Scour prevention in bottomless arch culverts

Bottomless arch culverts are employed as ecological bridges at road crossings with their most common application being fish passage. The simulated culvert streambed should mimic the existing natural channel but be engineered to resist erosion during high flow events. To provide some design guidance for simulated streambed stability in culverts, a culvert streambed stability study was conducted using a 0.61-m （2-ft） diameter smooth-walled bottomless arch culvert featuring streambed materials ranging in size from pea gravel to cobbles. Several culvert entrance geometries over a range of headwater depths （unsubmerged and submerged inlets conditions） were evaluated. Eight riprap stone-sizing stability relationships were evaluated, relative to the experimental data, to determine their potential applicability to arched bottomless culverts streambed stability design. Some general observations are discussed regarding the location and extent of scour events in bottomless culverts and incipient motion velocity variations between the bottomless arched culvert and a rectangular flume for the same substrate materials.