For the purpose of maintaining and operating such flood control works or other similar projects as provided in sections 23-320.01 to 23-320.07 when the works or projects have been completed and turned over to the county and also for the purpose of developing and carrying out a coordinated soil and water resource program and program of flood control for the county, the county board of such county shall be empowered to make an annual tax levy of not to exceed one and seven-tenths cents on each one hundred dollars upon the taxable value of all the taxable property in such county. Pending approval of an authorized flood control plan, the county involved may establish a special flood and erosion control reserve fund. Such fund may be used for obtaining land, easements, and rights-of-way and relocating utilities in connection with water and erosion improvements that have authorization and construction approval. To aid in the growth of such fund, it may be invested in short-term securities authorized by section 77-2315. Money remaining in the fund at the completion of construction or the discontinuance of an authorized project may revert to the general fund. It shall be the duty of the county board and the county engineer to keep all such flood control works or other similar projects in serviceable condition and to make such repairs as may, from time to time, be necessary.