The finance director is authorized and directed to overdraw the local improvement revolving fund in any amount necessary to purchase any and all local improvement bonds which may mature after the ordinance codified herein becomes effective, and for which there is insufficient money in the local improvement fund available for the payment of the bonds, but sufficient outstanding valid unpaid assessments to pay the same, or where the deficiency in such local improvement fund shall not exceed the sum of $100.00. (1957 code § 1.36.064.)