(A) Applicability and exemptions. The storage and controlled release rate of excess stormwater runoff shall be required for all new business, commercial and industrial developments, residential subdivisions, planned development, rural estate subdivisions and any redevelopment or other new construction located within the town. The Town Drainage Board and/or the Town Engineer, after thorough investigation and evaluation, may waive the requirement of controlled runoff for minor subdivisions and parcelization. Additional exemptions regarding the detention requirements are provided under division (B)(1)(e) below.
(B) Policy on stormwater quantity management.
(1) Detention policy. It is recognized that most streams and drainage channels serving the town do not have sufficient capacity to receive and convey stormwater runoff resulting from continued urbanization. Accordingly, except for situations provided in divisions (B)(1)(c) and (d) below, the storage and controlled release of excess stormwater runoff shall be required for all developments and redevelopments (as defined in § 52.21) located within the town.
(a) General release rates. In general, the post-development release rates for developments up to and including the ten-year return period storm may not exceed 0.1 cfs per acre of development. The post-development release rate for developments for the 11 to 100-year return period storms shall not exceed 0.3 cfs per acre of development. For sites where the pre-developed area has more than one outlet, the release rate should be computed based on pre-developed discharge to each outlet point. The computed release rate for each outlet point shall not be exceeded at the respective outlet point even if the post developed conditions would involve a different arrangement of outlet points.
(b) Site-specific release rates for sites with depressional storage.
1. For sites where depressional storage exists, the general release rates provided above may have to be further reduced. If depressional storage exists at the site, site-specific release rates must be calculated according to methodology described in the McCordsville Stormwater Technical Standards Manual, accounting for the depressional storage by modeling it as a pond whose outlet is a weir at an elevation that stormwater can currently overflow the depressional storage area. Post developed release rate for sites with depressional storage shall be the two-year pre-developed peak runoff rate for the post-developed ten-year storm and ten-year pre-developed peak runoff rate for the post-developed 100-year storm. In no case shall the calculated site-specific release rates be larger than general release rates provided above.
2. Also note that for determining the post-developed peak runoff rate, the depressional storage must be assumed to be filled, unless the Town Drainage Board and/or Town Engineer can be assured, through dedicated easement, that the noted storage will be preserved in perpetuity.
(c) Management of off-site runoff.
1. Runoff from all upstream tributary areas (off-site land areas) may be bypassed around the detention/retention facility without attenuation. The runoff may also be bypassed through the detention/retention facility without attenuation, provided that a separate outlet system or channel is incorporated for the safe passage of the flows, i.e., not through the primary outlet of a detention facility. Unless the pond is being designed as a regional detention facility, the primary outlet structure shall be sized and the invert elevation of the emergency overflow weir determined according to the on-site runoff only. Once the size and location of primary outlet structure and the invert elevation of the emergency overflow weir are determined by considering on-site runoff, the 100-year pond elevation is determined by routing the entire inflow, on-site and off-site, through the pond.
2. Note that the efficiency of the detention/retention facility in controlling the on-site runoff may be severely affected if the off-site area is considerably larger than the on-site area. As a general guidance, on-line detention may not be effective in controlling on-site runoff where the ratio of off-site area to on-site area is larger than 5.1. Additional detention (above and beyond that required for on-site area) may be required by the Town Drainage Board and/or Town Engineer when the ratio of off-site area to on-site area is larger than 5:1.
(d) Downstream restrictions.
1. In the event the downstream receiving channel or storm sewer system is inadequate to accommodate the post-developed release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the receiving downstream channel or storm sewer system. Additional detention, as determined by the Town Drainage Board and/or Town Engineer, shall be required to store that portion of the runoff exceeding the capacity of the receiving sewers or watercourses. When the downstream restrictions are suspected, the Town Drainage Board and/or Town Engineer may require additional analysis to determine the receiving system’s limiting downstream capacity.
