Iowa Code § 28J.13

The board shall annually prepare a budget for the port authority. Revenues received by the port authority shall be used for the general expenses of the port authority and to pay interest, amortization, and retirement charges on money borrowed. Except as provided in section 28J.26, if there remains, at the end of any fiscal year, a surplus of such funds after providing for the above uses, the board shall pay such surplus into the general funds of the political subdivisions comprising the port authority as agreed to by the subdivisions.