The board of supervisors of said district shall have full power and authority to 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 said board of supervisors is hereby authorized and empowered to employ men and teams and to purchase machinery, employ men to operate same 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 plans adopted. They may, in their discretion, let the contract for such works and improvements either as a whole or in sections, and when such 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 such work and improvements, which contract shall be in writing and to which shall be attached and made a part thereof, complete plans and specifications of the work to be done and the improvements to be made under said contract, which plans and specifications shall be prepared by the chief engineer, and shall be incorporated in and attached to the contract, which contract shall be prepared by the attorney for the district, and before the work is commenced shall be approved by the board of supervisors and signed by the president of the board and 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 said board of all work done and improvements made and make such suggestions and recommendations to the board as he may deem proper; provided, however, that if and when the state of Missouri or the United States of America or any subdivision, department, division or agency thereof is willing to construct the works and improvements provided for in the plan for reclamation or any part thereof, the board of supervisors of said district is authorized to cooperate with such agency to the fullest extent and is hereby granted power and authority to accept any such work in aid of the project, irrespective of whether it be by way of grant of funds, labor, work, materials or otherwise and may, in the discretion of the board of supervisors, give such assurances as may be required to obtain the construction of the works and improvements provided for in the plan for reclamation.