Half the city was built on the flood plain only made possible after the river was contained. Periodic storms like this, the river would just cut a new path to the beach. Things might be able to be done to please the tree huggers but it would cost a furtune for the studies on how to do it never mind doing it.
Could you imagine if they wanted to build Hoover dam today. I dont think we could do that again in just 5 years.