text: The Hydraulic Engineering Circular Manual No. 23 (HEC-23) contains general design guidelines as scour countermeasures that are applicable to piers and abutments. The numbering in the following table indicates the HEC-23 design guideline section:
  Bend way weirs, spurs and guide banks can help to align the upstream flow while riprap, gabions, articulated concrete blocks and grout-filled mattresses can mechanically stabilize the pier and abutment slopes. Riprap remains the most common countermeasure used to prevent scour at bridge abutments. A number of physical additions to the abutments of bridges can help prevent scour, such as the installation of gabions and stone pitching upstream from the foundation. The addition of sheet piles or interlocking prefabricated concrete blocks can also offer protection. These countermeasures do not change the scouring flow and are temporary since the components are known to move or be washed away in a flood. The Federal Highway Administration (FHWA) recommends design criteria in HEC-18 and 23, such as avoiding unfavourable flow patterns, streamlining the abutments, and designing pier foundations resistant to scour without depending upon the use of riprap or other countermeasures.
  Trapezoidal-shaped channels through a bridge can significantly decrease local scour depths compared to vertical wall abutments, as they provide a smoother transition through a bridge opening. This eliminates abrupt corners that cause turbulent areas. Spur dykes, barbs, groynes, and vanes are river training structures that change stream hydraulics to mitigate undesirable erosion or deposits. They are usually used on unstable stream channels to help redirect stream flow to more desirable locations through the bridge. The insertion of piles or deeper footings is also used to help strengthen bridges.