Special bond redemption funds. Beginning with the fourth year after the bonds are sold the county court shall each year thereafter, until maturity of the bonds, set aside as a special fund for their payment such percentage of the face value of the bonds as at the date of their maturity shall aggregate their full face value. Where bonds are issued in different series maturing at different times a separate redemption fund shall be provided for each series

ORS 370.170 — under Chapter 370.