This subchapter shall be construed to be cumulative to existing laws relating to levee districts, drainage districts, or levee and drainage districts and shall not repeal any existing law unless the law is in direct conflict herewith. It is the purpose of this subchapter to permit consolidation by any levee district, drainage district, or levee and drainage district of the duties, obligations and purposes for which the district was originally created with those assumed by it under the provisions of subchapter 2 of this chapter and amendments thereto and not to eliminate the method by which levee districts, drainage districts, or levee and drainage districts, may enter contracts with the United States of America, the Secretary of the Army, the Chief of Engineers of the United States Army, or any other federal agency regarding the construction, operation, and maintenance of flood control and drainage works within the district.