The use of pilot points method on groundwater modelling for a degraded aquifer with limited field data: the case of Lake Karla aquifer

Groundwater depletion poses a major threat to global groundwater resources with increasing trends due to natural and anthropogenic activities. This study presents a surface-groundwater framework for water resources modelling of ill-posed problems in hydrogeologically data-scarce areas. The proposed framework is based on the application of a conceptual water balance model and composed of surface hydrological (UTHBAL) and groundwater flow simulation with the integration of a Newton formulation of the MODFLOW-2005 code (MODFLOW-NWT) and PEST suite modules. The groundwater simulation includes a pre-processor tool for automated calibration and a post-processor tool for automated validation. The methodology was applied to a rural region of Central Greece, Lake Karla Basin, which is degraded due to groundwater resources overexploitation to cover irrigation water demands. The aquifer is modelled focusing on precise simulation – validation procedure of the conceptual model. The groundwater model was calibrated with the calibration pre-processor tool for spatially distributed hydraulic conductivity with the pilot points method. The calibration process achieved satisfactory results as validated by the post-process analysis of observed and simulated water levels. The findings for the groundwater budget indicate that the groundwater system is still under intense pressure even though farming activity in recent years has turned to less water-intensive crops. HIGHLIGHT My research deals with the Pilot Points Method on Groundwater Modelling in area with scarce hydro-geologic data.

A Large-Scale Nature-Based Solution in Agriculture for Sustainable Water Management: The Lake Karla Case

This study demonstrates a new nature-based solution (NBS) project in agriculture, the ‘Karla’ reservoir in Central Greece, a unique example at European scale, of a lake ecosystem which was dried and is now restored with the purpose to maximize the efficiency of water provision in agriculture and biodiversity enhancement. In this article, we present: (a) The historical developments from the existence of the old natural Lake Karla until the reconstruction of the homonymous artificial reservoir, (b) the environmental and economic benefits that the new project delivers, and (c) the governance and management mechanisms that can ensure the efficient operation of the project. The analysis shows that the reconstructed Lake Karla can serve as a multi-purpose project to combat water scarcity, achieving a twofold crop yield production and respective agricultural income in the surrounding area, securing the coverage of the water supply needs of the closest city, improving the status of groundwater resources, developing a natural shelter for biodiversity and emerging recreation and touristic opportunities. At the same time, its construction and operation costs can be recovered, and the proposed governance plan can ensure the viability of the whole project inspiring similar multi-purpose water retention projects for investment in agriculture and the environment in southern Europe but also in other water scarce regions.

Pump and treat optimization schemes for nitrate removal from a rural basin aquifer

<p>Lake Karla aquifer, with extent of 500 km<sup>2</sup>, is located at the eastern part of the most cultivated region of Greece, Thessaly, where water demanding crops prevail. The last three decades is under a status of quantitative and qualitative degradation because of the long-term intense agricultural activities, the lack of any significant surface water body and of an organized irrigation network. About 80% of the pumped groundwater is used for irrigation. According to Lake Karla recreation project fifty wells have been established at the southern part of the aquifer in order to cover the drinking water needs for the nearby city of Volos. This area is characterized by the greatest depletion of aquifer’s water table and by high values of nitrate concentrations in groundwater resources.  The area is one of the seven vulnerable zones of Greece, with respect to nitrogen pollution from agricultural run-off, according to the requirements of the Nitrates Directive (91/676/EEC).</p><p>The study proposes a pump and treat optimization method for nitrates removal from the supply wells area with the use of a simulation-optimization modelling system through two scenarios regarding nitrate fertilization of crops during the remediation period:</p><ol><li>The crops receive the same amount of fertilizers as applied in the historical period.</li> <li>The crops receive the amount of fertilizers defined by the Nitrates Directive (91/676/EEC).</li> </ol><p>The classification of crop types at the study area of aquifer is implemented with the use of a Geographical Information System (GIS). Nitrate leaching to aquifer is achieved through water infiltration from surface to subsurface system and has been estimated to 40% of nitrogen fertilizer application. The simulation-optimization modelling system applied, consists of a groundwater simulation model (MODFLOW), a groundwater transport and a dispersion simulation model (MT3DMS) and a management model (GWM). The optimization problem targets to the minimization of the operation cost of pump and treat wells, subject to plume stabilization through reversing the hydraulic heads slope and to keeping the values of nitrate concentration in the supply wells area lower than the threshold of 25 mg/L introduced by Nitrates Directive. Pump and treat wells are proposed to be located at the boundary of the urban supply wells area, where the plume crosses it.  The historical period is from 1995 to 2007, while the remediation period starts on 2007.</p><p>The results indicate that, for the first scenario, the pump and treat wells must operate through the whole remediation period (2007-2017) since great volumes of nitrate pollutants continuously leach to aquifer concluding to high operation costs equal to 372.47 thousands of euros. On the contrary, for the second scenario, the remediation period is decreased to four years resulting to an operational cost lower than the half of the additional of the first scenario equal to 147.09 thousands of euros. These results highlight the importance of the full compliance with Nitrates Directive requirements by the farmers of rural basins, where the groundwater resources are used for potable use; otherwise any remediation design will be costly.</p>

