This Subpart and all other statutes authorizing levee districts and levee and drainage districts in the state to levy and collect taxes and local contributions or to issue bonds shall not be repealed or modified to the detriment of the bonds authorized by this Subpart, and it is hereby declared that this obligation not to repeal or modify these laws shall be binding upon the state and shall be and form a part of the contract evidenced by the bonds.
La. R.S. § 38:459