captions by vitac www.vitac.com hello. you re in the cnn newsroom this saturday, may 14th, i m fredricka whitfield. saving two of louisiana s biggest cities at the sacrifice of flooding homes and farmland. that s what will likely happen as the u.s. army corps of engineers opens the morganza spillway beginning an hour from now. while opening the gaelts would slowly divert floodwaters from baton rouge and new orleans, areas in yellow could get up to 20 feet of water, in green up to 15 feet. the morganza spillway hasn t been opened in nearly 40 years. but for the u.s. army corps of engineers, it s a necessary move to protect major cities. they re going to open it slowly so people and wildlife are not caught by surprise. there s a slow opening for a lot of reasons. one is from an engineering perspective. the water will come out of here pretty quickly. you don t want to scour the back side of this structure. from an environmental perspective, ofb yous think there are lots