For the purpose of obtaining lands, easements, and rights-of-way and maintaining and operating such flood control works or other similar projects as provided in sections 23-320.08 to 23-320.12 when the same 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 a designated watershed area. 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.