(A) General. All storm sewers, whether private or public, and whether constructed on private or public property shall conform to the design standards and other requirements contained herein.
(B) Design storm frequencies.
(1) (a) All storm sewers, inlets, catch basins and street gutters shall accommodate, as a minimum, peak runoff from a 10-year return frequency storm. Additional discharges to storm sewer systems allowed in this division must be considered in all design calculations.
(b) For rational method analysis, the duration shall be equal to the time of concentration for the drainage area. In computer based analysis, the duration is as noted in the applicable methodology associated with the computer program.
(2) Culverts shall be capable of accommodating peak runoff from a 24-hour, 50-year frequency storm when crossing under a road which is part of the INDOT Rural Functional Classification System or is classified as freeway, arterials and/or collectors by the City of Brazil Zoning Ordinance or provides the only access to and from and from any portion of any commercial or residential developments.
(3) For portions of the system considered minor drainage systems, the allowable spread of water on collector streets is limited to maintaining 2 clear 10-foot moving lanes of traffic. One lane is to be maintained on local roads, while other access lanes (such as a subdivision cul-de-sac) can have a water spread equal to 1/2 of their total width.
(4) Facilities functioning as a major drainage system as defined in § 51.04 must also meet IDNR design standards. (1) Determination of hydraulic capacity for storm sewers sized by the rational method analysis must be done using Manning's equation.
Where: | V=(1.486/n) R 2/3 S 1/2 |
Then: | Q=VA |
Where: | Q=capacity in cubic feet per second |
V=mean velocity of flow in feet per second |
A=cross sectional area in square feet |
R=hydraulic radius in feet |
s=slope of the energy grade line in feet per foot |
n=Manning’s "n" or roughness coefficient |
(2) The hydraulic radius, R, is defined as the cross sectional area of flow divided by the wetted flow surface or wetted perimeter. Allowable "n" values are maximum permissible velocities for storm sewer materials are listed in Table 9.
(D) Backwater method for pipe system analysis.
(1) For hydraulic analysis of existing or proposed storm drains which possess submerged outfalls, a more sophisticated design/analysis methodology than Manning’s equation will be required. The backwater analysis method provides a more accurate estimate of pipe flow by calculating individual head losses in pipe systems which are surcharged and/or have submerged outlets. These head losses are added to a known downstream water surface elevation to give a design water surface elevation for a given flow at the desired upstream location. Total head losses may be determined as follows: Total head loss=frictional loss+manhole loss+velocity head loss+junction loss.
(2) Various computer modeling programs such as HYDRA, ILLUDRAIN and STORMCAD are available for analysis of storm drains under these conditions. Computer models to be utilized, other than those listed, must be approved by the city engineer.
(E) Minimum size for storm sewers. The minimum diameter of all storm sewers shall be 12 inches. The rate of release for detention storage shall be controlled by an orifice plate or other device, subject to approval of the city engineer, when the minimum 12-inch diameter pipe will not limit the rate of release to the required amount.
(F) Pipe cover and grade. Sewer grade shall be so that, in general, a minimum of 1-1/2 feet of cover is maintained over the top of the pipe. If the pipe is to be placed under pavement, then the minimum pipe cover shall be 2 feet from the top of the pavement to the top of the pipe. Pipe cover less than the minimum may be used only upon written approval from the city engineer. Uniform slopes shall be maintained between inlets, manholes and inlets to manholes. Final grade shall be set with full consideration of the capacity required, sedimentation problems and other design parameters. Minimum and maximum allowable slopes shall be those capable of producing velocities of between 2.5 and 15 feet per second, respectively, when the sewer is flowing full. Maximum permissible velocities for various storm sewer materials are listed in Table 9.
(G) Alignment. Storm sewers shall be straight between manholes and/or inlets.
(1) Manholes and/or inlets shall be installed to provide human access to continuous underground storm sewers for the purpose of inspection and maintenance. The casting access minimum inside diameter shall be no less than 22 inches or a rectangular opening of no less than 22 inches.
(2) Manholes shall be provided at the following locations:
(a) Where 2 or more storm sewers converge;
(b) Where pipe size changes;
(c) Where a change in horizontal alignment occurs;
(d) Where a change in pie slope occurs; and
(e) At intervals in straight sections of sewer, not to exceed the maximum allowed.
