The Buoyant Foundation Project

Link to their website.  The basics:

"It basically works like a floating dock. A steel frame that holds the flotation blocks is attached to the underside of the house. There are four 'vertical guidance' poles not far from the corners of the house. The tops of the poles are attached to the steel frame. The poles telescope out of the ground, allowing the house to move up and down. Utility lines have either self-sealing 'breakaway' connections or long, coiled 'umbilical' lines. When flooding occurs, the flotation blocks lift the house, with the steel frame transferring the forces between the house and the blocks. The vertical guidance poles keep the house from going anywhere except straight up and down on top of the water."