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HomeMy WebLinkAboutOrdinance 1753 Ordinance. 1753 o Acfion Take.n ORDINANCE NO. 1753 AN ORDINANCE OF THE CITY OF NORTH RICHLAND HILLS, TEXAS PROVIDING.FOR DEVELOPMENT OF A DETENTION, RETENTION, OR DECORATIVE DRAINAGE FACILITY IN THE CITY OF NORTH RICHLAND HILLS; DECLARING PURPOSES: STATING SCOPE OF AUTHORITY; DEFINING TERMS; DESCRIBING DESIGN REQUIREMENTS; DESCRIBING THE PLAN REVIEW AND APPROVAL PROCESS; PROVIDING FOR MAINTENANCE; AND PROVIDING AN EFFECTIVE DATE. BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF NORTH RICHLAND HILLS, TEXAS: SECTION I. GENERAL A. Statement of Purpose This Ordinance sets forth the mlnlmum requirements for development of a detention, retention, or decorative drainage facility within the city limits of North Richland Hills. The purpose for stating the minimum requirements is to achieve the fOllowing: 1. Protect human life, health, and property. 2. Minimize expenditure of public funds for maintenance of these types of drainage facilities. 3. Help maintain a stable tax base and preserve land values. 4. Preserve the natural beauty and aesthetics of the community. B. Authority Any person, firm, corporation, or business proposing to develop property or improve property within North Richland Hills is subject to the provisions of this ordinance. The ordinances would also apply to anyone wanting to install a detention basin, retention basin, or decorative pond within an existing easement, right-of-way, or FIA/FEMA floodplain. C. Related Ordinances The adoption of this Ordinance does not change any of the previous provisions of the Subdivision Ordinance No. 1579, the Design Manual for Public Works/Utilities (Resolution No. 89-17), or the Flood Damage Prevention Ordinance No. 1471. The Detention/Retention/Decorative Drainage Facility Ordinance shall clarify, allow, and reasonably control the design, construciton, and maintenance requirements of these facilities. D. Definitions Unless specifically defined below, words or phrases used in this ordinance shall be interpreted to have their common usage meaning and give this Ordinance its most reasonable meaning, subject to final interpretation by the Public Works Department. 1 D.l Design Flood - The flood having a one percent chance of being equalled or exceeded in any given year based upon fully developed watershed conditions. This is commonly known as the lOO-year frequency flood, or Base Flood. "Fully developed" conditions shall be based on the most current Future Land Use Assumption Plan for the City of North Richland Hills, or current zoning map; whichever produces the higher runoff coefficients for the drainage area generating the design flood discharge. D.2 Decorative Pond - A still body of water installed on a drainage way. The pond will allow the lOO-year storm runoff to pass through without any detention storage. D.3 Detention Basin - A dry basin or depression constructed for the purpose of temporarily storing stormwater runoff and discharging all of that runoff over time at a rate of flow equal to or less than that which would have occurred prior to installation of the basin. D.4 Federal Emergency Management Agency (FEMA) - The federal agency which has and does assist the Federal Insurance Administration (FIA) administering the national Flood Insurance Program. D.S Federal Insurance Administration (FIA) - The division of the federal government which oversees the Flood Insurance Program with the help of FEMA. D.6 Freeboard - The vertical distance between the design flood surface and the top of an open channel, dam, levee, detention basin, retention basin, or decorative pond. The freeboard allows for wave runup, wind tide, hydraulic jump, or other design conditions without overtopping the structure. D.7 Frequency - The reciproc~l of the exceedance probability. For example, a lOa-year frequency storm is one which has a 1 percent chance of being equalled or exceeded in any year, a la-year storm has 10 percent chance of being equalled or exceeded in any year, and a 5-year storm as a 20 percent chance of being equalled or exceeded in any year. D.8 Hydraulics - Hydraulics, is concerned with the determination of the maximum stage or elevation reached by the waters of a flood at a given location. A flood is said to have occurred when the maximum stage or elevation results in an overflow upon lands that are traditionally useable by man and not normally covered by water. D.9 Hydrology - Hydrology is concerned with the magnitude and frequency of the flood flow. The magnitude of the flood flow is the statement of the quantity of water that results from a given storm, whereas, the frequency is the statement of the average return or occurrence of a flood event. D.lO Inflow Hydrograph - Inflow hydrographs are used to determine the stormwater flow volume into a detention basin, retention basin, or 2 decorative pond. A hydrograph describes the variation in flow rate over a fixed period of time. D.ll Normal Pool Elevation - The level at which a decorative pond or retention basin was designed to be prior to .a rainfall/runoff event. In a decorative pond, this elevation will be the flowline elevation of the outlet control structure. In a retention basin this elevation will be the water surface of the conservation pool. D.12 Open Channel - A channel, branch, creek, or stream in which water flows with a free surface. D.13 Pond - A still bOdy of water located on the surface of the earth. D.14 Rational