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Memorandum of Clarification - Issued June 21, 2011 1

MEMORANDUM OF CLARIFICATION DATE: Issued June 21, 2011 FROM: Departments of Public Works and Code Enforcement RE: Revised Storm Water Design and Construction Specifications Manual,

Clarification Document

The Departments of Public Works (DPW) and Code Enforcement (DCE) have developed this clarification document to assist in answering questions related to the revised Storm Water Design and

Construction Specifications Manual that went into effect on June 1, 2011. The DPW drafts and promulgates changes to the storm water standards and the DCE enforces those standards. This

document is a companion to the revised manual which can be found at: http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/UpdatedStormWaterManual.aspx

In this manual, there are references made to the DPW, DCE, DMD, Division, Department, Administrator, Indianapolis Department of Metropolitan Development and the Office of Code

Enforcement. In using the manual, consider that some of these references may not be up-to-date in the current version. Before submission of permit applications and plans to DCE, designers are strongly encouraged to contact a DCE representative with questions, requests for clarification and review of

current submittal requirements / procedures for their project at:

Department of Code Enforcement 1200 Madison Ave., Ste. 100 Indianapolis, IN 46225 Phone: (317) 327-8700 Fax: (317) 327-5174 http://www.indy.gov/eGov/City/DCE/

EXISTING APPROVED STORM WATER / DRAINAGE MASTERPLAN POLICY Projects that are currently included under an existing approved storm water / drainage masterplan, which includes detention and / or water quality will be reviewed on a case-by-case basis. The submitted project must demonstrate compliance with the previously approved masterplan design parameters for the detention and / or water quality design. Compliance must be demonstrated by providing a copy of the original masterplan calculations and mapping applicable to the project. If a copy of the existing masterplan is unavailable or the the existing parameters of the masterplan design are exceeded, then the design may be required to demonstrate that the pond has sufficient capacity based on the current DPW design standards. Pond modifications, including enlarging the pond or updating the pond outlet and emergency spillways, may be required to bring the pond in compliance to the current standards. If the submitted project is able to demonstrate compliance with the originally approved masterplan design parameters for the detention and /or water quality, then modifications to the pond may not be required. In all cases, the downstream conveyance systems must be able to demonstrate capacity for the proposed site flows.

http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/UpdatedStormWaterManual.aspx


CHAPTER 100 101.02 1 – Applicability – Mitigation Paragraph “Improvements to an existing developed site that is not developed to current storm water design standards and disturbs => 1/2 acre will be required to comply with the current storm water regulations for storm water quantity and quality, at twice the area disturbed within the existing contributing drainage area at the proposed site work and owned by the project/property owner.” Clarification 1: One of the goals of this paragraph is intended to increase the surface being treated for water quality beyond just the disturbed area especially in developed areas. Development projects disturbing greater than 0.5 acres must address water quality requirements and now must include up to twice the proposed disturbed area in the water quality system design. This requirement is limited to the total adjoining area under project ownership. If twice the disturbed area is greater than the total area of the site under ownership of the developer, then the total area required to be treated for water quality would be the site itself. The other goal of this paragraph is to reduce runoff from developments that do not meet current standards. However, many sites may already have a detention system that meets requirements. 101.04 2 – Updating Clarification 2: The website will include a means for registering for e-mail notifications when there are additional revisions, clarifications or other communication regarding the manual. Visit http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/UpdatedStormWaterManual.aspx These notifications will direct individuals to information on the website only and will not include the actual revisions. 102.02, 5. 3 – Plan Submittal and Approval Process “As a general rule, all land alterations will require a:… 5. Operation and Maintenance Manual for all detention, storm water, and water quality structures,…” Clarification 3: An operations and maintenance manual is now required for all storm water

infrastructure. The O & M Manual should be divided into the following sections:

Section I - Owner Information;

Section II- Site Information;

Section III - Inlet Maintenance;

Section IV - Conveyances Maintenance (pipes. swales, ditches);

Section V - Detention System Maintenance;

Section VI - Water Quality System Maintenance.

Section I should include all the owner information specified in Section 102.06, 1. of the Specifications Manual. This section should also include the statement the owner is responsible for all maintenance including cost. Section II should include an overall site drawing with all storm water systems labeled as well as the inspection points. Additional drawings zoomed with details of each inspection point should also be included. These drawings should be limited to a maximum size of 11” x 17”.

Section III addresses inlet maintenance / inspection. All inlet castings should be inspected monthly and after each rainfall event. More frequent inspections should be performed in areas where there is higher potential for trash or litter (e.g. retail establishments) and during the fall when leaves are present on the ground. Catch basins should also be inspected for sediment depth. A maximum depth should be specified in the manual (recommended no greater than 1/4 of the pipe diameter with a maximum of 6”).

http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/UpdatedStormWaterManual.aspx


Section IV will discuss inspection of conveyances. Swales should be clear of high plant growth with a maximum height specified of 5 inches. Swales should also be unobstructed by buildings, fences and have a uniform slope. Pipes need to be inspected for sediment and a maximum depth specified before cleaning is required. Section V should address outfall inspection and floatable debris. Removal of floatables and a frequency of inspection / removal provided. The removal method should also be discussed (e.g. netting of debris). General outfall condition including downstream erosion shall also be included. Mowing of pond berms and banks as well as dry-bottom ponds should also be required.

