Storm Sewer Systems and Roadway Drainage including catch basins, pipes, culverts, swales, ditches, and other open channels shall be designed in accordance with the latest editions of the Ohio Department of Transportation’s Location and Design Manual, Volume Two - Drainage Design and Construction and Material Specifications.
(a) Provide spreadsheet calculations for the storm sewer systems. All storm sewer systems shall be designed to flow just full for a 10 year frequency storm except where more stringent requirements are noted in the Location and Design Manual. For roadway pipe design, check the hydraulic grade line does not exceed the grate elevations based on a 25 year frequency storm.
(b) Provide spreadsheet calculations for the inlet spacing and pavement spread. Allowable pavement spread shall be six feet for a 10 year frequency storm.
(c) Open channels such as swales, ditches, channels, and ravines which are used as part of the Major Flood Path, as described in Section 1168.06, shall have more stringent design requirements.
(i) Provide channel linings and bank stabilization to prevent erosion in all open channels. Adhere to minimum ditch slope standards and maximum velocity standards outlined in the Location and Design Manual.
(ii) Provide easements over open channels as described in Section 1168.08.
(d) Provide a Storm Sewer Systems and Roadway Drainage drawing. Perform field surveying as necessary to insure that this drawing is an accurate representation of actual field conditions. The scale of this drawing must be sufficient to clearly present the following information:
(i) Existing and proposed elevation contours at an interval of two feet or less. Contour lines shall be labeled frequently enough to be easily read and interpreted.
(ii) All of the individual surface areas that drain to each intercepting structure of the storm sewer system must be outlined. The areas must be numbered or labeled to match the computer spreadsheet.
(iii) The path used to calculate the time of concentration for each individual drainage area where the time of concentration is greater than 10 minutes. Indicate the types of flow and provide calculations.
(iv) Indicate various types of surface areas within each of the individual drainage areas that have different runoff coefficient values. Use different colors of shading or another method as long as the information can be easily understood and read. Show how the weighted runoff coefficient for each individual drainage area was calculated.
(e) An adequate downstream outlet must be provided for all proposed storm sewers, such as an existing ditch, stream, river, storm sewer, pond or lake. The downstream outlet must be able to accommodate the flow of storm water from the proposed storm sewer system.
(f) Provide headwalls, energy dissipaters, riprap, erosion control mats, and other measures, as necessary, at all outlets to prevent erosion.
(g) For storm sewers intended to become publicly owned (such as storm sewers within roadways for a proposed subdivision), the following apply:
(i) Storm sewers less than or equal to 24 inch diameter shall be constructed using high strength vitrified clay pipe, reinforced concrete pipe, or PVC with bell and spigot joints.
(ii) Storm sewers greater that 24 inch diameter shall be constructed using high strength vitrified clay pipe or reinforced concrete pipe only.
(iii) All sewers within dedicated (or proposed dedicated) right-of-way or within a one-to-one slope from the right-of-way shall use crushed stone or gravel, ODOT 703.11, Type 1 backfill that meets the gradation of ODOT 304, or other approved premium backfill, as approved by the City Engineer.
(iv) Use ODOT MH-3 with City standard castings. Alternatively, use City brick manhole standards with City standard castings.
(v) Use City of Alliance standard catch basins and castings.
(vi) Storm sewer mains shall be designed to be in the center of one lane of pavement where possible (for example: sanitary sewer down the middle of road, waterline in the lane on one side of the road, and storm sewer in the lane on the other side of the road). Any variance from this must be approved by the City Engineer.
(vii) If it is necessary, the City may approve sewers off road or through a yard. In such instances, an easement with a minimum width of 20 feet shall be required. (Wider easements may be required for large or deep sewers, or based on terrain and topography.) Provide a gravel access drive, or gravel base topped with topsoil, per City standards, for the length and width of the easement for maintenance vehicle access.
(viii) Where culverts are required under the roadway, they shall extend across the entire right-of-way of the street. The minimum pipe diameter of a culvert shall be 18 inches. Headwalls shall be required.
(ix) Driveway culverts shall have a minimum length of 20 feet, and a minimum diameter of 12 inches. The driveway culverts shall be laid so as to maintain the flow lines of the ditch or gutter. Headwalls may be required by the City Engineer.
(h) Roof Drains and Sump Pump Discharges. (Ord. 35-07. Passed 3-19-07.)
(i) Roof drains may be discharged through the curb onto the street. They may tie directly into the storm system by an approved wye or tap connection, or by an approved core into a catch basin. Roof drains may be run to a designed dry well, infiltration basin, or infiltration ditch. They may discharge onto the ground using splash blocks. The downspouts must be run far enough away from the building to meet building codes and the ground must have positive grade away from the building. Roof drains are not permitted to discharge on the ground where the flow may cause flooding to adjacent properties, nor are they permitted to discharge across the back of any public sidewalk, street, or other public ground within the City.
(Ord. 45-09. Passed 9-8-09.)
(ii) Sump pumps may be discharged in the same manner as roof drains, except they are not permitted to discharge through the curb onto the street. Sump pump discharges tied directly to the storm sewer must be accounted for in the design of the storm sewer system.