In levee and drainage districts having pumping stations trustees shall hold office until the fourth Saturday in January three years after election. On the third Saturday in January of each year a trustee shall be elected for a term of three years to succeed the member of the board whose term will expire on the following Saturday. At the election there shall also be elected, if necessary, a trustee to fill any vacancy which occurred before the election. [S13, §1989-a52e; SS15, §1989-a52d; C24, 27, 31, 35, 39, § 7693; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §462.20 ] 83 Acts, ch 101, §99 ; 89 Acts, ch 126, §2 CS89, §468.519