Louisville City Zoning Code
CHAPTER 1164
Drainage Requirements
1164.01 DEFINITIONS.
For the purpose of this chapter, certain terms and words are defined as follows:
(a) Bio-retention Basin (Storm Water Wetland) – A constructed system that is explicitly designed to mitigate the impacts of storm water quality and quantity that occur during the process of urbanization. It does so by temporarily storing storm water runoff in shallow pools that create growing conditions suitable for emergent and riparian wetland plants. The runoff storage, complex microtopography, and emergent plants in the basin together form an ideal matrix for the removal of urban pollutants.
Bio-Retention Basins usually fall into one of the five basic designs, listed below.
(1) Shallow marsh system – The shallow marsh design has a large surface area, and requires a reliable source of baseflow or groundwater supply to maintain the desired water elevations to support emergent wetland plants. Consequently, the shallow marsh system requires a lot of space and a sizeable contributing watershed area (often in excess of 25 acres) to support the shallow permanent pool.
(2) Pond/wetland system – The pond/wetland design utilizes two separate cells for stormwater treatment. The first cell is a wet pond and the second cell is a shallow marsh. The multiple functions of the wet pond are to trap sediments, reduce incoming runoff velocity, and to remove pollutants. The pond/wetland system consumes less space than the shallow marsh, because the bulk of the treatment is provided by the deeper pool rather than the shallow marsh.
(3) Extended detention wetland – In extended detention (ED) wetlands, extra runoff storage is created above the shallow marsh by temporary detention of runoff. The ED feature enables the wetland to consume less space, as temporary vertical storage is partially substituted for shallow marsh storage. A new growing zone is created along the gentle side-slopes of ED wetlands that extend from the normal pool elevation to the maximum ED water surface elevation.
(4) Pocket wetlands – Pocket wetlands are adapted to serve smaller sites from one to ten acres in size. Because of their small drainage areas, pocket wetlands usually do not have a reliable source of baseflow, and therefore exhibit widely fluctuating water levels. In most cases, water levels in the wetland are supported by excavating down to the water table. In drier areas, the pocket wetland is supported only by storm water runoff, and during extended periods of dry weather, will not have a shallow pool at all (only saturated soils). Due to their small size and fluctuating water levels, pocket wetlands often have low plant diversity and poor wildlife habitat value.
(5) Fringe wetlands – Fringe wetlands are formed by shallow aquatic benches installed along the perimeter of the permanent pool of a wet pond. These benches are normally 10 to 15 feet in width on both sides of the normal pool (although they can be extended in width). Fringe wetlands are a very useful design feature in ponds, as they promote a more natural appearance, conceal trash and changes in water levels, reduce safety hazards, and provide some aquatic habitat. While fringe wetlands are a desirable feature in wet points, they provide only a minor increment of additional pollutant removal.
(b) Design Year – The frequency with which a storm of a specific intensity and duration will be experienced over time. Therefore, it signifies the probability of a storm with a specific intensity occurring within one year.
Probability = 1/Design Year
Example: 1/25 year = 4% probability of occurring every year
Typical design year events are the 1, 2, 5, 10, 25, 50, and 100-year storms
(c) Detention Basin – A storm water facility whose purpose is to detain storm water from a specific drainage area prior to discharging to a downstream channel. For the purpose of these requirements, a detention basin will be considered to be "dry" prior to a rain event.
(d) Development – A man-made change to any improved or unimproved real estate not including single-family residential homes (up to 4,000 square feet in floor plan including garages) and associated driveways and sidewalks.
(e) Drainage Outlet – Any location where storm water runoff leaves the proposed development site. The outlet typically is a ditch, stream, storm sewer or approved basin.
(f) Major Flood Path – A system that conveys and temporarily stores runoff from rarer storms, such as the 25-through 100-year events. The major flood path is utilized whenever the capacities of the street gutters, storm sewers, and inlets are exceeded. The major flood path components can consist of the following:
(1) Streets
(2) Swales
(3) Detention/retention basins – multipurpose
(4) Manmade channels – open and closed
(5) Natural creeks, streams and rivers
(g) Retention Basin – A storm water facility whose purpose is to detain storm water from a specific drainage area prior to discharging to a downstream channel. For the purpose of these requirements, a retention basin will be considered to contain water at all times.
