1178.04 STORM WATER CONVEYANCE SYSTEMS.
   (a)   General.
      (1)   All conveyance systems shall be designed in accordance with the ODOT, L&D, Volume II unless otherwise specified in these Standards.
      (2)   All subdivisions shall provide a storm water conveyance system to adequately handle storm water runoff from the entire area being platted, from all off-site flows through the platted area, and designed according to these Standards. These Standards shall govern all drainage systems and appurtenances within the existing or proposed public right-of-way and those facilities outside the proposed right-of-way, being within a storm sewer easement, required for drainage purposes.
      (3)   In all cases, the conveyance system shall have a clear, unobstructed outlet, and discharge into a channel, watercourse, or closed conduit system capable of handling the design flow at the expected velocity without causing erosion or damage to the receiving system. Storm water runoff control shall be provided as applicable and as detailed herein.
      (4)   No storm sewer, culvert, or ditch collecting storm water runoff from a subdivision may discharge into a state, county, or local right-of-way without approval by the appropriate jurisdictional authority.
      (5)   Storm water management facilities shall be designed so that they will continue to function with minimal maintenance and with specific regard to safety.
      (6)   A flood routing path shall be provided for all independent storm water conveyance systems provided within the project area and shall be designed to pass the 100-year, 24 hour storm event. The intent is to provide a routing path for runoff so that houses and basements are not flooded by storm water.
      (7)   The hydrologic methods utilized to calculate storm runoff volumes shall be as per Section 1178.03 and properly utilized in the design of the storm water conveyance infrastructure established herein.
      (8)   The storm water management systems listed below shall be designed based on a SCS Type II storm distribution. All design storm events are in relation to the post development condition.
Table 3. Summary - Design Storm Events
Description
DESIGN STORM FREQUENCY/EVENT
Design Storm
Design Condition
Ditches
10 year, 24 hour
Channel Depth
2 year, 24 hour
Channel Lining - Shear Stress
Storm Sewers
10 year, 24 hour
Pipe sizing - Full Capacity
25 year, 24 hour
Hydraulic Grade Line Not above grate elevation
Curb Inlets
2 year, 24 hour
Roadway spread
 
Culverts
10 year, 24 hour
Pipe Sizing - Full Capacity
50 year, 24 hour
Headwater Check Below Roadway Surface
100 year, 24 hour
Headwater Check Below Nearest First Floor Elevation
 
Detention/Retention Basins
Critical Storm Method
Runoff-Discharge Control See Section 1178.05(b)(4)
100-year, 24 hour
Basin Storage Volume & Emergency Spillway Discharge
Commercial Site
See Section 1178.05(c)
   Note: All storm events listed are in reference to the design year frequency and duration.
   (b)   Applicability. This section applies to subdivision development regarding the minimum design standards to be utilized in storm water conveyances systems.
   (c)   Ditches.
      (1)   Design Frequency. Ditches shall be designed and constructed with the capacity to adequately handle the discharge expected from a 10-year, 24-hour storm event. Shear stress protection shall be constructed with respect to the velocity from a 2-year, 24-hour storm event.
      (2)   Defined. A Constructed roadside open channel or swale with the purpose of carrying large amounts of storm water runoff away from streets and property improvements.
      (3)   Design Parameters. Ditches shall be designed to exhibit good flow hydraulic characteristics at times of low flow as well as at peak flow. Ditches shall be improved as necessary to carry the design flow without erosion.
         A.   Maximum side slopes of 3:1 shall be provided with the shape (trapezoidal, v-bottom, or rounded) dictated as per the hydraulic design of the open channel.
         B.   A depth of flow not to exceed 18- inches shall be required. If the depth of flow exceeds this amount, catch basins shall be provided to intercept sufficient flow to maintain a depth of less than 18" in the downstream ditch.
         C.   The minimum grade for swales and ditches shall be 1.0%. Low flow shall be addressed to prevent stagnation. The minimum ditch velocity (for normal flow conditions) shall not be less than 1.5 fps.
         D.   The maximum grade for swales and ditches shall be determined by the velocity at design conditions.
         E.   Temporary and permanent erosion control measures shall be provided for all open channels through examination of the shear stress placed upon the open channel.
         F.   Where special lining materials are required (other than seeding or sodding) turf reinforcing mat or biodegradable erosion control mat shall be utilized as applicable and according to manufacturer recommendations wherever possible in lieu of hard armor revetment in the ditch with the exception of culvert inlets and outlets.
         G.   Where a major drainage way is located outside a street right-of-way, easements shall be provided and a grading plan with cross sections shall be submitted with the plan submission. The site grading plan shall include elevations along the routing path and other elevations necessary to show that the major storm is contained within the planned area.
   (d)   Storm Sewers.