Section VI should include all the requirements of Section 102.06. Inspection checklist(s) should be provided addressing the specific inspection points and detailed procedures. The entire O & M Manual should be a single, inclusive document and must be submitted with an electronic copy for review. 102.02 4 – Plan Submittal and Approval Process “The zoning of any properties for which drainage permits are applied must be consistent with the proposed land use before drainage permits will be approved.” Clarification 4: The Technical Information Report (TIR) should include an appendix addressing zoning. Approved Zoning Commitments and the current zoning documentation must be provided. 102.03, 1.a. 5 - Platted Subdivisions, Commercial, and Industrial Developments Clarification 5: The City of Indianapolis Drafting Standards should be utilized for the completion of all plans and profiles. A copy of the drafting standards can be referenced from the following website: http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/DraftingStandards.aspx 102.03, 1. b. 6 - Platted Subdivisions, Commercial, and Industrial Developments “The following information must be submitted for approval:…

b. Cover Sheet: A cover sheet shall be provided, including location and vicinity map. A map

that indicates the location and vicinity of the proposed land alteration shall be included in the

storm water plan. It shall reference a nearby major roadway intersection. The cover sheet shall

also include site address, as assigned by DMD, the DMD Compliance Information Block and a

storm water structure summary table. The summary table shall provide each proposed pipe

size and respective length with the number of proposed structures. The cover sheet shall also

include a table of water quality structures with the state plane coordinates of the center of each

structure….”

Clarification 6: The cover sheet must be included with all plan submittals. The cover sheet should include the following:

DCE Compliance Information Block;

Storm Water Structure Summary Table;

Water Quality Structure Summary Table.

The Storm water Structure Summary Table should provide the total length of each pipe size on the proposed project and the number of each structure. For example:

http://www.indy.gov/eGov/City/DPW/Business/Specs/Pages/DraftingStandards.aspx


Item Type Count (units)

15 inch pipe CMP 450 (ft)

21 inch pipe RCP 350 (ft)

Manholes N/A 25 (ea)

Catchbasins N/A 15 (ea)

The Water Quality Summary Table should include the State Plan Coordinates of the center or outfall of

each type of water quality unit. For example:

Water Quality Unit

Description

Northing Easting

Water Quality Pond Outfall

Aqua-Swirl

Downstream Defender

102.03, 1. c. 7 - Platted Subdivisions, Commercial, and Industrial Developments “Indiana’s State Plane Coordinate System shall be used to identify the location of the outlet of each BMP included it the plan.” Clarification 7: The use of State Plane Coordinates is the preferred over the use of longitude and latitude. The State Plane Coordinates should be provided for the outlet of ponds, rain gardens, bio-swales etc. The coordinates of the center of manufactured units should be provided. The accuracy of all coordinates should be +/- 2 ft. 102.03, 1. e. 8 – Platted Subdivisions, Commercial, and Industrial Developments “1. Construction Features. The storm water plan shall demonstrate and describe surface and subsurface drainage and include the following:… e. The location of the predominant soil types on the site shall be described by a registered land surveyor or professional engineer. The description may be determined by the NRCS (Natural Resources Conservation Service, formerly the Soil Conservation Service, or SCS) County Soil Survey or an equivalent publication or as determined by a certified professional soil scientist.” Clarification 8: A soils map should be provided in the plan set complete with the appropriate soil descriptions. The map should be scaled to allow all symbols and landmarks to be clearly legible. As with all plan sheets, they should be sealed by an engineer or land surveyor. 102.04 9 – Technical Information Report “Included with this Technical Information Report shall be the following information: 1. Design Calculations. Design calculations are required as part of the storm water plan and shall, at a minimum, specifically include:

a. Estimation of storm water runoff. Runoff rates during the design and Q100 return interval

storms; C-values or runoff curve numbers; and computed times of concentration. A time-of-

concentration and time-of-travel calculation sheet has been provided on page A2-6. A C-

value or runoff curve number computation sheet has been provided on page A2-15.

Guidelines for determination of basin times-of-concentration and runoff rates are presented

within Chapter 200 of this Manual, "Hydrology"…”

Clarification 9: The required design storms include the 2-, 10-, 25- and 100-year storm events for both the existing and proposed conditions. Release rates are now rated on a percentage of the existing runoff rate of these storms.


102.04, 1. a. (1). 10 – Technical Information Report “1. a. Estimation of storm water runoff. Runoff rates during the design and Q100 return interval storms; C-values or runoff curve numbers; and computed times of concentration. A time-of-concentration and time-of-travel calculation sheet has been provided on page A2-6. A C-value or runoff curve number computation sheet has been provided on page A2-15. Guidelines for determination of basin times-of-concentration and runoff rates are presented within Chapter 200 of this Manual, "Hydrology".

(1) Drainage area calculations including both the gross and impervious area for each drainage basin/subbasin;…”

Clarification 10: The Technical Information Report (TIR) should include a table listing each basin and sub-basin and summarizing the gross or total area, impervious surface area, curve number (CN) and time-of-concentration (Tc). 102.06 11 - Operations and Maintenance Manual “An operations and maintenance (O&M) manual for all private infrastructure, including but not limited to pipes, ponds, ditches, and BMPs (when required), shall be submitted for the final plan approval and permit process. The manual will become a maintenance guide for the drainage infrastructure once development is complete. The final O&M manual will be provided to the City in both hard copy and digital formats. The O&M manual maintenance agreement along with a site map showing the BMP locations shall be recorded with the final plat….” Clarification 11: See #4 above. 103.03 12 – Construction Observation Services. Clarification 12: This section is currently being reviewed / revised. The construction observations services are currently handled by the Department of Code Enforcement (DCE) and the section should follow the DCE policy on observation services. Please contact the DCE office for details on construction observation services and fees associated with these services. BMP’s are considered Class I storm water facilities and may be subject to Construction Observation Services.

