Loading...
HomeMy WebLinkAbout1976-09-07 Ordinancemaximum rates . for the discharge or -storm: waters intou,uvai uy of the City for the purpose of promoting the health, safety and general welfare of the population by minimizing or eliminating dangers of flooding to life and =, property. It is further the intent of this ordinance that runoff control devices be, provided as areas of land are developed'.or redevelopedfor urban use. It is not the intent of this ordinance to utilize areas for them-sole.purpose of storing'�or detaining excess storm water, but ,to permit -such areas to be used for'other .compatible urban uses as well. -SECTION-II. DEFINITIONS. A. Storm Water Runoff. Water that results from precipitation.which is: not absorbed by soil or plant material. B. Natural Drainage. Waterwhich flows by gravity in -. channels -:formed:.by. -,the.-surface topography of theearthprior tochanges -made by -:the efforts ofman. C. Excess Storm -Water. --That portion of storm water runoff which exceeds the transportation capacityof.-storm sewers or natural drainage channels serving ,a specific watershed. - - D. Excess Storm Water Passage.- A channel formed in the ground 'surface.to .carry -storm water runoff through aspecific-area. h' h- t rm water runoff E. Storm --Water Runoff Release Rate. The rate , at w is ,s o is released from°dominant -to servient land. -- F. Storm Water Storage Area. -An area designated to temporarily accumulate excess storm water. G. Tributary Watershed. The entire catchment area that contributes storm water runoff to a given point. - H. Dry Bottom Storm Water Storage Area. A facility that is designed. -to --'be:normally _dry and which accumulates-excessstorm water only during,periods`when the restricted storm water runoff release sate is less than the storm water -inflow 'rate. _. I. Wet Bottom Storm Water Storage Area. A facility that contains a body of ordinance No. 76-2 • Page 3 withdrawn. The-hearingshallbe commenced not later than thirty (30) days after the date-on.whichthe petition was filed. After such hearing,, the Housing `Appeals -Board shall sustain, modify or with of of the Director, depending upon its findings. The proceedings draw the > - at such hearing,ineluding the findings, and decision of the Housing,,Appeals._. ced in writing entered as '.a matter of, public Board;. -shall be summarized, redu record'in the office of the'Director. Such.record shall also.include'a copy of - connection with the matter. No hearing shall be every notice or order issued in " valid unless a majority ofthe-Boardispresent and no,decision at a -.hearing:: shall be valid and binding unless reached by a majority of the whole;Board. Following the decision of the Housing Appeals Board, all parties shall be notified. of the decision by delivery. to them of a copy of such decision by personaLservice ' or by certified mail, return receipt requested. Any person aggrieved by the deci- Sion of the Housing Appeals Board may seek relief therefrom in any court of competent t e Housing pBoarded_in.the-.laws of this State. An appeal pursuant tothis-section -shall not stay the effect of the Director's:order unless so ordered by the Housing Appeals Board.. - SECTION VI. APPLICATION... This ordinance-shall.apply<to,"any residential _ development comprising a gross aggregate area of two:(2) acres or more or to any commercial, industrial -,'institutional, governmental, utility or other development, or redevelopment comprising a gross aggregate area of one (1) acre or more. The gross aggregate shall include streets and other dedicatedlands. SECTION VII. EMERGENCY.. Notwithstanding any other provisions of this.. ordinance, whenever in the judgment of ;the Director of Public Works a condition - occurs in''a storm water storage area'that createsa dangerous and imminent, health and safety :hazard,, the Directorshallorder: such action as-shall'be effective _ immediately or in the.time and manner prescribed in the order itself. SECTION VIII GENERAL REQUIREMENTS. A. -Storm Water Release Rate. The controlled -release -rate of_storm water runoffshallnot exceed theexistingsafestorm,water drainage capacity of the downstream system as determined by the Director. The release rate shall be the average value computed with excess storm water representing 50% of the available storage volume. - - - Such release rate shall be computed as:a direct ratio of'. the area of the - tributary watershed and shall not exceed 0.15 cubic feet per second per acre drained. _ - where aproposed development contains only a portion of a watershed or. portions of several watersheds, the release Irate and storage requirements shall be.based upon the proportion of the area being developed as: compared to the entire - "watershed tributary to the proposed storage area. Where it can be demonstrated by the Developer that a higher storm water dem e and release rate will not be cary'tIo the purpose ,and intent of this ordinanc where such proposed -r releaseratewill not adversely affect -properties in the, down- stream portion of the watershed, the Director may permit such rel'ease rate to be used as deemed appropriate.' Ordinance No. 76-28fp • ._..page 2 K. - Positive Gravity Outlet. A term used to describe the drainage of an .area in_amanner ..that .will -ensu re complete-removalofall surface-water:bymeans of. natural gravity. - . L.'_ Safe Storm Water Drainage CapacityThe quantity of::storm .water runoff _ -that can be transportedwithin -a channel, passage,, conduit,-..tube,rduct, or.:com- bination thereof in such'a manner that the elevation of the viater does not rise sufficiently above the level of the adjacent ground surface so.as to cause damage to structures or facilities located thereon. M. Low Flow. The transport or flow of a normal or usual volume of storm water as.opposed to a higher peak .volume which- wouldutilizeoverflow.. facilities.