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Designing effective stormwater management policies : the role of the urban forest and impervious cover… Lefrançois, Camille B. Nov 30, 2015

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Designing effective stormwater management policiesThe role of the urban forest and impervious cover  in Vancouver, B.C.by camille B. lefrançoisDESIGNING EFFECTIVE STORMWATER MANAGEMENT POLICIES The role of the urban forest and impervious cover in Vancouver, B.C.byCAMILLE B. LEFRANÇOISB.A.&Sc., McGill University, 2012A PROJECT SUBMITTED IN PARTIAL FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OFMASTERS OF SCIENCE (PLANNING)inFACULTY OF APPLIED SCIENCESchool of Community and Regional PlanningWe accept this project as conforming to the required standard............................................................................................................................................................THE UNIVERSITY OF BRITISH COLUMBIA November 2015 © Camille B. Lefrançois, 2015acknowleDgementsThis project came to fruition with the support of many people. First, I would like to thank my supervisor, Jordi Honey-Rosés, for his support and feedback which prompted me to surpass myself. Special thanks to Edward R. Porter, Amelia Needoba and everyone at Diamond Head Consulting for their ongoing feedback, their support and generosity in helping me throughout this project.I extend my thanks to the i-Tree team, who has been incredibly helpful throughout the project, as well as the numerous professors from the University of British Columbia who contributed to shape my project. Finally, I am extremely grateful to all the friends and family who gave me their support and affection over the past two years, and especially to Francis for helping me  go through these two years with a smile.executive summaryCities across the world deal with issues of water quantity and quality due to stormwater runoff, and many of those problems are expected to increase with climate change. To address those problems, the use of urban forest to manage stormwater quantity and quality issues is becoming more common. However, the way trees and plants contribute to stormwater management varies significantly based on the local climate and topography.In this project, I investigate the role of the urban forest for stormwater management in a small sewershed in Vancouver, BC. The area is located in Hastings-Sunrise within the single-family residential zone and contains approximately 200 homes. I use the i-Tree Hydro hydrology and water quality model to quantify the effect of surface cover changes on the sewershed. I first test the effect of changes in tree canopy in comparison with changes in impervious cover. Then, I investigate the effect over time of a business as usual case where the properties build laneway houses and street trees mature, and of a possible future where the country lanes program is implemented, as well as a downspout disconnection policy.My results indicate that changes in impervious cover have an impact eleven times higher than changes in canopy cover on surface runoff. My scenarios show that the biggest factor affecting stormwater runoff quantity and quality is directly connected impervious areas. It is illustrated with the downspout disconnection scenarios, which generate a 65% reduction in surface runoff. However, the substantial decrease also results in an increase in pervious flow (saturated soils). Increases in tree canopy have a significant impact on the reduction of pervious flow.Overall, I found that the most effective change for stormwater management policies in Vancouver would be to reduce directly connected impervious areas. Policies recommending a reduction of these surfaces should also enhance the urban forest and consider engineered green infrastructure solutions to allow for sufficient infiltration and evapotranspiration. Tools such as i-Tree Hydro require a significant time investment, but can offer key informations for planners and decision-makers to inform decisions on the contribution of the urban forest and other surface covers to stormwater management.taBle of contentintroDuction 6context 7Hydrology in urban areas 8Gray systems 9Green systems 9Gray infrastructure 10Combined sewers 10Green infrastructure 10Defining green infrastructure 11Precedents in the Pacific Northwest 11Stormwater management in Vancouver 12Climate change considerations 13methoDs 14Model selection 15Hydrology, Hydraulic, and Water Quality 15Selection criteria 15i-Tree Hydro 15Case study site selection 16Data collection 16Weather data 16Topography 16Surface coverage 16Advanced parameters 18Sensitivity testing 18Scenario creation 19Pre-development  19Current 19Business as usual 19Possible future 19finDings anD implications 21Results analysis 22Sensitivity testing 22Runoff quantity 22Water quality 26Model use for policy evaluation 26Implication of findings for urban forestry 26Model limitations 27Other model applications 28conclusion 30references 31appenDix 1 34Detailed scenarios 34Pre-development: forested 34Clear-cut scenario 34Current conditions 35Business as usual: Laneway houses 35Mature trees 36Possible future: country lanes 36Laneway house disconnection 37All houses disconnection 37Page 6 | IntroductionintroDuctionClimate change is expected to increase extreme weather events and will exacerbate existing management issues related to stormwater runoff in cities around the world. Urban regions have been dealing with challenges related to stormwater runoff for many years. In the past decades, our understanding of the role of trees, plants and soil on the urban water balance — and its impact on stormwater management — has grown substantially. The implication of the surface conditions on the water balance, however, varies significantly based on local conditions such as weather and topography. Many modeling tools offer a way for professionals to evaluate the role of the urban forest and many other surface cover parameters on stormwater runoff in those local conditions. My project tests the use of the hydrology and water quality model i-Tree Hydro to generate a better understanding of the role of the urban forest in Vancouver, British-Columbia. It also evaluates the impact of development and stormwater management policies on stormwater runoff. The report starts with an introduction to the problematics around urban hydrology and stormwater management. It includes a review of the traditional (gray) and alternative (green) stormwater infrastructure solutions, with examples of cities in the Pacific Northwest which have implemented some of those alternatives. I then provide the policy context for green stormwater management in the City of Vancouver.The methods section offers the rationale behind the choice of the model used, i-Tree Hydro. I discuss the choice of the case study area, along with the data collection process. I explain the design of the scenarios. Finally, the findings section takes a look at the results from the model simulation of all the scenarios. I discuss the implications of my findings with regard to stormwater and urban forest policies in the City of Vancouver.Context | Page 7contextThis section provides basic information on urban hydrology, as well as the infrastructure solutions that are used to manage those peculiar urban conditions. I introduce the readers with the common problematics of stormwater management in urban areas. Traditional and alternative rainwater management infrastructure are presented, as well as precedents for green stormwater infrastructure in the Pacific Northwest. Finally, I introduce the local policy context for the City of Vancouver regarding alternative stormwater management.The presence of pavement, rooftops, trees and plants in our cities all affect stormwater runoff quantity and quality.Page 8 | Contexthydrology in urban areasThe field of urban hydrology was created as a means to address issues of sanitation, health and flooding that emerged with the densification of human settlements (Fletcher, Andrieu, & Hamel, 2013). Indeed, the water cycle is deeply affected by the dramatic changes to the landscape brought by urbanization.At the watershed level, cities have a