Adequate drainage shall be provided on any property to be developed or changed from its current use or topographical conditions in accordance with recognized good engineering standards and construction practices relating to such drainage.

(Ord. 09-0721, passed 7-21-2009; Ord. 19-1022B, passed 10-22-2019)

   Sizing of inlets, storm sewers, outfalls, culverts and drainage ditches within a subdivision/development shall be based on the following and the latest revision (as of the adoption of this ordinance) of the Montgomery County Drainage Criteria Manual:

(Ord. 09-0721, passed 7-21-2009; Ord. 19-1022B, passed 10-22-2019)

   The design of storm sewers, outfalls, culverts and drainage ditches within a subdivision shall conform to the following:

      (1)   The pipe or storm drain shall be constructed of reinforced concrete pipe (RCP), high-performance polypropylene pipe (HP or PP), HDPE pipe, or as specified by the City Engineer, and shall be sized as shown on the approved plans. Pipe shall be a minimum of 18 inches or larger in diameter. Concrete pipe shall be reinforced ASTM C-76, class 3. High-performance polypropylene pipe shall be dual-wall, shall meet or exceed the requirements of ASTM F288 l and AASHTO M330, and shall be installed in conformance with section 12 of the AASHTO LRFD Bridge Design Specifications and section 30 of the AASHTO LRFD Bridge Construction Specifications. HDPE pipe shall be made from virgin polyethylene and comply with the requirements for test methods, dimensions, and markings found in AASHTO Designations M252, M294, and MP7-97.

      (2)   Pipes shall have a minimum cover of not less than one foot over the top of the pipe or in accordance with the pipe manufacturer's specifications, whichever is greater. When added strength of pipe is needed for traffic loads, excessive height of backfill, or cover of less than one foot due to uncontrollable constraints, reinforced concrete pipe meeting ASTM C-76, class 4 or 5, or high-performance polypropylene pipe with comparable strength properties and expected life span under similar design loads shall be used. Data demonstrating the strength characteristics, design life, or other information about the selected pipe materials and their appropriateness for the proposed application shall be provided at the request of the Director of Public Works or the City Engineer for evaluation. Proposed pipe materials may be rejected for a specific application by the Director of Public Works or the City Engineer.

(Ord. 09-0721, passed 7-21-2009; Ord. 19-1022B, passed 10-22-2019; Ord. 22-0621A, passed 6-21-2022) Penalty, see § 155.999

   The latest revision (as of the adoption of this ordinance) of the Montgomery County Drainage Criteria Manual shall be used as a base standard for open channels and detention/retention facilities within a subdivision, unless otherwise approved by the City Engineer.

      (1)   Channels may be left in their natural state, provided that the channel has capacity for the developed flows with one foot of freeboard and velocities are 6.0 feet per second or less.

      (2)   If the natural channel is to be replaced by an improved channel, the flow from the 100-year design flood must be contained within the improved channel while allowing for one foot of freeboard.

      (3)   Improved channels shall include a lined section if the design velocity is greater than four feet per second. Lining types, such as concrete, rock walls, erosion control mats and gabions, may be used upon the approval of the City Engineer. Improved channels with design velocities less than the permissible velocities given by the City Engineer may be earthen if the channels are revegetated properly.

      (4)   Lined channels shall have the entire channel bottom and at least the first three feet (vertical height) of the side slopes up from the channel bottom lined, unless approved by the City Engineer.

      (5)   Earthen sides above the lined section or totally earthen channels shall be on at least a three feet horizontal to one foot vertical slope, and shall have approved ground cover to prevent erosion.

      (6)   Improved channels shall have the following minimum side slopes, unless shown to be feasible in a soils report sealed by a registered professional engineer in the state, and approved by the City Engineer:

         (a)   Three feet horizontal to one foot vertical slope for earthen grassed side slopes.

         (b)   One and one-half feet horizontal to one foot vertical slope for side slopes in rock.

      (7)   The developer or owner shall use low maintenance vegetation for vegetative cover, as approved by the City Engineer prior to planting. The selection of planting materials shall comply with locally accepted industry standards.

      (8)   The developer or owner shall provide a drainage easement and required maintenance easement which shall be dedicated to the city as a permanent drainage right-of-way and open space corridor.

