I disagree and so does the good doctor. http://www.creationscience.com/onlinebook/
Walt Brown's PhD is in mechanical engineering. That is to say, in the engineering of machines and other human-created things. That does not qualify him to have an expert opinion on something in the field of geology (which is where this hydroplate theory of his would come from). So, his disagreement, while not moot, is not especially meaningful either.
By the way...where were Dr. Walt Brown's efforts to poke holes in this "hydroplate theory" of his? You lecture about scientists needing to do that, and yet you link us to a propagandistic Youtube video that purports to show how the supposed global flood happened, yet you don't show us any of his efforts to find problems this theory of his. Did you even look for them?
And also, this theory of his is more than a little too grand. It's not an effort to get at the truth, it's an effort by someone working outside their field of expertise to show that what they already believe is the truth (and more to the point, to attempt to explain away every piece of countervailing evidence in the process). He's already got this established idea of what he thinks happened - the flood written about in Genesis - and his theory is nothing more than a way to support what he already believes to be true.
EDIT--It took actually watching this video to really see just how awful of an explanation it really is. Seriously? He thinks that this water, stored in a circular layer ten miles down, simply burst free in a few moments and jetted into the stratosphere? Where much of it conveniently froze, allowing us to have frozen mammoths at the same time everything else was drowned? Totally ignoring what would happen to water that was moving at supersonic speeds to begin with. Friction creates heat, and the amount of friction (and thus, of heat) we're talking about would have caused this water to vaporize very quickly, generating a ballooning pocket of superheated air which would have gone outwards as well as outwards, frying anything that got anywhere near it to a crisp. In other words, instead of a great flood which drowned everything, it would have turned Earth (at least a large part of Earth) into a giant frying pan. Or maybe an expanding fuel-air bomb would be a better analogy. The point is that nothing anywhere near this event would have survived long enough to be drowned.
It gets even more fanciful after that. Instant creation of fossils due to sediment from eroded rocks? While I will grant that this kind of rapid burial is one of the requirements for fossils to be made, there are serious problems with this idea of his. First off, there's nowhere near enough fossils to account for the sheer number of animals which would have been killed in a mass extinction like this, second, there's too many different kinds of fossils to explain as dying in a single cataclysmic event such as this, and third, even straightforward carbon dating (which is accurate to about 50,000 years) demonstrates that most of these fossils are much older than his 5,000 year figure.
Then he talks about how these subterranean chambers would have buckled, creating the mid-Atlantic ridge. This is at least semi-plausible, though not in the way he suggested. This spherical, subterranean chamber he proposed, which had to be under a tremendous amount of pressure, simply couldn't have had enough support to keep from collapsing in on itself, which would have caused a worldwide catastrophe of shattering earthquakes as the entire upper crust of the planet settled in on itself. We're talking earthquakes that make the worst ones on record look tame. Doesn't matter if you were on a boat or on the land - it would probably have killed every human being, either from the direct effect of the earthquakes or the massive tsunamis that would have happened on bodies of water. Since the ark was on dry land, it would have been so badly damaged that it would have sunk almost instantly, assuming it could have survived getting hit by various walls of water in the first place.
And that completely ignores the fact that we have records from human civilizations from before the supposed time of the flood, and which continued on afterward, without breaks. If this flood had actually happened, all of these civilizations would have ended right then and there, and there would be no 'after' records'.
In short, this is garbage masquerading as science. A pitiful attempt by a mechanical engineer to devise a way for his belief to be true, rather than a serious attempt to come at the facts. And it's got logical and scientific holes big enough to sail an ocean liner through, as I just showed.