CWN-EN-Stormwater-Report-FINAL

INNOVATIVE STORMWATER MANAGEMENT:TRANSLATING SCIENCE INTO ACTIONSHANS SCHREIER, FACULTY OF LAND & FOOD SYSTEMS,UNIVERSITY OF BRITISH COLUMBIA

INNOVATIVE STORMWATER MANAGEMENT:TRANSLATING SCIENCE INTO ACTIONHANS SCHREIER, FACULTY OF LAND & FOOD SYSTEMS, UNIVERSITY OF BRITISH COLUMBIABACKGROUND:More than 3 billion people will move into cities over thenext 30 years and to accommodate them all will requireincreased densification that dramatically changes theurban landscape. This built up landscape is dominated byimpervious surfaces which no longer allow the rainfall toinfiltrate into the soil and will instead result in increasedoverland flow that contributes to more widespread flooding.At the same time climatic variability is increasing and thecombination of urban densification and climate changewill result in increasing runoff events that will result inincreased flood risk. When we change land use we changethe way the water is distributed in the hydrological cycle.As shown in Figure 1, a portion of the precipitation caneither be evapotranspired, converted into surface runoff,stored in the soils or percolated into groundwater. When weconvert a forested watershed into a paved urban landscapea much larger portion of the rainfall becomes surfacerunoff, which in traditional management is then conveyeddirectly into urban streams though an elaborate system ofstormwater pipes. It is becoming increasingly apparent thatconventional stormwater drainage systems are ill preparedto deal with increasing rain events and a drastically changedland surface.% of Total PrecipitationLand Use Effects on How Rainfall Moves through FourComponents of the Hydrological Cycle1009080706050403020100ForestPastureLawnsRural Res.LegendEvaporationSurface RunoffSub-UrbanMulti-FamilyCommercialSoil InterflowGroundwaterImperviousFigure 1. Land use impacts on the distribution of precipitationwithin the hydrological cycle.Most municipalities base their stormwater design on the100 or 200 year storm return period that uses the maximumhistoric rainfall event as a basis and then develops thereturn period graph that is known as the rainfall intensityduration-frequencycurve (IDF). If long term streamflow datais available this can be converted into storm runoff returngraph, which shows to probability of a storm flow of a certainmagnitude to reoccur over a different time period (Figure 2).However, such graphs are no longer valid because the landuse and the climate have changed over recent times and nolonger represent the historic conditions. This means that aStorm Peak Flow in m 3 /Sec25020015010050Current and Future Storm Return Period Chart012Based onEmergingConditionsStorm Return Periods in YearsFigure 2. Historic and emerging stormflow return period dueto increased climatic variability and increased impervioussurfaces. The historic line formed the basis for designingstormwater and flood protection infrastructure (In this examplea 100 year historic storm would now likely occur every 7years – based on blue line).previously expected one in one hundred rainfall or streamdischarge event is now occurring at a much more frequentrate. With these new environmental conditions, we anticipatethat much larger rainfall events will occur in the near futureand the frequency of flooding events over the past few yearsalready show and increasing trend. The questions that needsto be asked is how can we deal with this new reality andhow do we change the traditional stormwater managementsystem to cope with more frequent and higher flood events?TRADITIONAL STORMWATER MANAGEMENTThe traditional approach in stormwater managementhas been to convey the surface runoff directly into urbanstreams, without any consideration of contaminants thataccumulate on urban surfaces from land use activities,transportation and spills. This management scheme hasbeen very successful in removing water from roads andparking lots but has resulted in a stream flow regimethat became flashier, increased stream bank erosion andgenerated increased sediment transport. To cope with thesenew problems many urban streams were channelized usingprotective walls and protective structures, which pushed thewater through the stream more efficiently. As a result morewater ended up in the lowland portion of the watershed,which then required floodplain protective structures andland use regulations in the flood zone. As land becamescarce in many cities the pressure on development withinthe flood zone increased, which then required improvedflood proofing of the new infrastructure.If we hope to create greener and more environmentallyfriendly cities we now need to address not only the increasedflood risk but also the neglected urban pollution problemwhich resulted in deteriorating conditions in most urbanstreams.510Based onHistoric Data2050100200Canadian Water Network 1

