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03-09 - O5387 002895 TOWN OF PROSPER, TEXAS ORDINANCE NO. 03-09 AN ORDINANCE OF THE TOWN OF PROSPER, TEXAS PROVIDING FOR COMPREHENSIVE DRAINAGE AND FLOOD CONTROL IN THE TOWN OF PROSPER: PROVIDING A TITLE; DECLARING THE PURPOSE AND SCOPE; ESTABLISHING STANDARD PROVISIONS FOR STORM DRAINAGE; FIXING RESPONSIBILITY FOR DRAINAGE IMPROVEMENTS; ESTABLISHING ENGINEERING DESIGN REQUIREMENTS; PROHIBITING CONSTRUCTION OVER DRAINAGE FACILITIES OR IN FLOOD PLAIN; PROVIDING FOR STORM WATER STORAGE; PROVIDING FOR BUILDING OR STRUCTURE SET -BACK REQUIREMENTS; FIXING DUTIES OF THE TOWN ENGINEER AND PROVIDING FOR AN APPEAL TO THE TOWN COUNCIL; PROHIBITING THE ISSUANCE OF BUILDING PERMITS FOR NON-COMPLIANCE; PROVIDING FOR CONTRACTOR MAINTENANCE GUARANTEE; PROVIDING SAVINGS, REPEALING AND SEVERABILITY CLAUSES; PROVIDING A PENALTY; PROVIDING FOR AN EFFECTIVE DATE OF THIS ORDINANCE AND PROVIDING FOR THE PUBLICATION OF THE CAPTION HEREOF. WHEREAS, the Town Council of the Town of Prosper, Texas ("Town Council") has investigated and determined that it would be in the best interest of the Town of Prosper, Texas (the "Town") and its inhabitants to provide comprehensive drainage and flood control; and WHEREAS, the Town Council finds that controlling drainage and flood waters in the Town will help protect the health, safety and welfare of the citizens of the Town. NOW, THEREFORE, BE IT ORDAINED BY THE TOWN COUNCIL OF THE TOWN OF PROSPER, TEXAS: SECTION 1: Findings Incorporated. The findings set forth above are incorporated into the body of this Ordinance as if fully set forth herein. SECTION 2: Adoption — Title. This Ordinance is hereby adopted and shall be known as the "Official Drainage and Flood Control Ordinance" of the Town. SECTION 3: Purpose and Scope. The purpose of policies and design standards set forth herein is to insure adequate storm water drainage and flood control within the Town. The policies and standards herein are intended to protect public health and safety, to prevent property damage due to flooding, to equitably distribute the cost of necessary drainage improvements, and to minimize the maintenance cost of drainage facilities constructed. Any development or improvement of property affecting storm drainage and flood control in the Town is subject to the provisions of this Ordinance. Page 1 Town of Prosper Drainage Ordinance 5337l J90 The development of land shall consider all drainage elements normally used in the Engineering Standards of design. STORM WATER DESIGN SHALL CONSIDER THE MAXIMUM RESULTS FROM A 100 YEAR FREQUENCY STORM. THE RELEASE RATE OF STORM WATER SHALL BE SUCH THAT THE FLOWS OF RUNOFF WATER AFTER THE LAND DEVELOPMENT IS COMPLETED SHALL NOT EXCEED THE FLOWS EXISTING BEFORE LAND DEVELOPMENT IS STARTED. IN CASES WHERE THE LAND CONSIDERED FOR DEVELOPMENT IS ADJACENT TO A LAKE AND A DIRECT DISCHARGE SYSTEM CAN BE DIRECTED INTO THE LAKE AREA, THEN THE INCREASED RUNOFF MAYBE ALLOWED TO FLOW WITHOUT CONSIDERATION OF DETENTION SYSTEMS. Where existing development is in place upstream of the land area under consideration for development, provisions shall be made within the engineering design to provide capacities for the potential full flows, which may be created by the upstream properties based on the result of a 100-year rainfall event. All standards of the Corps of Engineers will be followed. The developer or his designee shall certify that all standards of the Corps of Engineers have been met. SECTION 4: Standard Provisions for Storm Drainage. All construction for storm drainage in the development or improvement of real property within the Town shall conform to the following standards and requirements: A. Storm sewer inlets shall be provided along paved streets at such intervals which will limit the depth of flow as follows: SPREAD OF WATER Type of Street Allowable Speed Major Thoroughfare One traffic lane in each direction to remain open Collector Street One moving traffic lane to remain open Residential Street Maximum depth for design storm as shown on Section VI herein (Fig. 2) is curb deep B. A closed storm sewer system shall be required to accommodate a run-off exceeding the street capacity, as provided above, up to and including the design capacity of a seventy two inch (72") concrete pipe. C. An open channel may be permitted to accommodate run-off exceeding the design capacity of a seventy two inch (72") pipe, as provided below: Page 2 Town of Prosper Drainage Ordinance 5387 002897 (1) Channels draining an area with a "CA" factor (coefficient of run-off and drainage area, as used in the hereinafter described "rational formula") of less than 600 shall be concrete lined to the design depth, plus six inch (6") freeboard except that a closed system as provided above may be used. A twenty foot (20) wide access easement shall be provided along at least one side parallel to channel. (2) Channels draining an area with a "CA" factor between 600 and 1,000 shall be improved to a capacity of the 100 year design discharge by excavation, straightening and realignment, as required, and also the construction of a concrete lined channel having a width of not less than the bottom width with concrete lined to a depth of at least two feet (2'). Earthen side slopes shall be no steeper then 4:1, horizontal to vertical, and shall be sodded to prevent erosion. (3) The setback for the building line shall be based on a minimum of 5 to 1 setback so that a minimum of twenty foot (20) of width access and maintenance strip is provided parallel and adjacent to each side of the top bank of all drainage channels in this section. D. In lieu of the improvements of a channel draining an area with a "CA" factor in excess of 1,000, the Town Council may elect to accept the dedication of all land within the natural 100-year flood plain of the existing drainage channel as a permanent right-of-way. E. The Town may, in its sole discretion, apply the criteria for drainage improvements as set forth in paragraphs A through D above to publicly owned lands. F. Excavation, fill and grading operations within the Town shall be undertaken only after a proper permit has been obtained from the Town. SECTION 5: Responsibility of Owner or Developer for Storm Drainage. A. The owner or developer of property to be developed or used shall be responsible for all storm drainage flowing