1. Ph.D. Student, Dept. of Civil Engineering, Univ. of Moratuwa, Moratuwa 10400, Sri Lanka; National Water Supply and Drainage Board, Sri Lanka (corresponding author).
2. Emeritus Professor, Dept. of Civil Engineering, Univ. of Moratuwa, Moratuwa 10400, Sri Lanka.
3. Professor, Dept. of Civil Engineering, Univ. of Moratuwa, Moratuwa 10400, Sri Lanka.
4. Senior Lecturer, School of Engineering, RMIT Univ., GPO Box 2476, Melbourne, VIC 3001, Australia.