INNOVATIVE STORMWATER MANAGEMENT: TRANSLATING SCIENCE INTO ACTIONSHans Schreier, Faculty of Land & Food Systems, University of British ColumbiaTHE NEED FOR INNOVATIONSAs part of the Canadian Water Network (CWN) researchinitiative a number of workshops were held in Vancouver,Calgary and Toronto to discuss the current problems inurban stormwater management, and to learn from casestudies how the increasing flood risks can be reduced, andhow best to address the non-point sources of pollution.Based on this cross-city experience it became evident that anumber of new initiatives are under way to radically changethe way we manage urban stormwater. Three key issuesemerged from these workshops:1. How effective are many of the new innovations andis there enough scientific evidence to show that theinnovative approaches are more effective than thetraditional measures;2. How can these innovations be incorporated intomainstream urban development to reduce the risk offlooding and contamination; and3. What are the most appropriate combinations ofinnovative approaches that work at all scales of watershedmanagement and different environmental settings?A wide range of innovative measures were identified andexamined and it became clear that not all of the proposedinnovative solutions are appropriate in all cities becauseeach urban watershed differs in geology, surface conditions,climate and land use. To document the effectiveness ofsome of the proposed innovative measures a numberof research projects were initiated with CWN support toaddress the above mentioned issues. We are now confidentthat many of the proposed changes are effective not onlyfrom the environmental point of view but also in terms ofcosts, particularly if they are introduced into new expandingurban areas. A major effort is now needed to promote theseinnovations so that they can become the main adaptivemeasures taken to cope with the increased risk of floodingand stream contamination.THE NEW STORMWATER MANAGEMENTPARADIGMWhen people move into cities they assume that the cityengineers will provide them with all the key services relatedto water management including safe drinking water, sewagetreatment, stormwater removal and flood protection. Giventhese new issues of densification and climate change it isnow apparent that the sole reliance on the engineeringstructural approach is no longer sufficient and the propertyowner will now have to be part of the solution in solving theemerging stormwater problems.The fundamental changes that are required in orderto cope with the new rainfall/runoff regime are to shiftfrom draining and removing water from sites, to storing,detaining and infiltrating rainwater and by enhancing thenatural processes that provide these functions. At the sametime these innovative approaches need to address both thehydrological processes as well as the impacts from nonpointsources of pollution. Enhancing soils, wetlands andplant cover in the watershed and within riparian bufferzones is essential in order to provide sufficient capacity toabsorb, convert and immobilize many of the contaminantsfrom different land use activities.As the water moves from the property to the neighborhoodand into the watershed, the processes change and so do thecontaminants. At the property scale it has been the normto drain all water away from the housing structure and intostormwater pipes. Pollutants from gardening, spills andhousehold activities are all removed through storm drains. Atthe neighborhood scale we have to deal with roads, parkinglots and commercial facilities and many of the transportrelated activities create a wide range of new contaminantssuch as hydrocarbons, oils, grease metals and industrialchemicals. Again these contaminants are directly releasedinto the storm sewer system. At the end of the pipe all ofthe runoff and contaminants end up in the urban streamand we hope that nature will provide sufficient remediationand dilution so as not to harm the ecosystem. To reducethe hydrological and pollution impact on urban streamsrequires a new approach, shown in Table 1, and this differssignificantly from what has traditionally been done.Table 1. Differences between the traditional approach versusthe new innovative approach at the three spatial scales.TRADITIONALAPPROACHINNOVATIVEAPPROACHPROPERTY SCALE Drain and remove rain & runoff Retain rain on site, slow releaseof water though infiltrationsystemsNEIGHBORHOODSCALEWATERSHED SCALEDrain and remove rain & runoffStore water in ponds, developprotective structures (dams &dykes), channelize streamsLand use restriction in floodplainStore and delay runoff usingdetention and filter systemsDelay runoff in wide bufferzone and naturalized streamchannels, improve flood storagewithin the watershed.INNOVATIVE ACTIONS AT DIFFERENT SPATIALSCALESAs shown in Table 2, there are a wide range of innovativeapproaches that need to be adapted in order to reduce theflooding and pollution risks. No single action will be ableto address all issues but a combination of actions at thedifferent spatial scales will be the best recipe for success.Not all of the listed actions in Table 2 will succeed in allareas due to the differences in climatic and site conditions.However, there is now sufficient evidence that using acombination of options can go a long way in reducing therisk of flooding and the amount of contaminants reachingthe urban streams.Canadian Water Network 2

