The administrative authority over municipally owned utilities shall be vested in a Board of five (5) members elected at large. The term of office of a member of the Board shall be four (4) years. At the Municipal election in the calendar year of 1951 five (5) members shall be elected to the Board; the three (3) who receive the highest number of votes shall be elected for a term of four (4) years, and the two (2) who receive the next highest number of votes shall be elected for a term of two (2) years. Thereafter, members shall be elected for a term of four (4) years to fill vacancies caused by the expiration of terms of members of the Board as they may occur.