Source: https://ecode360.com/29257289
Timestamp: 2019-09-16 22:39:50
Document Index: 219696365

Matched Legal Cases: ['§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435', '§ 435']

City of Bowling Green, MO Stormwater Management Regulations
§ 435.010 Definitions.
§ 435.020 Purpose.
§ 435.030 Applicability.
§ 435.040 Exemptions.
§ 435.050 Stormwater Management Plan Application.
§ 435.060 Stormwater Management Plan.
§ 435.070 Project Classification and Fees.
§ 435.080 General Design Requirements for Stormwater Management Plans.
§ 435.090 Hydraulic Design Considerations.
§ 435.100 Stormwater Management System Design Requirements.
§ 435.110 Rights-of-Way and Easements.
§ 435.120 Maintenance Responsibilities for Stormwater Management Facilities.
§ 435.130 Plan Adherence.
§ 435.140 Enforcement.
§ 435.150 Penalties for Violation.
§ 435.160 Vested Rights.
§ 435.170 Conflict With Other Ordinances and Codes.
§ 435.180 Other Permits.
§ 435.190 Interpretation.
§ 435.200 Abrogation and Greater Restrictions.
§ 435.210 Liability Disclaimer.
§ 435.220 Final Approval Required.
City of Bowling Green, MO / Land Use
Chapter 435 Stormwater Management Regulations
Section 435.010 Definitions.
Section 435.020 Purpose.
Section 435.030 Applicability.
Section 435.040 Exemptions.
Section 435.050 Stormwater Management Plan Application.
Section 435.060 Stormwater Management Plan.
Section 435.070 Project Classification and Fees.
Section 435.080 General Design Requirements for Stormwater Management Plans.
Section 435.090 Hydraulic Design Considerations.
Section 435.100 Stormwater Management System Design Requirements.
Section 435.110 Rights-of-Way and Easements.
Section 435.120 Maintenance Responsibilities for Stormwater Management Facilities.
Section 435.130 Plan Adherence.
Section 435.140 Enforcement.
Section 435.150 Penalties for Violation.
Section 435.160 Vested Rights.
Section 435.170 Conflict With Other Ordinances and Codes.
Section 435.180 Other Permits.
Section 435.190 Interpretation.
Section 435.200 Abrogation and Greater Restrictions.
Section 435.210 Liability Disclaimer.
Section 435.220 Final Approval Required.
[Ord. No. 1437 §I(435.010), 6-21-2004]
Unless specifically defined, words or phrases shall be interpreted so as to give them the meanings they have in common usage and to give this Chapter its most reasonable application:
15-YEAR STORM
Rainstorms of varying duration and intensity having a six and sixty-seven hundredths (6.67%) percent probability of being equaled or exceeded in any given year.
Rainstorms of varying duration and intensities having a four percent (4%) probability of being equaled or exceeded in any given year.
A rainstorm of varying duration and intensity having a one percent (1%) probability of recurring in any one (1) year.
The duly appointed City Administrator or their designated representative.
Any modifications, alterations or effects on a feature or characteristic of surface waters including their quality, quantity, hydrodynamics, surface area, species composition, living resources, aesthetics or usefulness for human or natural use which are or may potentially be harmful or injurious to human health, welfare, safety or property, to biological productivity, diversity or stability or which unreasonably interfere with the enjoyment of life or property, including outdoor recreation. The term includes secondary and cumulative, as well as direct impacts.
The record owner or his/her authorized representative of a tract of land that is the site of development or development activity within the scope of this Chapter.
The elevation at any location delineating high waters having a one percent (1%) probability of being equaled or exceeded in any given year (also known as the 100-year flood).
CAPACITY OF A STORM DRAINAGE FACILITY
The maximum ability of a storm drainage facility to convey, detain or retain stormwater flows without causing substantial damage to public or private property, and in the case of a pipe, without surcharging.
A natural or artificial open watercourse with definite bed and banks which periodically or continuously contains moving water or which forms a connecting link between two (2) bodies of water.
Any channel, pipe, sewer or culvert used for the conveyance or movement of water, whether open or closed.
An element of a discharge structure that allows the gradual release of water under controlled conditions.
Design elevation of a discharge structure at which, or below which, water is contained behind the structure.
The delay of storm runoff prior to discharge into receiving waters.
