The income and revenue derived or to be realized from the harbor improvement acquired or to be acquired from the proceeds of the bonds shall be deposited in a special fund and kept separate and apart from all other revenues of the district. It shall be applied, firstly, to the creation of an interest fund, herein designated as “interest fund,” for the payment of the annual interest due or to become due upon the bonds during the next ensuing fiscal year and before the time for the fixing of the next general tax levy in the county in which the district is located.