Aquifer Levels Research Articles

Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model

AbstractNitrogen (N) contamination within agricultural‐karst landscapes and aquifers is widely reported; however, the complex hydrological pathways of karst make N fate difficult to ascertain. We developed a hydrologic and N numerical model for agricultural‐karst, including simulation of soil, epikarst, phreatic, and quick flow pathways as well as biochemical processes such as nitrification, mineralization, and denitrification. We tested the model on four years of nitrate (NO3−) data collected from a phreatic conduit and an overlying surface channel in the Cane Run watershed, Kentucky, USA. Model results indicate that slow to moderate flow pathways (phreatic and epikarst) dominate the N load and account for nearly 90% of downstream NO3− delivery. Further, quick flow pathways dilute NO3− concentrations relative to background aquifer levels. Net denitrification distributed across soil, epikarst, and phreatic water removes approximately 36% of the N inputs to the system at rates comparable to nonkarst systems. Evidence is provided by numerical modeling that NO3− accumulation via evapotranspiration in the soil followed by leaching through the epikarst acts as a control on spring NO3− concentration and loading. Compared to a fluvial‐dominated immature karst system, mature‐karst systems behave as natural detention basins for NO3−, temporarily delaying NO3− delivery to downstream waters and maintaining elevated NO3− concentrations for days to weeks after hydrologic activity ends. This study shows the efficacy of numerical modeling to elucidate complex pathways, processes, and timing of N in karst systems.

Projection of 21st century irrigation water requirement across the Lower Mississippi Alluvial Valley

Lower Mississippi Alluvial Valley (LMAV) is the largest floodplain and one of the most productive agricultural regions in the United States. Irrigation is widely used in this region to improve crop production and resource use efficiency due to a mismatch between crop water requirements and precipitation timing and quantity during the growing season. In the recent decades, aquifer decline caused by groundwater withdrawals for irrigation has been recognized as a critical environmental issue threatening water security and agricultural sustainability in the LMAV. To improve agricultural water use efficiency and reduce groundwater withdrawals, it is pivotal to understand the spatiotemporal patterns of crop irrigation water requirements (IWR). In this study, we analyzed future climate changes over the LMAV cropland areas and estimated future IWR changes for major crops in the 21st century using two climate scenarios (i.e. RCP45 and RCP85) and two crop growth duration length (GDL) scenarios [i.e. Fixed GDL (GDL does not change with time) and Varied GDL (GDL changes with time)]. Results show that croplands in the LMAV would experience continuous warming, and either no significant change or a decreasing level of precipitation under the RCP45 and the RCP85. If keeping current cropland areas and cropping systems unchanged, average crop IWR by the end of the 21st century would increase by 4.2% under the RCP45 + Varied GDL scenario, 14.5% under the RCP45 + Fixed GDL scenario, 9.2% under the RCP85 + Varied GDL scenario, and 29.4% under the RCP85 + Fixed GDL scenario. The greatest increases would occur in the summer months. Aquifer levels in the LMAV, therefore, are expected to decline at an accelerated pace if no effective mitigation strategies are implemented. This study made the first attempt to reveal the spatially-explicit crop IWR and its future changes in the LMAV, which provides a scientific basis for developing management strategies that can enhance water use efficiency and improve agriculture sustainability.

Mechanism of mine water inrush from overlying porous aquifer in Quaternary: a case study in Xinhe Coal Mine of Shandong Province, China

Mine water inrush from coal seam roof is one of the serious disasters that threaten safe production of coal mines. Identification of water inrush source and water inrush pathway is a key task for preventing and controlling such mine water hazards. A water inrush accident at approximately 1316 m3/h occurred at no. 3301 working face of Xinhe Coal Mine in Shandong Province, China. Multiple lines of evidence including characteristics of mine water inflow rate, dynamic monitoring data of water levels in different aquifers, geochemical fingerprinting, and drill hole core examination suggest that the water inrush source originated from the overlying Lower Quaternary porous aquifer with calcite cementation. Structural analysis and numerical simulation with FLAC3D indicate that a low-angle fault, DF49, and mining-induced fractures provided the pathway for the water inrush. Mining activities made the fault hydraulically conductive and connected to the Quaternary aquifer. The numerical simulation demonstrated that the water-conducting fracture zone in the coal seam roof extended to the fault. Groundwater gushed into the mining area from the Quaternary aquifer via the combined pathway of the activated fault and mining-induced fractures. Presence of the fault in the overlying formations played a critical role in occurrence of the water inrush. Results from this case study can be of reference to all coal mines with faults or other geological discontinuities present in the overlying formation. These discontinuities may significantly extend the height of the mining-induced water-conducting fracture zone in the roof and thus increase water inrush risks.

