ORDINANCE NO.____
AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF CATHEDRAL CITY , CALIFORNIA, AMENDING CHAPTER 8.24 OF THE CATHEDRAL CITY MUNICIPAL CODE
RELATING TO FLOODPLAIN MANAGEMENT AND STORMWATER STORAGE FACILITIES WHEREAS, Cathedral City Municipal Code (CCMC) Chapter 8.24 establishes the City’s floodplain management regulations and minimum standards for flood and stormwater drainage, retention, and detention facilities; and
WHEREAS, CCMC Chapter 8.24 has not been comprehensively updated since 2013, and federal, state, and regional agencies —including FEMA, the State Water Resources Control Board, and the Riverside County Flood Control and Water Conservation District—have since adopted updated hydrology data, stormwater regulations, and engineering standards; and WHEREAS, updated rainfall intensity data, including NOAA Atlas 14 and RCFC&WCD Plate E-5.2, now supersede the methods referenced in the existing CCMC and are necessary for accurate hydrologic analysis and stormwater facility design; and WHEREAS, recent intense storm events and associated drainage issues in the City highlight the need for modernized drainage and stormwater storage standards to protect public health, safety, property, and infrastructure; and
WHEREAS, the proposed amendments update the City’s stormwater regulations by incorporating current hydrology practices, enhancing design and safety requirements for stormwater storage facilities, and establishing standards for regional stormwater storage facilities within the City’s jurisdiction; and
WHEREAS, the City Council finds these updates necessary to reduce flood hazards, minimize downstream impacts, and align local regulations with current federal, state, and regional requirements; and
NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF CATHEDRAL CITY DOES ORDAIN AS FOLLOWS:
SECTION 1. AMENDMENT OF SECTION 8.24.010 (STATUTORY AUTHORIZATION,
FINDINGS OF FACT, PURPOSE AND METHODS)
Section 8.24.010 of the Cathedral City Municipal Code is hereby repealed in its entirety and replaced with the updated text set forth in Exhibit A, which is attached hereto and incorporated herein by this reference.
SECTION 2. AMENDMENT OF SECTION 8.24.020 (DEFINITIONS)
Section 8.24.020 of the Cathedral City Municipal Code is hereby repealed in its entirety and replaced with the updated text set forth in Exhibit B, which is attached hereto and incorporated herein by this reference.
SECTION 3. AMENDMENT OF SECTION 8.24.070 (STORM WATER STORAGE FACILITIES) Section 8.24.070 of the Cathedral City Municipal Code is hereby repealed in its entirety and replaced with the updated text set forth in Exhibit C, which is attached hereto and incorporated herein by this reference.
SECTION 4. SEVERABILITY
If any chapter, section, subsection, subdivision, sentence, clause, phrase, or portion of this ordinance is held invalid or unconstitutional by a court of competent jurisdiction, such decision shall not affect the validity of the remaining portions.
The City Council declares that it would have adopted this ordinance, and each part thereof, irrespective of any portion being declared invalid.
SECTION 5. POSTING
Within fifteen (15) days after passage, the City Clerk shall post this ordinance in at least three (3) public places and shall certify to its adoption and posting as required by law.
SECTION 6. EFFECTIVE DATE
This ordinance shall take effect thirty (30) days after its adoption.
SECTION 7. CERTIFICATION
The foregoing ordinance was approved and adopted at a meeting of the City Council of the City of Cathedral City on the ___ day of __________, 2026, by the following vote:
Ayes:
Noes:
Absent:
Abstain:
_______________________________________
Raymond Gregory, Mayor
ATTEST:
_________________________________
Christina Burton, City Clerk
APPROVED AS TO FORM:
________________________________
Eric S. Vail, City Attorney
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“EXHIBIT A”
8.24.010 Statutory authorization, findings of fact, purpose and methods.
A. Statutory Authorization. The Legislature of the state of California has in Government Code Sections 65302, 65560, and 65800 conferred upon local governments the authority to adopt regulations designed to promote the public health, safety, and general welfare of its citizenry. Therefore, the city council of the city of Cathedral City does hereby adopt the following floodplain management regulations.
B. Findings of Fact.
1. The flood hazard areas of the city of Cathedral City are subject to periodic inundation which results in loss of life and property, health and safety hazards, disruption of commerce and governmental services, extraordinary public expenditures for flood protection and relief, and impairment of the tax base, all of which adversely affect the public health, safety, and general welfare.
2. These flood losses are caused by uses that are inadequately elevated, flood proofed, or protected from flood damage. The cumulative effect of obstructions in areas of special flood hazards which increase flood heights and velocities also contributes to flood losses.