INNOVATIVE STORMWATER MANAGEMENT: TRANSLATING SCIENCE INTO ACTIONSHans Schreier, Faculty of Land & Food Systems, University of British ColumbiaMinimizing impervious surfaces and developing parkingsurfaces that allow water to infiltrate is not only effective inreducing the flood peak and the pollution problem but is alsomore cost effective and more appealing than conventionalpaved parking lots.The key option for dealing with storm events is to developdetention ponds and wetlands that function as waterstorage devices and water filtering systems. Sediment whichabsorbs many metals can be collected in a forebay beforethe water enters the wetland systems. The organic matterhelps to retain water and the vegetation and the microbialcommunity is useful to uptake, dilute and convert many ofthe contaminants before the water is slowly released belowthe wetlands. Constructed urban wetlands are proving to bevery effective water storage and filter systems.Many urbanites are apprehensive about having wetlandsin their neighbourhood because of the concern aboutmosquitos and West Nile virus issues. As part of the researchit was shown that the mosquito problem can be reducedsignificantly by designing the wetland so as to alwaysmaintain slowly moving surface water, to minimize thedevelopment of blue-green algae (minimize eutrophication),to plant a wide range of wetland plants, to make sure thereis open space between the plants for UV light penetrationand by introducing fish, like stickleback, that eat larvae andcan survive in somewhat degraded water quality conditions.THE WATERSHED SCALEAt the watershed scale the focus has to be on maintainingwide vegetated riparian buffer zones that allow naturalstream channels to be maintained. Buffer zones have manyfunctions, as shown in Figure 5, and if we leave a sufficientlywide corridor before urban development takes place we canincorporate wetlands and detention structures that delayand moderate peak flow, allowing the vegetation and soils toretain sediments and the plants to take up excess nutrients.These wide and protected buffer zones can also be usedfor recreational purposes because they attract significantpopulations of birds and wildlife, promote biodiversity andare a major food source for aquatic organisms.It is also essential to no longer put stream channels intoconcrete structures but rather allow the channel to meanderand follow a natural pathway because significant amountsof water can then flow laterally in order to dissipate energyand help recharge groundwater, and store and delay waterin back-channels and oxbow lakes in the lowland.Rather than building more protective structures in the formof dykes and protective walls in the floodplain a major effortneeds to be made to search for topographically appropriatesections within the watershed where water during very highstorm events can be stored on a temporary basis. Thesecan be areas in parks, playgrounds and agricultural areasFunctions and Size of Riparian Buffer ZonesNoise ReductionWater Temperature ModerationSediment RemovalPollution ReductionSpecies DiversityStormwater Retentention and Wetland Protection10 30 50 70 90The Decision is Usually a Compromise Between Political and Public AcceptabilityDEPENDENT ON:Functional Value of ResourceIntensity of Adjacent UseBuffer Zone CharacteristicsSpecific Buffer RequirementsSize of Streammetres of bufferModified from Castelle et al 1994.GENERAL GUIDELINES:5-10 m Buffer is too Small15-30 m Buffer is a Minimum30-100 m is a Realistic CompromiseVariable Size is Best but Difficult to Enforcefrom a Legal PerspectiveFigure 5. The appropriate size of the riparian buffer zones toaccommodate all effective functions.and this can significantly reduce flooding in the lowland.The damage caused by large storms in these temporarystorage areas is small and it is a much cheaper andeffective solution than building and maintaining protectivestructures and flood proofing properties in the lowland. Ofcourse restricting land use activities in the floodplain needscontinuous enforcement.Each watershed has multiple uses and this makes evaluationscomplex. The most important functions are to protect thewater sources and to ensure that all environmental servicesare fully functioning. This means that each watershed willhave slightly different sensitivities and a different range ofadaptive measures will be needed.CONCLUSIONEmerging changes in land use and climate show thatconventional stormwater management systems in urbanwatersheds are no longer adequate to deal with increasedrunoff and flooding events. The conventional approachfocuses on rapid drainage and removal of stormwater runofffrom all urban surfaces without addressing the problemof contaminants from urban land use activities. The CWNresearch has shown that a major shift is needed to addressthese new conditions by focusing on runoff detention,temporary storage and infiltration of runoff water whichalso reduces the contamination problem. To accomplishthis and to reduce the flooding and contamination riska wide range of innovations are required to deal with theemerging runoff, flooding and pollution problems at threedifferent spatial scales.For the first time the property owners need to participatein retaining precipitation and delaying the runoff from theirproperties. This can be accomplished by using green roofs,Canadian Water Network 4