A facility constructed or modified to restrict the discharge of stormwater to a prescribed maximum rate and to concurrently detain the excess waters that accumulate behind the outlet. A wet bottom detention basin is a structure designed to retain a permanent pool of water after having provided its planned detention of runoff during a storm event. A dry bottom detention basin is designed to be completely dewatered after having provided its planned detention of runoff during a storm event.
DETENTION STORAGE
The temporary detaining or storage of stormwater in storage basins or rooftops, in streets, parking lots, school yards, parks, open space or other areas under predetermined and controlled conditions with the rage of drainage therefrom regulated by appropriately installed devices.
DETENTION VOLUME
The volume of water equal to the difference between the control elevation of a discharge structure and the maximum level at which water can be accumulated prior to discharge times the average area of open surface storage (between the control elevation and maximum level) behind the discharge structure.
Any individual, firm, corporation, association, partnership or other entity involved in commencing proceedings under this Chapter to effect the development of land for him/her or another.
DEVELOPMENT OR DEVELOPMENT ACTIVITY
Any manmade change to improved or unimproved land including, but not limited to, buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operation. Any subdivision of land as defined in the City's subdivision regulations.
DIFFERENTIAL RUNOFF
The difference in rate and volume of stormwater runoff from a parcel or project in its undeveloped natural condition and its developed condition is known as the differential runoff.
The rate of outflow of water from detention storage.
DISCHARGE STRUCTURE
Structural device, usually of concrete, metal, timber, etc., through which water is discharged from a project to the receiving water.
The area from which water is carried off by a drainage system, a watershed or catchment area.
An element in a drainage system which includes, but is not limited to, any of the following: conduits and appurtenant features, canals, channels, detention basins, ditches, streams, culverts, streets and pumping stations.
The surface or subsurface system that conveys water from over the land including all watercourses, water bodies and wetlands (also referred to as the stormwater management system).
A grant by a property owner to the public, a corporation or a person of the use of land for a specific purpose.
Height in feet above mean sea level according to national geodetic vertical datum (NGVD).
Saddle or low point facility located around the rim of dammed impoundment such as a detention or retention basin for providing an efficient and safe means of conveying the maximum design flood discharge through the impoundment without overtopping the dam.
The wearing away of the land surface by the action of the wind, water, ice, gravity or any combination thereof.
EXCESS STORMWATER RUNOFF
The volume and rate of flow of stormwater discharged from a drainage area that is or will be in excess of that volume and rate that is specified in this Chapter.
The higher portion of the floodplain, immediately adjacent to and on either side of the floodway, occupied by quiescent or slow-moving waters during floods.
The special flood hazard land adjoining a watercourse, the surface elevation of which is equal to or lower than the base flood elevation (the 100-year flood), which is subject to periodic inundation during floods.
The channel of a watercourse and those portions of the adjoining floodplain that are reasonably required to carry and discharge the base flood.
HIGHWATER ELEVATION
The elevation of floodwaters of a flood of specified frequency or occurrence at any given point.
A surface that has been compacted or covered with a layer of materials so that it is highly resistant to infiltration of water. The term includes most conventionally surfaced streets, roofs, sidewalks, parking lots and similar structures.
A structure on, or other alteration of land on, a given site including, but not limited to, grading, street paving, storm sewers, sanitary sewers and utilities.
OFF-SITE DETENTION BASIN
A feature or structure for temporarily storing excess stormwater originating at two (2) or more sites having devices for controlling the rate of release of the stored water and located downstream of all sites where the runoff originates.
ON-SITE DETENTION BASIN
A feature or structure for temporarily storing excess stormwater, having devices for controlling the rate of release of the stored waters and located within the sites where the runoff originates.
Design elevation of a discharge structure at which point or above which point, water leaks out or bleeds out through a control device down to the control elevation.
The maximum rate of flow of water at a given point in a channel or conduit resulting from a predetermined storm or flood.
POST-DEVELOPMENT CONDITIONS
Those conditions that are expected to exist or do exist after alteration, resulting from human activity, of the natural topography, vegetation and rate, volume or direction of surface or subsurface flow.
PRE-DEVELOPMENT CONDITIONS
Those conditions that existed at the time this Section becomes effective in terms of topography, vegetation and rate, volume or direction of surface or subsurface flow as indicated by the best available historical data.
