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It is the purpose this article to set forth the minimum requirements necessary to provide and maintain a safe, efficient, and effective stormwater management system within the City and to establish the various public and private responsibilities for the provision thereof with the least possible disruption of the natural drainage system and of the environment.
A. It shall be the responsibility of any applicant engaged in the activity of land subdivision, development, or improvement to:
1. Control and manage all drainage from the subdivision resulting from the development including the control and management of any determined, approved increase in runoff or runoff rate.
2. Prepare all drawings, plans specifications, statements, studies, justifications, and other data required by this article in form that permits an orderly and comprehensive review and approval to assure that all assigned responsibilities have, sufficiently and correctly incorporated.
3. Control and manage all stormwater runoff and drainage from points and surfaces within the subdivision.
4. Provide detention or retention facilities or storm sewer, or improved or natural channels, or a combination thereof to provide control and management of increased discharge.
5. Prevent soil dispersal, sedimentation, erosion, or other similar forms of pollution:
a. From any surface of the site into drainage channels provided or created within the development.
b. From the site into drainage channels adjacent to and remote from the site.
6. Prevent any and all drainage interferences, obstructions, or other adverse effects upon drainage into, through, or adjacent to the development from upstream or higher elevation source by the use of temporary or permanent by-pass channels, channel improvements, or other facilities as may be required.
7. Improve or modify all drainage systems and channels lying within or adjacent to the subdivision to a level that meets all requirements of this article.
8. Improve or modify drainage systems downstream from the subdivision to a level that will accommodate all allowable, significant increases in stormwater quantity or rate without adverse effect and in accordance with the requirements of this article.
9. Fully consider and provide natural drainage in the design of drainage systems and classifications applicable to the development.
10. Prepare and submit a professional evaluation of the impacts of proposed development.
11. Maintain all installed drainage facilities in a clean, fully functioning manner, from installation through final acceptance by the City.
12. Prevent any contribution to existing flooding, drainage, erosion, runoff, pollution. Or other stormwater management problems within an area already under a high level of development.
13. Prevent drainage, runoff, flooding, or problems associated with any adverse contribution to any such potential problems.
B. It shall be the responsibility of all owners of property, whether undeveloped, developed, or undergoing development, to:
1. Mow and provide minor maintenance of drainage channels and their slopes for that portion of the channel lying within their property line.
2. Keep clear all drainage channels within the boundaries of their properties in accordance with the requirements of this article.
3. Control all stormwater runoff and drainage from points and surfaces on the property.
4. Prevent any and all drainage interferences, obstructions, blockages, or any other adverse effects upon drainage, into, through, or out of the property.
C. It shall be the responsibility of the City to:
1. Repair and maintain drainage channels and their slopes when located within or upon rights-of-way dedicated to and accepted by the City.
2. Develop and implement standards and specifications required to clearly and accurately interpret the physical requirements of this article.
3. Make such necessary improvements of primary and secondary drainage channels that cannot or will not be improved through private development.
4. Improve and maintain floodway and flood fringe areas that are dedicated and accepted-public areas, rights-of-way, park lands, or public-owned buildings or developments.
5. Improve and maintain all public owned drainage channels or systems outside the flood fringe area.
D. It is the intent of this article that the following principles shall be used in the design of modifications to or the improvement of the stormwater management system.
1. Natural drainage channels and techniques shall be given priority consideration in preparation of drainage system designs and shall be designed or improved as an integral part of the landscape of the area and shall be kept in good repair.
a. The design of any development shall provide for the maximum use of open channels and natural streams for flows and detention or retention storage of volumes and flows in excess of those present prior to development.
b. Drainage channel improvement shall be developed and designed that preserve and protect large trees and other worthy botanical and geological features to the greatest possible extent.
c. Wherever channel improvements are required to accommodate calculated flows in a specified manner, the designs shall provide maximum utilization of turf, sodding, and other natural drainage techniques.