Prediction of groundwater levels from lake levels and climate data using ann approach

There are many environmental concerns relating to the quality and quantity of surface and groundwater. It is very important to estimate the quantity of water by using readily available climate data for managing water resources of the natural environment. As a case study an artificial neural network (ANN) methodology is developed for estimating the groundwater levels (upper Floridan aquifer levels) as a function of monthly averaged precipitation, evaporation, and measured levels of Magnolia and Brooklyn Lakes in north-central Florida. Groundwater and surface water are highly interactive in the region due to the characteristics of the geological structure, which consists of a sandy surficial aquifer, and a highly transmissive limestone confined aquifer known as the Floridan aquifer system (FAS), which are separated by a leaky clayey confining unit. In a lake groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through the underlying confining unit to a deeper highly transmissive upper Floridan aquifer. This provides a direct hydraulic connection between the lakes and the aquifer, which creates fast and dynamic surface water / groundwater interaction. Relationships among lake levels, groundwater levels, rainfall, and evapotranspiration were determined using ANN-based models and multiple-linear regression (MLR) and multiple-nonlinear regression (MNLR) models. All the models were fitted to the monthly data series and their performances were compared. ANN-based models performed better than MLR and MNLR models in predicting groundwater levels.

Radon in groundwater baseline study prior to unconventional shale gas development and hydraulic fracturing in the Karoo Basin (South Africa)

The prospect of unconventional shale gas development in the semi-arid Karoo Basin (South Africa) has created the prerequisite to temporally characterise the natural radioactivity in associated groundwater which is solely depended on for drinking and agriculture purposes. Radon (222Rn) was the primary natural radionuclide of interest in this study; however, supplementary radium (226Ra and 228Ra) in-water measurements were also conducted. A total of 53 aquifers spanning three provinces were studied during three separate measurement campaigns from 2014 to 2016. The Karoo Basin's natural radon-in-water levels can be characterised by a minimum of 1 ± 1 Bq/L (consistent with zero or below LLD), a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The mean radon-in-water levels for shallow aquifers were systematically higher (55 ± 10 Bq/L) compared to deep (14 ± 3 Bq/L) or mixed aquifers (20 ± 6 Bq/L). Radon-in-water activity concentration fluctuations were predominantly observed from shallow aquifers compared to the generally steady levels of deep aquifers. A collective seasonal mean radon-in-water levels increase from the winter of 2014 (44 ± 8 Bq/L) to winter of 2016 (61 ± 16 Bq/L) was noticed which could be related to the extreme national drought experienced in 2015. Radium-in-water (228Ra and 226Ra) levels ranged from below detection level to a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio was characterised by a minimum of 0.93, a maximum of 6.5 and a mean value of 3.3 ± 1.3. Developing and improving baseline naturally occurring radionuclide groundwater databases is vital to study potential radiological environmental impacts attributed to industrial processes such as hydraulic fracturing or mining.

Construction of a numerical groundwater flow model in areas of intense mine drainage, as exemplified by the Olkusz Zinc and Lead Ore Mining Area in southwest Poland

Abstract Areas of intense mine drainage that are subjected to numerical modelling require the construction of a complex model structure that will properly reflect actual conditions. This paper presents the process and results of constructing such a structure for the Olkusz Zinc and Lead Ore Mining Area, an area situated in a cone of depression the extent of which reaches 500 km2. This size range calls for a selection of appropriate external boundaries, properly separated from these of the mine drainage area. The complex geological structure of the Olkusz area, associated with considerable variation in the thickness of rock formations, discontinuities of rock levels and occurrence of numerous faults, must be schematised so that calculation layers can be identified. The faults in the study area have to be reflected in the regional model structure, although only those faults that actually affect groundwater flows should be selected. The model structure needs to include detailed recognition and reflection of hydraulic contacts between aquifer levels, together with a selection of hydrogeological parameters that are different for particular formations. Only a complex structure built in such a manner may be the foundation of further model studies.

