From the NASA image it looks like the whole area is a flood plain. Similar to a large area of the Los Angeles basin. We have a paved riverbed system to get rid of water from heavy rains which periodically occur. I assume Pakistan doesn't have the resources to do something like that.
You have a paved riverbed system to get rid of moderate rains which periodically occur.
That will be insufficient for a 100-year flood (~1000 acres underwater by current mapping), and a 200-year or 500-year flood would put significant fractions of the city underwater.