PRIMARY DRAINAGE (WATER MANAGEMENT) SYSTEMS
Includes major waterways and appurtenant structures or systems whose total tributary area from origin to outfall exceeds or equals fifty (50) acres.
PROFESSIONAL ENGINEER OR ARCHITECT
An engineer or architect duly registered or otherwise authorized by the State to practice engineering.
RATIONAL METHOD
An empirical formula for calculating peak rates of runoff resulting from rainfall. Expressed mathematically, the formula is:
Peak flow in cubic feet per second (c.f.s.)
Runoff coefficient or fraction of runoff to rainfall, dependent on type of surface cover and topography.
Rainfall intensity, in inches per hour, for a specific storm and duration.
Watershed area, in acres.
RECEIVING BODIES OF WATER
Any water body or stream into which surface waters flow.
The process by which suspended solids from erosion are transported and deposited.
The plan, usually in map form, prepared pursuant to the City Council's zoning or other land development ordinances as requirement for the development of property.
The waters derived from rain falling or snow melting within a tributary drainage basis, flowing over the surface of the ground or collected in a stormwater drainage system, storm sewer or watercourse.
As defined in Chapter 410, Subdivision of Land, Section 410.020, Definitions.
Elapsed time for stormwater to flow from the most distant point in a drainage basin to the outlet or point in question.
Any stream, creek, brook, branch, natural or artificial depression, slough, gulch, reservoir, lake pond or natural or manmade drainage way in or into which stormwater runoff and floodwaters flow either regularly or intermittently.
[Ord. No. 1437 §I(435.020), 6-21-2004]
The purpose for this Chapter 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.
[Ord. No. 1437 §I(435.030), 6-21-2004]
Any person or government entity within the City shall apply to the Administrative Officer for approval of a stormwater management plan and obtain a permit before commencing any development or development activity.
A stormwater management plan shall be required of any platted subdivision for which no improvement plans have been submitted at the time this Section takes effect.
Detention requirements are directly related to permitted land use in the zoning ordinance of the City. The permitted densities and minimum lot areas are important factors in the anticipated runoff. Table I lists the zoning districts with the major permitted use category, minimum lot area and the corresponding percent of imperviousness.
For permitted land uses, other than those listed in Table I, such as schools, churches, fire stations, etc., the rate of imperviousness shall be determined by the same method as for commercial uses listed in Table I.
For conditional land use in any zoning district, the same ration determination criteria shall apply
Stormwater Data By Zoning District
Major Permitted Areas
Percent of Impervious Area for Design Standards in Table II
Residential two-family
Medium density multi-family
High density multi-family
"RMH"
Residential manufactured home
"BR"
Business-residential overlay
Highway business district
"B-2"
For these classifications, the percent impervious area shall be the actual proposed ration of impervious area to total area for the lot. Also, any lot in any district greater than ten thousand (10,000) square feet shall use an actual ration for determining the percent impervious area.
[Ord. No. 1437 §I(435.040), 6-21-2004]
Development within a subdivision shall not require approval of a stormwater management plan if each of the following conditions has been met:
Drainage provisions for the project were previously approved and remain valid as part of a final plat.
The development is conducted in accordance with the stormwater management provisions contained in the development plan submitted with the final plat as approved.
Development on isolated lots or record for single-family and two-family dwelling purposes shall not require approval of a stormwater management plan nor a grading permit, unless the development involves altering, rerouting, deepening, widening, obstructing or changing in any way existing drainage facilities, degrades the quality of water, adversely affects any wetland or adversely affects any sinkhole, watercourse or waterbody; or unless said lot is one (1) acre or more in size as State law now requires a land disturbance permit for any construction that disturbs more than one (1) acre.
Stormwater management plans may be waived for building construction or other development that will not increase the amount of impervious area on the site and will not adversely impact an existing area or drainage on adjoining properties.
Written notice of intent to commence development shall be delivered to the Administrative Officer prior to undertaking any development activity, whether exempt from plan provisions or not. Application for a building permit may constitute notice of intent.
[Ord. No. 1437 §I(435.050), 6-21-2004]
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.
Required Information. It is the responsibility of an applicant to include sufficient information in the stormwater management plan to enable evaluation of the environment quality of the affected area, the potential and predicted impacts of the proposed activity of 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 sealed by a registered professional engineer or architect.