through or abutting such property. This responsibility includes, but is not limited to, the drainage directed to that property by prior development, as well as the drainage naturally flowing through the property by reason of topography. The owner or developer shall provide for storm drainage in accordance with Section 4 above, at such time as any property is proposed for development. B. Where the improvement or 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 required improvements at the time of development, including, but not limited to, the Page 3 Town of Prosper Drainage Ordinance 5387 002898 dedication of all necessary right-of-way or easements, to accommodate the improvements. C. Where a property owner proposes development or use of only a portion of his property, provision for storm drainage in accordance with Section 4 above shall only be required in that portion of the property proposed for immediate development or use, except as construction or improvements of a drainage facility outside that designated portion of the property is deemed, by the Town's Engineer, essential to the development or use of that designated portion. D. The owner(s) shall dedicate to the Town the required drainage easements. Determination of minimum easement required shall be made by the Town Engineer. E. In the event that an owner or developer desires to impound storm water by excavation, filling or construction of a dam within a property, thereby creating a lake, pond, or lagoon as a part of the planned development of that property, the standard provisions for storm drainage as established in Section 4 of this Ordinance shall not be applicable, provided: 1. an engineering plan for such construction, accompanied by complete drainage design information, prepared by a registered professional engineer, shall have been approved by the Town; 2. the owner or developer agrees to retain, under private ownership, the lake, pond, or lagoon constructed, and to assume full responsibility for the protection of the general public from any health or safety hazards related to the lake, pond, or lagoon constructed; 3. the owner or developer agrees to assume full responsibility for the maintenance of the lake, pond, or lagoon constructed; 4. the obligations herein run with the land, resulting in a continuing obligation of the owner or owners of such land; 5. the requirements of the Texas Water Code pertaining to impoundment of surface water are complied with, including, but not limited to, the design construction and safety of the impounding structure; and 6. on any existing structure, the owner furnishes the Town with a study proposed by a professional engineer for the Town's approval. SECTION 6: Responsibility and Participation of the Town in Storm Drainage Improvements. Page 4 Town of Prosper Drainage Ordinance 5337 to L9_899 A. The Town may, in its sole discretion, participate in the cost of the improvements required by this Ordinance in an amount not to exceed twenty percent (20%). B. The Town may, in its sole discretion, participate in any project of improvements required by this Ordinance by the levy of a special assessment against the lands to be enhanced in value by such improvements. C. The Town may acquire any drainage easement(s) necessary for the improvements required by this Ordinance by dedication, purchase, or condemnation. D. The Town shall, upon acquisition of the drainage easement and the completion of improvements required by this Ordinance, assume full responsibility for the maintenance of such drainage facilities. SECTION 7: En 'nig eering Design. The design of all storm drainage facilities shall be in accordance with the following criteria: A. Design Frequency: Drainage Facility Storm Frequency Closed Storm Sewer Systems 10 yr. with emergency 100 yr. overflow Closed Storm Sewer System at 25 yr. with emergency 100 yr. overflow Street Low Point or Sag Culverts and Bridges 100 yr. Concrete Lined Channels 50 yr. with emergency 100 yr. overflow Earthen Channels 100 yr. B. Computation of storm water run-off shall be by the "rational method", which is based on the principle that the maximum rate of run-off from a given drainage area for an assumed rainfall intensity occurs when all parts of the area are contributing to the flow at the point of discharge. The formula for calculation of run-off by the "rational method" is: Q = CIA, where Q = the maximum rate of discharge, expressed in cubic feet per second. C = a run-off coefficient which varies with the topography, land use and moisture content of the soil at the time the run-off producing rainfall occurs. This run-off coefficient shall be based on the ultimate use of the land as recommended by the Master Plan for the Town and shall be selected from Table I herein on the basis of the use shown on the land use and zoning map of the Comprehensive Zoning Ordinance for the Town. If an area has had a change of zoning to give the area Page 5 Town of Prosper Drainage Ordinance 5387 002900 land use for which the "C" in Table II is higher than the use shown on land use and zoning maps, the higher "C" factor shall be used. For drainage areas where the use of the rational method does not provide reliable data, a Unit Hydrograph Flow Determination shall be used. The use of a Unit Hydrograph calculation will be based upon standard and accepted Engineering Principles normally used in the Profession subject to the approval of the Town Engineer. I = Rainfall intensity in inches per hour from the applicable curves of Figure 1. Time of Concentration or Duration of Rainfall for use in Figure 1 shall be calculated by data shown in Table 2. A = The drainage area, expressed in acres, contribution to the runoff at the point in question. Calculation of the drainage area shall be made from a topographic map, a copy of which shall be submitted with the engineering plans for Town approval. Computation of runoff shall be based on a fully developed drainage area, or watershed, in accordance with the land use projected in the then current comprehensive land use plan for the Town. TABLE I Slope Land Use from Master Plan Value of "C" (Run-off Coefficient) Flat 0% to 1 % Park Areas - No Developable Land 0.20 Park and School Land Tract 0.30 Single Family Residential 0.40 Duplex 0.45 Multiple Family 0.50 Local Business 0.60 Central Business 0.75 Commercial 0.75 Industrial 0.70 Rolling 1 % to 