Green Infrastructure: Assessing the Benefits of Bioretention over Traditional Stormwater Management

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1 Green Infrtructure: Aeing the Benefit of Bioretention over Trditionl Stormwter Mngement Dine JONES Aitnt Profeor, Grdute Deprtment of Lndcpe Architecture Morgn Stte Univerity 1700 Et Cold Spring Lne Bltimore, MD USA Emil: nd Mnoj K. JHA Aocite Profeor, Deprtment of Civil Engineering Morgn Stte Univerity 1700 Et Cold Spring Lne Bltimore, MD USA Emil: Abtrct:- Stormwter mngement i key component of Green Infrtructure, which i bed on ecoytem conervtion, nd low impct development prctice (LID). One low impct development prctice utilized long highwy nd rod pvement i bioretention. Bioretention ytem employ the nturl element of lndform, oil nd vegettion, to cpture nd remove hrmful pollutnt from tormwter runoff. Filtrtion, borption, nd evpotrnpirtion re the key mechnim reponible for the removl of impuritie from the oil. The infiltrtion time tht hppen before runoff reche the tormwter outlet llow thee function to occur. Thi pper ue Sytem Optimiztion (SO) pproch tht incorporte link performnce function bed on oil permebility rte, for comprion between bioretention ytem nd conventionl tormwter mngement ytem. Further, the pper put forth everl comprion between bioretention ytem nd conventionl tormwter mngement ytem, but contend tht the dely time to llow runoff to permete the oil i the mot importnt one. The SO pproch i ued to predict runoff rte nd flow volume on tormwter mngement ytem. It how tht the rte of flow i increed but the volume of outflow i decreed when compring the bioretention cell to the conventionl torm dringe ytem. Key word: Green Infrtructure, Bioretention, Infiltrtion, Sytem Optimiztion 1. Introduction Green Infrtructure i ecoytem conervtion, through trtegic plnning nd mngement of open pce, lndcpe, nd other nturl lnd network, which dd vlue nd provide benefit to humn popultion. (1) The vlue dded by thee network i tht tormwter i nturlly mnged, the rik of flooding i reduced, pollution i cptured, nd wter qulity i improved. Criticl element of green infrtructure implementtion include Low Impct Development (LID) prctice, Stormwter Bet Mngement Prctice (BMP), conervtion development nd green/grey interfce. An re where green infrtructure component hve been uccefully implemented i in the development of green highwy (2). ISSN: ISBN:

2 1. Green Highwy utilize technique to reduce the impct on the nturl environment. The reult i tht highwy become more etheticlly pleing in citie nd more prt of the nturl environment in rurl re. Another benefit of green highwy i tht lower long-term or life-cycle cot i chieved through utinble highwy contruction. Uing bioretention ytem to mnge tormwter nd reduce runoff volume i vible technique for green highwy deign. 2. Reerch Scope In thi pper, the benefit of bioretention over trditionl tormwter mngement will be dicued. A ce tudy demontrting how prticulr bioretention ytem hve been utilized by the Mrylnd Deprtment of Trnporttion will lo be preented. Finlly, we will introduce Sytem Optimiztion (SO) pproch to meure the rte of outflow for both bioretention cell nd conventionl ytem where runoff goe directly to pipe with no infiltrtion time. A numericl exmple howing the pplicbility of the SO pproch will lo be preented. 3 Bioretention Sytem Bioretention ytem re torm wter bet mngement prctice tht ue filtrtion to tret torm wter runoff. Uing vegettion to remove pollution from runoff, bioretention cell often ue uplnd terretril foret or medow ecoytem model. Bioretention ytem re deigned to tret tormwter form imperviou urfce. Bioretention employ implitic, ite integrted, terretril bed deign tht pond runoff for infiltrtion nd uptke by vegettion. Runoff i cptured nd filtered through prepred oil medium. Once oil pore pce cpcity i exceeded, runoff will pool t the urfce of the oil. Soil ponding will lt for le then1/2 hour with the ue of the recommended engineered oil nd n underdrin ytem. Ponding will lt longer if the ytem i dewtered by infiltrtion lone. Runoff cn be directed into the ytem directly through wle, cutter collection ytem or pipe. Runoff filter through vegettion nd oil in the bioretention re i collected in n underground dringe ytem or llowed to filtrte into the ground. Unlike end of pipe ytem, bioretention fcilitie cn be ditributed cro ite reulting in mller more mngeble wterhed. Thi help to control runoff cloe to the ite where it i generted. 3.1 Performnce Bioretention remove tormwter pollutnt through phyicl nd biologicl procee including borption, plnt uptke, filtrtion, microbil ctivity, decompoition, nd edimenttion. Aborption i the proce where prticulte pollutnt ttch themelve to oil nd vegettion. Adequte contct time between the urfce nd pollutnt removl mut be provided in the ytem deign for dequte borption to occur. A runoff pe through the bioretention medi infiltrtion occur. Pollutnt removl my decree if the infiltrtion rte of the oil exceed thoe pecified in the bioretention cell deign. Pollutnt removl my include metl, phophoru, nd hydrocrbon. Pollutnt uptke by plnt lo occur through the biologicl proce tht occur in the wetlnd. Common prticulte removed by plnt include phophoru, upended olid, nd prticulte orgnic mtter. Vegettion in mot bioretention cell i modeled fter propertie of terretril foret community. Thi include n ecoytem dominted by mture tree, ub-cnopy of under tory tree, hrub, nd herbceou plnt. Plnt re elected bed on their tolernce to vrying hydrologic or wetlnd condition, nd oil nd ph requirement. The oil in the ytem contin mixture of diintegrted mteril, humu, nd minerl nd biologicl complexe. Plnt mteril growth i utined by intke of nutrient from the olid. Woody plnt lock up thee nutrient for ue during the eon. Microbil ctivity within the oil contribute to the removl of nitrogen nd orgnic mtter. Nitrogen i removed by nitrifying nd denitrifying bcteri. The decompoition of orgnic mtter i ccomplihed through the work of erobic bcteri, thoe tht live only in the preence of oxygen. Therefore, if bioretention ISSN: ISBN:

3 re i not dequtely erted depletion of oxygen occur, which i needed for microbil procee. Studie hve hown tht properly deigned nd contructed bioretention cell cn chieve efficient removl of hevy metl (3). Copper (Cu), Zinc (Zn) nd led (Pb) reduction of greter thn 80% percent (ee, Tble 1) with only mll vrition in reult hve occurred. Led nd Zinc hve hd removl effectivene high 90% to 99%. The mulch lyer i credited with hving the mot effect on thi uptke, nerly ll the metl removl occurring with the top few inche of bioretention. Phophoru removl incree linerly with depth, reching mximum of pproximtely 80% by 2-3 feet depth. Seventy to eighty percent reduction in mmoni i chieved in the lower level of mple cell. Nitrogen removl lo depend on depth. Tble 1 Pollutnt nd their Removl Rte due to Bioretention 6. Horticulture 7. Lndcpe rchitecture 8. Ecology One primry objective of bioretention ytem i to minimize pot development runoff by mimicking predevelopment hydrology. Bioretention cell cn reduce overll ite runoff volume nd help predevelopment pek dichrge rte nd timing through infiltrtion nd temporrily toring runoff. Ue of n under drin mke the ytem ct more like filter tht dichrger wter to torm drin ytem thn tht n infiltrtion device. The ponding cpbility of the cell reduce volume lod on the torm drin ytem, reduce the pek dichrge rte nd reult in increed ground wter rechrge. An dditionl hydrologicl benefit i the reduction of therml pollution. Heted runoff from imperviou urfce i filtered through the bioretention fcility nd cooled. One tudy oberved drop in temperture of 12 degree centigrde between influent nd ffluent wter. 3.3 Deign of Bioretention Sytem 3.2 Benefit of Bioretention Sytem Bioretention ytem demontrte multitude of benefit, mot importntly, the protection of ecoytem integrity. Importnt benefit to element of the ecoytem protected by bioretention include: 1. Non point pollutnt tretment 2. Reource conervtion 3. Hbitt cretion 4. Nutrient cycle 5. Soil chemitry The bioretention cell hould be ized to cpture the pvement deign torm runoff (ee, Figure 1). In re where the ntive oil permebility i le thn 0.5/hr. n under drin hould be provided. The cell hould be deigned to drin completely in 72 hour. Wter hould not be llowed to pond for more thn 4 dy. The ponded re hould hve mximum depth of 6 inche, nd the plnting oil hould hve minimum depth of 4 feet. The minimum depth of bioretention cell hould be feet. The length hould be minimum 40 feet nd t let twice the width. Approximtely one tree or hrub per 50 feet qured of bioretention hould be included in the bioretention lndcpe (4). The lnd within the re need gentle lope for overlnd flow nd dequte torge. The bioretention hould not be etblihed until the wterhed to which it contribute i tbilized. The mjor component (Figure 2) of bioretention cell re follow: 1. Pretretment ISSN: ISBN:

An uptrem pretretment re my be needed for rod nd prking lot where lrge volume of debri or upended mteril will be conveyed by tormwter. Thi my include:.

