Sec. 26. With respect to bonds for which a pledge has been made under section 25 of this chapter, the general assembly covenants with the holders of these bonds that:
(1) this chapter will not be repealed or amended in a manner that will adversely affect the imposition or collection of the user fees under this chapter; and
(2) this chapter will not be amended in a manner that will change the purpose for which revenues from the user fees imposed under this chapter may be used;
as long as those bonds are outstanding.