1. Lect., Inst. of Irrigation and Devel. Studies, Dept. of Civ. and Envir. Engrg., Univ. of Southampton, Highfield, Southampton, SO17 1BJ, U.K. E-mail: A.A.Anwar@soton.ac.uk
2. Lect., Inst. of Irrigation and Devel. Studies, Dept. of Civ. and Envir. Engrg., Univ. of Southampton, Highfield, Southampton, SO17 1BJ, U.K. E-mail: D.Clarke@soton.ac.uk