There are authorized to be appropriated to the Department of State for the use of the Commission, out of any money in the Treasury not otherwise appropriated, such sums as may be necessary to carry out the provisions of the Treaty of February 3, 1944, and other treaties and conventions between the United States of America and the United Mexican States, under which the United States Section operates, and to discharge the statutory functions and duties of the United States Section. Such sums shall be available for construction, operation and maintenance of stream gaging stations, and their equipment and sites therefor; personal services and rent in the District of Columbia and elsewhere; services, including those of attorneys and appraisers, in accordance with the provisions of section 3109 of title 5, at rates for individuals not in excess of the maximum daily rate for grade GS–15 of the General Schedule and the United States Commissioner is authorized, notwithstanding the provisions of any other Act, to employ as consultants by contract or otherwise without regard to chapter 51 and subchapter III of chapter 53 of title 5, and the civil-service laws and regulations, retired personnel of the Armed Forces of the United States, who shall not be required to revert to an active status; travel expense, including, in the discretion of the Commissioner, expen