(a) In order to meet preliminary expenses and to do the work, the board may issue the negotiable notes or bonds of the district, signed by the members of the board and bearing a rate of interest not exceeding six percent (6%) per annum. The board may pledge and mortgage all assessment of benefits for the payment thereof.
(b) No bonds issued under the terms of this chapter shall run for more than thirty (30) years, and all issues of bonds may be divided so that a portion thereof may mature each year as the assessments are collected or they may all be made payable at the same time with proper provisions for a sinking fund.
(c) The bonds shall not be sold for less than par value without the unanimous vote of the board.