A.   Flood hazard areas of the community are subject to periodic inundation which results in loss of life and property, health and safety hazards, disruption of commerce and government services, and extraordinary public expenditures for flood protection and relief, all of which adversely affect the public health, safety, and welfare.

   B.   These flood losses are created by the cumulative effect of obstructions in flood plains which cause an increase in flood heights and velocities, and by the occupancy of flood hazard areas by uses vulnerable to floods and hazardous to other lands because they are inadequately elevated, floodproofed or otherwise protected from flood damage. (Ord. 1997-4, 3-20-1997)

   A.   It is the intent of this chapter to protect the general health, safety and welfare of the public from:

      1.   The hazards and damages of flood from the various drainage areas in the city.

      2.   To provide clean and sanitary channels for runoff.

      3.   To prevent pollution of watershed, streams and natural drainage channels.

      4.   To prevent the encroachment of buildings or improvements on natural drainage channels.

      5.   To equitably apportion the cost of improvements.

      6.   To protect natural scenic areas.

      7.   To provide for the conservation of the natural resources of the area.

All subdivisions of land and all developments or improvements of any character which affect drainage in any portion of the city shall be subject to the provisions of this chapter. This chapter is not intended to repeal, abrogate, or impair any existing easements, covenants, or deed restrictions. However, where the chapter and another ordinance conflict or overlap, whichever imposes the more stringent restrictions shall prevail. (Ord. 1997-4, 3-20-1997)

The degree of flood protection required by this chapter is considered reasonable for regulatory purposes and is based on scientific and engineering considerations. On rare occasions greater floods can and will occur, and flood heights may be increased by manmade or natural causes. This chapter does not imply that land outside the flood plain areas or uses permitted within such areas will be free from flooding or flood damages. This chapter shall not create liability on the part of the city or any officer or employee thereof for any flood damages that result from reliance on this chapter or any administrative decision lawfully made hereunder. (Ord. 1997-4, 3-20-1997)

The following words, terms and phrases, when used in this chapter, shall have the meanings ascribed to them in this section:

ADMINISTRATOR: The federal insurance administrator, to whom the secretary of HUD has designated the administration of the national flood insurance program. Local flood plain administrator means the city manager of the city of Harrah or his designee.

APPEAL: A request for a review of the local flood plain administrator's interpretation of any provision of this chapter.

AREA OF SHALLOW FLOODING: A designated AO, AH, or VO zone on a community's flood insurance rate map (FIRM) with a one percent (1%) chance or greater annual chance of flooding to an average depth of one to three feet (3') where a clearly defined channel does not exist, where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow.

AREA OF SPECIAL FLOOD HAZARD: The land in the flood plain within a community subject to a one percent (1%) or greater chance of flooding in any given year. The area may be designated as zone A on the flood hazard boundary map (FHBM). After detailed rate making has been completed in preparation for publication of the FIRM, zone A usually is refined into zone A, AE, AH, AO, A1-99, VO-30, VE or V.

BASE FLOOD: The flood having a one percent (1%) chance of being equaled or exceeded in any given year.

CRITICAL FEATURE: An integral and readily identifiable part of a flood protection system, without which the flood protection provided by the entire system would be compromised.

DETENTION STORAGE: Consists of reducing the rate of runoff for a short period of time to reduce peak flows by controlling the discharge.

DEVELOPER: The owner of property or his agent engaged in the subdivision or improvement of, or in the construction of structures upon land within the city.

DEVELOPMENT IN FLOOD-PRONE AREAS: Any manmade change to improved or unimproved real estate, including, but not limited to:

   A.   Buildings or other structures.

   B.   Mining.

   C.   Dredging.

   D.   Filling.

   E.   Grading.

   F.   Paving.

   G.   Excavations.

   H.   Drilling operations.

ELEVATED BUILDING: A nonbasement building:

   A.   Built, in the case of a building in zones A1-30, AE, A, A99, AO, AH, B, C, X, and D, to have the top of the elevated floor, or in the case of a building in zone V1-30, VE, or V, to have the bottom of the lowest horizontal structure member of the elevated floor elevated above the ground level by means of pilings, columns (posts and piers), or shear walls parallel to the floor of the water.

   B.   Adequately anchored so as not to impair the structural integrity of the building during a flood of up to the magnitude of the base flood.

In the case of zones A1-30, AE, A, A99, AO, AH, B, C, X, D, "elevated building" also includes a building elevated by means of fill or solid foundation perimeter walls with openings sufficient to facilitate the unimpeded movement of flood waters. In the case of zone V1-30, VE, or V, "elevated building" also includes a building otherwise meeting the definition of "elevated building", even though the lower area is enclosed by means of breakaway walls if the breakaway walls meet the standards of section 60.3(e)(5) of the national flood insurance program regulations.

EXISTING CONSTRUCTION: For the purposes of determining rates, structures for which the "start of construction" commenced before the effective date of the FIRM or before January 1, 1975, for FIRMs effective before that date. "Existing construction" may also be referred to as "existing structures".

50-YEAR FLOOD PLAIN AREA: That maximum area of the flood plain that on the average is likely to be flooded once every fifty (50) years (i.e., that has a 2 percent chance of being flooded each year).

