A.   A drainage plan prepared in accordance with the provisions of this chapter shall be submitted to and accepted by the city engineer prior to the approval of any final plat or final replat of any subdivision of land, prior to the approval by the planning commission of any minor subdivision, prior to the issuance of any building permit, or prior to the approval of any development.

B.   At application for review of any item that may require a drainage plan, a drainage study shall be submitted to the city engineer. If the drainage study shows that no increase in peak stormwater flows will result from the development, the city engineer may waive the requirement for a final drainage study and a drainage plan. Drainage studies shall contain adequate information and calculations to demonstrate the validity of the conclusions being made and that they are in compliance with these standards. A drainage study shall be formulated under the direct supervision and sealed by a registered professional engineer licensed by the state.

C.   Two (2) weeks prior to review at a public meeting by the planning commission, a final drainage study must have been submitted to the city engineer.

D.   A final drainage study prepared in accordance with the provisions of this chapter shall be reviewed and accepted by the city engineer prior to approval by the planning commission of any preliminary plat of any subdivision of land, and prior to the approval by the city commission of any final plat or final replat of any subdivision of land, development, site plan or use permit.

E.   Upon approval by the city commission and/or the planning commission of any item that requires a drainage plan, a revised final drainage study that reflects any special conditions of the city commission and/or the planning commission approval shall be submitted and accepted.

F.   A drainage plan accepted by the city engineer is a prerequisite to the issuance of a building permit. (2010 Code § 22-144)

A.   Under the following circumstances, the development of a final residential plat shall not have to be redesigned for drainage:

   1.   Any subdivision for which a final plat was approved prior to May 13, 2003; and

   2.   Which has not been designed in accordance with the provisions of this chapter; and

   3.   In which improvements were installed prior to May 13, 2003; and

   4.   The sale of lots in said subdivision began prior to May 13, 2003; and

   5.   The development of said subdivision is being accomplished with the same general use as originally intended when approval was granted for the final plat; and

   6.   Structures have been built on more than fifty percent (50%) of the lots by the effective date of this chapter.

B.   Nothing in this section shall be construed to relieve a developer of property from obligations under any other laws, including, but not limited to, the Oklahoma stormwater act. (2010 Code § 22-145)

A.   Requirements: All drainage facilities shown as part of an accepted drainage plan for any portion of a development shall be installed as a part of the first phase of construction or earthmoving activity on that portion of the development. If only a portion of the drainage facilities are installed on any development due to phased construction of the development, these facilities shall be constructed to function in such a manner as to be consistent with the purpose of this chapter. The use of temporary drainage facilities may be permitted so long as they function in such a manner as to be consistent with the purpose of this chapter and that they are replaced with permanent drainage facilities prior to occupancy or use of the development. Minor deviations from the requirement for installing the drainage facilities as a part of the first phase of construction or earthmoving activity may be granted by the city engineer if deemed necessary for technical reasons related to the construction as long as the purpose of this chapter is met.

B.   As Built Drawings: As built drawings shall be prepared and sealed by a professional engineer registered in the state and shall be submitted to the city engineer upon completion of the construction of the final drainage plan. As built drawings shall clearly show any changes from the accepted final drainage plan. The as built drawings shall be reviewed by the city engineer. If the submitted as built drawings cannot be accepted, the certifying engineer and applicant shall be advised in writing of the reasons for their disapproval. As built drawings must be accepted prior to the issuance of a certificate of occupancy and the use or occupancy of a site, development or other improvement.

C.   Maintenance Bond: Before acceptance by the city commission of any public improvement for city maintenance, a maintenance bond for the total cost of the improvement and for a period of one year shall be filed with the city clerk to ensure the correction of any defect in materials or workmanship that may be found in the improvement. (2010 Code § 22-146)

A.   General Requirements: All final drainage studies shall be formulated under the direct supervision of a registered professional engineer licensed by the state. Studies submitted for final acceptance shall be accompanied by payment of a fee in accordance with the schedule approved by the city commission, and bear the signature and seal of the submitting engineer and, additionally, the following statement shall immediately precede the signature and seal of the submitting engineer:

B.   Statements:

   1.   All final drainage plans shall be formulated under the direct supervision of a registered professional engineer licensed by the state. Plans submitted for final acceptance shall bear the signature and seal of the submitting engineer and, additionally, the following statement shall immediately precede the signature and seal of the submitting engineer:

   2.   Following the signature and seal of the submitting engineer, the drainage plan shall bear the name, address, phone number and signature of the owner, which shall be subscribed below the following statement:

   3.   In the case of property owned by a corporation, the statement shall use the parenthetical language and the owners information shall also include the title of the authorized person signing the owners certification and a notarized corporate seal.

