was increased by 53.1%-152.5%, and the thickness of biocrust was decreased by 24.1% under G5. Soil wetting front velocity decreased with increasing rainfall intensity, and that of 0-5 cm layer under the G2 grazing intensity decreased by 60.0% to 83.3% under rainfall between 18.0 mm and 70.3 mm compared to NG. The effect of grazing on soil wetting front velocity was significantly related to biocrust coverage and soil bulk density of 0-5 cm soil layer. Generally, grazing did not affect soil water recharge rates of the slope grassland on the Loess Plateau. G2 grazing may prolong the migration time of soil water in the surface layer by increasing the coverage of cyanobacteria biocrusts, which may be beneficial to the restoration of soil microenvironment. Our results provided scientific basis for water management in the enclosure grassland of the Loess Plateau in the "post-conversion era".

Assessing spatial and temporal changes in diversity of copepod crustaceans: a key step for biodiversity conservation in groundwater-fed springs

Despite the close attention springs have received from a hydrologic perspective and as biodiversity hotspots, the multiple dimensions of spring meiofaunal assemblage diversity are still poorly investigated. Knowledge of beta diversity patterns and drivers can inform and improve management decisions on biodiversity conservation. Here, we analyzed beta diversity of copepod assemblages in karst springs in Central Italy by focusing on: 1) relative contributions of turnover and nestedness components to taxonomic and phylogenetic beta diversity; 2) temporal variation of species richness and beta diversity within and between the target springs in conjunction with models of the influence of physical-chemical parameters on within-spring diversity changes; 3) expected risk of habitat loss due to variation in groundwater recharge under climate change. To this end, we gathered data from 168 samples collected in four karst springs from 2004 to 2016. Overall, we found 48 copepod species, 22 of which are obligate groundwater dwellers while the remaining 26 usually occur in surface freshwaters. All springs showed significant changes in taxonomic and phylogenetic beta diversity over time. Total beta diversity was high for both the taxonomic and phylogenetic dimensions, and turnover was the main component. Inter-site variability in dissolved oxygen explained a noticeable part of temporal variation in beta diversity, likely reflecting the role of microhabitat heterogeneity in shaping site-specific assemblages. However, most of the temporal variation in species richness and beta diversity remained unexplained, suggesting a major role of other factors, such as seasonal discharge variations. Modelling of recharge rates for all the four springs over 2001–2020 suggested a potential &amp;gt;40% recharge deficit under dry conditions. Moreover, Cellular Automata-based modelling of rainfall over the Gran Sasso-Sirente hydrogeologic unit (feeding three of the four springs) predicted an overall precipitation decrease in the 2081–2095 period. Such changes could produce severe effects on springs’ microhabitats and related communities. Our results indicate that partitioning beta diversity, monitoring its temporal changes and assessing its environmental drivers are critical to evidence-based conservation of springs. Particularly, the high species turnover we have observed suggests that conservation strategies should seek to preserve as many microhabitats as possible within and among karst springs.

Selecting suitable sites for groundwater recharge in Jordan using the spreading techniques via the integration of multi-criteria decision analysis and geographic information system tools

Over exploitation of groundwater resources in Jordan has resulted in the depletion and degradation of many groundwater aquifers. Most aquifers are heavily exploited and are expected to dry up by 2040. These pressing challenges require Jordan to find creative and sustainable solutions. Since the annual natural groundwater recharge rate is limited to 0.1–5%, managed aquifer recharge is a proposed solution for Jordan to enhance recharge. The spreading technique is one method used to deliberately recharge water into groundwater aquifers for subsequent recovery or environmental benefits. This study presents a tool based on a geographic information system-multi criteria analysis to identify the potential sites for groundwater recharge in Jordan using the spreading technique. Large sets of spatial data were used to develop a potential site suitability map for managed aquifer recharge spreading methods; the criteria were chosen based on technical, economic, and environmental considerations. The site assessment combined fourteen thematic maps to create suitability maps using the weighted linear combination approach, which were combined with constraint mapping using the Boolean logic. Constraint mapping showed that nearly 47% (7198 km2) of the study area did not meet the minimum criteria. The site assessment criteria on the remaining areas showed that about 4% (618.7 km2) of the study area has low suitability, 14% (2123 km2) has moderate suitability, 20% (3101 km2) is suitable, and 15% (2388 km2) is highly suitable. Managed aquifer recharge has a great potential in the relief of water stress in arid areas. Existing geospatial tools and the increasing availability of spatial data are a great asset to local authorities in water planners.

