LOL - yeah well I guess there is that....
What is really needed is a 60 to 65 foot deep channel that is 120 feet wide. Not a whole lot of places qualify for that. But I'm sure your solution would work very well.
Well, I know people go crazy thinking about radiation but if the blast is deep enough the top of the subsurface fireball would never even get close to the water's depth AND the rock would compress the fallout into a nice thin black line somewhere DEEP underground.