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§ 160.21 DESIGN CRITERIA.
   The following rules shall govern the design of improvements with respect to managing stormwater runoff:
   (A)   Methods of determining stormwater runoff rate and volume. The volume of required stormwater storage and runoff shall be calculated on the basis of the runoff from a 25-year frequency storm with 24-hour duration. The calculations can be made in accordance with the instantaneous runoff factor method, the rational method or other methods that may be deemed appropriate by the Stormwater Manager.
   (B)   Release rate.
      (1)   All developments undertaken as outlined in that chapter shall be done in such a way as to insure that stormwater falling on a given site shall be absorbed or detained on site to the extent that the controlled release rate of stormwater runoff from all developments shall not exceed the pre-development stormwater runoff rate. The rate at which stormwater runoff is delivered to a designated stormwater storage area shall be unrestricted.
      (2)   In the event that the Stormwater Manager determines that the natural downstream channel or storm sewer system is inadequate to accommodate the release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the downstream channel or storm sewer system.
   (C)   Development design.
      (1)   Where it can be demonstrated by the developer that a higher storm water release rate will not be contrary to the purpose and intent of this chapter and where such proposed release rate will not adversely affect properties in the downstream portion of the watershed, the Stormwater Manager may permit such release to be used as deemed appropriate.
      (2)   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 floodplain within parks and other public grounds.
   (D)   Excess stormwater passage.
      (1)   An excess stormwater passage shall be provided for all stormwater areas. Such passage shall have the capacity to convey through the proposed development the excess stormwater. The capacity for a passage shall be such that it will be able to transport the peak rate of run-off from a 100-year, 24-hour return frequency storm.
      (2)   There shall be no buildings or structures constructed within excess storm water passage, however, parking lots, playgrounds and park areas, which shall not impair or endanger the water holding capability of a development, shall be considered compatible uses.
      (3)   Appropriate land planning shall be undertaken to preserve the existing natural drainage of a proposed development as part of the excess stormwater passage.
      (4)   Open channels shall be protected from erosion by appropriate vegetative covers, lining or other treatment and earthen channel side slopes shall be no steeper than two to one. Open channels with lining shall have a maximum gradient on side slopes of 67% and channel side slopes steeper than 67% shall be designed as structural retaining walls.
   (E)   Stormwater storage/detention areas. The increased stormwater runoff resulting from the proposed development may be accommodated by the provision of appropriate detention facilities including wet or dry bottom reservoirs, flat roofs, parking lots or streets. Storage areas shall be designed, if possible to provide secondary purposes for recreation, open spaces, parking lot or other types of use that will not be adversely affected by intermittent flooding. The following shall govern the design of detention facilities:
      (1)   Storage volume.
         (a)   All stormwater storage areas must be designed to contain and safely pass stormwater runoff. The combined capacity of these storage areas shall be sufficient to contain the storm from the development. The detention facility must be designed for periodic maintenance and energy dissipaters shall be provided at points necessary.
         (b)   The ponding of stormwater runoff shall not exceed a depth of one foot on a pedestrian mall area or 1-1/2 feet maximum in parking lots. Where these areas are used for ponding the maximum depth should occur in the most remote and least used areas.
         (c)   The drainage and grading design shall be prepared to insure that in a 100-year storm the depth of water run-off in any street, alley, or pedestrian mall will not exceed the level of the first floor of any building.
         (d)   For wet pond storage areas when calculating the storage capacity, only the volume available to store excess stormwater shall be considered. Permanent water storage does not constitute control of excess storm runoff.
      (2)   Release rate. At no time during the design storm shall the stormwater runoff release rate exceed the allowable release rate as set forth in division (B) of this section.
      (3)   Release velocity. Detention facilities shall release stormwater at a non-erosive velocity. The protected channel receiving the detention discharge shall incorporate features to reduce velocity to non-erosive 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.
      (4)   Spillway.
         (a)   Overflow for each stormwater storage area shall be provided in the event of a storm in excess of the design capacity occurs. Such overflows shall be constructed to function without specific attention and shall become part of the excess stormwater passage.
         (b)   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 state law.
         (c)   Where rooftop storage or excess stormwater is provided, the building shall be provided with adequate structural design to insure that roof failure does not occur. Overflow areas shall be provided so that the weight of stored stormwater will not exceed the structural capacity of the roof.
      (5)   Freeboard. Detention facilities shall have adequate capacity to contain 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 or as required by state law.
   (F)   Sinkholes and subterranean water channels.
      (1)   The use of sinkholes or subterranean water channels for direct drainage of excess stormwater shall not be permitted although they may be used to drain a stormwater storage area. The introductions of any foreign matter or the filling, clogging or interfering with the natural drainage capabilities of the sinkholes shall not be permitted.
