An Experimental Study on the Effects of Debris Accumulation at the Culvert Inlet on Downstream Scour

The major damage of hydraulic structures at river crossing occurs during floods and culverts is the structure which use as a part of drainage system in ephemeral streams. Failure in structures is caused for different reasons but pier and abutment scour is the main reason. The presence of debris causes larger scours and sediment removal compared to the absence of debris accumulation. In this study, the common problem of the flow blockage at culvert inlets is investigated applying a hydraulic model set in laboratory. Experiments were performed to understand the changes and interaction of scour depth over a range of downstream flow depths, ht and densimetric Froude number, Fo. The debris accumulation is modelled by rectangular plates of constant width (30 cm) and various heights (4, 8, 12, 16 cm) set at the culvert entrance. When culvert inlet area decreased by the smallest solid debris accumulation - which covered 20% of inlet area-, the upstream water level raised up to 12% and by the biggest solid debris size- which covered 80% of inlet area- water level increased up to 60%. Debris accumulation causes larger scours and sediment removal, so the scour hole area extended extremely in flow direction. A new maximum scour depth predictor equation has been proposed to predict the effects of debris accumulation at culvert inlet on downstream scour. This equation is well fitted with the experimental results of the current study and the results of experiments from the previous studies used to analyze presented formula.