Portaikos river is a tributary of Pinios River located in Thessaly. It drains the southern part of Thessaly basin, and specifically the south part of the district of Tricala. This region is located at the border with the district of Karditsa. Portaikos River drainage basin covers an area of 294 km2, which is 2.8 % of the total drainage basin of Pinios River. The direction of Portaikos river drainage basin extends from SW-NE. The evolution of Portaikos River drainage network presents some specific morphometric features. Its analysis required the use of digital data, which were analyzed with G.I.S. software. During the study of the drainage network with the laws of drainage composition, we found a certain deviation of the 4t h and 5t h order streams. Geology has influenced significantly the estimated values of drainage density and frequency of the sub-basins. In some specific areas previous hydrographie features are inherited by the underlying rocks, which constitute the current surface morphology. The analysis of the rose diagrams of the tributaries showed a clear tendency in two main directions. The one extends from NE-SW and the other from NW-SE, almost vertical to each other. To conclude, the hypsometric (area altitude) analysis revealed that Portaikos River drainage network has developed upon a landmass of the western tectonic border of Thessaly basin.

Έρευνα των περιβαλλοντικών διεργασιών εξέλιξης των υγροτόπων και της πεδιάδας του Μαραθώνα κατά το Ολόκαινο με τη χρήση Γεωγραφικών Συστημάτων CO LO CD CO σ>

The hazard of erosion in the Xeropotamos river drainage basin on the eastern side of Kastoria lake is examined in this paper, through G.I.S. techniques (methodology).Eight levels of information were taken into account: The channel network, the Digital Elevation Model (DEM through TIN), the surface slope degree and orientation, the lithology, the vegetational cover, the rainfall distribution and the wind blown factors.The combination of the above levels of information allowed the production of two alternative erosional hazard assessment maps. One counts for equal and another counts for not equal influence of all the above factors in the model. The erosional capacity of Xeropotamos is reflected on the flatlands of the eastern side of Kastoria lake,where the river deposits heavy sediment loads, thus forming a deltaic lobe into the lake. It threatens to split the lake, unless antierosional measures on the drainage basin reduces its capacity.