Conference Paper

Modelling Groundwater -Surface Water Interactions Under Climate Change Scenarios: insights from Axios Delta, Greece

Conference Paper

Modelling Groundwater -Surface Water Interactions Under Climate Change Scenarios: insights from Axios Delta, Greece

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Competing multi-sectorial water demands as well as demands for ecosystem services in coastal aquifers exert significant pressures to local water resources. Climate change is already altering spatiotemporal rainfall and runoff distributions intensifying the management challenge. In this context, this work is looking at the impact of water allocation practices on the aquifer of the Axios river delta under climate change impact scenarios. The area is characterized by agricultural activities, primarily water intensive rice cultivation. Urban water supply is supported by the exploitation of the local aquifer. Reduced precipitation is expected to increase the risk of salinisation of this coastal aquifer. At the same time, a decrease in river flow was recorded during the last decades. Numerical simulations of groundwater-surface water interactions are carried out to understand process dynamics. A drought scenario is simulated to assess the impact of climate change and the corresponding drought management response plan on the shifting fresh/saltwater interface. The drought response scenario involves banning irrigation and increasing groundwater abstraction. The groundwater model shows that flood irrigation forms a hydraulic barrier to saline intrusion. This type of groundwater model predictions can inform water resources management policies and examine the effectiveness of interventions to support sustainable socioeconomic activity while protecting environmental health.

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... With regard to interannual variation, winter months tend to be wet and summers dry. The mean annual precipitation is 663 ± 151 mm (Chalastra Station, British Antarctic Survey) (Kapetas et al., 2019). ...
... Such climatic impacts comprise pressures specific to the area and are considered in Section 3.1. Kapetas et al. (2018Kapetas et al. ( , 2019 showed that the coastal aquifer is also under risk of salinisation, particularly as climate change can alter river flow and rainfall patterns, and increase groundwater abstractions as a response. Sea level rise is also expected to shift the fresh-salt water interface. ...
... The discrimination of groundwater pollutants is also critical important for groundwater monitoring (Busico et al., 2018). Vulnerability maps form outputs of this type of integrated assessment tools that are based on numerical modelling (Kapetas et al., 2019;Kazakis et al., 2015Kazakis et al., , 2019Patrikaki et al., 2012). Additionally, decision support systems can contribute to the management of groundwater and surface water depended systems (Bournaris et al., 2015). ...
... The research, amongst others, investigates the impact of climate change on the Kalamas and Axios hydrosystems, an issue that is rather limited in its address within the literature. Focusing on the Axios River, very few scholars are identified to have worked on the thematic of water resources and climate change, e.g., Kapetas et al. [64] evaluated the way that climate change (use of CMIP5 climate model under the RCP4.5 scenario), by altering the river flow and precipitation patterns, could affect the coastal aquifers of the Axios basin in terms of salinization, or Poulos et al. [65] assessed the consequences of future sea-level rise (by using two customed scenarios of 1.0 and 0.5 m of sea-level rise) on the coastal plain of the Axios River. At the upstream part of the Axios River in North Macedonia (aka the Vardar River) there exists relevant literature; exceptions are Monevska [66], demonstrating precipitation and runoff decreases of 13.0% and 18.8%, respectively, by 2100 based on averaged ensemble values from four General Circulation Models (CSIRO/Mk2, HadCM3, ECHAM4/OPYC3, NCAR-PCM) scaled to six emission scenarios (SRES A1T, A1Fl, A1B, A2, B1, and B2) and Granados et al. [67], where the averaged values of the utilized Water Availability and Adaptation Policy Analysis (WAAPA) model triggered by eight model runs for the A2 scenario, four model runs for the B2 scenario, three model runs for the A1B scenario, and five model runs for each RCP-2, RCP-4, RCP-6 and RCP-8 scenario, demonstrated a decrease in the Vardar/Axios's river runoff of 23.0%. ...