It mut hve mximum ponding depth nd limited durtion of ponding. 4. Groundcover 5.

4 An uptrem pretretment re my be needed for rod nd prking lot where lrge volume of debri or upended mteril will be conveyed by tormwter. Thi my include:. A gr or buffer trip to filter prticle nd reduce runoff. b. Oil nd gree eprtor. c. Stilling bin. 2. Ponding re 3. A ponding re provide urfce torge for tormwter runoff. It mut hve mximum ponding depth nd limited durtion of ponding. 4. Groundcover 5. An orgnic ground cover lyer provide medium for biologicl growth nd crbon ource for biologicl ctivitie t the ir/oil interfce. 6. Plnting Soil 7. A thick lyer of oil locted below ground cover lyer upported by underlying initu or foundtion oil will provide for deep root plnting growth. The oil mut hve high infiltrtion rte to borb nutrient nd pollutnt nd provide dditionl torge cpcity for tormwter. Soil with 2.5 to 10% cly content nd 1.5 to 3 percent orgnic content i preferred. 8. Initu oil 9. Initu oil provide foundtion for plnting oil nd drin the infiltrted tormwter from the bioretention cell. If the cell drin poorly, the bioretention ytem will fil unle nother men of dringe, like n under- drin, i etblihed. Percoltion tet hould be performed to demontrte tht initu oil proce t 12.7 mm/h infiltrtion cpcity. 10. Plnt mteril 11. Plnt mteril ct to ue nutrient, nd remove wter from the oil through evpotrnpirtion. Plnt mteril hould be tolernt of urbn condition, low mintennce, hve Figure 1. ethetic ppel, nd be dptble to runoff inundtion. Vegettion hould proper when flooded to depth of 0.15m (0.5ft.) or more frequent intervl. Inlet nd outlet control Inlet nd outlet control depend on whether bioretention cell i online or off-line. An on-line fcility doe not hve byp tht divert exce tormwter round the bioretention fcility once it become full. Therefore, the inlet nd outlet mut be deigned to enure tht the runoff rted doe not dmge the bioretention ytem. Rip rpped inlet nd outlet cn provide protection from eroion. Poible outlet for online re include drop inlet or overflow weir tht feed downtrem wle or pipe ytem. Offline bioretention require mller inlet then online fcilitie becue inlet re deigned to convey runoff from the time of runoff of the ite. Without ping through the bioretention cell, ll of the runoff mut be diverted round the cell nd downtrem to ubequent wle or pipe ytem. Thi diverion cn be chieved by creting ponding re in the bioretention cell which cue bckwter condition nd reulting hift in dichrge direction. Inlet to bioretention ytem mut be ized to keep entrnce velocitie in exce of 0.15m/ec. (0.5ft. /ec.) to help prevent clogging the inlet re. ISSN: ISBN:

Figure 2 3.4 Mintennce of Bioretention Sytem Inpection, repir or replcement of the bioretention re component, i required for good mintennce.

Through plnt growth, root growth, orgnic decompoition, nd the development of nturl oil horizon the fcility life pn will be lengthened nd reduce the need for extenive mintennce. 3.

