Leadington City Zoning Code
ARTICLE XIV
Stormwater Regulations
Section 405.800 Purpose.
[Ord. No. 257, 7-13-2010]
The purpose of this Article is to lessen or avoid hazards to persons and property caused by uncontrolled stormwater runoff or by obstructions to drainage and to lessen the degradation of the quality of surface runoff.
Section 405.810 Applicability.
[Ord. No. 257, 7-13-2010]
A.
Any person or entity shall, prior to commencement of any work, construction or development activity which is subject to the regulations contained in this Article:
B.
A stormwater management plan shall be required of any subdivision which has been platted, but for which no development work or construction has yet been done, unless the developer of such subdivision has already submitted to the City and received prior approval of its stormwater improvement plans.
C.
Detention requirements are directly related to permitted land use in this Chapter 405, Zoning Regulations, of the Code of the City of Leadington. The permitted densities and minimum lot areas are important factors in the anticipated runoff. Table 1 lists the zoning districts with major permitted use category, minimum lot area and the corresponding percent of imperviousness.
D.
For permitted land uses other than those listed in Table 1, such as schools, churches, fire station, etc., the rate of imperviousness shall be determined by the same method as for commercial uses listed in Table 1. For conditional land use in any zoning district, the same ratio determination criteria shall apply.
Table 1 Stormwater Data by Zoning Districts | |||
|---|---|---|---|
Zone | Major Permitted Areas | Minimum Lot Area (square feet) | Percent of Impervious Area for Design |
R-1 | Single-Family Dwellings | 7,500 | 70 |
R-2 | General Residential | 12,500 | 60 to 70 |
MH | Mobile Home Park District | 3,500 to 4,000 | 30 |
C-1 | Commercial District | 7,500 to 12,500 | 60 to 70 |
A | Agricultural District | 43,560 (1 acre) | 70 |
I | Industrial District | ||
Section 405.820 Permit.
[Ord. No. 257, 7-13-2010]
A.
A development permit shall be required for any of the following.
1.
Land Disturbance. Any land disturbance that impacts two thousand five hundred (2,500) square feet or more.
a.
Any construction activity, including, but not limited to, grubbing, grading, excavation or otherwise destroying the root zone on a land area two thousand five hundred (2,500) square feet or greater.
b.
The land area considered shall include all of the land disturbance activities that are a part of a common plan and the total land area to be disturbed over the life of the project.
2.
Land Disturbance Within Valuable Water Resource Areas. Any land disturbance activities that impact one (1) acre or more, near valuable water resources. For purposes of this Article, "valuable water resources" are defined as follows:
a.
Within one thousand (1,000) feet of a lake used primarily as a public water supply.
b.
Outstanding waters, such as cold water trout streams.
c.
Lakes participating in EPA's "Clean Lakes Program," at or within one hundred (100) feet of major reservoirs or permanent streams.
d.
Sinkholes, losing streams or other direct conduits to groundwater.
3.
Stormwater Point Sources. The operation, use or maintenance of existing stormwater point sources or disturbing land which would result in a stormwater point source.
4.
Waivers. The Administrative Officer may waive specific information from time to time as deemed appropriate, subject to the following requirements:
a.
Sufficient documentation shall be provided to the Administrative Officer to determine whether a waiver is appropriate.
b.
A statement from a registered design professional certifying that the differential runoff shall result in no adverse impact.
c.
The Administrative Officer may require a review and written supportive recommendation from City Engineer or other persons having specialized technical knowledge prior to waiving such information whenever necessary.
d.
No waiver on the part of the Administrative Officer shall have the effect of a variance or relieve any person from complying with all other applicable provisions of this Article.
5.
Plan Adherence. The owner or authorized agent of the applicant shall be required to adhere strictly to the stormwater management plan as approved. Any changes or amendments to the plan must be approved by the Administrative Officer in accordance with the procedures set forth in this Article.
Section 405.830 Application And Process.
[Ord. No. 257, 7-13-2010]
A.
Purpose. The purpose of the stormwater management plan review process is to provide an organized framework for evaluating and acting upon proposals for development as they relate to stormwater management issues.
B.
Required Information.
1.
It is the responsibility of an applicant to include sufficient information in the stormwater management plan to enable evaluation of the environmental quality of the affected area, the potential and predicted impacts of the proposed activity on affected waters, and the effectiveness and acceptability of the measures proposed by the applicant for preventing or reducing adverse impacts. The applicant shall furnish the Administrative Officer with three (3) copies of the stormwater management plan application form and stormwater management plan, sealed by a professional engineer or architect registered in the State.
2.
The owner or an authorized agent of the owner shall submit an application and obtain a permit prior to commencement of any work requiring a permit.
C.
Applications. A complete application shall consist of the following:
1.
Application Form. The application form shall contain information including, but not limited to, the following.
2.
At least three (3) copies of a Stormwater Pollution Prevention Plan (SWPPP) complying with this Article.
3.
At least three (3) copies of a Stormwater Management Plan complying with this Article.
4.
Any required fees.
D.
Process. The Administrative Officer shall review all applications to determine if they are complete.
1.
Complete application shall be submitted to an Engineer appointed by City or other persons with special technical expertise as needed.
2.
The application shall be approved, denied or conditionally approved within a reasonable time.
3.
All reasons for denial or conditions of approval shall be clearly stated with the denied application or permit as applicable.
