Exactly, there are usually few to no issues environmentally with replacing a building with another building for the same purpose. Same goes for flood zones. When I worked on NEPA reviews. you couldn't build new in certain flood zone areas, but you could replace something already in those zones. I don't thinkg their would be that many issues in Natomas.
Of course, the railyards would be under as much as 20 feet of water if a levee broke. My house isn't in a flood insurance-required area, because its "protected" from 100 year flooding by a levee. I find that very amusing. The levee broke twice just across the river in fairly recent times.
I recently read that the Netherlands have already started improving their flood control system to 10,000 year flood protection due to the predictions about rising sea levels. If the oceans rise 3 feet, Sacramento and the delta are is serious trouble. We'll have to row to work.