Hydrological, socioeconomic, engineering and water quality modeling aspects for evaluating water security: experience from Greek rural watersheds.

<p>Water security poses one of the biggest challenges of the century. It is a versatile problem, going beyond the traditional concepts of hydrology and water quality. It is difficult to give a single definition, since water security signifies a "safe operating subspace" within a multi-dimensional space that maps physical resource availability, water quality, demand, infrastructure and economic choices. The main idea of water security, as addressed in the present study, is the need to balance human and environmental water needs.</p><p>In arid and semi-arid areas, including Greece, intensification of agriculture accompanied with poor management is a common phenomenon. These attempts to meet economic and productive objectives, combined with the physical characteristics of these areas, has led to quantitative and qualitative water degradation, questioning the sustainability of water resources. In Greece, the Ministry of Environment Management Plans found that only 1 or 2 cases in the country are in “a good status”. This study aims to propose a way towards integrated and sustainable management, through hydro-economic tools: water balance, profits from agricultural activities, water value, and water quality. Water security is examined based on these terms in several Greek rural watersheds.</p><p>The methodology consists of the estimation of water availability, water demand, and thus water balance in surface and groundwater resources. The profits from the agricultural activities are estimated from a straightforward economic model, based on the gross profits and production costs. Water quality is based on measurements on concentrations of fertilizers, chemical parameters and pesticides, and its improvement is examined through the quantitative replenishment due to several strategies exploiting dilution processes in surface and groundwater. The analysis used data from the period 2005-2015, and a set of management scenarios were examined, suggesting technical measures (e.g. reducing losses, improving irrigation methods) and crop replacement scenarios, taking into account factors affecting these decisions, and also the Ministry’s recommendations. The water value was calculated using the “change of the net-income” method. All the above factors’ results indicate the degradation of the examined areas.</p><p>More specifically, the watersheds of Lake Karla, Almyros, Koronia, and Loudia were selected as the most representative cases. These watersheds seem to have limited water availability, intensified agriculture, poor water quality and management issues. The Lake Karla watershed is characterized from overexploited surface and groundwater resources, Loudia and Koronia watersheds face the same issues plus a strong qualitative degradation, Almyros watershed main issue is the salinization of its coastal aquifer. In conclusion, the first steps that are introduced in this study can be a starting point for more integrated water security management, helping local water managers understand and address the above issues.</p><p>Overall, it is a novel attempt to integrate all the above parameters in one framework, for a ten-year horizon, and comparing rural Greek case studies. Non-comparable factors also exist among different case studies, which are discussed, however the evidences support the finding of the general degradation and unsustainable management in the country.</p><p><strong>KEYWORDS:</strong> Water Security, agricultural watersheds, Greece, Water Resources Management, Hydro-economic modeling, water quality, scenario analysis.</p>

Nutrient Concentrations in Seven Irrigation Reservoirs (Lake Karla Watershed Thessaly Greece)

The construction of irrigation reservoirs is a technical global solution for enhancing the agricultural production especially in arid and semi-arid areas. These water bodies are treated as technical projects and not as freshwater ecosystems. Eutrophication in new reservoirs becomes a hot issue in the world. The aim of the present study is to present the assessment of the key-eutrophication parameters in seven reservoirs located in the catchment area of Lake Karla. We suggest that the studied artificial ecosystems are sensitive in nutrients concentrations especially in the warm-dry period, influenced mainly by agricultural activities in the watershed.

