Perhaps something the New Orleans government should consider...

[Amianthus]

Apparently Tokyo is subject to flooding a number of times every year. So, they built what is, in essence, an underground river that leads out of the city to an underground storage tank. This river is normally dry, but when the city is innundated with water, it can handle 100 million gallons of water is a short period of time. They built an underground storage tank (picture below) that can fill to hold the runoff, and then they slowly (slow in this case being a relative term) feed the water via pump into the bay.

http://japansugoi.com/wordpress/worlds-largest-underground-waterway-is-tokyos-g-cans-project/

[Plane]

Apparently Tokyo is subject to flooding a number of times every year. So, they built what is, in essence, an underground river that leads out of the city to an underground storage tank. This river is normally dry, but when the city is innundated with water, it can handle 100 million gallons of water is a short period of time. They built an underground storage tank (picture below) that can fill to hold the runoff, and then they slowly (slow in this case being a relative term) feed the water via pump into the bay.

http://japansugoi.com/wordpress/worlds-largest-underground-waterway-is-tokyos-g-cans-project/

There would have to be somewhere downhill from NewOrleans , and there isn't.

I can imagine  huge salt dome being evacuated and used as a dry well or cystern for excess water to be dumped into which could be empyed again wen the eather became mild again , but how big would his tank have to be to contain the Surgeing Gulfof Mexico?

[Amianthus]

There would have to be somewhere downhill from NewOrleans , and there isn't.

There isn't anywhere downhill from Tokyo, either. That's why the built it under the city.