      (2)   Sinkholes shall not be altered in any way which would negatively affect the drainage capabilities of the sinkhole. Development within the 100-year floodplain of a sinkhole shall not be permitted.
(Ord. 2809, passed 12-10-2012) Penalty, see § 160.99
§ 160.22 PERFORMANCE STANDARDS.
   (A)   Stormwater channel location. Generally acceptable locations of stormwater channels in the design of a subdivision may include but are not limited to the following:
      (1)   Adjacent to roadways.
      (2)   In a depressed median of a divided roadway, provided the median is wide enough to permit slopes of one foot drop in six feet horizontal or flatter.
      (3)   Centered on lot lines or entirely within the rear yards of a single row of lots or parcels.
   (B)   In each of the foregoing cases drainage easement with sufficient width to facilitate maintenance and design flow shall be provided and shown on the plat.
   (C)   Storm sewer outfall. The storm sewer outfall shall be designed to provide adequate protection against downstream erosion and scouring.
   (D)   Lot lines. Whenever the plans call for the passage and/or storage of stormwater runoff along lot lines, the grading of all such lots shall be prescribed and established for the passage and/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 the prescribed grades and contours of the specified stormwater channels.
   (E)   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.
   (F)   Easements. Permanent easements for the detention and conveyance of stormwater, including easements of access to structures and facilities, shall be dedicated to the city.
   (G)   Obstruction of drainage. The keeping or disposal of grass clippings, trash, debris, obstruction 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.
   (H)   Maintenance. Required maintenance for detention basins or other structures shall be permanently provided by the developer with responsibility becoming that of the private landowner after complete development, subject to inspection of the Stormwater Manager. Every entity shall be specified. Refer to § 160.31 for maintenance requirements.
   (I)   Encroachment permit (city right-of-way).
      (1)   All new construction projects (residential, commercial or industrial) which require a permanent or temporary entrance onto an existing city street or a newly developed street which is to be dedicated to the city at a later time and which can impact proper street drainage shall apply for an encroachment permit at the Office of Public Works. The encroachment permit form will be supplied by the city. The encroachment permit should be complete in sufficient detail to show the location of said entrance with respect to property lines. The encroachment permit shall detail the pipe size, material and slope/grade.
      (2)   This encroachment permit shall be obtained prior to issuance of a building permit by the Planning and Zoning Office.
      (3)   The fee required for the encroachment permit shall be as listed in § 97.17 Application Fee; Bond. This encroachment permit fee is fully refundable provided the entrance is constructed as detailed and approved on said encroachment permit.
(Ord. 2809, passed 12-10-2012) Penalty, see § 160.99
§ 160.23 POST-CONSTRUCTION STORMWATER MANAGEMENT PLAN.
   (A)   Purpose.
      (1)   Land development projects and associated increases in impervious cover alter the hydrologic response of local watersheds and increase stormwater runoff rates and volumes, flooding, stream channel erosion and sediment transport and deposition; this stormwater runoff contributes to increased quantities of water-borne pollutants and; stormwater runoff, soil erosion and nonpoint source pollution can be controlled and minimized through the regulation of stormwater runoff from development sites.
      (2)   The purpose of this chapter is to establish minimum post stormwater management requirements and controls to protect and safeguard the general health, safety and welfare of the public residing in watersheds within this jurisdiction. The goal is to maintain or improve the quality of all streams within the MS4 boundaries to meet their designated use. This chapter seeks to meet that purpose through the following objectives:
         (a)   Minimize increases in stormwater runoff from any development in order to reduce flooding, siltation and stream bank erosion and maintain the integrity of stream channels;
         (b)   Minimize increases in nonpoint source pollution cause by stormwater runoff from development which would otherwise degrade local water quality;
         (c)   Minimize the total annual volume of surface water runoff which flows from any specific site during and following development to not exceed the pre-development hydrologic regime to the maximum extent practicable.
         (d)   Reduces stormwater runoff rates and volumes, soil erosion and nonpoint source pollution where possible, through stormwater management controls and to ensure that these management controls are property maintained and pose no threat to public safety.
   (B)   The Post-Construction Stormwater Management Plan shall be submitted for all subdivisions that discharge to MS4 high quality waters. This includes residential, commercial, and industrial developments. The PC-SWMP is required for all sites one acre and larger in size, and all sites part of a greater common development.
   (C)   The city reserves the right to develop or adopt other guidance documents to serve as design and implementation standards. Other guidance documents distributed by the city should be reviewed and considered when preparing the Post Construction SWMP. These documents may be applied as standards by which designs are to be prepared and controls implemented.
   (D)   The city shall have the authority to implement this chapter by appropriate regulations, guidance or other related materials. In this regard, technical administrative or procedural matters may be modified as needed to meet the objective herein.
(Ord. 2809, passed 12-10-2012)
§ 160.24 POST-CONSTRUCTION PERFORMANCE STANDARDS.
