The Chief of Engineers, under the supervision of the Secretary of the Army, shall at the expense of the United States Government construct a system of levees substantially in accordance with general plan shown on map designated as sheet numbered 1 entitled "Tributary Levee Location Survey—White River Levee District—Proposed Levee Location" accompanying report dated April 2, 1925, and filed in office of First and Second Mississippi River Commission Districts, Memphis, Tennessee. The Chief of Engineers shall have the right to alter, change, or modify said plan as to the grades and levee sections: Provided, however, That no work shall be commenced on the above-mentioned project until the State, levee boards, or other responsible local interests have given assurances satisfactory to the Secretary of the Army that they will (a) provide without cost to the United States all rights-of-way necessary for the construction of said project; (b) provide drainage facilities made necessary by construction of levees; (c) acquire and provide without cost to the United States all flowage and storage rights and easements over, upon, and across the lands and properties within the protected area in the event it becomes necessary in the judgment and discretion of the Secretary of the Army or the Chief of Engineers to use said area, or any part thereof, for an emergency reservoir; (d) hold and save the United States free from liability for damages on account of the use of said area for reservoir purposes during said emergency.