These are referred to as "collar dams" and develop primarily due to sand accumulation from both bunker and topdressing sand over a period of time. On several greens, the collar is now higher than the putting surface, thus preventing surface run-off of rain water.
Removing the dam requires a bit of delicate surgery on the green, collar and surrounds. The first step includes checking the existing grades with a transit, and determining the area which needs to be regraded. In order to have a smooth tie-in to the surrounding area, it's often necessary to start the grading well beyond the low point.
In the case of #3, we knew that an issue existed prior to last fall's construction on the surrounds. The grading adjacent to the green and bunkers was done in a manner which would allow us to get some drainage once the green itself was addressed this winter.