3-1 /2% Park Areas - No Developable Land 0.30 Park and School Land Tract 0.40 Single Family Residential 0.50 Duplex 0.55 Multiple Family 0.60 Local Business 0.70 Central Business 0.80 Page 6 Town of Prosper Drainage Ordinance Commercial 0.80 Industrial 0.75 Rough 3.5% and over Park Areas - No Developable Land 0.35 Park and School Land Tract 0.45 Single Family Residential 0.60 Duplex 0.65 Multiple Family 0.70 Local Business 0.75 Central Business 0.85 Commercial 0.85 Industrial 0.80 Page 7 Town of Prosper Drainage Ordinance 53U 002002 INSERT FIGURE 1 Page 8 Town of Prosper Drainage Ordinance 5383 002903 INSERT FIGURE 2 Page 9 Town of Prosper Drainage Ordinance 5337 002904 INSERT FIGURE 3 Page 10 Town of Prosper Drainage Ordinance 5381 002905 AVERAGE VELOCITY FOR USE IN DETERMINING TIME OF CONCENTRATION TABLE II Description 0% to 3% 4% to 7% 8% to 11 % Over 12% ofWater Course V in fp.s V in fp.s. V in . .s V in f.s Surface Drainage 5 10 15 18 Channels Determine V by Manning's Formula Storm Sewers Determine V by Manning's Formula Average velocity of the runoff for calculating time of concentration or duration of rainfall for use in Figure 1. These average velocities in this table shall be used unless the designer shows calculation of velocity by streets and/or storm sewers. Using the average velocities from this table the designer shall calculate the time of concentration by the following formula unless more data are shown on the plans for calculating time of concentration. T = "Inlet Time" + D / (V*60) Where: T = Time of concentration in minutes for use in Figure 1. D = Distance in feet from point of concentration to upper end of drainage area under consideration. V = Velocity in feet per second from this table or velocity calculated by designer by streets and/or storm sewers. "Inlet Time" = 5 minutes from property zoned for multiple family, local business, central business, commercial, or industrial. "Inlet Time" = 10 minutes for property zoned for parks, schools, single family residential, and duplex. C. The capacity of storm sewers, culverts, bridges, and open channels shall be determined by the use of the Manning's Formula, and the design of the facility derived accordingly. The Manning's Formula is: Q= 1.486 R "' S 1 z *A Where: n Q = Discharge, expressed in cubic feet per second. Page 11 Town of Prosper Drainage Ordinance '387 0019-906 n = Roughness coefficient, based on condition and type of conduit lining. S = slope of hydraulic gradient, expressed in feet of vertical rise per foot of horizontal distance. R = Hydraulic radius (area of flow divided by the wetted perimeter). A = Cross sectional area of flow in conduit, expressed in square feet. D. The construction of all concrete improvements shall be in accordance with the standards set forth in the Paving and Drainage Specifications handbook of the Town. The frequency chart in years (Figure 1), the Inlet Capacity for low point inlets (Figure2), the drainage capacity road sections (Figure 3), are hereby adopted as a part of this Ordinance. E. Complete engineering plans for storm drainage facilities shall be prepared by a professional engineer, registered in the State of Texas, and experienced in civil engineering work. The total cost for such engineering plans and specifications shall be borne by the owner or the developer and shall be furnished to the Town Engineer for his review. F. In any development or improvement of property, the owner may be required to provide, at his sole cost and expense, a preliminary drainage study for the total area to be ultimately developed where the property is located, among any other locations deemed appropriate by the Town Engineer, adjacent to or within an area impacted by drainage within a designated flood prone area as identified by the Federal Emergency Management Agency (FEMA). This study shall be submitted to the Town Engineer prior to approval of the engineering plans for the total development, or any increment thereof. SECTION 8: Construction in Areas Subject to Flooding A. No building or structure shall hereafter be erected or relocated within the 100 year flood plains of the major drainage ways, unless the finished floor elevation of such a building or structure is a minimum of two feet (2') above the high water elevation calculated for the runoff from a rainfall having a design frequency of 100 years. In all other areas subject to flooding, the finished floor elevation shall be a minimum of the high water elevation calculated for the runoff from a rainfall having a design frequency of 50 years and shall not flood within the 100-year frequency. The owner or developer shall furnish, at his sole cost and expense, to the Town Engineer sufficient engineering design information to confirm that the minimum floor elevation proposed complies with this paragraph. B. No building or structure shall be erected or relocated within a flood plain or Page 12 Town of Prosper Drainage Ordinance 5387 002907 drainage channel, which will obstruct the natural flow of water within that flood plain or channel. C. No excavation, filling, or construction of embankment, or landscaping shall be permitted within a flood plain or channel which will obstruct the natural flow of the water within that flood plain or channel, unless sufficient engineering design information is furnished to the Town Engineer, enabling the Town Engineer to determine whether the same will adversely affect flow characteristics within that flood plain or channel and/or result in damage to that or any other nearby property, as solely determined by the Town. SECTION 9: Building or Structure Set -Back Requirement. No building or structure shall hereafter be constructed, reconstructed, or relocated within twenty feet (20') of any open drainage channelso as to insure that an unobstructed width of at least feet (20') is maintained between the top side slope of any such drainage channel and any building or structure. SECTION 10: Construction Over Drainage Facilities. No building or structure shall hereafter be constructed, reconstructed, or relocated over or across any storm drainage facility, unless specifically approved by the Town Engineer pursuant to the criteria established in paragraphs A and B of this section. A. Construction of buildings or structures may be permitted over or across closed drainage systems, to include concrete box culverts or