1. In drainage districts so making level assessments, the board of supervisors thereof may, with the consent of the owners of not less than three-fifths of the lands embraced in such districts, given at an election held in the district for that purpose, upon a notice, the same as required for the election of supervisors, for the purpose of constructing new works or of repairing or extending old ones, as well as for making surveys and acquiring rights-of-way, borrow upon the credit of the district a sum or sums the principal of which shall at no time exceed six dollars for each acre in the district. In voting at such an election, or at any election by the landowners, any landowner, not present, may vote by written proxy.

2. Loans negotiated under this section shall not run longer than twenty years nor bear more than six percent semiannual interest, nor shall the bonds be sold for less than ninety cents on the dollar clear to the district. Upon negotiating any such loan, it shall be the duty of the board of supervisors to make a levy of such sum, not exceeding fifty cents per acre in any one year, as will be sufficient to pay the principal and interest on such bonds as they mature.