Blockage of box-shaped and circular culverts under flood event conditions : a laboratory investigation

Culverts are used to allow runoff to pass through roads, railways, and embankments. Accumulation of debris during flood events reduces the culvert flow capacity and hence flow overtopping results in culvert failure both hydraulically and structurally. This paper presents the results of an experimental study of temporal variations of blockage upstream of culverts due to woody debris under unsteady flow conditions. To simulate flood conditions, a synthetic flow hydrograph was produced in the laboratory. Cylindrical wooden dowels with two different diameters were used to simulate the woody debris carrying during flood events. Two culvert shapes including box and circular pipe culverts are examined here. The results showed that the maximum percentage of blockage occurs during the falling limb of the hydrograph. Although the feeding rate of smaller diameter woody debris into the flow is of considerable importance in the culvert blockage, the blockage percentage is not influenced by the feeding rate of large woody debris. It was also found that the pipe culvert is more susceptible to blockage than the box-shaped culvert. Using regression analysis, predictive equations are suggested to estimate the percentage of culvert blockage during flood events.