Upon the filing with the secretary of the board of commissioners of a certified copy of the decree of the court, the board of commissioners of the district may reclaim the district or sub-district, in accordance with the plan for reclamation, and build, construct, excavate, and complete all or any works and improvements which may be needed to carry out, maintain and protect the plan for reclamation.  To accomplish that end, the board of commissioners may employ men and teams and purchase machinery, employ men to operate the machinery, and directly have charge of and construct the works and improvements, or by the use of other or more efficient means than provided for in the plan adopted.  They may, in their discretion, let the contract for the works and improvements either as a whole or in sections, and when the contract or contracts are let, they shall be advertised and let to the lowest and best bidder, who shall give a good and approved bond, with ample security, conditioned that he will well and promptly carry out the contract for the work and improvements, and further conditioned as may be otherwise provided by law.  The contract shall be in writing and complete plans and specifications of the work to be done and the improvements to be made under the contract shall be attached to and made a part of the contract.  The contract shall be prepared by the attorney for the district, and before the work is commenced shall be approved by the board of commissioners, signed by the president of the board and by the contractor, and shall be executed in duplicate.  The chief engineer shall be the superintendent of all the works and improvements, and shall, whenever required, and at least once each year, make a full report to the board of all work done and improvements made and make the suggestions and recommendations to the board as he may deem proper.