      (1)   Design Frequency. Public storm sewers shall be designed and constructed with the capacity to adequately handle the 10-year, 24 hour storm event at full capacity and nonsurcharging. A 25-year, 24 hour storm event shall be used to develop the hydraulic gradient which shall not exceed the window or grate elevation of the storm structure.
      (2)   Defined.
         A.   Storm sewer systems are designed to collect and carry storm water runoff from the first pipeline inlet or catch basin, routed through a designed network of storm piping and storm structures, and to the predetermined outlet or discharge location.
      (3)   Design Parameters.
         A.   The storm sewer shall be designed utilizing Manning’s equation.
            V = (1.486 r 0.67 s 0.5)/ n
            Where:
            V = average velocity (ft/s)
            n = Manning’s roughness coefficient = 0.013
            r = Hydraulic Radius (ft)
            s = Pipe Slope (ft/ft)
         B.   Storm sewers shall be designed to receive storm water from the entire tributary area. Any major channels which pass through the development from off-site shall be routed around the storm sewer system unless approved by the Village.
         C.   Minimum public storm sewer pipe diameter shall be 12 inches.
         D.   If the main storm sewer pipe line in the run is larger than 24-inches, it shall be separated from the inlets and act as a trunk sewer.
         E.   Allowable velocities of storm sewers shall be greater than 3.0 feet per second and less than 12 feet per second. Key block anchors shall be provided every 20 feet if velocities exceed this maximum. The system should be designed to avoid large differences in velocities between consecutive reaches.
         F.   The minimum grade is to be 0.50%. Any storm pipe with a grade of over 12% shall have key block anchors every 20 feet.
         G.   Provide a sufficient depth to permit the use of precast structures with the top of the pipe below the bottom edge of the precast top section.
         H.   Where a storm pipe outlets into a pond or lake, the invert of the pipe shall be no lower than the normal pool level of the pond or lake.
         I.   Headwall shall be required at the outlet of all storm sewers.
         J.   A minimum separation of 18 inches shall be maintained between the storm sewer and all water and sanitary sewer lines. A 12-inch separation shall be maintained between the storm sewer and all other buried utilities.
      (4)   Material.
         A.   All pipes used in the storm sewer system shall have watertight joints.
         B.   The minimum allowable cover for all pipe types shall be 12 inches in depth.
         C.   The following types of pipes shall be permitted:
            1)    Class IV Reinforced Concrete Pipe
            2)    Aluminized Metal -Type II Conduit
            3)    Polyvinyl Chloride Plastic (PVC) Pipe
            4)    Corrugated Polyethylene (HDPE) Smooth Lined Pipe
         D.   Bedding and Backfill requirements for storm sewer conduit shall be governed by ODOT Item 603.
   (e)   Manholes.
      (1)   Design Parameters.
         A.   Manholes shall conform to the ODOT, Standard Details. Manholes shall be ODOT, Standard Manhole No. 3 or Village approved equal.
         B.   Top section shall be an eccentric cone precast concrete section.
         C.   Precast bases shall be placed on a foundation with a minimum of 3-inches of compacted sand or crushed limestone. The compacted foundation shall be leveled to provide a uniform support for the entire area of the base.
         D.   All manholes shall be precast concrete having tongue and groove connecting sections to eliminate shifting.
         E.   Pipe inlets and outlets to the precast concrete sections shall be neatly grouted (nonshrink) in place removing any voids between the pipe and the concrete wall on the interior.
         F.   All lift holes and other openings in the structure shall be thoroughly and neatly grouted with cement mortar.
         G.   Manhole grates and frames shall be Neenah Type R-1916-D with the lid marked “STORM”. Alternate manhole frame and cover must be approved by the Village.
      (2)   Location.
         A.   Where surface drainage is not required Manholes shall be required at:
            1.   The intersection of multiple storm sewers.
            2.   Changes in sewer alignment and slope.
            3.   As required for maintenance.
            4.   Manholes shall be required in place of a Catch basin where the depth of the basin from the surface of the frame to the inside of the base is 10-feet or greater.
   (f)   Catch Basins and Curb Inlets.
      (1)   Design Frequency. Curb inlets shall be designed and constructed with the capacity to adequately handle the 2-year frequency. A 10-year frequency storm event shall be used to check the spread in a sag condition in depressed roadways where ponding water may be an issue. The minimum time of concentration shall be 10-minutes.
      (2)   Defined.
         A.   Catch basins are reinforced precast concrete structures typically located in ditch lines as they relate to roadway construction or in parking lots or other miscellaneous land development application to intercept storm water runoff at the surface and deposit the water into a subsurface storm sewer system for further transportation.
         B.   Curb inlets are catch basins with a specialized frame and grate to be used with a Curb and Gutter street. The curb inlet is placed in the gutter line for collection of the storm water runoff and deposited as previously referenced.
      (3)   Design Parameters.
         A.   The maximum pavement encroachment for storm water (spread) shall be one-half lane width. Multi-lane facilities may have one travel lane on each side of the roadway flooded. The allowable storm capacity of each street gutter section may be calculated based on the modified Manning's formula as follows.
