Section 44. For the purposes of sections 44 to 48B, inclusive, the following words shall have the following meanings:—

''Abandoned dam'', a dam that has no identifiable owner or a dam in which the owner fails to respond to the owner's obligations under sections 44 to 48, inclusive, and as a result of which the commissioner has taken emergency action under section 47 and created a lien upon the lots of land on which the dam is situated and upon the buildings and structures on the lots under section 48.

''Appurtenant works'', structures, either in dams or separate therefrom, including, but not limited to, spillways; reservoirs and their rims; low level outlet works; and water conduits, including tunnels, pipelines or penstocks, either through the dams or their abutments.

''Commissioner'', the commissioner of conservation and recreation or a designee of the commissioner.

''Dam'', any man-made artificial barrier, including appurtenant works, which impounds or diverts water, and which (1) is 25 feet or more in height from the natural bed of the stream or watercourse measured at the downstream toe of the barrier, or from the lowest elevation of the outside limit of the barrier, if it is not across a stream channel or watercourse, to the maximum water storage elevation or (2) has an impounding capacity at maximum water storage elevation of 50 acre feet or more. Any other artificial barrier, including appurtenant works, the breaching of which could endanger property or safety or which could cause significant harm to the aquatic ecosystem, may be designated by the commissioner as a dam, and shall be subject to sections 44 to 50, inclusive. The word ''dam'' shall not mean any of the following: (1) any appurtenant works which temporarily impounds or diverts water used on land in agricultural use as defined pursuant to section 131 of chapter 40, (2) any barrier or appurtenant works which has a size classification of small or low hazard potential classification that is used on land in agricultural use as defined in said section 131 of said chapter 40, and (3) any barrier which is not in excess of 6 feet in height, regardless of storage capacity, or which has a storage capacity at maximum water storage elevation not in excess of 15 acre feet, regardless of height. The commissioner shall make such determination by taking into consideration factors such as height, type of structure, condition of structure, volume of the impoundment, extent of development downstream, and other factors deemed appropriate by the commissioner.

''Department'', the department of conservation and recreation, as established in section 1 of chapter 21.

''Owner'', the person or persons, including any individual, firm, partnership, association, syndicate, company, trust corporation, municipality, agency, political or administrative subdivision of the commonwealth or any other legal entity of any kind holding legal title to a dam, but excluding the United States, its agencies or any person who operates a dam owned by the United States.

''Remove'' or ''Removal'', the controlled dismantlement or breaching of a dam, in compliance with applicable law, to the extent that water is not impounded or diverted by the dam and fish passage is no longer impeded; provided, however, that, following a controlled dismantlement or breaching of a dam, a minimal degree of impoundment necessary for agricultural uses or wetland retention and open water conditions may be allowed, so long as any impediment to fish passage has been removed and any threats to public safety or property have been alleviated.

''Unsafe dam'', a dam whose condition, as determined by the commissioner, is such that a high risk of failure exists.

''Water storage elevation'', the maximum elevation without encroaching on the approved freeboard at maximum design flood.