reinforced concrete pipe. Engineering plans and specifications shall be prepared by a Professional Engineer registered in the State of Texas and experienced in civil engineering work. The total cost and expense for such engineering plans and specifications shall be borne by the owner or the developer and shall be furnished to the Town Engineer for his review and approval. B. Construction of pedestrian bridges or small vehicular crossings may be permitted by the Town Engineer. Engineering plans and specifications shall be prepared by a Professional Engineer registered in the State of Texas and experienced in civil engineering work. The total cost and expense for such engineering plans and specifications shall be borne by the developer and shall be furnished to the Town Engineer for his review and approval. SECTION 11: Storage. A. General — Storm water management programs aimed at controlling increased stream water runoff generated by development are a top priority in urban watershed planning. More frequent flooding, increased rates and volumes of storm water runoff, increased stream channel erosion and degradation, increased sedimentation, and increased water pollution are all problems intensified by increased storm water runoff resulting from development. Storage of excess urban storm runoff shall be provided to prevent urban flood damage. Page 13 Town of Prosper Drainage Ordinance 5387 00290E Storm runoff storage with reduced release rates can hold downstream flood flows to within the safe conveyance capacity of the storm sewer and stream system. In most cases it can be shown that storage is more economical than increasing downstream conveyance capacity. Storage facilities shall be planned, designed and provided to assure an effective and efficient operation and maintenance program. Retention and detention are two generalized types of storm runoff storage used to control flooding. Retention storage refers to storm runoff collected and stored for a significant period and released or used after storm runoff has ended. Retention storage usually consists of "wet reservoirs" which often have agricultural, recreational, and/or aesthetic value. Detention storage consists of reducing the rate of runoff for a short period of time to reduce peak flows by controlling the discharge through an outlet structure and by extending the period of runoff. Skillful use of the procedures outlined in this section will assist in providing compliance with the drainage policy requirements set forth herein. B. Storage Classification. Storage can be classified by location as follows: (1) Rainfall Storage. The storage of water near the point of rainfall occurrence or before storm runoff accumulates significantly. Rainfall storage is usually accomplished by roof top ponding, parking lot ponding, property line swale ponding, and small on -site ponds. (2) Runoff storage. Water stored after storm runoff has accumulated significantly and begun to flow in a drainage system. Runoff storage is usually accomplished by off stream storage, channel storage, or onstream storage. C. Rainfall Storage. (1) Roof Tops. The building codes require roof load design for rain and snow. The design load may be converted to equivalent water depth in inches, which can be safely contained on flat roofs. The maximum storage allowed for design purposes shall not exceed this depth unless a building is designed to withstand a greater roof load. The depth of water must be controlled by proper sizing of downspouts and by constructing scuppers through the parapet walls. The possibility of overflows exist and will occur quite often during major storms. Overflow drains shall be used to protect against roof overloading. Periodic inspection and proper maintenance will reduce the possibility and Page 14 Town of Prosper Drainage Ordinance b387 0029109 W the hazards of overflows. Special attention must be given to the water tightness of the roof to assure that no leakage occurs due to the accumulation of water. (2) Parking Lots. Considerable area in urban development is occupied by parking lots. These paved areas must provide adequate storm water detention. There are two general methods of storm water detention that can be utilized on parking areas. One form involves the storage of runoff in depressions constructed near drains or outfall structures. The second method of storm water detention on parking lots consists of using the paved parking areas to channel storm water to grassed or gravel filled areas for maximum infiltration and decrease in overland flow. (3) Recreation Areas. Recreation areas, such as sports fields, generally have a substantial area of grass cover which often has a high infiltration rate. Storm runoff from such fields is minimal. A secondary use of such recreation fields can be made by providing for limited detention storage of runoff from adjacent areas. Since these areas are not used during periods of precipitation, detention ponding should not seriously impede their primary use. The recreation area shall be designed so that it will thoroughly drain. In addition, the vegetation used on the area shall be tolerant of periodic inundation and wetness. (4) Property Line Swales. Subdivision planning and layout requires adequate surface drainage away from buildings. This is obtained by sloping the finished grade in all directions away from the building. The layout often calls for a swale to be located along the back property line, which then drains longitudinally through the block. Where this is used, the design shall include a concrete flume section with baffles to slow the flow of water yet maintain constant point for discharge. Temporary ponding facilities along the rear lot line may include small controlled discharges along the back property line or, if the subsoil conditions are favorable, several inches of rainfall could be expected to percolate into the ground during and after a storm. Prior to planning for property line swale ponding, the engineer should determine that saturation of the subsoil will not have an adverse effect on building foundations. In cases where significant subsoil problems exist, water shall not be ponded or percolated into the ground. Page 15 Town of Prosper Drainage ordinance 5387 002910 (5) Combinations. In many instances, one on -site detention method cannot conveniently or economically satisfy the required or