The Secretary of the Interior is authorized and directed to, and he shall, promulgate charges, or the basis of computation thereof, for electrical energy generated at Hoover Dam beginning June 1, 1937, computed to be sufficient, together with other net revenues from the project, to accomplish the following purposes:

(a) To meet the cost of operation and maintenance, and to provide for replacements, of the project beginning June 1, 1937;

(b) To repay to the Treasury, with interest, the advances to the Colorado River Dam Fund for the project made prior to June 1, 1937, within fifty years from that date (excluding advances allocated to flood control by section 617a(b) of this title, which shall be repayable as provided in section 618f of this title), and such advances made on and after June 1, 1937, over fifty-year periods;

(c) To provide $600,000 for each of the years and for the purposes specified in section 618a(c) of this title;

(d) To provide $500,000 for each of the years and for the purposes specified in section 618a(d) of this title; and

(e) To provide, by application of the increments to rates specified in section 403(c)(2) of the Colorado River Basin Project Act of 1968, as amended and supplemented [43 U.S.C. 1543(c)(2)], revenues, from and after June 1, 1987, for application to the purposes there specified.

Such charges may be made subject to revisions and adjustments at such times, to such extent, and in such manner, as by the terms of their promulgation the Secretary shall prescribe.