Revised Clear-Water and Live-Bed Contraction Scour Analysis (2021) / Chapter Skim
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1-1 Introduction and Research Approach 1.1 Scope and Research Objectives 1.1.1 Background Bridge waterways commonly narrow or constrict natural channels, forcing water to flow through a contracted area, thereby increasing the magnitudes 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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1-2 Revised Clear-Water and Live-Bed Contraction Scour Analysis Analysis of existing laboratory datasets conducted under NCHRP Project 24-34 revealed that the clear-water contraction scour equation does not envelop the observed data as a design equation (Lagasse et al.
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Introduction and Research Approach 1-3 1.1.2 Objectives The objectives of this research were to develop live-bed and clear-water contraction scour equations suitable for use in risk-based bridge design encompassing a wide range of hydraulic conditions, including varying contraction ratios and various bed materials (cohesive, noncohesive, and rock)
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1-4 Revised Clear-Water and Live-Bed Contraction Scour Analysis 1.2.2 Research Tasks A set of 10 tasks were conducted in two phases to implement the research plan. Phase I involved five information-gathering and planning tasks.
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Introduction and Research Approach 1-5 1.2.4 Summary The findings of Phase I of the project supported development of the test plan for laboratory and numerical modeling that was conducted in Phase II. The most important outcomes from Phase I included the following: • A detailed review of the approximately 10 existing methods for predicting contraction scour depth • An evaluation of existing laboratory data on clear-water and live-bed contraction scour • An evaluation of the fairly sparse (and quantitatively unreliable)
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