Formula - A means of relating runoff from an area and the intensity of the storm rainfall as defined in the Design Manual for Public Works/utilities Department. D.15 Retention Basin - A pond which has been designed to have both a conservation pool for holding water indefinitely and a flood storage pool for storing stormwater runoff on a temporary basis for the purpose of reducing the peak discharge from the basin. D.16 Surface Water - Surface water or sheet flow is water on the surface of the ground, the source of which is so temporary or limited that it cannot maintain for any considerable time a stream or body of water having a well defined and established existence. Surface water is derived from falling rains and melting snows, and continues to be such until it reaches some well defined channel in which it concentrates and flows with other waters, whether derived from the surface or springs; and then it becomes the running water of a stream, and ceases to be surface water. D.l? Swale - A shallow waterway. Swales are required above underground storm drains with capacity, along with the storm drain, to carry a lOO-year frequency storm. The City's Design Manual requires that such swales shall be concrete lined. D.18 Time of Concentration - The estimated time in minutes required for runoff to flow from the most remote section of the drainage area to the point at which the flow rate is to be determined., D.19 Watercourse - A stream of water of such well defined existence as to make its flow valuable to the owners of land along its course. A "recognized" watercourse is further defined as a channel, creek, or underground storm drain which has at least a la-year conveyance capacity without flooding adjacent property. D.20 Watershed - The area contributing storm runoff to a stream, pond, or drainage system. 3 SECTION II. DESIGN A. General - The design criteria. shown or requirements to be allowed. reviewed and approved by the developer and his engineer. referenced in this section are themlnlmum . Any deviation from this criteria must be Public Works Department for Use by the B. Runoff Calculations Detention/retention facilities or decorative ponds shall be designed based on a lOO-year frequency storm runoff for the upstream drainage watershed area. B.l Rational Method The "rational method" can be used to calculate the runoff rate and volume for drainage areas less than 750 acres. The formula for this method is Q== CIA. B.2 Hydrograph Method The "hydrograph method" will be used to calculate the runoff rate and volume for drainage areas equal to or greater than 750 acres. One of the fOllowing unit hydrograph procedures shall be used. 1. HEC-l developed by the Hydrologic Engineering Center (HEC) of the U.S. Army Corps of Engineers. 2. TR55 developed by the U.S. Department of Agriculture, Soil Conservation Service. Use of other hydrograph methods must be approved by the Public Works Department prior to beginning design. C. Flood Routing Methods The flood routing computer program to be used shall be either HEC-2 from the U.S. Army Corps of Engineers or TR20 from the Soil Conservation Service. Use of other computer program routing methods must be approved by the Public Works Department prior to beginning design. D. Parameters D.1 Inlet The inlet structure shall allow for the upstream lOa-year runoff to be discharged to the pond in a manner which minimizes erosion. D.2 Outlet The outlet structure for detention basin, retention basin, or decorative ponds will be constructed to minimize erosion and allow for the lOO-year storm runoff to be discharged in a controlled manner. An outlet control 4 structure will be installed on detention/retention basins to achieve the design discharge equal to or less than the runoff rate which existed from the watershed prior to this proposed development. On the outlet structur~ for retentioQ,basins or decorative ponds, an emergency outlet valve and pipe shall be installed. The valve and pipe shall be at least eight inches in diameter and meet all City requirements for water system pipe and valves. Installation of the emergency outlet valve and pipe shall allow the basin or pond to be drained to within one foot of its design bottom or closer. D.3 Storage The detention/retention storage basin shall be designed to store that volume required to reduce the discharge rate out of the basin to not more than the runoff rate which existed from the watershed prior to this proposed development which includes the basin. The detention/retention storage volume excluding conservation pool shall drain out completely within 24 hours of the end of a rainfall runoff event. D.4 Freeboard A minimum freeboard of one foot shall be required. This will be the difference in elevation between the lOa-year storm design water surface elevation, plus increased elevation created by wave action, wind tide or hydraulic jump, anywhere on the detention/retention basin or decorative pond and the lowest point on the surrounding embankment within the drainage easement. D.5 Edge Treatments D.5.a Detention Basin No "edge treatments" will be required, but a minimum twelve foot wide, six inch thick reinforced concrete flume with six inch curbs along the entire length of the detention basin bottom will be installed The flume should drain to the outlet on a minimum of 0.50% grade. D.5.b Retention Basin Edge treatments shall be vertical walls made from reinforced concrete a minimum of six inches wide or brick/stone with concrete core a minimum of eight inches in total width will be required around the entire perimeter of the pool. The bottom of the edge treatment will be designed to be below the normal pool elevation (i.e. outlet flowline) as deep as required but no less than eighteen inches and the top of the edge treatment shall be above the normal pool elevation a minimum of twelve inches. The foundation and support edge treatment wall will be designed and sealed by an Registered Professional engineer and shown on the plans. Any deviation from these requirements must be approved by the Director of Public Works. 