Chapter 8 • Stormwater Best Management Practices 8.6 • Structural Best Management Practices
8.6.5 Green Roof A Green Roof consists of a series of la ers that cr e an en onment suitable for plant growth without damaging the underlying roof s em. R all is initially int ed b vegetation installed on the roof, held on oliage or ed up plant oots.y unoff thateat ceeds virthe holding capacity of the owing medium eleased from the r op thr ysth an underainf ain s em. A erceptGreen Roofy can be installed on either a new or xistingf r soakop, pr videdby the roofr structureR is ableex t hold the additional w ht and meetgr local buildingis code.r Green R s areooft not newoug t , withdr manyyst of their known benefits only being added t in r eears. Theooft technologyo pr vides an insulation benefit ot the installed building,eig decreasing r es,oof mitig es urban heatechnology island effects, and can pr vide st er quantity and qualityo benefitsecent makingy them a valuable structuralo BMP alt in ourban settings w e land area is limited.ooftop In addition, temperatury may pr vide anat aesthetic benefit helping a building t meeto potentialormwat landscaping r ements, and can be designed t be used b pedestrians and/orernative building occupants. As theher variations in Green Roof vary widel the focus of othis section will be t describe the k y componentso of a Green Roof s em. Eachequir s em will need be designedo fit the y e and purpose or the building. e e common y, elements and considerations thato are instrumentale t the success of each Green Roofyst s em. yst to to structur f respective However, ther ar design o yst
1 NC State University/ NC State University Bio & Ag Engineering and North Carolina Department of Environment and Natural Resources (NCDENR), 2011 2 Water Environment Research Foundation (WERF), 2005 for Media Filters 3 The effluent concentration from a Green Roof system is highly dependent on the characteristics of the unique soil matrix for each application combined with any contamination through atmostpheric deposition. A Green Roof only treats stormwater that falls directly on the Green Roof surface itself.
8.6.5.1 General Application een Roof s ems are a good BMP for use in urban areas, as they can be designed and/or r ofit in the defined building f . Green R s pr vide se al benefits for the building. Thr h the vegetation and Gr ed ystowing medium, a een oof vides an insulating mechanism. This can videetr vings, as well asootprint insulation from typicaloof urbano enveronment sounds, such as buildingoug s em equipment installedengineer on grr ops. The vegetationGr assistsR pro in insulating a building thr h the e pro ationenergy pr Thesa egetation and owing medium also eats andvir educes the olume of er runoffyst that ed b ooftthe roof area on which the Green Roof is installed. oug vapotranspir ocess. v gr tr r v stormwat is generat y
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Because er is ed a een oof and eleased er a period of time, er flow y seen following high intensity r all e ents are reduced and dela ed o er a period of time (Dunnet and stormwat, 2004). Thisstor by Gr Ream ainager ovems y stormwaty eased peaks antypicall e ended time period instead of increasedainf peakv flow o er a r shorty periodv of time, char eristic of Kingsburyy impervious areas. If aallows Greendownstr Roof is constructeddr withinsyst the todrainageconve area“moderatel of a downstreamincr BMP,flow” theover eaxt of the Green Roof can be subtr ed from the WQCV vcalculationelatively for the BMP. Because the r actall is not highl ed, a Green Roof acts as a filter and increases the time it takes for r all t reach the primary st ar er s em. In the case of a Greenact Roof with a slope of less than 25‐per , the result of st ainf infiltratering thr h a Green Roof is appr y a 45‐percent reduction in theainf volumeo of runoff orm seworschungsgesellschaftyst Landschaftsentwicklung Landschaftsbau [FLL], 2002).cent ormwater filt oug oximatel As(F Green R s capture and filter r all falling immediat y on the surface of the roof, their w er quality benefits e ed that e all. dditional er flow should not be ed a oof or oof . een s ainf been el at as a poorar BMPlimit for nutrientto immediatst age andrainf r A stormwat rout to Green dueR tf thetreatment fact that filtrationGr Roof of whaveer thr shownh plant erial and substr e will yieldor added nutrientemoval, runoffo (Minnesota, 2008). Concentrationsat oug of nutrientsmat in st at er runoff from Green R ems shown in studies be ery similar other v edormwat s ems that you would find oofin a typicalsyst landscapehave A, 2009). to v it to be notedegetat that e enyst if concentrations of nutrients e typical t other(EP v ed sHowever,ems, the shouldloading of a pollutant isv often reduced because the t ar er orunoff fromegetat a Greenyst Roof is r A, 2009). otal stormwat educed (EP e are two basic types of Green Roof s ems t consider for installation: Ext S ems and Figure 8-26 Saddlebrook School, Library, and Community Center, Omaha, Nebraska Ther S yst o ensive yst (www.omahaice.org) ExtIntensiveensive Systemsystems. An Ext S em consists of a lig ht Gr oof em, with a shallow depth that supports edensive varietyyst of vegetation. These shtweigems use een R systht t ant vegetation and can structur a supportlimit limited uses (such as maint yst personnel).droug oler e 8‐26 an ample ofally S enance Figur shows ex an IntExtensiveensive Systemsystem. An Int S em is a hea ht Green R em, having gr er soil depths which can supportensive a wideryst range of plantsvyweig and incr oof systpedestrian affic.eat e 8‐27 show an ample S ems in combination with Inteased Figure 8-27 Gallup Campus Green Roof, ems in atr GreenFigur Roof application. ex of Extensive yst ensive Omaha, Nebraska (www.omahaice.org) Syst
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8.6.5.2 Advantages and Disadvantages
8.6.5.3 Design Requirements and Considerations This Section pr vides a narr and discussion of typical design r ements and consideration for a Gr oof. Any diff ences in r ements between Ext S em and Int S em design and construction areo noted. Thisative information is outlined b how it wouldequir be pr ed on construction dr een R een Roof – Planer View, Greenequir Roof – Cross Section,ensive and Greenyst Roof – Calculations.ensive yst As the application of a een Roof will al vary with the building, the focusy of this Section is t esent look at the main function ofawings: k componentsGr in the Green Roof Section. Each of these k y components will need t be designed t meet crit ofGr a specific application.ways It is recommended that the designer consult and designo t the following minimumey industry standards for all Green Roof applications: e o o eria o • ANSI/SPRI RP‐14 Wind Design Standard for V Roofing S ems.
ANSI/SPRI VF‐1 ernal Fire Design Standardegetative for V R ysts.
• TM E2397‐05 ExtStandard Practice for Determinationegetative of Dead Loadsoof and Li Loads ed with Green Roof S • AS ve associatTM E2400‐06 Standard Guideystems for Selection, Installation, and Maintenance of Plants for een Roof S • AS Gr ystems
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Green Roof – Plan View a minimum, the ollowing components should be labeled on the plan view of a een oof
At f clearly Gr R design project: 1. Structural Supports. Placement of the heaviest components of the Green Roof should be on column heads or o er beams. A Green Roof r ofit should consider additional loads imposed on the existing roof. A structural support plan should be pr vided in addition t the plan view of the een R v etr o o 2. DrGrainage.oof.The location of ains in the el ballast should be ed, er of PVC pipe t be installed and perf ation r ements. All under ains should be ed a oof downspoutunderdr or means of grav ance om theclearly eendesignat oof em.including diamet ains e as oerflow points in the oreen oofequir em. The purpose drof these connectis yto eleaser cess runoff om gerconvey orm ents.away Allfr downspoutsGr orR meanssyst These underdrance serv omov the een oof emGr shouldR besyst underdrains to quickl r ex fr lar st ev of 3. Grconveyavel Ballastaway. A widthfr of grGr el, Rstone,syst or pa er materialclearly along labeled.the perimeter of the Green R vides se al functions. First, this volume of permeable material can pr vide additional st capacity of the een oof, avering and vying in cess of the . oof prowidth can prvervide pr ection from wind shears (Dunnet and Kingsbury, 2004).o Thir this ballastorage can serve as a separationGr R pointfilt between converoof components,flows andex can pr videWQCV a fireSecondly, break pointthis in the oof em. o ving thisot width along a een ’s edge can ent possible egetationdly, o the w oof la The perimeter gr el ballast should be labeledo with a width, depth, and r adationsyst forHa installation. Calculations GrshouldRoof be included on prevthe porosity of thisv material.growth All st usedint in theaterpr gr el ballastyer. should be triple‐wav gr one 4. Vertical Elements.av All vertical elements sitedashed. on or penetrating the Green Roof, such as air v and heating/air conditioning components should be labeled on the plan . It is ideal place el ballast along the er of all ertical elements on the een oof. This ents access t the element that may be r ed for periodicclearly maint view to grav perimet v Gr R allows 5. Slope. Theo slope of each ea of theequir een oof should be enance.ed in the plan , with an ying ow indicating the ection of slope. Slopes ceeding 15‐percent e additional stabilizationar measuresGr (horizontalR strapping,indicat laths, battens, viewor grids),clearly w labeled should beaccompan accounted forarr in the structural calculationsdir (Dunnet and Kingsbury,ex 2004). These willgr requirslopes can cr e a problem of slippage between the materials used in construction of the Grhich oof. eater eat een 6. VegetationR Plan and Schedule. The egetation zones on the een oof should be ed and dimensioned on the plan view. A planting plan, with list or schedule of plants and their method of installation should bev included on this sheet. GrFor moreR details on v clearly selectiondesignat see discussion in the ollowing egetation Green Roof – Cross Section f paragraphs. Each er in the een oof em should be labeled in oss‐section view and er/design specifications. The la ers described as f are the minimum t be installed as part of a functioninglay GreenGr RoofR ssystem. e 8‐28clearly the typicalcr een oof oss reference manufactur y ollows o yst Figur shows Gr R cr section.
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Growth Med/Soil Matrix Filter Mat Drainage Ballast Root Barrier Waterproof Layer Roof Deck
Figure 8-28 Typical Green Roof Cross Section
1. Waterproof Layer. An eff e, durable w oof la er is important t the longevity of a Gr oof installation. The w oof la er pr ects the building’s structural components from being xposed t the elements. Tectivo common typesaterpr of w y oof applicationso include tile/sheet single‐een R y roof membranes or fluidaterpr appliedy membranes.ot Either should be applied strictly according t the e o er’s instructions.w Tile/sheet anesaterpr e installed erlapping and sealing pl e it is important t inspect the seal at each joint prior t installing the next la er of theo manufactureen Roof s em t mitig e potential membrs em leaksar and opportunitiesby ov for vegetation r joints, thereforation. o o y Gr yst o at yst oot 2. Rootpenetr Barrier/Waterproof Protection Layer. A root barrier and/or w oof pr ection la should be installed as the xt er in the een oof em. This er ers oot owth aterpr ot yer the ying oof in addition viding ection the oof ne lay Gr R syst lay det r gr into om anything installed abo it during and after construction (City of Eugene, Oregon [E underl waterpr layer, to pro prot to waterpr membrane 2008). This er is y a dense erial such as a C . Sheets e erlapped fr ve ugene], sealed t . It is critical t e end this la er be ond the actual planting area, and install ar lay typicall mat PV sheet ar ov and y ertical elements e a barrier egetation oot owth in the em. ogether o xt y y ound should not be impr ed with pesticides or with copper, both of which could ad y affect the an v to creat to v r gr syst Membranes er quality of any runoff from the Green Roof (Eugene, 2008). It is recommended that an egnat versel ation of this er assess oot ation ollow ANSI/GRHC/SPRI VR‐1 2011 wat y 3. Drainageinvestig Ballast. Thelay drainageto ballastr shouldpenetr be designedf t con y the volume of st . runoff that can be absorbed the owth medium; the purpose of this er is not e other al BMP ems, cess runoffo isve ed as underflowormwater in een Roof s em; surface runoffby shouldgr not occur (Dunnet and Kingsbury,lay 2004). toIt isdetain important stormwater. r theUnlik e cess runoffstructur in order t prsystent o erex saturation of theconvey vegetation. The dr the ballastGr can beyst constructed from coarse, washed granular materials, porous mats, or manuf toainageemove modules,x and connected t theo perimeterev v gr el ballast ainage actured 4. Filterdr Mat. A semi‐permeable fabrico or mat should beav installed between. the drainage ballast and the owth medium/soil matrix. The purpose of this mat is er y small particles that be ed om the owth medium/soil matrix h the ation of runoff o ainagegr ballast; it pr ents the drainage ballast from becomingto filt cloggedan or from pot could transferr fr gr throug infiltr int the dr ev entially
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blocking any drainage outlets in the Green Roof s em. The filter mat should not only be installed as a horizontal but also y at all er edges of the owth medium/soil wrapping up around this la yst layer, verticall perimet gr matrix 5. Grlayer,owth Medium/Soil Matrix. Theyer. owth medium or the een oof should be designed e or filter the calculated W . If this is not feasible, additional BMPs on the building sit y be r ed. In addition, the depthgr and soil matrixf of thisGr la erR must be designed t supportto thepermeat vegetation t be installed (eitherQCV an Ext S em or an Int S em). Soil matrixes fe bothma mustequir be ell ained, hile at the same time being able yabsorb and etain oall viding a mediumo or een oof egetationensive yste. The eringensive capacityyst of the or medium and thew componentsdr w of the soil matrix should be designedto b a landscaper rainfar ectvolume, or otherpro appr ed vegetationf Gr specialistR v to thriv filt growth y chit Sizing Guidelines ov . All designs for new or existing Green R s must account for the dead and li loads associated with this type of construction in addition t the r ements of the existing building code, as adopted b the City of Omaha. dditional roof loads will r e an enhancedoof structural design and may limitve the r ofit of e buildings. The ollowing calculationso equir e ed as part of a een oof y A equir etr xisting • fLive Loads. If the Greenar Roofrequir is accessible, peopleGr loadR mustsubmittal: be accounted f Another e ample of li load is wind. Each li load must be itemized with appr e supporting calculations. or. x ve ve opriat • Dead Loads. Dead loads would include, but are not limited to, satur ed w hts of een oof erials, and ice. Each dead load must be emized with e supporting calculations. at eig Gr R mat snow, it appropriat • Building Structure Loading Capacity. The building’s structure capacity must be able t carry the calculated li loads and dead loads. o All submitted calculations must be sealedve and signed b a pr essional structural engineer licensed in the e of Nebr y of Thestat growth mediumaska. or soil matrix has two critical functions: t st e the WQCV and t permeate runoff in cess of the WQCV t the ballast la er with little t no ponding on top of the vegetation. As each Green R application is unique, the depth of owth medium/soil matrixo willor be unique each o . It execommended that a ominimum depthy of 2‐in. be usedo as a guideline t detain and filter the WQCV and supportoof egetation. gr to project is r o v er runoff in e cess of the WQCV will need t be con ed from the Green Roof. This in es using the ainage , the el , y in the oof em, and oof downspouts. Stormwatance will be uniquex t each Green Roof application.o It isvey recommended that the designer volvsubmit a outingdr plan forballast st graver runoffballast thatan includesoverflows all major elements,r syst completer with con anceThis and v calculations.convey o r ormwat vey olume Considerations for Vegetation Selection A Green Roof r es very diff ent plant material selection when compared t other v ed structur s (Minnesota, 2008). The vegetation selected must thri in very constrained growing conditions, and account for seasonalequir fluctuationser in t e and moisture. o egetat al BMP ve egetation should be installed using oneemperatur of two pr ed methods: vegetation mats/modular s ems or
V eferr yst
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ed plants.
plugs/pott• egetation mats/modular s ems are pr ed s ems that achie immediate full plant co age. These s ems pr vide se al immediate ad antages t the Green Roof installationV and establishmentyst process, includingegerminat a reductionyst in exposed vesoil which reduces entialver erosion and weedyst concernso duringver plant establishment.v Long‐termo maintenance is minimal, and may r e int ent w ering during very dry periods and weeding potugene, 2008). equir ermitt at • Plugs(E or potted plants pr vide can pr vide more options for Green Roof vegetation. A variety of plant species can be used in one Green Roof installation. Using plugs or potted plants will e initial mulching ofo the Green Roof,o pr enting erosion during vegetation establishment. Until establishing a minimum of 90‐percent v ed co er on the roof, subsequent mulching, requireeding, and irrigation may be necessary. ev egetat v The selection ofw plants t install on a Green Roof is primarily based on the depth of growing medium and the composition of the soil matrix, in addition t climate considerations (r all, t e). For Green R e the owing mediumo is eriscape plantings e y used. eriscape plantings include mix of sedum/succulent plant communitieso that are ideal for installationainf on a Greenemperatur Roof due t their droofs wherance, growth erns, lowshallow, enancex needs, ar , commonland e esistanceX ugene, 2008). or a deeper substr es, shrubs and trees may be used. In general, plants with deep root s ems typicalo of an ought toler ationgr type structuralpatt BMP maintmay not be suitable forresiliency a Green R fir r (E F richer, at yst 8.6.5.4infiltr Inspection and Maintenance oof. Critical inspection points occur during the Green Roof installation process t ensure the integrity of the Gr oof s em. In addition, k y maintenance activities for Green Roof s ems include both short‐term and long‐ erm tasks. The following industry standard pr es for in ation areo recommended for all Green Reen R yst e yst t ocedur vestig oof applications:• ANSI/GRHC/SPRI VR‐1 2011 e for In ating Resistance t Root P ation on V R s. Procedur vestig o enetr • TMegetative E2396‐05oof Standard Test Method for Satur ed W er Permeability of Granular ainage Media [Falling‐Head Method] for Green Roof S AS at at • DrTM E2398‐05 Standard Test Method for W er Captureystems. and Media R ention of e Drain La ers for Green Roof S AS at et • GeocompositTM E2399‐05 Standardy Test Method for Maximumystems. Media Density for Dead Load Anal sis of Green Roof S AS y Inspection During Installation ystems. 1. y een oof er applied as sheets, mats, or olls should be y erlapped and during the installation process, as dir ed per the manuf er instructions. An Gr R lay r sufficientl ov sealed 2. The w oof la er should be inspectedect prior t the subsequentactur installation of Green Roof la een Roof s ems may include a pre‐installed electronic leak detection s em. If this is not includedaterpr in the designy of the installation, it is advisedo t administer a w oofing test with anyers. Gr onic leakyst detection s em (such as v or mapping) prior t installationyst of subsequent een Roof la o aterpr electr yst ect o 3. ItGr is advised t yers. complete an inspection at the completion of each la er’s installation.
o y
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4. The installation of modular products can increase installation efficiency (Minnesota, 2008).
