Pub. Contract Code, § 21623

The board shall also have the right to reject any and all bids and readvertise for new bids, or by a two-thirds vote may elect to undertake such work by force account. When no proposals are received pursuant to advertisement therefor, or when the estimated cost of such work does not exceed the sum of five thousand dollars ($5,000), or when the work consists of channel protection, maintenance work, or emergency work necessary in order to protect life and property from impending damage, the board may, without advertising for bids therefor, have such work done by employees of the district by day labor under the direction of the board, by contract, or by a combination thereof. The district shall have the power to acquire in the open market without advertising for bids therefor, materials, equipment, and supplies for use in any work or for any other purpose; provided, however, that materials and supplies for use in any new construction work or improvement, except work referred to in the preceding sentence, may not be purchased if the cost thereof exceeds five thousand dollars ($5,000) without advertising for bids and awarding the contract therefor to the lowest responsible bidder.