significant impact on streamflow. While streamflow in undisturbed watersheds is driven by a more constant influx of baseflow1, urban watersheds become increasingly driven by surface runoff, which has a very different timing and magnitude (figure  1). Watersheds dominated by surface runoff2 reach their peak flow earlier during a rain event and do so at a higher discharge volume (magnitude). It recesses faster and to a lower flow magnitude at the end of the rain event as compared with natural areas where baseflow dominates. These changes to urban hydrology have important impacts on the ecology of streams, which will experience larger and more abrupt variations in flow and temperature (Poff et al., 1997). It also increases the likelihood of floods, which occur at higher frequency than in undisturbed areas. In addition to the changes in surface runoff volumes and timing, water quality is significantly worsened with sediments and other pollutants that are carried by surface runoff to water bodies.1Baseflow refers to the portion of water feeding the stream from the groundwater (Rideau Valley Conservation Authority, n.d.)2 For the purpose of this project, I consider surface runoff as coming from two distinct components: impervious and pervious flow. The latter is generated on impervious surfaces such as pavement that do not allow rainwater to infiltrate in the ground, while pervious flow originates from a pervious surface that has become saturated (i-Tree, 2014).DischargeTimeLag timeUrbanRuralfigure 1. typical hydrograph for urban and rural runoffThis hydrograph shows the volume of streamflow discharged over time during a rain event (National Weather Service, n.d.). The peak flow is the moment at which there is the highest discharge volume, while the lag time refers to the time difference between the highest rainfall and peak flow. The recession limb designates the decrease in discharge after the peak flow.The two curves depicted on this hydrograph show a typical streamflow discharge in a rural and urban condition. It is clearly apparent on this figure that the total discharge is much higher in urban conditions. The peak flow is also significantly higher, and has a shorter lag time than in the natural conditions. It is also important to note that baseflow is much higher in the rural conditions than the urban areas. Context | Page 9Gray systemsThe construction of grey infrastructure is at the origin of many of those urban hydrology issues. Martin-Mikle et al. (2015) designate two of those infrastructure changes as particularly significant. Firstly, with the pollution of many urban streams by sanitary and industrial waste, many became a public health concern. To respond to those concerns, numerous urban streams were buried and diverted into drainage infrastructure underground. Of course, this has significant impacts on the surrounding ecosystems and water balance.Secondly, the increase in impervious surface became an important disturbance to the natural hydrologic conditions (Martin-Mikle et al., 2015). As buildings and asphalt or concrete pavement covered more and more of our cities, the infiltration of rainwater into the ground decreased significantly. Many pollutants from human activity accumulate on those impervious surfaces. Additionally, the remaining soils are often compacted, which allows for less water infiltration.Green systemsThe conversion of urban landscapes to hard infrastructure also means that a significant portion of forest ecosystems and native soils has been lost (Nowak & Walton, 2005). In the Lower Fraser Basin, the coniferous forest cover decreased from 71% to 54% from 1827 to 1990 (Boyle, Lavkulich, Schreier, & Kiss, 1997).Yet, the urban forest – trees and vegetation present in the urban landscape – provides a wide array of benefits to our cities. Its value for stormwater management has been widely recognised (Berland & Hopton, 2014; Inkilainen, McHale, Blank, James, & Nikinmaa, 2013; Kirnbauer, Baetz, & Kenney, 2013; McPherson, 2006; Nowak & Dwyer, 2007; Xiao & McPherson, 2002). Trees and plants reduce stormwater runoff by intercepting rainfall and by other processes such as throughfall, evapotranspiration and stemflow (figure 2; Xiao & McPherson, 2002). Through these mechanisms, the urban forest allows for more infiltration of stormwater and a reduction in the flow rate during a rain event (Inkilainen et al., 2013). The results of those interactions is a reduction of the likeliness of flooding or the washing of pollutants into nearby streams and water bodies (Xiao & McPherson, 2002).Therefore, by increasing the hard surfaces and reducing the size of the urban forest, urban watersheds create widely different hydrologic conditions. Most of the rainfall is carried to the streams and water bodies through surface runoff, which conveys much higher loads of pollutants at an increased speed. figure 2. green infrastructure stormwater managementUrban vegetation intercepts rainfall with their foliage and branches. Some of it will then be released to the ground through stemflow and throughfall but over an extended period of time which allows for more infiltration. Evapotranspiration will also take place and reduce the volume or runoff.The streamflow components are also illustrated. Pervious flow will form over the saturated ground, while baseflow will be generated by groundwater, which is fed by rainwater infiltration. Finally, impervious flow is created on impervious surfaces that allow no infiltration.Stemflow ThroughfallInfiltrationEvapotranspirationPervious ow Impervious owBaseowPage 10 | Contextgray infrastructureTo deal with urban hydrologic conditions, engineers and city planners have built rainwater infrastructure to collect and carry surface runoff rapidly in order to minimize the risks of flooding (Nickel et al., 2012). Roads are built to drain surface runoff into catch basins and pipes which take the runoff into a water body. In many cities, rooftops also drain into downspouts which send rainwater to the same collection system. The extent of the impact of human infrastructure on hydrology is such that the term sewershed is used in urban areas to designate a watershed where the boundaries are defined by humanmade features such as stormwater catch basins and pipes (RiverSides, 2009). This gray infrastructure leads to a few shortcomings which can be simplified as quantity and quality issues. As mentioned previously, surface runoff has a higher discharge volume in urban areas. When it is carried directly into streams, it can be the cause of banks erosion as well as flash floods. Additionally, the conveyance system spills the pollutants carried in runoff directly into the water without any filtration, which affects water quality.Combined sewersStormwater drainage infrastructure usually transports water to a nearby water body, and this system is designed independently from the household sewage network which relies on a separate system to transport sewage to water treatment facilities. However, many cities do not have a separate stormwater system, and instead rely on a single combined sewer that carries domestic sewer and stormwater to a wastewater treatment plant. During big rain events where the drainage pipes reach their maximum capacity and in order to avoid sewer backups, the water is allowed to overflow into a water body in what is called a combined sewer overflow (CSO) event. During those events, raw sewage is spilled into our waterways. In Canada, the overflow events need to be reported to the ministry of Environment under the ‘Wastewater System Effluent Regulation’ adopted in 2012 (Environment Canada, 2015).Some cities have taken upon themselves to separate sewer and stormwater pipes completely in order to avoid CSO events. The City of Vancouver, for instance, is in the process of separating all its combined sewer infrastructure, which is expected to be completed by 2050 and represents a significant capital investment (City of Vancouver, 2013b). While this ensures a maximum reduction in overflow, it does not address concerns of rainwater runoff quality and quantity.green infrastructureFaced with the issues related to urban hydrology mentioned previously, many people have studied and put into practice alternative, complementary