Short Term: Installation – Year 1 1. A goal of 90‐percent v ed co age should be achie ed within 6‐months for Green R installed at the beginning of the owing season (Spring). egetat ver v oofs 2. T ary irrigation may be r gr ed in order t establish vegetation. A permanent irrig em may be needed, depending on vegetation selection in the Green Roof s em. empor equir o ation 3. Monthlysyst weeding of the Green Roof during Year 1 is recommended t deter weedyst seedlings and saplings from establishing. o 4. All ainage outlets and/or should be ed er y ain ent ceeding 0.5‐in. during the first ear of installation. The purpose of this inspection is e the flow of dr er from the roof surface.overflows During vegetationinspect establishment,aft an rtheseev outletsex are mor susceptible t clogging.y to ensur excess stormwat e Long Term: Year 1 – latero 1. Biannual weeding of the Green Roof is recommended t deter weed seedlings and saplings fr
o om 2. Conductestablishing. annual s erify that the oofing em emains ht below ed co er (Minnesota, 2008). survey to v waterpr syst r watertig the 3. Allvegetat ainage outletsv and/or should be ed at least o times per . The of this inspection is e the flow of cess er om the oof dr overflows inspect tw year purpose 4. After vegetation is wellto ensur established, it is recommendedex stormwat t fertilizefr the sr emsurface. only as needed, and not at an al e equent than ery other . ertilization at this al ent of nutrient in the substr e t become e ed,o and can theryst e enhance v owth andinterv morancefr (Dunnet and ev , 2004).year F ention should beinterv paid allowsthe impactthe contertilization will ha t the o atall wo er qualityxhaust of st er runoffefor from the Greenegetation R gr em. appear Kingsbury Att to any f ve o ver at ormwat oof 8.6.5.5 Submitsyst tal Requirements or view purposes prior construction, the ollowing minimum submittal ements
F re to f requir are recommended:1. Green Roof dimensions and set s from roof lines. This plan view should also include all components outlined in Section 8.6.5.3, back 2. Profile view of f , including typical cross‐sectionsclearly labeled. and dimensions, with all components outlined in Section 8.6.5.3, labeled. acility 3. Specifications of all materialsclearly t be used in the Green Roof construction, including but not limit o: owth medium/soil matrix specification, including depth; er mat specification; ballast specification; root barriero specification; w oof la er specification. ed t Gr filt drainage 4. Vegetation plan with schedule for installation andaterpr initial maintenance.y Appr e erosion contr
opriat ol
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es should be included.
5. Stmeasur er con ance and volume calculations.
6. Structuralormwat dead veyload and li load calculations. This should include verification that structure will support additional loads. ve 7. Long‐term inspection and maintenance plan. 8.6.5.6 References , Nigel and Kingsbury, Noёl. 2004. Planting Green Roofs and Living Walls. Timber Press, Inc.
DunnetA. 2009. Green R s for St er Runoff Control (EP ‐09/026). USEPA Office of Research and Development, National Risk Management Research Laboratory – Water Supply and Water Resources Division: USEP oof ormwat A/600/R
www.epa.gov/ordugene. 2008. St er Management Manual: .eugene‐
E ormwat http://www FLLor.gov/DocumentCenter/Home/View/4545 e.V. 2002. Guidelines for the Planning, Execution, and Upkeep of Green‐roof sit
es: Minnesotahttp://www.greenroofsouth.co.uk/FLL%20Guidelines.pdf St er Steering Committee and Minnesota Pollution Control Agency (Minnesota). 2008. Minnesota St er Manual Version 2. ormwat NCDENR. 2011.ormwat Jor alls Lake St er Load Accounting Tool (Version 1.0) User’s Manual:
dan/F ormwat http://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/3638/JAllen_NScott_2011.pdf?sequence=1le Ply Roofing Industry (SPRI). 2010. ANSI/SPRI RP‐14 Wind Design Standard for V R
Sing egetative oofing: Systemshttp://www.greenroofs.org/resources/ANSI_SPRI_RP_14_2010_Wind_Design_Standard_for_Vegetativ SPRI.e_Roofing_Systems.pdf 2010. ANSI/SPRI VF‐1 External Fire Design Standard for V R
egetative oofs: http://www.greenroofs.org/resources/ANSI_SPRI_VF_1_Extrernal_Fire_Design_Standard_for_Vegetative_Roof SPRI.s_Jan_2010.pdf 2011. ANSI/GRHC/SPRI VR‐1 2011 Pr e for In ating Resistance t Root P ation on R ocedur vestig o enetr Vegetative oofs: http://www.greenroofs.org/resources/ANSI%20GRHC%20SPRI%20VR1%20Procedure%20for%20Investiga ting%20Resistance%20to%20Root%20Penetration%202011.pdf. 2005. Median of A age Effluent Concentrations for BMP ASCE/EPA ISBMPD
WERF ver s. .
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8.6.6 Manufactured Systems A manuf ed s em is gener y a structural BMP whose function pr vides more traditional, treatment via settling and diff ent forms of filtration. Manuf ed s ems are typically proprietary units; how some y ha actur their componentsyst designedall separ y b the site designer. Theseo s ems are gener y designed t fit or rk withiner an xisting ance emactur yst , and can be ideal or e urban easever, openma spaceve is minimal. As manuf ed s atelems varyy depending on applicationyst and the manufall , this o wo’s guidance wille focus onconvey three mainsyst categoriescomponent of manuf ed s emsf andmor their r ar where functions: filtering, st age, and separation.actur yst acturer Section actur yst espective A manuf ed s emor whose primary function is filtration is typically designed t filt , at a minimum, the er quality discharge, Q Section 8.3.2). Filtration s ems typically r pollutants in st er b actur yst o er passing runoff thr h filter cartridges or filter media. wat WQ ( yst emove ormwat y ention s emsoug or manuf ed s ems whose primary purpose is t st e st er runoff ar designed t retain the W . Pollutants settle out in these s ems o er a period of time. Det yst actur yst o or ormwat e oed separationQCV devices include two types of s ems:yst chamberedv and h ynamic. In chamber ems, st er runoff passes thr h a series of chambers w e pollutant particles settle out Manufacturynamic ems e a motion runoffyst flow hich es ationydrod of pollutant particles ed syst ormwat oug her . Hydrod syst creat vortex to w driv separ for removal.
1 Metropolitan St. Louis Sewer District (MSD), 2009 2 Removal efficiencies are very variable. The use of phosphorus as the target pollutant is recommended when using performance based water quality criteria (Virginia, 1999). 3 Table 8-3
8.6.6.1 General Application In general, a manuf ed s em can be appr e for small drainage areas of hig y impervious co en, these ainage eas h ocarbon or sediment loadings that need be essed. should be en notactur ceedyst er’s opriatecommended flow es or olumes hl a em. ver. Oft ems are edr yar variablehave inhig designhydr details, design concept, and pollutant r to al charaddr Care tak to ex manufactur r rat v to syst Manufactured syst xtremel emov acteristics.
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A ed er em is designed er flow hich is ed an inflow pipe. The er is then r ed t a discharge point. The filters in these manuf ed s ems may be designed or manufactured t r filt specificsyst pollutants fromto stfilt w The filterregulat media isby typically based on thefiltered tar pollutantsstormwat t be r outed, ando can pr vide a pre‐treatment option for st actur er dischargingyst t another select alo BMPemove as part of a treatment train. Typicalormwater. applications of manuf ed filtration s ems includeget ofit applicationso emov into curb inlets ando catch basins. Maintenance of theseormwat s ems on a scheduleo similar t structurosion and sediment control inspections is critical t the long‐term successactur of these BMPs. Anyst e ample of a retr ed er em is shown in e 8‐29. yst o er o x manufactur filt syst Figur
INTERNAL WATER DISTRIBUTION ARCHED BAFFLE HIGH-FLOW BYPASS AND FILTRATION
OUTLET
Figure 8-29 Example of Manufactured Filter System
ed age, or ention, ems can be installed below or ound, viding the antage for a gi en space t be dual function. An e ample of this is pr viding under ound detention cells belowManufactur a parkingstor lot or det ollutantssyst in er runoff ed above thesegr emspro settle out addeder similaradv t the functionv of a typicalo e ended detentionx structural BMP. Similaro t e endedgr det al BMP, manuf alley.edP st age s stormwatems can be used asconvey downstreamto componentssyst in a treatmentov time,train if sized accoro . Regular inspectionxt of the outlet structure and at k y points ino thext s em susceptibleention t cloggingstructur is critical for theactur long‐termor functioningyst of this BMP. An e ample of a manuf ed st age s em is shown in dinglye 8‐30 e yst o x actur or yst Figur .
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Figure 8-30 Example of Manufactured Storage System
or ems er flow via aulics. These s ems are typically used t Separateat st syst er usingfilt gr vitationalsystem settling or hydrcular flow yst sediment and o tr y canormwat pr vide pre‐treatmenta of st runoffcir eto removeging eampollutants. either typicalThe con o ance s em, or anotherormwater structur HEAD DIFFERENTIAL befor dischar downstr to a REDUCED DURING BY-PASS BMP (as part of a treatment train). Applications of (NO SCOUR OR RE-SUSPENSION OF vey yst al POLLUTANTS IN LOWER CHAMBER) ors can be stand‐alone (part of new construction) or can be used in r o‐fit situations.separat Continual maintenance is critical f etr BY-PASS OVER WEIR these s ems t continue functioning at a hig el of service. An e ample of a chamber or emyst is showno in e 8‐31 and an ampleh alev ynamic xem is shown in ede 8‐32. syst Figur ex of hydrod syst Figur OIL RISES
SEDIMENTATION
Figure 8-31 Example of Manufactured Separator System, Chamber Configuration (Adapted from Virginia Stormwater Management Handbook, 1999)
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Vortechs Stormwater Treatment System - Model # 9000
Figure 8-32 Example of Manufactured Separator System, Vortex Configuration (Adapted from Virginia Stormwater Management Handbook, 1999)
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8.6.6.2 Advantages and Disadvantages
8.6.6.3 Design Requirements and Considerations Because each manuf ed s em varies in function, application, and manuf er (or vendor), design ements and considerations are pr ed in a generalized fashion. Each of these r ements and ations, alongactur with theyst appr e design calculations, should be e actured for the manuf requirem t be installed at a gi en site. It isesent appr e t request the design information equirfor filter s consider age s ems, and separopriat valuat actured syst o v opriat o ystems, detention/storDesign Flow Rate yst ators. ed ems that e sized using a flow e, including er ems and ors, must designed using the Q as discussed in Section 8.3.2. These s ems pr vide little t no st Manufactur syst ar rat filt syst separat be Volume WQ yst o o orage. ed s ems that include a st age volume component must be sized t treat and/or st e a v of st er gr er than or equal t the W . Manuf ed s ems may be designed t reduce the peak flowManufactur or theyst 2‐year ent meet ore‐de elopment peak flow e; o ond theor 2‐y olume entormwat peak flow eat should ypass theo QCV actur yst o rate f ev to pr v rat however, flows bey ear evPollutant Removalrate Characteristicsb facility. The specific pollutant r al char eristics of a manuf ed s em should be clearl specified. This includes listing all pollutants tr ed b the s em with estimates of median effluent concentration. emov act actur yst y or separ ors, if st er haseat the potentialy yst of containing h ocarbons (i.e. gasoline, oil, petr the s em should be sized t contain a spill of up t 60 gallons (City of Elizabethton, T F aton], 2006).ormwat In addition, separ ors must acti r ydr floatable debris. ochemicals) yst o o ennessee [Elizabetht at vely emove
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or any proposed installation of a manuf ed s em, monitoring may be r ed t verify the installed ormance r ed t pollutant r F actur yst equir o Overflowperf or Bypasselat o emoval. An erflow or ypass must be vided and/or specified as part of each ed em This erflow or ypass must be designed y in cess of the ed em design. It ecommendedov thatb the erflowpro or ypass point y cess flow at a pointmanufactur eam systof the installation. em,ov ather thanb at the em itself, to convee flowsying flowex ound themanufactur . The erflowsyst or is cannotr y flow in ovcess of the b eam conveem ex . All erflow orupstr ypass om manufactured syst r ed s em shouldsyst not re‐suspendtherefor and releaseconve materialar that may alrBMP y be trappedov in thebypass s conve ex downstr syst capacity ov b fr the Whilemanufactur ersionyst of in cess of the QCV should occur eam of all ead ed ystem. visions should still be made at the em itself y erflow or ypass er runoff clogging,div a blockage,flows or f exe occur (Elizabethton,W 2006). upstr manufactur systems, pro syst to safel ov b stormwat should On-line and Off-line ailur All filter s ems or separ ors must be constructed off‐line, meaning that runoff in e cess of the WQCV must ypass the s em thr h an upstream di ersion. St age or detention manuf ed s ems may be edyst on‐line, and beat designed for volumes in e cess of the W x b yst oug v or actur yst Tailwatconstructer Effects x QCV. or any manuf ed s em installation, h aulic design should consider the effects of tail er fr eam s or acilities. The ects of er flooding on the ’s aulic shouldF be consideractur yst ydr wat om downstr waterway f eff tailwat system hydr functionality Subsurface Devices ed. All subsurface installations of manuf ed s ems should consider dead and li loads that may be imposed on the structure. Sufficient and suitable access must be pr vided for each chamber in a ed s em for inspection acturand maintenanceyst activities. In addition, the designerve should ensure that e clearance is a ailable at the installation site for any operationso and maintenance equipment. A manufactural engineeringyst or geotechnical r view may be r ed, depending on the installation. adequat v Operationstructur and Maintenance Plan e equir retain a well functioning manuf ed s em, regular and continual inspections and maintenance is critical. Detailed operations and maintenance r ements that are critical t the manuf ed s continualTo functionality should be eactur ed.yst Maintenance responsibilities should be defined prior t installation. Considerations and priority shouldequir be made for points in the manufo ed sacturem susceptibleystem’s t clogging, any filter cleaning/disposalvaluat r ements, and frequency of vac‐truck cleaning. o actur yst o 8.6.6.4 Inspection and Mainequirtenance enance activities for manuf ed s ems depend on the s em installed. All activities are classified as continual and should occur ollowing all or Maint actur yst yst After rainfall equaling or exceedingf 0.5 in.rainf quarterly. 1. Inspect the ed em. Check all ers, outlets, and erflow points in the
2. If sediment,manufactur debris, or othersyst items ha accumulatedfilt in the s ovem, r system.
3. Clean ers if needed. Unclog or epairve outlets and erflow ystpoints asemove.
filt r ov needed.
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4. Identify inspection/maintenance activities specific t the manuf ed s em that are critical ollowing all. e the er’s specifications or the maximum els of accumulation ed e al is o actur yst f rainf Not manufactur f lev pollutant Quarterly: allow befor remov required. 1. Inspect the ed em. Check all ers, outlets, and erflow points in the
2. If sediment,manufactur debris, or othersyst items ha accumulatedfilt in the s ovem, r e. Clean the system.s em with a vac‐truck, as appr ve yst emov yst 3. Clean ers if needed.opriate. Unclog or epair outlets and erflow points as
4. Identifyfilt inspection/maintenancer activities specific tov the manuf edneeded. s em that are critical on a biannual basis. Note the manuf er’s specifications for the maximum le els of pollutant accumulation ed e al is o actur yst actur v 5. Inspect structuralallow componentsbefor remov of the s required.em for cracking, subsidence, spalling, erosion, and
yst 8.6.6.5 Submitdeterioration.tal Requirements or view purposes prior construction, the ollowing minimum submittal ements e
F re 1. Drainage area map,to specifically outliningf drainage area t the manufrequir ed s ar recommended.
2. St er plan/profile for site and/or drainage area; sto er ractur ystem.ance t ed em should be ormwat ormwat outing/convey o 3. Manufmanufactured ssystem plan, profile,clearly and detaileddelineated. sections. Each component of the manuf em should be labeled with actur yst actured 4. Ifsyst r ofit installation,clearly plan, profile, anddimensions. detailed sections for the r ofit installation should be
etr etr 5. Ifincluded. ed em is be installed either below or another e component parking lot with ound ed age em or building with ed oofmanufactur s em), apprsyst eto dead and li load calculationsabove must be submitted,sit signed and(i.e. sealed b a pr essional structuralundergr engineermanufactur stor syst manufactur Green R yst opriat ve y 6 Manufof er’s specifications for installation..