Resilience, stress and sustainability of alluvial aquifers in the Murray-Darling Basin, Australia: Opportunities for groundwater management

Study regionMain alluvial aquifers of the Murray-Darling Basin (MDB), Australia Study focusAround 75% of total metered groundwater use within Australia’s Murray-Darling Basin (MDB), arguably the nation’s most important food and fibre production region, is extracted from eight main alluvial aquifer systems. To date, regional-scale analyses of groundwater resilience, stress and sustainability for the region have not been completed. This study provides a systemic overview of the main alluvial systems anchored in these concepts. To achieve this, we combined three lines of evidence encompassing: a) long-term trend analysis of groundwater levels; (b) calculation of groundwater footprint indices considering volume and quality; and (c) an explicit comparison of groundwater management areas in terms of groundwater usage, sustainable use, storage volumes, presence and diversity of groundwater-dependent ecosystems (GDEs), and buffering capacity to absorb changes in recharge rates. New hydrological insights for the regionThe novelty of our work rests upon an integrated assessment of these three lines of evidence incorporating twelve different metrics to prioritise future groundwater management efforts. Results indicate that eleven out of twenty-two groundwater management areas show resilience, stress and/or sustainability issues, and a further two with emergent issues. Efforts to improve our understanding and management of these key groundwater resources would be most effective if focussed on these areas.

A common magma source for plutonic and volcanic rocks of The Geysers geothermal field, California: Volume and intrusive history derived from zircon

The Geysers Plutonic Complex (GPC) in the California Coast Ranges underlies one of the world's premier geothermal resources. The GPC consists of three major intrusive phases, orthopyroxene-biotite microgranite porphyry, orthopyroxene-biotite granite, and hornblende-biotite-orthopyroxene granodiorite (in sequence of emplacement). These are nearly coeval and compositionally equivalent to lavas of the overlying Cobb Mountain Volcanic Center which includes (from older to younger) rhyolite of Alder Creek, dacite of Cobb Mountain, and dacite of Cobb Valley. Zircon from GPC plutonic and associated volcanic rocks were analyzed at high spatial resolution for their trace element abundances along with oxygen and hafnium isotopic compositions. Pronounced negative Eu anomalies and high incompatible trace element (e.g., Y, Hf, and U) abundances in zircon along with low Ti-in-zircon temperatures reveal that the GPC microgranite porphyry magma was more evolved than GPC granite and granodiorite. Isotopically, GPC microgranite porphyry, granite, and granodiorite zircon crystals closely overlap (δ18O = +4.76 to +9.18; εHf = +1.4 to +10.7), but a subpopulation with elevated δ18O (∼8.05) and lower εHf (∼4.4) is only present in GPC granite and granodiorite. Zircon from coeval volcanic units share this dichotomy, with a dominant population at (δ18O = +4.92 to +9.38; εHf = +3.4 to +11.3) and a generally minor population with elevated δ18O and low εHf, which is particularly prominent in dacite of Cobb Valley. Anticorrelated δ18O and εHf values indicate progressive assimilation of Franciscan Complex basement rocks, but fractional crystallization was decoupled from crustal assimilation. Together with published U-Th-Pb geochronology, these data reveal distinct degrees of crust-mantle interaction and constrain the thermochemical conditions during different stages in the evolution of a composite intrusive body that fed the GPC and contemporaneous volcanoes. A thermal model for such a body emplaced at ∼7 km depth quantitatively matches the GPC zircon age distribution when magma accumulation started at low recharge rates (0.1 km3/ka), intermittently peaked during a brief flare-up (4 km3/ka for 50 ka), and then returned to a low recharge flux (0.1 km3/ka). This model also qualitatively explains the initial presence of small-volume, highly evolved melts forming the microgranite porphyry, followed by massive emplacement of less evolved magmas forming the GPC granite-granodiorite complex. During this second stage, crustal assimilation locally intensified due to prior thermal priming of the country rock. The total injected magma volume into the upper-crustal reservoir between c. 2.1 and 1.1 Ma amounts to ∼300 km3, which is about three to four times the known volume from geothermal well penetration into the GPC. The accumulation of large volumes of silicic magma along the western North American continental margin in the wake of the northward migrating Gorda slab edge thus appears limited to a brief (c. 50 ka) pulse of high magma influx from the mantle that was pre- and post-dated by protracted low-flux magmatism.

