From what I can see, I think some of the largeness of the carrier comes from the possibility that the anchorage is dry. From what it looks like the seas have receded and left the river dry.
Take a look at the river bottom in the forefront of the bridge, maybe my eyes are failing but it looks quite dry to me.
EDIT: It also looks like the ship is being propped up. Near the front of the carrier seems to be some kind of bracing, which would give credence to the hypothesis that the river has dried out.
Now, what most folks see of a ship like a carrier is above water, yet most of the hull is below the waterline.
So given those two things may have occurred, that would account for the huge hull profile. I also think that maybe there was an airburst off the coast that created the tsunami which pushed the carrier further up the river and then over the years the lack of rain and the receding of the oceans in a Fallout post apoc, where it is all desert-y and dry. So that could plausibly explain how the carrier got so far out of the water.
A li'l FYI, even in the Bimini test detonations, most ships survived, unless they were almost directly under point zero. So our carrier could have possibly survived a detonation.
Cheers, Þórgrímr