الفهرس 
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Abstract
ABSTRACT
The Large Concrete Dam, which was designed and implemented with a full storage capacity for the regional water supply that reaches the downstream countries, has a storage capacity of 74 billion cubic meter at 640 m (a.s.l). After the process of filling the reservoir, the storage capacity of water passes over uncompleted portions of dam body which have low crest level and bumping into the natural downstream bed level. The filling process of the reservoir allows water to fall from different heights depending on the operational
stage. The fallen water will perform deformation on riverbed and consequently on the soil layers at the downstream side. Therefore, a protective layer is required at the downstream side to reduce any corrosion. This study aims to quantify the effects of the fallen water jet on the structural model represented the jet impact force on the protection soil layer behind the dam.
A physical model was constructed in the Hydraulic Research Institute lab for the dam spillway with different crest levels to pass water over them. The structural model of the protective layer requires installing special equipment to measure the normal stresses and deformations occurred due to the flow impact, it is found that; the maximum deflection value is 3.4 m for prototype, the maximum normal tension stress reaches to 1.15 t/cm2 within protective layer boundary. These values are higher than the available tension strength of used material for construction of the protection layer. It leads to know the dangerous of scouring that occurs behind the dam at the impacted area of D/S side. A different modules of structural systems are attained in order to find an efficient and suitable system for the protective layer. If there was no any formation of scour downstream dam body, the most appropriate structural system should be case No. 3 (using 4 parallel cutoff walls).