The county engineer shall make written requisition to the county purchasing agent for all materials, machinery, equipment, and necessary supplies needed for the construction, maintenance, or repair of the public roads, bridges, and ferries of Butler County. The requisitions shall be filed and presented by the chair to the commission at its next meeting, for the approval of the commission. The county purchasing agent may make purchases without first obtaining the approval of the Butler County Commission if in the judgment of the engineer, the delay caused by this procedure may cause an unnecessary and harmful interruption in the operation of the county road system. The purchases shall be made in accordance with prevailing law. The county purchasing agent shall be solely responsible and accountable for purchasing the materials, machinery, equipment, and supplies under the approved requisitions and shall report these monthly to the Butler County Commission.