الفهرس 
CHAPTER ONE: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Zefta barrages on Damietta branch was built in 1903 with 50 vents each is 5.0 m width and it was remodeled in 1954. After the construction of high Aswan dam in 1968, the water is almost clear of sediment. Therefore, local scour occurs downstream barrages under “clear-water” conditions. These conditions are resulting from high velocity jets either from high head difference on the barrages or high unit width discharge due to gate operation schemes. Schemes of gate operations, which concentrate the whole river discharge from few gates and accordingly induce higher outlet jet velocities. These can easily erode the unprotected bed downstream the barrages or even can destroy the bed protective layer. The existence of significant scour holes downstream a barrages cause undermining of the bed material below the barrages foundation that might cause a collapse of the whole barrages. Therefore, it is important to estimate the expected maximum depth and length of scour hole downstream the barrages for any operating plans that might endanger the barrages structure.
Therefore, an analysis of the problem of local scour downstream Zefta barrages (case study) is presented here. This study aimed to develop empirical relationships between the flow conditions and the scour hole parameters. This study was based on about 63 observed field data represented by the bathymetric survey in April 1992, December 1994, March 2000 and September 2004 (contour maps) and the longitudinal sections for the scour hole profile downstream the barrage under various water management and operation scenarios. The problem has been studied by using the dimensional analysis based on Buckingham π theorem to correlate the scour hole depth and length with the other known variables to assist empirical relationships which help to predict the maximum scour depth and length.
Finally, the comparisons between the scour depths estimated by the present study ,Schoklitsch equation, Kotoulas equation and Youssef Hafez equation, with the observed scour depths downstream Zefta barrages vents, clearly show that the obtained relation is the most suitable one that its predication are close to the observed values and realistic in its order of magnitude