It shall be the duty of the proprietors or owners of any canal, ditch or other conduit constructed for the conveyance of water used principally for irrigation purposes to provide and construct all necessary bridges and viaducts for the use of the public in crossing the same. Every such bridge or viaduct shall be so constructed as to be safe and adequate for the purpose for which constructed, and the construction thereof shall in all cases be completed by the time when water shall be caused or permitted to flow in such canal, ditch or other conduit at the place where any such bridge or viaduct shall be required.

All such bridges and viaducts, when constructed, shall be and become a part of the public highway, and shall be maintained and kept in repair by the authorities having charge of such highways: Provided, That when such bridge or viaduct is located on a township road and the county engineer’s estimated cost is more than $600, said bridge or viaduct shall be maintained by the board of county commissioners, and when the county engineer’s estimated cost of such bridge or viaduct is $600 or less, it shall be maintained by the board of township highway commissioners: Provided further, That when any canal, ditch or other conduit constructed for the conveyance of water used primarily for drainage purposes, and belonging to a regularly established drainage district, shall cross a public highway, thereby necessitating the construction or maintenance of any bridge or viaduct, such bridge or viaduct shall be constructed and maintained by the board of county commissioners when located on a county road or when located on a township road and the county engineer’s estimated cost is more than $300; it shall be constructed and maintained by the township board of highway commissioners when located on a township road and the county engineer’s estimated cost is less than $300.