1164.02 GENERAL REQUIREMENTS.
(a) The City reserves the right to waive portions or all requirements of this chapter for certain proposed developments on a case-by-case basis.
(b) Developments shall be protected from flood hazard and inundation by storm water, springs and other surface waters. The design and construction of drainage facilities shall be such that all watercourses traversing the development and water emanating from outside and/or within the development will be carried through and off the development without any injury to roadway, residential sites, or residences to be installed within the tract, and without the exacerbation of existing problems (as identified by the City) upstream and downstream of the tract.
(c) Existing watercourses entering the development shall be received and discharged from the development as nearly as possible (with respect to location) that existed prior to construction of the drainage facilities within the development. Design of drainage facilities within the development shall conform to the ultimate drainage plan for areas within the development watershed. Runoff water originating in a development shall be drained to an adequate drainage outlet as determined by Planning Commission and/or City Engineer. All acts of pollution as defined in the Ohio Revised Code shall be prohibited. Also, no "sewage", "industrial wastes", or "other wastes" as defined in the Ohio Revised Code, may be discharged into any watercourse from the development.
(d) A drainage plan shall be submitted simultaneously with the plan of any development, showing the proposed scheme of surface drainage. All necessary facilities including underground pipe, inlets, catch basins, retention or detention basins, or open channels shall be installed to provide for the adequate conveyance and management of subsurface and surface water and maintenance of natural drainage courses. The types and sizes of all drainage facilities used to carry water through and off the development must be prepared, signed, and sealed by a registered Professional Engineer licensed to practice in the State of Ohio and must be approved by the City Engineer and conform to the specifications as required by the City Engineer.
(e) As a safety measure for the protection of the health and welfare of the people of the City, Council shall reserve the right to disapprove any development which is subject to periodic flooding, contains extremely poor drainage facilities or has other physical impairment. However, if the owner/developer agrees to make such improvements as will make the area safe for occupancy, provided that in lieu of the improvements the owner/developer shall furnish a surety bond or a certified check covering the cost of the required improvements, the development may be approved subject, however, to the approval of the City Engineer.
1164.03 DESIGN OF DRAINAGE FACILITIES.
(a) Hydrologic Design. The hydrologic methods and criteria used to estimate storm water runoff facilities shall comply with the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, latest edition, unless otherwise stated in these regulations or as required by the City Engineer. Those waterways and drainage facilities set forth in the most current City-adopted master plan (if available) for drainage in the City of Louisville shall be designed and constructed for the flow rates and quantities of water indicated in such master plan.
(b) Hydraulic Design. The hydraulic design of storm collection facilities shall comply with the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, latest edition, unless otherwise stated in these regulations or as required by the City Engineer.
Given the type of drainage structure to be designed, the rate of runoff shall be computed using the storm frequencies given below unless otherwise required by the City Engineer:
Structure Storm Frequency (Years) Storm Sewers 10 (Just Full Capacity) 25 (Hydraulic Grade Line) Open Channels 10 Culverts 25 Bridges 25 Catch Basin Spacing (As per ODOT L&D Vol. II) |
The design frequency to be considered for an individual structure may be altered by the City where the health and safety of the residents would be endangered by the hazards of flood waters or increased flows. All structures located in a designated flood zone shall meet the requirements of Chapter 1323.
Site grading within the development shall be such that all lots will easily drain and structures will be protected from the 100-year flood elevation.
(c) Structural Design. All bridges, culverts, pipes, catch basin, manholes, inlet structures, etc. constructed within the development shall conform to the latest editions of the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, Bridge Design Manual, the Construction and Material Specifications, and the Roadway and Structural Standard Construction Drawings. Structural design of all drainage facilities shall be subject to the approval of the City Engineer.
(d) Additional Requirements.
(1) Open channels. Minimum center line radius of constructed channel shall be a minimum of five times the top width of the channel. Minimum bottom width of constructed channels shall be two feet. Earth channels constructed within the development shall have side slope of 2:1 or flatter. Revetment, bank stabilization and stream bed stabilization along constructed or natural channels will be required as per the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, latest edition.
