Sec. 4. EXCLUSIVENESS OF PROVISIONS. Only the provisions of this Act and of Articles 1667, 1672, and 1673 of the Revised Civil Statutes of Texas of 1925, shall apply in counties having a population of not less than eighty-three thousand (83,000), and not more than eighty-three thousand, three hundred and fifty (83,350), according to the last preceding Federal Census, which contain Navigation Districts, Water Improvement Districts, and Water Control and Improvement Districts.