Revised Clear-Water and Live-Bed Contraction Scour Analysis (2021) / Chapter Skim
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From page 155... ...
9-1 9.1 Observations Bridge waterways commonly narrow or constrict natural channels, forcing water to flow through a contracted area, thereby increasing the magnitude of velocity and turbulent kinetic energy of flow passing through the waterway. If these increases cause erosion of the waterway boundaries, the contracted section may scour.
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From page 156... ...
9-2 Revised Clear-Water and Live-Bed Contraction Scour Analysis • Application of the revised equations to a typical field case of contracted flow in a bridge reach and comparison of the results with estimates obtained from the existing equations • Evaluating the reliability of the existing and recommended analysis approaches using the laboratory database developed under this study This study showed that the deepest region of contraction scour (not including the entrance corners) occurred along the vena-contracta formed by flow entering a contraction.
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From page 157... ...
Observations, Conclusions, and Suggested Research 9-3 and typically causes the bed-surface profile to become shaped like a gently upwardly curved mound. The form of the mound was complicated by the non-uniform development of bedforms along the contracted channel.
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From page 158... ...
9-4 Revised Clear-Water and Live-Bed Contraction Scour Analysis 11. The widely used HEC-18 equations for estimating the depth of contraction scour were adjusted to include a coefficient for estimating the minimum width of the vena-contracta.
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From page 159... ...
Observations, Conclusions, and Suggested Research 9-5 9.3 Suggestions for Further Research The results of this updated and revised analysis of the hydraulics of contraction scour lead to a set of recommendations regarding topics for further investigation: 1. The values of the vena-contracta coefficient, Kv, should be determined for different entrance shapes, notably shapes typical of bridge abutments (e.g., spill-through or vertical wall abutments)
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