5 Figure Mintennce of Bioretention Sytem Inpection, repir or replcement of the bioretention re component, i required for good mintennce. If plnt were ppropritely elected fertilizer, peticide, wter nd overll mintennce requirement hould be reduced. Through plnt growth, root growth, orgnic decompoition, nd the development of nturl oil horizon the fcility life pn will be lengthened nd reduce the need for extenive mintennce. 3.5 Cot Contruction cot etimte for bioretention ytem re lightly greter thn thoe tht re required for lndcping of new development. Commercil, indutril nd intitutionl ite cot cn rnge from $10.00 to $40.00 per qure foot, bed on the need for control tructure, curbing, torm drin nd under drin. Retrofitting ite typiclly cot more thn building new cell, verging $6,500 per bioretention re, due to demolition of exiting concrete, phlt, exiting tructure, nd the replcement of fill mteril with plnting oil (5). Bioretention reduce development cot by combining the deign nd contruction cot of lndcping nd tormwter mngement. 3.5 Comprion with trditionl end of pipe ytem The limittion of trditionl end of pipe tormwter mngement control uch pond, wetlnd in protecting wter reource hve been proven. While efficient in treting tormwter nd reducing pek flow, they incree volume nd temperture of runoff reulting in undeirble impct on locl trem nd dequte life. Bioretention ytem void ome of the flow volume temperture relted impct of pond on receiving wter. Runoff flow i nturlly infiltrted into the oil. Thi reduce the need for tretment, nd eliminte the need for underground or ite conuming detention fcilitie. Trditionl end of pipe control often tke up vlue lnd. Spce conumed for thee fcilitie cn be ued for open pce, lndcping, or other development. Bioretention i effective in reducing nd delying pek flow. Although bioretention cell my overflow, mot runoff infiltrte into the ground or releed bck into the tmophere through evpotrnpirtion. Intlltion of under drin help the infiltrted wter to rechrge groundwter nd ugment be flow in locl trem. They help eliminte downtrem flooding nd prevent trem eroion cued by pot development chnge to flow pttern. Compred to conventionl ytem, bioretention ytem re eier to contruct, nd require le infrtructure nd mintennce (6). The ue of bioretention cn decree the cot required for contructing tormwter conveynce ytem t ite. 4. Ce Study Mrylnd h been Ntionl leder in tormwter mngement over the lt two decde. The Stte h been motivted to protect it trem tht dichrge to the wter of the Chepeke By, the Atlntic Cotl By, nd the wter of the Ohio River in Grret County, Mrylnd (7). In n effort to incree onite rechrge nd runoff reduction volume the Mrylnd Deprtment of Trnporttion i implementing everl bioretention ytem longide highwy, in medin nd prking lot. Three of thee re hown in Fig. 3, 4, nd 5. The Edgewood Rod Bioretention Sytem in Hrford County i hown in Figure 3. Two Prk nd Ride Fcilitie re hown in Fig. 4 nd 5. The Stte h provided limited monitoring of the effectivene of the ISSN: ISBN:

bioretention cell completed to dte, lthough there re ongoing monitoring effort. Due to the imilrity between dry wle nd bioretention cell, the pollutnt removl cpbility hould be comprble.

Determined by the compoition of the plnting oil nd plnt intlled, the bioretention cell hould be cpble of mnging ome petroleum hydrocrbon concentrtion typicl of urbn etting.

6 bioretention cell completed to dte, lthough there re ongoing monitoring effort. Due to the imilrity between dry wle nd bioretention cell, the pollutnt removl cpbility hould be comprble. The monitoring reult of the bioretention cell re hown in Tble 2. Determined by the compoition of the plnting oil nd plnt intlled, the bioretention cell hould be cpble of mnging ome petroleum hydrocrbon concentrtion typicl of urbn etting. If there w high level of pollutnt, loding pretretment hould be implemented. Figure 5. Bioretention Cell t nother Prk nd Ride Fcility 4.1 Sytem Optimiztion Formultion A ytem optimiztion pproch will be dpted to how tht the infiltrtion period of the bioretention cell low down the time from inlet to outlet, which llow time for plnt intke nd removl of pollutnt. Uully thi formultion i ued to decribe the flow pttern reulting from ech motorit choice of the hortet trvel-time route from origin to detintion (8). A link performnce function cn be ued follow: = f x + B t ( x ) t 1 α ( ) c (1) Figure 3. The Edgewood Rod Bioretention Fcility in Hrford County where: t = Predicted runoff flow rte time on pipe ; A A= A et of pipe in given dringe network t =Free runoff rte of flow on pipe, f x =Pek runoff rte from dringe re C =Cpcity of pipe L =Length of Pipe B= Soil permebility rte for the bioretention re. To determine the pek rte of runoff the following Rtionl Method i ued: Figure 4. Bioretention Cell t Prk nd Ride Fcility q= CiA (2) ISSN: ISBN:

7 where: q = pek runoff rte, in cubic feet per econd ft 3 or cf C= dimenionle coefficient (between 0 nd 1) i = rinfll intenity, inche per hour (iph) for the deign torm frequency nd for the time of concentrtion of the dringe re A=re of dringe re 4.2A Numericl Exmple The following dt re given: Dringe re: 3 c of pvement, 3 c of lwn, 3 min. trvel time over pvement, 30 min. trvel time over lwn, 2.8iph (rin fll intenity), T =45min. (time of concentrtion ), C=0.3, Soil c permebility rte= 0.5iph, Storm durtion=20min Clcultion of Pek runoff rte: q=( ) = 2.5 ft 3 + = 9.2 ft 3 + ( ) 6.72 ft 3 Clcultion of Mximum flow rte q = C C i A Dur / T A q = / 45 q= 5.04 ft 3 c (3) (4) Predicted runoff flow rte uing Eq. (1) nd conidering the oil permebility rte=0.05 = f x + B t ( x ) t 1 α ( ) c t (9.2 ft ) =5.04+ ( ).03 ( 9.2 ft 3 ) = ft t 3 t = 2.2 ft 3 (5) Predicted runoff flow rte conidering the oil permebility rte=1 ( ) = f x 1+ ( t x t α ) c t (9.2 ft ) =5.04 ( )..03 t ( 9.2 ft 3 ) = ft 3 t = ft 3 (6) 5. CONCLUSIONS The Sytem Optimiztion (SO) pproch in the bove numericl exmple how tht when infiltrtion time cued by the ue of bioretention i included the predicted runoff rte t ) i increed (Eq. (6) bove). Thi i mot ( likely due to the decree in volume lo through evpotrnpirtion, borption nd plnt uptke. The mot importnt technicl difference in conventionl fcilitie nd bioretention ytem i the infiltrtion period which llow for borption, plnt uptke, nd filtrtion. Bioretention fcultie provide everl dvntge. Some of them cn be lited : ) Vrying pollutnt removing mechnim which include: 1. Filtrtion 2. Aborption to oil prticle 3. Biologicl up tke to plnt b) Stormwter tretment tht enhnce the qulity of downtrem wter bodie by temporrily toring runoff nd releing it overtime. Thi i due to low rte of flow llowing the pollutnt removing mechnim to be ffective. c) Vegettion ued in bioretention provide hde nd wind brek, borb noie nd improve the ite lndcpe. ISSN: ISBN:

8 d) Cot nd energy ving re provided The propoed SO pproch will be pplied in underground dringe network in future work. ACKNOWLEDGEMENTS Thi work w completed t the Center for Advnced Trnporttion nd Infrtructure Engineering Reerch (CATIER) t the Morgn Stte Univerity. Reference [1] Wie, Steve Bet Mngement Prctice. Plnning Prctice the Americn Plnning Aocition, Augut/September, pp Environmentl Monitoring nd Aement, Vol. 63. pp [8] Sheffi, Y. (1985). Urbn Trnporttion Network, Pub. Prentice-Hll, Inc. [9] Vn Seter, Tim, D. Smith nd G. McMilln Performnce Evlution of Permeble Pvement nd Bioretention Swle. Toronto nd Region Conervtion Authority, Toronto, Ontrio, pp.1-9. [10] Conenu Propol Core Environmentl Site Deign Principle for the Implementtion of the Mrylnd Stormwter Mngement Act of 2007, July 27, 2007, pp [2] Weintein, Neil Low Impct Development Retrofit Approch for Urbn Are, Seventh Biennil Stormwter Reerch & Wterhed Mngement Conference, My22-23, 2002, pp [3] Vn Bohemen, H.D. nd W.H. Jnen Vn De Lk The Influence of Rod Infrtructure nd Trffic on Soil, Wter, nd Air Qulity. Environment Mngement, Vol. 31, No. 1, pp [4] Bioretention. Cliforni Stormwter BMP Hndbook, New Development nd Redevelopment, Jnury 2003, pp [5] Bryce, Jme M Exploring Green Highwy. ASTM Stndrdiztion New, Vol. 35, No. 5, pp [6] US Deprtment of Trnporttion Federl Highwy Adminitrtion, Stormwter Bet Mngement Prctice in n Ultr-Urbn Setting: election nd Monitoring, pp. 1-5 [7] Weber, Theodore nd J. Wolf Mrylnd Green Infrtructure-uing Lndcpe Aement Tool to Identify Regionl Conervtion Strtegy. ISSN: ISBN:

Low Impact Development in Northern Nevada: An Introduction

Low Impact Development in Northern Nevada: An Introduction Nonpoint Eduction for Municipl Officils www.unce.unr.edu/nemo Protecting wter qulity through community plnning Fct Sheet FS-09-22 Low Impct Development in Northern Nevd: An Introduction Benefits of LID