The term of office of the members of the committee is three years. Appointment of the first members of the committee shall be so made that the terms of office of three of such members, of which one shall be a public member, shall expire at the end of one year, four at the end of two years, and four at the end of three years. Thereafter appointments shall be for full three-year terms. Any vacancies which occur during an unexpired term shall be filled by appointment for the unexpired term.