103.04 13 – Drainage Fees Clarification 13: The schedule of fees provided in the current manual was effective May 1, 2007. The fee schedule was revised January 1, 2011, and permit applicants MUST consult the City website for the current fee schedule (2011 Improvement Location Permit Fees) at: http://www.indy.gov/eGov/City/DMD/Planning/Resources/Pages/Rules.aspx 103.05 14 – Testing, 2. “Forty-two (42) inch diameter and smaller reinforced concrete and corrugated metal pipe may be required to be inspected through closed circuit television viewing (CCTV) by the Department's representative as described herein. In those instances where CCTV is a required part of the storm water permit approval, this televised viewing shall be completed in conformance with these minimum guidelines.” Clarification 14: CCTV testing will be required if pipe fails either the mandrel test or lamping inspection. 103.07 15 - Record Drawings ” Record drawings shall be certified by a Professional Engineer or Land Surveyor registered in the State of Indiana, and provide the following information;…

3. “Horizontal alignment of storm drain pipes, culverts, BMPs, streets, and storm drain structures, to a minimum accuracy of +/- two (2) feet. All BMPs will be located by Indiana State Plane Coordinates.

http://www.indy.gov/eGov/City/DMD/Planning/Resources/Pages/Rules.aspx


4. The as-built survey of all detention / retention facilities as well as as-built profile of all drainage conveyances (ditches, swales, etc). 5. The horizontal location and/or bank cross sections for all detention/retention facilities or other information sufficient to verify that the constructed detention/retention facility provides the required minimum runoff storage volume. 6. A tag reference to the operations and maintenance manual as required for storm water structures will be included.”

Clarification 15: Record drawings must include the State Plane Coordinates of all BMPs, contours of all detention / retention ponds to document volume and a tag reference to an operations and maintenance manual. The tag reference should read, “This site includes an Operation and Maintenance (O & M) Manuals for all storm water infrastructure. Contact the Department of Code Enforcement for a copy of the manual.” 104.02, 16 - Storm Water Quality – “ Floatables. The narrative standards in Section I.B.3 of the City’s NPDES Storm Water Permit (No. INS040001) state that certain categories of floatables, or floating debris are not permitted in storm water discharges. The policy for floatable control in Indianapolis is that the drainage from all areas of new development and redevelopment will be designed to so as to capture and retain floating material. Individual components of the storm water control system do not have to comply with this policy, but the final discharge from the development site must.” Clarification 16: Floatables must now be addressed in the water quality design. The designer must include a means to capture and retain floatables. Methods that can be used include rock dams, screens and inverted outlet pipes. Inverted outlet pipes are recommended because they are less prone to blockage and retain captured material. Screens can become blocked off and force floating debris into the emergency overflow. The O & M Manual should include monitoring of floatable collection devices and specific methods to clean the devices. 104.02 17 – Storm Water Quality (Cumulative disturbed area) “For the purposes of all projects, including commercial, industrial, residential, transportation, recreation, etc., if the cumulative disturbed area is less than ½ acre, the development will be exempt from requirements for on-site BMPs. The cumulative total disturbed area will be evaluated based on City records of permit activity from October 1, 2001.…” Clarification 17: The Technical Information Report (TIR) should include a section on the history of the site to 2001. This should include all previous permits with the City permit number and the disturbed area from each of those permits. The DCE website should be used as one reference for past permits (See http://permitsandcases.indy.gov/citizenaccess/ ) or check with the records department at DCE.

CHAPTER 200 201.03 18 – Off-site Hydrologic Analysis “Hydrograph generation and flood routing procedures shall be required when:

1. The total watershed area tributary to the design point is greater than five (5) acres or less than 5 acres with existing depressional storage;…”

Clarification 18: Existing depressional storage will require hydrograph analysis to determine the existing release rate. Existing depressional areas should be modeled as detention ponds with only weir overflows at the lowest ground elevation at which flow exits the depressional area.

http://permitsandcases.indy.gov/citizenaccess/


201.03 19 – Off-site Hydrologic Analysis “Hydrograph generation and flood routing procedures shall be required when:

1. The total watershed area tributary to the design point is greater than five (5) acres or less than 5 acres with existing depressional storage;

2. Multi-basin analysis must be performed (multi-basin analysis can be required due to drainage patterns as well as land use (cover) changes and changes in soil types),...”

