Nicole Ludzki Emily Angermann Madelaine Prince Everett Snieder

Transcription

1 March 3, 2017 Mr. Graham Seggewiss XCG Consulting Ltd. 820 Trillium Drive Kitchener, Ontario N2R 1K4 Subject: Stormwater Management Feasibility Study Exhibition Place, City of Toronto To Whom It May Concern, The following document has been prepared by WET Consultants Ltd., University of Guelph, and serves as the final report submission for the 2017 Student Design Competition. Presented by the Water Environment Association of Ontario, and in partnership with the Ministry of the Environment and Climate Change, the City of Toronto has provided the design problem which focuses on stormwater management using low impact development practices for the Exhibition Place in Toronto, ON. The succeeding report addresses Phase I and Phase II, as outlined in the WEAO SDC 2017 Project Statement. Phase I requires a stormwater management design be developed using low impact development practices to retrofit Exhibition Place, and Phase II, requires a conceptual proposal to manage external drainage onto the site from the elevated Gardiner Expressway highway. WET Consultants Ltd., University of Guelph, has developed this final design proposal which considers both Phase I and Phase II as a combined solution. This final design was developed to address the following hydrological objectives: water quality, flood management, water balance, and climate change impacts. Additionally, social, economic and environmental objectives are addressed in this proposal to achieve the best possible design recommendation for this challenge. Our best efforts were put towards the preparation and completion of this design and report. We truly hope to surpass your expectations for this 2017 Student Design Competition. Sincerely, WET Consultants Ltd., University of Guelph Nicole Ludzki Emily Angermann Madelaine Prince Everett Snieder

2 ENTRY FORM WEAO STUDENT DESIGN COMPETITION 2017 Name of College or University: University of Guelph Name of Team (optional): WET Consultants Ltd., University of Guelph... Name of Contact Person (Team Leader): Everett Snieder..... Address: B-2771 Rosebank Road..... City: Victoria. Province: British Columbia Postal Code: V9C 1A6 Name of Faculty Advisor: Andrea Bradford.. Address: School of Engineering, University of Guelph, 50 Stone Road E. City: Guelph...Province: Ontario Postal Code: N1G 2W Name of Consultant Advisor:. Company:.. Address:. City:. Province:... Postal Code:. . Names of Team Members: (use additional pages if necessary) Name Address Program Year/Level WEAO Member Number Madelaine Prince Water Resources Engineering Everett Snieder esnieder@mail.uoguelph.ca Water Resources Engineering Emily Angermann eangerma@mail.uoguelph.ca Nicole Ludzki nludzki@mail.uoguelph.ca Water Resources Engineering Environmental Engineering

3 Acknowledgements We would like to thank our academic advisor, Dr. Andrea Bradford, for her guidance, patience, and support throughout this project. Her flexibility in meeting more strenuous timelines allowed our team to compete in this design challenge, and we really appreciate her dedication towards our learning and successes. We would like to thank Mr. Graham Seggeweis, WEAO, for all his hard work in hosting this design competition. As well, we would like to extend our thanks to all the industry representatives from the City of Toronto, Exhibition Place and the Ministry of the Environment and Climate Change for their contributions and time in supporting this project.

4 Stormwater Management Feasibility Study Exhibition Place, Toronto March 2017 PREPARED BY: WET Consultants Ltd. Madelaine Prince Everett Snieder Emily Angermann Nicole Ludzki University of Guelph 50 Stone Rd E Guelph, ON N1G 2W1 PREPARED FOR: Background image source: blog.lashgroup.ca

5 Abstract In order to maintain a safe and healthy public facility, it has been identified that a stormwater retrofit design is required for the Exhibition Place in Toronto ON. The implementation of low impact development (LID) practices have been determined as the most effective solution. The design objectives include improving water quality, reducing flood risks, achieving a more natural water balance, and addressing climate change impacts. LID features included in this design include rain gardens, green roofs, tree boxes, raised planters, bio retention cells, permeable pavement, and a vegetated swale. Distribution of these LID features throughout the site reduced the runoff coefficient by 30%-40% for a 12 hour event for a range of 1 to 100 year return period using climate change projections. The LID features intercept and treat 47 % of runoff from impermeable surfaces on the site. The capital cost associated with year one of the design is $3,965, Operation and maintenance costs of the design were determined to be $18,620 for the first two years, and $8,620 per year after year two. Recommendations include implementation of permeable pavement parking lots and improved hydraulic analysis.

6 Project Description This report serves as an entry submission in the 2017 Water Environment Association of Ontario Student Design Competition. In association with the Ministry of the Environment and Climate Change, and the City of Toronto, the project aims to develop an effective stormwater management retrofit design for the Exhibition Place in Toronto ON. The following report includes a problem definition, background information, a design process description, design alternatives supported by decision matrices, and a final retrofit design proposal. The final design aims to address the project objectives and was developed to achieve defined criteria. The design team, representing the University of Guelph, consists of Everett Snieder (Water Resources Engineering), Emily Angermann (Water Resources Engineering), Madelaine Prince (Water Resrouce Engineering), and Nicole Ludzki (Environmental Engineering). Everett Snieder focused primarily on the design modelling and acted as the team lead in communicating with our industry contact, Mr. Graham Seggewiss, from the WEAO. Emily Angermann led the team through the design process by organizing and preparing decision matrices, and by contributing to report writing. Madelaine Prince contributed to report writing and editing, assisted in reviewing the model, and worked on team organization. Nicole Ludzki prepared the CAD drawings, and contributed in writing the report. A collaborative effort was taken in producing this final report. The individuals who supported this project include Dr. Andrea Bradford, University of Guelph, who acted as the Faculty Advisor for this project. We received support and guidance from Mr. Graham Seggewiss, our industry contact and project coordinator from the WEAO. There was additional support provided by members of the City of Toronto, the Ministry of the Environment and Climate Change, and Exhibition Place during the site tour as well as throughout the competition by way of Mr. Graham Seggeweiss.

