Bridge Abutment Scour in Compound River Channels | ||
| Journal of Agricultural Science and Technology | ||
| Article 3, Volume 2, Issue 2, 2000, Pages 95-106 PDF (773.1 K) | ||
| Author | ||
| S. Kouchakzadeh* | ||
| Irrigation and Reclamation Engineering Department, University of Tehran, Karaj, Islamic Republic of Iran. | ||
| Abstract | ||
| Most previous laboratory studies of local scour at bridge abutments were performed in rectangular channels in which the distributions of flow velocity and bed shear stress were considered uniform in the transverse direction. In reality however, bridge abutments are usually located in the floodplain zone of rivers where velocity and shear stress distributions are directly affected by the lateral momentum transfer. The influence of channel geometry and lateral momentum transfer in compound flow field on scouring phenomenon, however, has not been fully investigated and understood as yet. This paper presents the results of an experimental study performed to investigate the impact of both sediment size and lateral momentum transfer on local scour at abutments terminating in the floodplain of a compound channel. It is shown that, by accounting for lateral momentum transfer at small floodplain/main channel depth ratios (yalH<0.3), estimates of maximum local scour depth are increased by up to 30% . In relation to the sediment size, earlier studies of scouring around circular bridge piers proposed a limit for the relative size of sediment (pier diameter/median size of bed material) beyond which the sediment size has no effect on the equilibrium scour depth (Ettema, 1980; Chiew, 1984). The results of the current laboratory studies, however, indicated that the limit established for circular bridge piers might not be appropriate for the abutment case installed in the floodplain zones; further studies are required to draw a more general conclusion regarding the effects of relative grain size in the abutment case. | ||
| Keywords | ||
| Scouring; Floodplain; Momentum transfer; Compound channal; Bridge; Abutment; Pier | ||
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