http://www.popularmechanics.com/mil...nfirms-existence-of-russian-doomsday-torpedo/
Poorly written article.
The water molecules right next to a nuclear blast do not go immediately onto the enemy beach. They push on the water molecules next to them. Those water molecules push on the water molecules next to them. What comes ashore is a pressure wave, not the the radioactive water molecule next to the blast. Those radioactive molecules will eventually come ashore, but they will be carried by currents.
As I remember from school, fluid dynamics wasn't all that popular, anyway. Right up there with strength and materials...
It's actually just a line they wrote from the next apocalypse movie starring Gerard Butler and directed by Roland Emmerich.
I think you would be right if the bomb is out to sea and at significant depth, but a device detonated at an optimal distance and depth from shore would be powerful enough to simply displace most of the ocean in the onshore direction right up onto land. I believe one gets the effect you are describing if the weight of the water is greater than the force necessary to move the whole column in any given direction. Otherwise it accelerates like water blown through a straw. I know water is heavy but a 50Mt nuclear blast has a pretty big force so I think you can move a lot of water with that. Not to mention that the blast will rebound off the offshore side (because its much much heavier) and so most of the force of the blast will go to the shore. Then, after that first displacement, the rebound from the heavy, deep sea side of the blast would also push a whole bunch more water ashore with the weight of the ocean behind that wave.