7 Table of Contents 1 Introduction Site Conditions Problem Statement Proposed Solution Design Criteria and Constraints Background City of Toronto Stormwater Management Development of Stormwater Management Background Modeling Design Alternatives Design Methodology Design Decision Procedure Design Modeling Methodology Data Gathering and Preparation Final Design Overview LID Descriptions Bioretention Features Green Roofs Permeable Pavement Planting Plan Model Results Event Based Modelling Continuous Modelling Hydraulic Profile Value Added Design Component Environmental Benefits Operation and Maintenance Plan Source Control Measures Routing to Maximize at the Source Treatment Conveyance for Secondary Treatment Implementation Plan Economic Feasibility Design Defence Conclusions and Recommendations Design Limitations and Recommendations Technical Design Recommendations Increased Model Accuracy Model Calibration Improved LID Control Sizing Valve Controlled Underdrain References Appendix A Spatial Information and Site Maps... A-I Appendix B LID Feature Assessment and Design Decision Matrices... B-I Appendix C LID Control Engineering Drawings... C-I Appendix D PCSWMM Model Support... D-I Appendix E PCSWMM Model Results... E-I E.1 Predevelopment and Postdevelopment Results... E-I E.2 Postdevelopment and LID Control Results... E-II ii

8 E.3 Hydraulic Profiles... E-VII Appendix F Planting Plan... F-I Appendix G Value Added Components... G-I G.1 Educational Posters... G-I G.2 Community Garden... G-V Appendix H Operation and Maintenance Schedule... H-I Appendix I Economic Assessment... I-I Appendix J Implementation Schedule... J-I Appendix K PCSWMM Model Inputs... K-I iii

9 Table of Figures Figure 1-1: Exhibition Place as viewed in Google Earth, with region of focus outlined in red... 2 Figure 1-2: Flooding as viewed in PCSWMM... 6 Figure 3-1: LID Locations within the Subject Site... 8 Figure A-1: Subject site location... A-I Figure A-2: Existing Stormwater system in the and subcatchment boundaries in the subject area... A-II Figure A-3: Constructed DTM with stormsewer and subcatchment boundaries... A-III Figure A-4: Surface runoff paths and flow direction... A-IV Figure A-5: Land cover classification within the subject area... A-V Figure C-1: Permeable pavement cross-section... C-I Figure C-2: Swale cross section... C-II Figure C-3: Bioretention cell cross-section... C-III Figure C-4: Rain garden cross-section... C-IV Figure C-5: Tree box cross-section... C-V Figure C-6: Raised planter cross section adjacent to building... C-VI Figure C-7: Raised planter cross-section adjacent to highway... C-VII Figure C-8: Green-roof cross section... C-VIII Figure C-10: Green roof on Better Living Centre... C-IX Figure D-1: Stormwater system model as viewed in PCSWMM... D-I Figure D-2: Approximation of LID control catchment area with and without considering stormdrains. D-II Figure E-1: Retention for predevelopment and postdevelopment for 100-year 1-hour event... E-I Figure E-2: Outflow for predevelopment and postdevelopment for 100-year 1-hour event... E-I Figure E-3: Outflow for postdevelopment and LID for 10-year 12-hour event... E-II Figure E-4: Retention for postdevelopment and LID for 10-year 12-hour event... E-II Figure E-5: Water Balance for postdevelopment (L) and LID (R) for 10-Year 12-hour event... E-III Figure E-6: Retention for postdevelopment and LID for 10-year 1-hour event... E-III Figure E-7: Flooding for postdevelopment and LID for 10-year 1-hour event (with CC)... E-IV Figure E-8: Runoff from subcatchment A1 (Green Roof) for 10-year 1-hour event... E-IV Figure E-9: Total outflow for 11 events under continuous modeling conditions... E-VI Figure E-10: Total retention for 11 events under continuous modelling... E-VI Figure E-11: Locations of hydraulic profile transects... E-VII Figure E-12: Hydraulic profile of transect A... E-VIII Figure E-13: Hydraulic profile for transect B... E-IX Figure E-14: Hydraulic profile for transect C... E-X Figure E-15: Hydraulic profile for transect D... E-XI Figure G-1: Educational poster for bioretention-cell... G-I Figure G-2:Educational poster for site retrofit... G-II Figure G-3:Education poster for rain garden... G-III Figure G-4: Educational poster for raised planter... G-IV Figure G-5: Plan view of community garden and green roof on the Food Product Building... G-V Figure G-6: Sample planting plan for community garden planter... G-VI iv

