Kimberly Polk sits on a park bench with the New Orleans skyline visible across a stretch of water behind her. She is holding a picture of her daughter, Serena, who drowned in the flood that followed Hurricane Katrina.

The five-year-old was staying with her father in New Orleans when the storm struck in August 2005. Her body was found eight months later, under debris. "She came to me in a dream and said `Mamma, I'm falling,'" recalls Polk, sobbing. "All I could see was water that she was falling into... I never got a chance to say goodbye."