2. Closed, underground drainage conduits shall be employed only when there is no viable alternative to fit site or geographic conditions or to meet the requirements of this article and all specifications and performance standards pertaining thereto.
3. The rate of runoff after development shall not exceed that rate experienced before development.
a. In no case shall the release rate of stormwater runoff from all developments in a drainage area, controlled or uncontrolled, exceed the "safe" storm drainage capacity of the downstream outlet channel(s) or storm drainage system as determined by the City Engineer or other designated representatives by the City Manager.
b. Within already developing or developed areas where "safe" storm drainage capacity of downstream outlet channel(s) or storm drainage system has been exceeded, the developer shall add no increased runoff unless the downstream outlet capacity has been increased to accommodate all flows.
c. Improvements may be required in channels or sewers flowing into, through, or from the subdivision or development, or in channels or sewers located upstream or downstream that are affected by the flow of water from the subdivision; development, or change thereto. The following types of improvements, among others not specifically listed, may be required.
(1) Enlargement or replacement of undersized structures.
(2) Removal of obstructions.
(3) Straightening, widening, and/or deepening of channels.
(4) Construction of erosion and sedimentation facilities.
(5) Construction of closed- or open-paved or natural drains for the purpose of closing gaps or maintaining the continuation of the overall stormwater drainage system.
(6) Detention or retention facilities.
(7) Improvements as otherwise required by this article to assure efficient and safe stormwater management.
d. When subdivision development or property improvements will result in an increased runoff beyond the boundaries of the development or improvement which cannot be accommodated through channel improvements without flooding or potential flooding upstream or downstream, the City through its duly designated representative and/or board shall require the construction of one (1) or more detention or retention facilities on the subdivision or property being improved and/or required detention or retention techniques to be used off site which will result in flows, during construction and thereafter, from the property at a rate and volume no greater than the discharge from the undeveloped site.
4. All those engaged, in land improvements or modifications shall prevent the erosion of soil and movement of sedimentation into, unto, or through streets, gutters, catch basins, culverts, or other drainage channels and shall prevent erosion as a result of flows from streets, gutters, culverts, or other drainage channels.
a. Where it can be demonstrated that there is no alternative to rapid runoff water because of identifiable restrictions, the developer shall be required to provide measures to prevent erosion, damage, flooding, or other adverse effects.
b. The City Engineer or the duly appointed City representative shall require the cleaning, straightening, and/or repair of any natural drainage channel or natural features of other drainage channels when necessary to provide for the free flow of water or to eliminate and/or prevent erosion upstream and downstream.
5. The City Engineer or the duly appointed City representative may approve stormwater runoff into a street or alley provided the developer fully and adequately demonstrates that the street or alley or an improvement thereof will provide drainage in full conformance with all other provisions of this article and which will prevent runoff or overflow onto adjacent or nearby residential property.
E. It is the further intent of this article that the following requirements be met to ensure the least possible disruption to the existing drainage system.
1. Detention and retention, separately, or in combination, shall be considered and incorporated, where possible, in all drainage systems design consistent with safety, convenience, and restrictions place upon stormwater runoff rates and velocities for the developments, property, and drainage channels through or therefrom.
2. The City may require improvements, provision of drainage easements; and for provision of improvements, agreements, and/or easements beyond the boundaries of the subdivision, development, or property improvement to facilitate flow of stormwater from or through the property, to avoid damage from changed runoff conditions, to provide continuous improvement of the overall storm drainage system, and to accommodate all drainage conditions or requirements, where stormwater runoff flows require the logical extension of any street and its associated drainage in order to prevent flooding, ponding, or uncontrolled runoff, the extension shall be provided by the developer.
3. Improvements provided by the developer shall be fully and properly maintained from initial approval of installation(s) through final acceptance of the development improvements by the City. The continuing maintenance of detention or retention facilities shall be assured by the developer in the manner described for other drainage facilities.
