Two-Dimensional Analysis of the SR 107 Bridge Hydraulics and Scour Potential

State Route 107 (SR 107) crosses the Chehalis River just downstream of Montesano, Washington. Upstream of the bridge, a meander bend threatens to cut off and there is concern that this might worsen the hydraulic conditions at the SR 107 crossing and increase scour potential at the bridge. A high-flow bypass channel across the bend is proposed to prevent the cut off. To analyze the effects of these scenarios on the scour potential at the SR 107 Bridge, we developed a two-dimensional model of the area using the sedimentation and river hydraulics–two-dimensional (SRH-2D) model developed by the Bureau of Reclamation. The model found that the upstream avulsion would not have a significant effect on bridge hydraulics, while the proposed bypass changed both the flow dynamics and scour potential at the bridge. Additional investigation is required to ensure that the bypass does not have a detrimental effect on bridge hydraulics.