FLOOD HAZARD BOUNDARY MAP (FHBM): The official map furnished by the administrator, on which the administrator has identified the riverine flood plain area having special flood hazards, has provided water surface elevation data for the 100-year flood, and has provided floodway data. This may also be termed the flood boundary and floodway map (FBFM).

FLOOD INSURANCE RATE MAP (FIRM): An official map of a community, on which the federal emergency management agency has delineated both the areas of special flood hazards and the risk premium zones applicable to the community.

FLOOD INSURANCE STUDY: The official report provided by the federal emergency management agency. The report contains flood profiles, water surface elevation of the base flood, as well as the flood boundary floodway map.

FLOOD OR FLOODING: A general and temporary condition of partial or complete inundation of normally dry land areas from:

   A.   The overflow of inland or tidal waters.

   B.   The unusual and rapid accumulation or runoff of surface waters from any source.

FLOOD PLAIN MANAGEMENT: The operation of an overall program of corrective and preventive measures for reducing flood damage, including, but not limited to, emergency preparedness plans, flood control works and land use and control measures.

FLOOD PLAIN OR FLOOD-PRONE AREA: A land area adjoining a river, stream, watercourse or lake which is likely to be flooded.

FLOOD-PRONE MAP: An official map on which federal, state or local agencies have delineated one or more areas subject to flooding, pending receipt of data from the federal insurance administrator; however, when special hazard area designations and water surface elevations have been furnished by the administrator, they shall apply.

FLOOD PROTECTION SYSTEM: Those physical structural works for which funds have been authorized, appropriated, and expended and which have been constructed specifically to modify flooding in order to reduce the extent of the areas within a community subject to a "special flood hazard" and the extent of the depths of associated flooding. Such a system typically includes hurricane tidal barriers, dams, reservoirs, levees or dikes. These specialized flood modifying works are those constructed in conformance with sound engineering standards.

FLOODPROOFING: Any combination of structural and nonstructural additions, changes, or adjustments to properties and structures which reduce or eliminate flood damage to lands, water and sanitary contents of buildings.

FLOODWAY ENCROACHMENT: The lines marking the limits of floodway on official federal, state, and local flood plain maps.

FLOODWAY (REGULATORY FLOODWAY): The channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height.

FUNCTIONALLY DEPENDENT USE: A use which cannot perform its intended purpose unless it is located or carried out in close proximity to water. The term includes only docking facilities, port facilities that are necessary for the loading and unloading of cargo or passengers, and shipbuilding and ship repair facilities, but does not include long-term storage or related manufacturing facilities.

HIGHEST ADJACENT GRADE: The highest natural elevation of the ground surface prior to construction next to the proposed walls of a structure.

LEVEE: A manmade structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide protection from temporary flooding.

LEVEE SYSTEM: A flood protection system which consists of a levee, or levees and associated structures, such as closure and drainage devices, which are constructed and operated in accordance with sound engineering practices.

LOWEST FLOOR: The lowest floor of the lowest enclosed area (including basement). An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access or storage, in an area other than a basement area, is not considered a building's lowest floor; provided that such enclosure is not built so as to render the structure in violation of the applicable nonelevation design requirements of this chapter. Specifically, for all new construction and substantial improvements, fully enclosed areas below the lowest floor that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of flood waters. Designs for meeting this requirement must either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria: A minimum of two (2) openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided. The bottom of all openings shall be no higher than one foot (1') above grade. Openings may be equipped with screens, louvers, or other coverings or devices, provided that they permit the automatic entry and exit of flood waters.

MANUFACTURED HOME: A permanent structure as defined by the zoning regulations. For flood plain management purposes the term "manufactured home" also includes park trailers, travel trailers, and other similar vehicles placed on a site for greater than one hundred eighty (180) consecutive days. For insurance purposes the term "manufactured home" does not include park trailers, travel trailers, and other similar vehicles.

MEAN SEA LEVEL: For purposes of the national flood insurance program, the national geodetic vertical datum (NGVD) of 1929 or other datum, to which the base flood elevations shown on a community's flood insurance rate map are referenced.

MECHANICAL AND UTILITY EQUIPMENT: Any electrical, heating, ventilation, plumbing, and air-conditioning equipment or other service facilities associated with a structure.

NEW CONSTRUCTION: For flood plain management purposes, structures for which the "start of construction" commenced on or after the effective date of a flood plain management regulation adopted by a community.

100-YEAR FLOOD PLAIN AREA: That maximum area of the flood plain that on the average is likely to be flooded once every one hundred (100) years (i.e., that has a 1 percent chance of being flooded each year).

PRIMARY DRAINAGE CHANNELS: All drainage channels, streams or creeks which drain an area of five hundred (500) acres or more, excluding those areas defined as major river channels.

SECONDARY DRAINAGE CHANNELS: All drainage channels, streams, and creeks which drain an area of less than five hundred (500) acres, excluding those areas defined as major river channels.

SPECIAL FLOOD HAZARD MAP: An official map furnished by the administrator, on which the administrator has identified the flood plain area having special flood hazards, but has produced neither water surface elevation data nor data sufficient to identify the floodway.

