The dock board shall have power and it shall be its duty for and in behalf of any such municipality to prepare or cause to be prepared a comprehensive general plan for the construction and improvement of its harbor, water front, dock, and terminal facilities as it may deem necessary, to promote commerce and for the convenient and economical accommodation and handling of watercraft of all kinds and of freight and passengers, and the free interchange, receipt, and delivery of traffic between water and land transportation agencies. Such plan shall be filed in the office of the board and be open to public inspection, and may from time to time be changed, altered or amended by the board, as the requirements of shipping and commerce and the advance of knowledge and information on the subject may suggest. The board shall procure or construct such harbor, water front, dock, and terminal facilities in accord with such plan.