When creating a harbor, pier, or dock, it seems to be easier to figure out  how deep you want your water first, then build your land up to that point, especially if you want some features below ground (but above water). This slab is for a deep water dock built on a spur of land. When the water level is brought up to 1/3rd of the barrels, the desired effect is achieved.

All assets are in the system folder, no assets from individuals. This is my first completed slab after much trial and error. Hopefully, this will be useful for others as well. Enjoy!