Simulation of groundwater flow using the MODFLOW code in the alluvial aquifer of Korisos basis, NW Greece
Creators: name: Kirlas, Marios
Publisher: name: figshare
Year: 2020
Subjects: subject: Geology
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: 40603 Hydrogeology
subject: Hydrology

description: The study area is the hydrological basin of Agioi Anargiroi (Korisos basin), which is extended at the Kastoria Prefecture (West Makedonia), eastern of the city and the lake of Kastoria. The area of the study basin is 89.25 Km<sup>2</sup>, of which 24.6 Κm<sup>2</sup> belong to lowlands and 64.65 Km<sup>2</sup> belong to mountainous areas.A regular distribution of the different elevations is observed in the study area. Moreover, the altitude varies from 651 m to 1680 m (Kronos Mountain) and it has a mean altitude of approximately 984 m above sea level and a mean slope around 28.6%.Xiropotamos torrent drains the basin and it is classified as fifth class (Horton’s classification, 1945). The hydrographic network in mountainous area is highly developed too.The geological formations of the study basin belong to Pelagonian geotectonic zone. Ιn the lowlands τhe basin of Korisos is covered by quaternary deposits (27.6% of the area) and in the mountainous area is covered by crystalline and metamorphic rocks (72.4% of the area). More specifically the lowlands are covered by recent deposits, whereas in the mountainous and semi-mountainous areas occur schists and phyllites at the southeastern part, granite-gneiss at the northern part of the basin and gneisses and amphibolites, which cover the largest part of the basin. In addition, seven deformational events (DHP and D1 to D6) occur in the broader area during the Alpine orogeny.The mean annual precipitation in the area of study amounts to 663 mm (period 2004- 2007) and increases by 40.4 mm per 100 m of ground elevation. The total rainfall is 61x10<sup>6</sup> m<sup>3</sup> and the total runoff is equal to 16.73x10<sup>6</sup> m<sup>3</sup>.A productive unconfined aquifer is developed in the alluvial deposits, which consists of successive water bearing layers. The thickness of the alluvial deposits, based on borehole lithological profiles, ranges from 30 m in the eastern part to 140 m in the central part of the basin and increases from the northern part to the southern part of the study area.The groundwater recharge in the alluvial unconfined aquifer occurs via the following mechanisms: the most important mechanism is via direct infiltration of rainfall, then via infiltration through torrent beds and finally via return flow of irrigated water.Groundwater flow is from north-eastward to south-westward toward the Kastoria Lake. Moreover, as it was measured from the compiled piezometric maps, the mean hydraulic gradient (i) was 1.5x10<sup>-3</sup>.In Korisos basin the average hydraulic conductivity value (k) was 6.7×10<sup>–5</sup> m/s, the transmissivity value (T) varied between 1.4×10<sup>-3</sup> and 1.0×10<sup>-2</sup> m<sup>2</sup>/s and the storage coefficient value (S) varied between 1.9×10<sup>-4</sup> and 9.3×10<sup>-3</sup>. All the hydraulic parameters were deduced from the conducted pumping test analyses applying Jacob and Theis methods.Generally, the groundwater quality is suitable for irrigation use and domestic supplies. The predominant water type of groundwater in the study area is Ca-HCO<sub>3</sub>. Due to intensive agricultural activities, high nitrate concentrations were recorded locally. Furthermore, it was generally observed an increase of the electrical conductivity of the groundwater from the recharge area to the downwards (Lake of Kastoria).The mathematical code MODFLOW with the use of GMS 7.1 software (free edition from Aquaveo) was applied in the Quarternary deposits of the area for steady state conditions. The piezometric surface of the period May 2004 was used to describe the initial heads in MODFLOW code. Model calibration carried out successfully as the deviations between the computed and the observed head values were insignificant and also as the Root Mean Square Error (RMSE) had a value of about 0.61 m (calibration target within ±1 m).