Open channels shall be designed to avoid roadside hazards as per Ohio Department of Transportation Location and Design Manual, Volume I – Roadway Design, latest edition.
The top of the bank shall be so graded that side drainage will enter channel only at points where structures are provided to prevent bank erosion. The design of open channels shall be in accordance with the Bureau of Public Roads publication Design of Roadside Drainage Channels, Hydraulic Design Series No. 4. If this publication conflicts with the Planning and Zoning Code, the stricter of the two shall be met.
(2) Closed conduits. The alignment of closed conduits shall be as nearly straight as practicable without undue bends and angle points; manholes or catch basins shall be provided at all angle points and at intervals not to exceed 300 feet along the conduit. Inverted siphons shall not be permitted except for temporary structures.
(3) Bridges. All drainage structures having a span of ten feet or greater and all pipes having a diameter or span of ten feet or greater shall be designated as bridges. All calculations and plans pertaining to bridges shall require both preliminary and final approval from the County Bridge Engineer. The hydraulic and structural design of all bridges shall be as per the current version of the Ohio Department of Transportation Bridge Design Manual.
(4) Culverts. Culverts shall be designed to avoid roadside hazards as per the Ohio Department of Transportation Location and Design Manual, Volume I – Roadway Design, latest edition. Culverts shall be designed to meet the allowable headwater criteria in the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, with the design storm per Section 1164.03(c).
1164.04 STORM WATER MANAGEMENT.
(a) Drainage Outlet. Storm water runoff from a development shall be drained through an adequate drainage outlet as approved by Planning Commission and/or City Engineer. The outlet may be a ditch, stream, storm sewer, or approved basin, which has sufficient capacity and structural integrity to accommodate the runoff in an approved manner. If the proposed outlet has current problems downstream (as identified by the City), the City may either revise the proposed drainage criteria specified to alleviate the downstream problems or require that a storm drainage system be provided to an adequate outlet.
(b) Major Flood Path. The intent of planning a major flood path is to ensure that the storm water runoff that may exceed the capacity of the open channel or storm sewer system has a route to follow that will not cause a loss of property or life. Depending on topography, the site proposed for development may have multiple major flood paths or a single major flood path that could be comprised of the street and sewer system and/or swales or channels located outside of the street right-of-way.
The combination of the major flood path and sewer/channel system shall have the capacity to carry runoff from a 100-year frequency storm. Where a street is designated as a portion or all of the major flood path, the depth of flow shall not exceed 8" at the face of the curb. When a portion of the major flood path is located outside a street right-of-way, drainage easements shall be provided and a grading plan is to be submitted with detailed elevations showing the flood being contained in this area.
The minimum basement and first floor opening elevations of garages, doors, windows, etc. along all calculated one-hundred (100) year major flood paths are to be set by the design engineer. These elevations are to be a minimum of one (1) foot above the calculated one hundred (100) year water surface elevation. These elevations are to be clearly labeled on the plans and the subdivision plat (if applicable). In addition, all lots along the major flood path shall have the building "envelope" (that area where structures are allowed to be built) established by the design engineer.
Since streets may be used as a routing path, the major flood path system must be taken into account in the initial design of the development. If detention or retention is required, the major flood path shall be designed in such a manner so to direct the storm water into the detention or retention area. Calculations indicating the capacity of the major flood path and the excess storm water runoff from the sewer system and/or swales or channels shall be provided with the final drainage plan.
(c) Detention/Retention Facilities.
(1) Detention and/or retention basins or other structures shall be constructed as necessary to provide temporary storage of storm water runoff for newly developed and redeveloped areas where the proposed improvements increase the peak runoff rate from the site.
(2) Design criteria. The peak rates of runoff and volumes shall be controlled using the "Critical Storm Method". This method is used to determine the design frequencies utilized in the design of the detention/retention structures for the development.
A. "Critical Storm Method".
1. The peak rate of runoff from the Critical Storm (as determined below) and all more frequent storms occurring on the development area shall not exceed the peak rate of runoff from a 2-year frequency storm (of 24-hour duration) at the outlet location under pre-development conditions. The City may require the use of a 1-year pre-developed storm.