The application form requires the following minimum information:
The name, address and telephone number of the applicant and the owner if different from the applicant.
Name and address of the professional engineer or architect.
The legal description of the property.
[Ord. No. 1437 §I(435.060), 6-21-2004]
A stormwater management plan is designed to safely manage the stormwater runoff following the rainstorms that exceed the maximum allowable release rate and the capacity of the stormwater drainage system and/or the storm sewer by detention of the excess stormwater runoff. It is also designed to manage the quality of stormwater runoff during development through erosion and sedimentation controls. The plan shall provide or be accompanied by maps at a minimum scale of one (1) inch is less than or equal to two hundred (200) feet and other descriptive material, including the basis of computation, showing the following:
Required pre-development site information (map scales are minimums):
Detailed location sketch showing the parcel and major adjacent roads.
Topographic map of the site at a scale of one (1) inch is less than or equal to one hundred (100) feet with maximum two (2) foot contour intervals, except in floodplain or other areas of low relief where a smaller interval may be required.
Where percolation or infiltration systems are proposed, information as to the location and type of vegetative cover and soil types and characteristics representative of the design condition mapped at a scale of one (1) inch is less than or equal to one hundred (100) feet.
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 is less than or equal to one hundred (100) feet.
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 is less than or equal to one hundred (100) feet.
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 mapped at a scale of one (1) inch is less than or equal to one hundred (100) feet.
Location and description of nearby existing off-site water management facilities such as wells, lakes, drainage ways, etc., that are potentially directly affected by the proposed construction or development, mapped at a scale of one (1) inch is less than or equal to one hundred (100) feet.
For all existing drainage facilities that 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.
Location of all new drainage facilities, including detention basins, to be constructed. Provide design details on each facility as applicable.
Location and extent of existing and proposed impervious surfaces (roads, parking lots, buildings, etc.) and their elevations. Provide grading and paving plans and specifications.
Location and extent of rights-of-way and easements for the stormwater management system, including all areas to be dedicated for water management purposes.
Identification and description of any special or required maintenance procedures to keep the project functioning as designed.
Provide stormwater management system design calculations as follows:
Design storms used.
Calculated hydrographs of inflow and outflow of design storms for the project site under natural and undeveloped conditions.
Hydrographs of the runoff from the design storm for the project site under developed conditions.
For all detention basins, a plot or tabulation of storage volumes with corresponding water surface elevations and of the basin overflow rates for those water surface elevations.
Acreages and percentage of property proposed as:
Impervious surfaces.
Pervious surfaces (green areas).
Lakes, canals, detention areas, etc.
Total acreage of project.
Runoff routing calculation showing discharge, elevations and volumes retained and/or detained during applicable storm event.
Calculations required for determination of minimum building floor and road elevations.
Identify entity responsible for operation and maintenance of the system.
The requirements for specific plan elements cited above may be waived by the Administrative Officer upon written supportive recommendation of the City Engineer. The stormwater management plans for minor development activities may consist of a certification from a professional engineer or architect that the differential runoff equals zero.
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 City Administrator. Within a reasonable period after submission of the completed 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 application is denied or approved with conditions, the Administrative Officer shall state the reasons for denial or the specified conditions. If the applicant feels aggrieved due to the denial or conditions, he/she may appeal the decision to the Board of Aldermen.
[Ord. No. 1437 §I(435.070), 6-21-2004; Ord. No. 1614 §§I — II, 10-20-2008]
For the purpose of evaluation, projects will be classified into three (3) categories.
"R-1" and "R-2"
Lot square footage x .004
"R-3" and "R-4"/Residential Subdivision
Land square footage x .006
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.
The stormwater permit fee will be collected before the stormwater management permit is issued to the applicant and will reflect the cost based on the land square footage of the project. These fees may be adjusted from time to time by the Board of Aldermen to reflect cost changes.
[Ord. No. 1437 §I(435.080), 6-21-2004]
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 stormwater into the ground and to preserve and utilize natural streams, channels and detention basins and, wherever possible, to include streams and floodplains within parks and other public grounds.
The maximum allowable release rate of stormwater after development shall not exceed the before development rate based on a 15-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 by-passed or discharged via overflow spillway or other devices.
