Back when I sent in like a 200 page 'please may I' suggestion form on F4, I included a request for Destructor conversions for mining not only rivers but all roads that had been prerototilled with B-52 long-line strikes.
This gives you an 'influence' on further traffic/repair actions (including pontoon and vehicle launched bridges) even when you're not around. Area Denial/Traffic Denial of just this type was in fact practiced along the HCM Trail in South East Asia and yes, it does work.
Now about tanks underwater...
Everything I've read says "Yes Dorothy, it comes with a snorkel and here's a cross to stick in it". Fording to a depth of about 1.4 meters is possible but underwater passage gets you flooded 90% of the time and ultimately takes as much prep time as just waiting on the engineers (should be in-column or on an associated road if the group commander is smart).
APC/IFV do a /little/ better with 'swim trunks' and a light-hollow aluminum body but even here there are CG and overskirt waking problems that drowned like four out of five Bradleys tested.
Nowadays you would probably dump the bridge with a JDAM or ground demo charge, send in a nightflight with mines to make the bridging effort difficult and then seed the opposite-side embankment with GATOR or WAAM type screening curtains or even leave-behind teams of Sniper and/or Mortar-ATGW special forces.
This assumes that your Sensor Fuzed Weapon and JSOW/WCMD were unable to stop the advance in-place using direct attack.
IMO, that kind of overwhelming force ratio is what you would expect from a WARPAC level opponent, not Korean; channelization effects be hanged.