The levee low points on the lake are 13', so the lake isn't higher than 13'. The dome is just above sea level, so the water shouldn't get up to the 2nd level of the dome, where the lines to get in were on Sunday.
How would they get the people out of the dome - I think it would be better to move them to buildings where helicopters can air lift them out from the roofs if needed. You cannot do that from the dome I don't think - but I could be wrong.