10 Table of Tables Table 1.4-1: Defined objectives, constraints and criteria... 3 Table 3.1-1: Summary of resultant LIDs to be implemented from the decision matrices for each location 9 Table 4.2-1: Summary of ArcGIS Files for Maps and PCSWMM Inputs... A-I Table 4.2-1: Definition of decision matrix parameters... B-I Table 4.2-2: Evaluation of a rain barrel corresponding to the decision matrix... B-II Table 4.2-3: Evaluation of a bioretention cell corresponding to the decision matrix... B-III Table 4.2-4: Evaluation of a raised planter corresponding to the decision matrix... B-IV Table 4.2-5: Evaluation of a rain gardens corresponding to the decision matrix... B-V Table 4.2-6: Evaluation of a vegetated filter strip corresponding to the decision matrix... B-VI Table 4.2-7: Evaluation of a green roof corresponding to the decision matrix... B-VII Table 4.2-8: Evaluation of permeable pavement corresponding to the decision matrix... B-VIII Table 4.2-9: Evaluation of a vegetated swale corresponding to the decision matrix... B-IX Table : Evaluation of a dry swale corresponding to the decision matrix... B-X Table : Evaluation of a tree box corresponding to the decision matrix... B-XI Table : Evaluation of a perforated pipe system corresponding to the decision matrix... B-XII Table : Evaluation of an infiltration trench corresponding to the decision matrix... B-XIII Table : Decision matrix for LID practice selection in Catchment A7 at Location A... B-XIV Table : Decision matrix for LID practice selection in Catchment A7 at Location B... B-XV Table : Decision matrix for LID practice selection in Catchment A7 at Location D... B-XVI Table : Decision matrix for LID practice selection in Catchment A0 at Location E... B-XVII Table : Decision matrix for LID practice selection in Catchment A0 at Location F... B-XVIII Table : Decision matrix for LID practice selection in Catchment A0 at Location G... B-XIX Table : Decision matrix for LID practice selection in Catchment A9 at Location H... B-XX Table : Decision matrix for LID practice selection in Catchment A9 at Location I... B-XXI Table : Decision matrix for LID practice selection in Catchment A9 at Location J... B-XXII Table : Decision matrix for LID practice selection in Catchment A6 at Location K... B-XXIII Table : Decision matrix for LID practice selection in Catchment A8 at Location L... B-XXIV Table : Decision matrix for LID practice selection in Catchment A11 at Location M... B-XXV Table : Decision matrix for LID practice selection in Catchment A12 at Location N... B-XXVI Table : Decision matrix for LID practice selection in Catchment A10 at Location O... B-XXVII Table : Decision matrix for LID practice selection in Catchment A10 at Location P... B-XXVIII Table : Decision matrix for LID practice selection in Catchment A3 at Location Q... B-XXIX Table : Decision matrix for LID practice selection in Catchment A4 at Location R... B-XXX Table : Decision matrix for LID practice selection in Catchment A1 at Location S... B-XXXI Table 4.2-1: PCSWMM Catchment Properties... D-III Table 4.2-2: PCSWMM Junction Parameters... D-III Table 4.2-3: PCSWMM Conduit Parameters... D-IV Table 4.2-4: PCSWMM Simulation Parameters... D-IV Table E.2-1: Summary of key subcatchment results for a 10-year 12-hour storm... E-V Table E.3-1: Summary of plant species chosen... F-I Table E.3-2: Summary of vegetation selected for each LID... F-II Table G.2-1: Maintenance schedule for vegetated swale... H-I Table G.2-2: Maintenance schedule for Rain Garden... H-I Table G.2-3: Maintenance schedule for bioretention cell, tree box and raised planter... H-II Table G.2-4: Maintenance schedule for permeable pavement... H-III v

11 Table G.2-5: Maintenance schedule for green roof... H-III Table G.2-1: Summarized Economic Analysis of Design... I-I Table G.2-1: Construction timeline for vegetated swale, bioretention cell and rain garden... J-I Table G.2-2: Construction timeline for tree box... J-II Table G.2-3: Construction timeline for raised planter... J-II Table G.2-4: Construction timeline for permeable pavement... J-III Table G.2-5: Construction timeline for green roof... J-IV Table G.2-6: Cumulative construction timeline for all LIDs on the site... J-V Table G.2-1: Subcatchment inputs... K-I Table G.2-2: Junction inputs... K-II Table G.2-3: Conduit inputs... K-V Table G.2-4: Outfall inputs... K-VIII Table G.2-5: Aquifer inputs... K-VIII Table G.2-6: LID usage inputs... K-VIII vi

12 Abbreviations BMP Best Management Practices CC Climate Change CCDP Climate Change Data Portal CMS Cubic Meter per Second (m 3 /s) CVC Credit Valley Conservation DEM - Digital Elevation Model GTA Greater Toronto Area LID Low Impact Development LIDSMPDG Low Impact Development Stormwater Management Planning and Design Guide MOECC Ministry of the Environment and Climate Change PCSWMM Personal Computer Stormwater Management Modeling by Computational Hydraulics International SDC Student Design Competition SWM Stormwater Management TIN Triangulated Irregular Network TRCA Toronto Regional Conservation Authority TSS Total Suspended Solids WEAO Water Environment Association of Ontario WWFMG Wet Weather Flow Management Guide vii