START OF CONSTRUCTION: Includes substantial improvement, and means the date the building permit was issued, provided the actual start of construction, repair, reconstruction, placement, or other improvement was within one hundred eighty (180) days of the permit date. The actual start means either the first placement of permanent construction of a structure on a site, such as the pouring of slab or footings, the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the placement of a manufactured home on a foundation. Permanent construction does not include land preparation, such as clearing, grading and filling; nor does it include the installation of streets or walkways; nor does it include excavation for basement, footings, piers or foundations or the erection of temporary forms; nor does it include the installation on the property of accessory buildings, such as garages or sheds not occupied as dwelling units or not part of the main structure.

STRUCTURE: A walled and roofed building, including a gas or liquid storage tank, that is principally aboveground, as well as a manufactured home, and includes any building which is used for private residential, business, industrial or religious purposes, or which is occupied by a private nonprofit organization, or which is owned by a state or local government or any agency thereof. The term includes a building while in the course of construction, alteration or repair, but does not include building materials or supplies intended for use in such construction, repair or alteration unless such materials or supplies are within an enclosed building on the premises. The term, when used for determination of detention requirement only, shall not include agricultural buildings, sheds, barns, storage buildings or abandoned buildings of any kind.

SUBSTANTIAL IMPROVEMENT: Any repair, reconstruction, or improvement of a structure, the cost of which equals or exceeds fifty percent (50%) of the market value of the structure either:

   A.   Before the improvement or repair is started; or

   B.   If the structure has been damaged and is being restored, before the damage occurred.

For the purposes of this definition "substantial improvement" is considered to occur when the first alteration of any wall, ceiling, floor, or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. The term does not, however, include either:

   A.   Any project for improvement of a structure to comply with existing state or local health, sanitary, or safety code specifications which are solely necessary to assure safe living conditions; or

   B.   Any alteration of a structure listed on the national register of historic places or a state inventory of historic places.

VIOLATION: The failure of a structure or other development to be fully compliant with the community's flood plain management regulations. A structure or other development without the elevation certificate, other certificates, or other evidence of compliance required in this code is presumed to be in violation until such time as that documentation is provided.

WATER SURFACE ELEVATION: The heights in relation to mean sea level expected to be reached by floods of various magnitudes and frequencies at pertinent points in the flood plains or riverine areas. (Ord. 1997-4, 3-20-1997)

   A.   It is intended by this chapter that the improvements of primary drainage major river channels shall be the long-range responsibility of the developer and the community as a whole, since the developer and the whole community are benefited materially. The developer of land or improvements within an area containing a primary drainage channel shall design, plan and carry out his developments in a manner that will not interfere with or restrict the natural flow, of water or materially change the condition of runoff within the calculated area below the 100-year maximum flood elevation. Increased runoff and changes in primary channels which are created by such developments within primary drainage areas shall be the planning responsibility of the developer and shall be made in accordance with the provisions of this chapter. The improvement of secondary drainage channels shall be the responsibility of the developer, since the primary benefit is to the area served by the secondary channel and not to the community as a whole.

   B.   Where construction of a storm drainage facility is required along a property line common to two (2) or more owners, the owner hereafter proposing development or use of his property shall be responsible for the improvements at the time of development, including the dedication of the necessary easements, to accommodate the improvements. (Ord. 1997-4, 3-20-1997)

   A.   The maximum condition of rainfall for a 50-year frequency shall be used for the purpose of determining all runoff for the sizing of drainage channels and structures, unless otherwise specified herein. The following formula and values shall be used for calculating all stream flow and runoff for the policies and regulations established herein unless otherwise specified herein:

      1.   Runoff from drainage areas of five hundred (500) acres or less shall be determined by the rational formula: Q = AIR

Where:

Q    =    Flow in cubic feet per second

A    =    Area to be drained in acres, determined by field surveys for areas less than one hundred (100) acres, and, by latest government quadrangle maps for larger area

I    =    Percent of imperviousness of the area; may vary between seventy percent (70%) and ninety five percent (95%). Coefficients lower than these indicated values may be used; however, in such instances, individual block calculations will be submitted with plans

R    =    Rate of rainfall over entire drainage area in inches per hour, based on time of concentration and latest government records for the area

      2.   Runoff from drainage acres greater than five hundred (500) acres will be determined by use of accepted engineering principles as approved by the local flood plain administrator.

      3.   The size of closed storm sewers, open channels, culverts, and bridges shall be determined by using the Manning formula which may be modified for use with runoff determined by the rational formula to:

Q = 1.486r2s2A

n

Q    =    Discharge in cubic feet per second

A    =    Cross-sectional area of water in conduit in square feet

r    =    Hydraulic radius of water in conduit

s    =    Mean slope of hydraulic gradient in feet of vertical rise per foot of horizontal distance

n    =    Roughness coefficient

Other design methods may be required to maintain hydraulic grade line below the ground or gutter elevation to eliminate flooding of the inlets or manholes. (Ord. 1997-4, 3-20-1997)

   A.   All primary drainage channels which are located within, or immediately adjacent to, an improvement, development or subdivision shall be protected and improved by the developer as follows:

      1.   All land having an elevation below the 50-year maximum flood elevation for the final improved channel shall be dedicated for the purpose of providing drainage, for public park, or drainage and utility easement use.