C. Statement of Purpose. It is the purpose of this chapter to promote the public health, safety, and general welfare, and to minimize public and private losses due to flood conditions in specific areas by legally enforceable regulations applied uniformly throughout the community to all publicly and privately owned land within flood-prone, mudslide (i.e., mudflow) or flood-related erosion areas. These regulations are designed to:
1. Protect human life and health;
2. Minimize expenditure of public money for costly flood control projects;
3. Minimize the need for rescue and relief efforts associated with flooding and generally undertaken at the expense of the general public;
4. Minimize prolonged business interruptions;
5. Minimize damage to public facilities and utilities such as water and gas mains; electric, telephone and sewer lines; and streets and bridges located in areas of special flood hazard;
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6. Help maintain a stable tax base by providing for the sound use and development of areas of special flood hazard so as to minimize future blighted areas caused by flood damage;
7. Ensure that potential buyers are notified that property is in an area of special flood hazard; and
8. Ensure that those who occupy the areas of special flood hazard assume responsibility for their actions.
D. General Drainage law principles
1. Downstream property owners shall accept natural drainage flows from the upstream property owners. Neither downstream property owners nor upstream property owners may alter or change the drainage patterns of natural drainage flows in any manner that causes damage or harm to other property owners.
2. Upstream property owners shall not concentrate drainage water where it was not concentrated before without making proper provision for its disposal and without damage to downstream property owners.
3. No property owner shall block, or permit to be blocked, any drainage channel, ditch, pipe, or other water conveyance system. No property owner shall divert drainage water without properly providing for its disposal.
E Methods of Reducing Flood Losses. In order to accomplish its purposes, this chapter includes regulations to:
1. Restrict or prohibit uses which are dangerous to health, safety, and property due to water or erosion hazards, or which result in damaging increases in erosion or flood heights or velocities;
2. Require that uses vulnerable to floods, including facilities which serve such uses, be protected against flood damage at the time of initial construction;
3. Control the alteration of natural floodplains, stream channels, and natural protective barriers, which help accommodate or channel floodwaters;
4. Control filling, grading, dredging, and other development which may increase flood damage; and
5. Prevent or regulate the construction of flood barriers which will unnaturally divert floodwaters or which may increase flood hazards in other areas.
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“EXHIBIT B”
8.24.020 Definitions
Unless specifically defined below, words or phrases used in this chapter shall be interpreted according to their common and ordinary meaning and in a manner that gives this chapter its most reasonable application.
"A zone. " See "Special flood hazard area. "
"Accessory structure" means a structure that is either:
1. Solely for the parking of no more than two cars; or
2. A small, low cost shed for limited storage, less than one hundred fifty square feet and one thousand five hundred dollars in value.
"Accessory use" means a use which is incidental and subordinate to the principal use of the parcel of land on which it is located.
"Alluvial fan" means a geomorphologic feature characterized by a cone or fan-shaped deposit of boulders, gravel, and fine sediments that have been eroded from mountain slopes, transported by flood flows, and then deposited on the valley floors, and which is subject to flash flooding, high velocity flows, debris flows, erosion, sediment movement and deposition, and channel migration.
"Apex" means a point on an alluvial fan or similar landform below which the flow path of the major stream that formed the fan becomes unpredictable and alluvial fan flooding can occur.
"Appeal" means a request for review of the floodplain administrator's interpretation of any provision of this chapter.
"Area of shallow flooding" means a designated AO or AH Zone on the Flood Insurance Rate Map (FIRM) where base flood depths range from one to three feet; a clearly defined channel does not exist; the path of flooding is unpredictable and indeterminate; and velocity flow may be evident. Such flooding is characterized by ponding or sheet flow. "Area of special flood hazard. " See "Special flood hazard area. " "Base flood" means a flood having a one percent (1%) chance of being equaled or exceeded in any given year (also referred to as the "one-hundred-year flood"). The term “base flood” is used throughout this chapter.
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"Base flood elevation (BFE)" means the elevation shown on the Flood Insurance Rate Map for Zones AE, AH, A1-30, VE and V1-V30 that indicates the water surface elevation resulting from a flood having a one percent (1%) or greater chance of being equaled or exceeded in any given year.
"Basement" means any area of the building having its floor subgrade, i.e., below ground level, on all sides.
“Bleed-off rate” means the maximum allowable controlled discharge rate from a detention or retention facility, expressed in cubic feet per second per acre, as specified in this chapter and in the standards established by the city engineer. "Building. " See "Structure. "
“Controlled bleed-off” means the intentional discharge of stormwater from a detention or retention facility at a predetermined, limited rate to a recognized watercourse, storm drain system, or other approved conveyance system, in accordance with city standards. “Detention basin” means a stormwater storage facility designed to temporarily hold stormwater runoff and release it at a controlled rate to reduce downstream peak flows. A detention basin is intended to fully drain within a specified time period after the conclusion of a storm event.