ways to deal with rainwater. They are often referred to as green infrastructure in opposition to the traditional gray engineering approach. Streets are design to drain stormwater runoff into catch basins.Context | Page 11Defining green infrastructureIn this project, I use the term green infrastructure to designate the urban forest. However, in the context of stormwater management the term green infrastructure can be understood to mean a few different things. On one hand, green infrastructure (GI) is used by many to refer to networks of green spaces which provide ecosystem benefits to our society (Gill, Handley, Ennos, & Pauleit, 2007). Those benefits include heat island effect mitigation, energy efficiency, rainwater management, life quality improvements and carbon storage, among others (Akbari, Pomerantz, & Taha, 2001; Brack, 2002; Sanesi, Gallis, & Kasperidus, 2011; Wolf, 2012). In the North American context, the concept of urban forest is often used to designate those trees and plants that are present throughout the urban landscape (Konijnendijk, Ricard, Kenney, & Randrup, 2006).On the other hand, the US Environmental Protection Agency (EPA) refers to green infrastructure more specifically as a method using vegetation and soil to manage rainwater in an engineered way that mimics natural ecosystems (US Environmental Protection Agency, 2014b). As the definition from the US EPA suggests, the use of green infrastructure for rainwater management attempts to restore some of the natural hydrologic processes that got disrupted in urban environments. At a large scale, a GI strategy might target the preservation or restoration of the natural landscape while at a smaller scale it might promote the use of low impact development techniques (Nickel et al., 2014). Low impact development (LID) aims at reducing the impact of urban development on rainwater runoff at the sub-watershed level through better land use planning and design (Martin-Mikle et al., 2015). The objective is to reduce the volume of runoff and to improve water quality and slow it down through the filtration of runoff by vegetation and soil. Typical LID interventions include green roofs, rain gardens, detention basins and other interventions that replace impervious surfaces or receive impervious runoff.Precedents in the Pacific NorthwestThe solutions to handle rainwater runoff will be determined by the local climate and topography, both of which have important impacts on the magnitude and timing of runoff. In the City of Vancouver, the climate is characterised by wet winters and dry summers (figure 3) and a temperate rain forest ecosystem, which is consistent across the Pacific Northwest region. For this reason, the examples in this section are located in the Pacific Northwest. In the United-States, the EPA recommends the use of GI for compliance on regulations for separate storm and sewer systems, combined sewers and total maximum daily loads (US Environmental Protection Agency, 2014a). For this reason, many cities across the country have been implementing ambitious GI programs. 050100150200Rainfall (mm)2014J DF M A M J J A S O Nfigure 3. Monthly rainfall at the Vancouver International Airport in 2014Page 12 | ContextIn the states of Oregon and Washington, Portland and Seattle both have decided to include green infrastructure as part of their strategy to reduce combined sewer overflow and water pollution associated with surface runoff (McGarvey, 2014). The City of Portland is already managing 35% of its combined sewer drainage basins with GI, and this number is predicted to continue increasing. In Seattle, it is expected that GI will reduce stormwater runoff volumes by 80%. They have been targeting combined sewer neighbourhoods where stormwater is discharged directly into natural watercourses, and significant reductions in peak flow and pollution have been observed. As an example, the re-design of a 660-foot block with GI in Seattle reduced impervious surfaces by 18%, and included 100 new coniferous trees and 1,100 shrubs (Porter-Bopp, 2011). The result was a 99% decrease in runoff.In British-Columbia, the City of Victoria will be implementing a new policy in 2016 which charges a stormwater utility tax to property owners based on impervious area, frontage, intensity, and codes of practice (Morgan & Steele, 2015). The new taxation policy is accompanied by one-time rebates for the installation of rainwater management infrastructure.stormwater management in vancouverStormwater management became an issue of interest at the City of Vancouver in the early 2000s, when a few policies started to emerge on the topic (figure 4). In May 2000, the city council adopted zoning amendments to regulate the impervious coverage in single-family residential (RS) zones across Vancouver (City of Vancouver, 2013a). The amended bylaw sets maximum coverage of buildings and other impermeable materials on the RS properties. The stated goal was to allow for rainwater infiltration, therefore reducing runoff and preserving green space. The maximum total coverage allowed is generally of 60%, including buildings (to a maximum of 35-55% lot coverage) and other impermeable surfaces. There are no provisions for the maximum impermeable cover in other zoning districts.However, a policy enacted in 2010 and amended in 2014 entitled ‘Rezoning policy for sustainable large developments’ specifies rules related with stormwater management (City of Vancouver, 2014b). The policy requires that applicants for a large site development submit a plan for rainwater management, with the intent to “reduce stormwater discharge, reduce the generation of runoff, treat surface runoff to reduce contaminants, and where possible, conserve potable water use.” The targets address both runoff quantity and quality concerns. They require to maintain the runoff rate and volume to the level it had in its prior land use, as well as to have the capacity to absorb 100% rainwater runoff for a two-year 24-hour storm. Additionally, the plan should enable the treatment of 90% of the average runoff volume in order to improve water quality. Rainwater treatment here is defined as the capacity to reduce a minimum of 85% of total suspended solids.In addition to the previous policies which target private property, the city put forward some initiatives in the public realm. In 2002, the Country Lane pilot project was put in place by the city’s Engineering Services (City of Vancouver, 2002). The project aimed at replacing traditional asphalted laneways with permeable lanes made of two concrete strips figure 4. Timeline of the implementation of green infrastructure stormwater management policies and programs2000 2010RS impermeable coverageLarge development rezoning2014Urban Forest Strategy + ISMP2012Climate Change Adaptation StrategyAmendments2002Country lanes pilotContext | Page 13for vehicles to drive on surrounded by structural grass which can support the weight of vehicles. Engineered soil was be used to allow for 90% of stormwater to infiltrate and to have the stability required to support large city trucks. Three country lanes were built by the city under the pilot project, and the objective was to allow citizens to petition to get a country lane for which they would pay the cost through their municipal taxes over a 15 year period (Hutchinson, 2013).  