Potential Drift Accumulation at Bridges
Estimating Potential for Accumulation by Location and Type
After estimating the potential for drift delivery to the site and assigning location categories and other bridge characteristics, estimate the potential for drift accumulation separately for each pier, each section of immersed superstructure, and each horizontal or vertical gap between fixed elements.
Estimate potential for drift to span an individual gap between fixed elements of the bridge opening, using the flow chart in figure 31. In addition to the estimated delivery potential, which is the same for the entire site, this flow chart uses two variables that must be selected for each horizontal or vertical gap: effective length of the span between fixed elements relative to design log length (gap wider or narrower), and location category of the gap.
Figure 31. Flow chart for determining potential for accumulation across a span or vertical gap.
Estimate the potential for accumulation on each pier and section of superstructure, using the flow chart in figure 32. In addition to the estimated delivery potential, which is the same for the entire site, this flow chart uses two variables that must be selected for each pier and section of superstructure: location category, and presence or absence of narrow apertures that carry flow.
Figure 32. Flow chart for determining potential for drift accumulation on a single pier.
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