      2.   The existing channel lying within or immediately adjacent to the subdivision or parcel of land proposed for development or redevelopment shall be cleaned to provide for the free flow of water, and the channel shall be straightened, widened, and improved to the extent required to prevent overflow, resulting from a 50-year frequency rainfall, beyond the limits of the dedicated drainage easement provided in subsection A1 of this section.

      3.   Site improvement shall provide for the grading of all building pads to an elevation where all building pads will not be subject to overflow from a 100-year frequency flood and in a manner that will provide for a rapid runoff of storm water. Manufactured home placement pads shall be elevated to the level of the 100-year frequency flood. All manufactured homes shall be anchored in accordance with requirements outlined in the federal emergency management agency flood plain management regulations. Substantial improvements to existing structures within the 100-year flood plain will be subject to all regulations and requirements of this code:

         a.   New construction or substantial improvements of residential structures (including manufactured homes) and accessory buildings shall have the lowest floor (including basements) elevated to one foot (1') above the level of the 100-year frequency flood.

         b.   New construction or substantial improvements of nonresidential structures and accessory buildings within the 100-year flood plain must have the lowest floor (including basement) elevated to one foot (1') above the 100-year flood level or floodproofed, including utility and sanitary facilities, up to one foot (1') above the level of the 100-year flood.

         c.   Mechanical and utility equipment for residential or nonresidential structures shall be designed or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

         d.   If a nonresidential structure is intended to be floodproofed, a registered professional engineer or architect shall develop or review structural design, specifications, and plans for the construction and shall certify that the design and methods of construction are in accordance with the accepted standards of practice for meeting the elevation requirements of this chapter. A record of such certificates which includes the specific elevation (in relation to mean sea level) to which such structures are floodproofed shall be submitted to and maintained by the office of the city manager or his designee.

      4.   Whenever channel improvements are carried out, sodding, back sloping, cribbing, and other bank protection shall be designed and constructed to control erosion for the anticipated conditions and flow resulting from a 50-year frequency rainfall.

      5.   A drainage channel shall not be located in a street easement unless it is placed in an enclosed storm sewer except under the following conditions:

         a.   Where a paved street surface at least two (2) lanes wide is provided on both sides of a paved channel so as to provide access to abutting properties.

         b.   Where lots are platted to back up to the street right of way where the drainage channel is located between the rear lot line and the paved street, provided, that there is no access to the rear of the lot from the street and further provided that at no time in the future shall access be allowed or constructed over the open drainage channel to the rear of a lot so platted. For the purpose of these regulations, a lot which sides to a public street is not considered to back up to the street right of way. and

         c.   When a condition outlined in either subsection A5a or A5b of this section is present, adequate space adjacent to the channel shall be dedicated as right of way to provide for maintenance of the paved drainage channel and its unpaved bank.

      6.   Culverts, bridges, and other drainage structures shall be constructed in accordance with the specifications and design criteria of the city when the city shall have present or future maintenance responsibility.

      7.   On the North Canadian River and any other applicable waterways, the regulations of the U.S. army corps of engineers shall be applied whenever these standards are more strict than the regulations in this code. (Ord. 1997-4, 3-20-1997)

   A.   All secondary drainage channels which are within, or immediately adjacent to an improvement, development or subdivision, shall be protected and improved by the developer as follows:

      1.   All land having an elevation below the 50-year maximum flood elevation for the final improved channel shall be dedicated for the purpose of providing drainage, for public park, or drainage and utility easement use.

      2.   Secondary drainage channels which have a primary function of collecting surface water from adjacent properties or intercepting and diverting side hill drainage shall be improved open channels.

      3.   Secondary drainage channels which have a primary function of transporting water through the block or collecting water from cross channels and which have a drainage area of less than forty (40) acres shall be improved with closed storm sewers unless special approval has been given by the city manager for construction of a concrete lined channel. Where the secondary drainage channel has a drainage area of greater than forty (40) acres, an improved open channel or closed storm sewer shall be provided. When the unit area to be drained is less than six (6) acres, the city manager may modify the requirements of the first part of this provision to permit a paved open channel, designated for use as a sidewalk, having a minimum width of four feet (4') and provided with six inch (6") curbs, when designed to drain from the street to a natural stream or improved open channel.

      4.   Site improvement shall provide for the grading of all building pads to an elevation where all building pads will not be subject to overflow from a 100-year frequency flood and in a manner that will provide for the rapid runoff of storm water. Manufactured home placement pads shall be elevated to the 100-year frequency flood elevation. All manufactured homes shall be anchored in accordance with requirements outlined in the federal emergency management agency flood plan management regulations. Substantial improvements to existing structures within the 100-year flood plain will be subject to all regulations and requirements of this chapter. New construction or substantial improvements of residential or nonresidential structures (including manufactured homes) shall have the lowest floor (including basements) elevated to one foot (1') above the level of the 100-year frequency flood. Nonresidential structures and accessory buildings may meet this requirement by floodproofing the structures, including utility and sanitary facilities, up to one foot (1') above the level of the 100-year frequency flood. Mechanical and utility equipment for residential or nonresidential structures shall be designed or located so as to prevent water from entering or accumulating within the components during conditions of flooding. If a nonresidential structure is intended to be floodproofed, a registered professional engineer or architect shall develop or review structural design, specifications and plans for the construction and shall certify that the design and methods of construction are in accordance with the accepted standards of practice for meeting the elevation requirements of this chapter. A record of such certificates which includes the specific elevation (in relation to mean sea level) to which such structures are floodproofed shall be submitted to and maintained by the office of the city manager.

