Stormwater Management Strategy

Transcription

1 PICKERING CITY CENTRE Stormwater Management Strategy FINAL REPORT APRIL 2015 Prepared on behalf of: THE One The Esplanade Pickering, ON L1V 6K7

2 this report has been formatted for double-sided printing

3 FINAL APRIL 2015 Executive Summary The Municipal Infrastructure Group was retained by the City of Pickering to establish a Stormwater Management Strategy to complement the re-development and intensification of the Pickering City Centre envisioned in the report Downtown Pickering A Vision for Intensification and Framework for Investment (Urban Strategies, June 2013). A number of alternative stormwater management strategies were analyzed and evaluated in the development of the strategy, ranging from business as usual (adopting current formalized criteria) to widespread and intensive application of emerging low-impact-development practices to significantly improve water quality, erosion and flooding conditions in Krosno Creek, to which the majority of the study area drains. The recommended Stormwater Management Strategy includes the following criteria and recommendations: Control of post-development peak flow rates to pre-development levels. A maximum runoff coefficient of 0.5 should be used to represent predevelopment conditions, regardless of how much impervious cover currently exists on a redevelopment site; Retention of the runoff from up to a 5 mm storm event on site for infiltration or re-use (i.e. no minor or major system flow from a site for up to a 5 mm storm); Enhanced water quality protection (80% TSS Removal), with consideration given to the water quality benefits associated with on-site runoff retention; Incentive programs to encourage development to achieve voluntary on-site runoff retention targets of 10 mm to 15 mm; Implementation of Low Impact Development practices within public right-ofways and integration of innovative stormwater management practices with public open space, where feasible and appropriate; and, Site specific requirements to preserve the existing storage volume and protect new development from flooding in the existing flood storage area at the south parking lot of the Pickering Town Centre. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE i

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5 FINAL APRIL 2015 Contents 1 Introduction Objective Study Area Background and Planning Framework Existing Conditions Study Area Characterization Existing Storm Sewers Drainage and Hydrology Pickering Town Centre Stormwater Management Criteria Quantity Quality Erosion Water Balance Criteria Summary Stormwater Management Approaches Conventional Stormwater Management Practices Low Impact Development Practices Development of the City Centre SWM Strategy Alternative Solutions Evaluation of Alternative Solutions City Street Strategies Stormwater Management in Public Spaces Special Considerations for the Pickering Town Centre Recommended Stormwater Management Strategy Stormwater Management Criteria Site Specific Criteria for the Pickering Town Centre Lands Aspirational Targets Public Realm Summary References Appendices Appendix A: SWMM5 Model Input and Output Appendix B: Pickering Town Centre Flood Storage Assessment TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE iii

6 FINAL APRIL 2015 Figures Figure 1-1: Pickering City Centre Vision... 5 Figure 1-2: Pickering City Centre Study Area... 6 Figure 1-3: Durham Region Official Plan... 7 Figure 1-4: City of Pickering Official Plan... 8 Figure 1-5: Civic District Rendering... 8 Figure 1-6: Krosno Creek Flood Reduction Project Area... 9 Figure 2-1: Existing Storm Sewer Network Figure 2-2: Krosno Creek SWMM5 Model Layout Figure 2-3: Pickering Town Centre Surface Storage Figure 4-1: Typical Impacts of Urbanization on the Hydrologic Cycle Figure 4-2: Example LID Approach within the ROW Figure 5-1: Sherbourne Common Water Features Figure 5-2: Pickering Town Centre Vision Tables Table 2-1: SWMM5 Model Output Existing Conditions Table 2-2: Pickering Town Centre Surface Storage Table 3-1: Stormwater Management Criteria Summary Table 5-1: Change in Peak Flow Alternative Table 5-2: Change in Runoff Alternative Table 5-3: Change in Peak Flow Alternative Table 5-4: Change in Runoff Alternative Table 5-5: Change in Peak Flow Alternative Table 5-6: Change in Runoff Alternative Table 5-7: Change in Peak Flow Alternative Table 5-8: Change in Runoff - Alternative Table 5-9: Alternative Evaluation Summary Table 5-10: Change in Peak Flow LID on City Streets Table 5-11: Change in Runoff LID on City Streets Table 5-12: Pickering Town Centre Storage Implications PAGE iv TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

