The effects of the thickness of the bed-sediment layer on the depth of the scour caused by a water-jet

In this study, the effects of the thickness of the noncohesive sediment layer at the canal bed on the depth of the scour caused by a water jet impinging the sediment layer are investigated. The dimensionless parameters affecting the depth of the scour are obtained by means of dimensional analysis and experiments are conducted to find the relations among these dimensionless parameters. Experimental results indicated that the depth of the scour increase with the thickness of the bed sediment layer. The main reason for this is as follows. As the thickness of the sediment layer increases the penetration depth of the air-bubbles (dragged and enforced by the impinging water jet) through the sediment layer just under the scour hole increase. Due to the buoyancy force as the air-bubbles rise upward they apply uplift forces and dynamic effects on the sediment particals thereby the sediment particals are easily dislocated, got into suspension and carried away from the bed. If the thickness of the sediment layer is increasing further beyond a limiting value for a given flow condition, the maximum depth of the scour does not change (it remains almost constant). It is observed and found that the effect of the thickness of the bed sediment layer on the depth of the scour is present but it is not excessively large. Science Code : 911.1.125 Key Words : Water jet, scour, sand layer, channel flow, water resources and hydraulic structures Page Number : 72 Adviser : Prof. Dr. Nevzat YILDIRIM