SINKING FUND: EXCESS MONEY.

(a) At the time obligations are authorized under this chapter, the board may provide that all money in the sinking fund in excess of the amount required for the payment of the principal of and interest on the outstanding obligations, for a period the board determines, shall be spent once each year under the board's order to purchase obligations for the account of which the sinking fund has been accumulated, if the obligations can be purchased at a price the board considers reasonable.

(b) The board may provide that, if the obligations contain an option permitting retirement before maturity, the excess amount shall be paid out as provided by this chapter for the purchase of the obligations. If the board is unable to purchase sufficient obligations of the issue to absorb all the surplus, the board shall call for redemption of a sufficient amount of the obligations to absorb, so far as practicable, the entire surplus remaining in the sinking fund.

(c) The board may provide that any excess amount in the sinking fund that cannot be applied to the purchase or redemption of obligations shall remain in the sinking fund to be used for payment of principal or interest, when due, or for the subsequent call of obligations for purchase or redemption in the manner provided by this section.