7 FINAL APRIL Introduction 1.1 Objective The Pickering City Centre area has been identified as an area for growth via intensification, as recognized by its designation as an Urban Growth Centre in the Growth Plan for the Greater Golden Horseshoe, and as an Anchor Hub in Metrolinx s Big Move. The Downtown Pickering Vision and Redevelopment Framework (June 2013) has articulated the desired form of Figure 1-1: Pickering City Centre Vision redevelopment, as illustrated in Figure 1-1. The City is also evaluating and planning for the infrastructure needed to support this vision for growth, which includes provision for an appropriate stormwater management strategy and related criteria to mitigate the impacts of intensification on the receiving water systems. To this end, The Municipal Infrastructure Group Ltd. (TMIG) was retained by the City of Pickering to establish a Stormwater Management Strategy corresponding to the vision for the Pickering City Centre area. In essence the City Centre vision entails redevelopment and new development within the study area, occurring over time to replace many or all of the existing older developments. The majority of the existing development in the City Centre area pre-dates the adoption of modern stormwater quantity and quality controls. Current stormwater management strategies typically endeavour to mitigate the impacts of new development, premised on the notion that development will introduce hard surfaces, increase runoff, and degrade water quality. However, where redevelopment is proposed in existing developed areas, intensification does not necessarily yield significant increases in the extent of hard surface or corresponding increases in surface runoff. As a result, and from a stormwater management perspective, intensification can represent an opportunity to modernize and update existing infrastructure to more than offset potential environmental impacts and strive for current quantity, quality, erosion, and water balance criteria. Within this context, the objective of the stormwater management strategy for Pickering City Centre is to target enhancement rather than maintenance of existing conditions. In addition, intensification provides an opportunity to introduce or modify infrastructure to better complement and integrate with the urban form desired for the community. The evaluation of the stormwater management strategy for Pickering City Centre is being undertaken in parallel with the Krosno Creek Flood Reduction Project (Section 1.3.4), which establishes the most effective means of protecting people and property from existing flooding problems in the Krosno Creek watershed. The TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 5

8 FINAL APRIL 2015 models, analyses, and recommendations of the Krosno Creek Flood Reduction Project have been applied and considered in the development of the stormwater management strategy for Pickering City Centre. 1.2 Study Area The Pickering City Centre study area boundaries are generally consistent with the Urban Growth Centre designation in the Growth Plan for the Greater Golden Horseshoe, with minor changes to include additional contingent properties recognized as appropriate for growth. These boundaries capture, at the core, the civic centre, regional shopping centre and existing urban neighbourhoods while embracing the Kingston Road, Liverpool and Bayly corridors, along with the GO Transit station to optimize the transit integration to the City Centre (Figure 1-2). Figure 1-2: Pickering City Centre Study Area PICKERING CITY CENTRE STUDY AREA BOUNDARY The specific boundaries of the Pickering City Centre study area are the Pine Creek corridor to the west, Diana Princess of Wales Park to the East, Bayly Street to the South, and north parcels facing Kingston Road to the north, representing a total area of 134 hectares. The majority of the study area falls within the Krosno Creek watershed, with a small area west of Liverpool Road draining westward to Pine Creek. Both Krosno and Pine Creeks ultimately drain to Frenchman s Bay and are within the jurisdiction of the Toronto and Region Conservation Authority (TRCA). PAGE 6 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

9 FINAL APRIL Background and Planning Framework The study area lies entirely within the City of Pickering, which forms part of the Region of Durham Durham Region Official Plan The Durham Region Official Plan (Adopted 1993, consolidated August 2013) provides broad land use designations and policies. It shows the study area as Urban, including both Living Areas and Employments Areas. It also designates the Pickering Town Centre and surrounding lands as a Regional Centre. The Durham Region Official Plan has been significantly updated through Regional Official Plan Amendment 128 (ROPA 128). ROPA 128 is in full force and effect, save and except as it applies to specific policies that remain under appeal. None of the specific policies under appeal to the Ontario Municipal Board are relevant to current and planned development in the Krosno Creek watershed. The Living Area and Employment Area designations through the study area shown in ROPA 128 are generally unchanged from the previous consolidation, but the Pickering Town Centre and surrounding areas are now also identified as an Urban Growth Centre. Figure 1-3 illustrates the location of the Pickering City Centre study area within the context of the Durham Region Official Plan. Figure 1-3: Durham Region Official Plan STUDY AREA Excerpt of Schedule A, Regional Structure TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 7