7. Manufactur er’s specifications for maint
8. An as‐builtactur surv of the manuf ed enance.s em is recommended t confirm actual construction/installation adheres t appr ed construction plans. ey actur yst o 9. A long‐term inspection/maintenanceo plan.ov
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8.6.6.6 References on. 2006. Commercial/Industrial De elopment St er BMP Guidance:
Elizabetht v ormwat http://www.elizabethton.org/business/BMP%20Design%20Guidance%20Final.pdf. 2009. Proprietary W er Quality Products and the Metropolitan St. Louis Sewer District’s St Management Pr MSD at ormwater ogram: amGuidance‐080213r http://www.stlmsd.com/portal/page/portal/engineering/planreview/PlanReviewInformation/ProprietaryB MPs/MSDProprietaryBMPProgrginia. 1999. ginia er Management Handbook,ev090105.pdf olumes 1 and 2, First er_3‐15.pdf Vir Vir Stormwat V Edition: http://www.dcr.virginia.gov/stormwater_management/documents/Chapt
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8.6.7 Permeable Pavement ermeable ement ems e comprised of a ement ace hich the ation of er multiple subsurface la ers. Depending on the specific design of this BMP, it has the potential t capture and P ypav st e st syst er arrunoff, and filter andpav infiltr esurf st w er runoffallows into theinfiltr subsoil. Therewat arinto al types of pa ementy surfaces, including: o temporaril or ormwat at ormwat e sever 1. Perviousv Concr e – composed of w coarse aggr e, cement, and little t no fine aggr This e has ge oid spaces, allowing er y e h . e applicationset should conformater, t the r ementsegat of the American Concro e Instituteegate. CI)concret 522.1, Specificationlar v for Pervious Concr wate P to rapidl, publishedinfiltrat bthroug the Americanit Pervious Concr concrete, F on Hills, Michigan. Theo specificationequir should be r ed b a qualifiedet engineer and(A modified for the proposed pervious concret e avementapplication, as needed.y ete Institut armingt eview y 2. P ous Asphalt – a mixture of asphalt cement, etcoarse aggr e, and admixtures. As with pervious e, little no fine e is used, oducing ge oid spaces hich allow er or y infiltr e t subsurface la egat concret to aggregat pr lar v w wat to 3. rapidlermeable aters o– a em of yers.erlocking s hich e placed with spaces een These spaces then allow or the apid ation of A permeable er can be comprised Popenings upPav t 20‐percentsyst of theint o all area.block w ar betw them. f r infiltr water. pav of 4. P ous Gr elo – used in place of traditionalver gr el dri es. This s em has a gr er depth of gr than a traditional application and includes a filter mat or av av v yst eat avel 5. R ced Grass – a s em of plastic or concr e pa erserial. which ha large openings intended f the placement of aggr e or turf. einfor yst et v ve or Underneath each of these pa ementegat surfaces, a crushed stone aggr e base la The aggr e should be clean, washed, and free of fines. This aggr e la er serves as a r , and holds the WQCV until it can be y infiltr ed into the subsoil.v An under ain s em is included tegat ensure theyer. aggr e r egatoir dr or orm ents oducing runoffegat olumesy ger than theeservoir . e conditions y also call fulluse of perimeterat barriers t pr ent lat aldr infiltryst o egat eserv ains properly f st ev pr v lar WQCV Sit ma for o ev er ation.
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1 Chicago Stormwater Ordinance Manual, 2011 and USEPA Pervious Concrete Pavement, September 2009 2 Median effluent concentrations apply to events with measured discharge. Geosyntec Consultants and Wright Water Engineers, Inc 2008
8.6.7.1 General Application ermeable pa ement s ems should be sited at locations hich e ‐speed, ‐traffic eas, asP s, v s, parkingyst stalls, and paths. Theyw shouldar notlow be locatedlow in a placear w such park drivewayer could con y large amountspedestrian of sediment it, as this would clog pores and reduce infiltrhere stormwates. In addition, runoffve from construction acti to eam of a permeable pa ement s em mustation be rat y controlled t pr ent clogging. As this vitiesBMP upstrvides high r es of st v er infiltration,yst it must notcarefull be placed w e contaminantso ev such as pesticides, proertilizers, or otherat solubleormwat contaminants may be ed t the hergr er table. f conveyermeableo concr oundwate installations can be sited f Figure 8-33 Example of a Permeable Paver her traffic areas. Such sites r e a gr Installation thicknessP for the etconcr e pa ement la er thanor installationshig in low traffic areas.equir An engineereater should specify the thickness of the concr e on a site‐b ‐sit basis. If a permeable paetementv s em yis sited next t an existing or a proposed structure, including buildings or other infr e, the impact of the increased infiltration on the structure’s foundationet must bey e ed. v yst o astructur considere 8‐33 an ample of a permeable er
Figur shows ex pav installation.
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8.6.7.2 Advantages and Disadvantages
8.6.7.3 Design Requirements and Considerations Overall Design Guidance 1. Permeable pa ement should not be constructed until the entire drainage area is permanentl stabilized against erosion or a pre‐treatment practice is implemented, nor should any activities be ed whichv could cause large sediment loads t be con ed t the permeable pa y such as staging of landscape mulch or soil on or near the pa . Heavy sediment loads t the completement will reduce infiltration r es and r e additionalo vey maintenanceo t r e thevement, ation r t design le vement o pav at equir o estor 2. Permeableinfiltr paateemento shouldvels. not be sited w e infiltration into the soil at the bottom of the e r oir could cause damage t surrounding structures due t e soils and/or ock. The vaggr e r oir drains primarilyher thr h infiltration, and would not function aggregat if noteserv ed do o o xpansive bedr egat eserv oug 3. Coordinationproperly andallow communicationto so. between all parties in ed, including, but not limited to, the , the engineer, and the installer, is important in construction of a permeable pa ement s Prior t the construction phase, a meeting between all involv ed parties should be conducted t City e the design process and pr es and t establish lines of communication.v ystem. o volv o 4. Thecommunicat aggr e r oir should be designedocedur t capture oat a minimum the r ed V . The design olume is equal t the WQCV unless routing of impervious areas t pervious areas (i.e. cascading planes) occursegat withineserv the drainage area of theo permeable pa ement s em.equir The WQCVD is based onv 0.5 in. of runoff.o If cascading planes are pr , the design volumeo can be reduced because a portion of the WQCV from the impervious area is infiltr ed. vR er t Sectionyst 8.3 determine the design volume t use for sizing the permeableesent pa ement s em. at ef o to 5. The design volumeo should be drained from the s v em withinyst 48 hrs.
6. Subsurface in ations and the design of the subsurfaceyst s em should be completed b a qualified engineer. vestig yst y
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7. A qualified engineer with experience in the design of both con entional and permeable pa should complete the pa ement design when it will carry vehicular traffic. The engineer should e that the ade is designed, and should v e inspections both duringvements er construction v e that the em is ed and can support affic ensur subgr properly complet and 8. Foraft permeable asphaltto ensur and concr e applications,syst construct a test panelproperly of the pa ement should trbe pr loads. the installer prior t construction using the proposed design mix and the specification. This panel should ha had 30 da t et cur v ovided by o 9. After construction,ve the infiltrationys o r e. of the permeable pa ement installation should be t using the process outlined in A TM C1701 for pervious concr e and A TM D5093 for permeable ers and the results f y r ateed t the City v ested S et S 10.pav The most current ACI 522.1ormall specificationeport o shall be utilized. for each installation.
11. Special consideration should be gi en t ensure that settlement of the pa ement is accounted f An increase in the pa ement ele ation of up t one‐quarter in. may be r ed t account for the effects of settlement v o v or. v v o equir o Excavation and Subsurface Investigations. 1. Ex ation is r ed t construct the aggr e r oir and/or the under ain s em.
2. A desktopcav r viewequir of a ailableo geologic and geotechnicalegat eserv information should bedr completedyst prior t y field tests t determine the suitability of a proposed site for a permeable pa ement application. e v o 3. Ifan the desktop analo sis does not r eal any issues pr enting permeable pa ementv from being ed on a proposed site, a geotechnical engineer should scope and perform a subsurf Table 8‐18 outlinesy the subsurfaceev in ationsev which should be considered.v The constructechnical engineer may modify the recommendations in Table 8‐18 or r e additionalace study.esting depending on site conditions. vestig geot equir t Table 8-18 Subsurface Investigations Guideline for Permeable Pavement Applications
1 UDFCD, 2010
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Aggregate Reservoir The aggr e r oir will vary in depth and should be composed of American Association of State Hig and T ansportation Officials (AA O) No. 57 coarse aggr e with all fr ed faces. Stone should be clean with no smallegat particleseserv t clog soils. Additional depth may be used t pr vide additional st age gr er thanhway the r , if e conditions SHT esting of the eegat should be actured using the Los asion test as specifiedo b A TM C131‐06. The results of the LA Ao asiono test should be orsubmittedeat t the CityWQCV for apprsital prior t constructionallow. T of the permeableaggregat pa ement installation.complet A porosity of 40‐percentAngeles or lessAbr should be used t calculatey S st age capacity. The bottom of the aggrbr e la er should be 2 ft. abo o the normal ov er table.o Disturbance of the ade soilv construction vities should be oided. en geot xtileo fabric shouldor be placed at the bottom and sides of allegat aggr y e r oirs, unlessve a groundwater barrier is r ed t pr ent lat alsubgr e ation. Ifby placement of paactiement does not occurav A nonwov y followinge aggr e installation, the aggr e r oir should beegat pr eserved b erosion and sedimentperimet control t ensureequir thato sedimentev iser not carriedxfiltr t the r oir as a resultv of other construction immediatel egat egat eserv otect y o o eserv Theactivities. ability of a permeable pa ement s em t capture w er varies depending on if it is installed on a flat or a sloped subgrade. A flat installation, shown in Figure 8‐34, is pr ed as it has a simpler design and maximizes the volume of w ver the aggryst e or oir canat st e per unit area of permeable pa . B comparison, sloped installations e ge partitions or flow eferrbarriers. As shown in es 8‐35 and 8‐36, these flow barriers areat r ed t egat fully utilizeeserv the aggr or e r oir for st age and filtrationvement of they . The ability of the pa ementrequir t infiltrlar e the WQCV is reduced as the velocity of wFigurer on the pa ace increases and pot equiry e ceedso the infiltration r egat of the eservpa . Becauseor of this, sloped installationsWQCV with longitudinalv slopeso gr erat than 1 percent should be designed for onlyat rain falling dirvement onsurf the ement ace. entiallNo contributingx ainage ea shouldate be vemented ain the ement or such installations. Flat installations witheat 1 percent or less longitudinal slopes can r st erectly flow om adjoiningpav drainagesurf areas in combinationdr with thear pa ement surfallow to dr to pav surface f eceive ormwat Afr qualified engineer should e e the aggr e r oirv design t ace. ensure that it has structural int or the traffic loadings r ed at the permeable pa ement sit valuat egat eserv o egrity f equir v e.
Figure 8-34 Profile View of a Flat Permeable Pavement System
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PAVEMENT SURFACE
INVERTED ELBOW 1" MIN BEDDING LAYER FLOW BARRIER
DAR SUBRESERVOIR
LFB
INFILTRATION
SS
AGGREGATE RESERVOIR SUBSOIL UNDERDRAIN
Figure 8-35 Profile View of a Sloped Permeable Pavement System
INVERTED ELBOW
OUTLET PIPE
SUBRESERVOIR
WAR
AGGREGATE RESERVOIR UNDERDRAIN
Figure 8-36 Plan View of a Sloped Permeable Pavement System
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Perimeter Barriers and Flow Barriers A perimeter barrier is r ed for sites w e the geotechnical engineer has deemed lat al infiltration a risk surrounding structures due t e soils and/or bedrock. An e ample of such a scenario would be hen the permeable paequirement installationher is surrounded b con entional pa . Theer perimeter barrier shouldto y ound ando containxpansive the permeable ement xem. It should end om below w e la er t the edgev of the installation. y v vement completel surr pav syst ext fr the Flowaggregat barriersy shouldo be vided or sloped permeable ement installations, as shown in e 8‐36 These barriers should be buried into the subsoil and e end up into the aggr e base. A least 1‐in. of ance between the toppro of the barrierf and the bottompav of the permeable pa ement must beFigur maintained. These barriers must be impermeable eep er omxt flowing the estegat point in thet clear . If a proprietary s em is used for either perimeter or flow barriers,v such as an ane liner, the manuf er’sto instructionsk wat fr and specificationsto forlow its installation shouldaggregate be f reservoir yst impermeable geomembrUnderdrain System and Outlet Pipeactur ollowed. An ain em should be included in the permeable ement em e that the inflow er volume is gr er than the WQCV or design volumes are con ed from the aggr e r Theunderdr under ainsyst should run the entire length of the installationpav so that systthe in ertto ensurof the pipe rests on theof stormwatade soil. eaty e the pipe es the eam end ofvey the installation, anegat edeservoir. should be installed,dr as shown in e 8‐34. The ed elbow is a erticalv portion of pipe hich subgrthe pipe at theImmediatel bottom of thebefor aggr e r leavoir t a pipedownstr at a higher ele ation. The higher eleinvertation pipeelbow should be placed so that its ertFigur the QCVinvert be ed in thev e base, as shownw connects e 8‐34. egat eserv o v v inv allows W to stor aggregat in FigurThe ain should be made of ed Chloride C) pipe meeting the dimensions en in Table 8‐19. The in ed elbow and higher ele ation pipe should be made of normal PVC pipe with no slots. The designerunderdr should consider slottementsPolyvinyl limit peak flow(PV es elopment conditionsgiv below 2) when sizing the undervert v requir to rat to predev (Chapter drain. Table 8-19 Slotted Pipe Dimensions
Note: Variations in these values are expected from available pipe diameters; however, the maximum slot width should not exceed 0.032 inches, and the ability of the pipe to completely drain the reservoir within 48 to 72 hours should be evaluated if large deviations in open area per foot of pipe are encountered.
or sloped permeable pa ement installations, an under ain pipe should be placed in each subr hich runs parallel t the flow barrier along the base of the barrier. These should connect t an outlet pipe F v dr eservoir hich spans the e length of the permeable , as shown in e 8‐35. For a sloped installation, w o o an ed elbow is ed or each , as shown in es 8‐35 and 8‐36. The higher in w entir pavement Figur outlet pipe has no restrictions and can be constructed using con entional methods with any material pipe invert requir f subreservoir Figur vert y used for st er drainage, so long as it has capacity t drain the aggr e r oir according t v the calculations described in Section 8.6.7.6. The outlet pipe should be constructed using con normall ormwat o egat eserv o methods, and no material la er is r ed t surround it ventional y equir o .
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A cleanout should be placed near the bend of the ed elbow on the er ation pipe in both and flat installations, as shown in e 8‐34. This will allow or enance of the er ation invert low elev sloped High Flow Conveyance Figur f maint low elev pipe. h flow ance must be vided ert er om permeable ement during orm e ents. This con ance can be located upstream of the pa ement or be a structure which con Higerflow conveyom the e pro , asto withdiv thestormwat ainaway emfr and outlet pipe.pav It can ect large st veam s as partvey of a eatment ain, or ge a v er ance em. Theveys ovflow fr ance aggregatem shouldreservoir be sized such that allunderdr eria orsyst maximum able eet dir oachmentflows to downstr asBMP discussed in Chaptertr 3: Stormtr Drainagedischar S em,to isstormwat maintained.convey syst high convey syst crit f allow str encr by Inststormwater,allation of Concrete Section around Perimeter yst e permeable pa ement is installed, a concr e section is r ed t be installed around the perimeter of the pa ement t ensure the pa ements are held tig y together under r ed traffic loading. Exceptions can beWher made in non‐vehicularv applications subject t et City appr al.equir Use of a onormal curb section is acceptable in most cases.v Theo bottom of the vconcr e section shouldhtl e end t at leastepeat the bottom depth of the pa o ov 8.6.7.4 Inspection and Mainet tenance xt o vement. enance activities for permeable pa ements are vital and should be performed at the fr ed Maint v equencies Asindicat neededbelow. 1. Maintain e‐treatment es ed strips, ales, mechanical vices) sediment and soil from being carried t the permeable pa pr measur (vegetat sw de to prevent 2. or ermine if the e o oir ains vement. er typical ents via and under Monit to det aggregat reserv dr properly aft ev infiltration 3. egetationdrain. owing in the permeable
4. RemoveEnsure surfacev is freegr of sediment and clean surfacepavement. if clogging is observ
Biannual ed. 1. Clean e ace oom, otary brush, or
2. Repairentir and/orsurf replaceby jointbr aggrblower,e afterr cleaning (forsweeping. permeable pa er applications).
3. Inspect and clean outlet structuregat v
4. Inspect surface for det ation es.or settling.
Every Five Years erior acuum the e ace and eplace the joint e. or pervious e, ashing can ed bef e vacuuming t loosen sediment. P ashing is not recommended for permeable pa V ems andentir vacuumingsurf is the onlyr recommendedaggregat maintenanceF pr concrete. Alt powerw, vacuuming couldbe be completed eror a all in lieuo of owerw ver syst ocedur ernatively completWinter Conditionsaft rainf powerwashing. ermeable ements cept or ous el) can be ed. Mechanical al of ice and snow ed. Sand should not be placed on permeable pa , as it can cause clogging. In addition, deicers P pav (ex f por grav snowplow remov is preferr vement
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should be used on a ed basis, as y will flow h the ement and o 8.6.7.5 Submitlimittal Requirementsthe throug pav int groundwater. or view purposes prior construction, the ollowing minimum submittal ements
F re to f requir are recommended:1. Drainage area map, including drainage area t the permeable pa ement s
2. Existing contour map with ele ations r encedo t N VD 88 andv proposedystem. grading la
3. Results of geotechnical in vation ofefer sit o A yout.
4. Plan view with aerial photvestig y of the drainagee. area with any long term sources of sediment identified, flow paths om these ces the permeable ement em, and eatment used t mitigographe sediment. fr sour to pav syst any 5. Stpretr er plan/profileo forat sit
6. ermeableormwat ement em plane. view and ofile view with all components labeled
P pav syst pr clearly with 7. Alldimensions. design calculations (r er t Design Example). If pr eatment is used, all design calculations f the device or devices should be submitted. ef o etr or 8. Detail of oposed ain, , and/or h flow ance es with dimensions construction. Include appr e design calculations (r er t Design Ex pr underdr outlet hig convey structur for 9. A st er control plan opriatwhich identifies appr e erosionef o control measuresample). should be
ormwat opriat 10.included. Documentation of the infiltration r of the permeable pa ement as determined b A TM C1701.