“Developer” means any person, firm, corporation, partnership, or other entity that undertakes, proposes, or causes development to occur on a property, including but not limited to the owner, applicant, or authorized agent. The term “developer” includes a subdivider when a project involves the subdivision of land. "Development" means any man-made change to improved or unimproved real estate, including, but not limited to, buildings or other structures, subdivisions of land (subdivisions), mining, dredging, filling, grading, paving, excavation or drilling operations or storage of equipment or materials. "Encroachment" means the advance or infringement of uses, plant growth, fill, excavation, buildings, permanent structures or development into a floodplain that may impede or alter the flow capacity of the floodplain.
“Energy dissipation” means structural or nonstructural measures designed to reduce water velocity at an outfall or within a drainage facility to prevent erosion, scour, or damage to downstream drainage facilities or natural channels.
"Existing manufactured home park or subdivision" means a manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including, at a minimum, the installation of utilities,
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the construction of streets, and either final site grading or the pouring of concrete pads) is completed before December 4, 1991.
"Expansion to an existing manufactured home park or subdivision" means the preparation of additional sites by the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads). "Flood, flooding, or flood water" means:
1. A general and temporary condition of partial or complete inundation of normally dry land areas from the overflow of inland or tidal waters; the unusual and rapid accumulation or runoff of surface waters from any source; and/or mudslides (i.e., mudflows); and
2. The condition resulting from flood-related erosion.
"Flood Boundary and Floodway Map (FBFM)" means the official map on which the Federal Emergency Management Agency or Federal Insurance Administration has delineated both the areas of special flood hazards and the floodway.
"Flood Insurance Rate Map (FIRM)" means the official map on which the Federal Emergency Management Agency (FEMA)has delineated both the areas of special flood hazards and the risk premium zones applicable to the community. "Flood Insurance Study" means the official report provided by FEMA that includes flood profiles, the Flood Insurance Rate Map, the Flood Boundary and Floodway Map, and the water surface elevation of the base flood.
"Floodplain or flood-prone area" means any land area susceptible to being inundated by water from any source. See "Flood, flooding, or flood water. " "Floodplain administrator" is the community official designated by title to administer and enforce the floodplain management regulations.
"Floodplain management" means the operation of an overall program of corrective and preventive measures for reducing flood damage and preserving and enhancing, where possible, natural resources in the floodplain, including, but not limited to, emergency preparedness plans, flood control works, floodplain management regulations, and open space plans.
"Floodplain management regulations" means this chapter and other zoning ordinances, development regulations, building codes, health regulations, special purpose ordinances (such as grading and erosion control) and other applications of police power which control
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development in flood-prone areas. This term describes federal, state or local regulations in any combination thereof which provide standards for preventing and reducing flood loss and damage.
"Floodproofing" means any combination of structural and nonstructural additions, changes, or adjustments to structures which reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures, and their contents. For guidelines on dry and wet floodproofing, see FEMA Technical Bulletins latest edition.
"Floodway" means 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 one foot. Also referred to as "regulatory floodway. " "Floodway fringe" is that area of the floodplain on either side of the "regulatory floodway" where encroachment may be permitted.
"Fraud and victimization, " as related to Section 8.24.060 of this chapter, means that the variance granted must not cause fraud on or victimization of the public. In examining this requirement, the city council will consider the fact that every newly constructed building adds to government responsibilities and remains a part of the community for fifty to one hundred years. Buildings that are permitted to be constructed below the base flood elevation are subject during all those years to increased risk of damage from floods, while future owners of the property and the community as a whole are subject to all the costs, inconvenience, danger, and suffering that those increased flood damages bring. In addition, future owners may purchase the property, unaware that it is subject to potential flood damage, and can be insured only at very high flood insurance rates. “Freeboard” means the vertical distance between the maximum anticipated water surface elevation within a stormwater detention or retention facility during the design storm event and the top of the basin, embankment, or channel, that is intended to prevent overtopping. “Full-capture trash treatment system” means a stormwater control device, or series of devices, certified by the State Water Resources Control Board Executive Director (or designee) to capture all trash 5 millimeters or larger under the full range of permitted hydraulic operating conditions. A full-capture system screens, traps, or removes trash from stormwater before it enters the municipal separate storm sewer system (MS4) and is typically installed at storm drain inlets, catch basins, or other designated stormwater entry points. Full-capture systems must be installed, operated, and maintained in accordance with applicable NPDES permit requirements.
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"Functionally dependent use" means 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 ship building and ship repair facilities, and does not include long-term storage or related manufacturing facilities.
"Governing body" is the local governing unit, i.e., county or municipality, that is empowered to adopt and implement regulations to provide for the public health, safety and general welfare of its citizenry.
"Hardship" as related to Section 8.24.060 of this chapter means the exceptional hardship that would result from a failure to grant the requested variance. The city council requires that the variance be exceptional, unusual, and peculiar to the property involved. Mere economic or financial hardship alone is not exceptional. Inconvenience, aesthetic considerations, physical handicaps, personal preferences, or the disapproval of one's neighbors likewise cannot, as a rule, qualify as an exceptional hardship. All of these problems can be resolved through other means without granting a variance, even if the alternative is more expensive, or requires the property owner to build elsewhere or put the parcel to a different use than originally intended.
