Okla. Stat. tit. 82 § 637
To maintain, operate and preserve the reservoirs, ditches, drains, dams, levees, canals or other improvements made pursuant to this act and to strengthen, repair and restore the same, when needed, and for the purpose of defraying the current expenses of the district, the board of directors may upon the substantial completion of said improvements and on or before the first day of October in each year thereafter, levy an assessment upon each tract or parcel of land and other property, upon corporate property, within the district subject to assessments under this act, to be known as a "Conservancy Maintenance Assessment". Said maintenance assessment shall be apportioned upon the basis of the total appraisal of benefits accruing for the original and subsequent construction, shall not exceed one percent (1%) thereof in any one year unless the court shall by its order find a necessity exists and authorize an assessment of a larger percentage, and shall be certified in duplicate to the county clerk of each county in which lands of said district are situated, said maintenance assessment shall be entered in the same book as general assessments but in a separate column, or in a separate book kept for the purpose of maintenance assessments and if in a separate book, it shall be entered in like manner and at the same time as the annual installment special assessment is entered. Said county clerk shall certify the same to the treasurer of the county at the same time that he certified the annual installment of the bond fund, and make return thereof and shall be liable for the same penalties for failure or neglect so to do, as may be provided herein for the annual installment of the assessment. The amount of the maintenance tax paid by any parcel of land shall not be credited against the benefits assessed against such parcel of land; but the maintenance special assessment shall be in addition to any special assessment that has been or can be levied against the benefit appraisal.
Okla. Stat. tit. 82, § 637