Building facilities on a damn that is meant to hold back storm surge seems like tempting fate. Also what people need to understand is that the harbor islands themselves are natures way of reducing the impact of storm surge.
..just got to build it on the inland side of the dike, van...
...and i think that science and experience say that the islands will contain a pounding from breaking waves, but cant do much about the sea-surface increase that comes with a storm surge. cf. Sandy in New York harbor: the eastern shore of State Island got scraped clean by waves breaking down a long unbroken fetch that extended a thousand miles out into the Atlantic, whereas lower manhattan just got flooded but without any damaging waves (Staten Island and Long Island at the Narrows are set up in a way thats pretty analogous to the Roads between Deer Island and Long Island...) ... and the greatest risk in this area is clearly Hull, which feels about as dense as somerville but with no clearance above sea level....(how to protect / manage that is a different can of worms)
Bottom line (and i know you agree with the need to build the thing Van, but anyway....) We've all seen the edge of the harbor get real wet from run-of-the mill storms (the end of long wharf, columbus park, the basin at the end of jeffries point)...and we've been within 6-18 inches of having water flowing into the blue line multiple times in just the last decade.
All a long way of saying that this seems like the king of the no-brainers to me, and i can't figure out why its not is active design and permitting already...i mean the saved insurance premiums alone could finance the thing...