(v)"Construction" and "construct" include any alteration which would materially extend the area irritable by a canal or any other alteration irrigable by a canal or any other alteration of material importance or the renewal of a canal after disuse for six years, but do not include the re- excavation of a canal-head to a change in the river, the excavation of a new head necessitated by a change in the river or a change of water-courses to render existing irrigation more efficient;