5 D.5.c Decorative Pond The edge treatment for the decorative pond shall be the same as that for, the retention basin. D.6 Side Slopes The embankment side slopes for the different basins or ponds will be as noted below unless concrete lined. Concrete lined slopes can be 1.5:1 or milder. D.6.a Detention Basin Detention basin slopes shall be 5:1 or milder. D.6.b Retention Basin Retention basin slopes shall be 4:1 below normal pool depth and 5:1 above. D.6.c Decorative Pond Decorative pond slope requirements shall be the same as for retention basin slopes. D.7 Overbank The overbank shall be hydromulched or block sodded with a Public Works Department approved native grass. The grass must be relatively well established prior to final approval of the construction by the City. D.8 Depth The minimum depth of the retention basin or the decorative pond will be four feet from the normal pool elevation to the bottom between the toe of slopes. The maximum depth shall be no greater than 10 feet. The maximum depth the detention storage in a parking lot can be designed for is one foot. For all other detention storage basins, the maximum depth shall not exceed 10 feet. D.9 Velocity The average velocity of flow through the detention basin, retention basin, or decorative ponds shall be no greater than five feet per second. D.10 Erosion Control Erosion control upstream and downstream of the basins or ponds shall be considered in the design. Erosion control systems shall be 6 installed where necessary as determined by the Public Works Department. D.l1 Aeration All retention basins and decorative ponds will require aeration systems be installed. The aeration system will be designed to keep the standing water from stagnating. All electrical service and maintenance costs for an aeration system shall be the Owner/Developer or Homeowners Association's responsibility to pay. D.12 Water Supply Provisions shall be made to keep the water surface elevation in a retention basin or decorative pond at the normal pool elevation. This will require the Developer to submit plans and specifications for installation of a water well or wells. Another alternative is a separate irrigation service connection to the City's water system to provide the water supply to recharge the basin or pond as needed. The cost of the water used to recharge the basin or pond shall be the Owner/Developer or Homeowners Association's responsibility to pay. Recharge design shall comply with all State and Federal requirements. E. Access Ramps and Easements All basins and ponds will be located totally within a drainage easement and require an access ramp from a parking lot or a public street which is made of reinforced concrete and is at least twelve feet wide, six inches thick, with six-inch curbs. A minimum fifteen-foot wide public ingress and egress easement will be dedicated along the access route to the basin or pond. The ramp will extend down into the detention basin to connect with the flume. Slope on the ramp shall not be any steeper than a 6:1. F. Fencing A minimum six-foot high galvanized chain link fence with twelve-foot double swing gates shall be constructed around the entire basin or pond. The fence will be located at the edge of the drainage easement, parking lot, access ramp or headwall whichever is appropriate as determined by the Public Works Department. Fencing will not be required around a parking lot area which is utilized as a detention storage basin. SECTION III. REVIEW AND APPROVAL A. Submittal Requirements Sufficient information should be submitted on all proposed detention basins, retention basins, and decorative ponds. This includes the following items. 7 A.I Hydraulic Study All necessary computer runs should be submitted in a bound and labeled booklet form. This should include backwater curve runs on existing conditions prior to development of the subject property, proposed- existing conditions after development of the subject property, and fully- developed conditions after development of the subject property. A.2 Final Construction Plans Construction plans should be submitted on standard twenty-four by thirty- six inch blueline sheets. The plans will include plan and profile of all the basin or pond with its inlet and outlet structures, edge treatments, fence, and upstream and downstream erosion control. All design calculations and graphs showing the detention or retention storage design must be included in the construction plans. A grading plan for the basin or pond area along with the drainage area map must be included. B. City Review and Approval The normal subdivision review process will be followed. Preliminary construction plans will be submitted with the preliminary plat. Upon Planning and Zoning Commission's approval of the preliminary plat, the final construction plans with final plat can be submitted to the Planning and Zoning Department. The final