I know the chinese are worried about this problem.

I would be too if I had the Three Gorges Dam in my country. In fact, it would not have to be a missile - imagine a terrorist attack on the dam, by flying a Boeing 747 into it! A large heavily populated and fertile area of China would be flooded. China is lucky not to be on the Islamist priority list.

The famous Wallis rolling skip bomb was high technology when it first came out, but 3 years latter, the same squadron (617th) were dropping 6,000kg and 12,000kg 'Earthquake' bombs (also a Wallis invention) that did a far better job (and also took out bridges, reinforced sub-pens and the Tripitz). A Tomahawk with a penetrating warhead, or a B2 with GPS'bunkerbuster' bombs would do the same job quite handily now.

3 Gorges would require something a little more substantial than an "asssisted" 747. I would assume that 4-5 multiple PGM strikes at the same point and at least 1 on the control room would be a minimum In fact I would think that a tactical nuke dialed up for 3 Gorges would be better than targeting a city.

The reason that the bouncing bomb (6,000lb of torpex) was required was that there was no precision guided weapons available at the time , it this is regarded as the first precision bombing mission. Today three or four weapons could be dropped on the target, however, you would actually require a greater bomb to destroy the dam, as the upkeep (as the bouncing bomb was known) was designed to blow up under the water, and so use the effect of the water behind it. Though a deep penetration weapon would have a similar effect.

Actually, Barnes Wallis originally wanted a ten ton bomb, but came up with the bouncing bombs as something more practical. He was never was satisfied with the bouncing bomb concept, as it took a direct placement on the dams to drop them. Then there was the cost of all those dead Lancaster crews who had to fly low, slow, and with two spotlights aimed at the water to get an exact height. The bouncing bomb was a one off, but gave him enough prestige to push his Earthquake bomb concepts through, first the 12,000 lb Tallboy, then the 22,000 lb Grand Slam. These bombs were designed to penetrate concrete, rock or earth, and explode under their target, causing shock cavities that were equivalent to a sudden, very localised earthquake. They were dropped from a 'relatively' safe height, and a near miss from a Grand Slam was usually enough to bring down a viaduct.

The main reason for the "bouncing bomb" is that a bomb's explosive force is greatly amplified when under water. I seriously doubt a Tomahawk would stand much of a chance at breaching the dam, even if fitted with a shaped-charge warhead. A much better option would be a "bunker buster" (GBU-28).

Undoubtedly a 'Bunker Buster' would give more penetration but I specified a 'missile' in order to provide more stand-off range. I sort of hoped the pilot might live long enough to fly a second mission.

http://www.history.navy.mil/nan/2001/may-jun/dambusters.html A little incident from the Korean War not too well known

If memory serves me: Mosquitoes with bouncing bombs were operational against shipping target up to about 1960.