The project for flood control of the Yazoo River shall be as authorized by sections
642a,
702a–1,
702a–2 to
702a–12,
702g–1,
702j–1,
702j–2,
702k–1, and
702k–2 of this title, except that the Chief of Engineers may, in his discretion, from time to time, substitute therefor combinations of reservoirs, levees, and channel improvements; and except that the extension of the authorized project and improvements contemplated in plan C of the report of March 7, 1941, of the Mississippi River Commission are authorized, including the extension of the levee on the east bank of the Mississippi River generally along the west bank of the Yazoo River to a connection in the vicinity of Yazoo City with the Yazoo River levee, authorized by the existing project for protection against headwater floods of the Yazoo River system, and the adjustment in the discretion of the Chief of Engineers of the grades of the existing levees in the backwater area on the east bank of Yazoo River below Yazoo City, all at an estimated additional cost of $11,982,000: Provided, That the Chief of Engineers shall fix the grade of the extension levees along the Yazoo River, with higher levees in his discretion, so that their construction will give the maximum practical protection without jeopardizing the safety and integrity of the main Mississippi River levees: And provided further, That prior to the beginning of construction local authorities shall furnish satisfactory assurances that they will