While it is still possible to petition with a sufficient number of residents on a block to fund a country lane, this program has been dormant since the three pilot demonstration projects were built. Finally, the following strategies include some stormwater management elements. Firstly, the city council adopted the Urban Forest Strategy in April 2014 (City of Vancouver, 2015b). The strategy offers an assessment of the state of the urban forest, as well as targets to protect, plant and manage it better. The stormwater management benefits of the urban forest are mentioned as one of the services it provides. In that regard, it aims at increasing the canopy cover as well as providing soil conditions to enable proper rainwater infiltration. Secondly, in 2012 the City of Vancouver released its Climate Change Adaptation Strategy (City of Vancouver, 2012). The plan states the changes expected to occur in the region as well as their impact and associated risks for the city and its residents. A series of actions is associated with each of the main impacts. The “increase in intensity and frequency of heavy rain events” is described as a risk, with which many actions are listed to improve our resiliency in these conditions. They include:•	 Recommending stormwater management opportunities that could be transferable from the large site development to other types of developments•	 Removing barriers to the use of parks to drain streets runoff•	 Conduct an evaluation of the impermeable surface allowance bylaw for the single family residential zones, and make recommendations for a better enforcement of the rulesSince the publication of the strategy, both the zoning bylaw on impermeable cover and the rezoning policy for sustainable large site development have been revised. The Integrated Stormwater Management Plan has not been released yet,  which makes it is impossible to know how some of the action items will be addressed within it. However, the revisions to existing policies indicate the importance of the strategy for the city and their willingness to act upon stormwater management issues with new approaches. climate change considerationsIt is expected that climate change will have impacts on the rainfall patterns across the globe (Gill et al., 2007). Indeed, regions such as Metro Vancouver are expected to see an increase in the intensity of precipitations in the future (ClimateBC, 2014; Denault, Millar, & Lence, 2006). From a hydrological perspective, more intense rain events could lead to higher peak flow. This is problematic considering that typical drainage infrastructure is built for probable maximum flood (1-in-100-year events), with important consequences if the system exceeds its capacity (Denault et al., 2006; Watt, Anderson, Marsalek, & Waters, 2003).Clark Park in Vancouver’s Cedar-Cottage neighbourhood has a few perforated curbs that allow runoff from the streets into the park, where small rain gardens have been built to facilitate infiltration.Page 14 | MethodsmethoDsIn this section, I explain my choice of the modeling tool used for this project. I also explain the choice of the case study area in the City of Vancouver, and detail my data collection and scenario creation process. Lawn intercepts rainfall, enables evapotranspiration and increases infiltration.Methods | Page 15model selectionModels are simplifications of reality that allow us to look at interactions of interest. It is limited by our understanding of the processes at play, as well as by the availability of data inputs. More complex models are likely to create more accurate depictions of reality, but might not be useful if the information required to use them is too detailed or hardly available. Hydrology, Hydraulic, and Water QualityWhen it comes to studying stormwater, there are three main types of models which all look into different aspects of the water balance processes. Hydrology models produce estimates of peak flow and runoff volumes based on weather, topography and surface cover inputs (Minnesota Pollution Control Agency, 2015b). Hydraulic models look more specifically at the movement of water (velocity, flow rates, etc.) through gray infrastructure. Some combined hydrology and hydraulic models allow for both phenomena to be investigated, often using the outputs from the hydrology model as inputs for the hydraulic part. Finally, water quality models provide information of that aspect of stormwater management. Many stormwater modeling tools integrate more than one of the model types. A well-known example is the Storm Water Management Model (SWMM), created by the US EPA in the 1970s (Minnesota Pollution Control Agency, 2015a). This tool integrates the hydrology and hydraulic components as well as a water quality model (US Environmental Protection Agency, 2015). It is meant to test low impact development (LID) for the prevention of CSO and the reduction of water pollution. Numerous other models combining those three elements are available, at different levels of complexity and data requirement.Selection criteriaFor this project, my intent was to get a detailed assessment of the role of the urban forest on the local hydrology, as well as the impact of related surface cover conditions such as impervious and directly connected impervious areas. A preference was given to free or low-cost tools that can be easily accessed. The models considered were hydrology and water quality models. Hydraulic models are useful to understand the impact of various scenarios on the traditional infrastructure, but they also require more technical information on the conveyance systems. Therefore, while it would have been valuable to understand the impacts of changes in hydrology on our infrastructure, the priority was given to understanding the hydrologic and water quality changes.i-Tree HydroThe USDA Forest Services has a series of tools named i-Tree aimed at analysing the benefits provided by urban forest (i-Tree, n.d.). i-Tree Hydro allows users to study the impact of vegetation and impervious cover on the water balance and water quality. The software methodology is peer-reviewed and published, and the tools are free (Wang, Endreny, & Nowak, 2008). While it is built for use in the American context, many of its tools have been used and even adapted to other countries. Initially designed for watershed simulations, i-Tree Hydro has been adapted for use in non-watershed context such as cities or neighbourhoods. The model allows for a base case and alternative scenario to be integrated into a single simulation.Once the data is inputted in the model and the simulation ran, its outputs are available in three formats. First, a document summarizes information about the scenarios, as well as basic information on the changes in streamflow and water quality. Graphs for total flow, streamflow components and pollutants in the base case and alternative scenarios are also available and customizable within the model interface. Page 16 | MethodsFinally, the outputs can be exported as tables into Microsoft Office’s Excel format. case study site selectionI chose to conduct my case study in the City of Vancouver because of its proximity as well as the willingness of a few key staff members to help frame the project and collect data. More specifically, a single-family housing sewershed in East Vancouver was suggested because the flow at the outlet of the area had been recorded over most of the year 2014. The case study site is therefore located in the Hastings Sunrise neighbourhood in Vancouver (figure 4). The sewershed is within a single-family RS-1 zone which includes approximately 200 houses with a combined sewer infrastructure. It represents a typical subset of Vancouver, where over half of the territory is zoned for single-family housing (City of Vancouver, 2014a). I made the decision to study a small area in order to allow for a better familiarity and detailed data collection. Data collectionThe data input requirements for the model include local climate and topography, surface coverage and other more advanced parameters. This section goes through the process used to retrieve the information needed to run the model. Weather dataThe software requires a lengthy list of weather parameters at an hourly time step formatted based on American standards from the US National Oceanic and Atmospheric Administration (NOAA). This makes the use of i-Tree Hydro more challenging for international users because it requires additional manipulation to convert the local data to US units and format (i-Tree, 2014). The data available freely on Environment Canada’s climate website is also often missing some of the required weather parameters. In order to obtain the data I needed for this project, I downloaded the climate data from Vancouver International Airport station on the NOAA database, which includes a certain number of stations outside of the United-States. It contained all of the required weather elements to the exception of precipitation. It also has the advantage of being pre-formatted according to the standard required by i-Tree Hydro. I ordered the missing precipitation data for the same weather station