It shall be the duty of the port commission of any port district, before creating any improvements hereunder, to adopt a comprehensive scheme of harbor improvement in the port district, after a public hearing thereon, of which notice shall be published once a week for two consecutive weeks in a newspaper of general circulation in the port district, and no expenditure for the carrying on of any harbor improvements shall be made by the port commission other than the necessary salaries, including engineers, clerical and office expenses of the port district, and the cost of engineering, surveying, preparation and collection of data necessary for the making and adoption of a general scheme of harbor improvements in the port district, unless and until the comprehensive scheme of harbor improvement has been so officially adopted by the port commission.