مشخصات پژوهش

Culverts are hydraulic structures designed to convey flow safely; however, flow exiting the culvert may impinge on the downstream bed and cause scour. For this scour, installing an apron downstream of a culvert is considered an effective measure for protecting and stabilizing the structure. The present study investigates downstream topography under different apron widths and downstream bed elevations. Experiments were conducted with aprons of varying widths installed downstream of the culvert and compared with the no-apron condition. The effect of downstream bed elevation on the outflow jet and bed morphology was also examined. The experiments were carried out in a straight flume with a rectangular cross section. The results showed that, for all investigated bed elevations, apron installation reduced the maximum scour depth compared with the no-apron condition. At the bed elevation level with the culvert outlet, the apron width equal to 0.4 times the channel width produced the greatest reduction in maximum scour depth, decreasing it by 38.5%. At a bed elevation 0.2 times the culvert opening width below the culvert level, the maximum reduction in scour depth was obtained for an apron width equal to 0.2 times the channel width, corresponding to a 15.8% decrease. However, at a bed elevation 0.067 times the culvert opening width below the culvert level, scour depth increased for all apron widths compared with the no-apron condition. These findings demonstrate that apron effectiveness depends strongly on downstream bed elevation and apron width, and can provide useful guidance for culvert design and scour mitigation.