Upon the adoption of the resolution mentioned in section 46-166, the board shall order that an election be held within the district to determine whether the boundaries of the district shall be changed as mentioned in the resolution, and shall fix the time at which such election shall be held, and cause notice thereof to be given and posted and published, and such election shall be held and conducted, the returns thereof shall be made and canvassed, and the result of the election ascertained and declared, and all things pertaining thereto conducted in the manner prescribed by section 46-194 in case of a special election to determine whether bonds of an irrigation district shall be issued. The ballots cast at the election shall have the words For change of boundary, or Against change of boundary, or words equivalent thereto. The notice of election shall describe the boundaries in such manner and terms that it can be readily traced; Provided, that in case contract has been made between the district and the United States as provided in section 46-126 or 46-156, no change shall be made in the boundaries of the district and the board shall make no order changing the boundaries of the district until the Secretary of the Interior shall assent thereto in writing and such assent be filed with the board of directors.