Whenever revenue bonds are issued and outstanding under this law, the entire revenue received from the operation of the harbor or facilities shall be deposited in a separate fund which shall be used only in paying the principal and interest of these revenue bonds and reserves therefor and the cost of maintenance, operation and depreciation of the harbor and facilities in such order of priority as shall be provided by the respective ordinances authorizing revenue bonds, provided, however, no priority accorded by such an ordinance may be impaired by a subsequent ordinance authorizing revenue bonds unless specifically so permitted by a covenant of the kind authorized to be included in an ordinance by Section 11.1-7. Such revenue in excess of requirements for payment of principal of and interest upon these bonds and reserves and for payment of cost of maintenance, operation and depreciation of the harbor and facilities may be used for rehabilitation of the harbor and facilities, necessary reconstructions and expansion, construction of new facilities or for retirement of any outstanding bonds issued for harbor purposes. After all such bonds have been paid, such revenues may be transferred to the general corporate fund of the park district and be used for the maintenance, operation, repair and development of the harbor or facilities or for any corporate purpose.