needed amount of storm water storage. Limitations in storage capacities, site development conditions, soils limitations and other related constraints may require that more than one method be utilized. For example, roof top, parking lot, and surface pond storage might all be required to compensate for the increase in runoff due to development of a particular site. Whatever combinations deemed suitable by the Town Engineer may be incorporated into a site development plan. D. Runoff Storag . (1) Offstream Storage. The storage of water in depressed open areas, in reservoirs, and on low lying recreation fields to which storm peak flows are routed is usually termed offstream storage. It is usually characterized by a side channel spillway or overflow from the main channel. (2) Channel Storage. Although all channels inherently store water, channels can be made to attenuate runoff by altering their hydraulic characteristics in a way that will reduce peak flows. Side channels that run essentially parallel to the main stream channel are also a means of temporarily storing water during excessive rainfall events. (3) Onstream Storage. The construction of an embankment across a channel so that a storage pond is formed represents offtream storage. Spillway considerations are important to pass large floods exceeding the storage capacity. Properly protected roadway embankments are well suited for this purpose. E. Multipurpose Use. Rainfall storage and runoff storage systems are most practical when designed for multi -purpose use. For maximum land use efficiency the design engineer must consult early with the Planning Department and the Parks and Recreation Department of the Town. (1) Lower Cost Recreation - Making use of detention storage areas as parks and greenbelts, ball fields and playing fields, satisfies two needs and reduces the cost of each. The mini -park concept, where small recreational areas are provided in neighborhoods within safe walking distances for children, can be a typical joint effort of the drainage design engineer and the planning and recreational staffs of the Town. Provisions must be made for maintenance of such areas. (2) Multi -Use Criteria - The multiple use of storage areas is a field of endeavor where the fervent disciplines shall develop desirable and acceptable criteria fitting the needs of the local community. It is with storage, including both detention and retention storage, that an important Page 16 Town of Prosper Drainage Ordinance 5387 002911 potential exists for the reduction of flooding, drainage costs, and to some degree recreation costs. F. Hydraulic Design Criteria. (1) General. Hydraulic and hydrologic design criteria provide the guidelines for design and construction of storm water storage facilities. These criteria are a necessary part of a storm water management program needed to protect low-lying areas by preventing unacceptable increases in runoff rates as urban development progresses. The engineer shall be familiar with the drainage policy of this ordinance before considering the feasibility of a storm runoff detention facility. Existing land contours of the property should be a consideration in developing the drainage plan. In many instances, storage can be achieved economically by blocking the overland flow of storm water runoff with various land forms, curbs, walls, terraces, and other means. The amounts to designing a drainage system that will minimize the reduction in the critical time of concentration as the property is developed. A drainage project located in a watershed that has a master plan may involve additional considerations, which require review. Consultation with the Town is required to insure compliance with the overall watershed master plan. (2) Design Factors and Procedures. Before proceeding with engineering design of an on -site storage facility, the physical and technical factors shall be identified and the basic design procedures established. Design factors and procedures are as follows: a. The drainage plans for a particular storage facility shall include all property lines, topography, area, location, and all other items necessary to meet policy requirements outlined in the "Drainage Policy for the Town". b. The storage facility shall be designed and located in a manner which insures safety and ease of maintenance. C. The rate of inflow to the storage facility (inflow hydrographs) and all hydrologic considerations must assume ultimate development of the site's contributing area. Several inflow hydrographs shall be prepared to examine their effect on downstream flooding for the various design storm frequencies. The number of inflow hydrographs to be provided may vary but should always adequately describe the range of flows expected for the design storm frequencies. These various design storm inflow hydrographs and an acceptable flood routing procedure will be necessary in Page 17 Town of Prosper Drainage Ordinance sizing the outlet works for the storage facility. An emergency spillway shall be provided to pass runoff that exceeds the design capacity of the detention facility. d. The maximum allowable release rate from a storage facility is based on a 100-year event. However, specific site conditions may require that additional consideration be given a particular area. The Town Engineer shall be contacted to identify special design conditions. The maximum allowable peak flow released from a particular site is selected to comply with the policy section of this manual. In all cases, the maximum release rate shall be calculated using the hydraulic gradient created when the storage area is being utilized at full capacity. Key items to consider in determining the maximum allowable release rate are: i) the peak flow rates for the various design storm frequencies prior to development; ii) the capacity of the downstream storm water channel or storm sewer; iii) compliance with a master plan for the watershed; iv) problems, if any, that are created onsite by the storage of storm water runoff, and v) potential problems created downstream when the onsite storage capacity is fully utilized and the excess runoff flows overland into downstream areas. e. The storm water storage volume required is given by the maximum difference, at any time, between cumulative total inflow volume and cumulative outflow volume measured from the beginning of inflow for