Fulton Design criteria and performance standards ordinance (§ 46-63)

(a) Applicability.

(1) A stormwater management plan shall be submitted to the city engineer by the owner of any proposed residential, commercial or industrial development within the city, unless the city engineer waives such requirement for one of the following reasons:

a. Offsite facility, two or more developments. If two or more developments, including that of the applicant, have provided for a common system.

b. Offsite facility by city. If an offsite stormwater management system has been either constructed or programmed or identified for construction by the city and the applicant has agreed to contribute to or participate in the construction thereof.

c. Contribution in lieu of facility construction. If the applicant agrees to contribute to the city fund an amount based upon square footage of the hard surface. The fee schedule to be agreed upon by the council.

Any hard surface of 500 square feet or less can be waived by the city engineer and code enforcement officer.

Any surface area in excess of 75,000 square feet is not eligible. This development must have their own stormwater management system.

d. Other management techniques. Management techniques other than detention facilities may be utilized by the development, provided the techniques proposed meet the intent of this article and provide a benefit to the watershed that equals or exceeds the benefit that a detention facility would provide.

(2) No final subdivision or development plat shall be approved and no building permits shall be issued until the stormwater management plan has either been waived or reviewed and approved by the city engineer.

(b) Stormwater management plans. The required stormwater management plan shall identify means for controlling the stormwater runoff release rate from the development and providing storage potential for the excess stormwater runoff. All computations, plans and specifications related to the implementation of this article must be prepared and sealed by a professional engineer registered in the state. The entire catchment shall be studied to determine the runoff impact within the subwatershed. The stormwater management plan shall contain but not be limited to the following information, unless specifically excluded by the city engineer:

(1) A topographic map of the project site and adjacent areas, of suitable scale and contour interval, which shall define the location of streams, the extent of floodplains and calculated high-water elevations, the shoreline of lakes, ponds and detention basins, including their inflow and outflow structures, if any within the designated catchment.

(2) The location and flow line elevation of all existing sanitary, storm or combined sewers and other waterways within the catchment.

(3) Detailed determination of runoff anticipated for the entire project site following development indicating design volumes and rates of proposed runoff for each portion of the watershed tributary to the storm drainage system, the calculations used to determine such runoff volumes and rates and restatement of the criteria which have been used by the project engineer throughout his calculations.

(4) A layout of the proposed stormwater management system, including the location and size of all drainage structures, storm sewers, channels and channel sections, detention basins, and analyses regarding the effect the improvements will have upon the receiving channel and its high-water elevation.

(5) For all detention basins, a plot or tabulation of storage volumes with corresponding water surface elevations and of the basin outflow rates for those water surface elevations.

(6) For all detention basins, design hydrographs of inflow and outflow for both the 25-year, 24-hour, and 50-year, 24-hour, design runoff events for the site under predeveloped conditions and the calculated 25-year, 24-hour, and 50-year, 24-hour, peak flows from the site under predeveloped conditions.

(7) A profile and one or more cross sections of all existing and proposed channels or other open drainage facilities, showing existing conditions, and the proposed changes thereto, together with the high-water elevations expected from stormwater runoff under the controlled conditions called for by this article and the relationship of structures, streets and other utilities to such channels.

(c) Design criteria. The following shall govern the design of improvements with respect to managing stormwater runoff:

(1)

Methods of determining stormwater runoff rate and volume. Drainage and storage facilities shall be designed using the soil conservation service urban hydrology, TR-55, method of calculating runoff discharge rate and the total volume.

(2) Release rate. The controlled release rate of stormwater runoff from all developments described in section 46-91 shall not exceed the predevelopment rate. The rate at which stormwater runoff is delivered to a designated stormwater storage area shall be unrestricted. If the natural downstream channel or storm sewer system is inadequate to accommodate the release rate provided in this subsection, the allowable release rate shall be reduced to that rate permitted by the capacity of the downstream channel or storm sewer system.

(3) Development design. Streets, blocks, lots, parks and other public grounds shall be located and laid out in such a manner as to minimize the velocity of overland flow and allow maximum opportunity for infiltration of stormwater into the ground and to preserve and utilize existing and planned streams, channels and detention basins and include, whenever possible, streams and floodplains within parks and other public grounds.

(4) Detention. The increased stormwater runoff resulting from the proposed development may be accommodated by providing appropriate detention facilities, including wet or dry bottom reservoirs, flat roofs, parking lots or streets. The following shall govern the design of detention facilities:

a. Storage volume. The volume of storage potential provided in detention facilities shall be sufficient to control the excess stormwater runoff, as determined to be the difference between the stormwater quantity from the site in its developed state for a 50-year, 24-hour frequency rainfall as published by the U.S. weather bureau, less the allowable release rate as set forth in subsection (2) of this section. The allowable stormwater release rate shall not be exceeded, regardless of the depth of stormwater contained in the required stormwater detention facility.

b. Release rate. At no time during the design storm shall the stormwater runoff release rate exceed the allowable release rate as set forth in subsection (2) of this section.

c. Release velocity. Detention facilities shall release stormwater at a nonerosive velocity. Protected channels receiving detention discharge shall incorporate features to reduce velocity to nonerosive levels at the point where such discharge enters the unprotected channel. If release is into a subsurface conduit, the energy gradient in the receiving facility shall not be increased beyond the slope of the conduit.

d. Spillway. Emergency spillways shall be provided to permit the safe passage of runoff generated from a 100-year, 24-hour storm, or greater, if required by regulations of the state department of natural resources.

e.

Freeboard. Detention facilities shall have adequate capacity to contain the storage volume of tributary stormwater runoff with at least one foot of freeboard above the water surface of flow in the emergency spillway in a 100-year, 24-hour storm.

(d) Performance standards.

(1) Stormwater channel location. Generally acceptable locations of stormwater channels in the design of a subdivision may include but are not limited to the following:

a. Adjacent to roadways.

b. In a depressed median of a double roadway, street or parkway, provided the median is wide enough to permit slopes of one foot drop in six feet horizontal or flatter.

c. Centered on lot lines or entirely within the rear yards of a single row of lots or parcels.

d. In each of the cases in subsections (a)(1) through (3) of this section, a drainage easement with sufficient width to facilitate maintenance and design flow shall be provided and shown on the plat.

(2) Storm sewer outfall. The storm sewer outfall shall be designed to provide adequate protection against downstream erosion and scouring.

(3) Lot lines. Whenever the plans call for the passage or storage of stormwater runoff along lot lines, the grading of all such lots shall be prescribed and established for the passage or storage of waters, and no structure or vegetation which would obstruct the flow of stormwater shall be allowed nor shall any change be made to prescribed grades and contours of the specified stormwater channels.

(4) Manholes. All utility sewer manholes constructed in an area designed for the storage or passage of stormwater shall be provided with either a watertight manhole cover or be constructed with a rim elevation of a minimum of one foot above the high-water elevation of the design storm.

(5) Easements. Permanent easements for the detention and conveyance of stormwater, including easements of access to structures and facilities, shall be dedicated to the city.

(6) Obstruction of drainage. The keeping or disposal of grass clippings, trash, debris, obstructions or unwanted materials into the storm sewers or within or along stormwater channels or in adjacent floodplain areas which may wash into sewers and channels is prohibited.

(7) Maintenance. Provisions acceptable to the city for perpetual maintenance of detention facilities, outlet works, and appurtenances shall be made, as provided in section 46-107.

(e) Reserved.