1. Department of Civil Engineering, Dar es Salaam Institute of Technology, P.O. Box 2958, Dar es Salaam, Tanzania E-mail: shija.kazumba@dit.ac.tz
2. Environment Water Resources, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Kiryat Sde-Boker 84990, Israel E-mail: gidi@bgu.ac.il
3. Ramat Negev Agricultural Experimental Field Station, Ramat Negev, Doar Naa Chalutsa 85515, Israel
4. Deceased March 2006