      (1)   The minimum amount of storage volume of the detention basin shall be the volume required to reduce runoff rates to an undeveloped rate. Dedicated detention/retention basins shall also include an additional one foot of freeboard.

      (2)   Detention areas in parking lots shall not be:

         (a)   In required parking spaces, but shall be in extra spaces.

         (b)   Behind speed bumps, unless the speed bumps are made with reinforced concrete.

         (c)   Deeper than six inches, unless warning signs are posted.

      (3)   Drainage easements shall be provided for all regional detention/retention facilities and for other detention/retention facilities where two or more owners are involved.

      (4)   Detention/retention facilities shall be designed to empty all detention storage in less than 24 hours.

      (5)   Detention/retention facilities shall not be counted as an erosion control technique, unless:

         (a)   The basin is designed to empty a minimum of 24 hours after the storm event; and

         (b)   Adequate sediment storage areas in the basin have been set aside and are maintained.

      (6)   Detention/retention facilities shall be maintained by the owner, unless such facilities are dedicated to and accepted in writing by the city.

      (7)   The engineer shall certify that the detention/retention facilities were constructed in accordance with the plans and specifications. The engineer shall provide a signed as-built drawing showing dimensions and elevations of the detention/retention facility.

      (8)   Any existing subdivision/development that increases the impervious (or semi-impervious) area by more than 15,000 square feet must provide detention/retention/mitigation for the increase in impervious or semi-impervious development.

(Ord. 09-0721, passed 7-21-2009; Am. Ord. 10-0803, passed 8-3-2010; Ord. 19-1022B, passed 10-22-2019) Penalty, see § 155.999

   (A)   The owner or developer of property to be developed or changed shall be responsible for all storm drainage flowing from a fully developed watershed. Such responsibility shall include drainage directed to the property by ultimate development, as well as drainage naturally flowing through the property due to topography. When property is proposed for development, use or modification, provisions shall be made for storm drainage in accordance with this chapter.

   (B)   Where the improvement or construction of a storm drainage facility is required along a property line common to two or more owners, the owner proposing development of his or her property shall be responsible for the required improvements at the time of development, including the dedication of all necessary rights-of-way or easements, to accommodate the improvements.

   (C)   When a property owner proposes development or use of only a portion of his or her property, provision for storm drainage in accordance with this chapter shall be required in the portion of the property proposed for immediate development. Improvements of a drainage facility outside such designated portion of the property shall be required for the handling of the development of the designated portion.

   (D)   When a property owner proposes a development, provisions shall be made in the comprehensive drainage plan for control of excess siltation and downstream erosion.

   (E)   The owner shall dedicate the required drainage easements. Determination of the minimum easement required shall be made by the City Engineer.

   (F)   If a property owner or developer desires to modify an existing pond or lake, or impound storm water by constructing a dam within a property for retention or detention, thereby creating a lake, pond, lagoon or basin as a part of the planned development of the property, the standard provisions for storm drainage as established in this chapter shall be applicable, and shall provide that:

      (1)   An engineering plan for such construction, including the comprehensive drainage plan and a storage facility study prepared by a registered professional engineer, shall have been approved by the city;

      (2)   The owner and developer shall retain the constructed lake, pond, lagoon or basin under private ownership, and assume full liability for the protection of the general public from any health or safety hazards related to such construction;

      (3)   The owner and developer shall assume full responsibility for the maintenance of the constructed lake, pond, lagoon or basin;

      (4)   The obligations set forth in this division shall run with the land, and shall be a continuing obligation of the owner of such land; and

      (5)   All Federal, state and county laws pertaining to impoundment of surface water are complied with, including the design, construction and safety of the impounding structure. Any existing structure which is included in a project development area shall be improved to comply with the applicable Federal, state, county and city safety requirements for structures. The design flows shall be based on a fully developed watershed in accordance with the comprehensive land use plan for a 100-year flood. All improvements shall be made to the dam structure at the expense of the developer prior to acceptance of the adjacent street, utilities and drainage improvements.

   (G)   On any existing structure, the owner shall furnish to the city a study by a professional engineer, registered in the state, for approval prior to any proposed alteration. Compensatory storage shall be provided so that a 100-year flood retention capacity is provided.

