The net proceeds of such sales after deducting all expenditures on account of such lands, and the project construction charge, for the irrigable area of the lands so sold where irrigation or drainage works have been constructed or are proposed to be constructed, shall be disposed of as provided in section 501 of this title. Where the project construction charge shall not have been fixed at the date of any such sale, same shall be estimated by the Secretary of the Interior.
(Mar. 2, 1929, ch. 541, §2,