Christos Mattas

Given the lack of rainfall during the dry season in Greece and other countries, groundwater is important in meeting water needs for all uses. Reliable simulation of groundwater flow and predictions of groundwater levels under different management scenarios, in light of water crisis, are essential tools for the sustainable management of aquifers. In this paper, the MODFLOW code for simulating groundwater flow was applied to the Greek section of the transboundary Serres river basin in a complex aquifer system developed in alluvial deposits. The groundwater of the basin is critical for the fulfillment of both the irrigation requirements of an extensive local agricultural activity and the domestic needs of a significant population. Data necessary for model construction and simulation was provided by the relevant authorities and literature. The model calibration is considered successful as the simulated values show a statistically acceptable fit to the measured data. Sensitivity analysis shows that the aquifer’s storage coefficient change has the greatest impact on the groundwater level. In a management scenario where groundwater extraction is reduced by 5% over a ten-year period, the groundwater level is projected to rise by approximately 0.17 m. In contrast, in the worst-case scenario, where groundwater extraction increases by 6.5% reaching at a critical point regarding the sustainability of the groundwater resources in the area, the average groundwater level is expected to drop by 0.72 m, resulting in the reduction of aquifer reserves. The model serves as a valuable tool for mitigating and adapting to the impacts of the climate crisis, as well as for formulating policies that promote the sustainable management and rational use of the aquifer.

The objective of this research is the groundwater quality analysis in the Mygdonia basin (North Greece), where intensive agricultural activities take place. Groundwater sampling was carried out in May (17 samples) and in September (26 samples) for the years from 2013 to 2015. In situ physicochemical parameters (pH, EC, and T) were tested, whereas major ions (Ca²⁺, Na⁺, Mg²⁺, K⁺, NO₃⁻, SO₄²⁻, Cl⁻, and HCO₃⁻) were analyzed in the laboratory. Conventional statistical methods were applied for the classification of the groundwater hydrochemical type and the identification of the prevailing hydrogeological processes. Finally, some recommendations are presented for the protection of groundwater quality.

Dams are expensive technical constructions that ensure food production, sustain farmers’ income, and cover a large percentage of urban water supply demands. However, the threat of a dam break flood, which can be extremely dangerous for the local society, should be taken into account, and proactive mitigation measures should be planned. Towards this direction, dam break modelling and flood hazard assessment are essential for developing flood crisis management and evacuation plans. In this study, a hypothetical case of failure of the Papadia dam in the Florina Regional Unit in northern Greece is examined. Two scenarios of failure were considered: overtopping and piping. A two-dimensional numerical model for the two failure scenarios was used to simulate the dam break process and flood wave routing using HEC-RAS software. A sensitivity analysis of the mesh size and breach parameters was performed to better understand their impact on the critical outputs of the simulation model. Flood hazard maps were produced in GIS environment based on water depth and velocity criteria. Furthermore, two classification approaches were adopted to assess the flood hazard using the product of water depth and velocity. The results showed that the extent of the inundated area could affect most of the study area and could cause severe damage to agricultural activities.

Due to the fact of water resource deterioration from human activities and increased demand over the last few decades, optimization of management practices and policies is required, for which more reliable data are necessary. Cost and time are always of importance; therefore, methods that can provide low-cost data in a short period of time have been developed. In this study, the ability of an artificial neural network (ANN) and a multiple linear regression (MLR) model to predict the electrical conductivity of groundwater samples in the GallikosRiver basin, northern Greece, was examined. A total of 233 samples were collected over the years 2004–2005 from 89 sampling points. Descriptive statistics, Pearson correlation matrix, and factor analysis were applied to select the inputs of the water quality parameters. Input data to the ANN and MLR were Ca, Mg, Na, and Cl. The best results regarding the ANN were provided by a model that included one hidden layer of three neurons. The mean absolute percentage error, modeling efficiency, and root mean square error were used to evaluate the performances of the methods and to compare the prediction capabilities of the ANN and MLR. We concluded that the ANN and MLR models were valid and had similar accuracy (using the same inputs) with a large number of samples, but in the case of a smaller data set, the MLR showed a better performance.

Climate changes in the Mediterranean region, especially those related to changes in rainfall distribution and occurrence of extreme events, affect local economies. Agriculture is a sector strongly affected by climate conditions and concerns the majority of the Greek territory. The Gallikos river basin is an area of great interest regarding climate change impacts since it is an agricultural area depended on surface water resources and an area in which extreme events relatively often take place (e.g., floods). Long time series precipitation (27 years) and temperature data derived from measurement stations along with reanalysis data (ERA INTERIM) were used for the estimation of water availability and climate type over time in the area. The Standardized Precipitation Index and De Martonne aridity index was employed. The water flow measurements were correlated in order to investigate the interrelation between the different river branches and the extent of the meteorological changes effect in the basin. Descriptive statistics and cumulative curves were applied to check homogeneity of data. The results revealed that the climate type varies from semi arid to very wet, and water availability ranges from moderately dry to extremely wet years. Reanalysis data overestimate precipitation. The meteorological changes affect, at the same time, the entire basin since the flow rate peaks occur simultaneously in the hydrographic network at different areas.

FLOOD HAZARD ASSESSMENT AND DELIMITATION OF THE LIKELY FLOOD HAZARD ZONES OF THE UPPER PART IN GALLIKOS RIVER BASIN

This paper investigates the suitability of a specific site for the construction of a sanitary landfill. The following works were performed: detailed geological mapping at a scale of 1:5,000, a geological-hydrogeological cross-section of the sanitary landfill, drilling exploration including the construction of a deep borehole for the detection of any perched aquifer, core logging and in situ permeability tests, implementation of the DRASTIC and EPIC methods to estimate the aquifer’s vulnerability. Finally estimation of the total annual amount of solid waste that will be deposited into the sanitary landfill and determination of the pollution load.