      5.   A drainage channel shall not be located in a street easement unless it is placed in an enclosed storm sewer except under the following conditions:

         a.   Where a paved street surface of at least two (2) lanes is provided on both sides of a paved channel so as to provide access to abutting properties.

         b.   Where lots are platted to back up to the street right of way where the drainage channel is located between the rear of the lot line and the paved street, and further provided that at no time in the future shall access be allowed or constructed over the open drainage channel to the rear of a lot so platted. For the purpose of these regulations, a lot which sides to a public street is not considered to back up to the street right of way.

         c.   When a condition outlined in either subsection A5a or A5b of this section is present, adequate space adjacent to the channel shall be dedicated as right of way to provide for maintenance of the paved drainage channel and its unpaved bank.

      6.   In single-family residential, duplex or manufactured home developments, site grading shall be carried out in such a manner that surface water from each dwelling lot will flow directly to a storm sewer, improved channel, sodded swale, or paved street without crossing more than four (4) adjacent lots.

      7.   Surface water collected in streets shall be diverted to storm drains at satisfactory intervals to prevent overflow of six inch (6") high curbs during 25-year frequency rain for the area and grades involved. Drainage area allowed for surface flow on streets at point of diversion shall not exceed twenty (20) acres, regardless of flow, and the low point in sumps shall be designed or contain runoff from a 50-year frequency flood.

      8.   Drainage easement of satisfactory width to provide working room for construction and maintenance shall be provided for all storm sewers with the minimum width being fifteen feet (15').

      9.   Open channels shall be improved by providing a paved section that will carry the runoff from a rain of 50-year frequency within the lined section and sodded section to carry the additional runoff from a rain of 100-year frequency. Whenever an open improved channel as required or authorized for a secondary drainage channel under the provisions of these regulations and the channel crosses residential lots which have been developed under the planned unit development, or where the channel improvement is to be designed as an area that will be maintained by a property owners' association, the city manager may modify the requirements of the first part of this provision to permit a channel improvement design in keeping with landscape architectural plans, provided all hydraulic requirements to support the overflow resulting from a 100-year frequency rainfall are met in such a manner as to prevent flooding of all building pads. (Ord. 1997-4, 3-20-1997)

   A.   The development of rural acreage subdivisions, that is, one acre or larger lots, shall be carried out in such a manner that surface water from each lot will flow to a swale, channel, natural creek, onto the roadway into a curb and gutter system or to a secondary drainage channel or detention pond. Side ditches parallel to the road will not be permitted, and all roadways must be provided with curb and gutter. Surface water collected at the roadway gutter shall be conveyed either to storm sewer inlets or a suitable secondary drainage channel. The storm sewers and drainage system shall be designed in accordance with the specifications contained in the ordinances and regulations relating thereto. Prior to final plat or building permit approval, the developer shall provide the City with detailed construction plans showing roads, curb and gutter, storm sewer inlets and closed storm sewer piping, secondary drainage channels, and grades, as well as erosion control measures necessary to prevent erosion of any proposed channel construction. These improvements shall include, but not limited to, sodding, channel lining or ditch checks as required to prevent erosion of the proposed or existing channel. These improvements shall be the responsibility of the developer and shall be installed by the developer and inspected by the City prior to issuance of building permits.

   B.   Runoff from a twenty-five (25)-year frequency storm shall be used for the purpose of determining the sizing of roadway storm sewer inlets and piping. Surface water shall be directed to a secondary drainage channel not located within the street right of way as often as the terrain will allow.

   C.   Runoff from a fifty (50)-year frequency storm shall be used for sizing channels, creeks, and any structures that are needed for street crossings.

   D.   Site improvements shall provide for the grading of all building pads to an elevation that will not be subject to overflow from a one hundred (100)-year frequency flood and in a manner that will provide for the rapid runoff of storm water. Manufactured home placement pads shall be elevated to the level of the one hundred (100)-year frequency flood. All manufactured homes shall be anchored in accordance with requirements outlined in the federal emergency management agency flood plain management regulations. Mechanical and utility equipment from residential or nonresidential structures shall be designed and located so as to prevent water from entering or accumulating within the components during conditions of flooding. Substantial improvements to existing structures within the one hundred (100)-year flood plain will be subject to all regulations and requirements of this chapter. The areas projected for inundation by the fifty (50)-year frequency flood shall remain free of all structures and shall be preserved in as natural a condition as possible. The maintenance of channels serving drainage areas of less than five hundred (500) acres shall be the responsibility of the property owner, the adjoining or abutting property owner or owners, or a duly constituted homeowners' association unless such improvements are installed by the developer in accordance with the provisions of these regulations and accepted for maintenance by the City. Drainage areas containing more than five hundred (500) acres shall be improved as outlined in section 12-508 of this chapter. (Ord. 1997-4, 3-20-1997; amd. Ord. 2019-15, - - )

   A.   All development except for the following specific exclusions shall be subject to the detention requirements of this section:

      1.   Single-family residences being constructed either on lots final platted prior to January 1, 1997, or on unplatted properties.

