(A) It is the policy of the town that developers of new development and redevelopment within the jurisdiction of the town submit for approval a drainage plan that prevents increased stormwater runoff resulting from land alteration. The drainage plan shall provide for the proper drainage of stormwater runoff from the developed site and the drainage basin in which it is contained. The drainage system shall be constructed and installed in accordance with the plans and specifications as approved by the town. Drainage approval for all projects must be received from the town prior to construction.
(B) Permits as required by Indiana Department of Environmental Management (IDEM, including Rule 5), Indiana Department of Natural Resources (IDNR), Army Corps of Engineers (COE), Indiana Department of Transportation (InDOT), Hamilton County Surveyor's Office, the Hamilton County Drainage Board, and any other local, state, and federal regulatory agencies are the responsibility of the property owner and the developer.
(C) Stormwater discharged to county-regulated drains, either direct or indirect, must be coordinated with and approved by the Hamilton County Surveyor's Office and/or the Hamilton County Drainage Board.
(D) Private developers shall submit to the Sheridan Planning Administrator a complete set of plans and specifications, for a proposed subdivision or planned development. Plans and specifications shall be prepared and signed by a professional engineer licensed in the State of Indiana.
(E) The town or its engineer shall not commence drainage review until all applicable items in division (B) above have been submitted to the relevant agencies.
(F) Plans submitted to the town shall at a minimum show the following information:
(1) Locations of all stormwater drainage facilities and appurtenances, inverts, elevations, storm sewer profiles, pond cross section and all applicable installation and construction details;
(2) Public right-of-way and utility easements for the facilities;
(3) Date, north arrow and bar scale;
(4) Existing and proposed site conditions, including contours, elevations, utilities, building footprints, finish floor elevations, streets, drives, parking areas, property lines, bench marks, floodway/floodplain boundaries, and erosion control measures and details;
(5) Technical specifications for drainage facilities and appurtenances.
(G) A technical information drainage report shall be submitted and shall include the following information. (Pertinent data must be highlighted if computer printouts are submitted.)
(1) A narrative explanation of the existing drainage patterns both onsite and offsite when offsite drainage passes through the developed property. The narrative shall include a summary of all pertinent calculations listed in division (L)(3) below or reference the page number where the information is located in the submittal package.
(2) A narrative explanation of proposed drainage patterns after development. The narrative shall include a summary of all pertinent calculations listed in division (L)(3) below or reference the page number where the information is located in the submittal package.
(3) Stormwater runoff calculations including:
(a) Drainage subarea calculations;
(b) Weighted runoff coefficient or curve number calculations;
(c) Time of concentration calculations showing overland (sheet) flow, shallow concentrated flow, and flow time in a channel, gutter or pipe;
(d) Grate capacities;
(e) Storm pipe and open channel design calculations including:
1. Size of pipe and typical channel cross section;
2. Pipe and channel slopes;
3. Material and roughness coefficient;
4. Velocities in feet per second (fps);
5. Structure headloss calculations upon request;
6. Hydraulic grade line (HGL) calculations upon request;
7. Flow capacities in cubic feet per second (cfs).
(f) Detention design summary with outlet control structure information (outlet structure discharge rating curve, stage/storage/discharge information during storm event).
(H) Upon initial review, the reviewer will notify the design engineer in writing of deficiencies, if any, in meeting the town design standards. Upon satisfying noted deficiencies, an approval letter will be issued to the developer by the town.
(I) In designing storm sewer systems, the following minimum standards shall apply:
(1) The rational method is acceptable for calculating peak flows to storm sewers (for watersheds less than 200 acres in size). Manning's equation is acceptable for sizing storm pipes for gravity flow, nonsubmerged outfall conditions. Figure 1 contains runoff coefficients for use in the rational formula.
(2) Due to the town's close proximity, rainfall intensities specified by the City of Indianapolis shall be employed for rational method drainage analysis. The intensity-duration frequency (IDF) table in Figure 2 from the City of Indianapolis Stormwater Design and Construction Specifications Manual shall be used for rainfall intensity values.
(3) Storm sewers shall have a minimum diameter of 12 inches and the sewer system shall pass the ten-year storm event under gravity flow conditions (no surcharging). A 25-year storm event shall stay within the system and not cause aboveground flooding. More stringent storm event criteria may be required at the discretion of the town. Design calculations for sizing of the storm pipe may be submitted on the storm pipe flow calculation form provided in Figure 3, a similar design summary, or highlighted computer output data.