a 25-year storm. The maximum allowable release rate is not to be exceeded by the outflow peak discharge. f. The outfall or outlet structures shall be designed on the basis of inlet or outlet control, whichever is applicable. The structures shall be capable of safely and properly passing the flow range of design storm frequencies including the 100-year storm without causing downstream flooding or exceeding the maximum allowable release rate. Outlet works must also pass all of the runoff from the 100- year design storm within a reasonable length of time or a permit may be required from the Texas Commission on Environmental Quality (TCEQ). Wet ponds will in many cases also require a permit from the TCEQ. g. Special attention shall be given to the provision of an emergency or overflow spillway which would pass excess flows greater than those of the 25-year design storm and overflows caused by clogging of the principal outlets. It is advisable to contact the state agencies such as the Texas Water Development Board Page 18 Town of Prosper Drainage Ordinance 5387 002913 (TWDB) and the TCEQ when planning a storage facility in order to meet their criteria. G. Hydraulic Design Methods. (1) General. The two basic methods suggested for predicting the volume of runoff with time and the peak flow rate are the Rational Method and the Standard Method. The Standard Method is best suited for storage analysis of urban runoff but for relatively small drainage areas some form of the Rational Method if generally acceptable. (2) Rational Method Storage Analysis. When designing storage facilities for an area smaller than 400 acres, it is often justifiable to use the Rational Method to compute the design inflow hydrographs. One of the Rational Method techniques has been utilized by the Federal Aviation agency in designing airport drainage facilities. The procedure is presented in "Airport Drainage", prepared by the Federal Aviation Agency (FAA, 1966). The FAA technique is basically a graphical procedure, which represents the cumulative storm runoff volume and the cumulative volume released from the storage facility through an outlet structure as functions of time. The maximum difference between the two volume curves represents the required storage volume of the storage basin. The procedure will consistently result in under designed storage facilities if a constant release rate is assumed from time zero. This is caused by sizing the outlet pipe using the Manning Equation and not recognizing the stage - discharge relationship. A reservoir routing technique unitizing the stage - discharge relationship of the storage facility should be used. It is recommended that in most instances the contributing drainage area not be more than 25 acres when using this technique. A second technique that employs the Rational Method is referred to as the Modified Rational Method Analysis. This technique manipulates the Rational Method to reflect the fact that storms with durations greater than the normal time of concentration for a basin will result in a larger volume of runoff even though the pear discharge is reduced. Even though rainfall intensities and resulting peak discharges associated with longer duration storms are less than those for short duration storms, the inflow may still be considerably greater than the outflow thus requiring more storage than in the case of shorter, higher intensity storms. This approach becomes more valid on progressively smaller basins, The technique should, therefore, be limited to relatively small areas such as parking lots, roof tops, or other upstream facilities with contributing areas less than 25 acres. Page 19 Town of Prosper Drainage Ordinance 5333 002-9114 SECTION 12: Detention Facilities. A. Intent. The Town of Prosper encourages the use of detention basins based on the multi -faceted benefits of the community outlined below: (1) Control of Flood Discharges: The intent of detention basin (storage) design shall be to reduce flood discharges for the ultimate watershed development conditions without increasing peak discharges above the peak discharges for undeveloped watershed conditions. This storage method serves as a key strategy for the storm water management plan. (2) Environment: As development occurs, there is a loss of wildlife and bird life habitat. It is possible to create a natural micro -environment around ponds that can offset this loss of habitat. These "natural" environmental pockets in conjunction with natural open space areas can help maintain the rural setting of the Town. Detention Ponds also benefit downstream water quality by allowing the sedimentation of pollutants. (3) Recreation: Detention basins offer many recreational opportunities in an urban setting; for example, a normally dry detention basin could be used for athletic fields or picnics areas, while the banks of the pond offer valuable park space. (4) Aesthetics: As an integral part of the Town of Prosper, a detention basin needs to blend into the landscape and into the community. Simple yet inexpensive measures, such as gentle side slopes, planting of trees and shrubs, and other landscaping features can transform the detention facility into an attractive amenity for the neighborhood. B. Requirements. (1) Detailed engineering studies of the entire basin shall be required to evaluate the timing of hydrographs from regional and on -site facilities, as well as backwater calculations to determine the effect of the detention/retention facilities on upstream water surface elevations. (2) All detention facility designs shall be performed by a professional engineer registered in the State of Texas and shall meet the requirements of Permanent Rule 31, Texas Administration Code (TAC) Chapter 299, and other requirements, as applicable. (3) The minimum amount of storage volume of the detention basin shall be that volume required to reduce runoff rate to the undeveloped condition rate. Dedicated detention basins shall also include an additional one foot Page 20 Town of Prosper Drainage Ordinance 5387 002915 (1') of freeboard and two feet (2') of sediment storage. The volume of runoff storage for drainage areas greater than 160 acres shall be compared using unit hydrograph procedures. Acceptable unit hydrograph procedures include the Soil Conservation Service Dimension less Unit Hydrograph and Snyder's Unit Hydrograph. Manual