C.   Final Drainage Study Elements: A drainage study shall consist of text statements, engineering drawings, contour maps, and all supporting engineering drawings, supporting contour maps, and supporting engineering calculations applicable to the land area covered by the study and which are required to demonstrate full compliance with the requirements of this chapter and the city drainage standards. A study shall include all pertinent information required by the city engineer and may include, but shall not be limited to, any or all of the following elements:

   1.   An engineering report showing compliance with the applicable provisions of this chapter and the city drainage standards, clearly detailing the scope of the engineering problem and the proposed solutions;

   2.   An engineering hydrologic analysis of stormwater runoff under existing site conditions and under proposed developed site conditions;

   3.   A detailed evaluation of the projected effects on property adjoining the site and on existing drainage facilities and systems both on and off the site;

   4.   The location of all existing and planned temporary and permanent drainage facilities;

   5.   The on site regulatory flood elevations and the boundaries of any floodplain area. In every instance, the plan shall include a determination of the area required to carry the regulatory flood;

   6.   The proposed method of handling all runoff from the development and demonstrated capability to handle the pass- through of upstream runoff;

   7.   Proposed fill or other structure elevating techniques, levees, channel modifications and detention facilities;

   8.   The location and size of all existing and proposed drainage easements and areas; and

   9.   The location, size, character and estimated effectiveness of all temporary and permanent erosion and sedimentation control facilities with specifications detailing all on site erosion control measures which will be established and maintained during all periods of development and construction. An outline of the sequence of construction activities shall be provided that notes when the various aspects of the drainage study will be implemented. (2010 Code § 22-147)

A.   General Design Criteria:

   1.   Drainage facilities shall be designed to provide a sufficient stormwater drainage system for the conveyance of stormwater runoff received from upstream and from the subject property with due allowance having been made for continued conveyance of stormwater runoff from adjacent properties as the drainage basin develops.

   2.   The drainage system, including streets, bridges, culverts, open channels, detention/retention facilities, etc., shall be designed to carry all probable storm recurrence intervals up to and including the 100-year storm.

   3.   A dedicated drainage easement shall encompass all land lying below the water surface elevation generated by the 100-year storm event and resulting stormwater runoff.

   4.   Site improvement shall provide for the grading of all building pads to an elevation where the lowest finished floor elevations will not be subject to overflow from the design storm. All developments, surface water from each dwelling lot will flow away from each dwelling to an approved collection or disposal location as required under section 10-17-17 of this chapter.

   5.   Erosion and sedimentation control facilities with construction specification and operation and maintenance procedures detailing all erosion and sedimentation control measures which are established and required maintenance during the life of the development shall be provided.

   6.   No improvements shall be constructed which will increase the frequency or the depth of flooding.

B.   Existing Drainage Structures: Existing structures within and adjoining a proposed development shall be evaluated in terms of hydraulic capacity and structural soundness. Those structures found to be structurally inadequate shall be completely removed by the developer and replaced. Structures found to be hydraulically inadequate for flow and/or for protecting property as a result of the changing runoff characteristics shall be replaced or modified to provide the required capacity and/or protection.

C.   Utilities: All utilities located within the floodway shall be designed to prevent infiltration of floodwater and to protect against washouts. Location of the utilities shall not restrict flood flows. (2010 Code § 22-148)

Any reference to official maps shall mean the highest order of floodplain designation recognized by the city. The city engineer will maintain an up to date file of such designation. The highest available order of study shall be the basis of design unless it can be clearly shown that the subject study is in error. Contested studies shall be brought to the attention of the city engineer. (2010 Code § 22-149)

A.   Preparations:

   1.   Plan and profile shall be drawn on sheets twenty four inches by thirty six inches (24" x 36") to a horizontal scale of one inch to twenty feet (1" = 20') or one inch to forty feet (1" = 40'), and vertical scale of one inch to two feet (1" = 2') or one inch to four feet (1" = 4') (except that scales may vary on special projects, such as culverts and channel cross sections).