Modeling Flow and Nitrate Transport in an Over-Exploited Aquifer of Rural Basin Using an Integrated System: The Case of Lake Karla Watershed

The paper proposes an integrated modeling system consisting of a surface hydrology model, a water reservoir model, a Lake-Aquifer Interaction model, aground water model, and a transport and dispersion model to study ground water quality through two different operational management scenarios. The first scenario is examining the existing condition of groundwater quality without the reservoir operation while the second scenario is assessing the impact of the reconstruction of Lake Karla in the groundwater quality. The study highlights the importance of using an integrated hydrological modeling approach to investigate the groundwater quality in a region which is characterized by extensive agricultural activity.

Monitoring a newly re-born patient: water quality and cyanotoxin occurrence in a reconstructed shallow Mediterranean lake

Lake Karla (Central Greece) is a unique example - at European scale - of a shallow lake ecosystem that was dried in the 1960s and in 2009 started to be restored. The lake is listed in the network of the Greek protected areas as it is considered a vital aquatic ecosystem, in terms of biodiversity. It has, however, already been adversely affected by both agricultural and industrial land uses in the surrounding area, leading to eutrophication and shifting algal community towards bloom-forming toxic cyanobacterial species. After repeated heavy-blooms, cyanotoxin occurrence and mass fish kills, the local ecosystem management authority has implemented a water quality monitoring program (July 2013 - July 2015) to assess environmental pressures and the response of aquatic biota in the lake. Microscopic, immunological, and molecular techniques combined with physico-chemical parameters, complemented by liquid chromatography tandem mass spectrometry (LC-MS/MS), were used to monitor cyanobacteria blooms and the associated cyanotoxin production from three different sites in Lake Karla and from the adjacent Kalamaki Reservoir. Water quality was also assessed by the structure of benthic invertebrate community on the sediment. Cyanobacteria were the main phytoplankton component, representing more than 70% of the total phytoplankton abundance; dominant taxa belonged to Cylindrospermopsis raciborskii, Limnothrix redekei, Anabaenopsis elenkinii, and Microcystis spp. Euglenophytes (Euglena), diatoms (Nitzschia), and chlorophytes (Scenedesmus) were also important phytoplankton constituents. LC-MS/MS confirmed the co-occurrence of microcystins, cylindrospermopsin, saxitoxin, neo-saxitoxin and anatoxin-a. The occurrence of cyanotoxins in relation to the persistent and dominant cyanobacteria and the impact of cyanobacterial harmful algal blooms on the newly constructed lake along with the land uses and the emergent mitigation measures are discussed.

THE FLUVIAL ACTION OF THE KARLA BASIN STREAMS IN A NATURAL AND MAN – MADE ENVIRONMENT

This study investigates the fluvial action of streams draining the Lake Karla basin, located in the plain of Thessaly, in Central Greece. Until a few decades ago, a large part of this area had been occupied by a lake. In order to find out the relation between the channel bed morphology and the oscillations of the local base level due to variations in water level and human intervention in the lake, the following streams were investigated: the flumes of Mpegiatiko, Bagiorema, Bathurema, Xerias and Maurorema. The width and the length of all channels were measured with a laser range finder while the incision and the erosive events were recorded by GPS with sub-meter accuracy. Furthermore, an integrated GIS analysis was undertaken in order to illustrate the changes in the water level of Lake Karla coupled with historical data and data from previous studies. It will be shown that there were two main evolutionary stages which controlled the local base level changes of the studied area. The first one is connected to the continuous changes in the lake’s water level and its reduction from 64m to 45m a.s.l. This resulted in the incision of the channels and the creation of characteristic knick points upstream. The second stage is associated with the draining of Lake Karla in 1962. This intervention mostly altered the streams that developed into fine-grained material channel beds.