The only people who needed to evacuate were those in likely flood zones. Evacuation of the entire city of Houston is not realistic, but specific areas could have been evacuated.

I live in SOCAL and for wildfires you only evacuate areas under direct threat -- wind conditions and fuel. In the case of Houston, it was known that Harvey would be a major rain event. City officials should have known which parts of Houston were prone to flooding and acted accordingly. They told everyone to shelter in place.

This is why people learn to disregard city officials. They totally blew it and now they are trying to justify their decision with talks of how it's impossible to evacuate the entire city.