The preliminary plat shall be accompanied by profiles showing the elevations of existing ground surface, proposed fill, proposed street grades, and proposed homesites, including extensions for a reasonable distance beyond the limits of the proposed subdivision; typical cross sections of the proposed grading, roadway and sidewalk; the preliminary plan of proposed sanitary and stormwater sewers with grades and sizes indicated; and information regarding the impact that a ten-year, 25-year and 100-year flood with a 24-hour duration will have on the improved tract. All elevations shall be based on the n.g.v.d. of 1929. In addition, at the discretion of the planning and zoning board, a traffic impact survey or analysis may be required.