Abutment setback (ft/m)
Setback is the horizontal distance measured from the channel bank or edge of channel to the abutment:
- For a vertical wall or a wing-wall abutment, measure the setback from the channel bank to the face of the abutment.
- For a bottomless arch culvert, measure the setback from the channel bank to the culvert wall
- For an abutment on a spill-through slope, measure the setback from the channel bank to the point where the ground line intersects
the spill-through slope. If the ABSCOUR cross-section is above the existing ground, use the ABSCOUR cross-section to define the ground line.
If the ABSCOUR cross-section is below the existing ground, use the existing ground to define the ground line.
- If there is a pier on the over-bank section, the pier width should not be included in the top width value T. This may result in a condition
that the top width as measured from the channel edge will not extend to the abutment, and abutment scour will be computed as zero. For this case,
the setback distance needs to be adjusted to equal the top width, T.
- If the abutment projects into the channel beyond the channel bank, enter the setback as a negative number.
When the overbank sections are relatively small, and where the channel is likely to move laterally within the structure, consider analyzing the flow
as being all channel flow without overbank sections. For this case the setback is zero.
Click here to see a definition sketch of setback for an abutment
Click here to see a definition of setback for a bottomless culvert