2. If the proposed development makes up only a portion of the undeveloped watershed upstream of the limiting restriction, the allowable release rate for the development shall be in direct proportion to the ratio of its drainage area to the drainage area of the entire watershed upstream of the restriction.
(e) Exemptions for detention requirements. Detention will not be required for the following:
1. Notwithstanding the requirements for an individual lot plot plan permit in this subchapter, land alterations where the primary basis on which a stormwater drainage permit is required is the construction, enlargement or location (on a permanent foundation) of a one-family dwelling, two-family dwelling or accessory structure appurtenant to either a one- or two-family dwelling;
2. Accepted fill areas or one-time addition to existing commercial buildings that do not increase the amount of impervious area on-site by more than a total of 0.5 acres, provided the existing runoff patterns and flow capacity within the property will not be altered by the filling operations;
3. Not withstanding the provisions of division (B)(1)(d) above, those site developments where the stormwater management system has been designed so that:
a. After combining flows from both the off-site and on-site drainage areas, there will be no increase in the total peak discharge from the developing site during the two-, ten- and 100-year storm events;
b. The volume of runoff for each project site outlet has not been increased for the two-, ten- and 100-year storm events; and
c. The flow width and velocity at the property boundary line for each sub-basin is less than or equal to that flow width and velocity which existed prior to the development for the two-, ten- and 100-year storm events.
4. Where the direct release of runoff from the proposed development meets the conditions set forth in division (B)(1)(f) below.
(f) Direct release provisions. It is the policy of the Town Drainage Board and/or the Town Engineer to not allow the direct release (no detention) of runoff from a proposed development to an adjacent stream since there is no large watershed area (more than 100 square miles) of contributing drainage area in any of the watersheds within the town.
(2) Grading and building pad elevations.
(a) Maximum yard slopes are 3:1 where soil has been disturbed during construction processes. Finished floor elevation must be no less than six inches above finished grade and a minimum of 15 inches above an adjacent road elevation unless a written variance is granted by the Town Drainage Board.
(b) For all structures located in the special flood hazards area (SFHA) as shown on the FEMA maps, the lowest floor elevations of all residential, commercial or industrial buildings, shall be such that lowest floor elevation, including basement, shall be at the flood protection grade and therefore have two feet of freeboard above the 100-year flood elevation.
(c) The lowest adjacent grade for residential, commercial or industrial buildings outside a FEMA or IDNR designated floodplain shall have two feet of freeboard above the flooding source’s 100-year flood elevation under proposed conditions, unless the flooding source is a rear-yard swale. When the flooding source is a rear-yard swale, the lowest adjacent grade for residential, commercial or industrial buildings shall have two feet of freeboard above the 100-year flood elevation under proposed conditions or be separated by a minimum distance of 50 feet from the proposed-condition 100-year flood boundary.
(d) For areas outside a FEMA or IDNR designated floodplain, the lowest adjacent grade (including walkout basement floor elevation) for all residential, commercial or industrial buildings adjacent to ponds shall be set a minimum of two feet above the 100-year pond elevation or two feet above the emergency overflow weir elevation, whichever is higher. In addition to the lowest adjacent grade requirements, any basement floor must be at least a foot above the permanent water level (normal pool elevation).
(e) The 100-year flow paths throughout the development, whether shown on FEMA maps or not, must be shown as hatched area on the plans and 30 feet along the centerline of the flow path contained within permanent drainage easements.
1. A statement shall be added to the plat that would refer the viewer to the construction plans to see the entire extent of overflow path as hatched areas.
2. No fences or landscaping can be constructed within the easement areas that may impede the free flow of stormwater. These areas are to be maintained by the property owners or be designated as common areas that are to be maintained by the homeowners association.
3. The lowest adjacent grade for all residential, commercial or industrial buildings shall be set a minimum of one foot above the noted overflow path/ponding elevation.
(f) It shall be the property owners’ responsibility to maintain the natural features on their lots and to take preventive measures against any and all erosion and/or deterioration of natural or human- made features on their lots.
(3) Acceptable outlet and adjoining property impacts policies.