"Highest adjacent grade" means the highest natural elevation of the ground surface prior to construction next to the proposed walls of a structure. “Historic drainage relief route” means the natural or previously established drainage path by which stormwater historically flowed from a property or development site prior to grading or construction, including natural channels, swales, and any previously designed or constructed drainage facilities.
"Historic structure" means any structure that is:
1. Listed individually in the National Register of Historic Places (a listing maintained by the Department of Interior) or preliminarily determined by the Secretary of the Interior as meeting the requirements for individual listing on the National Register;
2. Certified or preliminarily determined by the Secretary of the Interior as contributing to the historical significance of a registered historic district or a district preliminarily determined by the Secretary to qualify as a registered historic district;
3. Individually listed on a state inventory of historic places in states with historic preservation programs which have been approved by the Secretary of Interior; or
4. Individually listed on a local inventory of historic places in communities with historic preservation programs that have been certified either by an approved state
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program as determined by the Secretary of the Interior or directly by the Secretary of the Interior in states without approved programs.
“Historic upstream flows” means stormwater runoff originating from areas upstream of a development site under natural or existing conditions, which must be accommodated by proposed drainage improvements without increasing flood hazards on upstream properties.
“Interception drain” or “terrace drain” means a drainage facility, swale, or constructed conveyance designed to intercept, divert, or redirect stormwater from slopes or upland areas so as to prevent uncontrolled flow into streets, structures, or stormwater basins. “Infiltration rate” means the rate at which surface water penetrates into the soil, expressed in inches per hour, as determined by a geotechnical field-tested double ring infiltrometer or by other site-specific testing approved by the city engineer. "Levee" means a man-made 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" means 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 accord with sound engineering practices.
“Local stormwater facility” means a stormwater detention basin, retention basin, or other on-site stormwater management facility designed to accommodate stormwater runoff generated by an individual development site or a small local drainage area, and not intended to provide citywide, multi-project, or regional hydrologic benefits. Local stormwater facilities are governed by the standards in Section 8.24.070."Lowest floor" means the lowest floor of the lowest enclosed area, including basement. See "Basement."
1. An unfinished or flood-resistant enclosure below the lowest floor that is 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 it conforms to applicable non-elevation design requirements, including, but not limited to:
a. The flood openings standard in Section 8.24.050(A)(3)(c); b. The anchoring standards in Section 8.24.050(A)(1);
c. The construction materials and methods standards in Section
8.24.050(A)(2); and
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d. The standards for utilities in Section 8.24.050(B).
2. For residential structures, all subgrade enclosed areas are prohibited as they are considered to be basements (see "Basement). This prohibition includes below- grade garages and storage areas.
"Manufactured home" means a structure, transportable in one or more sections, which is built on a permanent chassis and is designed for use with or without a permanent foundation when attached to the required utilities. The term "manufactured home" does not include a "recreational vehicle. "
"Manufactured home park or subdivision" means a parcel (or contiguous parcels) of land divided into two or more manufactured home lots for rent or sale. "Market value" is defined in the city of Cathedral City substantial damage/improvement procedures. See Section 8.24.040(B)(2)(a).
“Maximum drawdown rate” means the maximum allowable time within which a stormwater storage facility must fully drain from the peak water level to completely empty, not to exceed thirty-six hours for local facilities unless otherwise specified in this chapter. "Mean sea level" means, for purposes of the National Flood Insurance Program, the National Geodetic Vertical Datum (NGVD) of 1929, North American Vertical Datum (NAVD) of 1988, or other datum, to which base flood elevations shown on a community's Flood Insurance Rate Map are referenced.
“Municipal Separate Storm Sewer System (MS4)” means a conveyance or system of conveyances, including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains, that is owned or operated by a city, county, or other public body and is designed or used for collecting or conveying stormwater. An MS4 does not include combined sewer systems or publicly owned treatment works. The term “MS4” includes all municipal stormwater collection, conveyance, and discharge facilities regulated under the applicable NPDES permit. "New construction, " for floodplain management purposes, means structures for which the "start of construction" commenced on or after December 4, 1991, and includes any subsequent improvements to such structures.
"New manufactured home park or subdivision" means a manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is completed on or after December 4, 1991.
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"Obstruction" includes, but is not limited to, any dam, wall, wharf, embankment, levee, dike, pile, abutment, protection, excavation, channelization, bridge, conduit, culvert, building, wire, fence, rock, gravel, refuse, fill, structure, vegetation or other material in, along, across or projecting into any watercourse which may alter, impede, retard or change the direction and/or velocity of the flow of water, or due to its location, its propensity to snare or collect debris carried by the flow of water, or its likelihood of being carried downstream.
