Tex. Parks and Wildlife Code § 21.106

(a) Accrued interest received in the sale of bonds, net income received from entrance or gate fees to state park sites, and income from investments of the development fund and the interest and sinking fund shall be credited to the interest and sinking fund. A portion of the net income from the sale of conservation permits authorized by Chapter 43 of the Parks and Wildlife Code may be credited to the interest and sinking fund.

(b) In the resolution authorizing a series of bonds, the commission may appropriate from the proceeds of the sale of bonds an amount which, together with accrued interest received, is sufficient to pay interest coupons coming due during the fiscal year in which the bonds are sold and to establish appropriate reserves.