I assume cutting a trench is far cheaper than making the massive pipes that would be needed to move that amount of water.

But I would be interested to see how a solar panel covering compares economically to some other, cheaper setup.

I was wondering, but "earthquakes" perhaps. It's much easier to fix a canal, even with some of the water flowing.

There's a cost to pipes, but at least part of that would be offset by the structural support for the solar panels and the fact that you need to pipe less waters. Also I assume that the canals are lined in some way. I don't know, maybe the canals are just prettier to look at?

A similar problem is plaguing the Aral sea. The Amu Darya river is being drained by ineffective and leaky canals.

These canals are the size of rivers. They are hundreds of miles long.

Building a solar roof is going to be orders of magnitude cheaper, and the pipes wouldn't generate electricity.