"One-hundred-year flood" or "100-year flood. " See "Base flood. " “One-hundred-year, one, three, six or twenty-four-hour storm event” means a rainfall event having a statistical probability of occurrence of one percent in any year, with total precipitation measured over a one, three, six or twenty-four-hour durations. Precipitation values shall be based on Riverside County Flod Control District Plates E-5.2 or NOAA Atlas (latest edition), whichever is greater.
“Outfall protection” means erosion-control measures installed at the discharge point of a storm drain, pipe, channel, or basin, including riprap, aprons, energy-dissipation structures, or other devices approved by the city engineer to prevent downstream erosion and scour.
“Precipitation level” means the total depth of rainfall used for stormwater design calculations, as determined from the Riverside County Flood Control District hydrologic plates or NOAA Atlas (latest edition).
“Pre-development peak discharge” means the maximum rate of stormwater runoff from a site in its natural, ungraded, or existing condition prior to any development activity, and that shall be used as a baseline for hydrologic analysis and facility design under this chapter. "Program deficiency" means a defect in a community's floodplain management regulations or administrative procedures that impairs effective implementation of those floodplain management regulations.
"Public safety and nuisance" as related to Section 8.24.060 of this chapter, means that the granting of a variance must not result in anything which is injurious to safety or health of an entire community or neighborhood, or any considerable number of persons, or unlawfully obstructs the free passage or use, in the customary manner, of any navigable lake, or river, bay, stream, canal, or basin.
"Recreational vehicle" means a vehicle which is:
1. Built on a single chassis;
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2. Four hundred square feet or less when measured at the largest horizontal projection;
3. Designed to be self-propelled or permanently towable by a light-duty truck; and
4. Designed primarily not for use as a permanent dwelling but as temporary living quarters for recreational, camping, travel, or seasonal use. “Regional stormwater storage facility” means a stormwater detention or retention facility that is designed to collect and manage stormwater runoff from a broad drainage area serving multiple public agencies, development sites, or an entire watershed sub-basin, and that provides area-wide, inter-project, or regional flood control or hydrologic benefits. A Regional stormwater storage facility may be designated by the City in coordination with other local and regional agencies. Regional stormwater facilities are subject to Section
8.24.070(D)."Regulatory floodway" means 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 one foot. "Remedy a violation" means to bring the structure or other development into compliance with state or local floodplain management regulations, or if this is not possible, to reduce the impacts of its noncompliance. Ways that impacts may be reduced include protecting the structure or other affected development from flood damages, implementing the enforcement provisions of the ordinance or otherwise deterring future similar violations, or reducing state or federal financial exposure with regard to the structure or other development.
“Retention basin” means a stormwater storage facility designed to retain stormwater runoff without surface discharge, where stormwater is removed solely through infiltration into the ground or evaporation. Retention basins are intended to store runoff for extended periods to promote groundwater recharge and water quality treatment. Retention basins shall incorporate health, safety, and water quality measures as required by the City. "Riverine" means relating to, formed by, or resembling a river (including tributaries), stream, brook, etc.
“Runoff index number” means the numerical coefficient used to determine stormwater runoff quantities based on land use, soil classification, and hydrologic conditions, as defined in the Riverside County Flood Control District Hydrology Manual, as amended, or other technical publications approved by the City Engineer. "Sheet flow area. " See "Area of shallow flooding. "
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"Special flood hazard area (SFHA)" means an area in the floodplain subject to a one percent or greater chance of flooding in any given year. It is shown on an FHBM or FIRM as zone A, AO, A1-A30, AE, A99, or AH.
"Start of construction" includes substantial improvement and other proposed new development and means the date the building permit was issued, provided the actual start of construction, repair, reconstruction, rehabilitation, addition, placement, or other improvement was within one hundred eighty days from the date of the permit. 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 and/or walkways; nor does it include excavation for a 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. For a substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building. “Stormwater” means water resulting from precipitation events, including rainfall and snowmelt, that flows over land surfaces, rooftops, or other impervious areas and enters the municipal separate storm sewer system (MS4) or natural drainage courses. Stormwater may carry pollutants picked up from land surfaces and is regulated under applicable National Pollutant Discharge Elimination System (NPDES) permit requirements. "Structure" means a walled and roofed building that is principally above ground; this includes a gas or liquid storage tank or a manufactured home. “Subdivider” means any person, firm, corporation, partnership, or entity engaged in the division or development of land into a subdivision, and responsible for the design, construction, grading, or installation of stormwater management facilities required by this code.
