Assessments; validation.

After the special drainage district has been constituted and the assessments have been made and levied by the board of county commissioners, and before awarding the contract for the construction of any such ditch, drain or canal, the board of county commissioners shall, as soon as practicable, issue and sell district drainage bonds for the total amount of such assessments, less the interest charges. Said bonds shall bear interest not to exceed 7.5 percent per annum, payable semiannually, with interest coupons attached thereto, and shall be issued in denominations of not exceeding $1,000. The board of county commissioners shall, in issuing and selling said bonds, and in disbursing the proceeds thereof, act in substantial conformity with the provisions of these statutes applicable to the issue and sale of bonds for the purpose of constructing hard-surfaced highways or public buildings; with the exception, that the assessments for the payment of interest and to provide a sinking fund for the payment of the bonds shall be assessed and collected only upon the taxable property within the boundary of such special drainage district; and the bond trustees shall reside in the county, but not necessarily in the drainage district, but in no case shall district bonds be issued or sold against any drainage district for a greater amount than the assessment imposed upon lands in such district, and the bonds shall be issued in such maturities as will enable them to be paid in installments from time to time as fast as substantial amounts shall accumulate from the collection of the assessments. The validity of all bonds issued under this chapter may be determined and established in the manner provided by law for the validation of bonds issued by cities and municipalities.