plat and plans will be reviewed and approved by the Public Works Department and submitted to the Planning and Zoning Commission (P&Z) for their consideration. If the P&Z recommends approval, then the City Council will consider the plat and plans. If the plat and plans are approved by the City Council, then construction can begin subject to any state or Federal review being necessary. C. Federal and State Review and Approval All projects will be reviewed in accordance with the Flood Damage Prevention Ordinance. Those projects which require a Flood Insurance Rate Map revision will be required to comply with the paragraphs contained in this subsection. C.1 Conditional Letter of Map Revision (CLOMR) The Developer's Engineer will submit the necessary hydrologic and hydraulic studies along with an application for a CLOMR. The application will include the preliminary application fee along with all of the support documentation deemed necessary by the City. After review and approval by the City, the application will be forwarded to the appropriate State and Federal agencies. A permit to construct the necessary fill and/or public improvements will not be issued until a favorable response is received from the appropriate State and Federal agencies. 8 C.2 Revision to the current Flood Insurance Rate Map After the items of construction have been installed and inspected by the City, the Developer's Engineer will submit an application for a map ~~vision or ammendment as appropriate. The City'will review the application and supportive documents for compliance with City ordinances. After review and approval by the City, the application and supporting documents will be forwarded to the appropriate State and Federal agencies for review. The City will not grant permission to occupy a new structure within the existing floodplain until a favorable response has been received from the necessary State and Federal agencies. SECTION IV. CONSTRUCTION A. Preconstruct ion Meeting The normal preconstruct ion conference must be held for any project to be constructed in the City. The following items will be required for the basin or pond prior to or at the meeting. * City inspection fees for Public Works construction. Any necessary State, Federal, railroad company, or utility company permits. Owner/Developer Maintenance Covenant. Homeowners Association Deed restrictions (filed copy). * * * B. Erosion Control The Owner and the Contractor are totally responsible for the control of erosion during construction. The Contractor and Owner shall provide all erosion control systems necessary during the construction period in order to minimize the detrimental effect of the sedimentation on downstream property owners and its accumulation in the public rights-of-way and drainage system. C. Landscaping All landscaping must be installed prior to the Public Works Department approving the construction. D. Maintenance Bond A two-year Maintenance Bond on the construction of all basins and ponds and their associated facilities will be required. The Maintenance Bond will be for twenty-percent of the total construction price for the basin or pond facility. E. City Approval The Public Works Department will issue a "letter of approval" for the detention basin, retention basin, or decorative pond after all construction on the pond is complete. No bUilding permits will be issued 9 in a residential subdivision until this approval has been given. commercial, industrial, or multi-family addition, only the permit install the plumbing and foundation will be allowed prior to this approval unless federal or state permits are required. In a to SECTION V. MAINTENANCE RESPONSIBILITIES A. General The maintenance of the detention basin, retention basin, or decorative pond is essential to its proper functioning. This section outlines those maintenance responsibilities with reference to all parties involved. B. Contractor The Contractor is initially responsible for all erosion control and other maintenance items related to the basin or pond construction until it is approved as complete in writing by the City. C. Owner/Developer The Owner/Developer shall execute the Detention/Retention/Decorative Pond Storage Facility prior to the Council approving the plat. An example of the covenant is shown below: OWNER/DEVELOPER COVENANT FOR MAINTENANCE OF DETENTION/RETENTION/DECORATIVE POND STORAGE FACILITY WHEREAS, by plat approved of Addition on , 19____, by the City Council of North Richland Hills; and WHEREAS, a Detention/Retention/Decorative Pond Storage Facility will be constructed for the said addition; and WHEREAS, the owners and developers of the Addition are willing to pay the full cost of construction of the Dentention/Retention/Decorative Pond storage Facility, and arrange for perpetual maintenance of said drainage facility; and WHEREAS, the owners and developers of the Addition, or their heirs and assigns, shall agree to reimburse the City of North Richland Hills for the full cost of maintenance of the said drainage facility in the event that the private owners default on their obligation to maintain the Facility as required by the Public Works Department. WHEREAS, the owners and developers of the Addition also agree to hold the City of North Richland Hills harmless against any claim of damage from the downstream property owners that may result from overflow of the Detention/Retention/ Decorative Pond Facility due to inadequate design, construction or maintenance