"Substantial damage" means:
1. Damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or exceed fifty percent of the market value of the structure before the damage occurred; or
2. Flood-related damages sustained by a structure on two separate occasions during a ten-year period for which the cost of repairs at the time of each event, on
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the average, equals or exceeds twenty-five percent of the market value of the structure before the damage occurred. This is also known as "repetitive loss. " "Substantial improvement" means any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds fifty percent of the market value of the structure before the "start of construction" of the improvement. This term includes structures which have incurred "substantial damage, " regardless of the actual repair work performed. The term does not, however, include either:
1. Any project for improvement of a structure to correct existing violations or state or local health, sanitary, or safety code specifications which have been identified by the local code compliance official and which are the minimum necessary to assure safe living conditions; or
2. Any alteration of a "historic structure, " provided that the alteration will not preclude the structure's continued designation as a "historic structure. " “Tributary drainage area” means the total land area, whether on-site or off-site, that contributes stormwater runoff to a particular drainage facility, structure, or basin. “Underground storage chamber” means a subsurface stormwater storage structure designed to provide temporary storage of stormwater runoff, where stormwater is removed solely through infiltration to promote groundwater recharge and water quality treatment.
Only the internal chamber volume (no storage within surrounding gravel pack or stone voids shall be utilized for volume calculations) shall be credited toward required storage capacity.
"Variance" means a grant of relief from the requirements of this chapter which permits construction in a manner that would otherwise be prohibited by this chapter. "Violation" means the failure of a structure or other development to be fully compliant with this chapter. A structure or other development without the elevation certificate, other certifications, or other evidence of compliance required in this chapter is presumed to be in violation until such time as that documentation is provided. "Watercourse" means a lake, river, creek, stream, wash, arroyo, channel or other topographic feature on or over which waters flow at least periodically. Watercourse includes specifically designated areas in which substantial flood damage may occur. "Water surface elevation" means the height, in relation to the National Geodetic Vertical Datum (NGVD) of 1929, North American Vertical Datum (NAVD) of 1988, or other datum, of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas.
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“EXHIBIT C”
8.24.070 Stormwater storage facilities.
A. 1.Except as noted below, development of all land within the city must include provisions for the management of stormwater runoff from the property which is to be developed, in compliance with this chapter and with Chapter 15.10 of this code, and with the following provisions. Management of stormwater shall consist of constructing storm drain systems and stormwater storage facilities, which includes retention and detention basins. As a minimum, all development will make provisions to store runoff from rainfall events up to and including the one-hundred-year, one-, three-, six-, and twenty-four-hour duration events.
2. For design purposes, the design storm shall be the 100-year storm event that produces the maximum peak volume out of the one-hour, three-hour, six-hour, and twenty- four-hour duration stormwater flow reaching the detention or retention basin when considering infiltration or other basin outflow. Developers proposing development within the City shall prepare runoff/retention calculations utilizing RCFC Hydrology Manual guidance to calculate the required retention capacity for each of the following storm events: one-hour, three-hour, six-hour and twenty-four-hour duration storms. Retention and detention basins shall have a minimum of 1-foot of freeboard between the ‘peak volume’ worst case 100-year water surface level and the top of the basin, and a minimum of 1-foot freeboard between the ‘peak volume’ worst case 100-year water surface level and the inlet elevation of the lowest catch basin, and street gutter flowline, draining into the Retention Basin.
B. The requirement for construction of a detention basin or a retention basin may be waived in the following cases:
1. The runoff has been included in an existing storage facility or in the design of an existing storm drain facility;
2. An application for a building permit to construct a single-family residential structure on an already subdivided or existing legal lot or parcel, not a part of an active development or parcel map;
3. Development which will drain directly into a floodway or a watercourse drainage channel which has been approved by the city engineer, or regional floodway jurisdiction using engineering analyses provided by the developer, as well as approved by applicable regulatory agencies, and that has the capacity and will be constructed to handle the additional runoff flow without increasing the potential for flood damage on any other downstream property;
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4. Development of a parcel under 5,000 sq ft in area where it can be demonstrated by local flood control agency required engineering analyses that no significant increase in the potential for flood damage will be created by the development. C. Stormwater storage facilities shall be designed and constructed according to the procedures and criteria established by the city, and shall comply with the following requirements:
1. The runoff area to be used to compute the stormwater storage requirements for a development shall be the entire area of the development, including any streets, alleys or easements within or abutting the development, and any areas tributary thereto, unless passed through per section 18.24.070 C(17).
2. If possible, storage facilities are to be located so they can intercept the flow from the entire development.
3. If portions of the area cannot drain to a primary storage facility, then additional smaller facilities are to be added for these areas as approved by the director of project review.
4. Individual lot facilities are prohibited except when a clear unobstructed access from a public right-of-way, for maintenance purposes, is conveyed by dedication or easement to the city.
5. No stormwater storage facility shall detain or retain standing water longer than thirty-six hours unless the basin has been designed and constructed to be a permanent body of water with appropriate health, safety and water-quality measures for such a body of water.
