Whenever land, subject to regulation under this chapter, abutting upon any lake, river, or stream is subdivided, the subdivider must show on the plat or other document containing the subdivision a contour line denoting the present shoreline, water elevation, and the date of the survey. If any part of a plat or other document lies within the one hundred year floodplain of a lake, river, or stream as designated by the department of water resources or a federal agency, the mean sea level elevation of that one hundred year flood must be denoted on the plat by numerals. Topographic contours at a two-foot [60.96-centimeter] contour interval referenced to mean sea level must be shown for the portion of the plat lying within the floodplain. All elevations must be referenced to a durable benchmark described on the plat with its location and elevation to the nearest hundredth of a foot [0.3048 centimeter], which must be given in mean sea level datum.