Experimental investigation of baffle configurations, blockage, and flow variability on downstream scour in box culverts

This research utilized physical models to examine changes at the culvert outlet under diverse scenarios, including three different designs of baffle configurations, different levels of blockage, and flow discharges during both steady and unsteady flow states. The study assessed a box culvert with three outlets of different baffle arrangements and blockage rates of 0%, 25%, and 50% at the inlet. For unsteady flow conditions, two hydrographs were created, each containing seven unique flow discharges. Conversely, for steady flow conditions, flow rates of 13.8 l/s and 20 l/s were employed. The sediment and flow scenarios were meticulously chosen to maintain clear water throughout the experimental procedures. According to the findings, the scour patterns under both steady and unsteady flow conditions, as well as the effectiveness of the baffle in minimizing scour depths, were compared with the base case scenario at different blockage levels at culvert outlets. In-depth analysis of baffles application versus the base case scenario under the same blockage conditions showed that the deepest scour depths were typically found further from the outlet in the base case scenario. During steady flow conditions, the first design configuration of baffle reduced the deepest scour depth by 29.87% at a flow rate of 20 l/s with 25% blockage and configuration three was most effective at 37.70% reduction for 13.8 l/s with no inlet blockage. In unsteady flow conditions, during the first hydrograph, the first design configuration reduced the deepest scour depth by 37.33% at 25% blockage, while configuration two achieved a 34.48% reduction during the second hydrograph with 25% blockage. However, with baffles introduced, the greatest scour depth occurred much closer to the outlet. Additionally, an increase in flow rate resulted in larger scour holes, and scouring intensified with incremental increases in hydrograph steps. Nevertheless, an increase in blockage did not consistently result in a proportional increase in scour depth across all instances.