[DB]

The Mississippi is significantly higher in elevation (I believe). They can pump it out quicker into the lake.

[sefarkas]

The pump/canal system for Jefferson and Orleans parishes is set up to lift water from behind the levees into the lake. The pump stations have several pumps each, similar to circulating water pumps (in size) at a power plant. The 17th St Canal is a discharge flow path for one of the pumping stations.