Sections 323 to 328 of this title shall not in any manner amend or repeal the provisions of the Federal Water Power Act of June 10, 1920 (41 Stat. 1063), as amended by the Act of August 26, 1935 (49 Stat. 838) [16 U.S.C. 791a et seq.], nor shall any existing statutory authority empowering the Secretary of the Interior to grant rights-of-way over Indian lands be repealed.