   (H)   The property owner shall keep the city advised in writing of the current name and address of the responsible agent.

   (I)   All existing water seepage springs or flowing water shall be connected into an underground storm sewer system or shall be discharged into an appropriate facility intended to carry storm water runoff. Such flow shall not be permitted to discharge directly into the street gutter line.

   (J)   Fences (private and public screening) shall be constructed so that an obstruction to surface water flow shall not occur. Such requirement shall include the requirement that erosive conditions shall not be created around, under or near a fence structure.

   (K)   Since urbanization is anticipated on all drainage areas, all improvements shall be designed for the case of full watershed development. The developer shall be responsible for the necessary facilities to provide drainage patterns and controls so that properties within the drainage area, whether upstream or downstream of the development, are not adversely affected by storm drainage from facilities on the development. A letter from an engineer licensed in the state shall be provided certifying that properties within the drainage area will not be adversely affected. The letter shall be sealed, signed and dated.

   (L)   A storage facility study and comprehensive drainage plan shall be provided to the City Engineer with the final engineering drawings. The storage facility study and comprehensive drainage plan shall be prepared in a quantitative manner. The comprehensive drainage plan shall include:

      (1)   Methods to be used for the disposal of storm water runoff from the proposed development;

      (2)   Provisions for contributing drainage from adjacent properties;

      (3)   A topographic drainage area map, indicating all areas contributing drainage runoff;

      (4)   On-site and off-site drainage easements;

      (5)   Proposed and existing storm sewers, curb inlets and open channels;

      (6)   A table showing the drainage subareas, land use, C-factor, rainfall intensity, time of concentration, frequency factor, area in acres and amount of runoff;

      (7)   An indication of runoff at all inlets, dead-end streets and alleys and to adjacent off-site property;

      (8)   An indication of floodplain and flood way boundaries;

      (9)   An indication of siltation and erosion control measures for the entire development and/or stage development;

      (10)   An indication of flow arrows on drawings;

      (11)   A detailed off-site drainage plan.

   (M)   All storm drainage improvements or modifications shall be planned in the best interest of the immediate and adjacent properties, and shall be designed using the design criteria adopted by the City and the most current Federal Emergency Management Agency (FEMA) flood data. The floodplain and floodway boundaries indicated on the drawings shall be determined based on a fully developed watershed, in accordance with the comprehensive land use plan of the City. The FEMA flood boundaries shall represent the minimum flood boundaries to be used.

   (N)   All development shall be designed and constructed in a way to have no negative affect on surrounding areas or unreasonably:

      (1)   Impede the natural flow of surface waters from higher adjacent properties;

      (2)   Alter the natural flow of surface waters so as to discharge them upon adjacent properties at a more rapid rate or in a different location than would result from the pre development natural flow of surface waters; or

      (3)   Collect or concentrate the flow of surface waters for discharge into an existing natural or artificial drainage way in a manner which exceeds the capacity of the receiving water course.

   (O)   Storm drainage released from the site will be discharged to a watercourse of an adequate size to control the peak runoff expected after development. The City Engineer shall be provided the necessary data showing the adequacy of the watercourse. Criteria for on-site development shall apply to off-site improvements. Any discharge point exiting the property shall be within the required drainage easements or right of way on adjacent property. Determination of the minimum easement required shall be made by the City Engineer.

   (P)   The design, size, type and location of all storm drainage facilities shall be subject to the approval of the City Engineer. The requirements set forth in this section shall be considered minimum requirements. The developer and his or her engineer shall bear the total responsibility for the adequacy of the design. The approval of the facilities by the City shall in no way relieve the developer of such responsibility.

   (Q)   Requests for a variance, detailing specific reasons for the variance, shall be submitted in writing. The City Engineer shall make a recommendation to the City Council for its approval of the variance. Variations and modifications to the storm drainage requirement of the city may be made when special or peculiar factors and conditions warrant such variations and modifications, and when such variations and modifications do not affect the general intent, application or spirit of the storm drainage rules and regulations of the city.

(Ord. 09-0721, passed 7-21-2009; Ord. 19-1022B, passed 10-22-2019) Penalty, see § 155.999