2. Storms of less frequent occurrence than the Critical Storm, up to the 100-year storm, shall have peak runoff rates no greater than peak runoff rates from equivalent size storms under pre- development conditions at the outlet location.
The Critical Storm for a specific development area is determined as follows:
a. Determine, by appropriate hydrologic methods (described below), the total volume of runoff from a 2-year frequency, 24-hour storm occurring over the development area before and after development.
b. From the volumes determined above, calculate the percentage increase in volume of runoff due to development, and using this percentage, select the 24 hour Critical Storm from the following table:
% Increase in Volume of Runoff “Critical Storm” Discharge Limitation | ||
(at least) | (but less than) | Year |
0 | 20 | 2 |
20 | 50 | 5 |
50 | 100 | 10 |
100 | 250 | 25 |
250 | 500 | 50 |
500 | or more | 100 |
B. For detention/retention structures located "off-line" (not within a channel draining upstream off-site flows or otherwise receiving off- site flows), storage volume does not have to be provided for runoff from off-site upstream areas. Upstream runoff should be conveyed through the site in accordance with the current runoff conditions (with respect to flow rate and location).
For all detention structures located "in-line" (receiving flows from upstream off-site areas), the upstream peak flow and volume shall also be detained. The "in-line" basin volume shall be designed to function according to the above design criteria assuming the upstream watershed is fully developed in accordance with the current zoning.
C. The requirements of this section for runoff rates and volumes shall be satisfied at each location where runoff leaves the development area.
D. For areas less than 5 acres, the Modified Rational Method shall be used to develop the inflow hydrographs. For areas between 5 and 20 acres, the Modified Rational and Technical Release 55 (TR-55) Methods are acceptable. Any development over 20 acres shall use the TR-55 Method or USGS Regression Equations as approved by the City.
Pre-developed and developed hydrographs shall be completed for a 24-hour duration when using the Soil Conservation Technical Release 55 (SCS TR-55) and the applicable durations when using other methods, as approved by the City.
E. Routing calculations and their corresponding inflow and outflow hydrographs shall be provided for the Critical Storm and all less frequent storms up through the 100-year storm, the results of which shall be tabulated and included in the drainage plan. The table shall include, but is not limited to: peak inflow, peak outflow, storage volumes, and maximum water surface elevation.
F. The peak 100-year water surface elevation of the detention basin and/or retention basins or other structures shall be 1 foot lower than the lowest grade of the adjacent parcel of land or as directed by the City to prevent property damage.
G. Detention and/or retention basins or other structures and appurtenances shall be designed to avoid hazardous conditions and prevent stored runoff from seeping through or undermining the facility.
(d) Detention Basin.
(1) Allowable side slopes – The grading of the detention basin shall be such that it reflects the surrounding topography. The embankment slopes for the detention basin should be 4'horizontal to 1' vertical (4:1) preferred or at a maximum of 2' horizontal to 1' vertical (2:1).
(2) Outlet/overflow structure(s) – The outlet structure(s) shall be designed to maximize the available storage area. For non-water quality purposes, the outlet structure(s) should be a minimum of 6" in diameter. Access to the entire outlet structure for maintenance and inspection purposes shall be provided. Any orifices or other outflow devices needed for water quality purposes shall not be considered in the detention routing analysis. The total allowable discharge from the basin shall be subject to approval by the City Engineer.
(3) Emergency spillway – An Emergency Spillway shall be provided and set at an elevation equal to 0.5' (minimum) above the 100-year water surface elevation in the basin. The design of the spillway shall be as follows:
A. For outlets having a primary orifice diameter less than or equal to 15" – The emergency spillway shall be designed to pass the 100-year storm minus the flow through any secondary outlets. The depth of water in the spillway shall be no greater than 1 foot.
B. For outlets having a primary orifice diameter greater than 15" – The emergency spillway length shall be 10 feet and set at an elevation 1 foot below the top of the embankment.
Permanent erosion control measures at the emergency spillway may be required by the City based on potential erosion at the site.
(4) Low flow channel – Detention facilities shall be graded to drain to the outlet structure. The minimum grade in the pond shall be 3%. Paved gutters shall not be used as the low flow channel.
(e) Retention Basin.
