S.D. Codified Laws § 46A-10A-75
At any time after adopting a drainage plan or other official control, a board may construct drainage or let contracts for its construction. A contract may be for construction of an entire drainage project, for any portion thereof, or for material and labor separately, and the contract shall be let by competitive bid. A board may reject any bid. The lowest responsible and capable bidder shall be accepted. If a responsible and capable landowner affected by the project submits one of several low bids, the landowner shall be given contract preference. If a contract is let, the contractor shall post a bond in the amount of the contract, conditioned on faithful performance of the contract and full completion of the contract to the satisfaction of the board. For purposes of bids on a proposed project, all plans and specifications for the project shall be filed in the office of the county auditor. If, in the judgment of the board, the entire project or any part thereof can be constructed for less money than the amount of the lowest bid submitted, the board may hire the necessary labor and purchase the necessary material for the construction without letting contracts, the provisions of chapters 5-18A and 5-18B notwithstanding.
SDCL 46A-10A-75