10 FINAL APRIL City of Pickering Official Plan The City of Pickering Official Plan provides more specific land use designations and policies. The current Official Plan was adopted in 1997, and was last consolidated in There are a number of different land use designations throughout the Krosno Creek watershed. Lands north of Kingston Road are generally designated Low and Medium Density Residential. The area between Highway 401 and Kingston Road, including the Pickering Town Centre and City Hall, is designated Downtown Core, and the area between Highway 401 and Bayly Street is designated Mixed Use Corridor. South of Bayly Street, lands are generally designated Low Density Residential (west of Sandy Beach Road) and Employment (east of Sandy Beach Road). The major utility and infrastructure uses in the study area include Highway 401 and the CN Rail corridor. Figure 1-4 illustrates the Pickering City Centre study area location within the context of the Pickering Official Plan Land Use Structure. Figure 1-4: City of Pickering Official Plan STUDY AREA Excerpt of Schedule 1, Land Use Structure Pickering City Centre Intensification Project As previously noted, the Pickering City Centre area has been identified as an area for growth via intensification, as recognized by its designation as an Urban Growth Centre in the Growth Plan for the Greater Golden Horseshoe, and as an Anchor Hub in Metrolinx s Big Move. The Downtown Figure 1-5: Civic District Rendering Pickering Vision and Redevelopment Framework (June 2013) has articulated the desired form of redevelopment, and provides a comprehensive vision that will guide growth, inform investment, and that clearly illustrates a long-term vision of the City Centre as a distinct and vital centre of Pickering. The study and subsequent planning processes have resulted in recommendations for amended Official Plan policies (OPA 26) and urban design guidelines, and will also recommend zoning strategies to effectively plan for the intended growth in the City Centre area. PAGE 8 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

11 FINAL APRIL 2015 The stormwater management strategy for the City Centre area utilizes the vision to evaluate anticipated impacts and the effectiveness of mitigation mechanisms that should accompany development Krosno Creek Flood Reduction Project As noted in Section 1.2, the Pickering City Centre area falls almost entirely within the Krosno Creek watershed. Known flooding and erosion concerns along reaches of Krosno Creek have led to the completion of several flood risk and mitigation studies over the years. The Krosno Creek Flood Reduction Project was initiated by the City of Pickering, in parallel with the Pickering City Centre Stormwater Management Strategy, to establish and implement the most effective means of protecting people and property from existing flooding problems in the Krosno Creek watershed. Figure 1-6: Krosno Creek Flood Reduction Project Area The models, analyses, and recommendations of the Krosno Creek Flood Reduction Project have been applied and considered in the development of the stormwater management strategy for Pickering City Centre. In particular, the Krosno Creek Flood Reduction Project generated a calibrated and verified SWMM5 hydrologic/hydraulic model of the Krosno Creek watershed to predict the peak flow rates and water levels along the drainage systems for a range of standard design storm events. This model was applied to simulate the effectiveness of various practices to define the stormwater management strategy for Pickering City Centre, and simultaneously explore the impacts of intensification within Pickering City Centre to the broader watershed. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 9