4. No action shall be taken in any land improvement by any developer, contractor, or lot owner that will alter or otherwise change designed and installed stormwater management control, nor shall any action be taken on existing property that shall adversely affect stormwater runoff in any manner contrary to the provisions of this article, whether temporary in nature to service, only the construction phase of development, or whether a combination of temporary and permanent serving a dual purpose, the first techniques to be employed in the development of a site shall be the management of stormwater and drainage in manner consistent with the requirements of this article.
F. If any determination based upon the provision of this subsection is felt to be unreasonable or inapplicable, a developer or lot owner may appeal that determination to the board of adjustment. Upon the written request for the appeal which shall include all justifications and reasons for that appeal, the question will be heard at the next available meeting of the board of adjustment. If not satisfied with the decision of the board of adjustment, a developer or, lot owner may appeal the decision of the board of adjustment to district court.
(Ord. No. 02-08, § 3, 5-6-2002)
A. Preliminary plats submitted for review and approval shall be accompanied by the following documents, which shall be submitted to the City Engineer or the duly appointed City representative:
1. Five (5) copies of predevelopment report accurately describing:
a. Dimensions, size and location;
b. Existing topography;
c. Soil types;
d. Vegetation;
e. Flood hazard areas;
f. Other significant surface features;
g. Existing land use;
h. Existing runoff volume;
i. Existing runoff rates;
j. Existing runoff routing.
2. Five (5) copies of a plan for the control of erosion and sedimentation which shall contain:
a. Data showing the nature and extent of the proposed clearing, grading and development or improvement operations;
b. An estimate of soil loss during and after development;
c. Proposal for the control of erosion and sedimentation during and after development including a statement of actions proposed to assure erosion control for all areas of the site that will be unprotected for long periods or during peak rainy periods and for natural drainage ways prior to and during construction; and
d. Proposed topography of the site after development or improvement including the method of handling runoff and stormwater.
3. A written statement of the impact on upstream and downstream drainage prepared by an Oklahoma registered professional engineer and approved by the City Engineer or the duly appointed City representative. The accuracy and validity of any drainage impact statement and attachments shall be capable of withstanding serious challenge at any stage in the review and approval process in order to be accepted as a part of the project. Accordingly, the alleviation of adverse impacts by on-site and off-site improvements relating to the drainage are of important concern and shall be satisfactorily provided as required by this article.
4. A description of proposed easements and/or rights-of-way, and the provision of binding agreements between cooperating developers, for drainage improvements required outside of subdivision development boundaries. Public easements and right-of-way dedications shall be initiated by the developer, property owner planning property improvement, or legal agent thereof, shall be prepared in the manner prescribed by law, and shall be submitted in accordance with the timing and routing requirements of this or other applicable article.
B. Final plats submitted for review and approval shall be accompanied by the following documents, which shall be submitted to the City Engineer or the duly appointed City representative.
1. All documentation required by this section; and
2. Improvement plans meeting the requirements of this section.
C. Any person applying for a building permit or who otherwise intends to make changes in the contour of any land shall first submit the following documents to the City Engineer or the duly appointed City representative.
1. All documentation required by this section, allowing that, at the direction of the City Engineer, or others the documentation need not be prepared by a professional engineer; and
2. Plans for improvement or changes proposed, including site plans, plot plans, and building drawings for buildings and structures, clearly showing the method of handling rainfall runoff and stormwater.
3. The following activities are specifically exempted from the requirements of this section:
a. Bona fide agricultural or forestry operations.
b. Home gardening or other minor clearing or excavation work not incident to a change in the residential use of the land.
c. Emergency repairs necessary for the preservation of life, health, or property.
d. Routine maintenance or repair work on public or private roads an rights-of-way or utility line easements and rights-of-way.
e. Changes that would occur on single-family residential lots or property of less than two (2) acres, unless the proposed action(s) conflict with previously approved reports required by subsection (D).
