Houston - Floodwaters have breached a levee south of the city of Houston, officials said on Tuesday, urging residents to leave the sector immediately."The levee at Columbia Lakes has been breached!!" the Brazoria County government tweeted on its official feed. "GET OUT NOW!!"The Columbia lakes area lies south of Houston, large parts of which remain under water four days after Harvey made landfall on the US Gulf Coast, triggering widespread flooding.