12 FINAL APRIL Existing Conditions 2.1 Study Area Characterization Physiography and Topography: The Pickering City Centre study area lies within the Iroquois Plain physiographic region, as defined in the Physiography of Southern Ontario (Chapman and Putnam, 1984). This is the area below the former Lake Iroquois shoreline which was smoothed by wave action and glacial deposits. The width of the Iroquois Plain (as measured from the current Lake Ontario shoreline) widens rapidly west of Scarborough, with sandy soil deposits near the north end of the plain, and a mix of till deposits, drumlins and sandy lacustrine deposits across the remainder of the width to Lake Ontario. Soils and Groundwater: Information on soils throughout the Pickering City Centre study area was obtained from the Soil Survey of Ontario County (Olding et. al., 1956), and the findings agree with the overall physiography of the Iroquois Plain. From Bayly Street north to Finch Avenue, which encompasses the Pickering City Centre area, the soil is predominantly Smithfield Clay Loam, transitioning to Brighton Sandy Loam north of Finch Avenue and Schomberg Clay Loam south of Bayly Street. Smithfield Clay Loam is considered Type C under the US Soil Conservation Service (SCS) classification, with limited infiltration capacity. Land Use: Pickering City Centre today hosts a range of land uses, building forms and several important public spaces, spanning the 134-hectare area. Just south of Highway 401, Krosno Creek emerges as an open channel in the area north of Bayly Street and therefore creates a small, natural area within the City Centre core. With respect to population, the City Centre area is presently home to about 5,000 residents and 5,000 jobs. The current land use breakdown (as presented in the Downtown Pickering report, Urban Strategies, June 2013) includes: 3% office 6% civic and recreation space 16% residential 42% retail, commercial, and light industrial 12% stand-alone surface parking or undeveloped 20% road surface and right-of-way 2.2 Existing Storm Sewers The existing storm sewer system is shown in Figure 2-1. Major trunk sewers run along Glenanna Road, Valley Farm Road, Pickering Parkway and Bayly Street. The Pickering Town Centre is serviced by the storm sewer running just west of Glenanna Road. This system also receives flows from the upstream residential neighbourhoods. All of the storm sewer systems north of Highway 401 converge at a single storm outfall to the north of the Highway 401 ditch just west of Glenanna Road. PAGE 10 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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15 FINAL APRIL 2015 A 4.3 m wide x 2.4 m high concrete box culvert carries the flow under Highway 401, and then transitions to a pair of CSP culverts (1500 mm and 2100 mm diameters) that continue through the CNR corridor. A large storm sewer on Bayly Street conveys runoff from most of the areas between Bayly Street and Highway 401 to Krosno Creek. 2.3 Drainage and Hydrology A new SWMM5 hydrologic/hydraulic model of the Krosno Creek watershed was created, calibrated and verified to support the Krosno Creek Flood Reduction Project, which is being undertaken in parallel with this study. The model was developed to establish existing flows, water levels and potential flood damages through the Krosno Creek watershed, and to evaluate alternatives to reduce flood damages. More information on the development, calibration and simulation of the SWMM5 model can be found in the Project File Report (PFR) for the Krosno Creek Flood Reduction Project (TMIG, 2014). The calibrated SWMM5 model of the Krosno Creek watershed was then used to simulate the 2 year through 100 year return period storm events. The 1 hour AES distributions from the City of Pickering Stormwater Management Guidelines were adopted for the 2 year through 100 year storms. The existing peak flow rates at key locations along Krosno Creek are presented in Table 2-1. The model subcatchments and flow node locations are presented in Figure 2-2. Table 2-1: SWMM5 Model Output Existing Conditions Location (Node) 2 Year 5 Year Peak Flow Rate (m 3 /s) 10 Year 25 Year 50 Year 100 Year Within Study Area Highway 401 (A) Bayly Street (B) Morden Lane (C) Downstream of Study Area Reytan Boulevard (D) Alyssum Street (E) At Confluence with the Eastern Tributary (F) South Sandy Beach Road Culvert (G) Outlet to Frenchman s Bay (H) TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 13

