Subject to the written assignment, consent, and approval of the drain commissioner administering a county drainage district or the written assignment, consent, and approval of the drainage board of an intercounty drainage district, the county drain commissioner and the drainage board of intercounty drainage districts may grant unto the United States or to any irrigation district the right to use all the easements and rights-of-way conveyed to their respective drainage district or to any county lying wholly or in part in such districts for the construction, use, and maintenance of any county or intercounty drain by the United States or any irrigation district in connection with any irrigation project undertaken by the irrigation district, solely or in cooperation with the United States or any other federal department or agency. Private rights of persons acquired by reason of the establishment and construction of the drain or part of the drain shall not be interfered with or in any way impaired by the use of the drain for irrigation purposes within the scope of this part.