70 ILCS 605/11-12

A judgment fixing the amount of annual benefits between the parties constitutes the measure of liability between them for the repair, maintenance and operation of the work for which such judgment was given and any amounts coming due thereunder shall be payable at such times as the court may direct. The judgment for such benefits may, however, be modified or set aside upon the application of either the plaintiff or the defendant when circumstances have so changed as to make the judgment inequitable or unjust as to either party.