(a) The board of trustees shall designate an actuary who shall be its technical advisor on matters regarding the operation of the funds created under this chapter and who shall perform such duties as are required in that regard.

(b) At least every five years, the actuary shall conduct an actuarial investigation into the mortality, service, and compensation experience of the members and beneficiaries of the retirement system and shall recommend for adoption by the board of trustees mortality, service, and other tables needed in the operation of the system. Taking into account the results of such investigations, the board of trustees shall from time to time adopt for the retirement system such mortality, service, and other tables as it shall deem necessary for use in all calculations required in connection with this retirement system. The board of trustees shall also determine from time to time the rate of regular interest to be used by the retirement system, which rate shall be limited to a minimum of 2 percent.

(c) On the basis of the rate of regular interest and the tables last adopted by the board of trustees, the actuary shall make annual valuations of the contingent assets and liabilities of the retirement system.