   2.   Stationing shall proceed upstream with the north arrow pointing to the top of the sheet, or to the right.

   3.   Plan for the proposed drainage system shall include property lines, lot and block numbers, dimensions, right of way and easement lines, floodplains, street names, paved surfaces (existing or proposed), contract limits, location, size and type of inlets, manholes, culverts, pipes, channels and related structures. Outfall details, miscellaneous riprap placement, two foot (2') contour lines, flow arrows, title block.

   4.   Profiles shall indicate the proposed system (size and material) with elevations, flow lines, gradients, left and right bank channel profiles, station numbers, inlets, manholes, ground line and curb line elevations, typical sections, riprap construction, filling details, minimum permissible slab elevations adjacent to 100-year floodplains, open drainage features, pipe crossings, design flow capacities, and title block.

   5.   Official floodplain designations and delineations of floodways denoting limits of permissible developments shall be shown on all preliminary plans and final plats submitted for approval wherever such plans and plats contain floodplains and/or floodway segments. In any case in which official floodplains are not delineated, they shall be determined on the basis of these standards and shall be shown on all preliminary plans and final plats submitted for approval.

B.   Submittals: Computations and plans to support all drainage designs shall be submitted to the city engineer for review. The computations and plans shall be in such form as to provide the basis for timely and consistent review and will be made a part of the permanent record for future evaluation. The computations and plans shall be accompanied by the certification of a registered professional engineer licensed to practice in the state. Before final approval, the submitting engineer shall provide an as built plan, accompanied with a letter of certification, stating that the submitted plan complies with all governing ordinances and adopted drainage standards of the city. (2010 Code § 22-150)

Numerous methods of runoff computation are available on which the design of storm drainage and flood control systems may be based. The rational method will be accepted as adequate for drainage areas up to forty (40) acres. For larger areas, the U.S. army corps of engineers, hydraulic engineering circular (HEC) 1 and 2 shall be used. Other methods may be approved by the city engineer. (2010 Code § 22-151)

A.   Runoff Coefficient "C": The runoff coefficients shall be chosen to represent the integrated effects of infiltration, detention storage, evaporation retention, flow routing and interception. Recommended ranges for "C" are provided in table 2.1, "Runoff Coefficients For The Rational Formula By Hydrological Soil Group And Slope", which is on file in the city office. The hydrological soil group is to be determined from Oklahoma County, Oklahoma, soil survey provided by the United States department of agriculture soil conservation service.

B.   Rainfall Intensity (i): The average rainfall rate in inches per hour considered for a particular drainage basis or subbasin and selected on the basis of design rainfall duration and design frequency or occurrence.

   1.   Intensity duration curves acceptable for the city are shown on figure 2.1.

   2.   The time of concentration is the time associated with the peak runoff from the watershed to the point of interest. Street flow shall be considered as being in an open paved channel. Manning's equation is acceptable for determining open channel and free water surface conduits flows.

An acceptable formula for use in determining overland flow is:

 

An acceptable formula for determining channel flow time is:

      Time = K (L 2/S)•385

      Values of K

      Curbed street - .0035

      Concave lined channel - .006

      Sodded swale - .008

      Bar ditch - .012

The time of flow in a closed conduit is the quotient of the length of the conduit and velocity of flow as computed using the hydraulic factors of the conduit.

C.   Drainage Area (A): The size and shape of the watershed must be determined. Drainage areas shall be determined through the use of planimetric topographic maps, supplemented by field surveys. A drainage area map shall be provided for each project. The drainage area contributing to the system being designed and drainage subarea contributing to each inlet point shall be identified. The outlines of the drainage divides must follow actual lines rather than artificial land divisions.

(2010 Code § 22-152; amd. 2012 Code)

A.   The location of inlets and permissible flow of water in the streets should be related to the extent and frequency of interference to traffic and the likelihood of flood damage to surrounding property. Interference to traffic is regulated by design limits of the depth and spread of water into traffic lanes, especially in regard to collector streets and arterials.

   1.   Flow in gutters which are on straight or parabolic crown pavement may be determined by using Manning's formula for channel flow or acceptable monographs.