Section 405.840 Stormwater Pollution Prevention Plan.
[Ord. No. 257, 7-13-2010]
A.
A Stormwater Pollution Prevention Plan shall be submitted as a part of any application for a development permit for a land disturbance activity. A Stormwater Pollution Prevention Plan shall be prepared by a registered design professional.
1.
General. Drawn and written descriptive materials shall be provided which contain information including, but not limited to, the following:
a.
A site and physical condition description.
b.
How the drainage area will be protected.
c.
Description of Best Management Practices (BMP) that will be used.
d.
How the drainage area will be protected from erosion.
e.
Locations at the site where BMP will be installed.
f.
A description of the types of temporary and permanent non-structural BMP that will be used.
g.
A description of the types of temporary and permanent structural BMP that will be used.
h.
Location of the sedimentation basin for each drainage area with ten (10) or more acres disturbed at one (1) time.
i.
Additional site management BMP to be used, such as solid and hazardous waste management, provision of portable toilets, proper storage of construction materials, installation of containment berms and use of drip pans at petroleum product and liquid storage tanks and containers.
2.
Drawings. The drawn portion of the overall plan shall also conform to the following requirements:
a.
Shall be of sufficient clarity to clearly indicate proposed buildings, structures or uses or other features shown on the plan.
b.
Shall be drawn to scale not greater than one (1) inch equals twenty (20) feet nor less than one (1) inch equals two hundred (200) feet.
c.
Shall identify property by lot lines and location, including dimensions, angles and size, correlated with the legal description of said property.
d.
Shall show the scale, North point, boundary dimensions, natural features such as woods, streams, rivers, lakes, drains, topography (at least five-foot contour intervals; when terrain is irregular or drainage critical, contour interval shall be two-foot) and similar features.
e.
Shall show existing man-made features such as buildings, structures, easements, high tension towers, pipelines, existing utilities such as water and sewer lines, etc., excavations, bridges, culverts and drains and shall identify adjacent properties within one hundred (100) yards and their existing uses.
f.
Shall show the location, proposed finished floor and grade line elevations, size of proposed main and accessory buildings, their relation one (1) to another and to any existing structures to remain on the site and the height of all buildings and structures, as well as building elevations and materials proposed for the structures under consideration.
g.
Shall show the proposed streets, driveways, sidewalks and other vehicular and pedestrian circulation features within and adjacent to the site; also the location, size and number of parking spaces in the off-street parking areas and identification of service lands, service parking and loading zones in conformance with the requirements set forth in this Article.
h.
Shall show the location and size of all existing utilities serving the property as well as the location and size of all proposed utilities to serve the property.
i.
Shall show any proposed alterations to the topography and other natural features shall be indicated.
j.
Shall show the pre-development or pre-development activity site information.
k.
Shall show the location of any adjacent streets or roads.
l.
Shall show the location of vegetative cover and soil types and characteristics representative of the design conditions, where percolation or exfiltration systems are proposed.
m.
Shall show the location of farm drains, inlets and outfalls, storm, sanitary and combined sewers and outfalls, septic tank systems and outlets, if any, and seeps, springs and flowing and other wells.
n.
Shall show the location and description of nearby existing off-site water management facilities such as wells, lakes, drainageways and other similar features which are potentially directly affected by the proposed construction or development.
o.
Shall show all existing drainage facilities which are to be maintained, altered or enlarged as part of the stormwater management system; provide information as to their size, slopes, depths, outfalls, receiving waters, elevations, cross sections, profiles, construction materials and other design details as applicable.
p.
Shall show the location of all new drainage facilities, including detention basins, to be constructed and provide design details on each as applicable.
q.
Shall show the location and extent of right-of-way and easements for the stormwater management system, including all areas to be dedicated for water management purposes.
r.
Shall identify and describe any special or required maintenance procedures for the project to continue to function as designed.
s.
Shall include provisions for any off-site development activity related to the project. All land within the City on which development activity related to a project is proposed shall be identified and included in the plan. All owners of property where development activity related to the project is proposed shall be identified and included in the application.
t.
Shall include any other information required by the Administrative Officer to determine compliance with this Article.
3.
Construction Details. Detailed construction drawings clearly indicating the proposed locations, materials and specifications of any structural BMP shall be submitted.
4.
Additional Requirements. Additional requirements pertaining to the Stormwater Pollution Prevention Plan shall be as follows.
a.
After a permit is approved, a copy of the Stormwater Pollution Prevention Plan shall be kept on site during the entire term of the land disturbance activity and shall be made available to all local, State and Federal authorities having jurisdiction upon request.
b.
The SWPPP shall be amended or updated as appropriate during the term of the land disturbance activity.
c.
Amendments or updates shall be also be submitted to the Administrative Officer to be included in the permit record.
Section 405.850 Stormwater Management Plan.
[Ord. No. 257, 7-13-2010]
A.
A stormwater management plan is designed to safely manage the stormwater runoff following the rainstorms which exceed the maximum allowable release rate and the capacity of the stormwater drainage system and/or the storm sewer system by detention of the excess stormwater runoff. The plan shall provide or be accompanied by maps at a minimum scale of the (1) inch less than or equal to two hundred (200) feet and other descriptive material, including the basis of computation, showing the following:
1.
Required pre-development site information (map scales are minimums):
a.
Detailed location sketch showing the parcel and major adjacent roads.
b.
