A pipeline network throughout the country would be an idea. But could it be cost be warranted depending on how capable this system would be to handle that amount of water?
You would probably have to have at least a 4 foot main pipe in the flood zones that reduce down to several 10 inch or 15 inch pipes to go to different regions like the south west and south east and the pipes continue to individual states. Maybe have huge man holes in low areas that in times of flood the lids are opened to accept the water. Its seems doable. And I think the cost benefit would be good for times like this.