Oregon Revised Statutes Water Resources: Irrigation, Drainage, Flood Control, Reclamation § 545.391

(1) When a contract has been made with the United States, in addition to the amount determined and apportioned as provided in ORS 545.381, 545.385, 545.387 and 545.389, the board shall also fix the amount payable by each tract within the district, in accordance with the federal reclamation laws and the public notices, orders and regulations issued under the federal reclamation laws and in compliance with any contract made by the United States with the owners of the lands and with the contracts between the district and the United States. When the contract lands having a partial water right or partial rights in a system of irrigation, or irrigation and drainage, appurtenant to the lands, the amounts payable shall be according to the benefits to the lands, making due allowances for existing rights. The amounts so determined, fixed and apportioned shall constitute an assessment upon the lands of the district.

(2) In irrigation districts which enter into a contract with the United States providing for the payment of charges to the United States upon the basis authorized by the Act of Congress of December 5, 1924, entitled “An act making appropriations to supply deficiencies in certain appropriations for the fiscal year ending June 30, 1924, and prior fiscal years, to provide supplemental appropriations for the fiscal year ending June 30, 1925, and for other purposes,” annual levies of assessments for the purpose of making payment to the United States under the contract may be made by the board on the basis provided for in that Act and the contract, either before or after judicial confirmation of apportionment of benefits. In such districts annual levies for the purpose of making construction payments to the United States may be made on the basis of the gross average annual acre-income of the lands of the district or divisions of the district, or classes of lands in the district, as such gross average annual acre-income is determined by the Secretary of the Interior, until the amount apportioned against each tract has been fully paid.