11. An as‐built surv of the permeableate pa ement s em is recommendedv t confirm yactualS construction adheres t appr ed construction plans. ey v yst o 12. Long‐term inspection/maintenanceo ov plan. 8.6.7.6 Design Calculations A short summary of the design calculations is pr ed below A detailed design e ample is outlined in Section 8.6.7.7. esent . x Step 1 Conduct a subsurface investigation to characterize subgrade conditions. The testing should be ed b a geotechnical engineer. If the results of the in ation indicate that an impermeable barrier and/or a perimeter barrier is necessary, the type and material of the barrier(s) should be chosen and the barrierscomplet designed.y vestig
Step 2 Calculate the WQCV and the VD. The WQCV is based on 0.5 in. of runoff. R er t Section 8.3.1 guidance in calculating the W . If routing of impervious area t pervious area (i.e. cascading planes) occurs within the drainage area of the permeable pa , the design volume of the permeableef o pa ement canfor be educed because a portion of QCVthe WQCV from the impervious areao is infiltr ed. R er t Section 8.3.4 ermine the reduced WQCV t use the V orvement cascading planes. v r at ef o to det o D f
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= QCV or if cascading planes exist in permeable pa ement drainage area, see Section 8.3.4 or calculation of V VD W v f StepD .3 Size the depth of the aggregate reservoir. The depth of the aggr e r oir is based on the design volume (V ) ding Equation 8‐20 or a flat installation and Equations 8‐21, 8‐22, and 8‐23 sloped installations. Equation 8‐20 also accounts or 1‐in. of ance egateen theeserv op of the flow barrier D the bottom of the permeableaccor patoement surf f for f clear betw t and v ace. (8-20)
Where: = Depth of the aggr e r oir for flat installations (ft = Design volume (cu. ft DAR = Width of the aggregate reservoir (ft .) VD = Length of the aggr .)e r oir (ft WAR egat eserv .) LorAR a sloped permeable pa ementegat seservem w .)e the slope of the subsoil is appr y equal t the slope of the permeable pa ement surface, subr oirs with equal st age volume are cr ed. The length betw flowF barriers and otal numberv of theyst her oirs ed the flow barriersoximatel must be erminedo the depth of the v e oir caneserv be ermined. Equationor 8‐21 is used eatfind the length eeneen t subreserv creat by det before aggregat reserv det to betw flow barriers. (8-21)
Where: Length een flow boundaries = Design volume (cu. ft LFB = Slope ofbetw the subsoil (ft (ft.) VD = Area of the permeable.) pa ement (sq. ft ss = P osity of the aggr ./ft.)e r , less than or equal t 0.4 App v .) pEquation 8‐22or is then used t determineegat eservoir the number of subr ooirs. When the number of equally sized oirs is not an int , this signifies that a subr oir with a smaller volume than the others will be ed. o eserv subreserv eger eserv creat (8-22)
Where: = Number of equally sized subr = Length of the aggr e r oir (ft nr Length een flow barrierseservoirs LAR Width of the flow boundaries,egat eserv .)ed in the ection of flow LFB = betw (ft.) WFBer calculation= of the length een flowmeasur barriers and thedir esulting number(ft.) of oirs, Equation 8‐ 23 is used t determine the depth of the aggr e r . This equation allow for 1‐in. of clear Aft een the op of the flow barrierbetw and the om of the permeabler ement subreserv o egat eservoir s ance betw t bott pav surface. (8-23)
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Where: = Depth of the aggr e r oir for sloped installations (ft = Design volume (cu. ft DAR Length een flowegat boundarieseserv .) VD = Width of the aggr .)e r oir (ft LFB = P ositybetw of the aggr e r (ft.), less than or equal t 0.4 WAR = Number of equallyegat sizedeserv subr .) PAR = Slopeor of the subsoil egat(ft eservoir o nr eservoirs sIfs a permeable pa ement s em is./ft.) designed in which the soil slope does not match the slope of the permeable , the calculation of the depth of aggr e r ed t st e the design volume is not d. Thisv is becauseyst the heights of the flow barriers will v , creating subr oirs with pavementent st age volumes. Should such an installationegat equir be proposed,o or a depth of aggr e r oir should be assumedstraightforwar and calculations completed as described in Step 4 for this situation.ary eserv differ or egat eserv If a permeable pa ement s em is proposed which has a permeable pa ement slope that is ad erse t the subsoil slope, the ht of the flow barriers must allow or 1 in. of d een the om of ement and thev maximumyst w er surface in the subr v v o heig f freeboar betw bott the Stpavep 4 Calculate volume reductionat (if conditions allow).eservoir. urther volume reduction can be achie ed b easing the depth of the aggr e r . Once the desired aggr e depth has been determined, find the new V based on this depth. Equation 8‐24 the designF olume calculation or a flat installation,v y incrEquation 8‐25 the calculationegat oreservoir a sloped egat D shows v f and shows f installation. (8-24)
Where: = Depth of the aggr e r oir for flat installations (ft = Design volume, flat installation (cu. ft DAR = Width of the aggregate reservoir (ft .) VD = Length of the aggr e r oir (ft .) W AR = P osity of the aggregat eeserv r , less.) than or equal t 0.4 LAR egat eserv .) p or egat eservoir o (8-25)
Where: = Design volume, sloped installations (cu. ft = Number of equally sized subr VD = Depth of the aggr e r oir for sloped.) installations (ft nr = Width of the aggr e r eservoirsoir (ft DAR Length een flowegat boundaries,eserv e that Equation 8‐21.) is satisfied WAR or the resulting designegat volumeeserv (ft .) LFB = Slope ofbetw the subsoil (ft ensur = Pf osity of the aggr e r .), less than or equal t 0.4 ss ./ft.) Asp pr y ordescribed, w e theegat soileservoir slope does not match the paoement slope, calculation of the st olume of the proposed aggr e r oir is not str d. T calculate the st age volume, Equation 8‐25 shouldeviousl be modified b her dropping the term n and then it shouldv be used t calculate the st age volumeorage of eachv subr . The designegat volumeeserv is then the sumaightforwar of the volumeso st ed in all subror oirs. The result is y r o or eservoir or eserv
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then compared t the WQCV t see if adequate st age volume is pr vided b the assumed depth of aggr . If there is not, then a larger depth should be assumed and the calculations completed ag o o or o y egate Streservoirep 5 Size the underdrain and outlet pipe. Size the under ain t drain the aggr e r oirain. within 48 72 hrs. and design the connection t existing st er infr e. Equation 8‐27 gi es the pipe size or a flat installation which has one outlet pipe. Equation 8‐27dr is alsoo used t size outletegat pipeseserv for sloped installationto subr oirs, w e V iso the volumeormwat st ed in eachastructur subr , and not the totalv design f olume. Calculation of V is en in Equation 8‐26. The pipe er shouldo be ounded up the 4‐in. or 6‐in. PVCeserv pipe sizes listedher ins able 8‐19. If oneor 6‐in. pipe is noteservoir large enough, multiple outlet pipes vshould be used. s giv diamet r to standard T or a sloped installation, Equation 8‐26 is used t find the volume st ed in each subr oir when they ar all equally sized. F o or eserv e (8-26)
Where: = Volume st ed in each subr oir (cu. ft = Number of equally sized subr V s or eserv .) norr sloped installations w e n is not aneservoirs int , a subr oir with a volume smaller than the others will be cr ed. T determine the volume st ed in this smaller subr , Equation 8‐26 should first be used t F ermine the volume st hered in rthe equally sizedeger subr eservoirs. The volume of the smaller r oir is then eated as othe V ed in Equationor 8‐26 multiplied theeservoir ence een ed in o detEquation 8‐22 and oundedor down the est eserv eserv calculat S calculat by differ betw nr calculat Equation 8‐27 is usednr rt size the outletto pipes.near For theinteger. diameter of an outlet pipe from a flat installation or the main outlet pipe from a sloped installation, the volume used t size the pipe is the design volume, V . For the oir outlet pipeso in a sloped installation, the volume used is the volume st ed in each subr . Equation 8‐27 will be used twice in a sloped installation t o size the subr oir outlet pipes andD the main subreservoutlet pipe from the subr or eservoir, Vs o eserv eservoir. (8-27)
Where: = Diameter of the outlet pipe (in.) = Design volume (V ) or flat installation size main outlet pipe ving flow om DP outlets; or, Volume st ed in each subr oir (V ) for a sloped installation subr oir outlet V pipe (cu. ft D f to recei fr subreservoir = Manning’s n value foror pipe material, 0.009eserv – 0.011s for PV eserv = Slope of the.) outlet pipe, minimum 0.005 (ft n C spor a sloped installation, the outlet pipe from a subr ./ft.)oir smaller than the equally sized subr should be the same size as is r ed in the equally sized subr oirs. F eserv eservoirs Step 6 Size overflow conveyance.equir Size erflow ance eserv pass ge up the 100‐year ent maintain the peak discharge r es during the two‐year storm e ent t existing conditions. If the outlet pipe is t be used for this purpose, r eov the r conveyed diameterto of thelar outletflows pipe usingto other means.ev and to at v o o ecalculat equir
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8.6.7.7 Example Design a permeable pa ement s em BMP that will be used as a pedestrian path. The permeable pa em will be 100‐ft. long with a 6‐ft. width and will int cept flow from 1,050‐sq. ft. of drainage area. The ainage area is hig y vurban withyst 85‐percent impervious area. The pa ement will ha a longitudinalvement slope ofsyst 3 per , as prior appr al from the City was obtained,er and the subsoil slope will match the pa dr hl v ve cent ov vement Stslope.ep 1 Conduct a subsurface investigation to characterize subgrade conditions. esting was complet a geotechnical engineer. The results of the in ation indicate that an impermeable barrier and/or a er barrier is necessary, the type and material of the barrier(s) should be chosenT and the barriers ed designedby t pr ent lat al mo ement of w vestig perimet o ev er v ater. Step 2 Calculate the WQCV and Design Volume (VD). The drainage area, A , is 1,050 sq. ft., or 0.024 ac. The QCV is based on 0.5 in. of runoff. No routing of impervious area t pervious area (i.e. cascading planes) T occurs within the drainage area of the permeable pa . R er t Section 8.3.1 or guidance in calculating W o the W vement ef o f QCV.
Pretreatment unoff from the hig y urbanized drainage area is lik y t carry high sediment loads. Thus, a pr vice is ecommended. ed er strips and ed ales rk educe the elocity runoffR and pr ehl settling of suspended sediments.el In situationso w e area is limited, utilize underetreatment de stronglyed vicesr detain andVegetat slow runofffilt C, 2009).vegetat or thissw ample,wo it isto assumedr thatv of eatmentomot is implemented pr and that all runoff volume is trher ed complet y t the permeableground manufacturement s de to (MAR F ex the pretr operly anslat el o Stpavep 3 Sizeystem. the depth of the aggregate reservoir. Because this s em will be constructed on a sloped ace, flow barriers will be ed. The length een flow barriers must be ed . Equation 8‐ 21 is used t calculate the maximum length between flow barriers.yst A porosity of 0.3 is assumed for the surf e r requir betw calculat first o aggregat eservoir.
or this e ample, it is assumed that a length between flow barriers of 10 ft. is ideal due t constructability aints and will be used. Because this is less than the calculated 12.15 ft., it satisfies the condition F ed x Equation 8‐21. o constr requir, the bynumber of oirs is ed using Equation 8‐22. or this ample, the ement length of 100 . and a flow barrier with a width of 0.5 . is Next subreserv calculat F ex permeable pav ft ft assumed.
e the depth of the e , Equation 8‐23 is
To calculat aggregat reservoir used.
The minimum able depth or an e oir is 12 in., so a of 12 in. is used.
allow f aggregat reserv DAR
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Step 4 Calculate volume reduction. or this e ample, volume reduction is attained because the D of 12 in. is higher than the 6.2 in. depth r ed t st e the W . Because this is a sloped installation, the volume of AR er the aggr e r oir st es, isF the totalx volume captured in each subr . T calculate the t olume of age capacity in theequir e o or e QCV , Equation 8‐25 is wat egat eserv or eservoir o otal v stor entir aggregat reservoir used.
Step 5 Size the underdrain and outlet pipe. or this e ample, the under ains for the subr oirs must be sized, as ell as the outlet pipe taking flow om each of the oir ains. Equation 8‐27 used t find the diameters for both types of pipes.F For thex subr oir outletdr pipes, the volumeeserv in each oirw is used in the equation, as fred using Equationsubreserv 8‐26. underdr is o eserv subreserv calculat
This value is then used in Equation 8‐27 t find the size of the subr oir outlet pipes. The minimum ed slope or the pipes is o eserv allow f 0.5%.
The calculated pipe diameter of 0.75 in. is rounded up t 4‐in., in accordance with able 8‐19. The sizing of the outlet pipe uses the otal design olume and the longitudinal slope of 3% in Equation 8‐27: o T t v
The calculated pipe diameter of 1.2 in. is rounded up t 4 in.
Step 6 Size overflow conveyance. erflow anceo is sized pass up the 100‐year ent ol structures upstream of the permeable pa ement installation. In addition, peak discharge r es ar maintained during the two‐year stormOv e ent tconvey match existing conditions.to flows to ev using contr v at e v o
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8.6.7.8 References City of Chicago, Illinois. 2012. Stormwater Management Ordinance Manual
: http://www.cityofchicago.org/dam/city/depts/water/general/Engineering/SewerConstStormReq/2012Stor mManual.pdfec Consultant and W ht W er Engineers, Inc. 2008. Overview of P ormance b BMP Category and Common Pollutant Type: ISBMPD (1999‐2008): Geosynt rig at erf y http://www.bmpdatabase.org/Docs/Performance%20Summary%20Cut%20Sheet%20June%202008.pdfC. 2009. Manual of Best Management actices or er , Section
MAR Pr f Stormwat Quality Edition. Cityhttp://kcmetro.apwa.net/chapters/kcmetro/specs/APWA_BMP_ManualAUG09.pdf of Omaha. 2006. Omaha Regional St er Design Manual: . or‐ ors‐a‐consultants ormwat http://www.ci.omaha.ne.us/pw/f contract. 2010. Urban orm ainage eria Manual, Best Management actices ol. 3. (listings b v UDFCD St Dr Crit Pr V Denver, Colorado: http://www.udfcd.org/downloads/down_critmanual.htm y olume)
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8.6.8 Retention Wet Ponds The primary components of a r ention wet pond include the permanent pool, the litt al bench surr the permanent pool, and the li st age volume abo the permanent pool. The li volume is sized such that the WQCV displaces a portion ofet the permanent pool and is released within 12 hrs. of ora storm e . Theounding aulic residence time of theve permanentor pool is typicallyve two w s or more. Theve primary pollutant al mechanism is settling as st er runoff resides in the permanent pool, but pollutantvent uptak hydr of nutrients, also occurs t some degree thr h biologicaleek and chemical activity in the pond removA, 2003). Wet ponds are a higormwaty utilized st er BMP practice due t community acceptancee, and amenityparticularly value (Schuler et al., 2007). Ro ention wet pondsoug should be used for drainage areas of 10 ac. or mor and(CASQ are typically not used in r ofitshl due t theirormwat typically large area r o . et e etr o equirement
1 Department of Environmental Protection – Bureau of Watershed Management (DEP), 2006 2 Geosyntec Consultants and Wright Water Engineers, Inc 2008
8.6.8.1 General Application ention et ponds can be used e er runoff quality om oads, parking lots, hborhoods, commercial areas, and industrial sites. A r ention wet pond is more applicable t treat lar tributaryRet areasw than other BMPs, andto improv can be utilizedstormwat as a second BMP infr a treatmentr train. R entionresidential w pondsneig may be used for a smaller site if the drainage area iset sufficient for sustaining a permanent pool.o W ger ponds may also be incorpor ed into an e ended st age or a detention pond design for flowet control (Metret Council, 2001) and rk ell in conjunction with other s such as eam ce ols. et at xt or o Under the proper conditions,wo w r ention wet ponds can satisfyBMP multiple upstrobjecti es,sour includingcontr w er quality , erosion pr ection, creation of wildlife and aquatic habitats, and r eational and aesthetic vision (UDF , 2005). Wet etponds are gener y ineff at reducing runoffv volumes b themselat improvemento Council 2001) butot can be used educe runoff flow es if additional floodecr ol olume provided abo CD the permanent pool (UDF , 2005).all Wetective ponds also pr vide some volume reductiony vesthr (Metr ation, typically less than 5‐percentto r (Str er et al., 2004rat as r enced b Schulercontr et al.,v 2007).is pro ve CD o ough evapor eck efer y
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8.6.8.2 Advantages and Disadvantages
8.6.8.3 Design Requirements and Considerations vious studies shown that 90‐percent of pollutant al in a et pond occurs een ents (MD DEQ, 1986 as cited in Metro Council, 2001), and modeling results indicate that two‐thirds of the Pre , nutrients,have and trace metal loads are r ed withinremov the firstw 24 hrs. after a stormbetw e entrainfall (Metr evCouncil, 2001). Correct permanent pool st age volume, li st age volume, basin configuration, and outlet sedimentsizing are thus very important emov v o or ve or The e or designing a . ention et pond is outlined in the ollowing sub‐sections. The components are described in the order of construction starting with e ation for construction of the permanentprocedur poolf st age area, prret eatmentw f and inlet/outletf structur design xcav Overall Design Guidanceor etr orebay, es. ention wet ponds should not be constructed until the entire drainage area is permanently stabilized against erosion and sedimentation, or a pre‐treatment practice is implemented. • Ret vy sediment loads t the pond will reduce eff eness and r e pr e dredging of the pond t r e its perf Hea o ectiv equir ematur maintaino baseflowestor theormance. permanent pool in een all ents, the minimum ea t the detention wet pond should be at least 10 ac. Other en onmental conditions • Tosuch as a age ET r toes and soil infiltration r betwes shouldrainf be considered.ev High ET and drainage ar oation r es are undesirable for a detention wet pond. Infiltrationvir should be pr ed in e conductiver soilsat with a liner t sustain aat permanent pool. infiltr at event Basin Configurationmor ve o encourage settling/sedimentation, designers should maximize the horizontal and vertical flowpath een the inlet and outlet and oid “dead zones” in the basin design o • ToCouncil, 2001). A minimum length t width ratio of 3:1 is recommended. Other w t a oid short‐circuitingbetw include a edge‐shaped pondav with on the shallow end (Metr, o ays o v Permanent Pool Storage Area & Live Volumew (WQCV) inflows (DEP 2006). ention wet ponds should be designed such that the li volume (WQCV) is released o er 12 hrs. (EPA, 2006). • Ret ve v The pond depth is an important design f or as it controls sediment deposition. The optimum
• act
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pond depth should range from 2 t 3 ft. minimum, up t 12 ft. maximum, with an a age depth of 4 8 . Shallow et ponds end e solids al than their deeper erparts. in opools less than 2 . deep,o wind will y e‐suspendver particles (Metroto ft Council, 2001).w If thet permanentto have poolmor iseffective designed t supportremov fish, sufficient permanentcount pool depthHowever, should be maintained. ft likel r o Side slopes of the r ention wet pond should be no gr er than 4:1. Embankment side slopes y be 3:1 with site‐specific appr • et eat maDesign of the permanent pool olumeoval. should allow or 14 aulic esidence time allow or e settling and nutrient e. A longer aulic esidence time will • age better settling and sedimentation.v This isf accomplisheddays hydr b sizingr the pool usingto egionalf precipitationparticulat data and char eristicsuptak of the tributaryhydr area. Theser considerations are encour ed in the design e ample at the end of this section. y r act Inlet illustrat x 1. ypical inlet es include, but e not ed o, op manholes, rundown es, es, and pipes with impact basins (Muthukrishnan et al., 2006). T structur ar limit t dr chut baffle 2. Allchut inlets should include some type of energy dissipater t reduce sediment resuspension C, 2009). o Forebay/Pretreatment(MAR 1. Wet pond design should include pr eatment t capture sediment. For ponds gr er than 4,000 cu. ft. (Metro Council, 2001), a f y is recommended. For smaller ponds, the design should include a ation , such as etrale or er o eat oreba 2. The f filtry should BMPbe a 4 t 6 ft.sw deep cellfilt delineatedstrip. b a barrier and should be sized t contain at least 10 percent of the design volume (MARC, 2009). oreba o y o 3. The minimum length t width ratio of the f y should be gr er than 2:1 t pr ent short‐ cuiting (Muthukrishnan et al., 2006). o oreba eat o ev Littoral Benchcir 1. The litt al bench slopes should be no steeper than 2:1 (Metro Council, 2001).
