Colorado, New Mexico, Arizona, Utah and Nevada don’t have access to the pacific. My understanding of the proposal was to siphon off the winter and spring excess just below Cairo. It might take a few years to fill Mead and Powell on only spring excess but once the reservoirs are filled, problem solved. No effect on barge traffic. What’s you idea for the tens of millions of landlocked folks so dependent upon the Colorado? Piping desalinated pacific water to Flagstaff doesn’t make any better sense.
Send the Colorado water to Flagstaff instead of to California. Break the rotten old deal under which California stole water from all the rest. They have plenty, if they want it enough. If they don't want to power desalination with nukes they have loads of in state and coastal oil resources to power it. Works fine in deeper waters in the Gulf in spite of a lot more Hurricanes. Pipe the desalinated stuff just a bit inland, where most of the Californian consumers live.
Aside from the engineering problems of moving an intermittent variably huge surplus of water a huge distance through some kind of huge piping and over the continental divide to fill two huge reservoirs have your engineering friends considered what all the good midwest fertilizers in that water might do to Mead and Powell? They complain enough about it's affect on the much larger Gulf. Also there'd be a lot of sediment with that water, which would tend to silt up the diversion pipe whereas the force the excess water instead just adds to the delta in LA. And folks in the delta wouldn't like it when their land started to net erode away.
I'm in Davenport so I can understand the view from outside here, but actually Davenport area has adjusted pretty well to Mississippi spring floods the past 55 years. The mid 60s flooding I remember was bad mainly because a generation without significant flooding conned folks into investing capital onto the flood plain. Breaking that flood record made nice photo-ops for Clinton, but not much harm here. Since the 60s most of our money is either behind adequate flood walls, pulled back far enough to higher ground or consists of stuff that being under water a couple months won't much hurt. Problems get worse further down stream and also up stream along some of the tributaries that join the Mississippi further south, cf. Cedar Rapids, Des Moines and Iowa City floods. Quite a bit more excessive water if you tap it south of Keokuk (adding the Missouri and much of Iowa's land) and more if you tap it south of Cairo (adding the Ohio.) But doing so costs altitude when you want gravity drainage west as much as is possible.
Sure it does. It doesn't affect trade or barge travel like draining the Mississippi. Also--even if you limit any draining to floods only, it will soon expand beyond that like all good gov't programs. Soon the entire midwest would be in the same condition as the west is currently, and the world literally cannot afford to have its breadbasket go without water just so some Hollywood types can fill their pool.