(a) Design and construction of the stormwater facility shall provide for the discharge of the stormwater runoff from off-site land areas as well as the stormwater from the area being developed (on-site land areas) to an acceptable outlet(s) (as determined by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner) having capacity to receive upstream (off-site) and on-site drainage. The flow path from the development outfall(s) to a regulated drain or natural watercourse (as determined by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner) shall be provided on an exhibit that includes topographic information. Any existing field tile encountered during the construction shall also be incorporated into the proposed stormwater drainage system or tied to an acceptable outlet.
(b) Where the outfall from the stormwater drainage system of any development flows through real estate owned by others prior to reaching a regulated drain or watercourse, no acceptance shall be granted for the drainage system until all owners of real estate and/or tenants crossed by the outfall consent in writing to the use of their real estate through a recorded easement. In addition, no activities conducted as part of the development shall be allowed to obstruct the free flow of flood waters from an upstream property.
(c) If an adequate outlet is not located on site, then off-site drainage improvements may be required. Those improvements may include, but are not limited to, extending storm sewers, clearing, dredging and/or removal of obstructions to open drains or natural watercourses, and the removal or replacement of undersized culvert pipes as required by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner.
(4) No net loss floodplain storage policy.
(a) Floodplains exist adjacent to all natural and human-made streams, regardless of contributing drainage area or whether they have been previously identified or mapped. Due to potential impacts of floodplain loss on peak flows in streams and on the environment, disturbance to floodplains should be avoided. When the avoidance of floodplain disturbance is not practical, the natural functions of floodplain should be preserved to the extent possible.
(b) In an attempt to strike a balance between the legitimate need for economic development within the town and the need to preserve the natural functions of floodplains to the extent possible, compensatory excavation equivalent to the floodplain storage lost shall be required for all activities within floodplain of streams located in the town where drainage area of the stream is equal or larger than one square mile. This requirement shall be considered to be above and beyond the minimum requirements provided in the applicable flood hazard areas ordinance currently in effect in the town. The Town Drainage Board and/or Town Engineer may alter the compensation ratio, based on extenuating circumstances, for a specific project.
(c) Note that by definition,
COMPENSATORY STORAGE is the replacement of the existing floodplain and, in rare exceptions, the floodway storage lost due to fill. Compensatory storage is required when a portion of the floodplain is filled, occupied by a structure or when as a result of a project a change in the channel hydraulics occurs that reduces the existing available floodplain storage. The compensatory storage should be located adjacent or opposite the placement of the fill and maintain an unimpeded connection to an adjoining floodplain area.
(d) Computations must show no net loss of floodplain storage for two-year, ten-year, 50-year and 100-year storm events. That is, the post-development two-year floodplain storage along a stream shall be the same as two-year pre-development floodplain storage along the stream within the property limits, the post-development ten-year floodplain storage along a stream shall be the same as ten-year pre-development floodplain storage along the stream within the property limits, and so on.
(e) Calculations for floodplain volume shall be submitted in tabular form showing calculations by cross-section. The volume of floodplain storage under the without-project conditions and the with-project conditions should be determined using the average-end-area method with plotted cross-sections at a horizontal to vertical ratio of between 5:1 and 10:1, with two- through 100-year flood elevations noted on each cross-section. The scale chosen should be large enough to show the intent of proposed grading. Cross-sections should reflect both the existing and proposed conditions on the same plot. The location and extent of the compensatory storage area as well as the location and orientation of cross-sections should be shown on the grading plan.
(C) Calculations and design standards and specifications. The calculation methods as well as the type, sizing and placement of all stormwater facilities shall meet the design criteria, standards and specifications outlined in the McCordsville Stormwater Technical Standards Manual. The methods and procedures in the Stormwater Technical Standards Manual are consistent with the policy stated above.