16 FINAL APRIL 2015 Note that there is a significant increase in flow rates at Bayly Street, where drainage from a large area to the east enters Krosno Creek. Below Bayly Street, flows are relatively constant until the open channel systems from the east enter Krosno Creek where it flows east of Sandy Beach Road. 2.4 Pickering Town Centre As noted in Section 2.2, the entire Krosno Creek watershed north of Highway 401 drains to the single concrete box culvert under Highway 401, which is directly connected to a pair of CSP culverts (1500 mm and 2100 mm diameters) under the CNR tracks. These culverts significantly restrict the flow in the Krosno Creek system and contribute to high flood levels upstream of Highway 401. With the potentially elevated flood levels upstream of the CNR rail embankment and associated extent of flooding, a significant volume of water would be stored on the surface of the south Pickering Town Centre parking lot, and this volume could attenuate flows in the system. The potential storage volume in the parking lot at different elevations was calculated from the DEM, and the resulting volume was represented in the SWMM5 model (up to 24,500 m 3 at 85.0 m). The area of ponding at different elevations up to and including 85.0 m is shown in Figure 2-3, and the corresponding storage volumes are summarized in Table 2-2. Table 2-2: Pickering Town Centre Surface Storage Elevation Area (m 2 ) (m 3 ) Notes Flooding contained in Hwy 401 ditch , Flooding contained in Hwy 401 ditch ,825 6,990 Flooding on Pickering Town Centre south parking lot ,195 13,670 Pickering Town Centre first floor elevation ,370 24,540 Highway 401 overtopped PAGE 14 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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19 FINAL APRIL 2015 The City of Pickering was undertaking a City-wide master plan for stormwater management during the design and construction of an expansion to the Pickering Town Centre in the early 1980 s. The Stormwater Management Study (Simcoe Engineering, 1984) specifically identified the need for 20,000 m 3 of flood storage in the area upstream of the Highway 401 culvert. This was deemed necessary in order to limit peak flows to the capacity of the CNR culverts and the downstream concretelined channel. However, construction had commenced on the Pickering Town Centre expansion and south parking area before the Stormwater Management Study was completed. The 1984 report states that the City worked with the developers of the Pickering Town Centre to re-design the south parking lot to create approximately 12,350 m 3 of flood storage which, although less than the previously established requirement, was determined to be sufficient for the purposes of managing flood risk and maintaining the downstream drainage regime. This generally agrees with the storage calculations summarized in Table 2-2, which estimate that approximately 13,700 m 3 of flood storage is available up to the first floor elevation of the Pickering Town Centre (84.73 m). The SWMM5 model indicates that the combination of the storage and culvert restrictions reduce the 100 year storm peak flow rate by approximately 35% in the most flood prone reaches of Krosno Creek downstream of Highway 401. The SWMM5 model also predicts that approximately 8,800 m 3 of water would be temporarily stored on the south parking lot at the Pickering Town Centre during a 100 year storm, corresponding to a maximum ponding elevation of m.. This is only 7 cm below the level of the first floor at the Pickering Town Centre (84.73 m). The internal storm sewers connecting the Pickering Town Centre to the municipal system on Pickering Parkway were not represented in the SWMM5 model of the Krosno Creek watershed. It is possible that, with energy losses along these internal storm sewers, flood levels could approach or exceed the first floor elevation of the Pickering Town Centre during a 100 year storm. The Pickering Town Centre was reportedly flooded during the severe storm of August While the August 2005 storm generated more rainfall than a 100 year storm, there continues to be a risk of flooding at the Pickering Town Centre. More information on the significance of the storage on the south parking lot at the Pickering Town Centre is included in Section 5.5. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 17

20 FINAL APRIL Stormwater Management Criteria Relevant stormwater management design criteria for the study area have been compiled as part of this study and are in accordance with City of Pickering Design Criteria, Toronto and Region Conservation Authority (TRCA) standards, and the Ontario Ministry of Environment (MOE) Stormwater Management Planning and Design Manual (March 2003). 3.1 Quantity Water quantity control describes measures intended to offset the increases in peak flow that result from the introduction of impervious surfaces, in an effort to mitigate the potential for increased flood risk to downstream areas. Where quantity control criteria have been established through a watershed or subwatershed study, these are to form the basis for defining targets. For areas where quantity control criteria have not been established through such studies, the City of Pickering requirement is to provide post-development to pre-development peak flow control for the 2 year through 100 year storm events. Specific water quantity control targets have not been defined for the Krosno Creek watershed. Therefore, the requirement is to provide post-development to predevelopment peak flow control for the 2-year through 100-year storm events. This also fulfills the requirements set by the TRCA. Additionally, it must be noted that the City s preference is to control the postdevelopment to pre-development peak flows based on a maximum runoff coefficient of 0.5 for pre-development conditions. This criterion has been applied to more recent redevelopment sites in the City of Pickering and has been considered during the evaluation of the alternative solutions. 3.2 Quality Water quality control describes measures intended to protect receiving water bodies from the water quality degradation that may result from development. The water quality requirement for all watercourses and water bodies within TRCA s jurisdiction is to provide an Enhanced level of protection (80% TSS Removal), in accordance with the Ministry of Environment s Stormwater Management Planning and Design Manual (2003). Section 4.3 of the City of Pickering Stormwater Management Guidelines stipulates the same requirement for all development within the City. The City s Guideline also notes that Reducing the volume of runoff has inherent water quality benefits as reducing the volume of runoff from a site will also reduce the loading of pollutants to watercourses. The 5 mm volume control target associated with erosion and water balance, described in the following sections, can therefore also be deemed to provide some degree of water quality treatment. PAGE 18 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

