A separate sinking fund account shall be provided and kept for each refunding bond issue authorized under the provisions of Sections settlement, adjustment, or refunding of bonds” class=”unlinked-ref” datatype=”S” sessionyear=”2020″ statecd=”AL” title=”11″>11-88-102, 11-88-103, and 11-88-104 to which shall be credited all collections made on assessments levied with respect to the improvements financed by the original issues of bonds or the proper proportionate part thereof, and such sinking fund shall be used only for the purpose of paying interest and principal on such bonds in that particular group or series as they mature.