from Environment Canada, which was available to order at a small cost. I finally merged the two files with the help of the i-Tree team.TopographyThe model requires a digital elevation model (DEM) to be imported for the simulation to take topography into account. A Canada-wide DEM is available from the federal government, although at a very coarse scale for the simulation of such a small area. Instead, I used the fine scaled DEM from the Vancouver Open Data Catalogue (City of Vancouver, 2014a), which I converted to an ASCII format using a Geographic Information System (GIS) software.Surface coverageDue to the small size of the area studied, I chose to use photo-interpretation of a 2011 Vancouver orthophoto to trace the extent of pervious areas and obtain the impervious areas. This allowed me to produce maps representing surface coverage and to use the spatial information to inform my scenarios. However, the i-Tree Canopy tool – recommended by the i-Tree team – would facilitate data collection for large projects3.I estimated the canopy cover using the City of Vancouver’s tree canopy shapefile, which had been produced using Light Detection and Ranging (LiDAR) data collected in 2013. I used ESRI’s ArcGIS 10.2 to conduct an 3 The online tool i-Tree Canopy creates random points on a Google Map orthophoto which the user assigns to pre-defined surface cover categories. It is recommended that 500-1000 points are assigned in order to get an accurate estimate of the area being analysed.Methods | Page 17E  8th AveE  6th AveSlocan StE  7th AveE  5th AvePenticton StKaslo St    E BroadwayNLegendSewershed BoundaryLand coverBare soilPavementHerbaceousBuildingsCanopy coverEvergreenDeciduousShrubsPerviousImpervious0 30 60 90 12015Metresfigure 4. Surface cover in the case study area, located in the neighbourhood of Hastings-Sunrise, Vancouver.Page 18 | Methodsanalysis and derive the percentage of tree canopy over impervious surface as required for the model.In order to obtain the shrub cover and the building footprints, I downloaded the LiDAR data available on the City of Vancouver’s Open Data catalogue. I transformed the data to obtain polygons and calculate the surface covered by shrubs and buildings. Directly connected impervious areas (DCIA, also called effective impervious area) is an important parameter in the i-Tree Hydro model. DCIA represent the proportion of impervious surface which is drained directly into the area’s outlet (stream or pipe) via continuous surface, pipes or other conveyance infrastructure. The i-Tree team recommends the use of the Sutherland equation to estimate DCIAs when detailed information for the study area is not available (i-Tree, 2015). However, in the Vancouver context where downspouts are required for all houses, I estimated the proportion to be much higher than the equation suggested. Streets, lanes and houses were all included as impervious surfaces that are directly connected. This estimate might be low considering that based on observations of the area modelled, most garages also have downspouts.Finally, I used the property cadastral shapefile from the City of Vancouver to split the surface cover for pervious and impervious areas between private and public and classified them per type: streets, sidewalks and lanes for the public areas and house, garage, pavement and herbaceous for private property. This allowed me to create of scenarios described below. Advanced parametersThe i-Tree Hydro model allows users to define many additional parameters, such as soil type. For this project, the soil type – silt loam – was specified based on the Vancouver Soil Map from the University of British Columbia Virtual Soil Science Learning Centre (Virtual Soil Science Learning Group, 2013). The other parameters were kept at their default value.sensitivity testingThe first part of my analysis is designed to evaluate the impact of the urban forest (trees and herbaceous) on stormwater management. In order to do so, I ran two separate analysis. The first simulated changes in canopy cover from 1% to 100%. As the tree canopy increased, it first covered the bare soil and shrubs, after which it covered herbaceous and finally impervious surfaces. During the simulation, the pervious (herbaceous, shrubs and bare soil) and impervious cover remain constant. The second simulation looked at the changes in impervious cover from 0% to 100%, with tree canopy remaining constant. The impervious cover started by replacing the bare soil and shrub cover, after which it replaced herbaceous, and finally the surface cover under tree canopy. The proportion of DCIAs remained constant throughout, which means that the total DCIA increases and decreases with changes in impervious cover. The two simulations are not meant to represent realistic scenarios. Rather, I want to learn about the impact of the two elements on streamflow. The understanding of the magnitude of changes in runoff caused by trees and impervious cover helps explain the results from the realistic scenarios described below.Methods | Page 19scenario creationThe scenarios I considered for this project look at different time periods. Firstly, the pre-development period refers the baseline conditions for the undisturbed hydrologic flows, and the initial perturbations to that condition. Secondly, I examine current conditions, as well as a business as usual development trend. Finally, I consider a possible future in which the country lane pilot project and downspout disconnect policy are implemented in the neighbourhood. The scenarios presented below can be found in full details in Appendix 1.Pre-development Pre-development scenarios refer to the landscape in its undisturbed condition or after early disturbances. I documented the forested scenario using historical accounts of the regional ecosystems at the Europeans arrival from Boyle et al. (1997) and MacDonald et al. (1992). They describe the area as being forested, with evergreen trees largely dominating and a mostly deciduous shrub understory. As a comparison, a clear-cut scenario is also presented, where all the tree and shrub canopy has been removed and replaced by herbaceous. My intent is to show the beginning of the changes that affected the area’s hydrology.CurrentThe current scenario is based on observed land use and vegetation cover for the area between 2011 and 2014. The current conditions served as the starting point to build all of the following scenarios.The next scenarios bring us 30 years into the future. I created them to represent a business as usual development trend, and to explore a possible future with the implementation of stormwater management policies to mitigate the impacts of development.Business as usualLaneway housesOne of the current trends in the development of single family residential areas is the construction of laneway houses as infill development. Under current policies, laneway houses can be built on 32 feet (or wider) lots zoned within the single family zone (City of Vancouver, 2015a). Therefore, I assumed in this scenario that all properties in the area built laneway homes. The trend seems to be reflected with the changes I observed from data collected in 2011 (orthophoto), 2013 (LiDAR) and the Google Maps imagery from 2015. During that four year period, many laneway houses have been built in the area. The footprint of the laneway houses was set at 7 by 8 metres (56 m2) based on the footprint of existing laneway houses built in the area since 2011. In the study area, most properties have garages, which makes for a smaller net increase of the total building footprint coverage.  