   (A)   The city reserves the right to develop or adopt guidance documents to serve as design and implementation standards. Other guidance documents distributed by the city should be reviewed and considered when preparing the Post-Construction SWMP. Technical, administrative or procedural matters may be modified as needed to meet the objectives defined in this chapter as long as they are not contrary or beyond the intent of the objectives listed above. Such documents given authority by this chapter include Best Management Practice (BMP) manuals, design regulations and requirements, checklists that address submittals, plan review and inspections certification, stormwater manuals, and operation and maintenance manuals. Said documents may be updated periodically to reflect the most current and effective design and construction practices and be made available to the public. Failure to update the manual does not relieve the applicant from complying with this chapter.
   (B)   Post-construction stormwater BMPs shall be designed in accordance with the most current manual or requirements to achieve the following performance standards:
      (1)   The development shall be designed with management measures that are built and maintained to treat, filter, flocculate, infiltrate, screen, evapo-transpire, harvest and reuse stormwater runoff, or otherwise manage the stormwater quality produced from the 80th percentile rain event (0.6 inches of rainfall).
      (2)   BMP’s shall be designed to remove pollutants and reduce runoff volume. The designated use and any existing in-stream use of the stream being discharged to shall be protected. Some land uses produce higher concentrations of certain pollutants such as hydrocarbons or heavy metals, than those normally found in urban areas. These areas will be reviewed for effective removal of the particular pollutant which they discharge. Effective removal will be that which existed prior to development. Examples of land uses that produce higher levels of pollutants are:
         (a)   Gas/fueling stations.
         (b)   Restaurant dumpster areas.
         (c)   Vehicle repair facilities.
         (d)   Vehicle washing/steam cleaning facilities.
         (e)   Auto recycling facilities.
         (f)   Outdoor material storage areas.
         (g)   Loading and transfer areas.
         (h)   Landfills.
         (i)   Industrial sites.
      (3)   BMPs shall reduce or buffer increases in stormwater runoff temperature caused by contact with impervious surfaces as well as minimize increases in stormwater runoff volume and flow rate caused by increases in impervious surfaces.
      (4)   The PC-SWMP shall include provisions for buffers. A buffer shall be defined as:
         (a)   Area contained within a boundary established by the FEMA floodplain boundary or city master planning; or
         (b)   Where a floodplain is not defined or calculated, the buffer will be 25 feet on each side from the top of waterway bank as defined by geomorphic shape (not by current water surface elevation).
            1.   Buffers shall be provided to all blue-line streams as shown on the USGS map.
            2.   Buffer areas and floodplain may be used for stormwater quality devices provided erosion prevention, sediment control, cut-fill practices area addressed appropriately as determined by the city to meet this chapter.
            3.   Exemptions can be granted to buffers so long as erosion and sediment control, water quality are addressed. Exemptions for building in the buffer area shall be granted for:
               a.   Roads and utilities crossing waterways.
               b.   Pedestrian trails and walkways adjacent to waterways.
               c.   Other exemptions may be made at the discretion of the city representative.
      (5)   Redevelopment not previously addressing water quantity or quality control shall reduce the discharge from their site according to the formula below:
         Q(redeveloped) = Q(existing) + q(undeveloped)
                     2
         Q(redeveloped) = maximum discharge rate for the re-development
         Q(existing) = current discharge rate of the developed parcel
         Q(undeveloped) = discharge rate of the parcel prior to any development
         The reduction of allowable flow rate for redeveloped areas shall not exceed more than 30% of the existing developed flow rate. These flow rates are based on redevelopment sites that disturb one acre or more.
      (6)   The City of Glasgow reserves the right to require superseding or additional treatment criteria or objectives for specific pollutants(s) as necessary to meet overall stormwater quality management program objectives or directives under a watershed improvement or Total Maximum Daily Load (TMDL) program as administered by the USEPA or Commonwealth of Kentucky.
      (7)   The Stormwater Manager, in accordance with good engineering practice, may exercise the following options:
         (a)   Off-site mitigation option: Entails infiltration/evapotranspiration/reuse measures that may be implemented at another location within the same watershed as the original project, approved by the city. The city shall identify priority areas within the watershed in which mitigation projects can be completed.
         (b)   Payment-in-lieu option: Allows the owner of a project that falls within the quality criteria, to make a payment to the city in lieu of implementing post-construction BMPs. The city will apply the in-lieu funds to a public stormwater project. The fee shall be used for acquisition, design, construction or maintenance of one or more such facilities in the same watershed in which the development is located.
      (8)   Permanent easement for all stormwater drainage ways, quality and quantity facilities shall be dedicated to the City of Glasgow. There shall also be dedicated easement for access to all stormwater management facilities.
(Ord. 2809, passed 12-10-2012)
BONDS, MAINTENANCE, ASSURANCES AND FEES
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