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 25-year storm (under developed conditions). Control devices shall limit the discharge from storage to a rate no greater than that prescribed by this Section. 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.
Generally acceptable locations of the stormwater runoff channels in the design of the project area may include the following:
In a depressed median of a double roadway, street or parkway, provided the median is wide enough to permit required roadway shoulders.
Centered on the rear 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 Section.
In a depressed area along roadway, street or parkway, provided the area is wide enough to permit side slopes as required in other Sections of this Section.
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.
The smaller, uppermost reaches of drainage channels and swales forming the natural drainage system near a watershed divide may be relocated or eliminated and incorporated into the planned system of storm sewers and open channels designed consistent with the requirements of this Chapter.
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 areas 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.
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 back-ups into planned storage locations.
All sanitary sewer manholes constructed in a floodplain, in street designed for detention or in an area designed for the storage or passage of floodwater or stormwater shall be provided with either a watertight bolted manhole cover, a watertight concealed pick-hole cover or be constructed with a rim elevation at least one (1) foot higher than the high water elevation of the 100-year flood or the high water elevation of the design storm, whichever is applicable to the specified area.
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.
Systems such as curb and gutter, drop inlets and storm sewers shall discharge into closed conduits into a detention basin or natural drainage way. Suitable methods of erosion control shall be provided at the discharge of such enclosed conduits.
Flow Towards Streets. Any concentration of surface flow in excess of two (2) cubic feet per second (cfs) for the 10-year frequency rain shall be intercepted before reaching the street right-of-way and shall be carried by an enclosed storm drain to connect with a drainage structure at the low point in the street right-of-way or to discharge to a watercourse.
Detention facilities shall release stormwater at a non-erosive velocity. Protected channels receiving detention discharge shall incorporate features to reduce velocity to non-erosive levels at the point where such discharge enters the unprotected channel. If release is into a subsurface conduit, the energy gradient in the receiving facility shall not be increased beyond the slope of the conduit.
[Ord. No. 1437 §I(435.090), 6-21-2004]
Stormwater systems will be designed with sufficient hydraulic capacity as a minimum for the following frequencies and durations:
Design Frequency
Primary drainage systems
Secondary drainage systems, i.e., cross drains and ditches for interval subdivision drainage
The Administrative Officer may require alternative designs or features to reduce the cost of long-term maintenance.
In critical areas, the Administrative Officer may require additional hydraulic capacity above the minimums set forth above, up to the 100-year frequency design.
[Ord. No. 1437 §I(435.100), 6-21-2004]
Method Of Evaluation. Differential runoff evaluation consists of the determination or rates of runoff before and after development, the determination of required volume of detention and verification of adequacy of discharge and control structures.
Differential Runoff Rates. Differential runoff for all three (3) size classes of projects shall be evaluated by the rational formula. The runoff coefficients in Table II shall be used. Differential runoff rates shall be evaluated by equations:
(Rd-Rd)
Differential runoff rate
C.I. factor for developed conditions
C.I. factor for undeveloped conditions
Volume Detention. Volumes of detention for the three (3) classes of projects shall be evaluated according to the following methods:
Volume of detention for projects of less than twenty-five (25) acres shall be evaluated by the "simplified volume formula".
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 rational hydrograph method".
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) areas will be rendered before the method of evaluation of the detention is approved.
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.
Calculation Methods. Any of the following methods may be used for calculating detention volume as applicable:
Simplified volume formula. Total volume of detention shall be computed by the equation:
R x A x 30 x 60 (sec/min)
Total volume of detention
Area of project in acres
Graphic representation. For purposes of further analysis, the simplified volume formula may be represented by a triangular synthetic hydrograph with the following elements:
Base time of hydrograph for developed project without detention
Time of peak runoff of developed project
Total peak runoff of developed project in c.f.s.
A x Rd (See Equation 1)
Total peak runoff of unimproved project in c.f.s
A x RU (See Equation 1)
Total area of project in acres
Assumed time of peak differential for unimproved project
Qu/Qd x 40
Assumed recedence time differential for discharge at rates no greater than unimproved condition
(30 Qd/Qu) - 60
(Qd - Qu) x 30 (min) x 60 (sec/min)
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.
Steps to develop the hydrograph are as follows:
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 II and obtain Tc.