Topographic map of the site at a scale of one (1) inch less than or equal to two hundred (200) feet with maximum five-foot contour intervals, except in floodplains or other area of low relief where a smaller interval may be required.
c.
Where percolation or infiltration systems are proposed, information as to the location and type or vegetative cover and soil types and characteristics representative of the design condition mapped at a scale of one (1) inch less than or equal to two hundred (200) feet.
d.
Location of streams and other floodwater runoff channels, their normal channels, and the extent of the floodplains at the established high water elevations, and the limits of the floodway mapped at a scale of one (1) inch less than or equal to two hundred (200) feet.
e.
Location of lakes, ponds, swamps and detention basins indicating their normal shorelines, floodplains and lines of inflow and outflow mapped at a scale of one (1) inch less than or equal to two hundred (200) feet.
f.
Location of farm drains, inlet and outfalls, storm and sanitary sewers and outfalls, septic tank systems, and outlets, if any, and seeps, springs, and flowing and other wells mapped at a scale of one (1) inch less than or equal to two hundred (200) feet.
g.
Location and description of nearby existing off-site water management facilities such as wells, lakes, drainage ways, etc., which are potentially directly affected by the proposed construction or development, mapped at a scale of one (1) inch less than or equal to two hundred (200) feet.
2.
For all existing drainage facilities which are to be maintained, altered or enlarged as part of the stormwater management system, provide information as to their size, slopes, depths, outfalls, receiving waters, elevations, cross-sections, profiles, construction materials and other design details as applicable.
3.
Location of all new drainage facilities, including detention basins, to be constructed. Provide design details on each facility as applicable.
4.
Location and extent of existing and proposed impervious surfaces (roads, parking lots, building, etc.) and their elevations. Provide grading and paving plans and specifications.
5.
Location and extent of right-of-way and easements for the stormwater management system, including all areas to be dedicated for water management purposes.
6.
Identification and description of any special or required maintenance procedures to keep the project functioning as designed.
7.
Provide stormwater management system design calculations as follows:
a.
Design storms used.
b.
Calculated hydrographs of inflow and outflow of design storm runoff for the project site under natural and undeveloped conditions.
c.
Hydrographs of the runoff from the design storm runoff under developed conditions.
d.
For all detention basins, a plot or tabulation of storage volumes with corresponding water surface elevations and of the basin outflow rates for those water surface elevations.
f.
Runoff routing calculations showing discharge, elevations and volumes retained and/or detained during applicable storm event.
g.
Calculations required for determination of minimum building floor and road elevations.
8.
Identify the entity responsible for operation and maintenance of the system.
9.
The requirements for specific plan elements cited above may be waived by the Administrative Officer upon written supportive recommendation of the City appointed Engineer. The stormwater management plan for minor development activities may consist of a certification from a professional engineer or architect that the differential runoff is not significant.
10.
The Administrative Officer will ascertain the completeness of the stormwater management plan application. The Administrative Officer will return incomplete applications to the applicant for completion and resubmission. After determining that the application is complete, the Administrative Officer will distribute copies of the application for review and comment to other persons with special technical expertise as deemed appropriate by the Administrative Officer. Within a reasonable period after submission of the complete stormwater management plan application by the applicant, the Administrative Officer shall approve, approve with specified conditions, or deny the application and shall notify the applicant accordingly. If the stormwater management plan is denied or approved with conditions, the Administrative Officer shall state the reasons for denial or the specified conditions. Any applicant aggrieved by the denial or conditions may appeal the decision to the Board of Adjustment.
Section 405.860 Project Classification And Fees.
[Ord. No. 257, 7-13-2010]
A.
Subject to the exception provided in Subsection (A)(1) herein below, all applications shall be accompanied by payment of a fee based on ten dollars ($10.00) per acre or a fee in the amount of two hundred fifty dollars ($250.00), whichever is greater.
1.
Applications that do not require complete stormwater management plan review requiring special technical expertise shall be accompanied by a fee of twenty-five dollars ($25.00).
B.
The effective acreage for a project is not limited to a fractional part of the total concept; rather, if a project is developed in phases or small plots, the total acreage of the conceptual project will be considered.
Section 405.870 General Design Requirements For Stormwater Management Plans.
[Ord. No. 257, 7-13-2010]
A.
A stormwater management system shall be provided for protecting lots, roads, streets and buildings in the project area from the potential adverse impacts of stormwater runoff. Streets, blocks, depths of lots, parks and other public grounds, and ultimate land usage shall be determined, located and laid out in such a manner as to reduce the velocity of overland flow and allow the maximum opportunity for infiltration of stormwaters into the ground and to preserve and utilize natural streams, channels and detention basins and, wherever possible, to include streams and floodplains within parks or other public grounds.
B.
The maximum allowable release rate of stormwater after development shall not exceed the before-development rate based on a fifteen-year frequency storm. The total drainage area must be used in calculating the allowable release rate. The required storage volume will be based on the project area only, with extraneous flows from upland areas being bypassed or discharged via overflow spillway or other devices.
C.
The increased stormwater runoff resulting from the proposed development shall be detained on site by appropriate detention basins; by storage on flat roofs, parking lots or streets; or by other acceptable techniques. The minimum volume of storage shall be sufficient to store the volume from a twenty-five-year storm (under developed conditions). Control devices shall limit the discharge from storage to a rate no greater than that prescribed by this Chapter. Downstream property, watercourses, channels or conduits shall not receive stormwater runoff from proposed development at a higher peak flow rate than that which existed prior to the development.