21 FINAL APRIL Erosion Erosion control describes measures intended to mitigate increases in erosion potential to receiving watercourses resulting from development. The TRCA sets the minimum erosion criteria as the on-site retention of the first 5 mm of precipitation. If a site drains to a sensitive creek or if a comprehensive study is needed, then a geomorphic study is required to determine the erosion threshold and mitigation strategies. If a site includes a SWM pond then retaining runoff from a 25 mm storm for 48 hours may be required. The City of Pickering provides additional guidance with respect to erosion control. For small infill sites and site plans less than 5 ha the minimum erosion control requirements are: Extended detention of the 4 hour, 25mm Chicago distribution storm for 24 hours, or; Maximize runoff reduction from the site through infiltration, evapotranspiration and stormwater reuse; and, For greenfield developments, a detailed erosion control analysis shall be completed based on geomorphic assessment of critical erosion flow thresholds. Re-development within Pickering City Centre would not be considered greenfield development, and therefore the first and/or second criteria are applicable. 3.4 Water Balance Water balance describes the stormwater management approach that endeavours to replicate the hydrologic conditions that existed prior to development. The water balance criterion established by TRCA is generally to maintain existing groundwater recharge to the extent feasible, with a typical minimum criterion of 5 mm on-site retention (i.e. no runoff from the site for up to a 5 mm storm). 3.5 Criteria Summary Table 3-1 summarizes the stormwater management criteria that are applicable to redevelopment and intensification within the Pickering City Centre area. Table 3-1: Stormwater Management Criteria Summary Quantity Control Quality Control Erosion Control Water Balance Post-development to pre-development control for 2-year to 100-year storm events (preferred maximum runoff coefficient of 0.50 to represent existing conditions for re-development sites) 80% TSS Removal Extended detention of 25mm Chicago distribution storm for 24 hours OR Minimum 5mm on site retention Minimum 5 mm retention TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 19

22 FINAL APRIL Stormwater Management Approaches Stormwater management measures are intended to achieve one or a combination of several objectives, principally to address the impacts of urbanization. Specifically, during storm events, the increase in surface runoff usually generated by urban communities can result in flooding and erosive damage to our streams and structures. In addition, urbanization can contribute to degraded water quality in creeks, rivers and lakes. Stormwater management is needed to manage the quantity and quality of runoff generated by urban communities in order to prevent these impacts. Stormwater is conventionally managed in three stages: at the source, in the conveyance system, and/or at the end-of-pipe. The source, or lot level, is the landscape surface where the rain falls (roofs, lawns, parking lots, driveways). The conveyance system is the network of storm sewers and overland flow paths (roadways and ditches) that take the runoff from the source to the end-of-pipe. The end-of-pipe systems include stormwater ponds, wetlands, or infiltration basins. With respect to quantity control, conventional approaches are principally designed for peak flow management, which is the storage and slow release of runoff over time to achieve a desired peak flow target. These measures do not generally mitigate the increase in the volume of runoff that results from urbanization. Figure 4-1: Typical Impacts of Urbanization on the Hydrologic Cycle credit US EPA Low impact development (LID) is the next evolution in stormwater management that in some cases reintroduces older technologies, and provides an alternative set of mechanisms to manage stormwater volume, in a manner that can better integrate within the urban fabric, provide relief to hard downstream infrastructure such as sewers, ponds and channels, and distribute the management of runoff to improve our ability to adapt to climate change. In general the objectives of low impact development are to: maximize infiltration maximize evapotranspiration maximize reuse minimize hard surfaces Brief descriptions of both conventional and low impact development practices are provided in the following subsections. Detailed descriptions and design guidance PAGE 20 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

