After June 30, 1972, no drainage ditches or other improvements shall be initiated under the provisions of sections 31-101 to 31-134. All drainage ditches or other improvements which have been approved as provided for by section 31-107 before July 1, 1972, shall not be affected by this section, and the legality of any such ditch or other improvement shall not be subject to any legal action based upon this section. Attempted initiations of drainage ditches or improvements under sections 31-101 to 31-134 which have not been completed before July 1, 1972, shall be null, void and of no effect.