Still in my test moment to dig out what is doable or not in SH (actually on r 2513). Today the goal was to carve a moat on a big scale joining several lakes in one step with instant mining and see if the system could handle it.
So yes it’s doable, you can see in the far the moat all around the future city:

BUT don’t do it in one shot, it will bring the lua to 99,9% during a very, very, verrrrrry long time. I guess the flooding code isn’t optimal yet specially with several “sources” to stabilize…