Beginning on July 1, 1981, each water resource district shall assume all assets, liabilities, and obligations of any county drain board whose territory is included within the boundaries of the district. When the jurisdiction of any county drain board is included within two or more districts, the county auditor shall determine the apportionment of any assets, liabilities, and obligations. Such apportionment shall be based on the proportionate amount of taxable valuation included in each district, except that special assessment projects and funds, property    interests, and physical assets attached to the land shall be assumed by the district in which the project is located. Property interests and physical assets attached to the land shall be assumed by the district in which they are located. Prior to February 1, 1983, and for review by each affected water resource board, each water resource district and county drain board shall have a certified public accountant prepare a final audit of its financial records, including all special assessment funds and obligations, assets, and other liabilities. All necessary actions to accomplish the transfer of assets and obligations under this section shall be complete prior to January 1, 1982.