(D) Drainage easement requirements. There shall be no trees or shrubs planted, nor any structures or fences erected in any drainage easement, unless otherwise accepted by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner. All stormwater systems, including detention or retention basins, conveyance systems, structures and appurtenances, located outside of the right-of-way may be incorporated into the town’s system at the discretion of the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner. The developer shall petition to incorporate the storm system into the town’s system. The stormwater management permit shall not be approved until the petition is submitted in a form accepted by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner. The following specific areas shall be included in a petition.
(1) Subdivisions.
(a) All new channels, drain tiles equal to or greater than eight inches in diameter, inlet and outlet structures of detention and retention ponds, and appurtenances thereto as required by this chapter, that are installed in subdivisions requiring a stormwater management permit from the town shall be petitioned by the project site owner to become incorporated into the town’s system upon completion, proper inspection, and acceptance by the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner. New drain tiles refer to all sub-surface stormwater piping, tubing, tiles, manholes, inlets, catch basins, risers and the like.
(b) New drain tile, eight inches to 24 inches in diameter, shall be placed in a minimum 20-foot easement (ten feet from centerline on each side) and shall be designated on the record plat as 20-foot regulated drain easement (RDE). Pipes that are 24 inches or larger in diameter shall be placed in a 30-foot easement (15 feet from centerline on each side) and shall be designated on the record plat as 30-foot regulated drain easement. Wider easements may be required by Town Drainage Board and/or Town Engineer when the depth of pipe is greater than six to ten feet, depending on the pipe size.
(c) A minimum of 25 feet from top of the bank on each side of a new channel shall be designated on the record plat as a drainage easement.
(d) Rear-yard swales and emergency overflow paths associated with detention ponds shall not be included in petition for incorporation; however, a minimum of 30 feet width (15 feet from centerline on each side) needs to be designated as drainage easement.
(e) A minimum of 30 feet beyond the actual footprint (top of the bank) of stormwater detention facilities shall be designated as drainage easement. A minimum 30-foot width easement shall also be required as access easement unless the pond is immediately next to a public right-of-way.
(f) The statutory 75-foot (each side) drainage easement for regulated drains already within the town’s system may be reduced if the drain is re-classified by the Town Drainage Board as an urban drain.
(g) If the Town Drainage Board and/or Town Engineer accepts the petition for incorporation into their system, the following statement shall become part of the restrictive covenants of every platted subdivision and shown on the recorded plat: “Channels, tile drains eight inches or larger, inlets and outlets of detention and retention ponds, and appurtenances thereto within designated drain easements are extensions of the town’s stormwater drainage system, and are the responsibility of the Town Drainage Board and/or the Town Public Works Commissioner. Drainage swales and tile drains less than eight inches in inside diameter shall be the responsibility of the property owner or homeowner association”.
(h) The following statement shall be put on each subdivision plat: “A petition addressed to the Town Drainage Board has been filed in duplicate with the Town Engineer, requesting that the subdivision’s storm drainage system and its easements be accepted into the regulated drainage system. The storm drainage system and its easements that are accepted into the regulated drainage system are delineated on the plat as regulated drainage easements (RDEs). Regulated drainage easements are stormwater easements and drainage rights-of-way that are hereby dedicated to the public and to McCordsville, Indiana, for the sole and exclusive purpose of controlling surface water and/or for the installation, operation and maintenance of storm sewers and tile drains as defined in the McCordsville Stormwater Management Ordinance (code § 52.21). These drainage easements are established under authority of the Indiana Drainage Code and the Board may exercise powers and duties as provided in the code. All other storm drainage easements have not been accepted into the town’s system. All drainage improvements performed relative to the conveyance of stormwater runoff and the perpetual maintenance thereof, within the latter easements, shall be the responsibility of the owner or homeowner association. The Town Drainage Board assumes no responsibility relative to the improvements or the maintenance thereof. This subdivision contains linear feet of open ditches and linear feet of subsurface drains that will be included in the town’s regulated drainage system.” The noted regulated drain lengths, broken down by the length of open and tile drains, shall also be shown in tabular form in a prominent position on the plat. Any crossing and/or encroachment of a drainage easement requires application and acceptance from the Town Engineer and/or the Town Public Works Commissioner.