13 1 Introduction 1.1 Site Conditions Exhibition Place is a recreationally, culturally, and historically significant public area in Downtown Toronto. The site covers an area of approximately 77.7ha and is located along the west side of the Toronto waterfront (100 Princes Blvd). The lot is owned by the City of Toronto and is operated and managed by the Board of Governors of Exhibition Place (Exhibition Place, 2017). The site, Toronto Industrial Exhibition, was founded in 1879 and was renamed the Canadian National Exhibition in 1912 (Exhibition Place, 2017). Over 5.5 million patrons visit the facility each year for trade and consumer shows, as well as for business meetings and conferences (Exhibition Place, 2017). There are currently 22 tenants of year round businesses at the site (Exhibition Place, 2017). Exhibition Place is a largely developed space, with impermeable surfaces covering 15.8ha. The impermeable area on the site is predominantly comprised of building rooftops and asphalt parking lots. Due to the large impermeable surface coverage, improved stormwater management is becoming a major focus in order to foster a safe and accessible public facility. Stormwater is currently managed by an onsite network of storm sewers and drains. There is a stormwater system outfall of 1m diameter which discharges directly into Lake Ontario and no existing end-of-pipe stormwater treatment system was identified. The City of Toronto has recognized that the Exhibition Place requires a feasibility study be conducted to improve the stormwater management practices at the site. In order to perform this study, a select region of the site is being analyzed. This portion of the site possesses a total area of 27.4ha and has an impervious area coverage of 89.3%. The subsurface geology was assumed to be sandy clay loam and was assumed to be continuous over the site for both the pre-development and existing post-development conditions. The average slope over the analyzed portion of the site was determined to be 0.90%. Site layout diagrams and infrastructure schematics are included in Appendix A: Spatial Information and Site Maps. 1.2 Problem Statement Based on the recognition of a required stormwater management feasibility for the Exhibition place, the following problem description has been defined. Current challenges are the site include: High volumes of stormwater runoff due to large impermeable parking lot surfaces, and increased risk of flooding and damages to infrastructure with climate change projections Urban heat island effect due to existing impervious parking lot surfaces Poor quality, untreated stormwater runoff draining directly into Lake Ontario through stormwater infrastructure ultimately affecting aquatic life and recreation in the area Downstream flooding of Lake Shore Boulevard during significant storm events Additional stormwater runoff flowing onto the site from the raised Gardiner Expressway highway The City of Toronto s Wet Weather Flow Management Plan recommends managing stormwater onsite using a treatment train approach and Low Impact Development (LID) practices. The implementation of LID controls allows for the improved water quality and improved regional water balance, reduced flood risks, and management of climate change impacts. 1

14 Figure 1-1: Exhibition Place as viewed in Google Earth, with region of focus outlined in red 1.3 Proposed Solution LID practices provide a more holistic and innovative approach to managing urban stormwater. The implementation of LID controls for stormwater management is becoming a preferred solution in order to achieve objectives which work to foster safe and healthy communities. Three primary benefits of LID features include retention, detention, and treatment. Retention aims to re-emit stormwater back into the local environment to re-establish a more natural hydrological cycle. Detention works to reduce the peak runoff rate of a storm event to reduce the risk of flooding. Water treatment aims to improve the quality of stormwater that falls within the region of interest and can be achieved through both retention and detention processes. LID practices increase retention within a site by intercepting stormwater runoff at the source. Stormwater retention processes capture and store water until it is either infiltrated into the native soil, evaporated from the surface and upper soil layers, or taken up by plants and reintroduced into the environment through transpiration. LID features which aim to retain stormwater utilize pervious materials, which possess high hydraulic conductivities, to allow water to enter the features. In detention, runoff is stored onsite and eventually released back into the natural system to decrease and delay peak flows. This controlled stormwater discharge is conveyed through fabricated a conveyance systems such as drains, storm sewers and pipes. Rainfall can enter an LID feature as runoff from impervious surfaces or through conveyance infrastructure. LID features utilize the following treatment processes to increase water quality; infiltration sedimentation, filtration, soil adsorption, microbial processes, and plant uptake. Treatment can be achieved through both retention and detention processes. When stormwater is retained by an onsite system, the mass load of pollutants is reduced because the volume of water does not enter the stormwater conveyance system. When stormwater is detained by a feature, the concentration of contaminants is reduced due to physical and biological treatment processes which occur as the stormwater passes through the feature. 2

15 1.4 Design Criteria and Constraints In order to improve the stormwater management at the site of interest, specific hydrological, social and economic objectives have been defined. These objectives, with their corresponding constraints and criteria, can be seen in Table The specific parameters for achieving the objectives have been selected based on literature targets as defined by the MOECC, TRCA, CVC, and City of Toronto. Table 1.4-1: Defined objectives, constraints and criteria Hydrological Objectives Water Quality Criteria Maximize removal of TSS onsite (aim for >80%) as defined by MOECC Virtually eliminate toxins using source controls as pollution prevention as defined by WEAO SDC Project Statement Capture and treat 26.5mm of rainfall Constraints Maximize capture and treatment of rainfall Flood Management Criteria Eliminate or minimize threats to life and property from flooding as defined by WEAO SDC Project Statement Convey peak flow from 100-year storm as defined by City of Toronto WWFMG Constraints Mitigate flooding onsite Water Balance Criteria Preserve and re-establish a more natural hydrologic cycle as defined by WEAO SDC Project Statement Maximize onsite retention of rainfall Retain a minimum of 5mm rainfall onsite as defined by WEAO SDC Project Statement Constraints Maximize onsite retention Climate Change Criteria Social Objectives Value for Public Manage Climate Change projected events from Ontario s CCDP as defined by WEAO SDC Project Statement Criteria Design to maximize aesthetic appeal Achieve high standard for water discharge quality into Lake Ontario for body contact recreation as defined by WEAO SDC Project Statement Design space to service community as defined by WEAO SDC Project Statement Design to minimize site disruption during installation, operation, and maintenance as defined by WEAO SDC Project Statement Value for Environment Criteria Improve air quality on the study site Improve microclimate of the study site Economic Objectives Economic Cost Analysis Criteria Minimize excavation onsite to avoid remediation Design to minimize costs of installation, operation, and maintenance 3