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Renewable energy sources, due to their direct (e.g., wind turbines) or indirect (e.g., hydropower, with precipitation being the generator of runoff) dependence on climatic variables, are foreseen to be affected by climate change. In this research, two run-of-river small hydropower plants (SHPPs) located at different water districts in Greece are being calibrated and validated, in order to be simulated in terms of future power production under climate change conditions. In doing so, future river discharges derived by the forcing of a hydrology model, by three Regional Climate Models under two Representative Concentration Pathways, are used as inputs for the simulation of the SHPPs. The research concludes, by comparing the outputs of short-term (2031–2060) and long-term (2071–2100) future periods to a reference period (1971–2000), that in the case of a significant projected decrease in river discharges (~25–30%), a relevant important decrease in the simulated future power generation is foreseen (~20–25%). On the other hand, in the decline projections of smaller discharges (up to ~15%) the generated energy depends on the intermonthly variations of the river runoff, establishing that runoff decreases in the wet months of the year have much lower impact on the produced energy than those occurring in the dry months. The latter is attributed to the non-existence of reservoirs that control the operation of run-of-river SHPPs; nevertheless, these types of hydropower plants can partially remediate the energy losses, since they are taking advantage of low flows for hydropower production. Hence, run-of-river SHPPs are designated as important hydro-resilience assets against the projected surface water availability decrease due to climate change.
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Growing demand for agricultural commodities for food, fuel and other uses is expected to be met through an intensification of production on lands that are currently under cultivation. Intensification typically entails investments in modern technology — such as irrigation or fertilizers — and increases in cropping frequency in regions suitable for multiple growing seasons. Here we combine a process-based crop water model with maps of spatially interpolated yields for 14 major food crops to identify potential differences in food production and water use between current and optimized crop distributions. We find that the current distribution of crops around the world neither attains maximum production nor minimum water use. We identify possible alternative configurations of the agricultural landscape that, by reshaping the global distribution of crops within current rainfed and irrigated croplands based on total water consumption, would feed an additional 825 million people while reducing the consumptive use of rainwater and irrigation water by 14% and 12%, respectively. Such an optimization process does not entail a loss of crop diversity, cropland expansion or impacts on nutrient and feed availability. It also does not necessarily invoke massive investments in modern technology that in many regions would require a switch from smallholder farming to large-scale commercial agriculture with important impacts on rural livelihoods.
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Inland boundary conditions have significant impacts on seawater intrusion (SWI) due to sea-level rise (SLR). This study investigated the impacts of three inland boundary conditions (flux-controlled (FC), head-controlled (HC) and general-head boundary (GHB)) on modeling SWI due to SLR in coastal aquifers. First, we used the TOUGH2/EOS7 software program to solve the standard Henry’s problem and compared the results with those from the literatures. Numerical simulations were performed to investigate the impacts of the three inland boundary conditions on SWI induced by SLR in confined coastal aquifers (standard Henry’s problem) and unconfined coastal aquifers (Henry’s problem extended to unconfined domains). The simulation results show that HC systems in both confined and unconfined coastal aquifers are remarkably vulnerable to the effects of SLR owing to the resulting decreased head difference, while FC systems are relatively insensitive to SLR because the equivalent freshwater head at the inland boundary can increase by a similar magnitude to the SLR. The GHB boundary is more realistic than the other two boundary conditions: the recharge decreases because of SLR depending on the aquifer properties and the head difference between the reference head and the equivalent freshwater head at the seaside boundary.
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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.
