Hm. Your numbers and mine don't match by a few orders of magnitude. I came up with 2.5GW sustained, which is (2.5GW * 24h * 365) 21900 GWh ~= 21TWh/yr. Big, but not the same as your value.

An acre foot is 1233 m^3, and at 3kWh/m^3, that's 3.7 MWh/acre foot. Math checks out so far.

Times 2000000, that's 7400000 MWh / 7400 GWh / 7.4 TWh.

I think you're off by a factor of 1000 somewhere in your math. You're looking at ~the output of a large nuclear plant, not 1000 of them.

Or my math is wrong. That's entirely possible too.