However, the garages were assumed not to have downspouts and were thus not counted in the DCIAs. With the construction of laneway houses, I added all of the new rooftop area to the DCIA.Mature treesUnlike in some of Vancouver’s greener neighbourhoods, Hastings-Sunrise does not have a large canopy cover. However, many young trees line the streets. In this scenario, I projected that these street trees grow to maturity, creating a canopy cover arching over the residential streets. Possible futureCountry lanesIn this scenario, I inquire on the impact of the construction of country lanes in the area, based on the design of the pilot project. In the current conditions, all laneways in the sewershed are fully paved and directly connected. I based this scenarios on observations of the country lane design built south-east of Fraser Street and East 27th Avenue in Vancouver. The surface cover was estimated as two pavement stripes Page 20 | Methodsof 0.7 meters in width for the car tracks, and the remainder as grass. The concrete stripes dimensions were measured using Google Earth. Buildings downspout disconnectionThe two final scenarios I created implement a policy that many cities use to reduce stormwater volume in the gray infrastructure: downspouts disconnection. The change from previous scenarios is therefore limited to one parameter: directly connected impervious areas. In a first step, I disconnected laneway houses downspouts, followed by the remainder buildings in the last scenario. Findings and Implications | Page 21finDings anD implicationsIn this section, I discuss the results from the model simulations for the sensitivity tests and scenarios. My results analysis serves as a basis to discuss the impact of urban forests on stormwater management, as well as the model limitations and suggestions to use of the model for policy-making.Tree interception allows an increased proportion of rainfall to be evaporated. The remaining water drips slowly, delaying its arrival on the ground and thus increasing infiltration and evaporation rates.Page 22 | Findings and Implicationsresults analysisSensitivity testingThe results of my sensitivity tests reveal that impervious cover is a much larger contributor to changes in surface runoff than tree canopy. Indeed, a change in impervious cover has an impact on surface runoff which is more than 11 times bigger than a change in tree canopy (figure 5).The limited impact of tree canopy on surface runoff is partly due to the fact that most of the rainfall in Vancouver happens during the winter. Yet, most trees planted in the city are deciduous and have no leaves during the wet season. When trees have no leaves on, the i-Tree Hydro model bases its interception on the bark area index (as opposed to the leaf area index for the rest of the year) , which is significantly lower. The interceptions rate is therefore reduced accordingly. An increase in the proportion of evergreen trees would also increase rainfall interception. Currently, only 6% of the tree canopy is evegreen.  Runoff quantityMy results suggest that the biggest contributors to the change in surface runoff are the impervious cover and directly connected impervious areas (DCIAs). With no surprise, I find that the transition from the pre-development to the current conditions creates the biggest increase in surface runoff: more than 450%. I compiled the scenario results on figure 6, where the three flow components can be compared to one another across the scenarios.Percent change (from current scenario)0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%Surface coverCANOPY IMPERVIOUS-100%-80%-60%-40%-20%0%20%40%Current scenarioCanopy cover sensitivity testSurface ow changesPercent change (from current scenario)0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%Surface cover-100%-80%-60%-40%-20%0%20%40%Impervious cover sensitivity testSurface ow changesfigure 5. Impact of canopy cover and impervious cover on surface runoff (pervious + impervious flow)Findings and Implications | Page 230102030405060708090100Annual 2014 ow (thousands of m3 ) Forested Clear-cutCURRENTLaneway housesMature treesCountrylanesLaneway housedisconnectionAll housesdisconnectionPRE-DEVELOPMENT BUSINESS AS USUAL POSSIBLE FUTUREBaseowPervious owImpervious owSurface owfigure 6. total annual flow components in all scenariosThe changes in total flow and the proportion of each flow components varies widely across the scenarios. The surface runoff, which is made of pervious and impervious flow, represent a significant proportion of most scenarios from the current conditions onwards.percent change of surface flow and baseflow from the previous scenario Forested Clear-cut Current Laneway houses Mature trees Country lanesLaneway house  disconnectionAll houses disconnectionSurface flow0% 6% 456% 17% -2% -6% -16% -49%Baseflow 0% 7% -65% -9% -4% 10% 5% 10%Page 24 | Findings and ImplicationsPre-development to current stageMy results show a clear trend from the pre-development, forested conditions to the observed 21st century conditions. From the forested to the clear-cut scenario, baseflow increases slightly, reflecting the decrease in evapotranspiration from the trees. However, the transformation from the two pre-development scenarios to the current conditions is major (figure 7). Suddenly, surface flow has increased exponentially to largely dominate the total flow, with baseflow dwindling to a tiny proportion of total flow and a much reduced overall quantity. Business as usualIn the business as usual situation, I envision all of the properties in the area to build laneway homes. This leads to a small increase in impervious surface and a bigger increase in DCIAs. The increase in DCIAs has a significant impact notably on peak flow as shown on figure 8.The growth of street trees creates two changes: an increase in tree canopy, and an increase in impervious area covered by trees. The effects of those changes are illustrated with a few key observations. First, the canopy covering impervious surfaces leads to a decrease in surface runoff thanks to trees interception. Second, trees reduce the baseflow. However, the biggest change is a 7% reduction in pervious flow. The reduction in pervious flow and baseflow is explained by tree roots, which facilitate rainwater infiltration and increase evapotranspiration. Baseow Surface ow RainfallSurface ow Baseow Rainfall02,0004,0006,0008,00010,00012,00014,000050100150200250Flow (m3 )Rainfall (mm)2014Pre-development(Forested scenario)Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec02,0004,0006,0008,00010,00012,00014,000050100150200250Current scenarioJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec2014Rainfall (mm)Flow (m3 )rainfall interceptionIn the model, trees intercept water based on the extent of the canopy and their leaf area index. The trees intercept 10% of the rainfall over their canopies. In the mature tree scenario, that represent 2.7% of the total rainfall over the modeled area, a 3-fold increase from the previous scenario.However, the climate in Vancouver is such that most of the rainfall happens in the winter, when deciduous trees have no leaves. The interception rate is therefore much lower than it might be in other climates.figure 7.  monthly baseflow and surface runoff in the forested and current scenariosFindings and Implications | Page 25A possible futureThe remainder of the scenarios are either inspired by common stormwater management policies, or by local stormwater initiatives. By reducing impervious cover and DCIAs, the country lanes create a visible decrease in surface runoff despite the relatively small percentage of the sewershed covered by laneways (approximately 5%). The other impact they have is a 10% increase in baseflow due to the increased opportunities for infiltration. The baseflow under these conditions is slightly higher than it was prior to tree growth. However, it should be noted that the model is underestimating rainwater infiltration because it assumes that the soil is the same throughout the area. The country lanes were built with engineered soil that maximizes infiltration, which would increase the magnitude of the results from this scenario.For many cities that are trying to reduce stormwater runoff, downspout disconnection becomes a key strategy. Cities like Portland and Toronto have implemented programs with mandatory disconnection. By doing so, Vancouver could also significantly reduce DCIAs and the runoff that is carried into the gray infrastructure (figure 9). When disconnecting the rooftops in the model, it enables runoff to evaporate and to overflow onto pervious areas where it might infiltrate and be evapotranspired or recharge groundwater. In those two scenarios, surface runoff is drastically reduced, while baseflow increases due to a higher groundwater recharge. Increases in pervious flow of 14% and 34% are also observed from one scenario to the other, which indicates increasingly saturated soils. The overall result is a decrease in total flow as compared with all the other scenarios, as shown on figure  6. This might be explained by a significant increase in the evaporation of the water accumulating on impervious surfaces and saturated pervious areas. However, the model does not take into account the rooftops slopes, which would send the impervious runoff directly onto pervious surface, likely reducing the amount of evaporation currently estimated.figure 8.  