23 FINAL APRIL 2015 pertaining to these practices can be found in the Ministry of Environment s Stormwater Management Planning and Design Manual (2003), the TRCA Stormwater Management Criteria document (August 2012), the Low Impact Development Stormwater Management Planning and Design Guide (TRCA/CVC, 2010), and the City of Pickering Stormwater Management Design Guidelines. 4.1 Conventional Stormwater Management Practices Lot Level Controls Lot level controls provide stormwater management at the individual lot or site level, and can include conventional approaches such as rooftop and parking lot quantity control, and oil-grit separators for water quality. Rooftop Storage: Rooftop storage is a method of restricting the discharge rate from roof drains to provide rooftop detention of stormwater. Flat building roofs can be used to store runoff to reduce peak flow rates to storm sewer systems. Rooftop storage is economical, often requires little extra cost during construction, and is generally most applicable to large flat commercial and industrial rooftops; residential roofs are usually peaked with few opportunities for storage. Rooftop storage is widely applied for infill development scenarios to mitigate the need for downstream storm sewer size increases. Note, however, that current City of Pickering guidelines generally do not allow rooftop storage for water quantity control. Parking Lot Storage: Parking lot storage is the practice of introducing depressed areas within a parking lot, in combination with catchbasin restrictors or orifices in the storm sewer, to detain stormwater and reduce peak flow rates in receiving sewer systems. Parking lot storage is economical with slightly increased costs for construction, most suited to commercial and industrial lots, and less suited to residential areas due to the small parking areas. It has been widely applied for infill developments to mitigate the need for downstream storm sewer size increases. Oil-Grit Separators: An oil-grit separator is a device that provides water quality treatment of runoff. It is a structure that is installed underground, within the storm sewer system. A unit typically consists of one or more water-filled chambers that remove sediment, screen debris, and separate oil from stormwater. The water-filled chamber(s) has the effect of slowing the velocity of stormwater runoff, allowing some of the particulate matter to settle and allowing suspended oil to rise. There are a number of different oil-grit separator types and manufacturers, with varying performance and application specifications. Oil-grit separators only provide water quality treatment; there is little to no storage available in the devices to reduce the peak flow rate through the system Conveyance Controls Conveyance controls refer to controls placed en route from the source where runoff is generated to the outlet or receiving water body, and these function by providing attenuation, retention, and/or active water quality treatment while runoff is in transit from source to outlet. Some forms of conveyance controls include oversized storm sewers, oil-grit separators, infiltration galleries, or bioswales, and the majority of these measures can be categorized as either active controls or low impact TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 21

