When the work contemplated by the original or any supplemental reclamation plan is completed, the board may so report to the board of supervisors, and petition the board of supervisors to appoint valuation assessment commissioners.

The report and petition shall state that the work contemplated by the original or supplemental reclamation plan is completed, and that hereafter the district will only require funds for the maintenance, repair and operation of the reclamation works, or construction of works supplemental thereto or in replacement thereof.

Upon receipt of the report and petition the board of supervisors shall appoint three valuation assessment commissioners who shall qualify in the manner provided in Section 51230.

The commissioners shall view and fix upon the district land an assessment valuation per acre for each parcel which is in proportion to the benefits to be derived from the continuance in operation of the district reclamation works.

The commissioners shall prepare an operation and maintenance assessment roll in duplicate containing the following information in separate columns:

In preparation of the operation and maintenance assessment roll, the commissioners may, as one of the means of determining the assessment valuation per acre of each parcel, establish a base value per acre for each parcel of land according to the land use category or type of land use category for the parcel as reflected on the records of the county assessor. The base value may be adjusted to reflect the benefits derived by the parcel from continuance in operation of the district reclamation works in accordance with the benefit formula adopted by the commissioners. If land use categories are utilized by the commissioners, they shall file, with the operation and maintenance assessment roll, a report describing the basis for identifying the categories or category types utilized in establishing the assessment valuation per acre and the basis for future adjustment of that valuation, pursuant to Section 51346.5, to reflect changes in the land use category or type of land use category shown for each parcel on the records of the county assessor.

No error in the name of the owner or supposed owner of any parcel assessed, and no error in any other particular, shall render the assessment thereof invalid.

The assessment valuations shall be used as a basis for levying assessments against the parcels described in the operation and maintenance assessment roll for the purpose of raising funds for the maintenance, repair and operation of the district reclamation works, the payment of incidental expenses thereof, and for the construction of reclamation works supplemental to, or in replacement of, those already possessed, when in the opinion of the board, such works are necessary for carrying out the original or any supplemental plan of the district.

The operation and maintenance assessment roll shall be filed in the office of the clerk of the board of supervisors in the same manner as a report made under an original, supplemental or additional plan of reclamation.

Operation and maintenance assessment rolls adopted by any district prior to September 19, 1939, may be used for any or all of the purposes provided for in this article.

Upon receipt of the operation and maintenance assessment roll the board of supervisors shall appoint a time when it will meet for the purpose of hearing objections thereto.

No objection to the assessment valuations shall be considered by the board of supervisors, or allowed in any other action or proceeding, unless the objection is made in writing to the board of supervisors before the date of the hearing.

Notice of the hearing shall be given in the same manner and for the same time as the notice of the hearing of objections to an original assessment.

At the hearing, the board of supervisors shall hear any evidence offered in support of the written objections and may modify or amend the assessment valuations.

The board of supervisors shall then make an order approving the assessment valuation or any modification thereof and shall endorse the order on the assessment roll. The endorsement shall be signed by the chairman of the board of supervisors and attested by the clerk thereof.

The decision of the board of supervisors in approving the assessment roll is final, and thereafter the endorsed assessment roll is conclusive evidence that the assessment valuations were determined and fixed according to law, except in an action commenced pursuant to Section 51333.

Within 30 days after an operation and maintenance assessment roll is approved by the board of supervisors, any person aggrieved by the decision may commence an action in the superior court of the principal county to have the assessment valuations corrected, modified or annulled.

If the action is not commenced within 30 days after approval of the operation and maintenance assessment roll, no action or defense shall thereafter be maintained attacking the legality of the assessment valuations therein.

When the board determines that it is necessary to raise any sum for a purpose specified in Section 51326 it shall, by order entered in its minutes, state the total amount necessary to be raised and fix a rate designating the number of cents to be levied on each one hundred dollars ($100) of assessment valuation shown on the operation and maintenance assessment roll.

In the event the assessment for any parcel of land separately assessed, based upon the rate fixed pursuant to Section 51335, is less than twenty-five dollars ($25), a minimum assessment may be set by the board at an amount determined by the board to be adequate to defray the cost of collecting each minimum assessment, but which shall not exceed twenty-five dollars ($25) for each separately assessed parcel of land.