Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction (2013) / Chapter Skim
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A-1 A P P E N D I X A Glossary I Hydrologic, Hydraulic, and Geomorphic Terms*
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A-2 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Bed Material: Material found in and on the bed of a stream (may be transported as bed load or in suspension)
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Glossary A-3 Contraction Scour: Contraction scour, in a natural channel or at a bridge crossing, involves the removal of material from the bed and banks across all or most of the channel width. This component of scour results from a contraction of the flow area at the bridge which causes an increase in velocity and shear stress on the bed at the bridge.
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A-4 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Ephemeral Stream: A stream or reach of stream that does not flow for parts of the year. As used here, the term includes intermittent streams with flow less than perennial.
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Glossary A-5 Freeboard: The vertical distance above a design stage that is allowed for waves, surges, drift, and other contingencies. Froude Number: A dimensionless number that represents the ratio of inertial to gravitational forces in open-channel flow.
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A-6 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Instantaneous Discharge/Peak: The volumetric rate of flow passing a given cross section on a stream or river at a specific point in time. Invert: The lowest point in the channel cross section or at flow control devices such as weirs, culverts, or dams.
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Glossary A-7 Migration: Change in position of a channel by lateral erosion of one bank and simultaneous accretion of the opposite bank. Nonalluvial Channel: A channel whose boundary is in bedrock or non-erodible material.
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A-8 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Riprap: Layer or facing of rock or broken concrete dumped or placed to protect a structure or embankment from erosion; also the rock or broken concrete suitable for such use. Riprap has also been applied to almost all kinds of armor, including wire-enclosed riprap, grouted riprap, sacked concrete, and concrete slabs.
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Glossary A-9 Slope-Area Method: A method of estimating unmeasured flood discharges in a uniform channel reach using observed high-water levels. Spill-Through Abutment: A bridge abutment having a fill slope on the streamward side.
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A-10 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Ultimate Scour: The maximum depth of scour attained for a given flow condition. May require multiple flow events and in cemented or cohesive soils may be achieved over a long time period.
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Glossary A-11 II. Probability and Statistical Terms Bias: A statistical measure of systematic difference between a predicted value and the population parameter of interest, typically showing as the symbol ; a measure of consistent overprediction or underprediction.
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A-12 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Gaussian Distribution: The Standard Normal or "bell-shaped" probability distribution function. Kolmogorov-Smirnov Test: A nonparametric goodness-of-fit test that compares a probability distribution obtained from a sample to a reference cumulative distribution function, or to a distribution from a second sample.
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Glossary A-13 Probability (Conditional) : The likelihood (percent chance)
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A-14 Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Prediction Risk: The potential that a chosen action or activity (including the choice of inaction) will lead to a loss (an undesirable outcome)
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