16 1.5 Background City of Toronto Stormwater Management Infrastructure Urban and suburban stormwater management is an increasing concern in developing areas. Significant flooding from storms and heavy rainfall in the City of Toronto has raised concerns about the municipality s ability to manage stormwater, to protect city infrastructure and properties, as well as to protect public health and safety (Wang, 2014). Factors contributing to the stormwater infrastructure deficit include the expansion of impervious land due to urbanization, shortfalls in municipal budgets and political will, and climate change (Aquije, 2016). It is understood that traditional stormwater management infrastructure in urban areas lacks the capacity to handle large stormwater flowrates associated with the increasing severity of storms. Sustainable stormwater management emphasizes natural solutions which combine function and performance with environmental, economic and social benefits (Wang, 2014). Integrating these practices into existing stormwater systems poses several challenges. Reliance on traditional stormwater management solutions contributes to implementation barriers. The City of Toronto has acknowledged these challenges and has established a framework of policy, bylaws and guidelines to encourage the implementation of sustainable stormwater management practices (Wang, 2014). However, the general lack of knowledge and understanding of stormwater must be overcome to encourage facilitation of these guidelines (Wang, 2014). A successful completion of this design will be a useful example of how sustainable stormwater management practices can be effectively used in the heart of Toronto Areas of Concern Urbanization affects the hydrologic cycle by disrupting natural drainage paths and increasing the area covered by impervious surfaces that prevent stormwater from being absorbed into the ground. As a result of pollutant loading on impermeable surfaces (roadways, sidewalks etc.), urban runoff carries relatively high concentrations of a variety of pollutants (Behera, Li, & Adams, 2000). The increasing expansiveness of impervious surfaces in urban areas ultimately reduces the stability of streams and wetland systems, degrades habitats through pollution, and makes water sources unsustainable from poor quality (Behera, Li, & Adams, 2000). Surface runoff carries pollutants into storm sewers or directly into waterways during rainfall events. Urban runoff constituents in the City of Toronto include floatable materials, suspended solids, oxygen demand materials, nutrients, pathogenic microorganisms, heavy metals, pesticides, road salts, fuel by-products, vehicle oils and lubricants, among other hazardous contaminants. The contaminated surface runoff in Toronto is contributing to the degradation of aquatic ecosystems as well as the accumulation of plant nutrients and persistent toxins along the waterfront. Urban runoff is also attributed to thermal enrichment, where the temperature of the runoff (particularly in summer months) increases local water temperatures which can have significant impacts on native flora and fauna (Behera, Li, & Adams, 2000). The City of Toronto (including Exhibition Place) is a key area of concern as stormwater runoff is considered a major source of toxic contamination into Lake Ontario. Increasing global temperatures are leading to more frequent and intense storm events in the City of Toronto. Current urban stormwater infrastructure is designed to handle storms with a 5-year return period (Aquije, 2016). However these projected storms are produced from historical data and are in fact occurring more frequently due to climate change (Stanford, 2013). Under-investment in stormwater infrastructure makes the City of Toronto particularly vulnerable as severe flooding is an increasing risk due to climate change. Yearly damages due to basement flooding, property damages and halted public services (such as the Toronto Transit Commission) results in massive financial losses. The Toronto flood in July 2013 resulted in $850 million in property damage being claimed through the Insurance Bureau of Canada 4

17 (Aquije, 2016). Flooding and extreme storm events represent some of the most costly climate changerelated weather events, and have now surpassed fire as the leading cost of property damage in Canada. Polluted runoff will require more extensive water treatment procedures to ensure safe drinking water which will have major economic demands with increases in treatment costs. Contaminated runoff also results in unsafe swimming conditions due to poor water quality in Lake Ontario which harms business and tourism opportunities along the waterfront Development of Stormwater Management The objective of traditional stormwater management systems was simply quantity control. This practice consisted of rapid stormwater conveyance through sewer systems with a direct discharge (Dhalla). In the 1980 s, water quality and erosion prevention were taken into consideration (Dhalla). These new concerns were addressed through the implementation of stormwater facilities such as dry ponds and wet ponds (Dhalla). It was not until recently that a more holistic approach to stormwater management was taken which considers objectives such as quantity, quality, treatment, ecosystem stability and protection of groundwater (Dhalla). It is these requirements which introduced the use of a water balance treatment train approach using green infrastructure to manage stormwater (Dhalla). Low impact development is a method of stormwater management which aims to return urban environments to their natural hydrological cycle by managing rainfall at the source. LID practices increase infiltration and evapotranspiration, and reduce surface runoff in areas comprised of large impermeable surfaces. Effective LID designs attempt to decentralize drainage infrastructure, maximize onsite storage and infiltration, and make use of natural landscape features to best manage runoff. There are a variety of LID practices which can be used to retrofit existing sites each with different properties and benefits. The primary goal of LID features is to mimic the pre-development hydrology of a given developed site. This is achieved by maximizing onsite design techniques that intercept, evaporate, filter, store, and infiltrate runoff. In urban areas where human impacts are unavoidable, LID controls can restore, to an extent, natural water balance processes by managing with rainfall at the source. Instead of routing runoff from impervious surfaces through traditional pipe systems, LID controls use more cost effective landscape features distributed throughout the landscape to manage rainfall. The LID features used in this design are reported in detail in Appendix B Background Modeling Pre-development and post-development conditions were modelled in PCSWMM to serve as a baseline and comparison point. Returning the water balance to match the pre-development (natural) conditions is not reasonable for such an intensely developed site. The water balance objective, as defined in Section 1.4, aims to preserve and re-establish a more natural hydrologic cycle. The pre-development and post-development models serve to help better understand the impact of the existing development on the hydrological cycle and provide a target for the LID retrofit. For the post-development (existing) conditions model, the subject area was discretized into sixteen subcatchment areas based on the existing stormwater system and topographic conditions. Large buildings onsite were modelled as their own subcatchment areas, as they have a considerably different surface roughness value, and depression storage compared to other subcatchments. This practice also simplifies the addition of LID controls at later stages in the design. Subsequently, as observed in Figure E-1, the post-development 100-year 1-hour storm scenario has decreases in infiltration and evapotranspiration by roughly 10 times the pre-development case. As well, the post-development model of this 100-year 1-hour storm results in a peak runoff 6 times larger than the peak of the pre-development model, as observed in Figure E-2. This is to be expected given that the postdevelopment scenario has an average imperviousness of roughly 90%. 5