Clarification 19: A runoff analysis is considered multi-basin when there are at least two runoff basins with different times-of-concentration. Different times-of-concentration may result from different flow paths or surface types. This is especially true when an off-site basin is included and hydrographs should be used. When there are potentially times-of-concentration with greater than 20 minute differences, hydrographs should be used. 201.06 20 – When Downstream Conveyance Analysis and Detention/Retention not Required Clarification 20: “Downstream Analysis” or direct discharge without detention analysis is no longer allowed. Proposals for direct discharge will only be reviewed and approved on a case-by-case basis as a variance request. Designers should be aware that ‘Downstream Conveyance Analysis” is required. Evaluation of the capacity of the downstream facility that will be receiving runoff from the proposed development must be addressed in the design Technical Information Report (TIR) (see Section 302.02). 202.02 21 - Rainfall Distribution “Staff has determined that Huff rainfall distributions most accurately reflect rainfall conditions in Indianapolis. The appropriate Huff storm distribution‘s fifty percent (50%) probability curve or column shall be used for hydrograph computations, as is applicable for the design methodology. Figure 202-2 and Table 202-3 can be referenced for the appropriate distribution.” Clarification 21: Table 202-3 should be disregarded and Figure 202-2 used for all Huff Rainfall Ordinates. A revised Figure 202-2 is provided in Appendix C with an additional table specifying the appropriate storm durations applicable to each quartile. Table 205-03 22 Clarification 22: Table 205-03 has been revised to correct Curve Numbers (CN’s) for Row Crops with and without conservation Treatment (see Appendix A) Section 203.03 23 - Overland Flow Time Clarification 23: The maximum length for overland flow is now 100 lft. The Time of Concentration worksheet in Figure 203-1 has been revised to reflect this requirement. The Worksheet is provided in Appendix B. 205.03 24 - NRCS (SCS) Curve Numbers Clarification 24: Weighted curve numbers for all development sites should be calculated. The use of generalized or average curve numbers such as “Business, Commercial” or “Industrial” should not be used for the actual site runoff estimates. In addition, curve numbers for residential developments should also be calculated based on the maximum proposed home footprint and not generalized based on lot size. General or average curve numbers should be used for off-site areas only. 205.03 25 - NRCS (SCS) Curve Numbers “When two soils types are listed (e.g. drained / undrained) drained soil conditions should be used for the pre-developed / allowable release rate calculations and undrained conditions shall be assumed in the post-developed model for soils unaffected by the proposed construction.


Agricultural soils shall assume crops in good condition for the pre-developed / allowable release rate and bare with no cover for the post-developed model for soils unaffected by the proposed construction.” Clarification 25: Release rates and runoff estimates should assume the best-case scenario (minimal runoff) for determining release rates and the worst conditions (Maximum runoff) for determining detention volume. This is also to be applied to off-site basins passing through proposed development or into the proposed development detention pond. If there is a large watershed entering the site and potential pond area is limited, bypassing the off-site flow per Sections 302.03 and 302.06 can be considered by the designer. However, downstream receiving facilities may be restricted and the overall release rate including off-site runoff adjusted accordingly.

CHAPTER 300 302.02 26 - The Requirement for Detention/Retention Clarification 26: Appendix D provides a revised logic diagram and step-by-step explanation. “Downstream Analysis” as used in the previous versions of the Design Manual is no longer allowed. However, downstream receiving facility capacity analysis (“adequate place to receive runoff”) is still required for all proposed storm water facilities. 302.02 27 - The Requirement for Detention/Retention Clarification 27: Downstream Capacity Analysis should be performed to the first 15” or larger pipe, earthen drainage conveyance system, i.e. swale, or the first detention pond on the adjacent parcel, subdivision or as determined by the City. 302.03 28 - Minimum Performance Level of Detention/Retention Facilities Clarification 28: A 2-inch orifice minimum is specified in Chapter 700 for certain water quality designs. To be consistent, the City views a 2-inch orifice as the minimum for water quantity designs as well. However, when a smaller orifice is required, a variance should be submitted for the minimum 2-inch orifice. Measures to prevent blockage should also be provided. 302.03 29 – Minimum Performance Level of Detention/Retention Facilities Clarification 29: Velocity requirements for developments with off-site runoff entering the site must still meet the velocity requirements. This may result in increased detention volume. Any off-site runoff bypassed does not need to meet the velocity requirements if the bypass meets all the requirements of 302.03 and 302.06. 302.04 30 - Increased Detention/Retention In Lieu Of Downstream Analysis Clarification 30: The acceptable method of increased detention design to meet Section 302.04 requirements is the Modified Rational Method as outlined in 302.05. 302.05 31 – Modified Rational Method Clarification 31: The Modified Rational Method must follow the steps outlined in this section including use of the Cr factors. Use of other runoff coefficients (from tables or site specific calculations) to determine the allowable release rate is not acceptable. 302.05 32 - Modified Rational Method Clarification 32: If the use of a minimum 2-inch orifice results in a higher release rate than calculated per this section, calculations documenting the revised runoff rate must be included with the original Modified Rational Method calculations.


