The National Academies Press

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From page 16... ... presented a physically justiﬁed method (Equation 21) to estimate local scour depth at piers based on C H A P T E R 4 Equilibrium Local Scour Predictive Equations Read the entire page →
From page 17... ... Equilibrium scour predictive equations. (continued on next page) Read the entire page →
From page 18... ... units. V c = incipient velocity for local scour at a pier K = shape and alignment factor = 1 for clear-water scour < 1 for live-bed scour i.e., 10 9 3 5 2 23 D c V V . Read the entire page →
From page 19... ... Initial Screening of Equilibrium Scour Predictive Equations Twenty-three equations were assembled for evaluation and assessment. These equations are presented in Table 4. Read the entire page →
From page 20... ... Comparison of normalized local scour depth predictions using 22 different methods for a particular live-bed scour condition. Read the entire page →
From page 21... ... Comparison of normalized local scour depth predictions using 22 different methods for a particular live-bed scour condition. Read the entire page →
From page 22... ... Comparison of normalized local scour depth predictions using 22 different methods for a particular live-bed scour condition. Read the entire page →
From page 23... ... Comparison of normalized local scour depth predictions using 22 different methods for a particular live-bed scour condition. Read the entire page →
From page 24... ... Improvements in the understanding of local scour processes and scour hole development during this time period resulted in improvements to the equilibrium scour predictive equations/methods. For example, several of the earlier equations predicted negative scour depths for some of the input conditions. Read the entire page →
From page 25... ... The S/M local scour equations. 0 0.2 0.4 0.6 0.8 1 0 0.5 1 1.5 2 2.5 3 V1/Vc y s /a Data Sheppard & Miller 2006 S/M Figure 21. Read the entire page →
From page 26... ... a discontinuity in predicted scour depth with increasing pier width as shown in Figure 25. Evaluation of Equilibrium Scour Predictive Methods Evaluating predictive equations using laboratory data is relatively straightforward because, in most cases in the database, either the scour has reached equilibrium or the measured depth has been extrapolated to an equilibrium value. Read the entire page →
From page 27... ... Measured/predicted versus predicted time to reach 90% of equilibrium scour depth for the field data. Read the entire page →
From page 28... ... The errors associated with predicting the measured equilibrium scour depths were computed using the following equation for dimensional scour depths, ys: The corresponding equation for normalized scour depths, ys/a, is SSEn% y a y a y s measured s model s measure = − ⎛⎝⎜ ⎞⎠⎟∑ 2 d a ⎛⎝⎜ ⎞⎠⎟ × ∑ 2 100 27( ) SSE% y y y s measured s computed s measured = −( ) Read the entire page →
From page 29... ... Field data errors are not very informative by themselves because they do not include total errors. Total errors for the field data are also not meaningful because so many of the reported scour depths are not equilibrium values. Read the entire page →
From page 30... ... . Figures 31 through 34 are plots of predicted versus measured scour depths for six of the predictive equations for the various data sets. Read the entire page →
From page 31... ... Figure 28. Underprediction normalized scour error versus total error for laboratory data. Read the entire page →
From page 32... ... HEC-18 HEC-18-no wp corr S/M 32 Figure 31. Predicted versus measured equilibrium scour depths for six predictive equations for laboratory data. Read the entire page →
From page 33... ... %cases U.P.=7.25 0 1 2 3 0 0.5 1 1.5 2 2.5 3 Measured y s /a Pr e di c te d y s /a HEC-18 %cases U.P.=14.7 0 1 2 3 0 0.5 1 1.5 2 2.5 3 Measured y s /a Pr e di c te d y s /a HEC-18-no wp corr %cases U.P.=13.8 0 1 2 3 0 0.5 1 1.5 2 2.5 3 Measured y s /a Pr e di c te d y s /a S/M %cases U.P.=8.16 Figure 32. Predicted versus measured normalized equilibrium scour depths for six predictive equations for laboratory data. Read the entire page →
From page 34... ... Predicted versus measured normalized equilibrium scour depths for six predictive equations for field data. Figure 35. Read the entire page →
From page 35... ... Comparison of S/M and HEC-18 predictions of normalized scour depth versus V1 /Vc. Figure 38. Read the entire page →
From page 36... ... Comparison of S/M and HEC-18 equation predictions of equilibrium scour depth as a function of pier diameter (for D50 = 5 mm) Read the entire page →

From page 16...

... presented a physically justiﬁed method (Equation 21) to estimate local scour depth at piers based on C H A P T E R 4 Equilibrium Local Scour Predictive Equations