      2.   Two (2) unit or greater housing being constructed either:

         a.   On platted lots containing two (2) acres, or less, or

         b.   On unplatted properties where total ownership prior to January 1, 1997, consisted of two (2) acres or less.

      3.   It is the intent of this section that larger parcels may not be subdivided into smaller parcels through platting or lot splits to qualify for exclusion.

   B.   To facilitate city review and approval of on-site detention solutions, engineering plans and drainage calculations shall be provided to the city for review and approval when filing preliminary and final plats, when applying for approval of a lot split, or when applying for a building permit where no subdivision approval has been required.

   C.   The required volume for storm water detention shall be calculated on the basis of the runoff from a 100-year frequency rainfall of an appropriate duration. This volume of storage shall be provided for the fully developed watershed that is tributary to the area designated for detention purposes. The storm water release rate shall be considered when calculating the storm water storage capacity and the control structure designed to maintain a discharge rate not to exceed the historic rate regardless of the depth of storm water in the storage area.

   D.   Outlet control structures shall be designed as simply as possible and shall require little or no attention for proper operation. Each storm water storage area shall be provided with a method of emergency overflow in the event that a storm in excess of the 100-year frequency occurs. The emergency overflow facility shall be designed to function without attention and shall become a part of the "natural" or surface channel system. Hydraulic calculations shall be submitted to substantiate all design features. Detention storage facilities herein provided for shall not be dedicated to the public for public maintenance unless located on a primary or secondary drainage channel. All private on-site facilities shall be properly maintained by the owner such that they do not become a nuisance. Nuisance conditions shall include, but not be limited to:

      1.   Improper storage resulting in uncontrolled runoff and overflow.

      2.   Stagnant water with concomitant algae growth.

      3.   Insect breeding and odors.

      4.   Discarded debris.

      5.   Safety hazards created by the facility's operation and silting of the facility decreasing the designed storage capacity by twenty percent (20%) or more.

All detention facilities located in private property shall be accessible at all times for inspection.

   E.   Where development of a property presents the threat of increased flooding or damage by runoff to downstream structures, the facilities for storm water runoff control shall be constructed prior to any earthmoving or drainage construction on the project site.

   F.   The construction of the storm sewer water control system shall be accomplished as part of the cost of land development. If the amount of storage capacity can be increased to provide benefit to the municipality, the city may participate in the construction cost. In any event, the city's participation is subject to the availability of funds.

   G.   Exemptions Where No Downstream Flooding Exists.

      1.   In drainage areas where the City has no record of downstream flooding of structures, and development of the subject property using a runoff coefficient of 70 percent would not cause downstream flooding of existing structures, detention will not be required. Detention storage, however, will be required for the increased runoff resulting from development having an imperviousness in excess of 70 percent for all developments on parcels greater than two acres.

      2.   Detention shall not be required in drainage areas where the City has no record of downstream flooding of structures and drainage calculations provided by the developer or the City indicate projected flooding of existing downstream structures would not occur, assuming the drainage basin were totally developed.using the maximum projected land use as inducated in the Comprehensive Plan as a guideline.

   H.   Fee In Lieu of On-Site Detention.

      1.   When it has been determined by the City Manager and City Engineer that alternative methods of protecting downstream properties can be accomplished without causing substantial detriment to the public good, safety or welfare or without being contrary to the spirit, purpose and intent of this chapter, the City may accept a fee in lieu of requiring on-site detention facilities.

      2.   All applications for payment of a fee in lieu of on-site detention requirements shall be submitted to the City Engineer with the following information for review:

         a.   A plot plan drawn to scale showing location, property dimensions, and proposed construction or development including all impervious surfaces.

         b.   A summary showing total impervious surfaces in square feet.

      3.   After receipt of the above and evaluation by the City Engineer, the City may accept payment of a fee in lieu of on-site detention facilities or may deny the application and require on-site detention or other improvement to the stormwater control system.

      4.   Fees to be accepted shall be tendered prior to the issuance of a building permit. Should the impervious surfaces on a given property at the time of application for an occupancy or use permit be less than that stated on the building permit, then the permittee may request that the fees be recalculated, the excess fees refunded to the payee, and the building permit amended. Should the impervious surfaces on a given property be greater than stated on the building permit, additional fees shall be due pursuant to a recalculation of the fees and must be tendered before any occupancy or use permit may be issued.

      5.   Impervious surface shall mean any hard-surfaced areas which prevent or retard the entry of water into the soil in the manner and to the extent that such water entered the soil under natural conditions, or where water is caused to run off the surface in greater quantities or at an increased rate of flow than was present under natural conditions. Impervious surfaces shall include, but are not limited to, rooftops except roof overhangs; sidewalks; paving; driveways; parking lots; walkways; patio areas; storage areas; and asphalt, concrete, gravel, oiled macadam or other surfaces which similarly affect the natural infiltration or runoff patterns of real property in its natural state.

      6.   Impervious surface installed or constructed as a part or portion of a public street or a private or public sidewalk in the public street right-of-way shall not be calculated as a part of the fee collected in lieu of on-site detention.

