The French daily Libération published during the summer a couple of interesting articles on two gigantic water transfer projects. The first one, eventually abandoned, was aiming to divert some of the flow of Siberian rivers towards Central Asia. The second, about to be temporarily completed but whose benefits are dubious, is the "Great Man Made Canal" imagined by Qaddafi in Libya.
According to the first article, soviet authorities planned to divert some of the flow of major Siberian rivers (currently "uselessly" flowing northwards) to provide water for irrigation in Central Asia, thus both repairing and adding to the damage already done in this region. The project appears to have been abandoned by Gorbatchev at the end of the 80s for both environmental and political reasons. See (in French): "URSS : un plan à l’eau".
The second article deals with the "Great Man Made River" (also dubbed by critics the "Great Mad Man River") imagined by colonel Qaddafi to provide the Libyan coast with water from the Great Nubian Aquifer, located for the most part under the Sahara desert in Southern Libya. Work began about 15 years ago, but there are doubts whether it will actually ever be entirely completed because of technical difficulties in accessing large swaths of the aquifer. Furthermore, results actually achieved so far in terms of agricultural development on the coast are close to nil. See "A fond perdu".