Aquifer Dynamics and Atmospheric Electricity

Measurements of variations in the atmospheric electric field (AEF), soil and atmospheric radon concentration, and hydrogeological parameters have made it possible to establish links between the listed processes. A rise in aquifer levels increases the outflow of soil radon, which decreases the AEF; a decrease in levels leads to the opposite effect. The rise can be caused by the infiltration of precipitation, hydraulic fracturing, and lowering of atmospheric pressure; the fall can be caused by the pumping of artesian waters or by an increase in atmospheric pressure.

A simple contaminant fate and transport modelling tool for management and risk assessment of groundwater pollution from contaminated sites

Contaminated sites pose a significant threat to groundwater resources. The resources that can be allocated by water regulators for site investigation and cleanup are limited compared to the large number of contaminated sites. Numerical transport models of individual sites require large amounts of data and are labor intensive to set up, and thus they are likely to be too expensive to be useful in the management of thousands of contaminated sites. Therefore, simple tools based on analytical solutions of contaminant transport models are widely used to assess (at an early stage) whether a site might pose a threat to groundwater. We present a tool consisting of five different models, representing common geological settings, contaminant pathways, and transport processes. The tool employs a simplified approach for preliminary, conservative, fast and inexpensive estimation of the contamination levels of aquifers. This is useful for risk assessment applications or to select and prioritize the sites, which should be targeted for further investigation. The tool is based on steady-state semi-analytical models simulating different contaminant transport scenarios from the source to downstream groundwater, and includes both unsaturated and saturated transport processes. The models combine existing analytical solutions from the literature for vertical (from the source to the top of the aquifer) and horizontal (within the aquifer) transport. The effect of net recharge causing a downward migration and an increase of vertical dispersion and dilution of the plume is also considered. Finally, we illustrate the application of the tool for a preliminary assessment of two contaminated sites in Denmark and compare the model results with field data. The comparison shows that a first preliminary assessment with conservative, and often non-site specific parameter selection, is qualitatively consistent with broad trends in observations and provides a conservative estimate of contamination.

Groundwater Is Key to Salmonid Persistence and Recruitment in Intermittent Mediterranean‐Climate Streams

AbstractJuvenile coho salmon thrive in intermittent streams of the Pacific Northwest yet are in danger of increased mortality from drought and rising temperatures. With warmer temperatures and more frequent climate extremes projected, the need to understand how intermittent stream hydrology and biogeochemistry impact juvenile salmonid habitat and behavior is imperative. Previous investigations indicated that dissolved oxygen limits the persistence of coho salmon in intermittent streams, leading to the hypothesis that groundwater inflow would ultimately control patterns of salmon recruitment and persistence. Here we tested that hypothesis in paired tributaries of Salmon Creek, Sonoma County, CA during California's extreme drought of 2011–2017. We used the fluorescent fingerprint of dissolved organic carbon, together with a parallel factor analysis, to estimate groundwater influence in individual stream pools, corroborating those estimates with stable isotope and radon analyses. Repeat snorkel surveys provided fish counts in those pools at the beginning and end of the period of surface‐water disconnection. Results suggested that coho salmon fry preferentially selected pools with a groundwater inflow signal and persisted in pools maintaining that signal through the dry season. This groundwater inflow signal was distinct from hyporheic influence, which exhibited little correlation with fish distribution. Groundwater within pools was young, and spot measurements suggested that it was relatively oxygenated. Proportional groundwater contributions to pools increased as drought deepened. Results suggest that maintaining relatively high groundwater levels in coastal aquifers may be imperative to the persistence of vulnerable salmonid populations in a changing climate.