(4) Headloss through structures shall be accounted for in the design. Headloss computations may be required at the discretion of the town.
(5) Storm sewer systems with the potential of operating under submerged outfall conditions shall include hydraulic grade calculations using a reasonable tailwater elevation.
(6) For streets, inlets grates shall be sized to pass runoff from the ten-year storm with no more than 1½ inches of ponding above the street inlet grate or with a gutter spread of no more than one-half of the travel lane. (Ditch inlet grates shall have no more than six inches of ponding above the grate). Flow capacities of storm inlet grates shall be calculated using weir and orifice flow equations with consideration given to square footage of grate open areas and flow perimeter dimensions provided by casting manufacturers. Castings shall be the heavy-duty type and grates shall be bicycle safe.
(7) Storm street inlets shall be placed at all low areas and spaced a maximum of 300 feet apart or 300 feet from the high point in the street unless the town requires more restrictive spacing. Gutter spread calculations shall be submitted upon request.
(8) Exposed ends of storm pipes shall have six-inch thick reinforced concrete slope walls or riprap placed as directed by the town, unless the Hamilton County Surveyor's Office or the Hamilton County Drainage Board has different requirements for outfalls to county-regulated drains.
(9) For land disturbing activities, whenever evidence available to the Town Engineer indicates natural surface drainage to be inadequate, the developer shall provide an adequate storm sewer system.
(10) Height of cover for pipes shall meet the most restrictive requirements of either manufacturer's recommendations or AASHTO Standard Specifications for Highway Bridges. However, when installed under pavement, the minimum pipe cover shall be two feet, or one foot if the pipe is reinforced concrete.
(J) In designing stormwater detention facilities, the following minimum standards shall apply. In general, stormwater detention analysis shall be required for land-altering projects if the impervious surface area will be increased by 0.5 acre or more. Stormwater detention shall be required if the peak discharge of stormwater from the developed site will exceed the peak discharge from the site in its present land use during the 2-, 10-, or 100-year storm event. These general requirements will be reviewed on a case-by-case basis by the town when making a determination to allow direct discharge or for requiring detention facilities.
(1) The detention/retention facility shall be a stormwater control facility that stores stormwater runoff indefinitely or detains it in order to reduce the flow of stormwater runoff from a property, or a combination thereof.
(2) The USDA Soil Conservation Service (SCS) method of calculating runoff and generating hydrographs shall be utilized for detention/retention design. The SCS Type II rainfall distribution shall be used for hydrograph computations in conjunction with 2-, 10-, or 100-year, 24-hour storm event. Rainfall depths are as follows:
(a) 2-year, 24-hour 2.90 inches
(b) 10-year, 24-hour 4.15 inches
(c) 100-year, 24-hour 5.75 inches
(3) Tables provided in Figures 4 through 6 shall be referenced for determination of runoff curve numbers according to land uses and hydrologic soil groups.
(4) Time of concentration shall be the time it takes for runoff to travel from the hydraulically most distant point in the subarea to its outfall point.
(5) Time of concentration calculations shall consist of overland (sheet) flow time, shallow concentrated flow time, and travel time in channels, pipes, gutters, etc. The maximum sheet flow calculation shall be 300 feet for pervious area and 100 feet for impervious area. After these distances, flow over land is calculated as shallow concentrated flow or channel flow as appropriate. The minimum time of concentration shall be five minutes. A worksheet for time of concentration calculations is provided in Figure 7. A list of Manning's roughness coefficients for sheet flow is provided in Figure 8. These Manning's "n" values are used only in the sheet flow equation on the worksheet and not for open channel design.
(6) The peak discharge resulting from the 100-year post-developed storm event shall not exceed the peak discharge resulting from the ten-year pre-developed storm event. In addition, the peak discharge resulting from the ten-year post-developed storm event shall not exceed the peak discharge resulting from the two-year pre-developed storm event. Outlet control structures of ponds shall be designed to meet the required release rates.
