(a) Any drainage district in this state which has issued and sold bonds, prior to the assessment of benefits on the property of the district, for the purpose of paying preliminary expenses of the district is authorized and empowered to issue refunding bonds for the purpose of paying any bond or bonds of the district then outstanding.
(b)
(1) The refunding bonds shall mature at such time or times as the board of commissioners of the district may direct.
(2) The refunding bonds may not bear a greater rate of interest than six percent (6%) per annum. However, the bonds may be converted into a larger amount of bonds bearing a lower rate of interest on such terms that the district shall receive therefor and pay thereon substantially the same amount of money.
(c) The refunding bonds shall not be issued for a substantially greater amount than is necessary to pay outstanding bonds with all interest thereon in addition to such discounts and expenses only as may be necessary and incident to the refunding bond issue.