INNOVATIVE STORMWATER MANAGEMENT: TRANSLATING SCIENCE INTO ACTIONSHans Schreier, Faculty of Land & Food Systems, University of British Columbiaharvesting roofwater for outdoor and indoor use, improvingsoil conditions, reducing impervious surfaces, plantingurban trees and establishing rain-gardens. The conceptis source control that addesses both the quality and thequantity of water.The next level of innovation is at the neighbourhood scalewhere runoff from impervious surfaces and contaminantsfrom transportation are more intense. This can beaccomplished by re-designing roads and parking lots sothat the runoff water is directed into swales, sand filters,detention ponds and wetlands.Ultimately all runoff and pollution ends in the watershedand in the lowland floodplain. The key innovative solutionsat this scale are to establish wide riparian buffer zones thatallow the river to establish a natural channel which acts asa filter and storage systems for sediment and water andallows contaminants to be contained before they reachthe river. This also requires a new approach for how todeal with extreme flooding events. Designating temporarystorage areas in topographically appropriate sites withinthe watershed can help reduce the flood risk problemdramatically.None of the individually proposed innovations will besufficient to solve all problems but it is proposed that acombination of these approaches will help reduce the floodrisk and for the first time will help to reduce contaminantinput into urban streams. Not all of these innovations areappropriate in all urban watersheds because the local siteand climatic conditions vary from city to city. This requiresthat an adaptive management approach is needed to selectinnovations that are best suited for the local conditions.The research identified a new and innovative path toaddress a major urban problem and offers solutions thatare capable of not only reduce the flooding risks but alsosignificantly improving the environment of urban streams.The first step is to initiate all the above options in new urbandevelopments where these measures are most cost effectiveand can reduce potential problems in a significant way.A number of cities have taken the lead in using theseinnovative ideas to reduce the urban stormwater problemsand some of the innovations that are in place in theVancouver area are featured in a new video accessible onthe CWN website. The remaining challenge is how theseinnovations can become the main tools for any new urbanexpansion and how the knowledge generated by researchcan be translated into widespread action.FOR FURTHER INFORMATION PLEASE SEE HTTP://MLWS.LANDFOOD.UBC.CA/VIDEOS/RESEARCH TEAM:HANS SCHREIER, Professor, University of BritishColumbiaJULIE WILSON, Research Assistant, University ofBritish ColumbiaMICHAEL JACKSON, Research Associate, University ofBritish ColumbiaMARKUS WEILER, Assistant Professor, University ofBritish ColumbiaMIKE STONE, Professor, University of WaterlooKHOSROW FARAHBAKHSH, Assistant Professor at theUniversity of GuelphPARTNERS:ENVIRONMENT CANADADISTRICT OF NORTH VANCOUVERCANADA HOUSING AND MORTGAGE CORPORATIONTORONTO REGION CONSERVATION AUTHORITYCITY OF CALGARYCITED REFERENCEASADIAN, Y. 2010. Rainfall interception in an urban environment. M.Sc. Thesis, Faculty ofForestry, University of British Columbia, 84 pp.BRYDON, J., I.OH, J. WILSON, K. HALL, AND H. SCHREIER. 2009. Evaluation of mitigationmethods to manage contaminant transfer in urban watersheds. Water Quality ResearchJournal of Canada. Vol. 44 (1): 1-15BRYDON, J. 2004. The effectiveness of stormwater ponds in contaminant removal fromurban stormwater runoff, Lower Fraser Valley. M.Sc Thesis, Resources Management &Environmental Studies, University of British Columbia, 228 pp.BRYDON, J., M.C. ROA, BROWN AND H. SCHREIER. 2006. Integrating wetlands intowatershed management: Effectiveness of constructed wetlands to reduce impacts from urbanstormwater. In: J. Krecek and M. Haigh (eds.) Environmental Role of Wetlands inHeadwaters. Springer Verlag, pp 143-154.MARSALEK, J. AND H. SCHREIER. 2009. Innovation in stormwater management in Canada:The way forward. Water Quality Research Journal of Canada. (Overview of specialtheme Issue).Vol 44(1): v-xMAURER, N. 2009. Modelling urban development trends and outdoor residentialwater demand in the Okanagan Basin in B.C. M.Sc. Thesis. Resource Management &Environmental Studies, University of British Columbia , 92 pp.OH, I. 2007. Imperviousness and trace metals in stream sediments: Urbanization in theLower Fraser Valley between 1973-2006. M.Sc. Thesis, Resource Management andEnvironmental Studies, University of British Columbia, 172 pp.PAPPAS, S. 2008. An assessment of historic changes in aquatic biota, water and sedimentquality in a catchment at a developing urban front. M.Sc. Thesis, Resources Management& Environmental Studies, University of British Columbia, 217pp.Canadian Water Network 5