In any case where the board of drainage commissioners of any drainage district have issued or may issue bonds for the purpose of constructing or completing the drainage works in such district, the payment of which at maturity would in the judgment of the board of drainage commissioners be an unreasonable burden on the owners of the lands in such district assessed for the payment of such bonds and interest, or if it shall appear for other good and substantial reasons that the welfare of the district and the owners of lands therein would be promoted thereby, the board of drainage commissioners shall have the power to refund such bonds, or any part thereof, and issue new bonds equal to the amount of bonds outstanding and unpaid, or any part thereof. The new or refunding bonds shall bear a rate of interest not exceeding six percent (6%) payable semiannually, and shall be divided into such annual installments not exceeding ten percent (10%) and not less than five percent (5%) of the outstanding bonds so refunded. The new assessments shall be levied and collected with which to pay the principal and interest on the bonds in the manner provided by law. The first installment of principal on the bonds so refunded may be made payable at a certain date in the future not exceeding six years from the date of the refunding bonds, and in the meantime annual assessments shall be levied and collected for the payment of the interest. (1917, c. 152, s. 14; C.S., s. 5358.)