D. All plans and documentation required by this section must comply with all City standards, regulations, ordinances, and with the approved drainage master plan or drainage studies.
E. All documentation and plans required by this section must be approved by the City Engineer or other authorized City representative prior to their implementation. The City Engineer or other authorized City representative may submit any documents to the following agencies for their review and comment prior to his approval:
1. The City Public Works Authority; and
2. The United States Soil Conservation Service; and
3. Any other local, federal or State agency involved in floodwater detention or retention waters.
F. Appeals of the decision or requirements made as a result of this review, other than for improvement plans requirements, may be made first to the City board of adjustment and if still dissatisfied to district court.
G. Projects and tasks proposed in the plans and documents required by this section shall be implemented as proposed. Any changes or amendments to the plans or documentation must be approved by the City Engineer or other authorized City representative in accordance with the established review procedures.
(Ord. No. 02-08, § 4, 5-6-2002)
A. This section shall define the methods, performance, standards, and design criteria which shall be used in the preparation and evaluation of the reports and plans required as documentation in Section 110-254.
B. Drainage calculations.
"C" Coefficients According to Description of Drainage Area
Description of Area | Runoff Coefficients |
Description of Area | Runoff Coefficients |
Business | |
Downtown | 0.70 to 0.95 |
Neighborhood | 0.50 to 0.70 |
Residential | |
Single-Family | 0.30 to 0.50 |
Multi-units, detached | 0.40 to 0.60 |
Multi-units, attached | 0.60 to 0.75 |
Residential (Suburban) Apartment Industrial | |
Light | 0.50 to 0.80 |
Heavy | 0.60 to 0.90 |
Parks, Cemeteries | 0.10 to 0.25 |
Playgrounds | 0.20 to 0.35 |
Railroad Yard | 0.20 to 0.35 |
Unimproved | 0.10 to 0.30 |
"C" Coefficients According to Character of Surface
Character of Surface | Runoff Coefficients |
Character of Surface | Runoff Coefficients |
Pavement | |
Asphaltic and Concrete | 0.70 to 0.95 |
Brick | 0.70 to 0.85 |
Roofs | 0.70 to 0.95 |
Lawns, Sandy Soil | |
Flat, 2 percent slope | 0.05 to 0.10 |
Average, 2 to 7 percent slope | 0.10 to 0.15 |
Steep, 7 percent slope | 0.25 to 0.35 |
Acceptable formulas for determining time of concentration are as follows:
Time = K(L.37/S.2)
L = Length of flow in feet
S = Average slope in feet/foot
K = Constant for character of surface
Values of K: |
Values of K: | |
Pavement | .372 |
Bare Soil | .604 |
Poor Grass | .90 |
Average Grass | 1.00 |
Dense Grass | 1.13 |
Commercial | 0.445 |
Residential | 0.511 |
Cultivated Soil | 0.775 |
Timber; thin grass | 0.942 |
Pasture | 1.040 |
An acceptable formula for channel flow is:
Time = K(L 2/S).385
Values of K: |
Values of K: | |
Curbed Street | .0035 |
Concrete Lined Channel | .006 |
Sodded Swale | .008 |
Bar Ditch | .012 |
Straight; clean stream | 0.00592 |
Average Stream | 0.00835 |
Meandering; pooling stream | 0.01020 |
An acceptable formula for intensity is as follows:
I = average rainfall intensity, inches per hour
T = rainfall duration (or time of concentration), minutes
d
STORM RETURN
2YR | 5YR | 10YR | 25YR | 50YR | 100YR | |
a = | 56.43 | 72 | 82 | 95 | 108 | 120 |
11.5 | ||||||
c = | 0.810 | b = 15 | c = 0.80 |
WHERE T = TIME OF CONCENTRATION - d
a. Rational method analysis—Practices in Detention of Urban Stormwater Runoff, American Public Works Association. Special Report No. 43
b. Stormwater flood routing techniques.
