A Hydrographic Survey is essentially the same as a topographic survey except the contour lines represent the terrain of the bottom (under water) instead of on the upland surface.
The NY State Department of Environmental Conservation (DEC) requires Mean Low Low Water (MLLW) as the contour elevation reference for dock permits. MLLW has a known average elevation in the bays of eastern Long Island. The overall vertical datum for a project with both upland and underwater terrain contours and is currently required to be the 1988 North American Vertical Datum (NAVD88) in the Towns and Villages of Southampton, East Hampton and Shelter Island. We can refer qualified permit consultants for preparing and processing NYS DEC dock permit applications.