18 The post-development model experiences notable flooding for 1 hour storm events with a return period of 10 years and larger. This flooding occurred primarily from storm drains near Prince Edward Island Crescent and Ontario Drive. This flooding can be seen in Figure 1-2, where size/colour are adjusted to show flooding and flowrates for junctions and conduits, respectively. Flooding in this location would likely flow downgrade along Ontario Drive, into Lakeshore Boulevard. These results are consistent with the site description in the WEAO Figure 1-2: Flooding as viewed in PCSWMM SDC Project Statement, which described flooding along Lakeshore Boulevard for large storm events. The post-development model results support the existing stormwater infrastructure information that was provided by the WEAO SDC. This model has been developed without model calibration using field data, given that it is beyond the scope of this project. However, this method of investigation should be considered if further analysis on the existing stormwater system is required which is discussed further in Section Design Alternatives Background research was performed on a wide variety of LID features, and the potentially applicable LID controls were considered as potential solutions. The LID features which were considered as alternative designs in this project include; rain barrels, bio-retention features (cells, tree boxes, and raised planters), rain gardens, vegetative filter strips, green roofs, permeable pavement, perforated pipes, infiltration trenches, as well as vegetative and dry swales. An evaluation of performance for each feature, and how it aligns with the defined constraints and criteria (Section 1.4), along with a detailed feature description has been included in Table of LID Feature Assessment and Design Decision Matrices. 2.1 Design Methodology Design Decision Procedure A systematic design procedure was developed to determine the most appropriate LID controls for specific locations at the study site. The first step was to divide the criteria (defined in Section 1.4) into subcategories and weigh their importance relative to the final design goal. A detailed description of each criterion and the justification of their associated weighting can be found in Table The performance of each LID control considered was evaluated for each subcategory, as seen in Table to Table The site was then divided into catchment areas and each catchment were analyzed for potential locations to implement LID controls. The selected locations within each catchment were then assessed for restrictions and required specifications. For each specific location, suitable LID controls were identified and evaluated using the decision matrix found in Table Once the LID control with the highest weighting was determined, a detailed design of that chosen LID feature was developed. Due to the spacing limitations of the site, the LID controls were sized to maximize their effectiveness in achieving criteria and constraints. This process was repeated for all locations within each catchment. A comparative decision matrix for each potential location is included in Table to Table The TRCA LIDSMPDG defines a method for selecting BMPs. As well, the TRCA defines sizing for each LID feature based on their developed BMPs. The BMPs for sizing each of the LID features is included in Table Table

19 2.2 Design Modeling Methodology A modelling approach is used for this design in order to manage the considerable complexity of the stormwater system, site conditions, and final design. The following section outlines the steps required to model the existing site conditions and LID controls, in order to evaluate the effectiveness of the design. The model is also used to identify weakness in the design, such as undersized features. Model inputs are summarized in the Appendices. Figure D-1 is a plan view of stormwater system. The full model inputs are included in Appendix K Data Gathering and Preparation Digitization The site plans detailing buried infrastructure on the subject site were all georeferenced and digitized in ArcGIS. Given that the figures were in PDF format, some assumptions were made to fill in missing data. For example, missing stormwater pipe diameters and materials were estimated based on the properties of similar pipes or by interpolating the diameter from up and downstream pipe geometries. The digitized stormwater system as prepared to be input into PCSWMM can be found in Figure A-2. The study area provided by the City of Toronto and WEAO was digitized as described above, and modified slightly to ensure that the entire stormwater system flowing into Outlet 3 is included in the study area, as shown in Figure A-2. The portion of the subject area above the outlet pipe near Lakeshore Boulevard was also removed. These boundary modifications are quite minor and will have little impact on the hydrological conditions onsite. As shown in Figure A-5, land cover on the site was digitized based on aerial imagery. The land cover was classified into four categories: paved, parking lot, grass/vegetated, and building. These classifications were confirmed using Google Street View and during a site visit DTM and Runoff Characterization The DTM of the subject site, as seen in Figure A-3, was created by Georeferencing the AutoCAD point elevation file provided by the City of Toronto. The terrain was built using Kriging interpolation at a cell size of 0.5m This DTM was input into a surface runoff script which simulated surface runoff patterns using ArcGIS s Watershed Spatial Analysis tools. The results of this simulation can be observed in Figure A-4, which shows the simulated surface flow patterns, in addition to slope/flow direction raster files which have a vector field symbology. It is recognized that this figure is not a reliable representation of runoff conditions onsite, however the results act as a good approximation of the direction and patterns of runoff across permeable areas such as parking lots Gardiner Expressway Runoff Modelling As outlined in the Project Statement for Phase II of the design, a solution must be developed to manage the runoff generated from the Gardiner Expressway, which is located directly north of the subject site. Currently the downspouts from the highway are disconnected and runoff spills into the subject site. This was modelled in PCSWMM by creating three subcatchments (A13-A15) over the portion of the Gardiner Expressway directly adjacent to the site. These subcatchments are routed directly to the bordering catchment areas in the subject area PCSWMM Platform and Input Parameters PCSWMM is a hydrological modelling software built on the EPASWMM 5 engine. Its modelling capabilities match those of EPASWMM, with additional features such as offering spatial analysis support, increased LID control, and more detailed results reporting. LID input parameters, values, and justifications are summarized in Table through Table Input values are based largely the site-specific data 7