2. The littoral bench should e end in at least 10 ft. from the perimeter of the permanent pool and should be een 6 in. 12 in. below the permanent pool ace A, 2003; or xt ward betw to surf (CASQ UDFCD, 3.2005). The slope of the litt al bench should not e ceed 6:1. The bench should be planted with nati etland vegetation t pr e biological uptake of nutrients and dissol ed pollutants and r the formation of algalor mats. T maximize biologicalx uptake but pr ent plants from encroachingve on thew open w er surface,o theomot v ed litt al bench should comprise 25v percent t 50 percenteduce of the permanent pool surf oea (Nashville Metropolitan‐Davidsonev County [Nashville], 2006). at egetat or o Outlet Structure ace ar
1. Outlet ol vices should be designed ent clogging, allow enance and e benefits. This can be achie ed with a r erse sloped outlet w e the in ert of the outlet contris at thede permanent pool ation, butto prev the er ers the outletmaint 2 7 . belowprovide normaltemperatur w er surf v ev her v elev wat ent to ft the at ace.
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2. Outlet devices are gener y multistage structures with pipes, orifices, or weirs for flow contr Orifices, if used, should be at least 4 in. in diameter and should be pr ed from clogging b using a trash rack, well screenall or other method (DEP, 2006). ol. otect y 3. Outlet devices should be installed in the embankment for accessibility. If possible, outlet de should enable the normal er ace be aried. This the er el be ed necessary) seasonall as the wet pond accumulates sediment o er time, if desired grades arevices not ed, or for mosquito controlwat surf (DEP, 2006).to v allows wat lev to adjust (if y, v 4. Anachiev emergency drain t complet y drain the permanent pool for maintenance within 24 hrs. should be incorpor ed into the design (DEP, 2006). o el Siting Considerationsat 1. Do not locate on fill sites or on/near steep slopes. Depending on soils, bottom modifications can include compaction, incorporating clay into the soil or an artificial liner (Nashville, 2006)
2. The design w er surface depth should be a minimum of 20 ft. a from property lines and building structures or per agency specification. A gr er distance may be necessary when the ention facilityat may compromise foundations or slope stabilityway (KC Metro APWA, 2006) eat 3. Forret public safety considerations, fences and landscaping should be used t impede access t the . The facility should be cont ed t eliminate drop‐offs or other hazar o o 8.6.8.4 Inspectionfacility and Maintenanceour o ds. enance activities for r ention wet pond include short‐term and long‐term maintenance task
ShortMaint Term: Year 1 – Year 3et (Post-Installation) s. 1. W er young plants and seedlings a minimum of w y for the first three months. W ering ma be r ed more fr y during the summer months (June thr h August) during the first at . Try t maintain at least a 70‐percent vegetationeekl density t ensure stability at y equir equentl oug 2. year e o eeds using spot application of herbicide houto the first .
3. CheckEliminat for signsw of erosion or instability and make surethroug that aesthetics areyear. maintained thr the BMP f oughout 4. After r ootprintall equaling or e ceeding 0.5 in.:
ainf e that vegetationx and other erosion stabilizing mechanisms are intact and check inlet/outlet structures and surrounding area for signs of erosion or instability a. Ensur Inspect all inlet/outlets and epair or e clogged flow es as
b. sediment and debrisr from pr restoreatment BMP or F structur needed
c.Confirm Remove drainage s em functions andetr bank stability orebay
5. A oned. year after installation, ystinspect vegetation and all other supporting. structure. Replace dead plants and r in plant species. t 6. R ed sedimentsemove shouldvasive be t ed for t xicants and should comply with local disposal
emov est o requirements. Omaha Regional Stormwater Design Manual Rev. 06/2014 8-125 Chapter 8 • Stormwater Best Management Practices 8.6 • Structural Best Management Practices
Long Term: Year 3 – later 1. In spring, mow or trim egetation an e ht of 6 in. ade. ed debris. early v to approximat heig above gr Remove 2. Inspectaccumulat vegetation one t two times each year and r weeds and in species.
3. rim back or o own emove vasive
4. Tepair or removee cloggedovergr h flowvegetation. es as
5. R least twicerestor a , checkhig or subsidence,structur osion,needed. ee owth on the , accumulation around the outlet, and erosion within the basin and banks. At year f er tr gr embankment sediment 6. R ed sediments should be t ed for t xicants and should comply with local disposal
emov est o 8.6.8.5 Submitrequirements.tal Requirements or view purposes prior construction, the ollowing minimum submittal ements
F re to f requir are recommended:1. Drainage area map, including drainage area t the r ention wet pond.
2. Existing and proposed contour map of site (1‐ft.o contourset recommended). Additional spot ations may be helpful.
3. Geotechnicalelev in ation of site (soil borings, w er table location).
4. St er plan/profilevestig for sit at
5. ormwatention et pond plan view ande. ofile . Components labeled with
6. RetHy ologicw calculations (r er t Designpr Example)view and a ageclearly annual w er budgetdimensions. anal
7. Detaildr of y oposed outletef ando erflow es withver dimensions orat construction. ysis. e design calculations (r er t Design Ex an pr ov structur f Include 8. Vegetationappropriat plan with schedule for installationef o and initialample). maintenance. Appr e erosion contr es should be included. opriat ol 9. Anmeasur as‐built surv of the r ention wet pond is recommended t confirm actual construction es t appr ed construction plans. ey et o 10.adher Long‐termo inspection/maintenanceov plan with responsible party and dedicated funding sour
8.6.8.6 Design Calculations ce. A short summary of design calculations is ed A detailed design ample is outlined in
present below. ex Section 8.6.8.7Step 1 .Determine the WQCV and retention wet pond design live-storage volume (VD). The WQCV is based on 0.5 in. of runoff. If routing of impervious area t pervious area (i.e. cascading planes) occurs within the drainage area of the r ention wet pond, the design volume of the r ention wet pond can be r because a portion of the WQCV from the impervious areao is infiltr ed. R er t Section 8.3 determine the educed WQCV t use for etsizing the r ention wet pond. et educed at ef o to r o et
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= WQCV or if cascading planes exist in EDDB drainage area, see Section 8.3.4 or calculation of V
StVDep 2 Determine the Rational runoff coefficient for the tributary area. f D.
(8-28)
Where: = Rational runoff coefficient (unitless) = P cent Imperviousness of Drainage Area (unitless) C IStep 3 Determineer the permanent pool volume. ermine the permanent pool volume r ed t pr a minimum detention time of 14 da Det equir o ovide ys. (8-29)
Where: = Permanent pool volume (ac.‐ft = Rational runoff coefficient (unitless) V = Tributary area (ac.) .) C = 14‐day wet season r all for Omaha, NE (1.6 in.) AT 14 StR ep 4 Size the outlet. ermineainf the outlet type and size such that the V is detained and released o er 12 hrs. Outlet design must also consider acility dimensions and site constraints. For sizing all r ention wet pond D outlets, first calculate theDet a age discharge r for the V using Equation 8‐30. v f et Average Discharge Rate ver ate D (8-30)
Where: = A age discharge r for the V = Design li e‐st age volume for r ention wet pond (ac.‐ft QAVG ver ate D (cfs) VDxt the Q is usedv t calculateor dimensionset for a single orifice or v‐notch.) weir outlets.
Ne AVG o Single Orifice
(8-31)
Where: = Orifice diameter (in.) = A age discharge r for the V DO = Design li e‐st age volume for r ention wet pond (ac.‐ft AVG D Q = Orificever discharge coefficient,ate Where(cfs) C = 0.66 for weir plate thickness ≤ orifice diamet , and V D 0.80, otherwisev or et .) C O = acceleration due t gr vity (32.2 ft O er = A age head of V g o a ./s.) Havg ver D(ft.)
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V-notch Weir Dimensions of the V‐notch weir outlet include the V‐notch weir angle and the top width of the V‐not
ch opening. (8-32)
(8-33)
:
Where = R ed V‐notch weir angle, 20° minimum (degr = A age discharge r for the VD θ = V‐notchequir weir coefficient (2.5) ees) QAVG = verage head of V ateolume o er orifice(cfs) in ert (ft CV = Top width of V‐notch weir (ft.) H2yr = Aver Max V depth aboD v outlet (ftv v .) WV Zmax D ve .) Step 5 Size Outlet Protection to avoid clogging. If the chosen outlet structure discharges t a closed s or if debris in the outlet s ould be difficult e, ermine the e outlet ection oid clogging. Outlet pr ection t a oid clogging may include trash r s, hoods, or r ersedo slope pipes.ystem, ollow guidance in worker 6 w age acilities to remove thedet minimum appropriatash ack size ersusprot to av er or minimum dimensions.ot o v ack ev F Chapt Stor F to estimat tr r v outlet Stdiametep 6 Determine the forebay volume. The minimum f y volume should be 10 percent of the design olume (V oreba Stv ep 7 DetermineD). the littoral bench dimensions. ermine litt al bench dimensions based on permanent pool volume and litt al bench design guidelines. Det or 8.6.8.7 Exampleor Design r ention wet pond t accept runoff from an 18‐ac., single‐f y residential de elopment (30% impervious). The de eloper would like t design a wet pond with a single orifice outlet et o amil v
Step 1 Determine thev WQCV and retentiono wet pond design live-storage volume (V. D).The drainage ar the r ention wet pond is 18 ac. Using 0.5 in. of runoff, the WQCV is calculated as: ea to et
outing of impervious area t pervious area (i.e. cascading planes) reduces the design volume of the r et pond because a portion of the runoff from the impervious area is infiltr ed. When cascading planes ar R o etention used, estimate the r ention wet pond design volume using Section 8.3.4. For this e ample, no cascading w at e planes are present so the design li e‐st age volume (V ) is equal t the W et x v or D o QCV.
Step 2 Determine the Rational Runoff Coefficient for the tributary area. calculate the permanent pool olume, the ational runoff coefficient must first be ed. Using Equation 8‐28: To v r calculat
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Step 3 Determine the permanent pool volume. ermine the permanent pool volume r ed t pr a minimum ention time of 14 s. Using Equation 8‐29, the permanent pool olume Det equir o ovide det day v is:
Step 4 Size the outlet. The de eloper would like t install a single orifice outlet for this particular wet pond. size the , first the er quality ge should be ed using Equation 8‐30. v o To outlet wat dischar calculat
Then, the orifice diameter should be calculated using Equation 8‐31. The desired a age depth of the V the outlet is 2 ft ver D above .
Step 5 Size Outlet Protection to avoid clogging. or this e ample, the orifice outlet discharges t a closed em; ther e, a trash rack is pr vided. The openings for the trash rack should be calculated based on the orifice diameter calculated. The purpose of sizing openingsF forx the trash rack is t find the optimalo size of the openingssyst t letefor the r ed dischargeo pass while pr ecting the outlet from clogging. First the area of the orifice opening is calculat o o equir ot ed.
, using Figure 6‐13 in Chapter 6, the minimum area that the trash rack should co er around the outlet is
Next v calculated:
Step 6 Determine the forebay volume. The minimum volume of the f y is equal t 10‐percent of the design volume (V ). With a design volume of 0.75 ac.‐ft. the f y volume is 0.075 ac.‐ft. The minimum length t width ratio should be gr er than 2:1. oreba o D oreba Step 7 Determineo the littoral bencheat dimensions. The litt al bench slopes should be no steeper than 2:1 and should e end in at least 10 ft. from the perimeter of the permanent pool. The benches should be een 6 in. 12 in. below the permanent pool or xt ward betw to surface.
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8.6.8.8 References A. 2003. California Stormwater Quality Association Stormwater Best Management Practice Handbook
CASQ : http://www.dot.ca.gov/hq/construc/stormwater/manuals.htm. 2006. P ania St er Best Management Practices Manual‐Section 6.6.2: Wet P Basin. Document Number: 363‐0300‐002: DEP ennsylv ormwat ond/Retention A. 2006. National Pollutant Dischargehttp://www.jonestownship.com/Stormwater%20BMP.pdf Elimination S em Fact Sheet Series – Wet P
USEP yst onds: http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=factsheet_results&view=specific&b mp=68 ec Consultant and W ht W er Engineers, Inc. 2008. Overview of P ormance b BMP Category and Common Pollutant Type: ISBMPD (1999‐2008): Geosynt rig at erf y http://www.bmpdatabase.org/Docs/Performance%20Summary%20Cut%20Sheet%20June%202008.pdf Metro APWA. 2006. Division V Section 5600 Storm Drainage S ems and F
KC o Council. 2001. Minnesota Urban Small es BMP Manual‐Rystention acilitiesems: et onds. . aul, gs. 3‐251 t 3‐265: Metr Sit et Syst W P St P MN. P C. 2009.o Manualhttp://www.metrocouncil.org/environment/water/bmp/manual.htm of Best Management actices or er Quality –Second Edition. Section ended Wet Detention. MAR Pr f Stormwat 8.10 ExtMuthukrishnan, S. Field, R.http://kcmetro.apwa.net/chapters/kcmetro/specs/APWA_BMP_ManualAUG09.pdf and Sulli an, D 2006. The use of best management practices (BMPs) in urban ersheds (ed. 1, 118‐124) Field, R., Tafuri, A., Muthukrishnan, S., A o, B., and Sel , A. (Eds.), ania, U.S.: Destech Publicationsv . wat cquist vakumar Pennsylvville. 2006. St er Management Manual Volume 4: Best Management Pr
Nash ormwat actices: http://www.nashville.gov/stormwater/regs/SwMgt_ManualVol04_2009.asp, .; Hirschman, .; M.; and Zielinski, J. 2007.. Urban ershed ation Manual No. – Urban er ofit actices. olume 1.0. Office of er Management er or Schuler T D Novotney, Subwat Restor 3 Stormwat Retr Pr V Wastewat Cent f Watershed Protection. 2010. Urban orm ainage eria Manual, Best Management actices ol. 3. (listings b v UDFCD St Dr Crit Pr V Denver, Colorado: http://www.udfcd.org/downloads/down_critmanual.htm y olume).