Determine time of peaking by equation:
D/2 = .6 Tc
Time of peak discharge of developed project in minutes
20 min - storm duration in minutes
Determine the base time of hydrograph without detention by equation:
2.67Tp
Determine the base time of the hydrograph with detention by equation:
(Qd
(Qu- 1)
Additional time required for discharge at a rate no greater than that of undeveloped condition
Total runoff of unimproved project in c.f.s.
Determine the required volume of detention by equation.
½(Qd - Qu) Tb
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.
The design discharge (Q) for the low-flow weir shall not exceed the 15-year (frequency) with duration equal to the time of concentration for the watershed, runoff from the tributary area for five percent (5%) imperviousness (1.7 c.f.s per acre). The maximum discharge shall be designed to take place under total anticipated design-head conditions.
Sizing of the low-flow weir shall be by the appropriate weir formulas.
The overflow opening or spillway shall be designed to accept the total peak runoff of the improved tributary area.
The low-flow channel invert through dry detention facilities on other than permanently flowing streams shall be paved.
Detention design criteria. Detention in the overall system, including swales, lakes, canals, greenways, etc., shall be provided as follows:
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 25-year storm (under developed conditions) with a discharge no greater than the rate of flow from a 15-year storm (under undeveloped conditions).
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.
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 100-year storm.
Appearance. Designs should result in aesthetically pleasing configurations that will enhance public acceptability.
Dry Detention Facilities.
Perimeter maintenance easements of fifteen (15) feet (minimum) width at slopes no steeper than 3:1 (horizontal to vertical) shall be provided.
Side slopes of the facility shall not be steeper than 3:1 (horizontal to vertical).
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 subsurface drains.
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.
In no case shall the limits of maximum ponding elevation be closer than twenty-five (25) feet horizontally from any building and less than two (2) feet vertically below the lowest sill elevation. The entire reservoir area shall be seeded, fertilized and mulched, sodded or paved.
Wet Detention Facilities.
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.
Control elevations should be no higher than two and one-half (2½) 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.
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.
If fish are to be used to help keep the basin clean, at least one-quarter (¼) of an area of the permanent pool must be a minimum depth of ten (10) feet.
For emergency purposes, cleaning or shore line maintenance, facilities shall be provided or plans prepared for the use of auxiliary equipment to permit emptying and drainage.
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.
Any wet detention facility that is to be turned over to the City for operation and maintenance shall be secured by means of fencing. Fencing plans shall be detailed in the overall stormwater management plan and shall include at a minimum a lockable access point for maintenance personnel and equipment.
Impervious Areas. Paved parking lots may be designed to provide detention storage of stormwater 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 relegated to positions of the parking lots farthest from the area served.
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 downdrains, elevations of overflow scuppers, design loadings for the roof structure and emergency overflow provisions.
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 type of facility, depth and volume or storage, details of inlet and outlet devices and locations, emergency overflow provisions and measurers to be used for surface water and ground water pollution control.
Design Alternatives. The above listing of design criteria is not intended to preclude the use of other know state of the art methods and available Best Management Practices and should not be construed as a mechanism to discourage innovative design concepts.
Developments Adjoining A Floodplain. Where a development adjoins or encompasses a portion of a floodplain for a 100-year flood, the following shall apply:
The applicant shall show the floodplain and floodway on the stormwater management plan.
The applicant shall include in the stormwater management plan all other plans, plats, specification, 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:
All applicable zoning and subdivision requirements.
All applicable Building Code requirements.
All requirements of other Federal, State or local agencies exercising jurisdiction over the area.
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 which it conveyed in its pre-development state.
Modifications Of Channel. The applicant shall furnish, for the Administrative Officer's review and approval, the following information pertaining to proposed channel modifications:
Typical cross sections of the existing and proposed channel.
Plan view of the channel showing the location of existing constrictions, obstructions and other non-typical areas.
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.
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.
Minimum finished floor elevations that shall be set at or equal to an elevation one (1) foot higher than surface elevation as determined by either or both of the following:
Flood Insurance Rate Map published by the Federal Emergency Management Agency.
Backwater curve profiles of the proposed waterway due to a 100-year storm recurrence interval.
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.
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.
Verification Of Adequacy. 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 Section. 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:
Volume of detention for the total project.
Tributary (Q) peak runoff to basin.