D.
Generally acceptable locations of the stormwater runoff channels in the design of the project area may include the following:
1.
In a depressed median of a double roadway, street or parkway, provided the median is wide enough to permit required roadway shoulders.
2.
Centered on the rear lot lines in a block or entirely within the rear yards of a single row of lots or parcels, provided that in either case the lots are deep enough to permit side slopes in the runoff channel and a building site of the elevation required by other Sections of this Article.
3.
In a depressed area long roadway, street or parkway, provided the area is wide enough to permit side slopes as required in other Sections of this Article.
4.
Alternative systems such as curb and gutter and storm sewers that discharge into an appropriate detention basin may be incorporated into the stormwater management plan.
5.
The smaller, uppermost reaches of drainage channels and swales forming the natural drainage system near a watershed divided may be relocated or eliminated and incorporated into the planned system of storm sewers and open channels designed consistent with the requirements of this Article.
E.
A continuous easement may be provided abutting rear lot lines as shown in the stormwater management plan within which utility lines and open drainage facilities may be located and maintained, but on which no accessory buildings may be constructed. The utility-drainage easement shall be at least twenty (20) feet wide. Within the area so designed for the passage or storage of waters, no structure may be erected, no fences, shrubbery or trees planted, or changes made to the prescribed grades and contours of the specified floodwater or stormwater runoff channels.
F.
All storm sewer outfalls shall be so designed, by reason of elevation of the invert, by a flap gate or by other features that when the receiving stream is in full flood, the storm sewers will continue to drain the areas they are designed to serve unless the provision is made for sewer backups into planned storage locations.
G.
All sanitary sewer manholes constructed in a floodplain, in a street designed for detention, or in an area designed for the storage or passage of floodwater or stormwater shall be provided with either a water-tight bolted manhole cover, a water-tight concealed pick-hole cover, or be constructed with a rim elevation at or above the high-water elevation of the one-hundred-year flood or the high-water elevation of the design storm, whichever is applicable to the specific area.
H.
Projects that are to be developed in phases will normally require the submission of a master plan of the applicant's contiguous land holdings. Applications for individual project phases may be considered only when the phases are totally independent of, or make sufficient provisions for, adjacent lands.
I.
The plan shall include provisions for any off-site development activity related to the project. All land within the City on which development activity related to a project is proposed shall be identified and included in the plan. All owners of property where development activity related to the project is proposed shall be identified and included in the application.
Section 405.880 Hydraulic Design Considerations.
[Ord. No. 257, 7-13-2010]
A.
Stormwater systems will be designed with sufficient hydraulic capacity as a minimum for the following frequencies and durations:
Type of Facility | Design Frequency |
|---|---|
Detention basins | 25-year |
Primary drainage systems | 25-year |
Bridges | 50-year |
Secondary drainage systems, i.e., crossdrains and ditches for internal subdivision drainage. | 15-year |
B.
The Administrative Officer may require alternative designs or features to reduce the cost of long-term maintenance.
C.
In critical areas, the Administrative Officer may require additional hydraulic capacity above the minimum set forth above, up to the one-hundred-year frequency design.
Section 405.890 Stormwater Management System Design Requirements.
[Ord. No. 257, 7-13-2010]
A.
Method Of Evaluation. Differential runoff evaluation consists of the determination of rates of runoff before and after development, the determination of required volume of detention and verification of adequacy of discharge and control structures.
B.
Differential Runoff Rates. Differential runoff rates for all three (3) size classes of projects shall be evaluated by the rational formula. The runoff coefficients in Table 2, in Subsection (R) of this Section, shall be used. Differential runoff rates shall be evaluated by equation:
Equation 1 |
R = (Rd-Ru) |
Where: | |||
R | = | Differential runoff rate | |
Rd | = | C.I. factor for developed conditions | |
Ru | = | C.I. factor for undeveloped conditions | |
C.
Volume Detention. Volumes of detention for the three (3) classes of projects shall be evaluated according to the following methods:
1.
Volume of detention for projects of less than twenty-five (25) acres shall be evaluated by the "Simplified Volume Formula."
2.
Volume of detention for projects of twenty-five (25) acres or greater but less than two hundred (200) acres may be evaluated either by the "Simplified Volume Formula" or the "Modified Hydrograph Method."
3.
For projects larger than two hundred (200) acres, the owner's engineer shall submit his/her proposed method of evaluation for the sizing of the detention basin to the Administrative Officer. The method will be evaluated for professional acceptance, applicability and reliability. No detail review for projects larger than two hundred (200) acres will be rendered before the method of evaluation of the detention is approved.
4.
Other analytical methods of evaluation of volume of detention will be considered, provided that reliability, professional acceptance and proper application are approved by the Administrative Officer.
D.
Calculation Methods. Any of the following methods may be used for calculating detention volume as applicable:
1.
Simplified Volume Formula. Total volume of detention shall be computed by the equation:
Equation 2 |
V = R x A x 30 (min) x 60 (sec/min) |
Where: | |||
V | = | Total volume of detention | |
R | = | Differential runoff rate | |
A | = | Area of project in acres | |
2.
