Flat collar or concrete armor around the rectangular pier - tests in AUR's Flume Facility. A large scour hole was observed around the rectangular pier at large angle of attack.

Flat Collar - A Faulty Scour Countermeasure 
Flat collar or concrete armor around the circular pier - tests in AUR's Flume Facility
A scour hole is created by the vortex shedding behind the circular pier even with a flat collar around the pier.

Figure 2. Bed elevation contours of flume tests (D is the pier width and y is the bed elevation)

Hooked Collar - A Faulty Scour Countermeasure

Hooked Collar around the Circular pier, rectangular pier and the streamlined pier - tests in AUR's Flume Facility
The dash line shows the edge of the hook collar. In some cases, the hook collar did show some reduction of local scour at one height. However, the optimal collar location varies with the incoming flow conditions and other local conditions, which is not applicable in the real situation (Tian et al., 2010).

Figure 1. Bed elevation contours of flume tests (D is the pier width and y is the bed elevation)

​Unsuccessful Bridge Pier

Scour Countermeasures

Figure 3. Bed elevation contours of flume tests (D is the pier width and y is the bed elevation)