Balanced maximum outflow rate from the low-flow structure.
Ratios of inflow to outflow rates.
Sizing of the overflow facilities.
Stability of detention dikes.
Maintenance features.
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.
Projects over two hundred (200) acres in area shall provide documented verification of adequacy according to scope and complexity of design.
Average C.I. (P.I.) Factors in CFS/Acre
20 Minute Inlet Time
% Impervious Area
C or P (Factor)
100-year
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.
Erosion And Sedimentation Control Criteria. The Best Management Practices to control the occurrence of erosion and sedimentation are to be incorporated into the plan for the time land is disturbed by development activity. Permanent controls and practices shall also be identified where they are necessary to control an ongoing potential for erosion and sedimentation. Types of Best Management Practices include, but are not limited:
Use of State approved standard specifications of the City.
Tree, topsoil and vegetative cover preservation and restoration.
Surface stabilization with various natural or manmade materials.
Runoff control measures such as berms, dikes, sediment traps and barriers.
Inlet and outlet protection.
Streambank protection.
Scheduling of development activities and protection measures for minimal impact.
[Ord. No. 1437 §I(435.110), 6-21-2004]
All stormwater management facilities shall be constructed within an easement or 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 easement or rights-of-way shall not be required. The minimum widths of rights-of-way and easements shall be as follows:
Maintenance Access Width
Open drainage channel or facility
30 feet, 15 feet each side
Width of greenway
Pipes and culverts
15 feet, centered
Detention areas
15 feet continuous around total area
Connecting access
Easements must include the "top of the bank width" and the maintenance access width.
The maintenance access width begins at the point of the bank or slope of the facility.
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.
[Ord. No. 1437 §I(435.120), 6-21-2004]
Purpose. The purpose of this Section is to establish maintenance standards to ensure that after stormwater management facilities have been properly designed and constructed, they continue to function properly. Continued proper functioning is highly dependent upon the proper maintenance of the facilities.
Design Of Facilities. Maintenance costs over a period of years will generally surpass the costs of initially constructing water management facilities. The applicant and the Administrative Officer should utilize all appropriate methods, approaches and techniques to design and construct these facilities in such a manner that fulfills the requirements of this Section, facilitates their inspection and minimizes future maintenance costs.
Maintenance Responsibility. The growth of noxious weeds, the creation of conditions that support the growth of mosquitoes and other insects and the decrease in available storage by accumulated sediments shall be controlled. The cleanup of accumulated debris, flotsam and other materials after runoff events have subsided shall be assured.
Detention facilities, when mandatory, are to be in conjunction with the storm sewer installation and/or grading. Since these facilities are intended to control increased runoff, they must be partially or fully operational soon after the clearing of the vegetation. Silt and debris connected with early construction shall be removed periodically from the detention area and control structure in order to maintain close to full storage capacity.
The responsibility for maintenance of stormwater management facilities in single-lot development projects shall remain with the owner, developer and general contractor until final inspection of the development is performed and approved and a legal occupancy permit, where applicable, is issued. After legal occupancy of the project, the maintenance of stormwater management facilities shall be vested with the owner of the project.
The responsibility for maintenance of stormwater management facilities in subdivision projects shall remain with the developer until such time as responsibility is transferred, under appropriate legal arrangements, to the private individual owners in the subdivision, the trustees of the subdivision, the City or such other maintenance entity or authority as may be proposed and approved by the Board of Aldermen.
If responsibility is to be transferred to the private individual owners in the subdivision, the developer shall assure perpetual maintenance of the drainage management facilities, including detention systems, if any are included, through the adoption of maintenance agreements or covenants for any facilities that remain in private ownership. Such agreements or covenants shall be subject to the approval of the Administrative Officer.
If the responsibility is to be transferred to the trustees of the subdivision, the developer shall establish a suitable indenture of trust. Upon release of escrows required for the subdivision development, the responsibility for maintenance shall be vested in the trustees of the subdivision by virtue of the trust indenture. The indenture of trust shall clearly indicate resident responsibility for maintenance and shall be subject to the approval of the Administrative Officer.
If responsibility for maintenance is to be transferred to the City, the system to be maintained by the City shall have adequate easements, dedicated to the public for stormwater management use, to permit the City to inspect and enter upon the property, as necessary, to maintain the system.