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8.6.9 Soil Conditioning Soil conditioning is a post‐construction actice ended e disturbed and low anic soils mechanical compaction reduction and compost amendment in order t increase macr osity and impr er r ention. This practice is intendedpr t reduceint the generationto improv of runoff from the areaorg w e it is through o opor ove wat et o her implemented.
1 Median Effluent Concentrations were not available for this BMP. 2 Tyler, et.al. 2010.
8.6.9.1 General Application Soil conditioning is acceptable for any pervious area w e the soils ha lost their inherent infiltration and er st age capacity thr h compaction and disturbance. This BMP will be most applicable for large sit eas proposed for turf ass, low maintenance lawn, orher nature prairie plantings.ve It can also be applied t wateas withinor landscape bedsoug gi en all specifications are met for soil conditioning and tilling within the bed e areas, and the beds are grnot bermed with slopes gr er than 10%. Soil conditioning for the purpose of o ar er management shouldv be used: ar eat stormwat1. When slopes are less than 10%
2. Outside the dripline of a tree, t a oid damaging the root s
3. When existing soils are not saturo ved or seasonally w ystem
4. Gr er than ten (10) ft. of the foundationat of a buildinget
5. Wheneat the w er table is gr er than 1.5 ft. of the soil surf
6. Where runoffat velocities willeat not damage or undermine v ace
egetation
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8.6.9.2 Advantages and Disadvantages
8.6.9.3 Design Requirements and Considerations The ollowing eps should be ed condition disturbed soils or er
f st ep 1 – Ensure followsite conditionsto properly are dry prior t beginning the soilf stormwatconditioningmanagement. process t oid further compacting soils. • St o o avep 2 – R existing vegetation, including turf, and till the ground t a minimum depth of 6 in. • St emove o ep 3 – Place a 3‐in. deep la er of specified compost on top of the tilled ground and till compost into a depth of 6 in. of existing soil. See able 8‐20 or compost specifications. • St y ep 4 –Fine grade the site with minimum equipmentT passesf (no more than two (2) passes) reduce the potential for soil compaction. Finalizing all preliminary critical spot ele ation, • slopesSt and positi drainage criteria for the site should be completed as much as possible priorto t finish grading in order t ensure that equipment compaction is minimized afterv soil is ed an amended.ve o o workep 5 – Firm soil using one pass of a 50‐pound roller if v co er will be drill seeded or plugged t help ensure successful plant establishment • St egetative v ep 6 – Establisho v co er immediat y after finish. grading and take steps t pr ent osion during establishment, including but not limited t installing erosion control blankets, • Stsilt fence or str waddles.egetative Vegetationv may beel sodded, seeded, or plugged. For seedingo orev erplugging, all d es shall be ed or theo e mulching of e soil ace eas untilaw egetation is y established. Expectations of plant ormance must be understoodstandar (i.e.procedur – there may be a shortfollow periodf of plantappropriat stress due t nutrientbar cycling insurf compost)ar and incorporv ed intofull the management plan (see Stepearly 7). perf o ep 7 – A management planat is r ed in the PCSMP for all areas that ha undergone soil conditioning. The plan must be ed during the first o ears of plant . • ComponentsSt include weed management,equir spot reseeding, maintaining moistureve during germination and initial establishment,follow inspection and inttw y r all e ents,establishment and the al of erosion control measures as needed. ensive ainf v remov
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Table 8-20 Compost Specifications Compost Criteria for Soil Conditioning The compost used in soil conditioning shall be ed from plant material, and the result of biological degradation and tr ormation of plantderiv deri ed materials under conditions that e anaerobic decomposition.ansf The mat shall be wellv composted, free of viable weed seeds, andpromot stabilized with r t o gen consumptionerial and carbon xide ation. The compost a moisture contentegard thato hasxy no visible fr er or dustdio producedgener when handling the matshall Ithave shall meet the criteria pr ed in Table 8‐20,ee aswat r ed b the U.S. Composting Council S erial. Compost Technical Data Sheetesent pr vided b the eport. OmaGroy is a locally produced compostTA oduct that is acceptable for useo in soil y conditioning.vendor pr Vegetation ennial grasses are usually specified and nati grasses are pr ed. A range of plant material can be used in conditioned soils areas including legumes, deep r ed grasses, shrubs, and trees. Per ve eferr 8.6.9.4 Inspection and Maintenance oot Short Term: Year 1 – Year 3 (Post-Installation) 1. W er vegetation a minimum of w y for the first three months. W ering may be r ed mor y during the summer months (June thr h August) during the first y . Try t maintain atat least a 70% vegetation density teekl ensure stability at equir e frequentl oug ear o 2. e eeds y or usingo spot application. of herbicide hout the first
3. EliminatCheck for signsw ofmanuall erosion or instabilityby and make sure that aestheticsthroug are maintained thryear. the soil conditioned ar oughout 4. After r all equaling orea. e ceeding 0.5 in., ensure that vegetation and other erosion stabilizing mechanisms are intact. ainf x 5. A one year after installation, inspect vegetation and all other supporting structures. Replace dead plants and r in plant species. t Long Term: Year 3 – lateremove vasive 1. In spring, mow or trim egetation a ht no less than 6 in. ed
2. Inspectearly vegetation one t twov times eachto yearheig and r weeds andRemove in accumulat species. debris.
3. rim back or o own emove vasive
4. TA least twiceremove a y , checkovergr for subsidence,vegetation. erosion, and sediment accumulation.
t ear
Omaha Regional Stormwater Design Manual Rev. 06/2014 8-133 Chapter 8 • Stormwater Best Management Practices 8.6 • Structural Best Management Practices
8.6.9.5 Submittal Requirements or view purposes prior construction, the ollowing minimum submittal ements
F re to f requir are recommended:1. ea of oposed soil conditioning and y oposed or xisting eam
2. ArExistingpr and proposed contour map of sitean (1‐ft.pr contourse with eledownstrations tied BMPs.t N VD 1988 datum ecommended). Additional spot ele ations may be helpful. v o A 3. Geotechnicalr in ation of site (soilv borings, w er table location).
4. Vegetation planvestig with schedule for installation andat initial maintenance. Appr e erosion contr es should be included. opriat ol 5. Long‐termmeasur inspection/maintenance plan with responsible party and dedicated funding sour 8.6.9.6 Design Calculations ce. Equation 8‐31 can be used e the olume of compost ed or an ea oposed or conditioning. to calculat v requir f ar pr f soil (8-34)
Where: = olume of compost needed for soil conditioning, y = Area of proposed soil conditioning, ft 3 Vcompost =v depth of compost, in. 2 d. ASC . d8.6.9.7compost Example e the volume of compost necessary t implement 5,000 ft of soil conditioning, t be planted with turf ass. Use the recommended compost depth of 3 in. 2 Calculat o . o gr 8.6.9.8 References , s, . e, .2010. The Sustainable e – The Design Manual or e and Low Impact . Tyler Rodney. Mark Alexander Faucett Britt Sit f Green Infrastructurginia Department of ConservationDevelopment and R eation. 2010. Design Specification No. 4 Soil Compost Amendment Version 1.7. Vir ecr
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8.7 Lot-Level/Homeowner Non-Structural Best Management Practices er pollution is the untr ed contaminated w er that drains from lawns, parking lots and str h the municipal storm drain s em. When harsh chemicals from lawns and t xic substances from spills Stormwater w s, harmful pollutantseat kill fish, destr wildlifeat habitats, decrease aesthetic value and eets throug e the w er people use asyst a source for drinking, boating and swimming. Non‐structuralo BMPs that helpent reduceaterway the quantity of pollutants from reachingoy the w s include but are not limited to; using sustainablecontaminat methodsat of wn e and landscape enance, educing ash and pet e, and and cleaning impervious surfaces (Uni ersity of Nebr a‐Lincolnaterway W 2011). la car maint r tr wast sweeping 8.7.1 Lawn Care and Landscapev ask Maintenanceater, er runoff from a healthy dense lawn (with up t medium dense soil) r occurs, e cept during ense r all e ents (Uni ersity of Minnesota, 2006: Bierman, et al., 2010). In order t maintain a health Stormwat o arely x wn, it is important t select lawns that are adapted t the r ’s climate. The a Master Gar int ainf v v o y , ed the ersity of a‐Lincoln, vides a link a sustainable urban la o o egion Nebrask dener e hosted b the Uni ersity of Minnesota. The Uni ersity of Minnesota w e contains links t assist in Program host by Univ Nebrask pro to landscape wn management and sustainable landscape design. A maintenance is important t keep a health websit y v v ebsit o wn s em. Maintenance techniques that support a healthy lawn include; soil care, method of fertilizing, and la dditionally, o y method of mowing. la yst 8.7.1.1 Soil Care Soil is the foundation for a healthy lawn and landscape. Soil should be t ed t determine the soil’s compaction. Soil testing can be done b pushing a scr er into the soil. If the scr er r pounding t enter the soil, the soil is compacted (Center for W ershed estPr ection,o 2000). Soil pr and amendments are discussed in pr viousy Sections. ewdrivSoil that is compacted can be trewdrived usingequires a hand cor or a mechanicalo aer . Compost can be applied t existing lawnsat t improt e soil compaction (Centereservation f ershed Pr ection, 2000). e eat er ator o o ov or Wat8.7.1.2 Reduceot Turf Area ersion of wns ees, shrubs or meadow plantings can y educe the quantity er runoff as well as reduce the cost, time and effort needed t maintain turf based y (Center f Conv la to groundcover, tr greatl r of ershed Pr ection, 2000). Areas that are not suited for lawn are best for con ersion. These areas include stormwat o ard or ost pockets, exposed areas, shaded areas, steep areas and wet areas (Center for W ershed Pr Wat ot v 2000). A y areas that are difficult or dangerous t mow are good candidates for con ersion. Ar fr at otection, that are difficult t fertilize or w er e y are also good con ersion candidates. R er t Section 8.5.1 dditionall o v eas dens in Residential Areas for possible replacement landscape designs. o at venl v ef o Rain Gar8.7.1.3 Fertilizer Methods est soil’s pH and fertility le el, prior t adding any fertilizers, as many soils do not need additional f support a healthy lawn. The USDA pr vides a soil quality test guide. Nebr a Department of Agricultur T v o ertilizers vides a list of soil and plant testing labor that are in compliance with the Nebr a Soil and Plant to o ask e sis Labor ory Act Regulations. A y many home impr ement and har e st es carry pro atories ask soil testing kits, in their lawn and g den departments. Analy at dditionall ov dwar or inexpensive ar
Omaha Regional Stormwater Design Manual Rev. 06/2014 8-135 Chapter 8 • Stormwater Best Management Practices 8.7 • Lot-Level/Homeowner Non-Structural Best Management Practices
ving grass clippings or mulch/mowing typically pr vides adequate le els of nitrogen and phosphorus t maintain a healthy lawn. If a commercial fertilizer is used it is best t use a minimal amount of fertilizer with Lea ed ogen and no or low phosphorus. Theo use of slow eleasev ed) ogen and lowo no phosphorus fertilizer helps reduce st er pollutant loads. Unlesso a soil test indicates otherwise, encapsulatous isnitr only needed during the first year of establishment rof the lawn.(encapsulat When applyingnitr common off theor shelf commercial fertilizer use half the manuformwat er’s recommended r e, as studies ha found most la dophosphor not r e high doses of fertilizer (Center for W ershed Pr ection, 2000). A y when t appl ertilizer is equally important: cool season grassesactur are best fertilized onceat in the fall andve warm season grwns e bestequir fertilized in se al small doses during the atsummer (Centerot for W ersheddditionall Pr ection, 2000).o B y f ying fertilizers during the correct season the turf utilizes more of the nutrients which r es t a morasses costar eff method ofver maintaining the turf as well as helping t reduce theat amount ofot pollutants in y appl er runoff. elat o e ective o Instormwat order t keep the fertilizer on the lawn and plants w e it pr vides its benefits and t keep the f out of w s, a oid using fertilizer just bef e it rains. o her o o ertilizer 8.7.1.4aterway Lawn Carv e or ollow the ee in. rule: er cut our wn er than ee in. easing the mowing ht health of the turf is impr ed as it helps pr ent the grass crowns from being exposed t sunburn. Taller gr Falso keeps thethr soil from beingnev exposedy t la sunlightshort which canthr cause weedBy incr seeds t germinate. Incrheig the mowing ht agesov deeper oot owthev hich in turns causes the ass be o . utting ass ass at a taller height also helps retain theo moisture during drier seasons. o eased heig encour r gr w gr to healthier C the 8.7.2gr Trash and Pet Waste Reduction er disposed of in a storm drain can choke, suff e and disable aquatic life. Dispose of litter b throwing it in a trash can or r cling it. Litt ocat y 8.7.2.1 Trashecy Reduction Cleaning oducts and other household chemicals should er be dumped outside, down the sink or down orm drain. You can dispose of your household chemicals for free at Under the Sink, the City’s household pr nev a dous w e disposal f . Check their w e for drop off inf st Landscapehazar waste while or acilityanic can still be problematicebsit t w s;ormation. the problem occurs as this w es t higher le els of nutrients entering the w s which in turn encourage algae and r ast g o aterway aste plants ow in es and eams Janssen and , 2008). Methods educe e contribut o v aterway ooted utilizing lawn care tips listed in Section 8.7.1.4 and composting in backy ds. Uni ersity of Nebr a‐Lincoln to gr lak str ( Barrow to r yard wast include ension pr vides a w e ( er Management: Y W e Management with inf ar v ask ding how start composting and other e eduction Ext o ebsit Stormwat ard ast ) ormation 8.7.2.2regar Petto Waste Reduction wast r tips. et w e dumped in storm drains goes str ht into ri ers and lakes, contaminating the w Pet w e left on lawns can cause harmful bacteria and viruses t enter w s, causing pollutant damage. It is best t disposeP ast of pet e in the ash or flush it aigdown the v . The e will be ater.ed in the ast or w er treatment plant. When taking your odog for a aterwaywalk, remember t take some plastic bags t cleano up er them. wastDo not owtr the bag down the orm toiletain. wast er runoffproperly is not treat landfill astewat o o aft e pet w ethr stations in multi‐f y stand apartmentdr Stormwat complex common areastreated. and public park and ail s Incorporat ast amil s tr ystems.
8-136 Omaha Regional Stormwater Design Manual Rev. 06/2014 8.7 • Lot-Level/Homeowner Non-Structural Best Management Practices Chapter 8 • Stormwater Best Management Practices
8.7.3 Sweeping and Cleaning of Impervious Areas Do not lea grass clippings and lea es on impervious areas (such as dri and streets) when you ar doing rk. This debris can er the orm ain and cause clogs and e the ying e wveer’s o gen le els whichv can harm aquatic or veways e yard wo ent st dr pollut water. Deca leaves Pickdeplet up anyat spilledxy chemicals,v fertilizers, oils, etc as r ganisms.er can pick these pollutants up and deposit them o the s. Use cat er or other absorbents soak up liquid spills and then eep up and dispose of the used ainwat int waterway litt to sw properly 8.7.4 Referencesabsorbent. Bierman, P.M., Hor an, B.P., Rosen, C.J., Hollman, A.B. and P liari P.A. 2010. Phosphorus Runoff from T as Aff ed b Phosphorus Fertilization and Clipping Management. Journal of Environmental Quality. 39:282‐ g ag urfgrass ect y 292.er or ershed ection. 2000. a low input wn. Protection Techniques. 1(5), 254‐264.
CityCent of Omaha.f Wat 2003. UnderProt the sink: HouseholdToward Hazardous laW e Collection F
ast acility: http://www.underthesink.orgJanssen, and , 2008./ er Management: e . ersity of a Lincoln Extension, W operty Design and Management NebGuide: D. Barrow T. Stormwat Yard Wast Management Univ Nebrask – ater/Pr http://www.ianrpubs.unl.edu/epublic/pages/publicationD.jsp?publicationId=1010a Department of Agriculture. 2008. Nebr a Soil and Plant Testing Labor
Nebrask ask atories: http://www.agr.state.ne.us/division/lab/soil_plant_testing_labs.pdfA. 2001. Soil Quality Test Kit Guide:
USD ersity of Minnesota. 2006. Sustainablehttp://soils.usda.gov/sqi/assessment/files/test_kit_complete.pdf Urban Landscape ormation Series
Univ Inf (SULIS): http://www.sustland.umn.edu/maint/benefits_1.htmlersity of Nebr a‐Lincoln Extension. 2011. Nebr a Master Gardener Pr
Univ ask ask ogram. http://mastergardener.unl.edu/homeersity of Nebr a‐ Lincoln Extension. 2011. UNL W
Univ ask ater. http://water.unl.edu/web/landscapes/home
Omaha Regional Stormwater Design Manual Rev. 06/2014 8-137 Chapter 8 • Stormwater Best Management Practices
Appendix A
Simple Method to Calculate Urban Stormwater Pollutant Loads and BMP Performance
Appendix B
USEPA Class V Well Memorandum
Appendix C
PCWP Stream Setback Policy
Appendix D
Derivation of Peak Flow Rate for the Water Quality Storm Appendix E
Background Information on Cascading Planes Appendix F
Example Bioretention Facility Specification
8-138 Omaha Regional Stormwater Design Manual Rev. 06/2014 8.5 • References Chapter 8 • Stormwater Best Management Practices
8.5 References , Randall G. 1998. Better Site Design: A Handbook for Changing the De elopment Rules in Y . Center for Watershed Protection and Conservation Design for Subdivisions. Ellicott City, MD: Cent Arendtor W ershed Pr v our Community er f ansat Storm Wotection.er W e. 2011:
Caltrer for W ershedat Prebsitection: http://www.dot.ca.gov/hq/oppd/stormwtr/
Cent en e;at ot, vid R.;http://www.cwp.org and s, Larry 1988. Applied
Chow,City of VLeneT a.Maidment Municipal DaCode: May W. Hydrology.