   2.   Minimum gutter slope on residential streets shall not be less than 0.004 ft./ft.: (0.4%). Maximum gutter slope should not be more than 0.08 ft./ft.: (8.0%). In a gutter which has a radius of one hundred feet (100') or less, the design flow depth shall not exceed seventy percent (70%) of the curb height.

   3.   No lowering of the standard height of street crown or splitting of curb heights shall be allowed for the purpose of hydraulic design unless approved by the city engineer. In no case will it be allowed on collector streets or thoroughfares.

   4.   All street sections shall have a positive crown, except alleys.

   5.   The flow depth in the gutter arterial streets shall not exceed four inches (4") for the 50-year storm event or six inches (6") for the 100-year storm event. The flow depths in the gutter on other classification of streets shall not exceed six inches (6") for the 100-year storm event. Where two (2) or more streets flowing six inches (6") in depth intersect, the flow shall be intercepted by appropriate storm sewer techniques prior to the intersection of said streets such that the depth of flow within the intersection will not exceed four inches (4") in depth for the 100-year storm event.

B.   The use of a cul-de-sac or dead end street as the terminal point of residential street flow shall not be allowed for drainage areas exceeding five (5) acres. A minimum of seventy percent (70%) of the flow in a residential street shall be removed to a storm sewer or drainage system prior to reaching the point of curvature of a cul-de-sac or the end of the street for drainage areas exceeding five (5) acres in size. (2010 Code § 22-153)

A.   The use of the Manning equation or the use of appropriate charts or nomographs in the design of storm sewers will be considered acceptable. Investigations of the capacity of all existing structures on the waterway shall be made.

B.   In addition, runoff from storms exceeding the design storm shall be anticipated by the developer and disposed of with minimum damages to surrounding property. The sewer must be accessible for maintenance. (2010 Code § 22-154)

A.   Pipe Diameter: Pipes which are a part of the storm sewer system shall have a minimum diameter of fifteen inches (15").

B.   Storm Drain Design: Enclosed storm drains will be designed for open channel flow.

C.   Minimum Grades: The slope shall be such to maintain a minimum velocity of 2.5 fps.

D.   Roughness Coefficient: Acceptable roughness coefficient "n" for storm sewers:

 

 

E.   General Rules To Be Observed:

   1.   Do not discharge a larger pipe into a smaller one.

   2.   At change in pipe size match top of pipe.

   3.   A one foot (1') freeboard shall be maintained below the proposed finish grade through the storm sewer system. The submittal of energy calculations shall be required on any reach of a system which exceeds five hundred (500) linear feet; on the total system that exceeds one thousand five hundred (1,500) linear feet; on a reach of a system which has an elevation change exceeding ten feet (10').

F.   Manhole Locations: Manholes shall be located at intervals not to exceed three hundred fifty feet (350') for pipe sizes forty two inches (42") or less. Above forty two inches (42"), manholes shall be located as determined by the city engineer. Manholes shall be located at conduit junctions, changes of grade and changes of alignment, and changes in conduit size.

G.   Pipe Connections: The use of one material to extend a sewer constructed of a different material shall not be allowed except at manholes, junction boxes or inlets.

H.   Pipe Laid On Curves: Degree of curvature shall be as per manufacturer's recommendations.

I.   Erosion Protection: All storm sewer outlets shall have erosion protection provided by headwalls, flared end sections, curtain walls, etc. (2010 Code § 22-154a)

A.   Inlet design and location in street sections must be compatible with the allowable depth of water on the street section.

B.   Inlet location shall not interfere with vehicular or pedestrian traffic.

C.   Whenever possible, inlets will intercept water before it reaches a pedestrian crosswalk or street intersection.

D.   Inlets shall not be located in a curb radius. Where existing conditions exist that require an inlet in the radius, the radius shall not be less than thirty eight feet (38').

E.   Inlets shall be located to prevent water from minor streets spilling over and flooding major streets.

F.   All hoods in a sump condition shall be eight inch (8") opening with the gutter lowered to accommodate the inlet. Transition section shall be ten feet (10') each way.

G.   Where a curbed street crosses a bridge, gutter flow shall be intercepted and not allowed to flow onto the bridge.

H.   Inlets shall be installed at all low points with sufficient inlet design to ensure the ponding depth does not exceed four inches (4") in a 50-year storm event. All storm sewer systems at a low point shall provide for an overflow channel with a designated drainage easement.

