Jim,
The front right of the green sloped down toward the approach.
The DA was directly below the putting surface and as a result surface water flowed naturally into the DA.
Both irrigation and rainfall caused the face of the bunker to erode and become a maintenance headache.
Years ago, an eyebrow like berm was created above the bunker to divert surface water away from the top of the bunker and reduce the washout problem.
In addition, the green was allowed to recede with a buffer of rough rather than putting surface being immediately above/adjacent to the DA, probably as an additional defensive measure.
As Archie stated, over cooked putts could often end up in the DA when the hole was cut near it.
In addition, tee shots with spin and balls hit out of the DA, with either spin or not enough momentum, would often roll back into the DA.
If you had just played a recovery from the DA, that was a horrifying consequence as the ball would inevitably roll back into your foot prints, making your next shot even more difficult.
Now, with the mini-berm and buffer of rough, it's pretty rare when a ball can roll off the green, through the buffer and over the berm and down into the DA.
It's not nearly as frightening as it used to be, because it's not as functional..
Always happy to contribute to your architectural education.