- N. City: The City of Iowa City,- JohnsonCounty, State of Iowa.: O. Director -ofPublic Works. The Director of Public. Works or his/her, designate. SECTION III. :.REGULATIONS. The Department of Public Works of the City Of - ` Iowa City, Iowa, shall develop and establish written policies,' procedures, criteria and regulations concerning the inspection, determination and approval of the standards for the construction and/or development of storm water manage- ment structures: Such rules and regulations. shall be adopted by resolution `by'the_City Council. SECTION IV. ADMINISTRATION. A. Prior to the construction of any storm water .control .:structure orstorm -:water detention facility on the construction or development site,,the -developer shall obtain a building permit. No such permit shall:be issued until the following documents have been submitted to the Director of Public Works and approved: 1. Plans and proposed methods for the prevention and control of - soil erosion.. -2. Plans, specifications and all calculations for the control of. storm water runoff as required by this ordinance and any rules and regula- tions promulgated by the Director. B. No building permits for habitable structures shall be issued for any development or redevelopment"not complying' -with -this ordinance. C. Any decision of the Director shall be pursuant to written spec ifica tions and regulations as adopted by the City Council.-: - - SECTION V. ADMINISTRATIVE REVIEW. Any person affected by any decision of the, Director which has beengivenin.connection _.with the enforcement: of any provision of this. -ordinance -may request, and shall be..granted, ,'ahearing on the - matter before the Housing Appeals Board, provided that such person shall file in the office of the Director a written petition requesting such hearing, and setting forth a brief statement of the grounds therefore. Upon receipt of such petition, the ,Director shall set -:a time and place-forsuch hearing and shall give the petitioner written notice thereof. At"'such hearing, the petitioner -shall be given an opportunity to be heard and to show why such' -decision should be..modified:nor 1 I I Ordinance No. 76-28 Page 4 'B_ Excess Storm Water Passage. 1. -An excess storm water passage shall be,provided.for all storm water storage areas. Such passage'shall.have capacity:to convey through the proposed development the excess storm water from the tributary water- ` shed. The capacity of such excess storm water passage shall be constructed -in sucha: manner as to transport the peak rate ofrunofffrom a-'.100 year, - return frequency storm assuming all storm -sewers -are inoperative, all upstream areas are fully developed in accordance with the City's current land use plan, and that.antecedent rainfall'has`saturated the tributary watershed. 2. No buildings or structures shall- be constructed within such passage, however, streets, parking lots, playgrounds, park areas, pedestrian walkways, utility easements and Iother open spaceusesshall be.:considered ' compatible uses. In the event such passageway is reshaped or its capacity to transport excess storm water otherwise restricted, the Director shall notify - the agency, :.party or-partiescausing"said-restriction to remove the -same,,,- and set a reasonabletimefor its removal; If said presons refuse to or are unableto- comply with'saidcrder,.the Director shall cause said restrictions removed at the expense of said persons. : =i 3. Where -a proposed development contains existing natural drainage, appropriate land planning shall be undertaken to, 'preserveFsaid natural drainage as part of the excess -storm water passage. C. Determination' of Storage Capacity. 'The volume of required storm water storage shall be calculated on the basis of the runoff; :from a100 year -return. frequency storm. Such calculation shall be made in accordance with'thehydro- graph method of analysis as discussed in "A Computerized Method for the Hydrologic Design of Culverts," I.H.R.B.P. HR -164 published by the.Engineering Research Institute, Iowa State University, Ames, Iowa. Rossmiller and Dougal, February, 1974, or other method approved by the Director. The', applicable storm water runoff release rate shall be considered when calculating the required storm water storage capacity. D. Compensating Storage. In the event the orderly and reasonable develop- ment of an area requires the storage of excess storm water to be located elsewhere, compensating storage (the storage of an equal volume of excess storm water) may be provided at an alternative location provided, however, th.at:.the'feasibility and details of storm water control shall be approved by the bisector. E. Easements. Easements which cover excess storm waterpassages, 11 storm water storage -areas ..and other control structures shallbe-granted tothe City;`for - the purpose of repair,' alteration or to insure their proper operation, however, the city shall reserve the right not to accept such easement or any portion thereof. " SECTION IX. DRY BOTTOM STORM WATER STORAGE AREAS A... Design Criteria. 