(7) Wet detention/retention ponds shall have a minimum ten-foot wide safety ledge placed below the normal pool water level at a maximum slope of 10:1. The slope of the vegetated bank above the safety ledge shall not exceed 3:1. Below the safety ledge, ponds with slopes steeper than 3:1 shall be secured with riprap and no bank shall exceed a slope of 1'/2:1. The average depth of the normal pool of the pond shall be six to eight feet, and depths of more than eight feet should be avoided. A sediment forebay that consists of a separate cell formed by an acceptable barrier is required at each inlet to the pond unless the inlet provides less than 10% of the total design storm inflow to the pond. A fixed vertical marker is required to measure accumulated sediment in each forebay.
(8) Dry detention/retention ponds shall have a minimum bottom slope of 1% or be designed with subsurface drainage. Maximum vegetated bank side slopes on the pond shall be 3:1. Hamilton County Surveyor's Office or the Hamilton County Drainage Board may have more restrictive requirements for developments in which the runoff outfalls to a county-regulated drain.
(9) Detention/retention ponds shall have a minimum freeboard of one foot. Freeboard shall be considered the additional height above the 100-year event peak storage water surface elevation.
(10) All impervious area of the site shall drain through the detention/retention facility.
(11) The depth of stormwater runoff in parking lots providing detention shall not exceed ten inches during the 100-year storm event.
(12) Detention/retention facilities shall be designed with emergency spillways capable of handling 1% times the peak discharge resulting from the 100-year storm event. The developer is responsible for analyzing the ponding results of a 100-year storm event and establishing flood protection grade for all structures and verifying an adequate outlet for the 100-year storm.
(K) In general, Manning's equation may be used for open channel flow calculations for unobstructed channels. Open channels with culverts may require additional analysis. See Figure 9 for Manning's "n" values. In the design of open channels, the following minimum standards shall apply:
(1) Open channels shall be designed to pass the runoff from the ten-year storm event.
(2) Grass-lined channel side slopes shall be no steeper than 3:1.
(3) For yard ditches, longitudinal slopes of grass channels shall not be less than 1%. Slopes between 0.3% and 1% shall require subsurface drainage tile, shall be paved using six-inch reinforced concrete, or shall be provided with a fabric-wrapped, washed gravel trench. No channel shall have less than a 0.3% longitudinal slope. Alternative channel treatments shall be subject to approval of the town.
(4) For relatively large open channels, channel slopes and invert treatments shall be approved on a case-by-case basis.
(L) In the design of streets, the following minimum drainage standards shall apply:
(1) Generally, all streets shall be provided with an adequate storm drainage system consisting of curbs, gutters and storm sewers, or side ditches and culverts, as determined by the town. A four-inch minimum perforated pipe underdrain, with a minimum one square inch of opening per foot of pipe, may be required on each side of all streets if required by the town and shall:
(a) Be 18 inches below the soil sub-grade and parallel with the longitudinal pavement grade, but no lower than the invert of the curb bo;
(b) Have a minimum slope of 0.2%;
(c) Flow to the low point and into the storm drainage system;
(d) Be placed below the pavement under the curbing;
(e) Be backfilled with #8 washed gravel.
(2) Open channels along dedicated roadways and within right-of-ways, or on easements dedicated to the town, are not to be altered in any way without written permission from the town. Driveways may be constructed over these swales or ditches only when the town has approved appropriate sized culverts or other structures.
(3) Culverts under public roadways shall be RCP (minimum Class III, Wall B) and shall be sized to pass the peak runoff from the 25-year storm event. Runoff from the 100-year storm event shall be analyzed to assure overtopping of the roadway does not exceed six inches. More restrictive overtopping conditions may be required at the discretion of the town.
(4) Culvert materials used under private drives and driveways will be evaluated and approved on a case-by-case basis. A minimum diameter of 12 inches is required for all culverts.
(5) Downspouts shall discharge onto a grass surface and be no closer to the road than the building setback line. Sump pump outlets shall discharge to underdrains at the curb.
(M) A landowner, builder, developer, and any individual or corporate person who applies mortar or any other substance to brick, or who places any hardened cement, or who pounds a nail into a board for the purpose of starting to build anything in the town for which the approval of the town is required by this chapter shall be fined no less than $100 per day and no more than $2,500 per day for each day from the day construction begins until the day construction ends or approval of the town is granted.
(Ord. 2006-1-1, passed 1-10-06)