methods or use of the computer programs TR20, HEC-1, and NUDALLAS are allowed for runoff hydrograph computation and flood routings. The criteria contained in this section shall serve as the minimum requirements for detention basin design. For drainage areas less than 160 acres, the above methods are recommended; however, an approximate routing method may be used subject to approval of the Town Engineer. (4) The maximum allowable release rate from any site shall be equal to the 100-year peak runoff rate prior to site development. The maximum design release rate may be less. (5) Where storm water management improvements are required in the natural floodway or a permanent greenbelt or open space area, they shall be incorporated into existing lakes, or they shall be designed in as small an area as feasible to create natural contours. Note, however, that detention basins or retention ponds shall be a minimum of one acre in size to allow for proper maintenance, side slopes and outlet work operation. (6) Retention/Detention ponds shall resemble natural ponds; in addition: a. The pond shall expand gradually from the inlet towards the outlet, insuring that there are no "dead zones". That is, water entering the pond gradually spread out and uniformly displaces the water already present in the pond. b. The length -to -width ratio shall be 3 to 1 or greater, to provide a long flow path. C. The average permanent pond depth shall be greater than five (5) feet, where possible. d. A ten (10) to twenty (20) foot wide shallow bench shall be provided along the shores of the permanent pond for safety and to encourage the development of bottom growth in these areas. This vegetation will enhance the biologic treatment characteristics of the pond and also enhance the "natural" appearance of the pond. (7) If several ponds are required, they shall vary in size and shape, and be separated by tree groves, vegetated berms, or similar screening of a natural appearance. Page 21 Town of Prosper Drainage Ordinance 5381 002916 (8) When landscape are required by the Town Engineer, the materials shall enhance wildlife habitat. (9) Where slope erosion protection is needed for the side slopes of a pond, rock or geotextiles are required as approved by the Town Engineer. Exposed concrete surfaces shall be faced with embedded rock or aggregate masonry. Bare concrete shall only be permitted with the express written permission of the Town Council. Side slopes should be no steeper than 4:1 where feasible for reasons of public safety and maintenance. (10) Detention facilities of less than 10 acre-feet of flood storage shall have outlet structures designed for the 100-year frequency storm. Facilities greater than 10 acre-feet of flood storage shall have outlet structures designed for the 10-year and 100-year frequency storms. The release rates shall be such that the flows after land development are no larger than the flows before land development. (11) Outlets shall be provided with a trash rack to prevent plugging with debris and to provide safety to the public. Due to unique design considerations, the Town Engineer may approve alternative outlet design. (12) All Federal, State and County laws pertaining to the impoundment of surface water shall have been compiled with, including, but not limited to, the design, construction and safety of the impounding structure. Copies of any Federal, State or County permits issued for the proposed impoundments shall be submitted to the Town Engineer. (13) All detention/retention facilities shall include an additional one foot (1') of freeboard and two feet (2') of sediment in determining the design flood elevation. (14) Provisions (such as emergency spillways or reinforcing of embankments) shall be made for the occurrence of overtopping or failure of the outlet structure. Under no circumstances should the emergency overflow have a direct path to any buildings or other structures used for human occupancy, commerce, or industry. Details of these provisions shall be supplied to the Town Engineer for approval. (15) The flood storage volume of detention/retention facilities shall be designed to empty in a maximum of 12 hours if said facilities are to be considered an erosion/pollution control facility. (16) Where required by the Town Engineer, the placement of aerators and/or the stocking of retention ponds with fish shall be used to control algae growth and/or insects. Page 22 Town of Prosper Drainage Ordinance 5387 002917 (17) Inlet structures shall be designed to both dissipate the flow energy and drop the inflow elevation to below that of the pond's water surface or basin's flow line. SECTION 13: Duties of the Town and Appeal to the Council. The interpretation of the criteria herein above set forth in this Ordinance shall be made by the Town Engineer. Any person adversely effected by the decision of the Town Engineer may, within ten (10) days from the date of such decision, file an appeal in writing to the Town Council. Such appeal shall be filed with the Town Engineer and the Town Secretary and shall define the specific areas of controversy. The Town Council will attempt to hear any such appeal within thirty (30) days from the date it is received by the Town Engineer and Town Secretary. SECTION 14: Building Permits to be Withheld. No Building Permit shall be issued, nor Certificate of Occupancy approved for any construction, reconstruction, or development upon any land where such construction, reconstruction or development is not in conformity with the requirements and intent of this Ordinance. Anyone who violates any of the terms and provisions of this Ordinance shall, in addition to any other remedies, civil or criminal, be denied a Building Permit and/or a Certificate of Occupancy, until the violation is corrected. SECTION 15: Savings/Repealing Clause. All provisions of any ordinance in conflict with this Ordinance are hereby repealed to the extent they are in conflict; but such repeal shall not abate any pending prosecution for violation of the repealed ordinance, nor shall the repeal prevent a prosecution from being commenced for any violation if occurring prior to the repeal of the ordinance. Any remaining portions of said ordinances shall remain in full force and effect. SECTION 16: Maintenance Guarantee. A Contractor performing any improvement(s) required under this Ordinance shall guarantee