Whenever revenue bonds are issued under Section 15.1 of this Act, all revenue derived from the operation of the specified land or facilities shall be set aside as collected and shall be deposited in a separate fund designated as the “Revenue Bond Fund” of the conservancy district. This fund shall be used only in paying the cost of operation and maintenance of the facility, in providing an adequate depreciation fund, and in paying the principal of and interest upon the revenue bonds issued under Section 15.1.