A Framework for Ground Water Management Based on Bayesian Network and MCDM Techniques

Groundwater resources are steadily subjected to increasing water demands. The aquifers are considered as the most accessible source of fresh water. In recent years, they have been faced with severe water withdrawal in arid and semi-arid countries like Iran and thus some aquifers was considered as forbidden aquifers that it means the water withdrawal from these aquifers is unauthorized. Given a critical situation, groundwater resources management in the form of tools such as monitoring the level of the aquifers and developing the restoring scenarios is essential. Therefore, for this purpose, a framework has been developed based on prediction of groundwater level using Bayesian Networks (BNs) model. Furthermore, Multi Criteria Decision Making methods (MCDM) techniques proposed and employed for ranking of proposed groundwater management scenarios. This framework was evaluated for restoring the Birjand aquifer in Iran in different hydrological conditions. A probabilistic Dynamic BN was proposed for groundwater level prediction under uncertainties. After analyzing the obtained results, the applicable short term scenarios for groundwater management as well as appropriate economic, social and technical criteria were defined for decision making procedure. Then, using elicitation of decision makers’ opinions on the relative importance and performance of criteria, SAW, TOPSIS and PROMETHEE-II techniques were applied to rank the scenarios and the obtained results were aggregated by Borda method for final ranking of the scenarios. Lastly, the final results demonstrates the capability of the proposed framework for groundwater resources planning and management which can be employed for reducing the risk of aquifer level declining.

MODELING OF HYDROGEOFILTRATION GROUNDWATER FIELD IN THE INFLUENCE ZONE OF METALLURGICAL PRODUCTION

In order to detect technogenic violations, the hydrogeofiltration field of the aquifer closer to the land surface which is spreading within the site of metallurgical production of the Private Joint Stock Company “EVRAZ Dniprovskyi Metallurgical Plant” (PJSC “EVRAZ DMP”) was investigated. The data of the target analysis and the groundwater monitoring information (2010–2014) from the PJSC “EVRAZ DMP” local groundwater monitoring networks were used. A full-scale survey of observation wells and pilot filter work was carried out. Geoinformation approach was used for modeling the hydrogeofiltration field of the investigated aquifer. According to the results of geoinformation analysis, the presence of disturbances of level, balance and hydrogeotermal parameters of particular aquifer were observed. It was discovered the local “piezometric dome” perturbations of the water table and the stable abnormal groundwater temperature rise. Such changes indicate the presence of additional intensive anthropogenic sources of infiltration in local areas. The most relative level of water-ecological load is obtained the southwest zone of the industrial site with a borderline location. Therefore, the influence of the adjacent urbanized area on the deformation of the hydrogeofiltration field of the aquifer closer to the land surface within the studied area was not excluded. The preservation of the revealed tendencies of deformation of the hyd­rogeological conditions on the site might be produced a threat to safe ope­ration of industrial structures as a result of intensification of the floo­ding process and derivatives – mechanical and chemical phenomena.

An accurate evaluation of water availability in sub-arid Mediterranean watersheds through SWAT: Cega-Eresma-Adaja

Simulation of flow processes in hyper-regulated Mediterranean watersheds is critical when examining general water demand and established ecological flows of River Basin Management Plans. Weather dynamics in the Mediterranean zone in recent decades have been characterised by a natural variation of drought cycles. In addition, exacerbated climate change proves that water fluxes must be estimated with more exhaustive models. The aim of this study is to assess the water balance of the Cega-Eresma-Adaja (CEA) watershed, including a detailed assessment of land uses and management practices to quantify agricultural water demand for the time period 2004–2014. We used the Soil and Water Assessment Tool (SWAT), given that it is a widespread tool that involves complex processes of the water cycle on a basin scale, providing information on water dynamics related to land use as a fundamental characteristic for water balance calculation. The Nash-Sutcliffe coefficient efficiency value, the main index of calibration and validation performance, was 0.86 for the Eresma-Adaja River and 0.67 for the Cega River. This presents a good result considering the large-scale watershed studied. Analysing dry hydrological years, we found that the estimation of ecological flows for sub-arid zones needs to consider the shallow aquifer-river relationship. During spring-summer periods, with very low flow, monitoring the shallow aquifer levels ensures a good ecological status. The study reveals that aspects such as crop rotation, soil management and their associated measures in Mediterranean basins are key factors for water resource management during drought periods. These results are expected to serve stakeholders and river basin authorities in conducting better-integrated water management practices in the watershed.

