At least from skimming the Abstract, the "National Water Grid" on that OSTI.gov page would be nothing resembling a "national grid". It could only move water from the Mississippi R. to the upper Colorado R. Ignoring the pumps...just the aqueduct that you'd need to build - ~1,400 miles long, with the capacity of a major river - would have zero political chance of being approved & funded.

And for a water grid that could absorb extreme events - upgrade the sizes of all the aqueducts and pumps by an order of magnitude or two. And then you've got to extend it to every spot you want to protect from extreme weather...