1. Primary and Secondary Uses. Dry bottom storm water storage areas shall be designed to serve a secondary purpose for recreation,,open.space, .parking lot, or similar type of use that will not be�adversely:,affected`.by - occasional intermittent flooding.: Ordinance No. !6-2 - t Page 5 • 2. Drain System, A system of drains shall be Provide low flow storm water runoff through storage areas. Such draina systemst shall have a positive gravity outlet, to a natural passage or storm drain with adequate capacity as described in Section VIII, subsection B. Multiple outlets from a storm water storage area are to'be.avoided if the outlets are designed to be less ahanfoui (4)' -inches iii diameter. - 3. Storage Duration The combination of storage of excess st rm water runoff from a 100 year return frequency storm .and the allowable release' rate shall not result in a storage duration in`excess `of forty-eight (48) hours. 4. Grades. Where turf areas are used for the bottom of dry. bottom storageareas,.the minimum grades for_. such areas shall_be two (2) percent (50 units horizontal -to l unit vertical). Maximum side slopes . for turf shall be twenty-five (25) percent (9 units horizontal�to 1 unit vertical). Storage area side slopes shall follow the natural land-conto minimize the amount of earth work necessary to create the -storage urs in order to facility. S. Erosion Control. Erosion control measures consisting of mulch, - hydro -seeding, nurse crops, sodinstallationorother-approvedmeansshall be utilized to control soil movement within and around the storage basin, Energy dissipating devices or stilling; basins, shall be provided to 'ensure that agedowfacilitystream l erosion. is. alleviated and the -re regime of stream drainage facility g the_down- y is not disturbed: _ 6. Possible Control Structures. Control structures shall,'be designed as simple as possible and shall not require manual adjustments for normal as simple, Control structures shall be designed to=maintain a relatively uniform flow independent of storm water storage volume. Inlet structures shall be - constructed in such a manner to prevent high velocity:,flow; to:- :provide for trash the interception of and debris and for soil erosion control. Inlets shall be designed to eliminate turbulent -flow conditions during any portion of the -storm -water storage cycle. - Overflows for each storm water storage area shall be the event a storm in excess of the desigProvided in n caity shall be constructed to function withoutpacoccurs. Such overflows specific attention and shall become part of the excess storm water passage. SECTION X. -WET BOTTOM STORM WATER STORAGE AREAS.` A Design Criteria Wetbottom -storm water storage areas shall be designed in accordance -.with the design criteria: governing the construction of -.dry -bottom stormwaterstorage areas, except for drains as'required by -' Section "IX.A.2. The following additional regulations shall apply: 1. Construction.. The water surface area shall not exceed ;l/10 of the tributary watershed: Minimum If fish are to be used to keep the Pondlcleanr atPth eastal%4boffour the (4) feet. pond area shall.. have a_minimum depth of ten (l .0) feet.0. - - { _ Ordinance No, 76-28 • Page 6 Facilities shall be provided to lower the pond elevation by gravity flow for cleaning purposes and land/waterinterface maintenance. Protection of the land/water 'interface-shall :be-r provided:to -.alleviate-soil erosion due to wave action.' 2. Control Structures. Control structures for storm water release shall operate at their maximum rate with only minor increases in the water surface level. - - 3. Stagnation Control. -Measures shall be included in the design to., prevent pond stagnation. Such measures may include fountain aeration or other, approved means to ensure aerobic pond conditions. .. -- 4_.Determination of Storage Capacity. When calculating the storage capacity of wet bottom storage areas, only the volume available to store excess storm water 'shall be considered. Permanent water storage does not constitute-control-'of`. excess storm water runoff. SECTION XI. MISCELLANEOUS STORM WATER STORAGE AREAS. -- A. Paved Surfaces. Paved surfaces,including, _automobile,.parking lots.-in _ `proposed-storm water. storage areas shall have-'minimum gradesofone,(1) percent - -'(100-.units horizontal to-one-(1) unit vertical) and shall be limited-to storage depths of one and one-half (1-1/2) feet maximum. Pavement base design and :construc- tion shall be accomplished in such a manner asto prevent damage from flooding. Control structures in paved areas shall be accessible for maintenance and'clean- Ag. The use of vortex control facilities at inlets to ensure thatthemaximumin - allowable release rates are being developed shall be required as necessary. - Where parking areas are used to store storm water, the areas of greatest depth shall be restricted to the more remote, least used areas of-the parking facility. B. - Rooftop Surfaces. Rooftop storage .of excess storm water%shall be- designed -_-withpermanent-type control inletsandparapet walls.to contain .excess storm water. ----Adequate 'structural -roof -design -shall -be provided to ensurethat roof deflection does not occur which could cause roof failure. Overflow areas shall be provided to.ensure that the weight of stored storm water will never exceed'the structural capacity of the roof.'' C. -Underground Storage. Underground storm water storage facilities shall . be designed for easy access to accommodate the removal of- :accumulated sediment. such facilities shall beprovided with ,positive lgravity outlets. SECTION XII.- CONTROL IN EXCESS-OF--REQUIREMENTS. Provision of Control Exceeding Requirements. In the event storm water �I runoff control can be provided in excess of the requirements' of this ordinance• and --:the bnefit of such additional control would accrue-to. the City of Iowa', it at large,--the City may provide public participation in the increased cost of the control of storm water runoff in proportion to the additional benefits`' received.