Geospatial characteristics investigation of suitable areas for photovoltaic water pumping erections, in the southern region of Ghardaia, Algeria

During the on-site operation, the PV water pumping system can be faced different unexpected troubles, although the accurate sizing and the fit erection. Recently, different studies showed that the lack of enough information about the geospatial characteristics of the area, required during the sizing of a Photovoltaic Water Pumping System (PVWPS) is the main cause. In this attempt, an investigation study on geospatial characteristics has been conducted, in the Mansoura desert region; about 70 km south of Ghardaia headquarter. The main goal was to spotlight on different suitable locations for implementing PVWPS. The study has been carried out on six zones; namely: Ain Losseik, Old Mansoura, New Mansoura, Oued Ghazalat, Khanget-fedj and Zawiat Lacheikh. The evaluation consists on census and classifying the wells or boreholes according to the geographical location, the water source behavior, the soil specifics, agriculture and ranching activity, type of the crops, etc … It has been averred that the renewable aquifer levels vary between the averages of 20 and 45 m. However, the Albian borehole static levels can be reached between the averages of 3 and 8 m. The aquifer hydraulic behavior has been achieved by calculation of hydrogeology properties. Thus, the obtained data were compared and classified, whereas the suitable DC pumps were selected, accordingly. This method can be used to detect the different local geospatial effects influencing the system operation. Furthermore, it can be considered as a key point subject that could be extended, in future works.

Model Groundwater (Sustainable Management) Bill, 2017: a new paradigm for groundwater regulation

ABSTRACTThe Groundwater (Sustainable Management) Bill, 2017 drafted by the Ministry of Water Resources, River Development & Ganga Rejuvenation provides a new template that states can use to adopt legislation capable of addressing the fast-increasing groundwater crisis faced by many states. This Bill follows on an earlier model bill drafted in 1970 and updated several times until 2005 on which the dozen of existing groundwater acts are based. This 1970 template is unsuited to the present needs of a country where groundwater is now the primary source of drinking water and irrigation. In particular, it fails to provide for local-level regulation of what is often known as the most local source of water and fails to provide for conservation measures at aquifer level. The 2017 Bill integrates legal developments having taking place since the 1970s, such as the decentralization reforms kick-started in the 1990s, the recognition of water as a fundamental right and its recognition as a public trust. In doing so, it provides new bases for regulating groundwater as a public resource and to take measures at aquifer level, something that is crucial to address ongoing overexploitation and falling water tables.

IDENTIFICATION OF GROUNDWATER LEVEL DECLINE IN ZAGREB AND SAMOBOR-ZAPREŠIĆ AQUIFERS SINCE THE SIXTIES OF THE TWENTIETH CENTURY

This study examines historically measured groundwater levels on observation wells of Zagreb and Samobor-Zapresic aquifers since the 70-ies of the 20th century until today. The analysis also entails older groundwater level maps dating from the 60-ies of the previous century, which offer additional insights into the historical groundwater levels. The analysis of the existing groundwater levels and historical groundwater levels has identified changes of those levels in certain areas of the aquifer, special reference being taken to developments which, with time, led to deceleration of negative trends of groundwater levels in certain parts of the aquifer. The most significant such developments in the past 50 years or so are the construction of the weir of the Zagreb cogeneration plant (TE-TO) in the Sava river and occurrence of hydrologically above-average favourable years like 2013/2014, which have been separately analysed. The analysis has found that today's groundwater levels in Zagreb and Samobor-Zapresic aquifers are generally lower by approximately 3 to 6 m in comparison with the historical levels from the 60-ies of the last century.