6. Stormwater runoff volumes shall be calculated by procedures outlined in the Riverside County Flood Control District Hydrology Manual, as amended. The one- hundred-year, one-, three-, six- and twenty-four hour storm events shall be utilized with runoff index numbers and percent impervious area for land uses established in the Riverside County Flood Control District Hydrology Manual, or in other technical publications as designated by the city engineer. Soils Groups must be obtained by the Riverside County Flood Control Plates C-1.02 through C-1.65 or Web Soil Survey.
Precipitation levels for the one hundred year, one-, three-, six- and twenty-four-hour duration storm events must be obtained from Riverside County Flood Control Plates E-5.2 or NOAA Atlas 14 sources, whichever is greater.
7. Certified Trash Full-Capture Systems: All developments shall comply with applicable National Pollutant Discharge Elimination System (NPDES) permit trash- control requirements. This includes installation, operation, and maintenance of State Water Resources Control Board (SWRCB) Executive Director (or designee)
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certified full-capture trash treatment devices. Full-capture systems shall be installed at storm drain inlets, catch basins, or other approved stormwater entry points to ensure that all trash 5 millimeters or larger is fully screened and prevented from entering the municipal separate storm sewer system (MS4).8. Stormwater storage facilities are to be drained by infiltration and in limited cases, controlled bleed-off, discharge pump, dry well or other types of City-approved injection wells.
Methods which discharge stored stormwater underground by percolation must be in accordance with the approved groundwater master plan and approved in writing by the floodplain administrator.
9. Where controlled bleed-off is onto facilities with limited capacity, such as city streets or storm drains, bleed-off flowrate shall be limited to no more than the flowrate needed to drain the storage facility within 36 hours. Any proposed downstream conveyance from the facility must be first approved in writing by the City Engineer.
10. All retention and detention basins shall be maintained in accordance with the provisions of Chapter 15.10 of this code, or may be dedicated to the city, provided a maintenance district or other similar financing district or mechanism has been established to pay for the ongoing maintenance and care of the basin and related drainage facilities at no cost to the city.
11. If underground storage chambers are to be utilized, the only volume considered for purposes of calculating chamber volumes shall be in the respective chamber volume. Stone void volume shall not be considered or utilized to calculate chamber volume.
12. The maximum Infiltration Rate to be utilized in calculations for determining infiltration system rates shall be 50 percent (50%) of geotechnical field-tested double ring infiltrometer rate, not to exceed 2”/hr. The infiltration rate shall be considered zero unless site-specific data that indicates otherwise is provided.
All retention and detention facilities shall be required to have a maximum drawdown rate of 36 hours to totally evacuate said facility.
13. All exposed retention and detention basins shall be open bottom, with 3” - 6” placed angular rock sides over weed block. For retention and detention basins side slopes less than 6 horizontal: 1 vertical, alternative erosion resistant material may be approved in writing by the city engineer or designee. Retention and detention basins with side slopes steeper than 3:1 will be required to be fenced with materials approved in writing by the City Engineer.
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14. All retention and detention basins shall provide a maintenance access road with a minimum width of 12 feet and a maximum slope of 12%. Retention and detention basins with side slopes having a horizontal-to-vertical ratio greater than 6:1 shall also comply with additional slope-related requirements required by the City Engineer in their discretion. Retention and detention basins shall not exceed 6 feet in depth unless approved in writing by the City Engineer and shall provide a minimum of 1 foot of freeboard.
15. Retention and Detention Basin Depth Marker: All retention and detention basins shall have visible monument markers installed at the basin bottom to indicate the design invert and depth of the basin. At least one depth marker shall be provided in basins less than 200’ in length, with additional markers required for each additional 200’ feet or less in length.
16. The tributary drainage area for which the developer is responsible shall extend to the centerline of adjacent crown street sectioned public streets. The development shall be graded to permit stormwater flow in excess of required retention capacity to flow out of the development through a designated overflow outlet and into the historic drainage relief route. In cases where there is no downstream outlet, retention of 200 percent (200%) of the peak 100-year volume is required.
17. Stormwater drainage historically received from adjoining properties shall be received and retained, or passed through into the historic downstream drainage relief route.
18. The design of the development shall not cause any increase in flood boundaries, flood levels, flood duration, or flood occurrences in any area outside the development.
19. Interception Drains and Terrace Drains shall be designed to provide adequate freeboard based on the maximum peak flow of the 100-year storm event.
Freeboard requirements are as follows:
a. For peak flows (Q) of 10 cfs or greater: a minimum of 1.0 foot of freeboard shall be provided.
b. For peak flows (Q) of less than 10 cfs: a minimum of .5 foot of freeboard shall be provided.
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c. In all cases, the drainage facility shall provide no less than 25 perect (25%) additional capacity above the estimated peak 100-year flow to ensure adequate protection from overtopping.
