(a) If a watershed project established under this title crosses a public highway at the intersection of the highway with a natural watercourse or depression through which water flows during periods of high water, the county in which the bridge is located or the governmental unit required by law to maintain the highway that is intersected shall:

(1) pay the cost of an existing bridge, repairing or enlarging an existing bridge and culvert, or constructing a new bridge or culvert; and

(2) maintain the bridge or culvert described in item (1) of this subsection.

(b) If a watershed project established under this title crosses a public highway at a point where the highway does not intersect a natural watercourse or depression:

(1) the watershed association shall pay the cost of constructing a new bridge or culvert; and

(2) after construction, the county or other governmental unit required by law to maintain the highway that is intersected shall maintain the bridge and any culvert constructed.