Spatial distribution and temporal variation of methane, ethane and propane background levels in shallow aquifers – A case study from Lower Saxony (Germany)

Study regionThis survey was conducted in Lower Saxony/Northern Germany, the major German hydrocarbon province. Study focusThe study aimed at improving our understanding of background concentrations for dissolved hydrocarbon gases in shallow groundwater. More than 1700 groundwater wells were sampled, determining the concentrations of dissolved methane, ethane and propane. New hydrological insights for the regionMethane was detected in all wells with 34% < 0.001 ml/l and 14% > 1 ml/l (with 80% < 0.1 ml/l). A decreasing regional trend of methane concentrations from the North West towards South East was observed. Highest concentrations are encountered in marshes and lowlands although numerous exceptions are noted. Methane is prevalently of biogenic origin, as demonstrated by its isotopic composition. Generally, high methane concentrations are linked to high DOC, low sulfate and oxygen concentrations. Methane oxidation appears to be locally important. Ethane was detected in 30% of all wells, propane in 12.5%. The occurrence is interpreted as microbial/geogenic background related to methanogenesis or organic matter degradation during diagenesis. Low present day ethane and propane concentrations make them the preferred monitoring parameter with respect to possible anthropogenic induced input of thermogenic gas. Sampling of identical wells between 2014 and 2017 demonstrate that methane concentrations and carbon isotopic composition remain stable in general, although if it comes down to individual wells, significant fluctuations were noticed.

Landscape Based Agricultural Water Demand Modeling—A Tool for Water Management Decision Making in British Columbia, Canada

Regional water managers face challenges managing water demand and supply in response to climate change. In British Columbia (BC), less than 5% of the total land surface is suitable for cultivation and consequently, urban development and agriculture co-exist on lower elevation sites and compete for water. Surface and ground water supply all uses, affecting in-stream habitats and aquifer levels. To assess water needs, we used a GIS-based water demand model for agricultural water use, with layers for detailed land use, soils, a digital elevation model, sub-basins, aquifers, and socio-political jurisdictional boundaries. The model was driven by gridded daily minimum and maximum temperatures and precipitation at a 500m spatial resolution using historical data (1961-2010) and downscaled climate scenarios (1961-2100) derived from five CMIP5 climate models under two greenhouse gas concentration scenarios (RCP4.5 and RCP8.5). Two case studies were examined: 1. Changes in water use were determined for scenarios of climate change and expanded cropping within the BC Agricultural Land Reserve for 17 agricultural regions. Potential increases in irrigation water demand (IWD) in response to climate change ranged from 21-58% and 30-114% under low and high emissions scenarios respectively. Land use change scenarios resulted in very large potential increases in water demand, up to 2400%. Output from this work forms the basis for a web-based agricultural water licence calculator. 2. Effects of crop production systems on IWD were examined in the Okanagan region. Combinations of pasture and forage crops with inefficient irrigation systems were most vulnerable to drought as indicated by two indices: relative vulnerability index (IWD/ETo) and allocation vulnerability index (IWD/Maximum annual water allocation). In drought years, up to 70% of the irrigated area was vulnerable. A comparison of detailed land use surveys made in 2006 and 2014 indicated a large shift to highly efficient irrigation systems in the horticultural sector from 38% to 68% of the irrigated acreage. Similar shifts for other agricultural sectors may require financial support. On-going development of regional drought management will require collaborative decision making by water suppliers and users.

Putah Creek hydrology affecting riparian cottonwood and willow tree survival.