(3) The maximum distance between storm sewer manholes shall be as follows:
(4) In addition to the above requirements, a minimum drop of 0.1 foot through manholes should be provided. When changing pipe size, match crowns of pipes. Pipe slope should not be so steep that inlets surcharge (i.e. hydraulic grade line below rim elevation).
(5) Manhole/inlet sizing shall be as follows:
(I) Inlet sizing and spacing. Inlets or drainage structures shall be utilized to collect surface water through grated openings and convey it to storm sewers, channels or culverts. The inlet grate opening provided shall be adequate to pass the design 25-year flow with 50% of the inlet areas clogged. An overload channel from sag inlets to the overflow channel or basin shall be provided at sag inlets, so that the maximum depth of water that might be ponded in the street sag shall not exceed 6 inches during the 25-year frequency storm event. Inlet design and spacing may be done using the hydraulic equations by manufacturers or office/weir equations. Use of the U.S. Army Corps of Engineers HEC-12 computer program is also an acceptable method. Gutter spread on continuous grades may be determined by using the Manning's equation, or by using Figure 3.
(J) Workmanship. The specifications for the construction of storm sewers shall not be less stringent than those set forth in the latest edition of the INDOT, "Standard Specifications." Additionally, ductile iron pipe shall be laid in accordance with American Water Works Association (AWWA) C-600 and clay pipe shall be laid in accordance with either American Society of Testing Materials (ASTM) C-12 or the appropriate American Association of State Highway and Transportation Officials (AASHTO) specifications. Variation from these standards must be justified and receive written approval from the city engineer.
(1) Storm sewer manholes and inlets shall be constructed of cast in place concrete or precast reinforced concrete. Materials and construction shall conform to the latest edition of the Indiana Department of Transportation (INDOT) "Standard Specifications" § 720.
(2) Pipe and fittings used in storm sewer construction shall be extra-strength clay pipe (ASTM C-12), ductile iron pipe (AWWA C-151), poly vinyl chloride pipe (AASHTO M252), polyethylene pipe (AASHTO M252 or AASHTO M292) or concrete pipe (AASHTO M170). Other pipe and fittings not specified herein or in §§ 907-908 of the latest edition of the INDOT "Standard Specifications" may be used only when specifically authorized by the city engineer. Pipe joints shall be flexible and watertight and shall conform to the requirements of § 906, of the latest edition of the INDOT "Standard Specifications."
(L) Special hydraulic structures. Special hydraulic structures required to control the flow of water in storm runoff drainage systems include junction chambers, drop manholes, inverted siphons, stilling basins and other special structures. The use of these structures shall be limited to those locations justified by prudent planning and by careful and thorough hydraulic engineering analysis. Certification of special structures by a certified structural engineer may also be required.
(M) Connections to storm sewer systems.
(1) To allow any connections to the storm sewer system, provisions for the connections shall be shown in the drainage calculations for the system. Specific language shall be provided in the protective covenants, on the record plat or with the parcel deed or record, noting the ability or inability of the system to accommodate any permitted connections, for example, sump pumps and footing drains.
(a) Sump pumps installed to receive and discharge ground waters or other stormwaters shall be connected to the storm sewer where possible or discharged into a designated storm drainage channel. Sump pumps installed to receive and discharge floor drain flow or other sanitary sewage shall be connected to the sanitary sewers. A sump pump shall be used for 1 function only, either the discharge of stormwater or the discharge of sanitary sewage.
(b) Footing drains shall be connected to storm sewers where possible or designated storm drainage channels. No footing drains or drainage tile shall be connected to the sanitary sewer.
(c) No roof downspouts, roof drains nor roof drainage piping shall be connected to the storm drainage system. No down spouts or roof drains shall be connected to the sanitary sewers.
(d) Basement floor drains shall be connected to the sanitary sewers.
(2) In addition, none of the above mentioned devices shall be connected to any street underdrains.
(N) Maintenance responsibilities. Maintenance of stormwater facilities during construction and thereafter, shall be the responsibility of the land developer/owner. Assignment of responsibility for maintaining facilities serving 1 or more lot(s) or holding(s) shall be documented by appropriate covenants to property deeds and documented in sales agreements, unless responsibility is formally accepted by a public body.
(Ord. 01-2000, passed 7-18-2000)