peak flow inthe current and laneway house scenarios on a rain event in may 2014figure 9.  monthly surface runoff  in the country lane in comparison with the downspout disconnection scenarios0.00.51.01.52.02.53.03.54.04.5Laneway house Current Rainfall PEAK FLOW+17%Rainfall (mm/h)Hours050100150200Surface ow (m3)02,0004,0006,0008,00010,00012,00014,000050100150200250Flow (m3 )Rainfall (mm)Surface owCountry lanes Laneway house disconnect All houses disconnect Rainfall2014Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecPage 26 | Findings and ImplicationsWater qualityThe water quality model in i-Tree Hydro provides estimates of the pollutant loads. While the total quantities of the different pollutants vary within each scenario, the change in pollutant is constant from one scenario to the other. The percent change in mean pollutant load changes by the same proportion from one scenario to the other than surface flow (see page 23). The biggest increase is obviously coming from the transition between the pre-development period and the observed current conditions (figure 10). Aside from that jump, the biggest factor influencing water quality appears to be DCIAs, both for the increase from the current to the laneway house scenario and for the decrease in the last two scenarios. This is intuitive considering that directly connected pavement offers no opportunity for the pollutants to be filtered before reaching a water body. model use for policy evaluationMy results suggest that the first priority for stormwater management policies in Vancouver should be to reduce impervious cover, and especially DCIAs. The city’s stormwater management policies should prioritize those elements in order to get the biggest return on their investments. The urban forest, although its impact is of a smaller magnitude, will be key to help that transition.Implication of findings for urban forestryThe sensitivity testing suggests that impervious surfaces have a much larger impact on surface runoff than the tree canopy. This finding tells us that there is no way around the restoration of natural, pervious soils in order to control stormwater runoff. The replacement of pavement or buildings with pervious surfaces will produce the bulk of the change to that effect. However, I observed that trees make a significant difference to reduce pervious flow and thus soil saturation. If the City of Vancouver is to reduce impervious surfaces and DCIAs, the use of vegetation will be key to increase interception, infiltration and evapotranspiration. Increasing the proportion of evergreen trees and plants would also improve the rain interception rates throughout the winter, where most of the rainfall occurs. Additionally, trees have a bigger impact on surface runoff when their canopies are hanging over impervious surfaces. For that purpose, street trees with wide-spreading canopies should be encouraged.It is also worth noting that a recent study in Metro Vancouver on tree interception found much higher rates than other commonly accepted studies such as the one used in i-Tree Hydro’s routines (Asadian, 2010). The study was conducted in an urban context instead of a forested environment like most preceding studies. This indicates that while models such as i-Tree Hydro provide useful estimates, they are based on the best available science and will keep evolving to integrate new findings. 02,0004,0006,0008,00010,00012,000Forested Clear-cut Current Laneway house Mature trees Country lanes Laneway housedisconnectionAll housesdisconnectionMean pollutant load (kg)ScenariosPollutants in all scenariosPollutantsTotal suspended solidsBiochemical oxygen demandChemical oxygen demandTotal phosphorousSoluble organic pollutantsTotal Kjeldahl NitrogenNitrogen dioxydeCopperLeadZincTss BOD COD TP SolP TKN NO2_3 Cu Pb Znfigure 10. total annual mean pollutant in all scenariosFindings and Implications | Page 27While my research helps to point at the ways in which urban vegetation and soils can be used to maximize the stormwater management benefits, an ample body of literature demonstrates that stormwater management is only one of the benefits that urban forests bring to cities and their residents. When considering their urban forest targets, cities should take into account all those benefits. Model limitationsThe i-Tree Hydro model seeks to provide professionals with a tool to comprehend the impact of vegetation and landscape on hydrologic conditions. However, through my research I have identified limitations for the use of the model in the Canadian planning context.Non-watershed areasInitially, the tool was developed to look at watersheds, with the outputs estimating the effect of watershed conditions on streamflow at its outlet. Later on, the model was adapted for use in a non-watershed contexts to allow the use of political or other relevant boundaries. It also offers the opportunity to look at areas without streams, which is relevant for many urban areas where streams have been buried. However, in a non-watershed context the model outputs are not straightforward. For instance, it becomes impossible to assess them in comparison to actual streamflow, which can be done in a watershed. The water quality information also becomes more abstract as it might not be directed into a single stream where pollutant concentration can be estimated. Therefore, while the modeling of non-watershed areas allows a necessary, expanded use of the model in common urban conditions, it also makes it more difficult to explain and visualize the results.Data inputsThe i-Tree Hydro model was developed by the US government primarily for use in the American context. As expected, this represented a challenge for many data inputs. Weather was the most challenging data to collect, although many surface cover parametres also required specialized data such as LiDAR, and very involved transformations. i-Tree Canopy offers an excellent way to collect the surface cover data more easily, but it would have compromised my ability to create the detailled scenarios I used in my analysis.Valuing model outputsAdditionally, while the outputs are partially pre-processed into graphs and a summary report, they are still very technical and require a basic understanding of urban hydrology. In many cases, these types of results are expressed as ecosystem services. Often, they are expressed in values that facilitates their integration to our usual decision-making processes. While it is possible to do so with the results from i-Tree Hydro’, it is not provided by the model itself. On one hand, that allows users to be more Pervious flow forms in areas such as lawns when the soil becomes saturated. As my results show, adding more shrubs and trees can reduce pervious flow by increasing rain interception, evapotranspiration and infiltration.Page 28 | Findings and Implicationsregionally specific and transparent about how they derive value from the changes in hydrology. On the other hand, assigning value to such results represents another time-consuming step and requires an additional methodology. Additionally, many of the most straightforward benefits of a decrease in surface runoff would require a hydraulic model in order to understand how infrastructure costs might change.Potential improvementsEngineered green infrastructure solutions such as green roof and rain gardens are definitely a big part of any conversation on green stormwater infrastructure in urban areas.  