The board may order in the resolution of intention that all or part of the cost of any work be paid from the treasury of the flood protection district from the fund it designates when so ordered. The board, in making up the assessment, shall first deduct from the whole cost such part as has been ordered paid from the treasury or other source of monies and assess the remainder of the costs and expenses proportionately, according to the benefits received, on the lots, acres and parcels to be assessed for the work.
A.R.S. § 48-2840