Natomas Basin Flood Protection Improvements Act of 2013 - Modifies the project for flood damage reduction, American and Sacramento Rivers, California, to authorize the Chief of Engineers to construct improvements to flood damage reduction facilities adjacent to those rivers in the vicinity of Sacramento, substantially in accordance with the report of the Chief of Engineers entitled "American River Watershed (Common Features) Project, Natomas Basin, Sacramento and Sutter Counties, California," dated December 30, 2010, at a specified cost.