21. (1) It shall be lawful for the Engineer, or any person whom he may authorise in writing in that behalf, in order to carry out any of the purposes of this Act, to enter upon and survey, and take levels of any land; to dig or bore into the sub soil; to do all other acts necessary to ascertain whether the land is adapted to the purpose projected by such Engineer; to set out the boundaries of the land proposed to be taken and the intended line of the work proposed to be made thereon; to mark such levels, boundaries and line, by placing marks and cutting trenches; and, where otherwise the survey cannot be completed or the levels taken, to cut down and clear away any part of any standing crop, fence or jungle: Provided that the Engineer or such person shall not enter into any building or upon any enclosed courtyard or garden attached to a dwelling house without previously giving the occupier thereof at least seven days' notice in writing of his intention to do so, except with the written consent of such occupier. (2) The Engineer or other person so authorised shall, at the time of such entry, tender payment for all necessary damage to be done as aforesaid, and in case of dispute as to the sufficiency of the amount so tendered, he shall at once refer the dispute to the Deputy Commissioner whose decision thereon shall be final.