Each acre of land in private ownership of said project is hereby charged with $95.25 of construction cost assessable thereto at the date hereof (Dec. 1, 1932), which sum is based upon 50,000 acres of such privately owned lands, making a total charge or assessment due from the owners thereof of $4,762,250 on this date (Dec. 1, 1932), excluding the cost of operation and maintenance for the calendar year of 1933 which may be carried into construction cost as provided for by section 3 of the act of June 7, 1924 (43 Stat. 476), and also excluding interest at the rate of 4 percent which is charged against such lands by said act. Of the 50,000 acres constituting the lands in private ownership within the said project only 46,107.49 acres have at this date (Dec. 1, 1932) actually been designated as coming within the project. Should this present designated area be not increased within a reasonable time herefrom and prior to the due date of the first installment of the charge fixed in this section, namely, on December 1, 1935, so as to bring the total designated area up to the 50,000 acres, the per acre charge fixed in this section shall be proportionately increased against the then designated area so as to assure reimbursement of the total indebtedness due the Government by the owners of the lands in private ownership from the lesser designated acreage.