Bonds issued pursuant to this chapter shall not constitute or be a debt, liability, or obligation of the state or El Dorado County. The payment of both principal and interest of all bonds shall be secured only by the tolls or other revenues collected from the toll tunnel, other revenues and interest thereon, and sinking funds created therefrom received by the authority, and shall be paid from such tolls or revenues or from such other contributions or appropriations as may be made available pursuant to this chapter.