procedures. NOW, THEREFORE, KNOW ALL MEN BY THESE PRESENTS THAT: 10 , owners of Addition to the City of North Richland Hills agree to pay for the cost of construction of the proposed Detention/Retention/Decorative Pond Storage Facility which shall be constructed in accordance with the City approved plans and specifications~.and shall also agree to provide maintenance of the proposed Detention/Retention/Decorative Pond Storage Facility throughout the full duration of the site construction, and shall further agree to provide continuing maintenance of the Detention/Retention/Decorative Pond Storage Facility after completion of the site development and final approval of the Facility's construction by the Public Works Department. This covenant is made to the City of North Richland Hills, Texas, and shall run-with-the-land and shall be an obligation and charge against said Addition and its present and future owners. This covenant is given in connection with the platting processes of the City in consideration for approval of the plat of Addition on 19 - WITNESS THEIR HANDS this _____ day of ,19_. (for a natural person acting in his or her own right:) STATE OF TEXAS COUNTY OF This instrument was acknowledged before me on (date) by (name or names of person or persons aCknowledging). (Seal) Notary Public Signature My commission expires: (for a corporation:) Notary's Printed Name STATE OF TEXAS COUNTY OF This instrument was acknowledged before me on (date) by (name of officer), (title of officer) of (name of corporation aCknowledging) a (state of incorporation), corporation, on behalf of said corportion. (Seal) Notary Public Signature 11 . My commission expires: Notary's Printed Name The Developer is ultimately responsible throughout the construction phase for maintenance of the basin or pond if the Contractor does not accept responsibility. The Owner/Developer is responsible for maintenance after the City approves construction until a Homeowners Association accepts responsibility. D. Homeowners Association In residential subdivisions where a detention basin, retention basin, or decorative pond is to be constructed, a Homeowners Association (HOA) must be established. The HOA shall collect assessments no less often than once annually. This assessment shall include an amount to be collected and used for maintenance of the basin or pond. The amount shall cover expected annual routine maintenance costs plus creation of a reserve to be used to make major repairs around the basin/pond or to dredge the basin/pond. The reserve will be equal to no less than 20% of the original cost and accumulated over no more than the first five years. The reserve fund shall be replenished within two years after each expenditure. E. Lot Owners The Owner/Developer Maintenance Covenant will be executed by the Owner of the subdivision on which the basin or pond is to be installed and will run-with-the-land. This will be a lien on the property, which will allow the City to collect any monies spent by the City to provide maintenance services for the basin or pond. Ultimately the individual lot owners on which the basin or pond resides will be responsible for maintenance if the HOA dissolves. F. Citt The City will retain the responsibility to insure that the maintenance of a basin or pond is accomplished. The Owner/Developer Covenant authorizes the City to order maintenance be done if the Owner or HOA does not. If the City has to pay for the maintenance costs, it will invoke the lien provision in the Owner/Developer Covenant in order to collect the maintenance expense and any reasonable legal fees incurred. The City is required, by being a member of the National Flood Insurance Program, to assure that all drainage facilities are maintained which are located in the lOa-year flood plain as designated on the Federal Insurance Administration's Flood Insurance Rate Maps (FIRM). SECTION VI. REPEALER That ordinances or any parts thereof in conflict with the terms of this Ordinance shall be and hereby are deemed repealed and of no force or effect provided that such repeal shall be only to the extent of such inconsistency and in all other respects this Ordinance shall be cumulative of other 12 .. ordinances regulating and governing the subject matter covered in this ordinance. SECTION VII. SEVERABILITY CLAUSE Should any portion or part of this Ordinance be held for any reason invalid or unenforceable, the same shall not be construed to affect any other valid portion hereof, but all valid portions hereof shall remain in full force and effect. SECTION VIII. EFFECTIVE DATE That this Ordinance shall become effective immediately from the date of passage and approval. PASSED AND APPROVED, this the _____ day of , 1990. CITY OF NORTH RICHLAND HILLS Tommy Brown, Mayor ATTEST: Jeanette Rewis, City Secretary APPROVED AS TO FORM AND LEGALITY: Rex McEntire, Attorney for City Ordinance No. 1753 was considered by the City Council on August 12, 1991. The City Council approved a motion to send the item to the Planning & Zoning Commission for input and a joint work session beheld with the Council and the Planning and Zoning Commission. A report from the Planning & Zoning Commission was given to the Council during the March 23, 1992 Pre-Council meeting. The Planning & Zoning Commission recommended that it be handled on a case-by-case basis. The consensus of the Council was for the Director of Public Works to develop guidelines for a case-by-case review of detention/retention pond requests. 13