The board of directors of the Grand Valley drainage district shall, in accordance with the schedule prescribed by section 39-5-128, C.R.S., certify to the board of county commissioners a statement showing the aggregate amount which, in the judgment of said drainage board, is necessary to raise from the taxable property of said district to create a fund for any of the purposes of said district. It is the duty of the board of county commissioners to levy, at the same time that other taxes are levied, such rate as will produce the aggregate amount so certified.
C.R.S. § 37-31-141