The board of supervisors of any district organized under sections 31-301 to 31-305 shall appoint some competent person to award all contracts contemplated in sections 31-301 to 31-369 to the lowest bidder, subject to the approval of the board of supervisors, except as herein otherwise provided, to be known as the drain commissioner. He shall hold his office for one year and until his successor is appointed and qualified. He shall have general superintendence of all works put under contract by the district, subject to the supervision and control of the board of supervisors. He shall report the same when completed according to the terms and stipulations of the contract, and certify the same to the board of supervisors, which shall review and accept or reject the work so completed. The drain commissioner shall, before entering upon the discharge of his duties, enter into bond with proper surety, subject to the approval of the board of supervisors, in any sum not less than two thousand dollars, nor more than ten thousand dollars, to the drainage district of which he shall be appointed, conditioned that he will faithfully and honestly perform all of the duties required of him by law, and deliver to his successor in office all instruments, papers, and documents that may have come to his hands by virtue of his office. He shall take and subscribe the oath required by section 31-308, which shall be endorsed upon his bond, and filed in the office of the county clerk of the county in which the district, or the greater part thereof, shall be situated.