الفهرس 
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Abstract
In present research: The main objective is to investigate experimentally the semi-conical piers as a local scour countermeasure in relative to the vertical cylindrical pier. Also, semi-conical piers have been subjected to a number of modifications to make their usage in the field applicable. The second objective is to increase the efficiency of semi-conical piers in reducing the effect of local scour. Therefore, a number of devices have been applied or integrated with the leading edge of semi-conical pier. These devices are slot, openings, ladder face, curved face, trenched belt and aerofoil section. The final objective is to develop empirical formulas (pier scour equations) to estimate the maximum scour depth around piers which attained the main and second objective.To achieve the above objectives, six experimental sets have been conducted in the Irrigation and Hydraulic laboratory at the Engineering Faculty, Mansoura University, Egypt. All experiments with the test duration of four hours have been done in a straight flume which its dimensions are 6.8 m long, 0.74 m width and 0.40 m deep. Sand has been used as the bed material and its thick and d50 are 0.1m and 0.71 mm, respectively. Results have shown that, the scour depth and volume are decreased when: The semi-conical pier is used as alternative to the cylindrical pier for the first set. The semi-conical pier with a slot device is used instead of the same pier without slot for the second set. The semi-conical pier with openings, ladder or curved face device is used instead of the same pier without these devices for the third set. The semi-conical pier with trenched belt device or aerofoil section is used as alternative to the same pier without this device or section for the fourth set. As well, the empirical formulas develop a relationship between the normalized scour depth (as the dependent parameter) with: the Froude number or flow intensity and the side slope angle of semi-conical pier (as an independent parameters) for the fifth set. The Froude number or flow intensity and the normalized Arc height of semi-conical pier with curved face device (as the independent parameters) for the sixth set.