20 described above. When data was unavailable, reasonable assumptions were made based on recommended values in PCSWMM and EPASWMM support documentation LID Control Modelling The majority of the LID control feature parameters required for modelling purposes were selected during the design decision procedure. The control dimensions were typically selected towards the upper end of the ranges provided in design guidelines, given the limited amount of surface area available onsite. The surface area of the LID controls was determined in ArcGIS. The percentage of rainfall running off an impermeable area into an LID is a required parameter for LID controls. This value was approximated in ArcGIS based primarily on the surface flow direction vector field and location of stormdrains. Figure D-2provides an example of the approximation of this parameter for a bioretention cell LID control, using the vector field. Modelled LID controls were evaluated for a 10-year 12-hour storm. In several cases, the area allocated to the LID control was insufficient to manage inflow. In these cases, more space onsite was allocated to the LID control. An example of this is the raised planter control (Location ID H ) near the Gardiner Expressway. The initial model calculated that the LID would overflow. Consequently, the surface area of the LID features was increased as to accommodate the full runoff amount from the highway. 3 Final Design 3.1 Overview The final design is a stormwater feasibility plan focused on retrofitting Exhibition Place with LID practices to reduce runoff, pollutant loading, and return the water balance to conditions which more closely resembles the natural hydrological cycle. An integrated and collaborative design approach combines the teams multi-disciplinary knowledge of engineering, landscape architecture, terrestrial and aquatic sciences, geosciences (hydrogeology, fluvial geomorphology) and site planning as recommended by the TRCA and CVC. Figure 3-1: LID Locations within the Subject Site 8

21 Table 3.1-1: Summary of resultant LIDs to be implemented from the decision matrices for each location Subcatchment Location Identification LID Result from Decision matrix Total Footprint (m2) A7/A0 A Bioretention Cell A7 B Rain Garden A7 C Do Nothing A7 D Green Roof A0 E Rain Garden A0 F Permeable Pavement A0 G Rain Garden A9 H Raised Planters A9 I Raised Planters A9 J Bioretention Cell A6 K Rain Garden A8 L Bioretention cell A11 M Tree Box A10/12 N Tree Box A10 O Tree Box A10 P Dry Swale with Perforated Pipe System A3 Q Green Roof A4 R Raised Planters A1 S Green Roof Total LID Surface Area Total Impervious Area Directly Routed to LID 4.8 ha 47.6 % Percent of impervious site treated (%) 3.2 LID Descriptions The design uses seven different types of LID controls implemented at eighteen different locations, these locations can be found in Figure 3-1.Within the site there are; 3 bioretention cells, 4 rain gardens, 3 green roofs, 1 vegetated with a perforated pipe and 1 section of permeable pavement. A detailed list of each feature, their associated footprint and percent of imperviousness site treated can be found in above in Table Bioretention Features Bioretention LID controls significantly reduce runoff and increase retention because of high storage capabilities. As a result these are the most common LID controls used in the design. Five different types of bioretetention features have been included as part of the final design solution; bioretention cells, vegetated swales, rain gardens, raised planters and tree boxes. A bioretention cell has 3 key layers that contribute to its functionality. The surface layer includes storage represented as surface ponding contained by berms, curbs or gentle slope of the feature. It is important that the surface be level to encourage an even distribution of stormwater over the feature to help prevent premature clogging and erosion. When a bioretention cell is installed in a location with existing curbs, curb-cuts will be installed or curbs will be removed entirely to convey water into the depressed landscape or feature. Best management practice require that pre-treatment practices be installed to treat incoming flow. For this particular design site, where green space for LIDs is limited it has been decided that all bioretetion features will use gravel diaphragms for pre-treatment. By allowing the inflow to pass over a small trench filled with pea gravel, sheet flow will be maintained because water will be more evenly 9