Creating or recruiting new riparian forests to improve Lower Putah Creek (LPC) ecosystem functions is challenging under the modified stream flow regime developed after historic gravel mining and installation of Monticello Dam upstream. Hydrologic connectivity between riparian trees, shallow groundwater, and the low flow channel is essential towards maintaining these forests and related habitats through the annual summer and multi-year drought periods typical in this Sacramento Valley region of California. Despite increased average summer flows, significant mature cottonwood and willow tree mortality along the LPC riparian areas below the Putah Creek diversion dam in 2014 raised concerns over the soil and hydrologic factors affecting riparian vegetation survival. A forensic analysis was conducted combining annual canopy coverage fractions and tree ring studies with daily soil-water balances, low flow records, and available groundwater level Information from the past few decades to determine the key hydrologic factors affecting riparian tree survival along the LPC. The 2011-2016 drought was linked with greater than prior average soil-water deficits in 2012-2015 and lower initial soil-water storage on March 1 of 2012 and 2014 that would be expected to stress the trees. However, such stress was not apparent in decreased tree ring spacing during this period from mature (40-50years old), deceased, and living trees. Tree canopy coverage declined dramatically (by as much as 50% as compared to the previous decade average) only in the summer of the 2014 despite a ~ 35% increase in average summer flows from 2011 to 2014. However, the regional water table aquifer levels declined at an average rate of ~ 35mm/day in 2014 (as compared to ~ 17mm/day in previous decade) and by several meters overall between 2011 and 2016 suggesting that deceased trees lacked access to the water table aquifer or lateral stream seepage. The increased rates of water table decline and overall depth may be associated with a large increase in adjacent irrigated almond orchard areas in 2014-2016. Knowledge of the dynamic hydrologic factors controlling sustainability of riparian trees should better inform and guide future tree restoration efforts along the LPC.

Integrated assessment of future potential global change scenarios and their hydrological impacts in coastal aquifers – a new tool to analyse management alternatives in the Plana Oropesa-Torreblanca aquifer

Abstract. Any change in the components of the water balance in a coastal aquifer, whether natural or anthropogenic, can alter the freshwater–salt water equilibrium. In this sense climate change (CC) and land use and land cover (LULC) change might significantly influence the availability of groundwater resources in the future. These coastal systems demand an integrated analysis of quantity and quality issues to obtain an appropriate assessment of hydrological impacts using density-dependent flow solutions. The aim of this work is to perform an integrated analysis of future potential global change (GC) scenarios and their hydrological impacts in a coastal aquifer, the Plana Oropesa-Torreblanca aquifer. It is a Mediterranean aquifer that extends over 75 km2 in which important historical LULC changes have been produced and are planned for the future. Future CC scenarios will be defined by using an equi-feasible and non-feasible ensemble of projections based on the results of a multi-criteria analysis of the series generated from several regional climatic models with different downscaling approaches. The hydrological impacts of these CC scenarios combined with future LULC scenarios will be assessed with a chain of models defined by a sequential coupling of rainfall-recharge models, crop irrigation requirements and irrigation return models (for the aquifer and its neighbours that feed it), and a density-dependent aquifer approach. This chain of models, calibrated using the available historical data, allow testing of the conceptual approximation of the aquifer behaviour. They are also fed with series representatives of potential global change scenarios in order to perform a sensitivity analysis regarding future scenarios of rainfall recharge, lateral flows coming from the hydraulically connected neighbouring aquifer, agricultural recharge (taking into account expected future LULC changes) and sea level rise (SLR). The proposed analysis is valuable for improving our knowledge about the aquifer, and so comprises a tool to design sustainable adaptation management strategies taking into account the uncertainty in future GC conditions and their impacts. The results show that GC scenarios produce significant increases in the variability of flow budget components and in the salinity.

A generalized groundwater fluctuation model based on precipitation for estimating water table levels of deep unconfined aquifers

A generalized water table fluctuation model based on precipitation was developed using a statistical conceptualization of unsaturated infiltration fluxes. A gamma distribution function was adopted as a transfer function due to its versatility in representing recharge rates with temporally dispersed infiltration fluxes, and a Laplace transformation was used to obtain an analytical solution. To prove the general applicability of the model, convergences with previous water table fluctuation models were shown as special cases. For validation, a few hypothetical cases were developed, where the applicability of the model to a wide range of unsaturated zone conditions was confirmed. For further validation, the model was applied to water table level estimations of three monitoring wells with considerably thick unsaturated zones on Jeju Island. The results show that the developed model represented the pattern of hydrographs from the two monitoring wells fairly well. The lag times from precipitation to recharge estimated from the developed system transfer function were found to agree with those from a conventional cross-correlation analysis. The developed model has the potential to be adopted for the hydraulic characterization of both saturated and unsaturated zones by being calibrated to actual data when extraneous and exogenous causes of water table fluctuation are limited. In addition, as it provides reference estimates, the model can be adopted as a tool for surveilling groundwater resources under hydraulically stressed conditions.