Sec. 12. (a) The initial drainage commissioners serve for terms designated by the board of commissioners of the county as follows:
(1) One (1) drainage commissioner for one (1) year.
(2) One (1) drainage commissioner for two (2) years.
(3) One (1) drainage commissioner for three (3) years.
(b) Upon the expiration of the initial terms, the board of commissioners of the county shall appoint successors for terms of three (3) years.