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Global change encompasses changes in the characteristics of inter-related climate variables in space and time, and derived changes in terrestrial processes, including human activities that affect the environment. As such, projected global change includes groundwater systems. Here, groundwater is defined as all subsurface water including soil water, deeper vadose zone water, and unconfined and confined aquifer waters. Potential effects of climate change combined with land and water management on surface waters have been studied in some detail. Equivalent studies of groundwater systems have lagged behind these advances, but research and broader interest in projected climate effects on groundwater have been accelerating in recent years. In this paper, we provide an overview and synthesis of the key aspects of subsurface hydrology, including water quantity and quality, related to global change. Adaptation to global change must include prudent management of groundwater as a renewable, but slow-feedback resource in most cases. Groundwater storage is already over-tapped in many regions, yet available subsurface storage may be a key to meeting the combined demands of agriculture, industry, municipal and domestic water supply, and ecosystems during times of shortage. The future intensity and frequency of dry periods combined with warming trends need to be addressed in the context of groundwater resources, even though projections in space and time are fraught with uncertainty. Finally, potential impacts of groundwater on the global climate system are largely unknown. Research to improve our understanding of the joint behaviors of climate and groundwater is needed, and spin-off benefits on each discipline are likely.
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Climate change and human population growth are expected to have substantial impacts on global water resources throughout the twenty-first century. Coastal aquifers are a nexus of the world's oceanic and hydrologic ecosystems and provide a water source for the more than one billion people living in coastal regions. Saltwater intrusion caused by excessive groundwater extraction is already impacting diverse regions of the globe. Synthesis studies and detailed simulations have predicted that rising sea levels could negatively impact coastal aquifers through saltwater intrusion and/or inundation of coastal regions. However, the relative vulnerability of coastal aquifers to groundwater extraction and sea-level rise has not been systematically examined. Here we show that coastal aquifers are more vulnerable to groundwater extraction than to predicted sea-level rise under a wide range of hydrogeologic conditions and population densities. Only aquifers with very low hydraulic gradients are more vulnerable to sea-level rise and these regions will be impacted by saltwater inundation before saltwater intrusion. Human water use is a key driver in the hydrology of coastal aquifers, and efforts to adapt to sea-level rise at the expense of better water management are misguided.
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The fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance our knowledge of climate variability and climate change. Researchers worldwide are analyzing the model output and will produce results likely to underlie the forthcoming Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Unprecedented in scale and attracting interest from all major climate modeling groups, CMIP5 includes “long term” simulations of twentieth-century climate and projections for the twenty-first century and beyond. Conventional atmosphere–ocean global climate models and Earth system models of intermediate complexity are for the first time being joined by more recently developed Earth system models under an experiment design that allows both types of models to be compared to observations on an equal footing. Besides the longterm experiments, CMIP5 calls for an entirely new suite of “near term” simulations focusing on recent decades and the future to year 2035. These “decadal predictions” are initialized based on observations and will be used to explore the predictability of climate and to assess the forecast system's predictive skill. The CMIP5 experiment design also allows for participation of stand-alone atmospheric models and includes a variety of idealized experiments that will improve understanding of the range of model responses found in the more complex and realistic simulations. An exceptionally comprehensive set of model output is being collected and made freely available to researchers through an integrated but distributed data archive. For researchers unfamiliar with climate models, the limitations of the models and experiment design are described.
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Saltwater has intruded into many of the coastal aquifers of the United States, Mexico, and Canada, but the extent of saltwater intrusion varies widely among localities and hydrogeologic settings. In many instances, the area contaminated by saltwater is limited to small parts of an aquifer and to specific wells and has had little or no effect on overall groundwater supplies; in other instances, saltwater contamination is of regional extent and has resulted in the closure of many groundwater supply wells. The variability of hydrogeologic settings, three-dimensional distribution of saline water, and history of groundwater withdrawals and freshwater drainage has resulted in a variety of modes of saltwater intrusion into coastal aquifers. These include lateral intrusion from the ocean; upward intrusion from deeper, more saline zones of a groundwater system; and downward intrusion from coastal waters. Saltwater contamination also has occurred along open boreholes and within abandoned, improperly constructed, or corroded wells that provide pathways for vertical migration across interconnected aquifers. Communities within the coastal regions of North America are taking actions to manage and prevent saltwater intrusion to ensure a sustainable source of groundwater for the future. These actions can be grouped broadly into scientific monitoring and assessment, engineering techniques, and regulatory approaches.