Performance And Maintenance Security. Security against defects in workmanship shall be required for any portion of the drainage management facilities dedicated to the public. The terms of the performance security shall apply to any repairs needed and maintenance needed during the two (2) year period following completion. Inspection and repair of defects shall be required as a condition of release of the posted security.
[Ord. No. 1437 §I(435.130), 6-21-2004]
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 Chapter obtaining stormwater management approval. Enforcement officials shall be and are herein granted inspection rights and right-of-entry privileges in order to ensure compliance with the requirements of this Section.
[Ord. No. 1437 §I(435.140), 6-21-2004]
Approved Projects. The Administrative Officer or his/her designated representative shall carry out periodic inspections of the project site to insure the applicant's compliance with this Section. 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:
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.
Stop work order. Issue a stop work order directing the applicant or owner to cease and desist all or any portion of the work that violates the provisions of this Section, if the remedial work identified in the written notice is not completed within the specified time.
Revocation of approval. Should the applicant or owner not 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 penalties for violation.
Appeal. Any notice order or revocation issued pursuant to Subsections (A)(1), (A)(2) or (A)(3) above shall become final unless the person named therein requests, in writing, not later than ten (10) days after the date such notice order or revocation is served, a hearing before the Board of Aldermen.
Unapproved Projects. With respect to any development or development activity determined by the Administrative Officer or his/her designated representative subject to this Chapter and being carried out without approval, the Administrative Officer is authorized to:
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.
Stop work order. Issue a stop work order directing the owner to cease and desist all or any portion of the work that violates the provisions of this Section, if the remedial work identified in the written notice is not completed within the specified time.
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 penalties for violation.
Appeal. Any notice, order or revocation issued pursuant to Subsections (B)(1), (B)(2) or (B)(3) above shall become final unless the person named therein requests, in writing, no later than ten (10) days after the date such notice order or revocation is served, a hearing before the Board of Aldermen.
[Ord. No. 1437 §I(435.150), 6-21-2004]
General. Violation of the provisions of this Section or failure to comply with any of its requirements, including conditions and safeguards established in connection with variances or special use permits, shall constitute a misdemeanor. Any person who violates this Section or fails to comply with any of its requirements shall upon conviction thereof be fined not more than five hundred dollars ($500.00) or imprisoned for not more than three (3) months or both and, in addition, shall pay all costs and expenses involved in the case. Each day such violation continues shall be considered a separate offense.
Corrective Actions. Nothing herein contained shall prevent the City from taking such other lawful action as is necessary to prevent or remedy any violation. All such costs connected therewith shall accrue to the person responsible.
[Ord. No. 1437 §I(435.160), 6-21-2004]
This Section 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.
[Ord. No. 1437 §I(435.170), 6-21-2004]
In case of conflicts within this Section or any part thereof and the whole part of any other existing or future ordinance or code of the City, the most restrictive in each case shall apply.
[Ord. No. 1437 §I(435.180), 6-21-2004]
Before starting any work regulated by this Section, 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 Section and as may be required by State Statutes and the regulations of any department of State.
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.
[Ord. No. 1437 §I(435.190), 6-21-2004]
In the interpretation and application of this Chapter, 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.
[Ord. No. 1437 §I(435.200), 6-21-2004]
It is not intended by this Chapter to repeal, abrogate or impair any existing easements, covenants or deed restriction. However, where this Section imposes greater restrictions, the provision of this Chapter shall prevail.
[Ord. No. 1437 §I(435.210), 6-21-2004]
The performance standards and design criteria set forth herein establish minimum requirements that 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 uses permitted will be free from damages caused by stormwater runoff. Larger storms may occur or stormwater runoff heights may be increased by manmade or natural causes. Enforcement of these provisions, therefore, shall not create liability on the part of the municipality with respect to any legislative or administrative decision lawfully made hereunder, nor shall compliance relieve an owner, developer and/or committee from responsibility under any circumstances where liability would otherwise exist.
[Ord. No. 1437 §I(435.220), 6-21-2004]
Any stormwater management facility for which a permit has been issued as a part of a subdivision improvement plan must be included with as-built drawings and certified to have been constructed accordingly.
Any stormwater management facility for which a permit has been issued individually or as a part of a site development plan must be certified to have been constructed in conformance with the approved drawings prior to issuance of an occupancy permit.