For the purposes of this part, the estimated cost of the dam or reservoir or enlargement involved shall include the following:
(a) The cost of all labor and materials entering into the construction of the dam and appurtenant works or reservoir
(b) The cost of preliminary investigations and surveys.
(c) The cost of the construction plant properly chargeable to the cost of the dam or reservoir.
(d) Any and all other items entering directly into the cost of the dam or reservoir.