Colo. Rev. Stat. § 37-31-153
After adopting a plan for a drainage system, the board of directors may give notice by publication in a newspaper published within said district, in two consecutive publications of said newspaper, and in such other newspapers as may be deemed advisable, calling for bids for the construction of said work or any portion thereof; if less than the whole, then the portion of said system to be constructed shall be described in the notice. The notice shall set forth where the plans and specifications may be seen and that sealed proposals will be received at the office of the drainage district and a contract let to the lowest responsible bidder, giving the time and place for opening the proposals, which, at said time and place, shall be opened in public. The board of directors may enter into a contract, subject to the provisions of section 37-31-119, with the lowest responsible bidder for the construction of the whole or any portion of the work mentioned in the notice, or may reject all bids and readvertise for proposals, or may proceed to construct the work under the supervision of the board of directors.
C.R.S. § 37-31-153