الفهرس 
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Abstract
ABSTRACT : The sedimentation problem at the navigation channels is very crucial issue that has environmental and economic impacts. So, the sedimentation problem and its suggested solutions are studied in this research. Also, the sedimentation at the navigation channel of Damietta harbour is investigated in this thesis to determine the impact of channel development on the sedimentation and find more efficient and cost-effective solutions to mitigate the problem. For this purpose, CMS model was utilized to study the sedimentation and assess the performance of various structural alternatives. The sedimentation problem depends on various factors and its impacts differ from one location to another. Determining the dominant parameter is very essential to select the proper methodology for reducing the sedimentation. Also, the suitable solution for each case tends to be unique as it depends on many parameters. At the study area, sediment flux is transporting in both directions, so the western and eastern sides of the harbour should be considered to solve the sedimentation problem. The sedimentation of the navigation channel can be divided into two major components of bank encroachment, and the trapped sediments. Bank encroachment impacts the entire length of the navigation channel and depends on the difference between the channel depth and the surrounding bathymetry, and the second component is very clear at the harbour entrance. The existing jetties at Damietta harbour have insufficient length, so a significant part of sediments enter the inner part of the navigation channel and more than 50 % of the sedimentation occurred in the winter season. Also, the channel has a great impact on adjacent beaches and its impacts extend to 4.50 km on the western side and 3.0 km on the eastern side, where the implemented Y-groins at the eastern side showed an insufficient performance. Increasing the channel depth by 20% increased the sedimentation and the dredging costs by 33% and impacts the bank encroachment significantly. Also, the maximum impact of the channel deepening occurred at the harbour entrance. On the other hand, single side solutions cannot provide reasonable protection for the harbour entrance and the navigation channel. Jetties extension is a good structural alternative, where jetties extension by 2000 m decreased the sedimentation by 77.64%. However, increasing the extension length by more than 2000 m has an insignificant impact. Also, the overlap between the jetties heads is recommended to be minimum. Decreasing the angle between the protection jetty and the direction of currents increases its efficiency and reduce the sedimentation, however it increases the wave height at the harbour entrance. So, it is not recommended to increase the gap width and the angle between the channel axis and the protection jetties more than 15 degrees. Also, jetty spurs showed an acceptable efficiency and the use of jetty spurs seemed to be more economical than jetties extension. Also, the angle and length of spurs have a significant impact on their efficiency. Moreover, the jetty spurs with 135 degrees are the preferable configuration to achieve the best efficiency and economic costs. Also, submerged spurs are more economical than emerged spurs with an insignificant difference in their efficiency. In addition, using a combination of jetties extension and submerged spurs is a more efficient and economical solution, and the best solution was jetties extension with 500 m and 1000 m submerged jetty spurs with 135o. On the other side, keeping sediment out strategy seemed to be ineffective and have insufficient efficiency. Also, keeping the sediments away from the navigation channel is the best strategy that can be used to mitigate the sedimentation problem. Besides, the bank encroachment cannot be eliminated and the protection structures have less impact on this component. Also, using structural alternatives is more economical than the Do-Nothing scenario that depends on the dredging operations. But, the selection of the suitable solution depends on many criteria that will depend mainly on stakeholder decisions.