Laboratory study of scouring around the roughened pile groups in the presence of material harvesting pits and at different Froude numbers

Harvesting the river materials can cause negative effects on the river and can intensify scouring around the bridge piers. This study investigates local scouring around roughened pile groups with gravel in the presence of harvesting pits for Froude numbers of 0.1, 0.25 and 0.5. It was found that applying roughness reduced the scour depth by 4.8 cm (73%). Due to increasing pile stability because of reducing local scouring, results show that the application of roughness to the surface of piers is a suitable, straightforward, cost-effective, and easy-to-apply method to reduce scouring. In addition, the maximum scour depth upstream and downstream of the harvesting pit occurred upstream of the initial piers. A comparison of scour areas shows that scour expansion in the transverse direction was greater than in the longitudinal direction and the amount of expansion increases when Froude number has been increased. Also, the extent of scouring around the initial piers was greater than the extent of scouring around the other piers. The maximum scour depth was 15 cm in front of the first pier and corresponded to simple piers and flow with a Froude number of 0.5.