Some communities in the U.S. heartland are taking a more natural approach to preventing the kinds of floods that have devastated the region in recent years. For more than a century, flood control has relied mostly on man-made structures such as levees and walls to keep rivers in place. As climate change brings more extreme weather, the new idea is to let rivers behave more naturally. It means keeping some waterfront areas vacant or using them as parkland so no great harm is done when the rivers overflow.  In rural areas, officials are considering moving levees farther back to give rivers more room to roam.