[Atomic-S (OP)]

To deal with the aridity of the American southwest and the increasing demands on the limited resources (the Colorado River is running out as the demands have increased and the climate has tended drier), among the things suggested has been to desalinate ocean water from the Gulf of California and bring it in from Mexico; however, to reach Arizona, there must be a lift of in excess of 2000 feet, not considering also the horizontal distance. How does that compare with looking to the east, particularly along the Mississippi River which is noted for its severe floods, to relieve them of their excess water by piping it, during times of excess, to the lakes along the Colorado River, which of late have been well below capacity?

[CliffordK]

Most of the Mississippi is almost at sea level.  It would certainly be much easier to purify than sea water, but you would still have to pipe it uphill to get it to Colorado/Arizona/NM, etc.  You would also have to deal with the continental divide, although I suppose you could make an aqueduct tunnel under the mountains.

There are some Eastern rivers that have a little more elevation including the Missouri and Arkansas rivers, although their flow would be much lower at their higher elevation headwaters. 

One advantage of the Midwest over the West is that it rains much more uniformly throughout the year, and thus the river flow would be more stable.

There is, however, a lot of suspicion about stealing another region's water. 

The idea of diverting during floods is interesting, but might still require some active transport, and, of course, oversizing the system for the pulses.  I suppose, if one took water out of the Missouri river at flood stage, that would still reduce pressure on the Mississippi, from St. Louis, and further south.

[Atomic-S (OP)]

As I recall, the Missouri did have a severe overload a winter or two ago, due to a major snowfall. At that time it would have been advantageous to divert some of it to the West. If considerations of elevation rule out using Mississippi water, an issue would be how frequently the Missouri or other suitably situated river would have a significant excess. It would have to occur with enough regularity to be useful. I don't know if it does.