(1) Allowable side slopes – The grading of the retention basin shall be such that it reflects the surrounding topography. The embankment slopes for the retention basin shall be 4'horizontal to 1' vertical (4:1) leading to the permanent pond. All ponds shall have a 10-foot wide bench around the entire pond. The bench shall be set at an elevation 1 foot below the normal water surface elevation of the permanent pond.
(2) Outlet/overflow structure(s) – The outlet structure(s) shall be designed following the guidelines in subsection (d)(2) hereof except for the following:
A. The invert of the primary structure shall be set at an elevation such that the depth of the pond shall be a minimum of 3 feet.
B. Anti-seep collars shall be provided for all outlet pipes through embankments.
(3) Emergency spillway – Refer to subsection (d)(3) hereof.
(4) Miscellaneous – Retention basins shall have a minimum of 10 acres draining to the pond or as approved by the City.
Soil borings may be required by the City to verify the suitability of the soils at the site. If soils are highly permeable, a 6" clay liner may be required.
(f) Bio-retention Basin. The detailed design of bio-retention basins is to follow the guidelines shown in "Design of Stormwater Wetland Systems", prepared by Thomas R. Schueler. The manual can be obtained from the Metropolitan Washington Council of Governments. General guidance for the design of bio-retention basins is also available in the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, latest edition.
The allowable side slopes shall follow subsection (e)(1) of these standards. The plant materials shall be suitable for the environment created.
(g) Alternative Detention Facilities. In certain applications, alternative detention facilities may be permitted on a case-by-case basis. Alternative detention facilities could consist of (but are not limited to) the following:
(1) Infiltration Basin
(2) Underground Detention (Limited to sites with single owners having the ability to maintain the facility)
All requests for alternative detention facilities shall be submitted to the City with appropriate design standards. After review of the request, if approval is granted, soil borings shall be required for an infiltration basin.
(h) Detention Facilities on Small Sites. Small developments (less than 2 acres) may have difficulty providing the storm water management required, as described above. Maintenance problems arise when the outlet for common detention structures becomes small (less than 6"). Where this applies, the following options shall be considered to decrease the peak rate of runoff.
(1) Provide detention in parking areas utilizing catch basins with the orifice exiting from the bottom of the basins to the sewer.
(2) Provide a reduction in peak flows with the use of vegetative best management practices (BMPs). These include the use of grass swales and filter strips. To utilize these BMPs, the proposed parking areas and roof drains should discharge into these structures, which will detain the peak flow by increasing the flow time across the site. Detailed information on these structures is contained in "CONTROLLING URBAN RUNOFF: A Practical Manual for Planning and Designing Urban BMPs", which can be obtained by contacting the Metropolitan Washington Council of Governments. General guidance for the design of vegetative BMPs is also available in the Ohio Department of Transportation Location and Design Manual, Volume II – Drainage Design, latest edition.
(3) Provide detention using a drywell or other infiltration device with an overflow as approved by the City of Louisville.
If none of these practices are applicable, the City reserves the right to waive the storm water management requirements for developments under 2 acres. This may only be done after the designer has shown that all other options are not feasible.
1164.05 DEDICATIONS/EASEMENTS FOR DRAINAGE PURPOSES.
Easement and/or dedicated land shall be provided as described for the following cases or as otherwise required by the City. Certain restrictions may apply as defined by the City.
(a) Easements for Closed Conduits and Appurtenances. An easement of no less than twenty feet in width and sufficient to contain and maintain the closed conduits shall be dedicated on the final map of the subdivision as follows:
"Public Drainage Easement"
Drainage easements for closed conduits shall not traverse a building site and shall, insofar as possible, be placed along or adjacent to lot boundary lines in a straight alignment without angle points.
(b) Easement along Channels. Whenever any open channel or important surface drainage course (as defined by the City) is located within the area being developed, the owner/developer shall provide a permanent easement of sufficient width dedicated to the proper authority for the purpose of widening, deepening, relocating, improving, or protecting the channel for drainage or public use.
(c) Dedications/Easements for Detention/Retention Facilities. Lands encompassing detention/retention facilities that are constructed for residential or industrial subdivisions shall be dedicated to the City to provide for the proper function and maintenance of the facility. This does not apply to facilities on sites having single owners. Approved easements having sufficient width for access to the dedicated lands shall be provided on the final plat.