Graphic Representation. For purposes of further analysis, the simplified volume formula may be represented by a triangular synthetic hydrograph as shown in Figure III (in the Seeley Data Book for civil engineers) with the following elements:
Tb = Base time of hydrograph for developed project without detention |
Tb = sixty (60) minutes |
Tp = Time for peak runoff of developed project |
Tp = twenty (20) minutes |
Qd = Total peak runoff of developed project in cfs |
Qd = A x Rd (see Equation 1) |
Qu = Total peak runoff of unimproved project in cfs |
Qu = A x Ru (see Equation 1) |
A = Total area of project in acres |
Tq = Assumed time of peak differential for unimproved project |
Tq = Qu/Qd x 40 |
Tr = Assumed recedence time differential for discharge at rates no greater than unimproved condition |
Tr = (30 Qd/Qu) - 60 |
V = Volume of detention |
V = (Qd - Qu) x 30 (min) x 60 (sec/min) |
3.
Modified Rational Hydrograph Method. This is a modification of the "Unit Hydrograph Method" of hydrologic evaluation simplified to reflect features of present practice and some elements of topographic characteristics, concentration patterns and routing. Figure III from above illustrates the elements of the modified hydrograph. Steps to develop the hydrograph are as follows:
a.
Determine the time of concentration for the project by use of Chart IV or similar reference manual adopted by the City Engineer. Chart IV is based on overland flow time from Seeley Data Book for Civil Engineers. Enter chart with overland travel distance, follow horizontally to slope curve then vertically down to C or P factor listed in Table 2, in Subsection (R) of this Section, and obtain Tc. For analysis of large improved channels, time of travel for overland flow and channel are to be analyzed to determine reasonable (Tc) time of concentration.
b.
Determine time of peaking by equation:
Equation 3 |
T p = D/2 + .6Tc |
Where: | |||
T p | = | Time of peak discharge of developed project in minutes | |
D | = | 20 min = storm duration in minutes | |
c.
Determine the base time of the hydrograph without detention by equation:
Equation 4 |
Tb = 2.67 T p |
d.
Determine the base time of the hydrograph with detention by equation:
Equation 5 |
(Qd Tr = Tb _____ -1) (Qu |
Where: | |||
Tr | = | Additional time required for discharge at a rate no greater than that of the undeveloped condition | |
Qd | = | Total peak runoff of improved project in cfs | |
Equation 6 |
Qd = A x Rd (See Equation 1) Qu = Total runoff of unimproved project in cfs |
Equation 7 |
Qu = A x Ru (see Equation 1) |
e.
Determine the required volume of detention by equation:
Equation 8 |
V = 1/2 (Qd - Qu) Tb |
E.
Control Structures. Detention facilities shall be provided with obvious and effective control structures. Plan view and sections of the structure with adequate detail shall be included in plans.
1.
The design discharge (Q) for the low-flow weir shall not exceed the fifteen-year (frequency) with a duration equal to the time of concentration for the watershed, runoff from the tributary area for five percent (5%) imperviousness [one and seven-tenths (1.7) cfs per acre]. The maximum discharge shall be designed to take place under total anticipated design-head conditions.
2.
Sizing of the low-flow weir shall be by the appropriate weir formulas.
3.
The overflow opening or spillway shall be designed to accept the total peak runoff of the improved tributary area.
4.
The low-flow channel invert through dry detention facilities on other than permanently flowing streams shall be paved.
F.
Detention Design Criteria. Detention in the overall system, including swales, lakes, canals, greenways, etc., shall be provided as follows.
G.
General.
1.
Storage Volumes. The minimum volume of storage provided in detention basins, together with such storage as may be authorized in other on-site facilities, shall be sufficient to store the volume from a twenty-five-year storm (under developed conditions) with a discharge no greater than the rate of flow from a fifteen-year storm (under undeveloped conditions).
2.
Outlet Control Structures. Outlet control structures shall be designed to operate simply and automatically. They will limit discharges into existing or planned downstream channels or conduits so as not to exceed predetermined maximum authorized peak flow rates.
3.
Emergency Spillway. Emergency overflow facilities must be provided in all instances so that stored waters will not exceed the safe capacity of the basin. At a minimum, the emergency spillway must be able to pass without damage the one-hundred-year storm.
4.
Appearance. Designs should result in aesthetically pleasing configurations which will enhance public acceptability.
H.
Dry-Detention Facilities.
1.
Perimeter maintenance easements of fifteen (15) feet (minimum) width at slopes no steeper than 3:1 (horizontal to vertical) shall be provided.
2.
Side slopes of the facility shall not be steeper than 3:1 (horizontal to vertical).
3.
Provisions must be incorporated to facilitate complete interior drainage to dry-bottom basins, to include the provision of natural grades to outlet structures, longitudinal and transverse grades to perimeter drainage facilities, or the installation of sub-surface drains.
4.
Multi-purpose features may be designed to serve secondary purposes for recreation, open space or other types of use which will not be adversely affected by occasional or intermittent flooding.
5.
The entire reservoir area shall be seeded, fertilized and mulched, sodded or paved.
I.
Wet-Detention Facilities.
1.
Perimeter maintenance and operation easements of fifteen (15) feet (minimum preferable) width at slopes no steeper than 3:1 (horizontal to vertical) shall be provided.
2.
Control elevations should be no higher than two and one-half (2 1/2) feet below the minimum road centerline elevation in the area served by the control device in order to protect the road subgrade when structures are constructed near roads.
3.
Side slopes shall not be steeper than 3:1 (horizontal to vertical) out to a depth of two (2) feet below the control elevation, then as steep as soils stability will allow.
