If in the opinion of the board of drainage commissioners it would help the sale of the maintenance or improvement bonds, or they would deem it necessary under the provision of N.C. Gen. Stat. § 156-101, they may, with the approval of the clerk of the superior court, add to the amount estimated by the board of viewers a sufficient amount to pay off all outstanding obligations of the district, leaving this their only bond issue. (1923, c. 231, s. 5; C.S., s. 5373(e).)