I.   No method of determining capacity is prescribed in this standard. Theoretical capacities using clear water in nomograph form have been published by various sources such as the ASCE and highway research board. When using nomographs, submit the source along with drainage calculations.

J.   Any inlet grates over which a bicyclist can ride shall be of a design considered bicycle safe. (2010 Code § 22-155)

Natural drainage flow: The creation of swales, alteration of small channel capacity or direction, changing of ground cover and the lining of existing channels with other material, natural or man produced. May be necessary in some parts of the system to achieve the objectives of this standard. (2010 Code § 22-156)

A.   All land adjoining open natural or improved storm drainage channels having an elevation below the 100-year flood elevation of the channel shall be dedicated drainage easement for the purpose of providing a zone of protection to all property owners.

B.   Any channel improvements shall be approved by the city engineer prior to the commencement of any work thereon.

C.   Whenever channel improvements are carried out, sodding, backsloping, cribbing and other bank protection shall be designed and constructed to control siltation and erosion for the anticipated conditions and flow resulting from a 100-year frequency rainfall. (See section 10-17-8 of this chapter.)

D.   Any channel grading shall be such that water will not gather in pools.

E.   Drainage easements to provide working room for construction and access for channel maintenance shall be provided. (2010 Code § 22-157)

A.   Channels: Channels should be trapezoidal in shape, and on as flat a grade as possible.

B.   Hydraulic Characteristic Calculation: The use of Manning's equation in the calculations of hydraulic characteristics of channels will be acceptable. The "N" value(s) used for channels shall be based on the individual channel characteristics. When submitting calculations, include the source.

C.   Constructed Channel Geometry: The minimum bottom width shall be four feet (4'), with side slopes of not steeper than 3.5 to one for sodded sections and a minimum bottom width of three feet (3'), with side slopes of not steeper than one to one (1:1) for paved or rocklined sections. Care must be exercised by the engineer to provide a safe design in relations to public areas.

D.   Flow Velocities In Channels: Velocities shall not exceed four (4) fps for sections sodded in grass. Velocities in concrete lined or paved sections shall not exceed fifteen (15) fps. The dissipation of energy shall be required at the confluence of improved channels with natural channels through the use of dissipaters, stilling basins, etc.

E.   Trickle Channels: All channels altered or improved from the natural state will require a paved trickle channel. Sodding, or other methods of erosion control, shall be required adjacent to the paved channel.

F.   Concrete Flumes: Concrete flumes in lieu of enclosed pipe shall be allowed as overflow protection for storm sewer systems, and to drain areas not exceeding five (5) acres in size. All concrete flumes shall extend to the rear of adjacent lots and shall discharge into a dedicated drainage area or channel. (2010 Code § 22-158)

A.   Purpose: The purpose of this section is to require proper planning and execution of good grading layouts to ensure that the street grades, floor elevations and lot grades are in proper relation to each other and to existing topography, considering property protection, appeal and use.

B.   Design Considerations:

   1.   Nonresidential (Including Multi-Family): All roofs, paved areas, yards, courts and courtyards shall drain into a storm sewer system or to an approved place of disposal, not generally including existing streets. Site plans detailing the layout and design of the stormwater runoff system shall be submitted prior to site plan review by the planning commission or city commission, or the issuance of a building permit and/or work order. All design submittals shall detail the location and features of a proposed drainage system. The submittals shall include, but not be limited to, grading plans, drainage plans, utility plans and erosion control plans.

   2.   Residential (One-Family Or Two-Family Structures):

      a.   Requirements: In single-family residential, duplex or mobile home developments, stormwater runoff from each dwelling lot may be discharged onto flat areas, such as streets or lawns, if drainage is provided so that the stormwater will flow away from the building. It shall remain the responsibility of the builder/developer of a lot to ensure proper and prudent lot grading. The builder/developer shall follow the grading plan established for that lot, or, in the absence of such a plan, the builder/developer shall grade the lot following the existing, natural drainage patterns for the area. In no case shall a builder/developer direct, redirect or change the historic patterns of the stormwater runoff.

      b.   Development Grading Plans: The submittal of a master development grading plan shall be required as part of final plan submittal. The master development grading plan shall incorporate, but not be limited to, the following:

         (1)   Determine the type (front to rear, side to rear, rear to front, etc.) of grading for each block, lot or portion of a development and indicate the grading type for each area by identifying letter or drainage arrows.