the work, which he does against defective workmanship and materials for a period of two (2) years from the date of final acceptance of the work by the Owner/Town. Where defective workmanship and/or materials are discovered requiring repairs to be made under this guaranty, all such repair work shall be done by the Contractor at his own expense within five (5) days after written notice of such defect has been given to him by the Owner/Town. Should the Contractor fail to repair leaks or correct such defective workmanship and/or materials within five (5) days after being notified, the Owner/Town may make the necessary repairs and charge the Contractor with the actual cost of all labor and materials required. The Contractor shall arrange to have his faithful performance bond run for a period of two (2) years after the date of completion of the construction work to cover his guaranty as set forth above. SECTION 17: Severability. Should any section, subsection, sentence, clause or phrase of this Ordinance be declared unconstitutional or invalid by a court of competent jurisdiction, it is expressly provided that any and all remaining portions of this Ordinance shall remain in full force and effect. Prosper hereby declares that it would have passed this Ordinance, and each Page 23 Town of Prosper Drainage Ordinance BI 4141 v " �i '\ *mow R: s'F ► ' vIft I N �_ t: R k .:xr "C��^; .�s: ; j 4.4Y ..�• � '' � ;'t ai .: �.: 9�°" �' � n r $:ij 1z Fn IS gat S. ` 3 .°e s# ,i L ° i$ b t r ;; '• � I. t 'fl � � �� � ,;s a -. ct II ,A rP �'� _ S�'' '�a '*�'t•• �' s-�f. Ju ,,A..A,:.... s ,�^L�r ° i a t t �• z a t ei �' "�V f.f�_ ^*1• a-iY� "s a',-' `fir. t �<� F�'���.`}� � '•'� �R:.�# `'A _I, 4 i .kr- .a- *�.•yP t � � _ .w � �_. 1"" 4 . •�. '�* ' ° '�' 15 , � :. h'�i �6� �f.'S'"; f �''3 �' �$f�ir�, +' w���,�i+�c ' t-�'-�`�, .- •,�h ''I 4 * �y . y�'�.';>•i„ 'd# =ir' <airFfi r°� s`; ,�t R*�' «.-?F, s .��,,i �."<: ,.n .`#''+kd a+s;. �. i�`, s. d 'c'Y i fa vA S ;Vr r al �5 i, c a[� •nt4%p` '�, Q 7g - >,'� 60� 10,.l fii ii, �y �•AY tt °r�., �+i -�a cr pt Jr - 4i`. 5387 002918 section, subsection, clause or phrase thereof irrespective of the fact that any one or more sections, subsections, sentences, clauses and phrases be declared unconstitutional or invalid. SECTION 18: Penalty Provision. Any person, firm, corporation or business entity violating this Ordinance, or as amended, shall be deemed guilty of a misdemeanor, and upon conviction thereof shall be fined a sum not exceeding Two Thousand Dollars ($2,000.00). Each continuing day's violation under this Ordinance shall constitute a separate offense. The penal provisions imposed under this Ordinance shall not preclude Prosper from filing suit to enjoin the violation. Prosper retains all legal rights and remedies available to it pursuant to local, state and federal law. SECTION 19: Effective Date. This Ordinance shall become effective from and after its adoption and publication as required by law. PASSED AND APPROVED by the Town Council of the Town of Prosper, Texas, on this 19* day of MCW01' 2003. O... ,.,,.,, ,0.... 'AT�' : A-NpCORRECTLY r RE AMBER PHILLIPS, Town Secretary J ES DUNMIRE, Mayor Date of Publication: (McKinney Courier Gazette) Page 24 Town of Prosper Drainage Ordinance ••uw.-.w •---....sou.-...... 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SECTION Gutter Drop 2 4 6 8 Depth D (inches) INLET CAPACITY FOF LOW P, INT INLETS Figure 2 9 DATE APPROVED 5387 002922 yrsumPic) , Ry Sol Ph,OX ANY PROVISION HEREIN WHICH REBrICTS THE SALE, RENTAL, OR USE OF THE DESCRIBED REAL PROPERTY BECAUSE OF COLOR OR RACE IS INVALID AND UNENFORCEABLE UNDER FEDERAL LAW (COUNTY OFCOLLIN) (THE STATE OF TEXAS) hereby certify that this instrument was FILED in the File Number Sequence on the date and the time stamped hereon by me; and was duly RECORDED, in the Official Public Recordsof Real PraRany of Collin County, Texas on APR 01 2003 d o� r Brenda Taylor =�o F-i jid ft r %or� pn: ('n in oLM y, c i nney TX Honorable Brenda Taylor Collin County Clerk On Ate 11: 01 a n003 DC.)CMLIM : 2003- 0057603 Recording/Type:GR 63.00 Receipt #: 12195 PUSL = S HER ' S AFF = DAV = T THE STATE OF TEXAS COUNTY OF COLLIN Before me, this undersigned authority, on this day personally appeared Jim Moser who being by me duly sworn, deposes and says that he is the Publisher of The M-cKinney Cburier-Gazette and that said newspaper meets the requirements of Section 201.004, 201.005 and 201.006 of the Texas Government Code, to wit: Printer's Fee $ c� / " . No. e9,3 — U 2 Description: 1. It devotes not less than twenty-five percent (251) of its total column lineage to general interest items; 2. it is published at least once each week; 3. it is entered as second-cIass postal matter in the county where it is published; 4. it has been published regularly and continuously since 1897; and 5. it is generally circulated within Collin County. Publisher further deposes and says that the attached notice was published in said newspaper on the following date(s) to wit; Jim Moser Editor and Publisher SUBSCRIBED AND SWORN BEFORE ME by Jim Moser who ✓ a) is personally known to me, or 2003 AD b) provided the following evidence to establish his/her identity, on this the � day of D. 2003 certify which witness my ha and seal of office. Notary Pu ic, State of Texas (SEAL) COMMISSION EXPIRES ELAVER:NEGRAVESNotate of Texas+� on Expires'`2005 To be published in the McKinney Courier -Gazette on Friday, March 21, 2003. LEGAL NOTICE TOWN OF PROSPER,TEXAS ORDINANCE NO. 03-09 AN ORDINANCE OF THE TOWN OF PROSPER, TEXAS PROVIDING FOR COMPREHENSIVE DRAINAGE AND FLOOD CONTROL IN THE TOWN OF PROSPER; PROVIDING A TITLE; DECLARING THE PURPOSE AND SCOPE; ESTABLISHING STANDARD PROVISIONS FOR STORM DRAINAGE; FIXING RESPONSIBILITY FOR DRAINAGE IMPROVEMENTS; ESTABLISHING ENGINEERING DESIGN REQUIREMENTS; PROHIBITING CONSTRUCTION OVER DRAINAGE FACILITIES OR IN FLOOD PLAIN; PROVIDING FOR STORM WATER STORAGE;' PROVIDING FOR BUILDING OR STRUCTURE SET -BACK REQUIREMENTS; FIXING DUTIES OF THE TOWN ENGINEER AND PROVIDING FOR AN APPEAL TO THE TOWN COUNCIL, PROHIBITING THE ISSUANCE OF BUILDING PERMITS FOR NOW COMPLIANCE; PROVIDING FOR CONTRACTOR MAINTENANCE GUARANTEE, PROVIDING SAVINGS; REPEALING AND SEVERABILITY CLAUSES; PROVIDING A PENALTY; PROVIDING FOR AN EFFECTIVE DATE OF THIS ORDINANCE AND PROVIDING FOR THE PUBLICATION OF THE CAPTION HEREOF.