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§ 156.02 DRAINAGE SYSTEMS.
   (A)   The development of a comprehensive storm water management system requires providing two separate and distinct drainage systems–the minor system and the major system.
   (B)   The minor drainage system is for collecting and transporting run-off from frequently occurring storms. It includes open channels, street curbs and gutters, and underground storm sewers, manholes, catch basins, culverts, and the like. This system's purpose is to lessen or eliminate inconveniences and safety and health hazards associated with frequent storms. Except where otherwise indicated, the criteria included in these regulations are directed to the design of the minor drainage system.
   (C)   The major drainage system is to insure that storm water run-off which exceeds the capacity of the minor drainage system has a route to follow that will not cause substantial damage. It must be recognized that the major drainage system exists even when it is not planned and whether or not physical facilities are intelligently located in respect to it.
(Ord. C-604, passed 9-8-86)
§ 156.03 SUBMISSION REQUIREMENTS.
   Plans, profiles, and supporting documentation to verify conformance with these criteria shall be submitted along with the usual plan submissions required in Chapter 155, Subdivision Rules and Regulations, and shall be referred to as the Storm Water Management Control Plan. This plan shall include:
   (A)   Preliminary plans. In addition to the requirements of Chapter 155, Subdivision Rules and Regulations, a plan showing the total area contributing run-off to the subdivision or land development being considered (project area) shall be submitted with the preliminary plan. This plan shall contain, but is not limited to, the following information:
      (1)   A contour plan showing the outline of all areas outside the project area that contributes run-off to it.
      (2)   Estimated run-off (Q) before and after development for terminal points along natural streams, proposed open channels, and other strategic points such as existing storm sewers or culverts.
      (3)   Location of proposed detention/ retention areas.
      (4)   Any other information required by the village to clarify intent.
   (B)   Improvement plans. In addition to the requirements of Chapter 155, Subdivision Rules and Regulations, the improvement plan for the project area shall contain, but is not limited to, the following information:
      (1)   Diameter, length, slope, concrete pipe, and class (if other than Class II), of all storm sewers, culverts, and sub-surface drainage.
      (2)   Invert elevations on profiles of all pipes at terminal points such as manholes, inlets, catch basins, and headwalls.
      (3)   Top of grate elevations of manholes and grate flow lines of catch basins and inlets located outside the public right-of-way. This information shall be submitted for structures within the right-of-way when required by the Village Engineer.
      (4)   Type of catch basin, inlet, and manhole.
      (5)   Headwall type.
      (6)   Cross-sections of proposed open channels showing width of bottom, depth of water, erosion control measures and limits, and side slopes at each point of design along with a profile indicating the longitudinal slope and bottom elevations at the terminal points and points of design.
      (7)   High and low points, on the plan, indicating the direction of run-off flow on the roadway.
      (8)   Structural details and design data for detention/ retention facilities.
      (9)   Details of construction for all structures not included in the standard construction drawings of the Subdivision Rules and Regulations, these criteria, or other referenced standards.
      (10)   Easements.
      (11)   Other requirements of Chapter 153, Soil Erosion and Sediment Control.
      (12)   Any other information required by the village to clarify intent or design features.
   (C)   Drainage and grading plans. In addition to the improvement plan, a drainage and grading plan shall be submitted. This plan may be superimposed on the required improvement plan, or similar plan at a scale of 1 inch equaling 100 feet or larger, showing at least the following additional information:
      (1)   Contours indicating the existing and final grading at vertical increments of no more than two feet.
      (2)   Discharge (Q), co-efficient of run-off (c), and drainage area (A) along with the outline of the drainage area for each inlet, catch basin, culvert and open channel point of design, and at other locations designated by the Village Engineer. Drainage areas that lie partially outside the limits of the drainage and grading plan may be delineated on any contour map acceptable to the Village Engineer.
      (3)   Discharge (Q), before and after development at strategic points within and at the extremities of the project area.
      (4)   Delineation of the boundaries and contour elevation along with the route of the major drainage system through downstream areas to an adequate outlet although the outlet may be outside the project area.
      (5)   Delineation of the horizontal limits of ponding areas for storms with frequencies of 25 years and 100 years at low points (sags) in the street profile and low points outside the street right-of-way including, but not limited to, culvert headwater, natural stream water surfaces, and sump type inlets.
      (6)   High and low water horizontal limits and contour elevation of detention/retention/ sedimentation facilities along with water surface and control weir elevations, outlet structures, and the like.
      (7)   All requirements of Chapter 153, Soil Erosion and Sediment Control.
      (8)   Any other information required by the village to clarify intent, specified requirements, or design features.
   (D)   Supporting data. All data and design information used for the design of drainage facilities and for determining downstream flood information shall be submitted with the drainage and grading plan. To facilitate review and avoid confusion, legends, descriptions, structure numbering, and the like used on design forms or other calculations shall be identical to those used on the improvement plans and the drainage and grading plan. This data shall include, but is not limited to:
      (1)   Weighted run-off coefficient calculations for each contributing area.
      (2)   Pavement drainage computations.
      (3)   Storm sewer computations.
      (4)   Culvert design computations.
      (5)   Open channel computations.
      (6)   Detention/retention facilities computations.
      (7)   Any other information required by the Village Engineer to clarify intent or design features.
(Ord. C-604, passed 9-8-86)
§ 156.04 STORM WATER RUN-OFF ANALYSIS.
   Determining the peak rate of storm water run-off reaching the point of consideration is fundamental to the design of the storm water management system. Careful selection of variables is prerequisite to adequate design.
   (A)   Rational method. The rational method shall be used to determine peak rate of run-off from areas not larger than 50 acres. The basic formula for the rational method is Q = ciA where:
      (1)   Q = Peak rate of run-off in cubic feet per second (cfs).
      (2)   c = Run-off coefficient representing the characteristics of the drainage area.
      (3)   i = Average intensity of rainfall in inches per hour for a duration equal to the time of concentration (tc) for a selected rainfall frequency.
      (4)   A = Area drained in acres.
   (B)   Run-off coefficient. The following table presents values for use with the rational method. A weighted run-off coefficient must be individually computed for each drainage area contributing to a catch basin, an inlet, a culvert, an open channel, or any other drainage facility. The Village Engineer may permit a general weighted run-off coefficient to be used within a subdivision, land development, or for portions of the area. The calculations will be part of the drainage and grading plan submission.
Character of Surface         Run-off Coefficient
Pavements, roofs, and
other hard surfaces         0.90
Lawns, yards, and other
unpaved areas, except
wooded areas
Flat - less than 4:1 slope      0.40
Steep - 4:1 slope or greater      0.70
Natural dense wooded areas       0.1 to 0.40
      (1)   The use of the above run-off coefficients for natural dense wooded areas is restricted to areas 50 feet or more away from a building which will remain undisturbed and in their natural state; and where engineering data verifying the coefficient has been presented to and approved by the Village Engineer.
      (2)   Time of concentration. The time of concentration in minutes is the estimated time for storm run-off from the most remote part of the drainage area to reach the point being analyzed. Time for flow in open channels, gutters, pipes, and the like will be estimated using appropriate hydraulic methods. The total time of concentration in minutes is the summation of overland flow, open channels, gutters, pipe flow, and the like. The time of concentration to any drainage facility or point of design is the greater of the summation as defined above or the minimum time of ten minutes.
      (3)   Intensity of rainfall. The intensity of rainfall will be obtained from the most recent edition of the Hamilton County Storm Drainage Standards, Plate II. The frequency of storm to use is specified in the section of these criteria covering the type of facility being designed.
(Ord. C-604, passed 9-8-86)
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