4.
If fish are to be used to help keep the basin clean, at least one-fourth (1/4) of an area of the permanent pool must be a minimum depth of ten (10) feet.
5.
For emergency purposes, cleaning or shoreline maintenance, facilities shall be provided or plans prepared for the use of auxiliary equipment to permit emptying and drainage.
6.
The limits of maximum ponding elevations are to be no closer than twenty-five (25) feet horizontally from any building and no less than two (2) feet below the lowest sill elevation of any building.
J.
Impervious Areas. Paved parking lots may be designed to provide detention storage of stormwaters on all or a portion of their surfaces. Outlets will be designed so as to slowly empty the stored waters, and depths of storage must be limited to a maximum depth of twelve (12) inches so as to prevent damage to parked vehicles. Ponding should be regulated to those positions of the parking lots farthest from the area served.
K.
Rooftop Storage. Detention storage requirements may be met in total or in part by detention on flat roofs. Details of such designs to be included in the stormwater management plan application shall include the depth and volume of storage, details of outlet devices and down-drains, elevations of overflow scuppers, design loadings for the roof-structure and emergency overflow provisions.
L.
Underground Storage. All or a portion of the detention storage may also be provided for in underground facilities, as long as all applicable requirements of this Chapter are met. Details of such designs are to include the type of facility, depth and volume of storage, details of inlet and outlet devices and locations, emergency overflow provisions, and measures to be used for surface water and groundwater pollution control.
M.
Design Alternatives. The above listing of design criteria is not intended to preclude the use of other known state-of-the-art methods and available best management practices and should not be construed as a mechanism to discourage innovative design concepts.
N.
Development Adjoining A Floodplain. Where a development adjoins or encompasses a portion of a floodplain for a one-hundred-year flood, the following shall apply:
1.
The applicant shall show the floodplain and floodway on the stormwater management plan.
2.
The applicant shall include in the stormwater management plan all other plans, plats, specifications, etc., required by Federal, State, County and/or municipal laws or regulations detailing such provisions or restrictions as are necessary to comply with the following:
O.
Channel Flow. The applicant shall not alter any channel in such a way that would prohibit any section of the channel from conveying, in its post-development state, the same amount of flow at the same or lower maximum water elevation that is conveyed in its pre-development state.
P.
Modifications Of Channel. The applicant shall furnish, for the Administrative Officer's review and approval, the following information pertaining to proposed channel modifications:
1.
Typical cross sections of the existing and proposed channel.
2.
Plan view of the channel showing the location of existing constrictions, obstructions and other non-typical areas.
3.
Hydrographs and/or flood routing calculations and backwater curve profiles of the proposed waterway corresponding to a storm recurrence interval of one hundred (100) years.
4.
Engineering evaluation of all potential increases in flood hazards to the adjacent upstream or downstream private or public lands and facilities located thereon, showing provisions for eliminating any and all adverse impacts on such land and facilities at no public cost.
5.
Minimum finished floor elevations which shall be set at or above the maximum water surface elevation as determined by either or both of the following:
6.
Designation on the final plan of all areas reserved for flood routing, detention or storage, together with the required wording pertaining to restrictions, dedications and maintenance responsibilities of such areas.
Q.
Detention Storage. If detention storage is provided within a floodplain, only the net increase in storage volume above that which naturally existed on the floodplain shall be credited to the development. No credit will be granted for volumes below the elevation of the regulatory flood at that location unless compensatory storage is also provided.
R.
Verification Of Adequacy.
1.
Analysis of all elements of design is to be verified by the engineer of record submitting the plan. The following outline is provided to ascertain that certain critical elements are in workable compliance with the aims of this Chapter. For projects less than fifty (50) acres in area, there is no need for submittal of routing calculations or tabulated proof of adequacy of tributary runoff for detention; however, it is recommended that verification be made of:
2.
For projects of fifty (50) acres or greater but less than two hundred (200), routing calculations shall be submitted in legible tabulated form. Proof of adequacy of volume of detention and sizing computations for low-flow structure shall also be submitted. Features of stability and safety may also need to be documented if the scope of the project requires special attention in this area of design.
3.
Projects over two hundred (200) acres in area shall provide documented verification of adequacy according to scope and complexity of design.