2. Flow volumes. The calculation of runoff flow volumes used in the sizing of detention or retention facilities or other flood routing analysis shall be done by the use of accepted stormwater routing principals and the method shall be approved by the City Engineer or other authorized City representative.
3. Structure sizing. The sizing of all drainage facilities or structures shall be done by the use of established available engineering principles and practice and the methods shall be acceptable to the City Engineer or other authorized City representative.
a. The structure sizing shall include an analysis of the existence of inlet or outlet control design, freeboard; spillway design, and a backwater analysis where applicable.
b. Where Manning's Equation is used, the value for coefficients will be taken from the following references:
(1) Open channels.
(A) Open Channel Hydraulics. Chow. Ven T., McGraw- Hill Book Co., New York, N.Y. 1959.
(B) U.S.D.A. Handbook SCSTP-61, W.O. Ree.
(C) Roughness Characteristics of Natural Channels.
U.S.G.S. Water Supply Paper No. 1849, Washington, D.C. 1967.
(2) Closed conduits.
(A) Seelye's Handbook.
(B) Handbook of Hydraulics, King. H.W.
(C) USBR Hydraulic Tables.
(D) Modem Sewer Design, American iron and Steel Institute.
c. Natural open channels with vegetative linings shall be designed considering infrequent mowing unless other conditions are demonstrated and justified, guaranteed maintenance for exceptions must be established.
d. Cover vegetation for channel linings must be selected according to Standards established by The Soil Conservation Service of McClain County and shall be approved by the City Engineer or other authorized City representative.
4. When stormwater is conveyed via streets, flumes, swales, or open channels, consideration will be given to pedestrian and traffic convenience and safety. Special provisions may be required by the City Engineer or other authorized City representative to avoid sheeting of water across arterial intersections, inundation of crosswalks or sidewalks, inundation of driving lanes, and other safety or nuisance problems. These special provisions may include additional easements or rights-of-way, structures, flumes, or pavement width.
C. Performance criteria.
1. Detention or retention facilities shall have the following performance criteria:
a. Detention or retention facilities shall be sized by hydraulic stormwater routing through the detention basin and to accommodate or contain any changed drainage conditions due to the proposed development because of increases in the runoff volume or rate.
b. Detention or retention facilities shall have a release rate which does not exceed:
(1) The pre-development of runoff conditions for all return storms; or
(2) The "safe" capacity of the downstream drainage channel or system if any increase in runoff volume rate is approved.
2. Open channels, flumes, or swales shall have the following performance criteria:
a. All channels, flumes, or swales shall be designed to carry the fifty (50) year return frequency rainfall event.
b. The performance of all channels, flumes, or swales during the one hundred (100) year return frequency rainfall event must be indicated.
3. Storm sewers and appurtenances shall have the following performance criteria:
a. The combination of storm sewer and its overflow outlet shall have the capacity to convey the ten (10) year return frequency rainfall event within the drainage easement(s) or right(s)-of-way.
b. The performance of the overflow outlet(s) for the storm sewer system during the one hundred (100) year return frequency rainfall event shall be indicated under the condition that the storm sewer is plugged or inoperative.
c. The minimum velocity is a storm sewer flowing full shall be three (3) feet per second. Velocities less than three (3) feet per second may be approved if properly designed sediment traps which are accessible for maintenance are provided at the upstream end of the sections where the velocity is to be less than three (3) feet per second.
4. Streets with curb and gutters shall have the following performance criteria:
a. Arterial streets shall maintain two (2) clear ten (10) foot lanes of traffic during the twenty-five (25) year return frequency rainfall event.
b. Drainage on collector streets shall not exceed two (2) inches in depth at the crown of the street during the twenty-five (25) year return frequency rainfall event.
c. Drainage on residential streets shall not exceed three and one- half (3½) inches in depth at the crown of the street during the twenty-five (25) year return frequency rainfall event.
