NEW ORLEANS — A federal judge ruled Wednesday that the Army Corps of Engineers’ failure to properly maintain a navigation channel led to massive flooding in Hurricane Katrina. U.S. District Judge Stanwood Duval sided with five residents and one business who argued the Army Corps’ shoddy oversight of the Mississippi River-Gulf Outlet led to the flooding of New Orleans’s Lower Ninth Ward and neighboring St. Bernard Parish. He said, however, the corps couldn’t be held liable for the flooding of eastern New Orleans, where one of the plaintiffs lived. Duval awarded the plaintiffs $720,000, or about $170,000 each, but the decision should give more than 100,000 other individuals, businesses and government entities a better shot at claiming billions of dollars in damages.