ORS § 547.660
The board of supervisors of any drainage district desiring to issue refunding bonds to replace or in satisfaction or discharge of any outstanding indebtedness may exchange such refunding bonds for the outstanding indebtedness in full compromise, satisfaction and discharge thereof, and shall issue the bonds in such denominations and in such amounts to the several holders of the indebtedness as may be found expedient and necessary in funding or refunding the indebtedness. The bonds may be serial, on the level payment plan or each of the bonds may be amortized, as the board of supervisors may by resolution determine. When the bonds so issued do not exceed in principal and rate of interest the indebtedness to be satisfied and for which the bonds are to be exchanged, it shall not be necessary for the board of supervisors to advertise their sale or to offer them at public sale.
ORS 547.660