الفهرس 
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Abstract
Scour downstream the hydraulic structures is considered to be a very critical issue hat occupies many researchers concern due to its damageable effects that threaten
the stability of any hydraulic structures constructed along the Nile river. Scour can make remarkable damage to the structural elements of the hydraulics structures such as piers, abutment, and gates and it may cause also a sudden failure of these
hydraulics structures leading to massive economic losses that affect the agriculture and irrigation sectors in Egypt. Several previous studies paid enormous attention to study scour phenomenon to avoid its erosive effects. These previous studies aimed to find engineering solutions to protect these hydraulic structures from scour. Several engineering solutions were employed such as using end sills, employing corrugated apron instead of the concrete apron in addition to using recycled materials as bed materials such as Gabion Mattresses. All these previous methods were employed to make resistance to the shear stress produced from scouring to disperse the energy of the flow to minimize the scour’s effect. In this thesis, a laboratory experiment was performed in the hydraulic laboratory flume of the Civil Engineering Department, Faculty of Engineering, Al-Azhar University to study the effect of adding a Nano-material (silica fume) to the fine
sand to face the damage effects of scour downstream any hydraulic structure and
minimize its effect to prevent any threat to the stability of the barrages, regulators, and dams constructed along any stream line. Several variables were tested in this experimental study such as gate opening, tailwater’s depth, type of mixture, and percentage of silica fume added to fine sand. 99 experimental attempts were performed by using three different gate’s openings (1 cm, 1.25 cm, and 1.5 cm), three different tailwater’s depths (14 cm, 16 cm, and 18 cm), five different mixing
percentages of silica fume (1%, 2%, 4%, 6%, and 8%). That is in addition to study the effect of mixing silica fume without and with adding water to the mixture. The results of this experimental study showed that increasing the percentage of
silica fume caused an increase in the scouring and silting depth in the case of mixing fine sand and silica fume without adding any amount of water. But the scour effect decreased by increasing the percentage of silica fume in case of adding water to the mixture between sand and silica fume. Allowing the increase of tailwater’s depth had a remarkable effect on decreasing the discharge and the
velocity of flow leading to a decrease in scouring depth. Also, increasing the jet
Froude number leading to an increase of discharge and velocity caused an increase
in scouring and silting depths whether the type and the percentages of silica fume
added to the fine sand.