1. Research Associate, Dept. of Civil Engineering, Division of Hydraulics and Environmental Engineering, Aristotle Univ. of Thessaloniki, 541 24 Thessaloniki, Greece. E-mail: elefthe@civil.auth.gr
2. Professor, Dept. of Civil Engineering, Division of Hydraulics and Environmental Engineering, Aristotle Univ. of Thessaloniki, 541 24 Thessaloniki, Greece.