If the property on which a proposed subdivision is to be located is traversed by a watercourse of any kind, including a channel or a stream, the Planning Board may require that a stormwater and drainage easement and right-of-way along said watercourse be provided by the subdivider. The land which is the subject of such easement and right-of-way shall be a strip, which conforms substantially to the floodplain of such watercourse along both sides of the watercourse or extends along both sides of the top of the bank of the watercourse to a width of 15 feet in each direction or is not less than an encroachment line established by a competent higher authority, whichever is the greater; except, however, that if the location of such watercourse is at or near the boundary of the subdivision, the dimension of the easement and right-of-way shall be modified to retain it within the confines of the subdivision. Said easement and right-of-way shall include provisions assuring the following: preservation of the channel of the watercourse; prohibition of alteration of the contour, topography or composition of the land within the easement and right-of-way; prohibition of construction within the boundaries of the easement and right-of-way which will obstruct or interfere with the natural flow of the watercourse; and reservation to the Department of Public Works of a right of entry for the purposes of maintaining the natural flow or drainage of the watercourse, of maintaining any and all structures related to the exercise of the easement and right-of-way and of installing and maintaining storm or sanitary sewer systems or other public utility and the right to add additional utility lines when needed.