On streams not identified by said maps, the 100-year flood plain shall be as delineated by a developer's engineer and approved by the Board Engineer and the State of New Jersey Division of Water Resources. The flood hazard design elevation shall be determined on an individual basis based upon stream encroachment line data from the Division of Water Resources or, in the absence of that data, the flood elevation based on a 100-year storm frequency. One or the other shall be delineated on the plat. In addition, the Board Engineer may, upon receipt of the application and with the consent of the landowner, determine the precise location of the floodway and flood fringe area by close inspection, field survey or other appropriate method and cause the same to be marked on the ground and on the plat, notifying the owner, the New Jersey Department of Environmental Protection, Division of Water Resources, and the Board. Where State or Federal agencies have or will publish any reports which clearly delineate by contours the flood hazard design elevation of a watercourse, said report shall be the officially delineated flood hazard area as if said report were published in this Chapter.