Hydrogeological-geotechnical Characterization and Analysis for Construction of a Subsurface Reservoir at a Coastal Site in the Nakdong Deltaic Plain, Busan, South Korea

Store and recover clean groundwater from a man-made subsurface reservoir is useful for the development of coastal cities. A full-scale pilot field test of managed aquifer recharge (MAR) schemes were conducted in the Nakdong River plain, Korea. The process involved constructing a hydrogeological-geotechnical model based on investigation data, including the target aquifer that was located between 30 and 67 meters deep. The subsurface response to water pumping was analyzed, and this led to the creation of charts to determine the maximum allowable injection pressure and maximum recharge rate. For two factors of safety of 1.5 and 2.0, the maximum injection head rise was estimated to be 9.7 meters and 7.25 meters, respectively, corresponding to recharge rates of 5,000 and 3,800 m3/d. One-dimensional FE consolidation analyses were conducted for different groundwater drawdowns (2, 5, 10 and 15 m) and the results showed a good match with the monitored settlement and rebound for the 2-meter drawdown case. The study concluded that the injection rate could potentially be much higher than what was tested, which would increase the capacity of the subsurface reservoir. The lessons learned from this study are useful for similar coastal sites in terms of the application of MAR technology.

Paleo-Atmospheric Precipitation Recharged to Groundwater in Middle-Latitude Deserts of Northern China

It is a difficult and hot issue in the hydrological studies of arid areas to choose suitable methods to evaluate the recharge of atmospheric precipitation to groundwater and its response to climate change in desert areas. This study reviews the theories and problems of vadose (unsaturated)-zone tracing methods selected by predecessors in hydrological studies and takes the deserts in middle latitudes of northern China as an example to extract decadal, centennial, and millennian information of atmospheric precipitation to groundwater recharge on a regional scale since the late Holocene. The fluctuations of atmospheric precipitation and chronological sequences of desert unsaturated zone were estimated by using the chlorine mass balance (CMB) theory. It indicates that the Badain Jaran Desert in the central Alashan Plateau and the surrounding Gobi deserts have experienced fluctuations of groundwater recharge on a centennial scale during the late Holocene period from about 700 to 2000 years ago. Multiple CMB profile records can identify four periods of relative wetness (1330–1430, 1500–1620, 1700–1780, and 1950–1990) and three periods of relative drought (1430–1500, 1620–1700, and 1900–1950) over the past millennium. These records are consistent with other paleoclimatic records in the northern margin of the Qinghai-Tibet Plateau, and relatively correspond to those in the eastern part of China. This indicates that groundwater recharge in the Alashan Plateau broadly reflects the degree of climatic variability in northwest China over the centennial scale and may be affected by the changes in the intensity of the East Asian summer monsoon. The estimated average recharge rate of precipitation in the Alashan Plateau in the last millennium is about 1.3~2.6 mm/a, which brings new geological evidence for understanding the source of groundwater recharge in the region but is quite different from other environmental records. It should be noted that there are uncertainties in the CMB records of the vadose zone profiles, mainly due to the assumption of atmospheric Cl input in the CMB estimation and the selection of the homogeneous vadose profile (piston flow). This study suggests that this uncertainty and its error should be extensively tested in the future by comparing deterministic data (such as regional reference stations) with large-scale random atmospheric Cl input backgrounds.

Estimating vadose zone water fluxes from soil water monitoring data: a comprehensive field study in Austria

Abstract. Groundwater recharge is a key component of the hydrological cycle, yet its direct measurement is complex and often difficult to achieve. An alternative is its inverse estimation through a combination of numerical models and transient observations from distributed soil water monitoring stations. However, an often neglected aspect of this approach is the effect of model predictive uncertainty on simulated water fluxes. In this study, we made use of long-term soil water content measurements at 14 locations from the Austrian soil water monitoring program to quantify and compare local potential groundwater recharge rates and their temporal variability. Observations were coupled with a Bayesian probabilistic framework to calibrate the HYDRUS-1D model and assess the effect of model predictive uncertainty on long-term simulated recharge fluxes. Estimated annual potential recharge rates ranged from 44 to 1319 mm a−1 with a relative uncertainty (95 % interquantile range/median) in the estimation of between 1 % and 39 %. Recharge rates decreased longitudinally, with high rates and lower seasonality at western sites and low rates with high seasonality and extended periods without recharge at the southeastern and eastern Austrian sites. Higher recharge rates and lower actual evapotranspiration were related to sandy soils; however, climatic factors had a stronger influence on estimated potential groundwater recharge than soil properties, underscoring the vulnerability of groundwater recharge to the effects of climate change.