Here are just a few ideas/things to think of that come to mind, I'm sure others here will have some more thoughts. To put the Arc in the water, make sure you shoot it in a way so that you can remove that tree. Since you are going to have to paint/clone that out.
For the water, you will need some stormy footage that is shot in a perspective similar to how you shoot the Arc(probably best is to find the footage and try to match the perspective). If the shot is shaky, that might actually help as you could use AE's camera tracker to integrate the Arc into the shot.
You will need to layer the water, masking out the foreground water to put in front of the arc. You probably will want to mask out the arc also to have a water background plate.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.