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.
(A) Hydraulic capacity:
(1) The hydraulic capacity of storm sewers shall be determined using Manning's Equations:
V=1.486 R2/3 S1/2
n
V = mean velocity of flow in feet per second
R = the hydraulic radius in feet
S = the slope of the energy grade line in feet per foot
n = 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. Typical "n" values and maximum permissible velocities for storm sewer materials are listed in Appendix B, Table 4. Roughness coefficient (n) values for other sewer materials can be found in standard hydraulics texts and references.
(B) Minimum size. The minimum size of all storm sewers shall be 12 inches. Rate of release for detention storage shall be controlled by an orifice plate or other devices, subject to approval of the Board, where the 12-inch pipe will not limit rate of release as required.
(C) Grade. Sewer grade shall be such that, in general, a minimum of two feet of cover is maintained over the top of the pipe. Pipe cover less than the minimum may be used only upon approval of the Board. 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 2½ and 15 feet per second, respectively, when the sewer is flowing full.
(D) Alignment. Storm sewers shall be straight between manholes insofar as possible. Where long radius curves are necessary to conform to street layout, the minimum radius of curvature shall be no less than 100 feet for sewers 42 inches and larger in diameter. Deflection of pipe sections shall not exceed the maximum deflection recommended by the pipe manufacturer. The deflection shall be uniform and finished installation shall follow a smooth curve.
(E) Backfill requirements. Any storm sewer constructed within a street dedicated to the city must be approved by the Street Commissioner, City Engineer, or designee, prior to construction. Storm sewers constructed within a county highway must be approved by the County Highway Supervisor, or designee, prior to construction. Any sewer constructed within five feet of an existing or proposed street, alley, driveway, or sidewalk shall be backfilled with granular material. Granular backfill shall be crushed or washed stone compacted to 95% maximum density. Granular backfill shall extend from the bottom of the trench excavation to the restoration materials. Pavement restoration shall be a minimum four inches thick, consisting of three inches of bituminous intermediate binder and one inch of bituminous surface, or match existing pavement section, whichever is thicker.
(F) Allowable outlet location.
(1) It shall be illegal to outlet the discharge pipe, emergency spillway, tile underdrain, or any other water discharge structure from a wet or dry retention/detention basin, or any storm sewers, sump pump drains, downspout drains, perimeter septic system tile drains, farm tile drains, foundation or floor drains into the right-of-way of any roadway including all county roads, state highways, federal highways, private streets, regulated open or tile drains, onto adjacent property, and so on, without the written approval of the agency having jurisdiction over the roadway, regulated drain, or the owner of the property upon which the water will flow. Outletting of subsurface tile drains into a 6 or 8-inch outlet tile or open channel of a legal drain located within a county road right-of-way and which has been designed to serve such a purpose shall be permitted subject to plan approval of the County Surveyor or the County Highway Supervisor.
(2) The excavation, filling, paving, and/or any other type of construction of roadside drainage ditches located within county highway right-of-ways is prohibited. Exceptions may be granted by the Drainage Board or the County Highway Superintendent and must be in writing prior to beginning construction. Extension and paving of existing driveways within the road right-of-way shall be required to extend existing culverts and must seek and receive driveway construction approval from the County Highway Department.
(G) Manholes.
(1) Manholes shall be installed to provide access to continuous underground storm sewers for the purpose of inspection and maintenance. Manholes shall be provided at the following locations:
(a) Where two or more storm sewers converge.
(b) At the point of beginning or at the end of a curve, and at the point of reverse curvature (PC, PT, PRC).
(c) Where pipe size changes.
(d) Where an abrupt change in alignment occurs.
(e) Where a change in grade occurs.
(f) At suitable intervals in straight sections of sewer.
(2) The maximum distance between storm sewer manholes shall be as follows:
Size of Pipe Maximum Distance
(inches) (feet)
12 through 42 400
48 and larger 600
(H) Inlets. Inlets or drainage structures shall be utilized to collect surface water through grated openings and convey it to storm sewers, channels or culverts. Inlet design and spacing shall be in accordance with Section 36-2.08 of the Indiana Department of Transportation's Design Manual Part IV - Volume 2, or other approved design procedure. The inlet grate opening provided must be adequate to pass the design 10-year flow with 50% of the sag 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 seven inches.
(I) Workmanship and materials.
(1) Workmanship. The specifications for the construction of storm sewers shall not be less stringent than those set forth in the latest edition of the Indiana Department of Transportation's "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 American Society of Testing Materials (ASTM) C-12.
(2) Materials.
(a) Storm sewer manholes and inlets shall be constructed of masonry, cast in place concrete or precast reinforced concrete. Material and construction shall conform to Indiana Department of Transportation's "Standard Specifications", Section 720.
(b) Pipe and fittings used in storm sewer construction shall be extra strength clay pipe (ASTM C-700), ductile iron pipe (AWWA C-151), or concrete pipe (ASTM C-76). Other pipe and fittings not specified herein may be used only when specifically authorized by the Board. Pipe joints shall be flexible and watertight and shall conform to the requirements of Section 715.02 - Materials, of the latest edition of the Indiana Department of Transportation's "Standard Specifications."
(Ord. 2000-22, passed 12-28-00) Penalty, see § 157.99