Table 2 Average C.I. (P.I.) Factors in CFS Per Acre 20 Min. Inlet Time | |||||
|---|---|---|---|---|---|
% Impervious Area | C or P (Factor) | 15 Years | 25 Years | 50 Years | 100 Years |
5 | 0.37 | 1.7 | 2.00 | 2.18 | 2.37 |
10 | 0.39 | 1.79 | 2.11 | 2.30 | 2.50 |
15 | 0.41 | 1.89 | 2.21 | 2.42 | 2.62 |
20 | 0.435 | 2.0 | 2.35 | 2.57 | 2.78 |
25 | 0.455 | 2.09 | 2.46 | 2.68 | 2.91 |
30 | 0.475 | 2.10 | 2.57 | 2.80 | 3.04 |
35 | 0.495 | 2.28 | 2.68 | 2.92 | 3.17 |
40 | 0.52 | 2.39 | 2.81 | 3.07 | 3.33 |
45 | 0.54 | 2.48 | 2.92 | 3.19 | 3.46 |
50 | 0.56 | 2.58 | 3.02 | 3.30 | 3.58 |
55 | 0.58 | 2.68 | 3.13 | 3.42 | 3.71 |
60 | 0.60 | 2.76 | 3.24 | 3.54 | 3.84 |
65 | 0.625 | 2.88 | 3.38 | 3.69 | 4.00 |
70 | 0.645 | 2.97 | 3.48 | 3.81 | 4.13 |
75 | 0.665 | 3.06 | 3.59 | 3.92 | 4.26 |
80 | 0.685 | 3.15 | 3.70 | 4.04 | 4.38 |
85 | 0.705 | 3.24 | 3.81 | 4.16 | 4.51 |
90 | 0.73 | 3.36 | 3.94 | 4.31 | 4.67 |
95 | 0.75 | 3.45 | 4.05 | 4.43 | 4.80 |
100 | 0.77 | 3.54 | 4.16 | 4.54 | 4.93 |
Rainfall | 4.60 | 5.40 | 5.90 | 6.40 | |
From U.S. Weather Bureau Technical Paper No. 40: "Rainfall Frequency Atlas of the United States for durations from thirty (30) minutes to twenty-four (24) hours and Return Periods from one (1) year to one hundred (100) years." |
S.
Installation Of Stormwater Runoff Control Measures. Positive stormwater runoff control shall be provided for during development. Stormwater management plans shall include a schedule for the installation, construction or modification of all drainage facilities. Erosion control measures and a schedule for their installation shall be shown on the stormwater management plan. Installation of drainage facilities and erosion control measures shall proceed as scheduled in the approved stormwater management plan.
T.
Best Management Practices.
1.
Best management practices to prevent erosion, sedimentation and other contamination of the municipal storm sewer system or the waters of the State shall be incorporated into the Stormwater Pollution Prevention Plan. Such measures shall be implemented from the time the land is disturbed until final stabilization of the land is achieved. Permitted best management practices may include, but are not limited to, the following.
2.
The best management practices utilized shall be in accordance with the publication "Protecting Water Quality" as published by the Missouri Department of Natural Resources. Use of other State-approved standard specifications or methods which offer a higher level of protection may also be incorporated by the design professional.
Section 405.900 Rights-Of-Way And Easements.
[Ord. No. 257, 7-13-2010]
A.
All stormwater management facilities shall be constructed within an easement of right-of-way dedicated for stormwater management use and connected to a public road or other location from which operation and maintenance is legally available. Minimum rights-of-way and maintenance easements shall be provided by instrument or plat dedication for all waterways used to convey or detain runoff. Where permanent maintenance will be provided by the property owner, maintenance easements or rights-of-way may not be required. The minimum widths of rights-of-way and easements shall be as follows:
Facility | Maintenance Access Width |
|---|---|
Open drainage channel or facility | 30 feet, 15 feet each side |
Greenways | Width of greenway |
Pipes and culverts | 15 feet, centered |
Detention areas | 15 feet continuous around total area |
Connecting access | 15 feet |
B.
Easements must include the "top of the bank width" and the maintenance access width.
C.
The maintenance access width begins at the point of the bank or slope of the facility.
D.
Additional maintenance access width may be required by the Administrative Officer in special circumstances where more width on one (1) or both sides is necessary for maintenance purposes.
Section 405.910 Inspection And Completion Of Construction.
[Ord. No. 257, 7-13-2010]
A.
General. The Administrative Officer and other officials of the City charged with the enforcement of this Chapter are hereby granted inspection rights and right-of-entry privileges in order to ensure compliance with the requirements of this Article.
B.
Inspections During Construction. The owner or authorized agent shall employ a registered design professional to inspect all stormwater improvements during construction. The Administrative Officer or other officials may conduct inspections from time to time as necessary to ensure compliance with the provisions of this Article.
C.
After Construction. The following procedures shall apply after construction activity is completed.
1.
Upon completion of any stormwater improvements, the owner or authorized agent shall also submit a certification letter signed by a registered design professional to the Administrative Officer which states that the improvements have been completed in accordance with the project specifications and all ordinances and specifications of the City of Leadington.
2.
The inspection and completion of construction of public stormwater improvements shall comply with the City's subdivision ordinance(s).
3.
After final stabilization of the site is achieved, the owner or authorized agent shall submit a written notice of termination for the Administrative Officer to terminate the permit. The notice shall contain the following information:
4.
The Administrative Officer shall terminate the permit after determining that final stabilization has been achieved.
Section 405.920 Maintenance.
[Ord. No. 257, 7-13-2010]
A.
General. The owner or authorized agent shall utilize methods, approaches and techniques in the design and construction stormwater management improvements that will allow for the improvements to be properly maintained.
B.
Responsibility. The responsibility for maintenance of stormwater management facilities shall be as follows.
1.
The owner or authorized agent shall be responsible for all stormwater management improvements not officially accepted by the City.
2.
The owner or authorized agent shall be responsible for all stormwater management improvements on any lot that is not a part of a common promotional plan.
3.
The owner or authorized agent shall be responsible for the stormwater management improvements on property that is part of a common promotional plan until the improvements are either accepted by the City or the improvements are accepted by a board, association or other permanent maintenance organization.
C.
Maintenance Arrangements. Any maintenance arrangements shall conform to the following.
1.
No detention basin shall be considered accepted by the City unless specifically expressed, written approval and acceptance is made by the Board of Alderman.
2.
