You are most certainly correct that existing infrastructure did not have a chance.
Neither would proposed advanced infrastructure, though it would have saved a % of the water for transport and alleviated some of the flooding.
This storm hit us so hard and so fast that the canal system never had a chance.
I'm sure you're aware of water-proof lining we see on Interstates for erosion.
Imagine this waterproof lining in the ditches between Interstate 17 from Phoenix to Flagstaff--and then along I-40 to Lake Mead.
I put this out there now because I'm working on it in RL and won't live forever, especially at 60-YOA.
Imagine your flood right now.
Now look at the Archimedes screw--a genius invention over 2,000 years ago that raises water from a lower level to a higher level.
And that these Archimedes screws could actually be mobile intrastate and interstate.
These Archimedes screws could be at work right now draining your floods into canals which could then be pumping water upwill.
All that is needed is energy pumps that are easy--not to mention we have Hoover Dam very close.
We have many other energies available--energy is not the problem.
Nor is water pipeline technology--available right now from oil pipelines.
My experience in the Southwest has shown me that Utah is a shining example of public/private ventures.
I fully support this idea and believe former Utah governors such as Huntsman would be invaluable .