If I remember correctly, the diagram is pretty simplistic. I think the safety ledge is 18" on 3 sides, with a 45 degree slope down to the hopper bottom. The fourth side, which is the shallow end, has a longer, shallower slope. It's not really clear in the manuals, but the shallow end and safety ledge sand should cover the bottom 2" of the wall....but check on that. Also watch for a "gutter" forming between the ledge and the vertical. The idiots who installed my liner weren't careful and I've had that gutter for 12 seasons.
I'm going to be doing the same this year as the "Space Age" walls have been a major disappointment. Aluminum WILL corrode if not properly anodized and sealed, and it has done so, creating rough mounds under the liner threatening to pierce through. I was planning on using the wood waterwalls until J_Palmer_Cass suggested P/T and liner foam instead.
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