Step 1: create 128x128x4 brush.
Step 2: clone brush to fill a 2048x2048x4 area.
Step 3: transform all brushes into displacements.
Step 4: set noise to -10/+10
Step 5: sew all displacements
Step 6: subdivide all displacements simultaneously
If Hammer finishes Step 6 before the contest is over, I'll let you know what step 7 is. :
:
Seriously though, I've got what I think is a great idea. We'll see what everyone thinks of it when it's done.
Also, if you want a larger jetty, I suggest taking the bridge supports from 2fort and using some of the wood patches from Sawmill after you've reskinned them to better match up.