This act shall be construed as applying to districts organized for the purpose of providing and maintaining flood protection, river control, drainage, water storage for supplementing irrigation needs, constructing and maintaining distribution systems for irrigation; and other improvements for public health, safety, convenience and welfare either in cooperation with the United States government or any department thereof under federal laws, or to districts organized for the purpose of making such improvements under the powers in this act contained; but the provisions hereof shall not apply to or affect irrigation or drainage districts heretofore organized under any other laws of this state.