5. Streets without curb and gutters shall have the following performance criteria:
a. Arterial streets shall maintain two (2) clear ten (10) foot lanes of traffic during the twenty-five (25) year return frequency rainfall event.
b. Residential or collector streets shall maintain two (2) clear eight (8) foot lanes of traffic during the twenty-five (25) year return frequency rainfall event.
(Ord. No. 02-08, § 5, 5-6-2002)
Drainage systems shall be constructed in full accordance with approved designs and specifications, without variation, except as may be authorized by a change order or field change approved by the City Engineer or other authorized City representative.
A. The developer, land improver, land owner, or legal agent thereof engaging in any land improvement or change covered by this article shall be responsible for any and all construction activity as covered by approved designs, plans, and data.
B. This section shall not be construed to exclude the contractor or his responsible supervisor from providing installations in conformance with the requirements and constraints of this article whether a part of the design documents, or inadvertently excluded.
C. Upon determination and notification by the City Engineer or other responsible City authority that construction or any part thereof is in violation of this article. Such work shall be immediately discontinued and shall not be restarted until corrected.
D. All facilities, structures, and installations made under the provisions of this article shall be constructed in a workmanlike manner and using methods and procedures that shall assure a quality installation. The construction of any drainage system shall conform to the "Oklahoma Department of Transportation Specifications for the Construction of Drainage Systems" as approved by the City Engineer or other authorized City representative, unless specifically approved otherwise by the City Engineer or other authorized City representative. Materials, installations, and facilities that are not of the required quality or conformance shall be repaired or replaced as determined by the City Engineer or other authorized City representative.
E. The contractor shall provide barricades, guardrails, walkways, shoring, warning signs and flashers, and such other measures as deemed necessary to protect workmen; traffic, pedestrians, and any other person near or adjacent to a hazard from injury or damage. Such protection shall be provided upon start of a hazard area operation and shall be fully maintained until there is no longer a hazard and approval has been given for removal of the protection, signing shall be in accordance with Part VI-Traffic Controls for Street and Highway Construction and Maintenance Operations of the current Manual On Uniform Traffic Control Devices. The contractor shall, at his own expense, provide and maintain the appropriate traffic control devices.
F. The structural integrity of all drainage structures shall be maintained during all phases of construction.
G. A construction permit must be obtained from the City according to this section prior to the start of construction any drainage system or improvement which is owned or to be dedicated to the City, is to be constructed on a City right-of-way or easement, is a required "off-site" improvement of the platting process, or is otherwise required by the City. Construction inspections shall be made during and after construction by the City and shall serve as the basis of all approvals or disapprovals.
H. The erosion and sedimentation control plan shall be implemented using the "Best Management Practices" as adopted by the U.S. Soil Conservation Service of McClain County and any subsequent revisions to that document.
I. A flood plan permit is required to be obtained prior to any construction activity within the one hundred (100) year floodplain as required by the flood hazard zoning ordinance.
(Ord. No. 02-08, § 6, 5-6-2002)
A. Any person, firm, or corporation violation any provision of this article shall be fined not less than twenty dollars ($20.00) nor more than one hundred dollars ($100.00) for each offense, a separate offense shall be deemed committed for each day a violation continues.
B. During all construction activity, developers, property owners, and contractors shall be required to keep streets, gutters, inlets, drainage pipes, swales, ditches, drainage channels, and all drainage devices and structures clean and free from debris, sedimentation, soil, and any materials. Any failure to meet this requirement shall, upon notice and failure to immediately correct the notified condition, constitute sufficient ground for stopping all work until correction is completed.
C. Developers, land owners, or their legal agents, upon receipt of notice by the City that repair or maintenance is required within a channel lying within their property, shall be responsible for effecting such repair or maintenance within the time specified, or the City shall have repair and maintenance performed at the expense of the property owner.
(Ord. No. 02-08, § 7, 5-6-2002)