302.06 33 – Bypassing Flow Clarification 33: When bypassing off-site flows, the proposed conveyance for the bypassed flows must accommodate all design storms including the 100-year event. An easement should be provided for the off-site conveyance system. Bypassing may include a complete bypass of the runoff from of the detention system or through the proposed system. If the design bypasses through the existing detention system, the detention system must first be designed to meet all the requirements for the on-site runoff then bypass the off–site over the weir. However, all water quality systems must meet the requirements based on both the on- and off-site flows. 302.07 34 – Safety Bench Clarification 34: The safety bench shall have a slope no steeper than 4 (horizontal) to 1 (vertical). The designer may elect to have a flatter slope up to 10 (horizontal) to 1 (vertical) for the safety bench. Figure 505.01 shows a standard safety bench design. If a flatter slope is used then a modified detail will need to be provided on the plans. 302.07 35 – Detention/Retention Facility Design “When retention facilities are designed information must be provided on the plans that supports the ability of the structure to retain water, including the soil types on the site and a geologist’s report showing how the site will infiltrate water.” Clarification 35: Facility designed as retention or infiltration facilities must include a geotech or soil scientist report in the TIR documenting the infiltration rate and seasonal high water table. 302.07 36 – Detention/Retention Facility Design “If a retaining wall adjoins the normal pool of a wet detention pond the wall shall have either steps or a ladder incorporated into the construction at the center of the wall span.” Clarification 36: Retaining walls on ponds will only be accepted with City approval on a case-by-case basis. 302.07 37 – Detention/Retention Facility Design Clarification 37: It is recommended that a maximum drain down time for all detention / retention ponds be 72 hours. If the design does not drain down within this time period additional volume may need to be provided to accommodate another 100-year storm event. 302.08 38 – Design of Detention/Retention Facility Emergency Spillways “… All emergency spillways shall outlet to an easement containing a channel with acceptable capacity.” Clarification 38: An easement is only required to the development property line. However, the point at the property line at which the emergency overflow exits off-the property must be a drainage way leading away from structures on the adjoining parcel. This drainage way must have capacity for the design flow and can include an overland flow path within an easement If the downstream receiving facility does not have sufficient capacity for the design flow, a variance may be requested meeting the Chapter 561 variance requirements. 302.11 39 – Easements “All emergency spillways will have an easement that extends from the crown of the emergency spillway structure to the point where the spillway enters the downstream drainage system.” Clarification 39: See 302.08 above.


302.11 40 – Easements “All detention/retention basins shall be constructed within a storm water easement either platted or legally described and recorded as a perpetual storm water easement a minimum of twenty (20) feet horizontally outside of the design 100-year flood water elevation of the basin.” Clarification 40: When detention / retention facilities are constructed adjacent to a public R/W, the minimum 20 foot easement to R/W must still be provided. 303.03 41 – Grading and Depth of Open Channels / Swales “To prevent chronic wetness in the invert of open channels, subsurface tiles shall be installed a minimum of 1 ½ feet in depth (from the tile invert), with a #8 gravel or equivalent size washed stone as a granular envelope, as follows:

Minor drainage collector swales in rear yards and between homes shall possess a maximum channel length of 400 lineal feet and no off-site water, unless subsurface tile is also provided. The required channel slope and invert treatment for minor drainage collector swales shall be as follows: swales shall be grass lined; subsurface drainage tile shall be required if the channel slope is less than 2.0%; and, the minimum channel slope shall be 0.3%.

For basement residential lots a “tee” should be provided in the rear lot line’s subsurface drain for the purpose of discharging sump pump water directly into the drain. …”

Clarification 41: An underdrain is required for all swales over 400 feet in length. All residential swales regardless of length should have an underdrain with tees for sump pumps. Tee locations should be stationed on the plans and marked in the field with steel rebar. 305.02 42 – Easements Clarification 42: Easement minimum width for pipes up to and including 15 inch in diameter must be 15 feet wide. Pipes larger than 15 inches in diameter should have a 20 foot minimum width. 305.03 43 - Storm Drain Pipe Design “The use of Manning's equation shall be considered acceptable for determination of storm drain pipe sizes when the design discharge is ninety percent (90 %) or less of the capacity of a commercially available pipe as computed by Manning’s equation. The storm drain system must be capable of passing the 10-year storm event with free water surface elevations below the crown of the pipe. Clarification 43: Design computations of storm drain pipe systems using the Rational Formula and Manning's equation shall be submitted with the storm water permit application on the Storm Drain Flow Tabulation Form provided by Figure 305-1 or by suitable computer program output listing giving similar information. Typical Manning's "n" values for standard storm drain materials are provided in Table 305-1. Head loss computations shall be submitted with the storm water permit application on the form provided by Figure 305-2.” In addition Section 102.04 of the manual states: “1. Design Calculations. Design calculations are required as part of the storm water plan and shall, at a minimum, specifically include:

d. Storm drain flow and hydraulic grade line computations as described in Section 305.03 and

305.04. A Storm Drain Flow Tabulation Form has been provided on page A3-14. A Headloss

Calculation Sheet has been provided on page A3-16. A form to assist with completion of culvert

ratings has been provided on page A3-7.”


Also Note, the use of a manufactured BMP (SQU) also requires that HGL calculations be completed for the pipes upstream and downstream of the SQU. Both Sections 102.04 and 305.03 still require hydraulic gradeline (HGL) calculations be submitted for all storm drain pipe design. 305 .03 44 – Storm Drain Pipe Design Proper operations and maintenance practices for all storm drain and inlet structures and their appurtenances will be identified in the Operations and Maintenance Manual, as required in Section 102.06. Clarification 44: See 102.02, 5. above. 305.07 45 - Inlet Grate Design, 305.08 – Gutterline Hydraulic Evaluation “Inlets in roadway gutter lines must be spaced to prevent flow from entering public road intersections. In addition, inlets should be spaced intermediately in residential street gutter lines to allow one lane (based on the lane width of the road) of traffic to remain open during the 100-year storm event. Multi-lane facilities may have one travel lane on each side of the roadway flooded during the 100-year storm event. The design storm for all of the conditions is the 10-year storm event.” Clarification 45: The inlet grate design and the gutterline hydraulics should both be evaluated based on a 10-yr storm event as stated in Section 305.07 and the last sentence of Section 305.08. The 100-yr storm event reference should read a 10-yr storm event. It is however recommended that appropriate overflow routes be provided on the plans for the 100-yr storm event runoff. In addition, the maximum ponding depth above an inlet should be no greater than 6 inches. The gutterline hydraulics should demonstrate that one travel lane remains open. The travel lane does not include the curb and gutter, i.e. a 30’ b-b curb roadway with a 2’ curb and gutter on each side would require a 13’ open travel lane (30’ - 4’ = 26’ / 2 = 13’) in the analysis. The spread is determined from the face of the curb, which is typically 6” from the back of the curb.