In that regard, i-Tree Hydro has limited capabilities. For instance, a scenario such as the country lanes significantly underestimates rainwater infiltration because the model assigns the same soil type as for the rest of the area. To provide accurate results, it would need to take into account the engineered soil which allows for a much higher infiltration rate. However, an upcoming update of the model will bridge that gap to allow these types of GI to be modeled in details. This will provide an exciting opportunity to combine the detailed vegetation capabilities of the model with the use of engineered green infrastructure for stormwater management.Climate change is expected to result in wetter winters with more intense storms and drier summers in the region of Vancouver. Of course, the change in rainfall patterns will greatly affect the water balance and could have significant impacts on the city, as Vancouver’s Climate Change Adaptation Strategy suggests. Unfortunately, it is not currently possible to evaluate the hydrological implications of those changes in the i-Tree Hydro model. Indeed, the model requires hourly data which is more detailed than climate projection datasets produced to this day.Other model applicationsThe following ideas are suggestions that emerged through my analysis on how tools such as i-Tree Hydro might be used to inform policy targets in an integrated way in order to create mutually beneficial and supportive policies. For instance, if the reduction of impervious surfaces and DCIAs is a priority, the model would allow users to test for the implications of these changes, and how they might interact with changes in vegetation. Impervious cover and tree plantingFirstly, by considering the three flow components, the model allows for a nuanced understanding of runoff. i-Tree Hydro informs its users of the changes in surface runoff, and also provides information on groundwater. For instance, mature trees evapotranspire more water, which leads to a decrease in groundwater recharge and baseflow. In the City of Vancouver, maximum impermeable coverage on single-family residential properties is defined in the zoning bylaw while tree planting targets are hosted within the Urban Forest Strategy. The model could be used to suggest ratios of tree canopy targets and pervious areas required to allow for sufficient infiltration to provide water for trees without negatively affecting groundwater recharge. This would provide information on cumulative policy impacts, and how they might be adjusted to support one another. Downspout disconnection and infiltration capacityAs discussed previously, downspout disconnection is a policy that has been used in many cities, either to reduce CSOs as well as stormwater runoff volume and water quality issues. However, in the City of Vancouver which receives large quantities of rainfall during the winter months, this can be problematic once the soils are saturated and do not allow for proper infiltration.The i-Tree Hydro model allows its users to know when the soil is saturated, with pervious flow forming on the surface. Using these measures, it is Conclusion | Page 29possible to understand whether certain policies might overwhelm the infiltration capacity of the area. Additional infiltration solutions could then be considered to mitigate the issue, such as increasing tree and shrub canopy, or engineered green infrastructure. Overall, a model like i-Tree Hydro can provide planners and municipalities with useful information on hydrological changes resulting from new surface cover conditions with a peer-reviewed methodology. It remains at a level of details that makes it more accessible to planners and ecologists than other models that are geared towards engineers or hydrologists. Page 30 | ConclusionconclusionIn conclusion, according to my findings the reduction of directly connected impervious areas and impervious cover yields maximum stormwater  quantity and quality improvements in my case study area in Vancouver, B.C. The impact of the urban forest is most important with the increase of pervious cover. I found that the increase in tree canopy had a small impact on surface runoff compared with changes in directly connected impervious areas and the proportion of impervious to pervious (herbaceous) cover. Indeed, the downspout disconnection scenarios together yield a 65% reduction in surface runoff. However, the increase in pervious flow observed in those scenarios suggests that the infiltration capacity will need to be improved if such a policy is implemented. The urban forest, and in particular tree a canopy, could provide the increased interception, evapotranspiration and infiltration required.Overall, tools like i-Tree Hydro offer rich data for professionals seeking a better understanding of the impact of surface condition changes on the local water balance. However, while the model is accessible to non-hydrologists, it requires good technical skills to assemble the data inputs and analyse the outputs. Yet, it presents planners with a valuable opportunity to test and evaluate their policies and identify relevant targets and thresholds that will help us achieve better stormwater management.There is a commonly accepted need to improve our current stormwater management approach to address the water quantity and quality problems that are well documented in the City of Vancouver and across the world. Climate change and its expected impacts on rainfall patterns provide yet another reason to address those problems in innovative ways. 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Page 34 | Appendix 1appenDix 1Detailed scenariosPre-development: forestedSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 80.0% Coniferous 90.0%Trees over pervious100.0%Trees over impervious0.0%Shrubs 20.0% Evergreen 15.0%Herbaceous 0.0%Impervious 0.0% HousesGaragesResidential pavementStreets pavementLanes pavementDirectly connectedBare soil 0.0%Clear-cut scenarioSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 0.0% Coniferous 0.0%Trees over pervious0.0%Trees over impervious0.0%Shrubs 0.0% Evergreen 0.0%Herbaceous 100.0%Impervious 0.0% HousesGaragesResidential pavementStreets pavementLanes pavementDirectly connectedBare soil 0.0%Appendix 1 | Page 35Current conditionsSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 6.9% Coniferous 5.7%Trees over pervious58.5%Trees over impervious41.5%Shrubs 3.9% Evergreen 45.0%Herbaceous 23.0%Impervious 66.0% Houses 40.4%Garages 8.3%Residential pavement21.5%Streets pavement20.5%Sidewalks 6.9%Lanes pavement6.6%Directly connected64.7%Bare soil 0.2%Business as usual: Laneway housesSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 6.3% Coniferous 5.7%Trees over pervious49.3%Trees over impervious50.7%Shrubs 3.4% Evergreen 45.0%Herbaceous 22.0%Impervious 68.1% Houses 39.2%Laneway houses13.7%Residential pavement18.9%Streets pavement19.9%Sidewalks 6.7%Lanes pavement6.4%Directly connected75.6%Bare soil 0.2%Page 36 | Appendix 1Mature treesSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 26.7% Coniferous 5.7%Trees over pervious49.3%Trees over impervious50.7%Shrubs 3.9% Evergreen 45.0%Herbaceous 13.9%Impervious 55.3% Houses 46.2%Laneway houses16.1%Residential pavement22.3%Streets pavement23.4%Sidewalks 7.9%Lanes pavement7.5%Directly connected75.6%Bare soil 0.2%Possible future: country lanesSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 26.7% Coniferous 5.7%Trees over pervious49.3%Trees over impervious50.7%Shrubs 3.9% Evergreen 45.0%Herbaceous 15.0%Impervious 54.7% Houses 48.8%Laneway houses17.0%Residential pavement23.5%Streets pavement24.8%Sidewalks 8.4%Lanes pavement2.3%Directly connected72.6%Bare soil 0.2%Appendix 1 | Page 37Laneway house disconnectionSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 26.7% Coniferous 5.7%Trees over pervious49.3%Trees over impervious50.7%Shrubs 3.9% Evergreen 45.0%Herbaceous 15.0%Impervious 54.7% Houses 48.8%Laneway houses17.0%Residential pavement23.5%Streets pavement24.8%Sidewalks 8.4%Lanes pavement2.3%Directly connected58.9%Bare soil 0.2%All houses disconnectionSurface cover % of sewershedSub-cover % of coverTotal sewershed100.0%Trees 26.7% Coniferous 5.7%Trees over pervious49.3%Trees over impervious50.7%Shrubs 3.9% Evergreen 45.0%Herbaceous 15.0%Impervious 54.7% Houses 48.8%Laneway houses17.0%Residential pavement23.5%Streets pavement24.8%Sidewalks 8.4%Lanes pavement2.3%Directly connected24.8%Bare soil 0.2%

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