Fiteenth Internaional Water Technology Conference, IWTC 15‐ 2011, Alexandria, Egypt IMPACT OF FUTURE DISCHARGES ON DAMIETTA BRANCH MORPHOLOGY Abdel-Azim M. Negm¹, Tarek M.Abdel-Aziz² , Mohamed N. Salem³ and Wessam Yousef 4 1 Vice Dean and Professor of Hydraulics, Faculty of Engineering, Zagazig University, Zagazig 44519, Egypt, E-mail: amnegm85@yahoo.com 2 Professor, Secretary General of Nile Research Institute, National Water Research Center 13621, Qanater, Egypt, E-mail: aziztm@hotmail.com 3 Professor of Irrigation and Drainage Structures, Faculty of Engineering, Zagazig University, Zagazig 44519, Egypt. E-mail: mnsa30@yahoo.com 4 Civil Engineer, Ministry of Housing, Utilities, and Urban Development, Egypt. ABSTRACT Damietta Branch is very important for navigation and irrigation in Egypt. The hydraulic characteristic changes and morphological changes such as scour, deposition, bank erosion, beside the encroachment by people on the floodplain during the last three decades reduced its capacity to convey high discharges. This research work aims at preparing this branch to pass future releases more than the maximum current release. Comparisons between cross sections in many years under scenario of increasing the discharge from 60 to 80 million m³/day are carried out. Two- dimensional hydrodynamic mathematical model (CCHE) package is used to study the morphological changes in Damietta Branch and to predict the effect of high flows on water velocities and geometrical changes in different cross sections. Also the side effects on the navigational channel and over topping problems have been investigated. Consequently different solutions were suggested to increase the ability of Damietta Branch to convey high discharges. 1. INTRODUCTION Damietta Branch is one of the two River Nile Branches (Damietta and Rosetta Branches). It is considered an important waterway through the river Nile. It extends from downstream Delta Barrages at km 26.5 behind EL-Roda Gauge station to the Mediterranean Sea with length about 245 km. It has an average width of about 280 m and average sinuosity about 1.3. The water level slope of Damietta branch from Delta Barrage to Zefta barrage (119.85 km from EL-Roda Gauge station) is about 5.5 cm/km in case of high flow and 3.8 cm/km in case of low flow. But the water level slope downstream Zefta Barrage is about 2.7 cm/km in case of high flow and 2.4 cm/km in case of low flow. Delta Barrage is replaced by a new Barrage on Damietta Branch in 1982 downstream the existing one, which is located at 253.7 Km from EL-Roda Gauge with five vents. The vent's width is 5.25 m and the pier's width is 1.5 m to prevent salt water intrusion. The maximum flow rate should not exceed 22 million