CHAPTER 400 CHAPTER 400 46 - STORM SEWER PIPE AND OPENCULVERT MATERIALS Clarification 46: The following sections within Chapter 400 should have been updated to include the approval of the Nyloplast storm drainage structures for drainage basins, inline drains and ductile iron frames and grates per approval by the DPW New Products Committee on April 13, 2009. Although the specification approval was for Nyloplast inlets, similar products meeting the standards and specifications below would also be approved.

Nyloplast storm drainage structures for Drain Basins, Inline Drains and Ductile Iron Frames and Grates have been approved by the Director to be used in low volume traffic areas on private property and outside of pavement areas in Public Right of Way. Nyloplast PVC risers will only be allowed in non-traffic loading areas and in low volume traffic areas such as private streets and parking lots and in grass areas such as roadside ditches with Right of Way and non paved areas on private property. Section 400 of the Indianapolis Storm Water Technical Specifications is amended to include PVC drainage structures for Drain Basins, Inline Drains and Ductile Iron Frames and Grates as follows:

NOTE: ALTHOUGH THE USE OF PVC SURFACE DRAINAGE INLET STRUCTURES HAVE BEEN APPROVED, THE MINIMUM PIPE SIZE REMAINS 12 INCHES FOR STRUCTURES COLLECTING SURFACE RUNOFF. NYLOPLAST INLETS AND PIPES SHOULD BE SIZED ACCORDINGLY.


402.01 47 – Introduction Clarification 47: Section should read: “A network of pipe conduits and precast concrete manhole, box inlet and/or PVC surface drainage inlet structures, which collect and convey surface and subsurface (soil) water through gravity flow from a specified geographical area. A gravity flow system utilizes elevation gradients to cause water flow.” 403.06 48 - Polyvinyl Chloride Pipe (PVC) Clarification 48: Section should read: “2. PVC Joints

Second paragraph:

PRECAST MANHOLES, BOX INLETS AND/OR PVC SUBSURFACE DRAINAGE INLETS WILL BE

REQUIRED WITHIN PVC STORM SEWER SYSTEMS…”

404.01 49 - Introduction Clarification 49: Section should read: “A storm sewer manhole, precast concrete box inlet or PVC surface drainage inlet must be installed at the end of each ling segment…”

404.04 50 - Precast Concrete Box Inlets and Catchbasins Clarification 50: Section should read:

404.04 - Precast Concrete Box Inlets, Catchbasins and PVC Surface Drainage Inlets Insert after 5th paragraph: PVC surface drainage inlets must meet the following ASTM standards: ASTM D1784 “Standard

Specification for Rigid PVC Compounds and CPVC Compounds”, ASTM D3212 “Standard

Specification for Joints for Drain and Sewer Plastic Pipes Using Flexible Elastomeric Seals”, and

ASTM F477 “Standard Specification for Elastomeric Seals (Gaskets) for Joining Plastic Pipe”.

PVC surface drainage structures shall be installed according to manufacturer’s guidelines

including the placement of a minimum 6-inch concrete collar around the casting. PVC surface

drainage inlets shall be installed in accordance with ASTM D2321-05. PVC surface drainage

inlets shall be used only in grass areas within public right of way and in grass areas or low

volume traffic areas such as private streets and parking lots on private property. PVC surface

drainage inlets shall not be used in pavement areas within Public Right of Way and shall only

be used in low volume pavement areas on private property. PVC surface drainage inlets

designed to be within the pavement area the units must be designed with a concrete collar

support for the casting.

404.12 51 - Rejection of Damaged Box Inlet and Manholes Clarification 51: Section should read:

404.12 Rejection of Damaged Box Inlets, Manholes and PVC Surface Drainage Inlets

Insert after 1st paragraph:

PVC surface drainage inlets which possess any of the following defects shall be subject to

rejection: elliptical shape in structure intended to be round; illegible markings as required

herein; deep or excessive gouges or scratches of the structure wall; fractures; punctures; or

cracks passing through the structure; damaged or cracked ends where such damage would

prevent making a satisfactory joint or base.


405.03 52 - Rejection of Castings Clarification 52: Section should read:

All weights shall not deviate from the tolerances permitted by ASTM standards, as

specified within ASTM A 48, "Standard Specifications for Gray Iron Castings” or ASTM

A536 “ Standard Specification for Ductile Iron Castings”.

All castings shall be manufactured in accordance with ASTM A 48 Class 35 B, and shall

have a minimum tensile strength of 35,000 psi for Gray Iron Castings, or in

accordance with ASTM A536, and shall have a minimum tensile strength of

70,000 psi for Ductile Iron Castings.