Application of numerical models is a common method to assess groundwater resources. The versatility of these models allows consideration of different levels of complexity, but the accuracy of the outcomes hinges upon a proper description of the system behaviour. In seawater intrusion assessment, the implementation of the sea-side boundary condition is of particular importance. We evaluate the influence of the slope of the sea-side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters (freshwater inflow and longitudinal and transverse dispersivities). Model results reveal a multi-dimensional dependence of the investigated variables with an increasing relevance of the sea-side boundary slope for seawater intrusion (decrease of up to ), submarine groundwater discharge zone (reduction of up to ), and turnover times (increase of up to ) with increasing freshwater inflow or dispersivity values.
In this study, we define and characterize the saltwater upconing zone of influence (SUZI). The SUZI is the region around a pumping well within which significant rise in the saltwater-freshwater interface occurs. While the zone of influence of a pumping well can be clearly defined in terms of hydraulics (e.g. drawdown), the SUZI has not been recognised and characterised, despite its importance for groundwater decision-making in coastal regions. We explore the SUZI under various conditions and compare common methods of investigation using both axisymmetric (1D and 2D vertical cross-section) and 3D simulations of saltwater upconing at the field scale, based on a combination of numerical and analytical approaches. The SUZI was found to be dependent on the relative magnitudes of pumping, regional flow, distance of the well from the coast, and position of the well above the interface, as expected. The three-dimensional coastal setting simulations revealed an asymmetric shape of the lateral extent of the SUZI, which is largest in the direction parallel to the coast. This occurs because the ocean and the inland extent of the seawater wedge limit the propagation of the SUZI perpendicular to the coast. Predictions of the SUZI using the Ghyben-Herzberg approximation, including cases where sloping interfaces occur (i.e., in contrast to the artificiality of horizontal interfaces used in axisymmetric approaches), provide reasonable first approximations of the SUZI. Numerical modelling of dispersive upconing in the 3D inclined interface case is influenced by practical limits to the model domain size and grid resolution. For example, the no-flow boundary condition at 1500 m from the pumping well elongates the SUZI in the direction parallel to the coast. This study extends previous concepts of well interference, which have previously been based on hydraulics only, by introducing the SUZI and characterising its extent, with consideration given to differences in commonly adopted methods of upconing quantification.
This chapter provides a broad overview of water reclamation and sustainability. Some of the water pollution problems worldwide are highlighted. This chapter provides a short discussion on monitoring water quality and water reclamation to achieve sustainability. A number of recent developments in water reclamation and sustainability are covered at some length.
Conference Paper
Numerical simulation is an essential tool for investigation of seawater intrusion in coastal aquifer. For most groundwater modeling software, boundary condition along the beach is required. But it was normally assumed due to the uncertainty in the seawater - freshwater interface. Using FEFLOW, a groundwater simulation software based on finite element method, we investigated the intrusion scope and the exiting point of groundwater outflow under various boundary conditions. Seven cases were designed, among which three cases with boundary conditions of a freshwater layer over seawater, three cases with a triangle freshwater zone between seawater and the beach, and the last one without freshwater at the seawater boundary. Results showed that the last case has the longest intrusion scope. The scope of seawater intrusion is determined by both the horizontal water head gradient along the bottom of the aquifer and the vertical water head gradient along the beach. Both higher horizontal gradient and lower vertical gradient result in larger intrusion scope. In some circumstances, the vertical gradient has greater impact on seawater intrusion than the horizontal gradient, and act as the main power inhibiting seawater intrusion. (2011) Trans Tech Publications, Switzerland.
The annual march of the mean monthly number of thunderstorm days at a station shows certain characteristics, depending on the prevailing climate. For example, the main maxima in continental and marine climates occur in summer and in autumn to winter, respectively. A gradation of such an annual march of thunderstorm activity is successfully used in delineating transitional climatic zones in Greece, and it might also be applied to other regions of the earth.
