(1) Whenever any public drain, established and constructed under this chapter or under any statute in force prior to June 18, 1918, empties into a natural drain, the natural drain, from the mouth of the public drain to the mouth of the natural drain, shall become to all intents and purposes a public drain, and subject to the supervision and control of the board.
(2) Whenever any obstruction exists in any natural drain which is an outlet for any public drain, as provided in subsection (1) of this section, and the removal of the obstruction is necessary, in the opinion of the board, for the successful operation of the public drain, the board may remove the obstruction, paying the cost out of funds collected from any district for which it is an outlet. If there is more than one (1), the expenses shall be prorated between them as the board considers equitable.