The income fund is hereby created. It shall be the fund to which shall be credited all interest, dividends and other income from investments of the retirement system, all transfers from the members deposit fund by reason of lack of claimant or forfeiture of interest credits, and all other moneys received by the retirement system, the disposition of which is not specifically provided for in this article. The board of trustees may accept gifts and bequests and same shall be credited to the income fund. There shall be paid or transferred from the income fund all amounts required to credit regular interest to the members deposit fund, employers accumulation fund, and the retirement reserve fund, as provided in this article. Whenever the board determines that the balance in the income fund is more than sufficient to cover the current charges to the fund, the board may, by resolution, provide for contingency reserves, or for the transfer of such excess, or portions thereof, to cover the needs of the other funds of the retirement system.