Kazakis Nerantzis

Geoelectrical methods have been widely used for the estimation of aquifer hydraulic properties. In this study, geoelectrical methods were applied in a lithologically and hydrochemically complex porous aquifer to estimate its porosity, hydraulic conductivity and transmissivity. For this purpose, the electrical resistivity of the aquifer as well as the electrical conductivity of the groundwater was measured in 37 sites and wells. Initially, the Archie's law was used to generate sets of cementation factor (m) and alpha (α) parameter from which the mode values of α = 0.98 and m = 1.75 are representative of the studied aquifer. The transmissivity of the aquifer varies from 5.1 × 10 −3 to 3.1 × 10 −5 m 2 /s, whereas the mean value of its porosity is 0.45. The hydraulic conductivity of the aquifer which was calculated according to Archie's law varies from 2.08 × 10 −6 to 6.84 × 10 −5 m/s and is strongly correlated with the pumping test's hydraulic conductivity. In contrast, the hydraulic conductivity which was calculated using Dar-Zarrouk parameters presents lower correlation with the pumping test's hydraulic conductivity. Furthermore, a relation between aquifer resistivity and hydraulic conductivity was established for the studied aquifer to enable the estimation of these parameters in sites lacking data.

The present study introduces a multi-criteria index to assess flood hazard areas in a regional scale. Accordingly, a
Flood Hazard Index (FHI) has been defined and a spatial analysis in a GIS environment has been applied for the
estimation of its value.
The developed methodology processes information of seven parameters namely flow accumulation, distance
from the drainage network, elevation, land use, rainfall intensity and geology. The initials of these criteria gave
the name to the developed method: “FIGUSED”. The relative importance of each parameter for the occurrence
and severity of flood has been connected to weight values. These values are calculated following an “Analytical
Hierarchy Process”, a method originally developed for the solution of Operational Research problems. According
to their weight values, information of the different parameters is superimposed, resulting to flood hazard mapping.
The accuracy of the method has been supported by a sensitivity analysis that examines a range for the
weights' values and corresponding to alternative scenarios.
The presented methodology has been applied to an area in north-eastern Greece, where recurring flood events
have appeared. Initially FIGUSED method resulted to a Flood Hazard Index (FHI) and a corresponding flood
map. A sensitivity analysis on the parameters' values revealed some interesting information on the relative importance
of each criterion, presented and commented in the Discussion section.Moreover, the sensitivity analysis concluded to a revised index FHIS (methodology named FIGUSED-S) and flood mapping, supporting the robustness
of FIGUSED methodology. A comparison of the outcome with records of historical flood events confirmed
that the proposed methodology provides valid results.

The aim of this study is to simulate the groundwater flow in the Elassona-Tsaritsani basin aquifer with the MODFLOW code. The basin of Elassona – Tsaritsani is located in the central part of Thessaly and belongs to the prefecture of Larissa. In the last years, a continuous increase in water demands for irrigation use is observed in this basin. The water demands of the basin are mainly met by the alluvial aquifer which is located in the central part of the basin and which consists of pebbles, gravel and sand. The karstic aquifer of Tirnavos-Damasio is located in the southeastern part of the basin, while aquifers of fissured rocks - which are of local interest in fault zones - are located in the northwestern part. The groundwater flow simulation of the Elassona unconfined alluval aquifer was obtained with the MODFLOW code. The model was applied in steady state and the results presented a reliable model of the basin aquifer. In order to estimate the sensitivity of the model groundwater flow, three different scenarios were applied in which precipitation was decreased by 25% and 50% and the pumping rate was increased by 50%. The results of the steady-state MODFLOW model approach the observation data sufficiently. Moreover, the lateral subsurface recharge of the alluvial aquifer from the fissured rocks aquifer (NW) and the outflow to the karst aquifer in the southwestern part was confirmed. Also, the groundwater flow of the study area proved to be more sensitive to the increase of the pumping rates than to the decrease of precipitation. Finally, what is emphasized in this paper is the importance of reliable, continuous and high frequency monitoring of the hydraulic and hydrological parameters of the aquifers of Greece.