The maintenance of stormwater management improvements by a board, association or other permanent maintenance organization shall be arranged through appropriate legal means such as agreements, indentures or covenants. Any such documents shall be submitted to the Administrative Officer for review and approval.
3.
The owner or authorized agent shall dedicate all necessary easements to the City for all stormwater management improvements to be accepted by the City in accordance with the requirements of this Article and the City's subdivision ordinance(s).
D.
Minimum Standards. Stormwater management improvements shall be maintained in a clean, safe, sanitary condition complying with all applicable provisions of this Article and shall not cause a public nuisance as defined by the Municipal ordinance(s) of the City.
E.
Periodic Inspections. The Administrative Officer may inspect existing stormwater management improvements from time to time in order to ensure compliance with the provisions of this Section.
Section 405.930 Enforcement.
[Ord. No. 257, 7-13-2010]
A.
Approved Projects. The Administrative Officer or his/her designated representative shall carry out periodic inspections of the project site to ensure the applicant's compliance with this Article. If it is determined that the project is not being carried out in accordance with the approved stormwater management plan, the Administrative Officer is authorized to take the following action(s), in addition to any other actions or remedies which are otherwise authorized under Article XIX, Violations and Penalties, of the this chapter of the Code of the City of Leadington.
1.
Written Notice. Issue written notice to the applicant or owner, specifying the nature and location of the alleged non-compliance, with a description of the remedial actions necessary to bring the project into compliance within a reasonable specified time.
2.
Stop Work Order. Issue a stop work order directing the applicant or owner to cease and desist all or any portion of the work which violates the provisions of this Article, if the remedial work identified in the "written notice" is not completed within the specified time.
3.
Revocation Of Approval. Should the applicant or owner fail to timely bring the project into compliance with the written notice and stop work order, he/she shall then be subject to immediate revocation of his/her stormwater management plan approval and to the penalties described in Article XIX, Violations and Penalties.
4.
Appeals. The Board of Adjustment shall serve as the means of appeal or variance in accordance with the zoning regulation of the City.
B.
Unapproved Project. With respect to any development activity determined by the Administrative Officer or his/her designated representative to be subject to this Chapter and being carried out without approval, the Administrative Officer is authorized to:
1.
Written Notice. Issue written notice to the owner specifying the nature and location of the alleged non-compliance, with a description of the remedial actions necessary to bring the project into compliance within a reasonable specified time.
2.
Stop-Work Order. Issue a stop-work order directing the owner to cease and desist all or any portion of the work which violates the provisions of this Chapter, if the remedial work identified in the "written notice" is not completed within the specified time.
3.
Non-Compliance With Stop-Work Order. Should the owner not bring the project into compliance with the written notice and stop-work order, he/she shall then be subject to the penalties described in Article XIX, Violations and Penalties.
4.
Appeals. The Board of Adjustment shall serve as the means of appeal or variance in accordance with the zoning regulation of the City.
Section 405.940 Vested Rights.
[Ord. No. 257, 7-13-2010]
This Article shall not in any way limit or modify the vested rights of any person to complete any development or improvement to lands based upon prior law where a previous permit or authorization has been granted or applied for and where such previous permit or authorization remains in effect. The City may acknowledge vested rights in other circumstances where it is equitable and just.
Section 405.950 Other Permits.
[Ord. No. 257, 7-13-2010]
A.
Before starting any work regulated by this Article, an applicant shall comply with the requirements set forth in all other applicable ordinances with respect to the submission and approval of preliminary and final subdivision plats, site plans for construction and rezoning improvement plans and building, grading and zoning permits, along with those set forth in this Chapter and as may be required by State statutes and the regulations of any department of the State.
B.
A discharge permit from the State of Missouri shall be obtained individually or under the applicable general permit for any activity regulated under the Department of Natural Resources Clean Water Commission (10 CSR 20) Stormwater.
Section 405.960 Interpretation.
[Ord. No. 257, 7-13-2010]
In the interpretation and application of this Article, the provisions expressed herein shall be held to be the minimum requirements and shall be liberally construed in favor of the City and shall not be deemed a limitation or repeal of any other powers granted by State statutes.
Section 405.970 Abrogation And Greater Restrictions.
[Ord. No. 257, 7-13-2010]
It is not intended by this Article to repeal, abrogate or impair any existing casements, covenants or deed restrictions. However, where this Article imposes greater restrictions, the provision of this Article shall prevail.
Section 405.980 Liability Disclaimer.
[Ord. No. 257, 7-13-2010]
The performance standards and design criteria set forth herein establish minimum requirements which must be implemented with good engineering practice and workmanship. Use of the requirements contained herein shall not constitute a representation, guarantee or warranty of any kind by the municipality or its officers and employees of the adequacy or safety of any drainage management structure or use of land. Nor shall the approval of a stormwater management plan and the issuance of a permit imply that land use permitted will be free from damages caused by stormwater runoff. The degree of protection required by these regulations is considered reasonable for regulatory purposes and is based on historical records, engineering and scientific methods of study. Larger storms may occur or stormwater runoff heights may be increased by man-made or natural causes. Enforcement of these provisions, therefore, shall not create liability on the part of the municipality or any officer of the municipality with respect to any legislative or administrative decision lawfully made hereunder, nor shall compliance relieve an owner, developer and/or permittee from responsibility under any circumstances where liability would otherwise exist.
Section 405.990 Overland Flow Time.
[Ord. No. 257, 7-13-2010]
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