22 passed into the cell and coarse sediment will be captured. This increases water quality and aids to prevent clogging of the filter bed. Additionally, using a mulch layer on the surface around vegetation will also help prevent clogging and increase pollutant removal rates. The soil layer of the bioretention cell should provide optimal growing condition for the selected vegetation and be designed to filter contaminants and TSS from stormwater. The LID-SMPDG recommends the minimal depth of a soil layer to be 500 mm to achieve pollutant removal benefits however a feature will have better results if the depth ranges from meters (CVC & TRCA, 2010). The design used will have a soil layers thick enough to maximize treatment without increased risk of ground water contamination. For this design and premixed engineer soil with in the soil hydrologic Group A similar to a loamy sand will be used. Loamy sand is composed % sand, the remaining percentage being silt and sand particle which correlated directly within the recommendations provide by the TRCA and CVC to increase pollutant removal (CVC & TRCA, 2010). Note that tree boxes require that the soil depth be at least 1.2 m and the footprint be large enough to accommodate the large root system. Depending on the type of feature the depth a mandatory storage layer will vary from 0.5 m to 1.5 m. The bottom 300mm of storage is filled with 50 mm diameter clean stone with a high void ratio to allow for the maximum retention. The storage layer of a raised planter must be at least 10 ft away from an adjacent to building prevent seepage into the foundation. Figure C-6: Raised planter cross section adjacent to building and Figure C-7 illustrate the difference in layer configurations according to building locations. To ensure the risk of contaminating ground water is mediated particularly for pollutant heavy areas such as parking lots, an extra 100mm choking layer has been design for to function as a sand filter. Thus providing preventative treatment before storage to prevent groundwater contamination even if a seasonal spike in the groundwater table intersects the storage layer. Examples where sand filter will be implemented are a Location A and N. Additional filtration can also be achieved through the use of geomembranes and fabric textiles in raised planters and tree boxes adjacent to parking lots (Locations N and O). The design includes a large vegetated swale with a perforated pipe system swale at location P. A By adding an engineer soil beneath the basin of the swale sedimentation, filtration, infiltration and evapotranspiration is increase. All bioretention features can utilise a variety of bridges, walking paths, stepping stones and protective grates to prevent damages inflected by pedestrians. An example of a protected grate is included in the schematic drawing of a tree box show in Figure C Green Roofs Green roofs are a very effective LID features in terms of stormwater filtration and detention. Green roofs are most effective as an LID practice for large buildings with relatively flat roofs and adequate space for a large-scale installation (location S and Q). Large flat buildings will create notable delays in peak flow and reduction of peak flow intensities at the stormwater inlet. To complete detailed construction plans more information about the roof and building structural integrity is required. Green roofs provide energy gains to buildings, insulating the building in the winter, and providing cooling effects in the summer. Green roofs have the potential to increase solar panel efficiency by providing cooling effects during hot seasons. The plant life can serve as an ecosystem habitat and can reduce urban heat island effects. Green roofs require little maintenance or irrigation after the first two years of upkeep. Green roofs can only be built on infrastructure with proper structural stability. A complete green roof with have a surface layer which will be dominated by vegetation and possess minimal surface storage capabilities. Following the surface layer there is a soil, filter and storage layer. Waterproofing is constructed as an initial bottom layer to protect the roof from water damages. Industry 10

23 best management practices recommend water damage risk be mediated by installing a leak detection system along with regular maintenance and inspections. The planting media or soil layer of a green roof will typical will range from 75 to 150 mm and consist of engineered mixture (CVC & TRCA, 2010). For this design premanufactured sedum mats are used. The mats are rolled out over a root beerier sized to prevent sediment from draining into the drainage layer. The community garden on the Food Products building, requires a combination of sedum mats and planter boxes filled with at least 15 cm of engineered growing medium capable of retaining moister to grow leafy produce. A sample planting plan for garden planters can be found in Figure G-6. Note that fertilizer application should be avoided but if ever required a maximum of 5 grams of nitrogen per square metre will not be exceed to avoid excess nutrients in the runoff. The green roof design can be described as a deep storage system because of the extensive depth of the manufacture porous medium used to construct the drainage layer. The thick waffled, plastic sheets are 1-1/2 (38.1mm) thick and made of a recycled material. The sheets where chosen based on their capabilities to store over 7 L/m 2 for plant uptake and capabilities for high volume drainage for extreme weather events. As recommended by the TRCA and CVC the porosity of the drainage layer is greater than 25%. A schematic of the green roof design can be seen in Figure C Permeable Pavement Permeable pavement can replace regular pavement and asphalt in parking lots in order to increase infiltration rates, detain water and delay the rate of runoff due to stormwater events. Depending the use of the site and the native soil conditions there is a wide variety of suggested design types that include; permeable interlocking concrete pavers, plastic of concrete grid systems, pervious concrete, and pervious asphalt. A major constraint of the design was to limit any disruptions that might impede planned events on the Exhibition Place site. Retrofit any of the major lots on the site would involve removal of the existing surface, excavating, aggregate filling, regrading, and installation of the new permeable surface which would affect available parking on the site for an extended period of time. Wet Consultants Ltd. highly recommends future resurfacing of lot 2 to lot 4 with permeable pavement when the lifetime of the current lot surfaces is exceeded. This design includes plans to resurface a strip of recreational basketball courts (Location F) with permeable cement. Information posters near the courts will educate the public about LID stormwater management practice and the benefits of permeable pavement. Sample LID posters can be seen in Figure Figure G-1 to Figure Figure G-4. Similar to bioretention features, permeable pavement requires the implementation of pre-treatment practices to preserve LID efficiency. The 100 mm pavement or surface layer acts a pre-treatment practice by filtering out large sediment immediately before the water is filtered down into the storage layer therefore reducing the effects of clogging. Since the location will be almost exclusively used for recreational purposes, a study could be conducted to see if less regular maintenance than that of a high traffic parking lot is acceptable, thereby reducing future maintenance costs. The pavement mix selected for the design has a high porosity but is also capable of withstanding cold climate winter seasons (CVC & TRCA, 2010). Based on best management practices the depth of gravel storage layer is design to be 450 mm and will consist of 3 key layers. The layers are arranged to provide filtration to in flow and the void space between the aggerate materials provides retention storage till water is infiltrated into the native soil. From the surface down the layers include are as follows; a course bedding, a thick stone open graded base and gravel subbase. 11