(2) Non-subdivisions. Where the Town Drainage Board and/or the Town Public Works Commissioner is responsible for maintenance of the drainage system, drainage easements of 75 feet from the top of bank on each side of the channel or each side of the tile centerline must be dedicated to the town. In addition, a minimum of 25-foot width of vegetative fitter strip must be provided and maintained along top-of-bank, on each side, by the applicant within these easements.
(3) Establishment of new regulated drain. When the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner determines it is necessary to establish a new regulated drain, each developer shall provide the necessary information and meet the requirements of the 1965 State Drainage Code, being I.C. 36-9-27-1 et seq., as amended, for the establishment of a new regulated drain. Necessary easements for adequate maintenance of any new regulated drain shall be determined by the Town Engineer and/or the Town Public Works Commissioner if not already established in this subchapter.
(4) Municipalities and schools. All new channels, swales, drain tiles, inlet and outlet structures of detention and retention ponds, and appurtenances thereto as required by this chapter, that are installed on the municipal or school property will be maintained, repaired and constructed by the entity and will not become regulated drains. The design must meet the standards of this subchapter for sizing and installation. Any off-site portion of the drainage system must be within easements and have clearly defined maintenance agreements between the property owner and the municipality and/or school.
(E) Placement of utilities. No utility company may disturb existing storm drainage facilities without the consent of the Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner, whose decision may be appealed to the Town Council. All existing drainage facilities shall have senior rights and damage to the facilities shall result in penalties as prescribed in § 52.29.
(F) Structures near regulated drains. For regulated drains not located in platted subdivisions, unless otherwise accepted by the Town Drainage Board and/or the Town Public Works Commissioner, no permanent structure (including fences) shall be erected within 75 feet measured at right angles from: the existing top edge of each bank of a regulated open drain, as determined by the Town Drainage Board and/or the Town Public Works Commissioner; or the centerline of a tiled regulated drain. The State Drainage Code may be consulted for further details.
(G) Inspection, maintenance, record-keeping and reporting.
(1) After the approval of the stormwater management permit by the Town Drainage Board and the commencement of construction activities, the Town Drainage Board and/or the Town Engineer and/or the Town Public Works Commissioner has the authority to conduct inspections of the work being done to ensure full compliance with the provisions of this section, the Stormwater Technical Standards Manual and the terms and conditions of the approved permit.
(2) The Town Drainage Board and/or the Town Engineer and/or the Town Public Works Commissioner also have the authority to perform long-term, post-construction inspection of all public or privately owned stormwater quantity facilities.
(a) The inspection will cover physical conditions, available storage capacity and the operational condition of key facility elements.
(b) Stormwater quantity facilities shall be maintained in good condition, in accordance with the terms and conditions of the approved stormwater management permit and shall not be subsequently altered, revised or replaced except in accordance with the approved stormwater permit or in accordance with approved amendments or revisions to the permit.
(c) If deficiencies are found during the inspection, the owner of the facility will be notified by Town Drainage Board and/or Town Engineer and/or the Town Public Works Commissioner and will be required to take all necessary measures to correct the deficiencies.
(d) If the owner fails to correct the deficiencies within the allowed time period, as specified in the notification letter, the Town Drainage Board and/or the Town Public Works Commissioner will undertake the work and collect all cost to collect the deficiencies and attorney’s fees from the owner, using lien rights if necessary.
(e) Assignment of responsibility for maintaining facilities serving more than one lot or holding shall be documented by appropriate covenants to property deeds, unless responsibility is formally accepted by a public body, and determined before the final stormwater permit is approved.
(f) Stormwater detention/retention basins may be donated to the town or other unit of government designated by the Town Drainage Board and/or the Town Public Works Commissioner, for ownership and permanent maintenance providing the Town Drainage Board and/or the Town Public Works Commissioner or other governmental unit is willing to accept responsibility.
(Ord. 030805, passed - -2005)