Houston is facing 3 issues.... 1) Upstream, there are hundreds if not thousands of residences built on land that is on higher ground behind the dams, but below the level of the overflow spillways. The government didn't buy all the land contained within the reservoirs and developers were happy to cover it with homes and apartments.  2) Upstream, far behind the dams, what used to be miles of prairie land that could soak up rainfall is now concrete and rooftops that send it downstream faster.  Experts had warned for years that reservoirs would fill faster and build higher. 3) Downstream, homes built in the 60's and 70's never expected to be sacrificed in the middle of the night.  Expectation was that the dam was protection for them and what has occurred upstream has effectively removed that protection.  I'm not sure of the solution, but this is probably not the last time Houston will face this issue.