20. The sizing of grated inlets shall have a factor of safety of 2 (50% clogging of the openings). Pedestrian-rated grates shall have a maximum of a half-inch grate opening. Grates in traffic areas shall be rated (H-20). All traffic, ADA and bicycle rated grate inlets shall be labeled.
21. Pedestrian grates shall be used in all possible path of travel areas. All grates within pedestrian walkways shall be ADA compliant.
22. Outfall protection. All outfalls shall contain the following minimum protective measures:
a. Riprap apron or equivalent erosion protection.
b. Outfalls shall have a minimum length of 10 feet, or 3 times the pipe diameter, whichever is greater.
c. D50 stone size per City Engineer-approved methodology. d. Energy Dissipators shall be designed according to HEC-14 “Hydraulic Design of Energy Dissipators for Culverts and Channels” unless otherwise approved in writing by the City Engineer.
23. Stormwater Plan Requirements:
a. Comprehensive Analysis (All Facilities): All developments shall prepare stormwater plans that shall include the following information:
i. Total drainage area (on-site and off-site contributing areas) ii. Historic drainage patterns and flow paths
iii. Pre-development peak discharge rates
iv. Proposed Downstream Conveyance Systems
1. Proposed capacity may be approved in writing by the City Engineer.
2. Downstream Analysis
a. Impact Assessment: the developer shall conduct a
downstream analysis to:
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i. Identify downstream drainage infrastructure;
ii. Verify adequate capacity for proposed
discharge rates;
iii. Identify potential flooding or erosion
impacts; and
iv. Confirm acceptable outfall location/s.
3. Study Scope: The developer’s analysis shall extend
downstream to:
a. The first encounter with a recognized stream, lake,
or adequately size regional facility; or
b. The point where site represents less than 10 percent (10%)of total drainage area, or a minimum of 1,000
feet downstream, whatever is greater.
4. Improvement Requirements: If the downstream drainage system is inadequate to handle the proposed
development’s drainage flows, the City Engineer may
require that the developer perform one or more of the
following additional measures:
a. Additional on-site detention may be required;
b. Construction of downstream improvements;
c. Utilization of alternative discharge locations;
d. Phased release of flows.
v. All storm drain piping systems 12 inches (12”) or larger shall require design profiles in plans and calculations.
vi. Erosion and sediment transfer studies and other supporting data may be required as determined in the City Engineer’s discretion.
1. Erosion and sediment transfer studies, and other
supporting data shall be required for high-risk topography and soil types. Erosion and sediment transfer studies shall be required in all locations with steep slopes (> 15 percent), highly erodible soils (e.g. silty or sand soils), large exposed
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slopes, alluvial fans that flow to the proposed
development. or where there is evidence of active erosion. b. Additional Requirements for Regional Stormwater Facilities: Applies to facilities designated as “regional” per Section 8.24.070(D) (1) or
8.24.070(D)(2).
i. Upstream Flow Accommodation: Stormwater management
facilities shall be designed to safely pass historic upstream flows without:
1. Increasing floodplain potential on upstream properties;
2. Creating new drainage impacts; or
3. Overtopping critical embankments or structures.
ii. Bypass Design
1. Separate Conveyance: Where feasible as determined by the City Engineer, historic flows from upstream areas shall be:
a. Conveyed in separate channels or pipes;
b. Maintained at pre-development rates and volumes;
and
c. Protected from commingling with on-site controlled
flows
2. Combined Flow Management: Proposed developments
that will combine upstream and on-site flows must comply with the following requirements:
a. The development’s total combined drainage
discharges shall not exceed historic peak flows;
b. The development’s emergency overflow capacity
shall accommodate blockage scenarios; and
c. Upstream flows shall not compromise on-site
retention volume
D. Variances: Exceptions to the requirements of this chapter may be granted only through the variance procedures outlined in § 8.24.060. This section provides the exclusive method
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for addressing rare or unique circumstances where strict compliance would create exceptional hardship without the need for separate discretionary approval by the floodplain administrator or city engineer.
1. Regional Stormwater Storage Facilities (not under jurisdiction of regional stormwater provider): Regional stormwater storage facilities differ from local stormwater storage facilities in that they serve drainage areas larger than a single development and provide regional or multi-project stormwater management benefits. Projects designated by the City as regional stormwater storage facilities shall comply with the stormwater storage facility standards set forth in 8.24.
a. No stormwater storage facility shall detain or retain standing water longer than forty-eight (48) hours unless the basin has been designed and constructed to be a permanent body of water with appropriate health, safety and water-quality measures for such a body of water.
2. Regional Stormwater Storage Facilities (under jurisdiction of regional stormwater provider): The developer is responsible for all coordination with the regional jurisdiction(s) when a stormwater storage facility is designated as a regional stormwater facility by the regional jurisdiction. Where City standards and regional jurisdiction standards differ, the City Engineer shall have the discretion to require more stringent or protective city standards.