403.09 53 - High Impact Polypropylene or High-Density Polyethylene Plastic Facilities Clarification 53: Underground detention facilities should be provided with appropriate structure to access each row of the enclosed underground system for inspection and maintenance purposes. A minimum 2-foot diameter riser should be provided for maintenance for each row. 404.06 54 - Bench Walls The benchwall in all structures shall form a defined channel, to a minimum height of 80-percent of the inside diameter of the inlet and outlet pipes to form a “U” shaped channel… Clarification 54: All plan details should be revised to reflect this revision. Standard details in the manual will be updated to reflect this requirement in the near future. 406.03 55 - Accepted Materials Clarification 55: Table 406-01 – Subsurface Drain Tile Materials includes references to pipe sizes smaller than 6 inches. The ASTM designations are still applicable, however the minimum subsurface drain tile size that may be used is 6 inches per the previous section (Section 406.02, 5) Figures 400-04 through 400-09 56 Clarification 56: Section 502.02 requires a 6” stone base beneath all manhole and box inlet structures. The box inlet details should include the 6” stone base beneath the structure on all plans. Figure 400-11 57 Clarification 57: The figure references a Neenah R-1712-B-SP Frame, which is 9”. A R-1772-B-SP is also acceptable which is a 7” frame.

CHAPTER 500 505.04 58 - Minimum Freeboard Clarification 58: See 302.08 above 505.06 59 - Emergency Spillways Clarification 59: See 302.08 above Figures 501-09 through 501-12 60 Clarification 60: The bedding details should be adjusted to reflect the new requirements for mechanical compaction of the bedding material (plastic pipe, e.g. PVC, HDPE, etc. requires mechanical compaction of both the bedding and initial backfill). All details provided on the plans should reference the requirement for mechanical compaction.


Figure 505-01 61

Clarification 61: The standard detail should be updated to match the text requirements in Section 302.07. All plans utilizing a wet detention pond should have an appropriate detail of the safety shelf used in the design.

CHAPTER 600 CHAPTER 600 62 - EROSION AND SEDIMENT CONTROL Clarification 62: This chapter includes many references to the term “Erosion and Sediment Control Plan” (ESCP). In the past few years this term has generally been replaced with “Storm Water Pollution Prevention Plan” (SWPPP). An ESCP typically addressed the onsite erosion control parameters for the construction process only. An SWPPP will address the construction erosion control practices as well as post-construction practices and water quality requirements. A SWPPP is required for all disturbances of 1 acre and greater and is recommended to be provided for all land disturbances. Sheets should be labeled as a SWPPP plan to be consistent with current requirements. 601.02 63 - Authority Clarification 63: The “Indiana Storm Water Quality Manual” published by IDEM should be used for guidance on erosion and sediment control practices. The “Indiana Handbook for Erosion Control in Developing Areas” is no longer utilized and references should be removed from plans and replaced with the “Indiana Storm Water Quality Manual”.

602.02 64 - Requirements Clarification 64: Erosion control practices are required for land alternations less than 1 acre and single family residential (SFR) land disturbing activities. Gravel access drives should be provided and may be allowed to cross established easement areas. Other disturbances within the established easement areas should be avoided. 602.08 65 - Inspections Clarification 65: Reference to the “Department of Capital Asset Management” should be updated to the “Department of Code Enforcement”. 603.03 66 - General Criteria “Vegetative Control - Disturbed areas which are at finish grade shall be permanently seeded within seven (7) days. Vegetation must be established within one-hundred and eighty (180) days with 90% coverage or reseeded.” Clarification 66: The vegetative control should be established with a 90% density of the site. This section requires that the entire site be seeded at a density of 90% after 180 days and not 90% of the site be seeded.

603.06 67 - Straw Bale and Fabric Fence Barriers Clarification 67: The use of straw bales and fabric fence barriers should follow the guidelines set forth in the “Indiana Storm Water Quality Manual”. The use of straw bales for any sediment or erosion control measure has been strongly discouraged and/or not permitted by IDEM staff for several years. In addition, straw bales and fabric fences are also not considered an appropriate measure to be used in any open channel flow area. 603.11 68 - Temporary, Permanent and Dormant Seeding; Mulching and Erosion Control Blankets Clarification 68: Erosion control blankets should be installed on slopes of 4:1 and greater. The plans should indicate the specific type of erosion control blanket to be used and provide appropriate details for the method of installation.


CHAPTER 700

701.03 69 – Storm Water Quality Control Requirements “In addition, designers may be required to include the control of fecal bacteria or pollutants that are associated with a specific land use, such as hydro-carbons that are associated with retail gasoline outlets, in their designs.” Clarification 69: The control / removal of bacteria is not required under the City’s current NPDES permit. Certain sites may be required to address the control of fecal bacteria or pollutants if located within an impacted watershed as determined by the City. 702.01 70 – Storm Water Ponds Clarification 70: The design of storm water ponds should follow the requirements Section 302.07 in addition to those of Section 702.01. The minimum required normal depth should be eight feet for all wet ponds including micropools. 702.01, 1. 71 – Storm Water Ponds “1. Design the pond with a minimum length to width ratio of 3:1 (preferably expanding outward toward the outlet), measured from the pond inlet to the pond outlet. Irregular shorelines for larger ponds provide visual variety. This length to width ratio must be met for each inlet to the pond.” Clarification 71: The length to width ratio is from each inlet to the outlet of the pond. The inlet could be defined as the location of the forebay outlet for each forebay location. 702.01, 4. 72 – Storm Water Ponds “4. Provide a sediment forebay or other pretreatment upstream from the BMP inlet…” Clarification 72: A permanent sediment depth marker should be provided within all forebay designs. The sediment depth marker must be constructed as a permanent marker with permanent markings for sediment removal indication. Steel post (unless filled with concrete) and paint markings on the outside of a marker are not considered permanent. 702.01, 7. 73 – Storm Water Ponds “7. A wet storm water pond is characterized by a permanent wet pool. The designer must evaluate both the soils and the hydrology of the site to insure that the pond will maintain a permanent wet pool. (Note: Chapter 300 allows dry detention ponds, however, little water quality benefit is provided from dry detention ponds.)” Clarification 73: A geotech or soil scientist report must be included in the TIR documenting the soils and hydrology as well as the seasonal high water table.


