Do they really have to be that deep?
In order to accommodate the wife I use the FEL to carve out very slight 'U' grooves in our gravel driveway. You can hardly notice them when it's dry...and walk over them without any impedance. slight as they are they channel water out of way very efficient.
Just flip the bucket down , apply some downward pressure and slowly back up. I do this all over the back yard too...up here we call 'em 'swale holes' or ditches. Very gently sloping, easily accommodating to all wheeled vehicle traffic. A minimum effort to redirect drainage.
TSC does have a double furrerer, ditcher, 3PH attachment