1164.06 DRAINAGE PLANS.
(a) Preliminary Drainage Plan Requirements. For subdivisions or as otherwise required by the City Engineer, a preliminary development plan shall include and shall have appended to it sufficient data for the City Engineer to check the feasibility of the drainage system as proposed by the owner/developer. A preliminary drainage plan for all developments shall be submitted to the City of Louisville for review and approval. It shall include a drawing showing the general runoff pattern of the area to be improved, as well as the runoff patterns of adjacent areas which may affect or be affected by the proposed improvement. Preliminary hydraulic design calculations (approximate flow rates and structure sizes) for all proposed basins, bridges over waterways, and culverts greater than 4 feet in span shall be provided. A copy of the preliminary plat, which is required by the Planning Commission, may serve as the preliminary drainage plan provided sufficient data has been supplied to check the feasibility of the drainage system as proposed by the developer. In conjunction with the minimum requirements listed in Section 1164.06(b), calculations shall be performed and submitted, at a minimum, for all critical points within the development. Critical points are locations such as confluences of streams and tributaries, junctions of proposed storm sewers with existing storm sewers (or vice versa), upstream site limits, downstream site limits, etc.
(b) Final Drainage Plan and Report Requirements. A final drainage plan shall include drawings of the entire drainage system and be submitted to the City of Louisville for review and approval. The plan shall conform to the guidelines herein and to any special conditions of the Planning Commission in approving the preliminary and final plans. The plan shall also include the engineering calculations used in determining the design of the drainage courses, drainage structures, and storm water runoff control structures.
All plans shall be sealed with the stamp of a Professional Engineer as required by the Ohio Revised Code. The drainage drawings must be approved by the City of Louisville prior to the construction of any portion of the drainage system.
Minimum requirements for drainage and engineering calculations for the drainage systems shall comply with all aspects of Section 1164.05 and also the following:
(1) A narrative summarizing points of analysis, methodology used, assumptions made, and other pertinent information necessary for review (as determined by the City Engineer) shall be prepared and submitted with the calculations.
(2) A drainage map showing the existing topography of the development area and adjacent land within three hundred (200) feet of its boundary. The topographic map shall use a contour interval appropriate to clearly portray the surface conformation and drainage pattern of the area.
(3) A vicinity map at a scale of not less than two thousand (2,000) feet to the inch showing the development area in relation to existing roads and nearest existing thoroughfares, streams, and other water areas.
(4) The drainage area for storm water management structures shall be outlined and have the acreage shown. To show the entire drainage area, additional sheets may be required. If additional sheets are needed, existing aerial mapping or USGS mapping shall be sufficient.
(5) The location of any adjacent existing drainage structures shall be shown. This information shall be based on field investigations, measurements, and mapping.
(6) The acreage of all tributary drainage areas and their sum.
(7) Hydrologic calculations including the following items:
A. Times of concentration, intensity, and runoff coefficients used in the Modified Rational Method to estimate the inflow hydrographs.
B. Overland slopes, curve numbers, hydraulic lengths, etc., used in the SCS Peak Discharge Method or the TR-55 Method.
C. For methods other than those above, enough information must be provided to the City to allow for an accurate review.
(8) Discharge in cubic feet per second (cfs), velocities in feet per second (fps), and any additional data needed to establish that the drainage system will convey the flow.
(9) Size and types of all drainage improvements including the detailed drawings of each component, typical sections, and easement widths.
(10) Routing calculations and their corresponding inflow and outflow hydrographs shall be provided for the critical storm and all less frequent storms up through the 100-year storm.
(11) Tabulated results including peak inflow, peak outflow, and maximum water surface elevations for all storm water management facilities.
(12) Calculations determining the elevation(s) and location(s) of the major flood path(s).
(13) The plan and profile of all drainageways shall be provided, including a cross section of open channels showing the depth of flow for the design year and 100-year frequencies.
(14) Supporting calculations for upstream and downstream channel capacities as they affect overflow or backwater within the development. Such calculations shall be substantiated by such additional survey information as is required to determine profile and cross section of the upstream and downstream channel reaches under consideration.