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29 evaluate the S-SRICOS Method are the same cases that were used to develop that method. Therefore, this does not repre- sent an independent evaluation. Details of the prediction process can be found in Kwak et al. (2001). E-SRICOS and S-SRICOS described above do not include correction factors for pier shape, skew angle between the flow direction and the pier main axis, shallow water depth effects, and multiple pier effect. Chapter 5 will show how to calculate those factors. 4.10 CONCLUSIONS The SRICOS Method predicts the depth of the local scour hole versus time curve around a bridge pier in a river for a given velocity hydrograph and for a layered soil system (Fig- ure 4.21). The method described in this chapter is limited to cylindrical piers and water depths larger than two times the Figure 4.19. Predicted versus measured local scour for pier width. The prediction process makes use of a flood accu- the E-SRICOS Method. mulation principle and a layer equivalency principle. These are incorporated in the SRICOS computer program to gener- curve) within the maximum scour depth was generated. The ate the scour versus time curve. A simplified version of this maximum shear stress max around the pier before scour began method is also described and only requires hand calculations. was calculated using Equation 4.1, assuming that the pier was i was read on the The simplified method can be used for preliminary design circular (Table 4.2). The initial scour rate z purposes. Both methods were evaluated by comparing pre- average erosion function for that pier (Table 4.2). The equiv- dicted scour depths and measured scour depths for ten piers alent time te was calculated using Equation 4.7, using thydro at eight full-scale bridges. The precision and accuracy of equal to the time separating the two river bottom profile both methods appear good. observations, and vmax equal to the maximum velocity that occurred during thydro (Table 4.2). Knowing te, z i, and z max, the scour depth accumulated during the period of thydro was calcu- lated using Equation 4.3. Figure 4.20 is a comparison of the measured values of local scour and the predicted values using the S-SRICOS Method. The precision and accuracy of the method appear reasonably good. The 10 case histories used to Figure 4.21. Velocity hydrograph and predicted scour Figure 4.20. Predicted versus measured local scour for depth versus time curve for pier 1E of the existing Woodrow the S-SRICOS Method. Wilson Bridge on the Potomac River in Washington D.C.