City of Omaha.x Municipal Code: http://www.lenexa.com/LenexaCode/codetext.asp?section=001
Cityhttp://library.municode.com/index.aspx?clientID=10945&stateID=27&statename=Nebraska of Omaha, 2011. Post Construction St er Management Planning Guidance:
ormwat http://www.omahastormwater.org/images/stories/Development/pcsmp%20guidance%20document%20re Cityvised%20nov%202011.pdf of Omaha. 2009. Long erm ol Plan or the Omaha Combined er erflow ol am 1: T Contr f Sew Ov Contr Progr Vol City of Omaha. 2007. Green Streets of Omaha Part 3, Chapter V Installation and Maintenance Standar g/planning/urbanplanning/design‐guidelines (listings b part) ds. http://www.cityofomaha.orA. 2011. SWMM: , Accessedy July 2011
USEPA. 2008. Municipalhttp://www.epa.gov/nrmrl/wswrd/wq/models/swmm Handbook, Managing Wet Weather with Green Infr / e: Green Str
USEP astructur eets: http://water.epa.gov/infrastructure/greeninfrastructure/upload/gi_munichandbook_green_streets.pdforth, d K. and Thompson, win S. 1982. AA echnical eport NWS 34 Mean Seasonal, and Annual Pan E ation for the U.S. Office of Hy ology National Weather Service W Farnsw.C. Richar Ed NO T R Monthly, vapor dr ashington, D ec Consultant and W ht W er Engineers, Inc. 2011. Technical Summary Volume Reduction. ISBMPD
Geosynt rig at http://www.bmpdatabase.org/Docs/Volume%20Reduction%20Technical%20Summary%20Jan%202011.pdfec Consultant and W ht W er Engineers, Inc. 2008a. Anal sis of T eatment S em P ISBMPD (1999‐2008): Geosynt rig at y r yst erformance: http://www.bmpdatabase.org/Docs/Performance%20Summary%20June%202008.pdfec Consultant and W ht W er Engineers, Inc. 2008b. Overview of P ormance b BMP Cat and Common Pollutant Type: ISBMPD (1999‐2008): Geosynt rig at erf y egory http://www.bmpdatabase.org/Docs/Performance%20Summary%20Cut%20Sheet%20June%202008.pdfGuo; James C. Y.; Blackler, Gerald E.; Earles, T Andrew; and MacKenzie, Ken. 2010. Incenti Index De e orm‐ er ‐Impact Designs. SCE Journal of onmental . ve veloped to Evaluat St Wat Low A Envir Engineering.
Omaha Regional Stormwater Design Manual Rev. 06/2014 8-139 Chapter 8 • Stormwater Best Management Practices 8.5 • References
LID Cent , Inc. 2008. LID Center – Green Str
er eets: http://www.lowimpactdevelopment.org/greenstreets/background.htmC. 2009. Manual of Best Management actices or er Quality – Second Edition. Section ended Wet Detention. MAR Pr f Stormwat 8.10 NationalExt Climatic Data Centhttp://kcmetro.apwa.net/chapters/kcmetro/specs/APWA_BMP_ManualAUG09.pdf. Omaha Eppley Airfield Station rain g .
er auge: http://www.srh.noaa.gov/data/obhistory/KOMA.htmlal R ces Conservation Service WETS Station. 2005. Omaha Eppley Field, NE6255:
Natur esour http://www.wcc.nrcs.usda.gov/ftpref/support/climate/wetlands/ne/31055.txta Department of onmental . Section 303d List of ed
Nebrask Envir Quality Impair Waterbodies: http://www.deq.state.ne.us/SurfaceW.nsf/Pages/TMDLNorth Carolina DOT St er Best Management Practices T x, 2008:
ormwat oolbo http://www.ncdot.org/doh/preconstruct/highway/hydro/pdf/StormwaterBMPMarch08.pdfapillion Creek Partnership. 2009. Final Papillion Creek W ershed Management Plan:
P at http://www.papiopartnership.org/resources/documents/090430_Final_Drainage_Plan_BodyReport_Compili ed.pdfodie, St e, Hartsig, Ted and Szatko, And 2010. Sustainable Landscapes ‐ Rain Gardens, Bioswales and X dens: A Manual or Homeowners and Small operties in Omaha. ersity of a – R ev y. eric ension, W operty Design and Management W Gar f Pr Univ Nebrask Lincoln (listings b chapt Ext ater/Pr ebsite: Thehttp://water.unl.edu/web/propertydesign/publications Rouge Ri er Project: y er)
. 2010.v Urban ormhttp://www.rougeriver.com/proddata/wmm.html ainage eria Manual, Best Management actices ol. 3. (listings b volume) UDFCD St Dr Crit Pr V Denver, Colorado: http://www.udfcd.org/downloads/down_critmanual.htmCE. 1998. WRP‐ echnical Note HY‐DE‐4.1 Methods t Determine ythe Hy ology of P ential Wetland Sit
USA on Or anicT R cling Council. 2010. Building Soilo Guidelines and Rdr ces forot Implementing Soiles. Quality and Depth BMP T5.13 St er Management Manual for W ern W on. Soils for Salmon: Washingt g ecy esour ormwat est ashingt http://www.soilsforsalmon.org/pdf/Soil_BMP_Manual.pdfWinSLAMM:
Wisconsin Departmenthttp://www.winslamm.com/winslamm_updates.html of Natural R ces. 2004. Conservation Practice Standards 1002: Site E aluation f er Infiltration. esour v or Stormwat
8-140 Omaha Regional Stormwater Design Manual Rev. 06/2014 Chapter 8 • Stormwater Best Management Practices
Omaha Regional Stormwater Design Manual Rev. 06/2014 8-141 Appendix 8-A Simple Method to Calculate Urban Stormwater Pollutant Loads and BMP Performance (This page was intentionally left blank) Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Appendix 8-A Simple Method to Calculate Urban Stormwater Pollutant Loads and BMP Performance
Estimating the e ed annual pollutant loads from the de eloped area will assist in determining tar pollutants. Estimating BMP pollutant r al performance helps in selecting post‐construction BMPs that e most eff xpect in r ving the tar ed constituents fromv site runoff. get emov Estimatingar Aectivennual Pollutemoant Loads fromget Developed Areas
y e the ed pollutant load om an urban ea, the er Center’s Simple Method e Urban er ollutant can be used. The St er Center has To quickl calculat expect fr ar summarized e ent mean concentrations (EMCs) of pollutants1 from diff Stormwatent land uses. A summary of the ormwat toerCalculat Center data is shownStormwat in Table A‐1.P EMCs forLoads bacteria ha also been published b the P v er eek artnership and e shown in able ‐2. Stormwat ve y apillion Cr P ar T A Table A-1 Simple Method Model Default Value EMC
Source: Stormwater Center Website, accessed July 2011.
The Simple Method estimates pollutant loads for chemical constituents as a product of annual runoff v and EMC, as: olume Equation A-1
e:
WherL = Annual load (lbs) R = Annual runoff (inches) = EMC (mg/L) A = Area (acres) 0.226C = Unit con ersion f
or bacteria, the equationv is sligactory diff , t account for the diff ences in units. The modified equation or bacteria is: F htl erent o er f Equation A-2
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐ ‐
A i Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
e:
LWher = Annual load (Billion Colonies) R = Annual runoff (inches) C = EMC bacteria (Colony Forming Units (CFU)/100 ml) = Area (acr 1.03 * 10‐3 = Unit con ersion f A es) The annual runoff in inchesv is calculatedactor as a product of annual runoff volume, and a runoff coefficient (R unoff volume is calculated as: v). R Equation A-3
e:
RWher = Annual runoff (inches) = Annual r all (inches) Table A‐ Pj = F action of annual r all e ents that produce runoff (usually 0.9) P = Runoff Coefficientainf 3 r ainf v Rv Equation A-4
e:
Wher Impervious fr
Ia = action Table A-2 Possible Sources and Concentrations of Fecal Coliform and E. coli in the Papillion Creek Drainage Basin
8‐ ‐ii Omaha Regional Stormwater Design Manual Rev. 06/2014
A Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Table A-3 Annual rainfall for Municipalities within the Omaha Region
1Rain gauge information for Douglas and Washington County for NRCS based on time frame of 1971-2000 2Rain gauge information for Sarpy County (Ashland) for NRCS based on time frame of 1961-1990
Once the pollutant load from a particular land use is estimated, the BMP performance can also be estimat The pollutant load leaving a BMP is a function of the volume of w er leaving the BMP and the effluent ation. The Simple Method t Calculate BMP P ormance (Simple Method) can be used t estimate. the pollutant r al eff eness of BMP types. The Simple Methodat pr vides an estimate of BMP concentrormance; actual pollutant removo al performanceerf for a particular BMP can only be verifiedo usinge post-constructionemov monitoringectiv data. o perf Simple Method to Calculate BMP Performance BMP performance can be estimated b comparing the pollutant load entering the BMP t the pollutant load xiting the . The ernational BMP database ecommends using effluent ations and olumes t measure BMP performance.y The reasons for this recommendation are summarizedo in the P e al F BMP Int r concentr outflow v o 2 ercent RemovThe pollutantactsheet load entering. the BMP is estimated using Equation A‐1 or A‐2. The pollutant load exiting the BMP is estimated using Equation A‐5 which multiplies the median effluent concentration based on BMP type and the outflow olume.
by v Equation A-5
e:
EWher = Effluent Pollutant Load (lbs) O = Outflow olume in ershed Inches C = Median Effluent Concentration of BMP (mg/l) A = Area (acrV Wat (inches) 0.226 = Unit con ersion f es) v actor
http://www.stormwatercenter.net/monitoring%20and%20assessment/simple%20meth/simple.htm
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐ ‐iii
A Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
or s that do not vide significant eduction in er olume, then the outflow olume is equal the inflow volume. The International BMP Database indicated that volume reduction is most significant in F erBMP strips, assed proales and entionr s. olumestormwat centv al es or thesev s to vided in Table A‐4. filt gr sw bioret BMP V per remov estimat f BMP are pro Table A-4 International Stormwater BMP Database Percent Volume Reduction
Relative Volume Reduction = Study total Inflow Volume – Study Total Outflow Volume / Study Total Inflow Volume Source: Wright Water Engineers and Geosyntec Consultants, 2011
The International BMP Database also publishes median effluent concentrations for se al BMP types. A summary of the BMP Database information on median effluent concentrations for common pollutants (e eria) is vided in able ‐5. able ‐6 the median effluent ationsver of select s xcept bact pro T A T A shows concentr BMP for bacteria
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A iv Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Table A-5 Structural BMP Median Influent and Effluent Concentrations from the International BMP Database
1 Actual number of BMPs reporting a particular constituent may be greater or less than the number reported in this table, which was based on number of studies reported in database based on BMP category. Notes: xx- Lack of sufficient data to report median and confidence interval. Values in parenthesis are the 95% confidence intervals about the median. Differences in median influent and effluent concentrations does not necessarily indicate that there was a statistically significant difference between influent and effluent. See “Analysis of Treatment System Performance, International Stormwater BMP Database (1997-2007) (Geosyntec and Wright Water Engineers and Geosyntec Consultants 2007) for more detailed information. Source: International Stormwater BMP Database June 2008 (www.bmpdatabase.org) 2Source: Wright Water Engineers and Geosyntec Consultants, Pollutant Category Summary: Fecal Indicator Bacteria, December 2010
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A v Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Table A-6 Structural BMP Median Influent and Effluent Concentrations from the International BMP Database.
The section below vides an ample of calculating pollutant al eness of o BMP
Example Calculationpro of Pollutantex Removal Effectiveness remov effectiv tw options.
e the Fecal Coliform bacteria r al eff eness of an e ended dry detention BMP and a r et pond BMP for a medium density residential de . The TMDL for bacteria r es discharge fr theCompar drainage area t be below 23 Billionemov Coloniesectiv of Fecal Coliform.xt The drainage area t the BMP is 10etention acr withw percent imperviousness of 40‐per . velopment equir om o o es Step 1: Calculate the expected annualcent pollutant load from the development.
Use Equation ‐2 e the annual load of eria om the esidential . The EMC eria from medium density residential land use is 48,100 CFU / 100 mL as shown in Table A‐2. The annual ecipitation totalA to forcalculat Omaha is 30.26 inches (Tablebact A‐3). fr r development for bact pr
e:
LWher = Annual load (Billion Colonies) R = Annual runoff (inches) C = EMC bacteria (CFU/100 ml) = Area (acr 1.03 * 10‐3 = Unit con ersion f A es) Use Equation ‐4 ve the runoffactor coefficient or the esidential .
A to estimat f r development
The runoff coefficient is used in Equation ‐3 e the annual runoff olume (R) in inches.
A to calculat v
The runoff volume is used in Equation A‐2 t estimate the bacteria load from the residential de .
o velopment
8‐ ‐vi Omaha Regional Stormwater Design Manual Rev. 06/2014
A Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Table A-6 Structural BMP Median Influent and Effluent Concentrations from the International BMP Database.
The section below vides an ample of calculating pollutant al eness of o BMP
Example Calculationpro of Pollutantex Removal Effectiveness remov effectiv tw options.
e the Fecal Coliform bacteria r al eff eness of an e ended dry detention BMP and a r et pond BMP for a medium density residential de . The TMDL for bacteria r es discharge fr theCompar drainage area t be below 23 Billionemov Coloniesectiv of Fecal Coliform.xt The drainage area t the BMP is 10etention acr withw percent imperviousness of 40‐per . velopment equir om o o es Step 1: Calculate the expected annualcent pollutant load from the development.
Use Equation ‐2 e the annual load of eria om the esidential . The EMC eria from medium density residential land use is 48,100 CFU / 100 mL as shown in Table A‐2. The annual ecipitation totalA to forcalculat Omaha is 30.26 inches (Tablebact A‐3). fr r development for bact pr
e:
LWher = Annual load (Billion Colonies) R = Annual runoff (inches) C = EMC bacteria (CFU/100 ml) = Area (acr 1.03 * 10‐3 = Unit con ersion f A es) Use Equation ‐4 ve the runoffactor coefficient or the esidential .
A to estimat f r development
The runoff coefficient is used in Equation ‐3 e the annual runoff olume (R) in inches.
A to calculat v
The runoff volume is used in Equation A‐2 t estimate the bacteria load from the residential de .
o velopment
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐ ‐vii
A Appendix A • Simple Method to Calculate Urban Stormwater Pollution Loads
Step 2: Calculate the expected annual pollutant load from a dry pond BMP.
Use Equation A‐6 t calculation the annual bacteria load from a dry pond BMP. The dry pond r es the full annual runoff volume from the residential de elopment and the median effluent concentration from Table A‐ is used. Dry pond BMPso are e ed t reduce annual runoff volumes between 26 and 43 pereceiv. The median percent reduction in volume is 33 perv . 6 xpect o cent e the outflow olume (O) as a portion centof the inflow olume
Calculat v v (R).
Step 3: Calculate the expected annual pollutant load from a retention wet pond BMP.
Use Equation A‐6 t calculate the annual bacteria load from a wet pond BMP. The wet pond r es the full annual runoff volume from the residential de elopment and the median effluent concentration from Table A‐ is used. The wet pondo is not e ed t significantly reduce runoff volumes; ther e, the outfloweceiv volume is equal the inflow olume. v 6 xpect o efor to v
Step 4: Evaluate BMP alternatives.
The e ed annual pollutant load from the e ended dry detention basin is 62.8 Billion Colonies of F orm bacteria which is gr er than the limit of 23 Billion Colonies allowed b the TMDL. If an e dry detentionxpect basin is used for this site, additionalxt treatment of the e ended detention basin effluent mayecal be Colif ed educe ecal eatorm eria the TMDL . if a entiony et pond is used,xtended annual pollutant load is 15.3 Billion Colonies of Fecal Coliform whichxt is below the TMDL limit. This anal requires an estimateto r ofF pollutantColif loads.bact Actual topollutant loadslimit canHowever, only be verifiedret using wmonitoring data oncethe the BMP has been constructed and is operating. This type of anal sis is useful when planning BMP selectionysis t givermine the est elihood of ving eam er quality goals. y o det great lik achie downstr wat
8‐ ‐viii Omaha Regional Stormwater Design Manual Rev. 06/2014
A Appendix 8-B USEPA Class V Well Memorandum (This page was intentionally left blank) Appendix B • USEPA Class V Well Memorandum
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐B‐i Appendix B • USEPA Class V Well Memorandum
8‐B‐ii Omaha Regional Stormwater Design Manual Rev. 06/2014
Appendix 8-C PCWP Stream Setback Policy (This page was intentionally left blank)
Appendix 8-D Derivation of Peak Flow Rate for the Water Quality Storm (This page was intentionally left blank) Appendix D • Derivation of Peak Flow Rate for the Water Quality Storm
Appendix 8-D Derivation of Peak Flow Rate for the Water Quality Storm The current policy outlined in the City of Omaha Post‐Construction St er Management Planning Guidance or selecting a design orm or ‐thr h s ormwat “For stormwatf er BMPs that provide sttreatmentf basedflow on aoug flow BMPrate, theis: Designer may submit calculations that demonstrate water quality flow rates that are equivalent to treating the first one-half inch (0.5 inches) of stormwater runoff. On sites where the Rational Method is suitable and the time of concentration is 5 minutes, designers may estimate i using the 1-yr IDF curve with 20-minute duration. Designers may also use WinTR-55 to estimate flow rate, however, the model must show a correlation to a 0.5 inches runoff depth in the output report. Proprietary stormwater BMPs shall be pre-approved for use by the City of Omaha Public Works Department.”
