Impact of Bed Material on the Local Scour Downstream Fayoum Type Weir with Various Designs of Floor Jets

Local scour downstream hydraulic structures should be studied well to avoid damage or even failure of these structures. In this paper, an experimental model was conducted to study the influence of bed material size on the local scour downstream stilling basins of Fayoum type weir as a hydraulic structure. Two bed material were tested. The model included stilling basin and five rows of water jets. Forty-five test runs were carried out for each bed material. Different cases were implemented during this study including three flow discharges, three tail water depths and five various designs of floor jets. Based on the obtained results, it was found that the maximum and minimum scour depths for the two bed materials occurred by design A and design D. The maximum scour lengths happened for medium sand by design C and for fine gravel by both designs A and E, while the minimum scour lengths were recorded for medium sand by design D and for fine gravel by design A. The maximum scour volumes were found for the two bed materials by design A, while the minimum scour volumes occurred by both designs C and D for medium sand and by design E for fine gravel. Employing fine gravel instead of medium sand as a bed material achieved maximum reduction percentages of 86.8 %, 53.3 % and 89.8 % for scour depth, scour length and scour volume, respectively