Why can’t the US build infrastructure that automatically siphons water from flood zones to the west during flood seasons?

Question

Why can’t the US build infrastructure that automatically siphons water from flood zones to the west during flood seasons?

In: 4

Answer 1

Because 80% of the water in California goes to agriculture. And 10 to 12 % for watering lawns.

And Los Angeles sends it’s treated sewage water to the ocean instead of piping it back to spreading basins to recharge aquifers. (every US city on a river treats it’s sewage to drinking water standards before discharging into the river and the cities downstream make sure they do. )

So there is really no need for this massive project when they have not done other things to change water usage.