      7.   Fees accepted shall be deposited in a separate account; fees shall be utilized for the costs and expenses incurred or to be incurred in evaluating, preventing, reducing, eliminating, or attempting to eliminate, prevent, or reduce the known or projected flooding problems in the watershed of the subject property; and shall be utilized to maintain such facilities and stormwater control systems.

      8.   Should adequate fees have been accepted and all existing and projected flooding problems in a given watershed been resolved, on-site detention requirements, and fees in lieu thereof, shall be utilized to maintain stormwater control systems in that watershed.

      9.   The fees in lieu of on-site detention shall be 10.34 cents per square foot of additional impervious area created by the development.

      10.   As used in this Section, the fees tendered hereunder shall be deemed accepted when the funds required are received by the City Treasurer.

      11.   Whenever a property upon which an impervious surface is installed or constructed lies within two different watersheds, the fees shall be proportionately applied based upon the amount of impervious surface within each watershed. Whenever a property upon which an impervious surface is installed or constructed lies within and without a watershed requiring on-site detention facilities, or fees in lieu thereof, the fees shall be accepted and applied based upon the amount of impervious surface within the watershed so requiring.

      12.   It is unlawful for any person to erect, construct, install, enlarge, alter, repair, move, improve, make, put together, or convert any building, structure, improvement, facility, or impervious surface within the City, or cause the same to be done, without first paying any fee in lieu of detention required by this section.

   I.   Flooding and Sedimentation Runoff Prevention Required During Construction.

      1.   In drainage areas with known downstream flooding of structures, or if it is determined that development of subject property will cause or contribute to flooding or sedimentation of existing structures downstream, the developer shall install detention facilities maintaining a discharge rate not to exceed the historical runoff rate prior to development.

      2.   For common drainage locations that serve an area with ten or more disturbed acres at one time, a temporary (or permanent) sediment basin, or equivalent control measures, may be required by city erosion and sediment control regulations.

      3.   After the construction activities have been completed and site has undergone final stabilization, upon the approval of the City Manager structures may be removed. (Ord. 1997-4, 3-20-1997; amd. Ord. 2002-10, 10-24-2002)

   A.   Cost of construction of bridges and culverts at arterial streets and major thoroughfares will be borne by the city. The city may participate in the cost of construction of bridges and culverts at collector streets where the required hydraulic cross section of the bridge or culvert is greater than forty (40) square feet, provided in any event that participation of the city is subject to the availability of funds. Cost to be borne by the city will be determined by the total cost of bridge or culvert divided by the square feet of cross section multiplied by the square feet or required hydraulic cross section less forty (40) square feet.

   B.   Nothing in this section shall be construed to prevent an owner from bearing all costs if he so desires. (Ord. 1997-4, 3-20-1997)

When the planning commission, subsequent to the submission by a developer of a preliminary plat, requires a bridge or culvert at a residential street and the required hydraulic cross section is greater than forty (40) square feet, the city may participate in the cost of construction of the bridge or culvert in the same manner as provided for in these regulations. (Ord. 1997-4, 3-20-1997)

All flow of water across continuous streets or alleys shall be through culverts or bridges. Bridges and culverts shall be sized to accommodate a 50-year frequency rain, without increasing the depth of flow in the channel. Design of bridges and culverts shall conform to city construction specifications. (Ord. 1997-4, 3-20-1997)

Open paved storm drainage channels shall be constructed in accordance with city specifications. Side slopes above the paved sections shall be shaped and sodded on a slope of three (3) horizontal to one vertical or flatter. Fences shall not be erected closer than one foot (1') (measured horizontally) to the edge of the paved section. (Ord. 1997-4, 3-20-1997)

The city reserves the right to require improvements to preclude any backup of tail water inundating any areas outside of the dedicated drainage easements in the subdivision as a result of a 50-year frequency flood. (Ord. 1997-4, 3-20-1997)

The city manager or his designee is designated the local flood plain administrator to administer and implement the provisions of this chapter and appropriate sections of the national flood insurance program regulations pertaining to flood plain management. Prior to authorization of any building permit by the city, the city engineer shall review and approve all such stream flow and runoff calculations as he may require of a developer under the terms of this chapter. The city manager shall have final authority of engineering interpretations of all required 50- and 100-year flood elevations necessary to this chapter. He shall also be responsible for coordinating municipal programs of corrective or preventive measures for reducing flood damage. He shall also notify, in riverine situations, adjacent communities and the state coordinating agency, which is the Oklahoma water resources board, prior to any alteration or relocation of a watercourse, and submit evidence of such notification to the federal emergency management agency. The city engineer shall maintain and hold open for public inspection all records pertaining to the provisions of this chapter. (Ord. 1997-4, 3-20-1997)

   A.   The flood-prone area provisions of this chapter shall apply to all lands, tracts, parcels, or lots in part or in whole which are traversed by, encompassed by, or lying within two hundred feet (200') of the external boundaries of the delineated flood plain for that watercourse as shown on the official flood plain maps or an area deemed flood prone by the local flood plain administrator.

