(1) The board of improvement shall have control of the construction of improvements of the district.
(2) The board may: Advertise for proposals for doing any work by contracts and may accept or reject any proposals;
(3) Appoint all necessary agents and engineers for carrying on the work and making plans herein provided and may fix their pay;
(4) Buy all necessary material and implements;
(5) Sell any such material or implements as may be on hand and which may not be necessary for the completion of the improvement under way or which may have been completed; and
(6) In general, make all contracts in the prosecution of the work as may best subserve the public interest.