         (2)   Determine the necessity for easements and other provisions needed for satisfactory drainage and erosions control.

         (3)   Determine general grading limitations for local conditions, such as minimum gradients for grass slopes and swale.

         (4)   For each area, determine the necessity for specific grading limitations along a typical grading control line from street to the house and determine the minimum street to floor rise (if applicable).

         (5)   For each development, determine reference elevations for key points giving due consideration to street elevations and existing topography.

         (6)   The owner/developer shall provide a builder/developer with the approved grading plan.

      c.   Building Permit Applicant:

         (1)   The permit applicant (builder) shall become familiar with the various lot ending types proposed for a particular development.

         (2)   The builder shall submit along with the building permit application, a detailed site plan showing the proposed grading by identifying letter or drainage arrows.

         (3)   Establish key elevations or other referenced markers to the grading type and anticipated stormwater runoff for the development area.

         (4)   Prior to finish grading, establish grade stakes as necessary and check the entire lot for proper drainage according to the master grading plan. (2010 Code § 22-159)

A.   The use of stormwater storage basins in urbanizing areas does not guarantee that downstream runoff peak flows will remain below their predevelopment levels for a given rainfall event. Detention basins can be used in an attempt to replicate the characteristics of natural infiltration, storage, and the attenuation of flow that is lost through urbanization. The objectives are to provide a volume of storage to compensate for that lost by development of the land, and to control the detention basin discharge so that the peak flow after urbanization remains below the preurban peak for a given year.

B.   Although individual detention basins can meet the design objectives, the downstream peak flow may actually increase due to the timing characteristics of the resulting runoff within the watershed. Because of this "peak timing" effect, certain areas of a watershed may be more effective than others, as basin location sites, to control downstream peaks. (2010 Code § 22-159)

A.   Design of stormwater storage facilities shall include an analysis of the downstream effects on peak flows based upon the following drainage area criteria:

   1.   Residential developments, including duplex and mobile home developments of twenty (20) acres and larger, shall submit a model of the stormwater storage outflow hydrograph.

   2.   Nonresidential and all other developments not included in subsection A1 of this section, of ten (10) acres and larger, shall submit a model of the stormwater storage outflow hydrograph.

B.   Modeling of and routing of outflow hydrographs downstream shall be required under criteria of subsection A of this section, and will be accomplished through the use of HEC 1 and HEC 2, or equivalent computer programs.

C.   The length of a stream reach requiring modeling shall be either: 1) to a point where no increase in peak flow is demonstrated; or 2) to a point where an increase in peak flow does not increase the depth of flooding.

D.   The storm events to be modeled shall be the 2-, 5-, 10-, 25-, 50- and 100-year storm events.

E.   The city shall make available all existing data on stormwater flows from sources such as master stormwater studies or flood insurance studies (FIS). An engineer shall not be required to generate the files necessary for the modeling requirements listed above. However, an engineer will be required to furnish any information or computer software necessary for run to complete a peak flow study when supplied with the flood study data files.

F.   In the event peak flow studies indicate a development cannot comply with the criteria stated in subsection C of this section, then alternative methods of stormwater runoff control may be required. Alternative methods may include, but not be limited to, release of larger peak flows, decrease of peak flows released, release of all or some certain storm events in lieu of detention, and/or provides channel improvements in lieu of detention.

G.   The city commission shall review all stormwater storage studies and shall implement the conditions of this section of these drainage standards. (2010 Code § 22-160)

A.   Scope: Retention and detention are two (2) general terms relating to types of stormwater runoff storage that can be utilized to reduce the likelihood of additional flooding due to development and the subsequent change in stormwater runoff characteristics. Storage may be accomplished by the detention or retention of water in reservoirs, parks, side channels or ponds, either on or off site. Stormwater storage shall be required where proposed development will be changing the natural state of the drainage area and subsequent stormwater runoff.

B.   Definitions: The terms detention, retention and sedimentation basin shall have the meanings used below:

   DETENTION FACILITY: A surface water runoff storage facility that is normally dry but is designed to hold (detain) surface water temporarily during and immediately after a runoff event.

