الفهرس 
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Abstract
Riprap is normaly used D.S. stilling basin to prtect the river bed aganist scour. It is widely used and found to be economical and efficient. Proper design of such riprap protection reqires that a suitable size should be provided with full consideration given to the stability criteria. Stilling basins are considered one of the energy dissipators, which should be provided at downstream (D.S.) of hydraulic structures for dissipating the excessive kinetic energy.
This research investigates the stability of bed protection D.S. stilling basin with different operation scenarios. To achieve the aim of this research, three-dimensional (3D) physical model for NEW Assiut barrage (NAB) is used, which is constructed at delta barrage, egypt. The model is undistorted with model ratio 1:45. The riprap is replaced at D.S. the spillway of NAB with mean particle diameter equal to 16 mm.
Discharges over the spillway ranged from 700 to 7000 m 3/2 (prototype) (i.e.51.53 to 515.3 L/sec model). These discharges passed through number of gates ywo up to eight gates.