1. a M. IWRA Civil Engineering Department , University of Khartoum , P.O. Box 3968, KHARTOUM, Sudan
2. b Environmental Engineering Department , Lenox Institute of Water Technology , 101 Yokun Avenue P.O. Box 1639, LENOX, MA, 01240, U.S.A.
3. c Ar-Riyadh Development Authority (ADA) , P.O. Box 495, AR-RIYADH, 11411, Saudi Arabia