   RETENTION FACILITY: A surface water runoff storage facility that always contains (retains) a substantial volume of water to serve recreational, aesthetic, water supply or other function. Surface water runoff is temporarily stored above the normal stage during and immediately after runoff events.

   SEDIMENTATION BASIN: A surface water runoff storage facility intended to trap suspended solids, suspended and buoyant debris, and absorbed or absorbed potential pollutants which are carried by surface water runoff. The basin may be part of an overall multipurpose stormwater drainage system.

C.   Sizing Of Facilities: The sizing of storage facilities shall be by an approved method such as AFWA unit hydrograph, SCS, HEC 1, etc. All stormwater storage facilities serving drainage areas four (4) acres and larger shall be analyzed by routing an inflow hydrograph through the storage outlet structure(s). All data, calculations and assumptions shall be provided in report form.

D.   Maximum Allowable Release Rates: The detention facility shall be designed based upon the maximum allowable release rates. The release rates will be established based upon natural state runoff characteristics from the development site. A continuous probability or recurrence interval criterion shall be used in designing the outlet control structure. As a minimum, the outlet control structure shall be designed for the 2-, 5-, 10-, 25-, 50- and 100-year recurrence intervals. A single stage outlet control structure will not be considered acceptable.

E.   Storage Facilities: When a combination of storage facilities are used to control runoff, the system as a whole shall be designed with discharge rates in accordance with subsection D of this section.

F.   Emergency Spillway: All facilities shall be provided with an emergency spillway with scour protection. Earth embankments shall have side slopes not steeper than four to one (4:1). Proper materials shall be specified with the corresponding optimum compaction to provide stability and minimum seepage.

G.   Storage Volume Increase: The storage volume of a storage facility shall be oversized ten percent (10%) to allow for sedimentation.

H.   Trickle Channel: All storage ponds shall be provided with a concrete paved trickle channel from the inlet to the outlet structure to transmit low flows, unless the flow line of the storage facility is entirely on rock.

I.   Erosion Control: Erosion control for storage and/or detention facilities shall be in accordance with section 10-17-21, "Erosion And Sedimentation", of this chapter.

J.   Access Road: An all weather access road shall be provided to all storage areas for maintenance purposes. For those owned and maintained by the city, the access road shall be dedicated as part of the storage area.

K.   Dams And Embankments: Earth dams or other earth embankments shall be designed by a licensed professional engineer in accordance with accepted engineering practices to assure that dam or embankment failure will not occur. Design criteria used by the soil conservation service in the selection of materials and construction procedures will be acceptable.

L.   Ponds: Property line swale ponding and small on site ponds, if used, shall be examined for possible adverse effects on building foundations due to saturation of the subsoil.

M.   Parking Lot Storage: Parking lot storage shall be considered the last alternative of providing required detention. The use of parking lots for storage shall be well designed to minimize the potential damage and/or threat to pedestrians and parked vehicles. In no case shall the depth of ponding in a parking lot exceed six inches (6").

N.   Public Safety: Public safety of the detention pond and outlet works, both in a passive condition and when functioning shall be addressed in design.

O.   Visual Amenity:

   1.   The detention facility shall be designed as a visual amenity consistent with the existing topography and proposed development and should be designed with multiuse potentials related to recreation taken into consideration.

   2.   The use of large unnatural depressions which disrupt the continuity of the landscape shall be avoided. Length to width ratios should be investigated in relation to depth of the proposed facility to improve the aesthetic appearance of storage facilities. The geometric layout of detention facilities shall be such that multipurpose use is available. All storage facilities shall be provided with landscaping which includes the planting of trees and shrubs. The use of evergreen and wetlands adaptable plantings should be incorporated to improve the water quality of the storage runoff.

   3.   Outlet control facilities shall include headwalls and energy dissipaters. The outlet facilities, as a visible part of any storage facility, shall include landscape plantings to improve aesthetics and provide a more pleasant and appealing appearance.

