computer flood models don't include looting, police walking off the job, an incompetent governor, and a breakdown in civil order.
Actually it did: From the report:
It predicted that 200,000 people or more would be unwilling or unable to heed evacuation orders and thousands would die, that people would be housed in the Superdome, that aid workers would find it difficult to gain access to the city as roads became impassable, as well as many other of the consequences that actually unfolded after Katrina hit this week.