Prevention of sea water intrusion in coastal aquifers subject to groundwater withdrawal requires optimization of well pumping rates to maximize the water supply while avoiding sea water intrusion. Boundary conditions and the aquifer domain size have significant influences on simulating flow and concentration fields and estimating maximum pumping rates. In this study, an analytical solution is derived based on the potential-flow theory for evaluating maximum groundwater pumping rates in a domain with a constant hydraulic head landward boundary. An empirical correction factor, which was introduced by Pool and Carrera (2011) to account for mixing in the case with a constant recharge rate boundary condition, is found also applicable for the case with a constant hydraulic head boundary condition, and therefore greatly improves the usefulness of the sharp-interface analytical solution. Comparing with the solution for a constant recharge rate boundary, we find that a constant hydraulic head boundary often yields larger estimations of the maximum pumping rate and when the domain size is five times greater than the distance between the well and the coastline, the effect of setting different landward boundary conditions becomes insignificant with a relative difference between two solutions less than 2.5%. These findings can serve as a preliminary guidance for conducting numerical simulations and designing tank-scale laboratory experiments for studying groundwater withdrawal problems in coastal aquifers with minimized boundary condition effects.
Sea levels are expected to rise as a result of global temperature increases, one implication of which is the potential exacerbation of sea water intrusion into coastal aquifers. Given that approximately 70% of the world's population resides in coastal regions, it is imperative to understand the interaction between fresh groundwater and sea water intrusion in order to best manage available resources. For this study, controlled investigation has been carried out concerning the temporal variation in sea water intrusion as a result of rising sea levels. A series of fixed inland head two-dimensional sea water intrusion models were developed with SEAWAT in order to assess the impact of rising sea levels on the transient migration of saline intrusion in coastal aquifers under a range of hydrogeological property conditions. A wide range of responses were observed for typical hydrogeological parameter values. Systems with a high ratio of hydraulic conductivity to recharge and high effective porosity lagged behind the equilibrium sea water toe positions during sea-level rise, often by many hundreds of meters, and frequently taking several centuries to equilibrate following a cease in sea-level rise. Systems with a low ratio of hydraulic conductivity to recharge and low effective porosity did not develop such a large degree of disequilibrium and generally stabilized within decades following a cease in sea-level rise. This study provides qualitative initial estimates for the expected rate of intrusion and predicted degree of disequilibrium generated by sea-level rise for a range of hydrogeological parameter values.
Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable.
The effects of sea-level rise on the depth to the fresh water/salt water interface were simulated by using a density-dependent, three-dimensional numerical ground water flow model for a simplified hypothetical fresh water lens that is similar to shallow, coastal aquifers found along the Atlantic coast of the United States. Simulations of sea-level rise of 2.65 mm/year from 1929 to 2050 resulted in an increase in water levels relative to a fixed datum, yet a net decrease in water levels relative to the increased sea-level position. The net decrease in water levels was much greater near a gaining stream than farther from the stream. The difference in the change in water levels is attributed to the dampening effect of the stream on water level changes in response to sea-level rise. In response to the decreased water level altitudes relative to local sea level, the depth to the fresh water/salt water interface decreased. This reduction in the thickness of the fresh water lens varied throughout the aquifer and was greatly affected by proximity to a ground water fed stream and whether the stream was tidally influenced. Away from the stream, the thickness of the fresh water lens decreased by about 2% from 1929 to 2050, whereas the fresh water lens thickness decreased by about 22% to 31% for the same period near the stream, depending on whether the stream was tidally influenced. The difference in the change in the fresh water/salt water interface position is controlled by the difference in the net decline in water levels relative to local sea level.
Protection status -Axios Delta National Park
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Agricultural Reuse & Reclamation of Treated Effluents: The experience of the Thessaloniki Wastewater Treatment Plant that belongs to EYATH (Thessaloniki Water Supply & Sewerage Company, Greece)
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Identification of ecological water requirements of the target habitat types and species that depend on water, in the Axios River Delta, the Aliakmonas River Delta and at the Coastal Lagoon Kitros
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Presented at the Protection and Restoration of the Environment, 14th Series, Protection and Restoration of the Environment
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