Flow velocity immediately upstream of the pier
The flow velocity immediately upstream of the bridge as determined from HEC-RAS. For small channels compute the
velocity as V1=q/y1 where q is the unit flow in the channel or section closest to the upstream bridge face.
For larger channels, use the velocity distribution (flow tube) option in HEC-RAS to select the highest velocity in the channel.
For most cases, the recommended approach is to select the pier within the limits of the estimated channel lateral movement zone (CLMZ)
with the worst-case conditions (velocity and flow depth) for scour (typically at or near the channel thalweg). Design all piers within the CLMZ for this condition.