When, in the judgment of the county board, the assessments are too large for immediate payment, the board may issue negotiable bonds of the county with interest coupons attached, which bonds and coupons shall be signed by the chairman of the board and countersigned by the county clerk of the county, and shall be paid in not to exceed ten installments, one bond maturing each year, to pay the costs and expenses of location and construction, and all compensation and damages ascertained.