Grading and drainage plans, to the same scale as the preliminary plat map, shall be submitted for each plat, providing the following information to the standards set forth:
   (A)   Existing and proposed contour lines.
      (1)   Existing contours shall be shown at vertical intervals of two feet. Elevations shall be referenced to the national geodetic vertical datum (NGVD 1929).
      (2)   Contour lines shall be different line weights for existing contour lines versus proposed contour lines.
      (3)   Contours shall be shown to a minimum of 150 feet into adjacent property or to the centerline of the adjacent street.
   (B)   Lot and block layout.
      (1)   Lot dimensions to the nearest foot;
      (2)   Typical lot detail indicating where lot and house elevations are shown;
      (3)   Building setback lines;
      (4)   Front and rear lot corner elevations;
      (5)   House pads layout, showing hold down elevations and finished garage elevations;
      (6)   Spot elevations as appropriate to define drainage patterns on the lot; and
      (7)   Legend with type of house styles and grade difference for garage floor to walkouts or lookouts.
   (C)   Lot grading and drainage. Lots shall be graded so water drains away from building locations and flows along lot lines within the proposed drainage and utility easements. Any drainage flow from one lot onto an abutting lot must be within a drainage easement.
   (D)   Street layout.
      (1)   Typical street section;
      (2)   Preliminary street grades and drainage;
      (3)   Centerline street elevations at 100 foot stations with high and low points; and
      (4)   Cul-de-sac frontage along curb tines with spot elevations.
   (E)   Street grade. Centerline street gradients shall be in accordance with § 151.045.
   (F)   Storm sewer alignment. Storm sewer alignment shall be shown with top and invert elevations. Also, flared ends shall be shown with invert elevations.
   (G)   Easements. Existing and proposed easements, in accordance with § 151.046.
   (H)   Grading plan.
      (1)   The grading plan for all single-family residential subdivisions shall provide for an area with a slope not greater than 10% extending not less than a depth of 20 feet from the rear line of the building pad the entire width of the building pad, except as approved by the City Engineer.
      (2)   House pad setback from flood elevations: House pads shall be set back 30 feet from 100-year flood elevation for storm sewer ponds and lakes if the lake lot has municipal sewer; and 75 feet from the 100-year flood elevation for lakes if the lake lot is unsewered.
      (3)   Lowest opening elevation: two feet above the 100-year flood elevation of adjacent storm sewer ponds. Flooding elevations shall be one foot above the ordinary high water level of any standing water if determined. If sufficient data on known high water levels is not available, the elevation of the line of permanent aquatic vegetation shall be used as the estimated high water standing water elevation.
   (I)   Garage floors. Minimum elevation: 1½ feet above the top-of-curb elevation, as measured from the top-of-curb at the high side of the driveway to the garage floor.
   (J)   Driveway slopes. Maximum slope: 10% from the top-of-curb to the garage floor, as measured at the centerline of the driveway.
   (K)   Open areas, including yards and swales.
      (1)   Minimum slopes, 1%; and (Preferred design is 1.5% or greater.)
      (2)   Maximum slopes, 3:1, except existing slopes being protected, which are subject to review.
   (L)   Emergency overflows.
      (1)   Emergency overflows shall be labeled and shown with spot elevations and drainage arrows. Emergency overflows must be established for catch basins in the street and in rear lots. Areas along rear lot lines which are below the emergency overflow elevation shall be designated as drainage easement on the final plat.
      (2)   Minimum elevation is 2.0 feet below the lowest opening house elevation.
      (3)   Storm sewer ponds' slopes, 6:1 maximum grade.
   (M)   Elevations and boundaries of lakes, wetlands and ponds. Each grading and drainage plan shall show the following:
      (1)   Ordinary high water level contours of all lakes, streams, wetlands, watercourses, marshes, and surface water features required in M.S. § 505.02 (1), as it may be amended from time to time, obtained from United States Geological Survey quadrangle topographic maps or more accurate sources;
      (2)   Location of 100-year floodplain areas, 100-year flood elevations, and limits of floodway and flood fringe;
      (3)   Delineated wetland boundaries, completed by a qualified professional according to the most current U.S. Corps of Engineers methodology, and approved by the city’s designated official;
      (4)   Wooded areas;
      (5)   Rock outcrops;
      (6)   Power transmission poles and lines; and
      (7)   Other significant features required to be shown.
   (N)   Watercourses. No more than 50% of the minimum lot size for the underlying zoning district shall contain a wetland, watercourse or marsh. Setback shall comply with the standards established in Ch. 154, Zoning.
   (O)   Drainage design.
      (1)   Drainage arrows at high points and at major grade changes;
      (2)   Drainage design calculations which show that the proposed improvements shall not change runoff rates onto adjacent public or private property and shall not adversely impact downstream properties; and
      (3)   Drainage facility design shall be based on a 100-year 24-hour storm event for flood overflow ponds and based on a 10-year one-hour storm event for piping.
   (P)   Grading and drainage plan preparation. Grading and drainage plan must be signed by a registered engineer.
(`86 Code, § 10.42) (Am. Ord. 632, passed 12-15-92; Am. Ord. 706, passed 12-2-97; Am. Ord. 1006, passed 10-1-13)