            Q = 0.56 Z(-1) S 0.5 d (8/3) / n
            Where:
            Q = Discharge (cfs)
            N = Manning's roughness coefficient = 0.015
            Z = Cross slope of the pavement (ft/ft)
            S = Longitudinal grade of street (ft/ft)
            d = depth of flow in the gutter section at the curb (ft)
Drainage design charts have been developed by ODOT and other sources and are acceptable for use in design as properly documented.
         B.   Maximum spacing for curb inlets and catch basins in a storm sewer system shall be 400-feet.
         C.   Curb Inlets shall be provided upstream of radius turns, at all pavement sag points, at the low points of street intersections, at points of maximum pavement encroachment. Runoff will not be allowed to enter the intersection, except for approved "v" pavement areas. A double inlet shall be used in sag points.
         D.   Curb inlets shall be located upstream from the curb ramp. Curb inlets shall be located on the property line whenever possible to avoid conflicts with driveways and other utilities.
         E.   Catch basins shall be located when the calculated depth or velocity exceeds the maximum allowable at the checkpoint. In such an incidence a catch basin intercepts the flow such that the flow depth is reduced and the need for an erosion control ditch lining may be avoided where possible.
         F.   Catch Basins shall conform to the ODOT, Standard Details. Catch basins shall be ODOT, Catch Basin No. 2-3, 2-4, 2-5 or 2-6 depending upon the diameter of the inlet and outlet storm sewer pipes.
         G.   Curb Inlets shall be ODOT, Standard 6.
         H.   Alternate or modified catch basin or curb inlet types shall be approved by the Village.
         I.   Any catch basin with a depth over 10-feet will require the use of a manhole. A grated lid may be applicable as approved by the Village.
   (g)   Culverts.
      (1)   Design Frequency. Culverts shall be designed and constructed with the capacity to adequately handle the 10-year, 24 hour storm event . A 50-year, 24 hour storm event headwater shall not exceed the edge of the pavement at the nearest roadway adjoining the culvert inlet.
The 100-year, 24 hour storm event headwater shall not exceed any existing or proposed building first floor elevation.
      (2)   Defined.
         A.   Culverts consist of a single pipe open at both ends for transporting storm discharge from point A to B, typically under roadways, and not directly connected to any other piping network. Culverts are designed with a size, shape, and capacity to pass a predetermined design peak discharge without the depth of water at the entrance or the velocity at the outlet exceeding allowable limits.
      (3)   Design Parameters.
         A.   Culverts shall be designed according to methods outlined in the current version of the ODOT, L&D, Volume II.
         B.   Culverts shall be sized utilizing orifice and weir flow equations where applicable for individual site conditions and storm events. Inlet and outlet control nomographs may also be utilized to evaluate culvert hydraulics.
         C.   Pipe material shall be in accordance with ODOT Item 611, Type A - Conduit.
         D.   Minimum culvert diameter shall be 15-inches for fill depths. Larger diameter culvert pipe shall be required as per hydraulic design conditions and/or structural rigidity of the selected pipe as per manufacturer’s recommendations due to depth or loading conditions.
         E.   By definition, the maximum span for a culvert shall be restricted to less than 10 feet. Structures having a span greater than ten feet shall be considered bridges (see subsection (i) hereof).
         F.   The plan for each culvert shall have the drainage area (acres), the estimated runoff design discharge (cubic feet per second), and the maximum headwater elevation (HWE) shown on the plan and profile views.
         G.   Culverts shall be designed to receive storm water from the entire tributary area including any off-site channel flows and/or anticipated future development.
   (h)   End Treatments.
      (1)   Defined.
         A.   A Reinforced concrete structure, rock channel protection, and other materials utilized to protect the open end of conduits typically as a part of a storm sewer system outlet or culvert pipe.
      (2)   Design Parameters.
         A.   Headwalls or other approved end finishes shall be provided at the open ends of all conduits.
         B.   Full height headwall shall be required on all culverts 12-inch through 36-inch diameter.
         C.   Full height headwall with flared wing walls shall be required on 42-inch and larger culverts.
         D.   All other headwall types must be approved by the Village.
         E.   Rock channel protection shall be provided at culvert inlets and outlets as per the ODOT, L&D, Volume II. See also Appendix C, Exhibit C.3.
         F.   Storm sewers or culvert outlets greater than 18 inches in diameter accessible from any storm water facilities or watercourses may be required to provide safety grates. The design engineer shall coordinate this issue closely with the Village on a per case basis to determine the applicability.
   (i)   Bridges. All structures having a span greater than or equal to 10'-0" shall be considered bridges and designed appropriately. All bridges must comply with Standards of the Ohio Department of Transportation and be approved by the Pike County Engineer.
(Ord. 65-2015. Passed 11-3-15.)