That seems a very risky assumption for any car (self driving or human driver) during flash floods. "Turn around don't drown":
You think you know how deep it is under because you've taken that road many times before (or in your case you have historical laser measurement)
But you don't know:
- Maybe the road under fully collapsed
- Maybe the flow of water is extremely strong, so you need to accurately estimate that too.
I more meant that it could maybe see a significant difference in the road, and know to take caution, not to try to gauge the depth of a submerged roadway.
Flow should be able to be done with vision, radar can as well: some bridges use surface flow monitoring radar.