The board of a contracting district, within 30 days after execution of a reclamation contract or within 30 days after the effective date of this act, whichever date is the later, shall by resolution determine and establish an apportionment of the annual assessments to be thereafter made from year to year against the real property within the district between Class “A” property and Class “B” property as in this act defined, providing in such resolution the percentage or fractional part of such total annual assessments thereafter to be levied in accordance with Section 8 [73-18-8 N.M. Stat. Ann.] of this act which shall be apportioned to Class “A” property and that which shall be apportioned to Class “B” property. The action of the board of directors in establishing such apportionment shall be subject to the approval of the secretary of the interior and after the same shall have been approved shall be submitted to the conservancy court for judicial examination, approval and confirmation of such action as in Section 20 [73- 18-20 NMSA 1978] hereof provided. Such apportionment may be modified in like manner from time to time thereafter, but not more frequently than once in every five years, and no such modification or reapportionment shall become effective until the same shall have been first approved by the secretary of the interior nor until such proposed reapportionment shall thereafter have been judicially examined, approved and confirmed by the conservancy court in the same manner as the original apportionment.