   4.   Detention facilities which are planned for dedication to the city shall be reviewed by the parks and recreation department for proper recreational layout and design. Landscaping of all facilities including access roads and parking areas (storage facilities 3 acres and larger) shall be of sufficient size and number to provide a parklike setting. (2010 Code § 22-161)

A.   Purpose: The purpose of this section is to provide guidance in the design of effective management of erosion and sedimentation, and to protect water quality and the general health, safety and welfare of the residents of the city. (2010 Code § 22-162)

B.   General Requirements:

   1.   Design, Installation And Maintenance: Development activity shall not be conducted unless appropriate erosion and sedimentation facilities are designed, installed and maintained throughout the life of the development.

   2.   Plans: All erosion and sediment control methods shall be indicated on the final construction and/or building permit plans.

   3.   Sod And Vegetation: All earth slopes and earth areas, new or existing, subject to erosion, such as, adjacent to trickle channels, inlet structures and outlet structures, within any area designated for detention or drainage, shall be slab sodded with Bermuda sod or have permanent established growth of vegetation. All vegetation areas shall be fertilized, watered, and in an established growing condition prior to completion or acceptance of any stormwater drainage facility and/or development. (2010 Code § 22-163)

C.   Design Considerations:

   1.   General Design Principles: Practical combinations of the following principles shall be utilized, as a minimum, in planning measures to be installed for any land disturbing activity.

      a.   The land disturbing activity shall conform to existing topography and soil type so as to create the lowest practicable erosion potential.

      b.   The disturbed area and the duration of exposure of bare earth to erosive elements shall be kept to a practicable minimum through construction scheduling and management.

      c.   Cut and fill operations should be kept to a minimum.

      d.   Disturbed soil shall be stabilized as quickly as practicable.

      e.   Natural vegetation shall be retained, protected and supplemented whenever feasible.

      f.   Temporary vegetation or mulching shall be employed to protect exposed critical areas during development.

      g.   Permanent vegetation and structural erosion control measures shall be installed prior to final acceptance of developments, or as soon as seasonal planting restrictions allow.

   2.   General Practice: Soil and water conservation measures include, but are not necessarily restricted to, vegetation, sediment basins, dikes, grade stabilization structures, sediment traps, land grading, diversions, waterways or outlets, and riprap. Vegetative practices shall be applied to control erosion. The practice can be either temporary and/or permanent, depending on the site specific needs. (2010 Code § 22-164)

D.   Erosion And Sediment Control Criteria:

   1.   Long Term Permanent Seeding, Planting: Long term permanent seeding, sprigging or planting which produces vegetative cover, including Bermuda grass, Kentucky 31 tall fescue and weeping lovegrass shall be used to control erosion on a permanent basis.

   2.   Short Term Temporary Seeding, Planting: Short term seeding, producing temporary vegetative cover such as small grains like oats, rye and wheat, and sudans and sorghums shall be used to control immediate erosion. This practice effective for areas where soil is left exposed for a periods of six (6) to twelve (12) months shall not be deemed permanent erosion control. Straw bale dike may be utilized where no other practice is feasible, a temporary barrier with a life expectancy of three (3) months or less can be installed across or at the toe of a slope for the contributing drainage areas, in accordance with the adopted standards. Hay and sod mulching, as a temporary measure, may be used for embankment stabilization in areas where surface runoff is to be directed down a slope. Erosion matting shall be used for channel embankment and slope stabilization where a permanent erosion control cover has not been established prior to use. The specified material shall be installed as recommended by the manufacturer of the proposed material.

   3.   Construction Entrance: A stabilized construction entrance shall be built in accordance with the adopted standards to reduce or eliminate the tracking or flowing of sediment onto public right of way.

   4.   Outlet Structure: A concrete or stone outlet structure shall be constructed in areas where the entire drainage area to the structure is not stabilized or where there is a need to dispose runoff at a protected outlet or where concentrated flow for the duration of the period of construction needs to be diffused.

   5.   Grade Stabilization Structure: A grade stabilization structure in the form of a paved chute or flume shall be constructed to prevent erosion, where concentrated flow of surface runoff is to be conveyed down a slope of three percent (3%) or greater.

   6.   Temporary Sediment Basins: Stormwater detention facilities may be used temporary as sediment basins. A temporary outlet structure for the stormwater detention facility to work as a sediment pond shall be constructed. At the end of the construction activity, the developer shall remove all collected sediment from the detention facility and outlet structure and return the facility to a previous condition and/or to the approved cross sectional area. (2010 Code § 22-165)