Counties may supervise fords, ferries and bridges.  T.C.A. § 54-11-101 et seq.  Additionally, counties may issue bonds for the construction of county highways, roads and bridges and pledge up to 50% of the state-aid grant funds derived from the state gasoline tax for the retirement of such bonds.  However, state funds used in matching federal funds may not be included in this amount.  T.C.A. § 54-9-201.  The legislative body may build a bridge or bridges over and across any stream or river running through the county.  T.C.A. § 54-11-207.  The CAO has the authority to temporarily close roads or bridges as necessary for new construction or repair.  Op. Tenn. Atty. Gen. 81-618 (December 7, 1981).