The regional planning director shall be the chief administrative and planning officer and technical adviser of the board. The director shall, subject to the supervision of the board:
(a) Direct and administer the preparation, maintenance, regular review and revision of the regional plan, and administer and execute all of the other functions and duties of the district set forth in this chapter.
(b) Appoint and remove personnel of the district.
(c) Serve, or designate personnel to serve, as executive secretary to the board.
(d) Perform such other duties and exercise such other powers as the board may delegate to him.