The total depth of scour is a combination of long-term bed elevation changes, contraction scour, and local scour at each individual pier and abutment. Once the scour is computed, the HEC-RAS software automatically plots the scour at the upstream bridge cross section. An example plot is shown in the figure below.
Graphic of Contraction and Total Scour at a Bridge
As shown in the figure above, the program plots both contraction scour and total local scour. The contraction scour is plotted as a separate line below the existing conditions cross section data. The local pier and abutment scour are added to the contraction scour, and then plotted as total scour depths. The topwidth of the local scour hole around a pier is computed as 2.0 ys to each side of the pier. Therefore, the total topwidth of the scour hole at a pier is plotted as (4.0 ys + a). The topwidth of the local scour hole at abutments is plotted as 2.0 ys around each side of the abutment toe. Therefore, the total topwidth of the scour hole at abutments is plotted as 4.0 ys.