Appendices


Appendix A

Revised Table 205-1


Cover Description Curve Numbers for Hydrologic Soil Groups

Cover Type and Hydrologic Condition

A B C D

Cultivated Land (Row Crops): With conservation treatment Without conservation treatment

62 72

71 81

78 88

81 91

Pasture or Range Land Poor condition Good condition

68 39

79 61

86 74

89 80

Meadow Good condition

30 58 71 78

Wood or Forest Land Thin stand, poor cover, no

mulch Good cover

45 25

66 55

77 70

83 77

TABLE 205-03: Runoff Curve Numbers for Undeveloped Areas (SOURCE: 210-VI-TR-55, Second Ed., June 1986)


Appendix B Revised Tc Worksheet


By: Date

Checked: Date

Present Developed

Tc Tt through subarea

Segment ID

1

2

3 ft

4 in

5 ft/ft

6 Compute Tt hr 0.000 + 0 = 0.000

Segment ID

7

8 ft

9 ft/ft

10 ft/s

11 Compute Tt hr 0.000 + 0 = 0.000

Segment ID

12 ft2

13 ft

14 ft

15 ft/ft

16

17 Compute V ft/s

18 ft

19 Compute Tt hr + =

20 hr = 0.000

min =

Watershed or subarea Tc or Tt (add Tt I steps 6, 11, and 19)

(210-VI-TR-55, Second Ed., June 1986)

Tt = L/3600V

Manning's roughness coeff., n

Flow Length, L

V=1.49 r2/3

s1/2

/n

Hydraulic radius, r =a/Pw

Channel slope, s

Cross sectional flow area, a

Wetted perimeter, Pw

Channel flow

Surface description (paved or unpaved)

Flow Length, L

Watercourse Slope, s

Average velocity, V (figure 3-1)

Circle One:

Circle One:

Surface description (table 3-1)

NOTES:

Tt = L/3600V

Tt = 0.007(nL)0.8

/P20.5

s0.4

Shallow concentrated flow

Manning's roughness coeff., n (table 3-1)

Land slope, s

Sheet Flow (Applicable to Tc only)

Two-yr 24-hr rainfall, P2

Include a map, schematic, or description of flow segments

Space for as many as two segments per flow type can be used for each worksheet

Flow Length, L (total <= 100 ft)

Worksheet 3: Time of concentration (Tc) or travel time (Tt)

Project

Location


Appendix C

Huff Storm Ordinates and Applicability


FIGURE 202-02: Huff Rainfall Distribution

(SOURCE: Bulletin 71, "Rainfall Frequency Atlas of the Midwest", 1992)

Huff Quartile Storm Applications:

Quartile Storm Duration

1st 0 to 6.0 hrs

2nd 6.1 to 12.0 hrs

3rd 12.1 to 24 hrs

4th 24.1 +


Appendix D Revised Section 302.02

The Requirement for Detention/Retention


Figure 302.02.01 -

Yes Out

No

4. Is Site < 5 Acres

Want to do Dowstream Capacity Analysis?

5. Over Design Detention Basin

(Modified Rational Method)

Yes No

6. Perform Downstream Capacity Analysis

No

Yes

2. Pre/Post Flow

Analysis

Design Detention

Design D/S Mitigation

Modify Site Design

No Increase

1. Detention Exempt Per

201.06?

3. Downstream Capacity Analysis

Yes

No

Increased Runoff

7. Site Design

STEP 1: Is detention / retention exempt according to 201.06? If so, the designer proceeds to Step 3. Otherwise, proceed to Step 2. STEP 2: The designer next performs the pre / post development discharge analysis described in Section 302.03. If there is no increase in runoff, the designer proceeds to Step 3. If there is an increase, the designer proceeds to Step 4. STEP 3: Are the downstream facilities adequate to accept the proposed peak runoff flow (i.e. what is the available capacity of the downstream facilities)? The designer performs a downstream capacity analysis for the storm frequencies required for the storm water facilities encountered downstream. This will normally require the 10-, 25- and 100-year storms. This analysis may include the first detention pond downstream and / or the first 15 inch or larger pipe downstream.


If the downstream facilities have adequate capacity for the proposed flow and are exempt from 201.06, then the designer does not need to provide detention / mitigation. If the downstream facilities are not adequate for the proposed flow, the designer proceeds to Step 8. STEP 4: Are any individual potential detention/retention sites draining areas less than 5 acres total including off-site drainage? If “Yes" the designer may elect to perform an oversized detention/ retention design and proceeds with Step 5. If “NO" the designer goes to Step 6. STEP 5: If the designer wants to over design for detention, the designer must use the Modified Rational method as outlined in Section 302.05. STEP 6: If the site is greater than 5 acres or the designer elects not to over design the detention basin then a downstream capacity analysis should be completed as described in Step 3. After completion of the downstream capacity the designer proceeds to Step 7. STEP 7: The site design should be completed by designing the detention to meet the detention requirements and/or mitigate downstream restrictions.

memorandum of clarification date: from ......memorandum of clarification - issued june 21, 2011 5...

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