In any case in which it may be necessary or advisable in the execution of an authorized work of river and harbor improvement to exchange land or other property of the Government for private lands or property required for such project, the Secretary of the Army may, upon the recommendation of the Chief of Engineers, authorize such exchange upon terms and conditions deemed appropriate by him, and any conveyance of Government land or interests therein necessary to effect such exchange may be executed by the Secretary of the Army: , That the authority granted to the Secretary of the Army shall not extend to or include lands held or acquired by the Tennessee Valley Authority pursuant to the terms of the Tennessee Valley Authority Act [ et seq.]. This section shall apply to any exchanges heretofore deemed advisable in connection with the construction of the Bonneville Dam in the Columbia River.16 U.S.C. 831Provided further