The variable “i” is the r all intensity in inches per hour for storms with duration equal t the time of ation of the site. Use of the Rational Method r es the designer t select a value for the runoff coefficient (C) which r ainfesents a ratio of runoff t r all for future land‐use conditions. oBMPs sized using theconcentr City’s volume criteria are sized with 0.5 inches of runoffequir r dless of theo future land use conditions. epr o ainf vide an oach or sizing of ‐thr h s that isegar ent with the ’s olume eria, CDM Smith’s NetS ORM pr am was run using appr y 61 years of r all data collect withinTo pro the Omahaappr Region.f The resultsflow of the NetSoug BMPORM anal sisconsist w used t cr eCity capturev curvesdesign for a BMP withcrit a 24‐hour aindownT time ogre D‐1). oximatel ainf ed T y ere o eat dr (Figur
Figure D-1 Capture Curves for Omaha, Nebraska for BMP with 24-hour draindown time.
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐D‐i Appendix D • Derivation of Peak Flow Rate for the Water Quality Storm
e D‐ 1 that a BMP sized or 0.5 inches of runoff and a 24‐hour aindown es and een 70 t gr er than 95 percent of annual runoff e ents depending upon the runoff coefficient (C) Figurapplied t theshows de . If w applyf a 90‐percent treatment criteria t dr flow thr capturh BMPs (equaltreats t a sit withbetw C = 0.5 capturingo eat 0.5 inches of runoff), the 90‐percentv intensity can be used t calculate a peak flow r per acre ro edvelopment for tr e o oug o e o ate ORMequir was used t eatment. separ e the r all depths into e ent of 1‐hour, 6‐hour, and 24‐hour duration and the 90‐percent r all intensity was calculated. Figure D‐2 show the resulting plot for the 90‐percent along with thatNetST of the 1‐year returno int atal stormainf e . Values for durationsv other than 1‐, 6‐, and 24‐hours w ed usingainf the slope of the 1‐year intensity curve. s erv vent ere estimat
The 90‐percent curve in Figure D‐2 can be used t estimate the r all intensity t be used in the R equation for flow‐thr h BMPs. The 90‐percent r all intensities are less than those for the 1‐year r al; how they can be r ed back t a 0.5o inches runoff ainfcapture, and the o90‐percent intensityational curv can be used for multipleoug durations. ainf eturn interv ever, elat o e remain consistent with the City’s ordinance on the 0.5 inches of runoff, CDM Smith calculated the peak flow per acre of drainage area for a variety of storm durations based on a C = 0.5 as shown in Figure D‐3. The gr inTo e D‐3 can be used ermine a ed peak flow or flow h s. Using e D‐3 ermine a peak flow r is consistent with the BMP sizing criteria of capturing 0.5 inches of runoff, aph Figurdless of subarea runoffto detcoefficient requir rate f throug BMP Figur to det ate regar .
8‐D‐ii Omaha Regional Stormwater Design Manual Rev. 06/2014 Appendix D • Derivation of Peak Flow Rate for the Water Quality Storm
, ‐thr h s orm best hen applied small ainage eas that a small time ation. Ther e, the City could decide t simplify the design standard b choosing an estimated time ofAlternatively concentrationflow and designoug BMP duration,perf for e ample:w 10 minutes,to and r dr e all flow‐thrar haveh BMPs be sized of usingconcentr the correspondingefor cubic feet per second (cfs)o per acre (1.5 cfs per acre for y10‐minute dur x equir oug ation).
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐D‐iii (This page was intentionally left blank) Appendix 8-E Background Information on Cascading Planes (This page was intentionally left blank) Appendix E • Background Information on Cascading Planes Appendix 8-E Background Information on Cascading Plane
When st er that is gener ed as runoff fr impervious areas is con ed thr h pervious ar ormwat at om h ales, strips, turf eas, c.) the runoff olume vey oug eas peak flow is 1. When pervious areas r (throug sw ar et v and runoff om impervious eas the concept is known rate reduced eceive cascading planes.2 When pervious areas r runoff fr fr ar as impervious eas the concept is known as cascading 3 eceive om e E‐1 pr vides an illustration of the cascading planes ar planes. . Figur o concept impervious (I ) can be used t r esent the runoff olume eduction due cascading planes. The Effectiveainage and Flood ControlE District of oDeneprer uses the conceptv rof eff imperviousto t account for runoffUrban v thatDr are reduced b using LID con ance BMPsv such as gr ales, ectiveed ers, disconnectiono of oof ainsolumes other impervious areasy draining tvey pervious ar 4 ass sw vegetat imperviousbuff area concept is describedr indr Incentiand x eloped e orm‐o er eas.‐ImpactThe Designseffective b Guo, et 5 ve Inde Dev to Evaluat St Wat Low The par aphs below describe using the relationships described in Guo, 2010 as a method of estimating y .al. olume reduction for site de elopments that use LID con ance BMPs in the City of Omaha. The reduction in the designagr volume of the downstream structural BMP is based on the idea that a portion of the 0.5 inches of vrunoff is “captured and controlled”v within the con ancevey BMP or pervious area. The amount controlled is ed using the ollowing vey Depthcalculat of Runoff Controlled,f inchesequation: = 0.5 ‐ 0.5 x K Equation E‐1
Where: = e[‐0.0052(100‐I = pa ement‐area‐reduction f or (PARF), equation pr vided b Guo, 2010. = area‐w )f/i]ed imperviousness percent for cascading plane = UCIA / (UCIA + RP UCIAK = unconnectedA imperviousv area, acr act o y IA A = r vingeight pervious areas, acr A) f = infiltration r on the pervious surface,es in/hr iRP = aeceiage r all int , in/hres = 0.6 inches per hour for the City of Omaha (Figure 3‐1 fr Urban ainageate and Flood ol District Urban orm ainage eria Manual olume veremberainf 2010) ensity om Dr Contr St Dr Crit V 3, Nov
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐E‐i Appendix E • Background Information on Cascading Planes
able E‐1 the esults of Equation E‐1 or arying cent imperviousness of cascading planes and ation es. An ample application using able E‐1 is vided T shows r f v per soil infiltr rat ex T Tablepro E-1 below. Depth of Runoff Controlled (in inches) by Cascading Planes
1Values for conveyance-based BMPs from Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3, page 3-17 Example Application Consider a 10‐acre site with future impervious area of 70‐per . The ordinance r es the capture and eatment of the first 0.5 inches of runoff equating t a WQCV of 5 acre‐inches or 0.417 acre‐f . cent equir trScenario 1- Traditional Development o eet The 7 acres of impervious area is dir ed t the storm drain. There is no contribution of runoff from the impervious areas t the pervious areas. In this scenario, the design w er quality volume for the site is 0.417 ect o e‐feet as e is no ance or educing runoff o at Scenarioacr 2-ther LID Conveyanceallow Developmentf r volume. In Scenario 2, 6 of the 7 acres of impervious area is dir ed t the storm drain. The remaining 1 acre of impervious area flow t one acre of turf lawn on sand ‐cla ‐loam soil with infiltration r es of 0.34 ect o inches per hour. The volume runoff from the 1 acre of impervious area which flow t the pervious areas is s o y y at educed. First the percent imperviousness of the cascading planes is calculat s o r = UCIA / (UCIA + RPA) = (1 acre / (1 acre + 1 acres) = 50% ed.
Then,IA using able E‐1, the QCV ance or = 50 percent and f = 0.34 inches per hour is 0.068 inches.
The design WQCVT is reducedW t 0.432allow inchesf (0.5IA inches – 0.068 inches) for the 2 acres of cascading planes and the remainder of the site does not qualify for a reduction in W . If a structural BMP is placed o eam of the cascading planes, then it will be sized using the 0.432 inches of runoff. If a structural QCV downstr
8‐E‐ii Omaha Regional Stormwater Design Manual Rev. 06/2014 Appendix E • Background Information on Cascading Planes
BMP is placed at the eam end of the e e, the QCV ance applies y the planes portion. Ther e, the design volume for the BMP would be the area w ed total calculated as: downstr entir sit W allow onl to cascading efor eight
Table E-2 WQCV Allowance Summary
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐E‐iii (This page was intentionally left blank) Appendix 8-F Example Bioretention Facility Specifications (This page was intentionally left blank) Appendix F • Example Bioretention Facility Specifications
Appendix 8-F Example Bioretention Facility Specification BIORETENTION GARDENS 9003.1 Description ention g dens are small landscaped basins intended t pr vide w er quality management b filt er runoff e elease o orm ain ems or al channels. This rk shall consist installingBioret bior arention g dens as specified in the Contract Documents,o o includingat all materials, equipmenty ering laborstormwat and services befor edr intormst the drrk. syst natur wo of et ar , 9003.2 Materialsrequir to perf wo A. Bioretention Soil Mixture: The ention Soil e (BSM) is composed of the ollowing
Bioret Mixtur f materials:
The BSM shall be a uniform mix, free of plant residue, stones, stumps, roots or other similar objects lar than two inches e cluding mulch. No other materials or substances shall be mixed or dumped within the ention den that y be harmful plant owth, or e a ance the planting or ger ations. x bioret gar ma to gr prov hindr to maintenance B.oper Organic Compost: The compost used in the BSM and soil conditioned areas shall be deri ed from plant erial, and the result of biological degradation and tr ormation of plant deri ed materials under conditions that pr e anaerobic decomposition. The material shall be well composted, freev of viable w matseeds, and stabilized with gen consumptionansf and carbon xide vation. The compost a moisture contentomot that has no visible free w er or dust produced when handling the material. It shalleed meet the eria edregard belowto asoxy ed the .S. Compostingdio Councilgener A Compost echnical shall haveSheet pr vided b the v . OmaGro is a locally atproduced compost product that is acceptable for use in entioncrit g dens.present report by U ST T Data o y endor bioret ar
Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐F‐i Appendix F • Example Bioretention Facility Specifications
Shredded Hardwood Mulch: edded har ood mulch shall be aged a minimum of 6 months and consist of the bark and ood (50/50) om ood ees hich has been milled and eened a maximum 4‐ inch particle size and pr vide aShr uniform t dwe free from sa , cla soil, f eign materials, and an y introducedw chemicalfr compoundshardw thattr wouldw be detrimental t plant orscr animal tolife. o extur wdust y, or y Aggregatartificiall e: No. 7 and No. 57 Aggr e shall be double‐washed t reduceo suspended solids and potential f clogging. The e shall be placed as shown in the act wings. egat o or Water: eraggregat used in the planting, establishing, or caringContr for vegetationDra shall be free from any substance that is injurious t plant life. Wat 9003.3 Constructiono The under ain or BSM shall not be placed until all contributing drainage areas are permanently stabilized ainst erosion and sedimentation as shown on the Contract Plans and t the satisfaction of the Engineer y dischargedr of sediment that affects the performance of the cell will r e reconstruction of the cell t ag e its defined performance. No heavy equipment shall oper e withino the perimeter of a bior . An den during under ain placement, backfilling, planting, or mulching equirof the g den. o restor at etention A.gar Excavation: If the drbior ention g den is t be used as a t ary sedimentar basin the bior den shall be e ed t the dimensions, side slopes, and 6 inches above the bottom of the BSM ations shown on the et act Plans.ar y osediment om emporconstruction ations edetention in gar ention g denxcavat shall beo complet y r ed from the g den after all vegetation, including landscaping withinelev the drainage area Controf the bior entionAn g den, hasfr been established.oper The e ationdeposit limits shallthe then bebioret final gradedar t the dimensions, sideel slopes,emov and final arations shown on the act Plans. and backhoes, operating on the groundet adjacentar t the bior ention g den, shallxcav be used t e the den if possible,o low ound‐contact e elev , if appr ed b theContr engineer, b Excavatorse and/or backhoes ating on the ound adjacento the et entionar den. Low ound‐contacto xcavate gar e equipmentby is gr ed on pressurention equipmentdens minimizeor disturbanceov y establishedy xcavators ound perimeteroper of cell. No heavy grequipment shall tobe usedbioret within the garperimeter of grthe bior ention g pressure, during, or after preferrthe placementbioret of the BSM.gar to to areas ar et arden befor ed materials shall be r ed from the bior ention g den site. Ex ed materials shall be used or disposed of in conformance with the project specifications. Excavat emov et ar cavat B. Roto-tilling: er placing the under ain and aggr e and bef e the BSM, the bottom of the ation shall be r o‐tilled t a minimum depth of 6 inches t alle e any compaction of the g om. Any substituteAft method for r o‐tillingdr must beegat appr ed b or the Engineer prior t use. Any ponded excaver shall be r oted from theo bottom of the g den and the soilo shallviat be friable bef e r o‐tilling.arden The bott ot ov y o wat emov ar or ot
8‐F‐ii Omaha Regional Stormwater Design Manual Rev. 06/2014 Appendix F • Example Bioretention Facility Specifications
o‐tilling shall not be done w e the soil supports the aggr e bed underneath the “Under ain f (See ain or ” specifications .) rot her egat dr or C.Bioretention”. Underdrain for “Underdrbioretention:f TheBioretention under ain s em, aggr belowe bed, and geot xtile fabric shall be placed ding dimensions shown on the act Plans. dr yst egat e accorD. Observationto wells/cleanouts of 4‐inchContr non‐perf ed HDPE pipe shall be placed v y in the ention g den as shown on the Contract Plans. The wells/cleanouts shall be connected t the perf ain with the e ed connectionsorat as shown on the act Plans.erticall bioretells/cleanoutsar shall e end 6 inches abo the top ele ation of the bior ention g den mulch,o and shallorated be cappedunderdr with a screw appropriatcap. manufactur Contr The w xt ve v et ar E. Placement of the BSM: The BSM shall be placed and aded using low ound‐contact e , if appr ed b the engineer, b e ors and/or backhoes operating on the ground adjacent t the ention den. Low ound‐contact e equipmentgr is edgr on entionpressur densequipment minimizeor ovdisturbancey t establishedy xcavat areas around perimeter of cell. No heavy equipment shall be usedo within thebioret perimetergar of the bior grention g den befpressure, during, or after thepreferr placementbioret of the BSM. Thegar BSMto shall be placed in horizontal liftso in depths not e ceeding 12 inches for the entire area of the bior ention g den. The BSM shall be e‐mixed, withet a ar e orent low h ent clumping and compaction . If the BSM becomes contaminatedx during the construction of the g den, the etcontaminatar erial shallpr be r ed and replacedmoistur withcont uncontaminatedenoug to materialprev at the Contr or’s expense.during Final placementading of the BSM shall be performed after a 24‐hour settling period. Upon finalar grading the surfaceed of the BSMmat shall be r o‐tilledemov t a depth of 6”. Final ele ations shall be within 2 inches of eleact ations shown on the gr act Plans. ot o v v F.Contr Soil Conditioning of Ponding Area: e there is no standing w er within the ponding area prior t beginning the soil conditioning process t a oid further compacting soils. Existing vegetation, including turf, shall be r ed and the ground shall beEnsur tilled t a minimum depth ofat 6 inches. A 3‐inch deep la er of o specified compost shall be placed on top oof thev tilled ground and tilled into a depth of 6 inches of existing soil. Fine gradingemov of the site shall be completed with ao minimum number of equipment passes (no morey than tw (2) passes) t reduce the potential for soil compaction. Finalizing all preliminary critical spot ele ation, slopes and positi drainage criteria for the site shall be completed as much as possible prior t finish grading in o der o e that equipment compaction is minimized er soil is ed an amended. Soil shallv be using one vepass of a 50‐pound roller if v co er will be seeded or plugged t helpo ensure successful orplant establishmentto ensur co er shall be established aftimmediat worky after finish grading and erosion shallfirmed be pr ed during establishment, includingegetative but notv limited t installing erosiono control blankets, silt f or str waddles. Vegetation. Vegetative may vbe sodded, seeded, or plugged. Forel seeding or plugging, all standar eventes shall be f ed for the appr e mulching of bareo soil surface areas until vegetation is fullence established.aw d procedur ollow opriat y G. Mulching: Once grading is complete, the entire surface of the BSM shall be mulched t a uniform thickness of 3 inches. Mulching shall be complete within 24 hours t reduce the potential of silt accumulation on the ace. ell aged edded ood bark mulch is the y acceptable mulch. Mulchingo shall be y after grading t reduce potential of any silt accumulationo on the surface. surf W shr hardw onl done H.immediatel Plant Installation: ees,o shrubs, and other plant materials specified for Bior ention Gardens shall be ed as specified in the Contract Plans and applicable landscaping standards with the e ception that pesticides, herbicides, andTr fertilizer shall not be applied during planting under anyet cir plant e, pesticides, f , and any other soil amendments shall not be applied t thex bior den during landscape construction, plant establishment, or maintenance. cumstances. Furthermor ertilizer o etention gar Omaha Regional Stormwater Design Manual Rev. 06/2014 8‐F‐iii Appendix F • Example Bioretention Facility Specifications
9003.4 Method of Measurement ention g dens will be measured b the square foot and will be paid for at the Contract Unit Price. 9003.5Bioret Basisar of Payment y The payment will be full compensation for all material, labor, equipment, tools, and incidentals necessary t y complete the w rk. Biological plantings will be paid for separ y under other items of the . o satisfactoril o atel References:contract C and APWA. 2009. Manual of Best Management Practices for St er Quality
MARWisconsin Department of Natural R ces (WDNR).No ember 2010.ormwat Bior ention for. Infiltration (1004).
esour v et http://dnr.wi.gov/topic/stormwater/documents/Bioretention1004.pdf
8‐F‐i Omaha Regional Stormwater Design Manual Rev. 06/2014
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