   B.   The location and boundaries of the flood plain are shown upon the "Official Flood Plain Maps" of the city, which are hereby incorporated into this regulation and placed on file in the office of the city clerk. The maps together with everything shown thereon and all amendments thereto, shall be as much a part of this section as if fully set forth and described herein. Application of this chapter may be modified on portions of major river channels, primary channels, and secondary channels only by specific application of "Type 15" or "Type 19" federal insurance administration studies (flood hazard boundary maps) as completed and received from the administrator.

   C.   The boundaries of the flood plain shall be as they appear on the official flood plain maps kept by the city clerk. The boundary lines on the map shall be determined by the use of the scale appearing on the map. When there is conflict between the boundary lines on the map and actual field conditions, the dispute shall be settled by the local flood plain administrator. In all cases the person contesting the location of the boundary shall be given a reasonable opportunity to present his case to the local flood plain administrator and to submit his own technical evidence if he so desires. The local flood plain administrator shall not allow deviations from the boundary line as mapped unless the evidence clearly and conclusively establishes that the mapped location of the line is incorrect.

   D.   The current area of special flood hazard identified by the federal emergency management agency in its scientific engineering publications, with the accompanying flood insurance rate maps, flood boundary floodway maps and any revisions thereto, is hereby adopted by reference and declared to be part of this chapter. (Ord. 1997-4, 3-20-1997)

   A.   The following provisions apply only to lands designated as "flood-prone areas". Special review and measures shall be required to assure protection from flooding as set forth:

      1.   Special Review Of Building Permits In Flood Prone Areas: No permit shall be issued for new development or for the start of new construction or for expansion or additional construction to existing structures for any residential or nonresidential structure or accessory building including manufactured homes, unless the application for permit is submitted accompanied by the following information for review:

         a.   Plans in triplicate drawn to scale showing the nature, location, dimensions, and elevation of the lot, existing or proposed structures, fill, storage of materials, floodproofing measures, and the relationship of the above to the location of the channel.

         b.   A typical valley cross section showing the channel of the stream, elevation of land areas adjoining each side of the channel, cross-sectional areas to be occupied by the proposed development and high water information.

         c.   Plans (surface view) showing elevations or contours of the ground, pertinent structures, fill or storage elevations, size, location, and special arrangement of all proposed and existing structures on the site; location and elevations of streets, water supply, sanitary facilities, photographs showing existing land uses and vegetation upstream and downstream, soil types, and other pertinent information.

         d.   A profile showing the slope of the bottom of the channel or flow line of the stream. This profile shall cover a minimum of three hundred feet (300') upstream and downstream from the property limits unless additional information is requested by the city.

         e.   Specifications for building construction and materials, floodproofing, filling, dredging, grading, channel improvements, storage of materials, water supply and sanitary facilities.

         f.   Copies of all other permits required by state or federal law, including, but not limited to, federal or state water pollution control permits.

         g.   Plans and specifications demonstrating that construction will incorporate methods and practices that minimize flood damage and that material resistant to flood damage will be used for all new construction and substantial improvements.

      2.   Use Restrictions In Designated Floodway: When floodway data has been provided by the federal insurance administrator, the following control measures will apply to that portion of the floodway outside of the dedicated channel as required by this regulation:

         a.   Fill or encroachments are prohibited within the designated floodway that would impair its ability to carry and discharge waters resulting from the 100-year flood;

         b.   The designation of the floodway shall be based on the principle that the area chosen for the floodway be designated to carry the waters of the 100-year flood without increasing the water surface elevation of the flood more than one foot (1') at any point.

         c.   No structure, improvement, or development, temporary or permanent, shall be constructed in the floodway, nor shall any obstruction, fill or storage of goods, materials or equipment be permitted within the floodway.

         d.   Existing nonconforming uses in the floodway shall not be expanded but may be modified, altered or repaired to incorporate floodproofing measures, provided such measures do not raise the level of the 100-year flood.

         e.   An exception to items, subsections A2a through A2d of this section, may be made solely for oil and gas drilling operations performed within the floodways of the North Canadian River, provided the following special requirements are met:

            1.   A special permit, not to exceed one hundred twenty (120) days in duration, shall be required from the city prior to commencement of such operations. A separate permit shall be required for each and every drilling operation and for each subsequent, periodic drilling or maintenance operation performed on each well.

            2.   All permanent well structures or appurtenances shall be elevated to a minimum of one foot (1') above the 100-year flood elevation and located outside the limits of the floodway. A permanent completed wellhead may remain within the floodway, provided that the wellhead be located in a reinforced concrete vault constructed completely belowground with a protective cover so that no portion of the structure extends above the elevation of the natural ground surrounding the well site that existed prior to construction.

            3.   Any fill placed for access road construction or site leveling shall not exceed six inches (6") in height above the existing natural ground elevation. Prior to issuance of the permit, complete hydraulic calculations will be required to demonstrate that no increase in flood elevations will occur due to the proposed fill.

            4.   Well site construction and drilling operations shall be accomplished in a manner which will allow all facilities, equipment and materials to be dismantled, secured, or evacuated from the floodway within a two (2) day time period during anticipated high waters. (Ord. 1997-4, 3-20-1997)

Any person who shall violate any of the provisions hereof shall be deemed guilty of an offense and upon conviction thereof shall be punished as provided in section 1-108 of this code. Each day of violation shall constitute a separate offense. (Ord. 1997-4, 3-20-1997)