24 FINAL APRIL 2015 development measures. These measures can be particularly effective for road drainage, which is normally directed without control to either end-of-pipe facilities or receiving water bodies. The feasibility of implementing conveyance controls is usually dependent on the ability to accommodate these features within the municipal right-ofway. The following are examples of conventional conveyance controls. Underground Storage: Underground storage is a method of providing storage through the use of oversized sewer pipe and implementing orifices in the sewer to detain the stormwater in the underground storage facility. Rear Yard Storage: Rear yard storage is a method of implementing catchbasin restrictors in rear yard catchbasins to create stormwater storage within the yard; for a neighbourhood these function together as a conveyance measure to attenuate peak flows End-of-Pipe Controls End-of-pipe controls are facilities that receive stormwater runoff from a conveyance system and provide treatment prior to discharge to a receiving water body. Within the context of the treatment train approach, an end-of-pipe facility is designed as the last stage of runoff treatment. It is common for a new greenfield development to incorporate a stormwater management pond or similar facility as a method of end-ofpipe control. In general the implementation of an end-of-pipe solution is dependent on the amount of space available to build a facility that is able to service the applicable site. Pickering City Centre is a fully urbanized and developed corridor and therefore has limited space to build a facility that is large enough to service the area. Opportunities to implement an end-of-pipe facility that services the broader Krosno Creek watershed, including the City Centre area, were explored as part of the Krosno Creek Flood Reduction Project. Wetland: The constructed wetland is one of the preferred end-of-pipe SWM facilities for water quality enhancement. These have shallow depths for both the permanent pool and the active storage zone, are suitable for providing the storage needed for erosion and flood control purposes. These types of facilities are typically used for drainage areas greater than 5 ha. Wet Pond: Wet ponds are also preferred end-of-pipe SWM facilities for water quality enhancement. They are constructed basins that maintain a permanent pool of water throughout the year. These ponds treat the stormwater by allowing the particles to settle and algae to take up the nutrients, and are typically more effective than wetlands for water quantity control. These types of facilities are typically used for drainage areas greater than 5 ha. Infiltration Facility: Infiltration facilities involve the capture and infiltration of stormwater runoff from impervious surfaces to reduce water pollution, and stabilize stream flows. A method of infiltration is a rock-filled trench with no outlet that receives stormwater runoff. The stormwater runoff passes through some combination of pretreatment measures, such as a swale or sediment basin, before entering the trench. The runoff is stored in the voids of the media and will slowly infiltrate through the bottom and into the soil matrix over time. PAGE 22 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

25 FINAL APRIL 2015 An infiltration facility can also take the form of a planted depression area that captures stormwater runoff from either landscaped or impervious surfaces, and similarly allows runoff to be stored and infiltrated through the base of the facility. These are referred to as bio-retention cells, and typically have engineered and constructed subgrades to account for altered and compacted soil conditions. The subgrade ensures adequate percolation of captured runoff by using a perforated drain pipe in a rock bed covered by a sandy soil mixture. Infiltration facilities are typically suited to drainage areas less than 5 ha. 4.2 Low Impact Development Practices Low impact development practices (LID s) refer to those measures that are intended to provide volume management, and in other words manage the rain where it lands via methods that encourage infiltration, reuse, and evapotranspiration. As previously noted the Low Impact Development Stormwater Management Planning and Design Guide (2010) provides detailed information on the suitability, selection, design, installation, and anticipated effectiveness of the full range of LID practices. In general LID practices promote decentralization of stormwater management infrastructure, and add resiliency in the face of potentially changing climate conditions. Beyond achieving stormwater management objectives, low impact development approaches also represent an opportunity to satisfy the broader notions of sustainability and quality of life that are consistent with the vision for Pickering City Centre. Furthermore, LID practices can often be integrated as amenities into the urban fabric. The following subsections briefly describe a few of the many LID approaches that could be considered as part of urban redevelopment within the study area that are appropriate for high density areas. Review of the Low Impact Development Stormwater Management Planning and Design Guide (2010) is recommended to comprehensively explore options and suitability as part of specific development applications Low Impact Development Approaches Green Roofs: Green roofs are an extension of traditional rooftop storage techniques. A green roof is a roof with a layer of drainage and growing media that supports living vegetation. Green roofs can achieve reduced peak flows and runoff volume, improved air quality, lower energy use and can moderate summer air temperatures. A rooftop garden can provide a 45% reduction in runoff via evapotranspiration. Applicability within Pickering City Centre is dependent on the anticipated form and function of each individual development. Rainwater Harvesting: Rainwater harvesting is the storage and utilization of rooftop runoff for, typically, landscape irrigation or greywater reuse. In general, the concept entails the conveyance of rooftop runoff to a cistern for storage and eventual use, with the cistern size based on typical reuse demands. Rain barrels are a common approach to rainwater harvesting in low density residential applications. In high density applications, TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 23

26 FINAL APRIL 2015 underground tanks are often needed to store a sufficient volume of rooftop runoff. Rainwater harvesting provides a number of benefits, including the reduction in runoff volumes and rates from the site, along with a reduction in the usage of municipal water. While the cost savings in terms of municipal water to the owner are nominal based on current potable water charges, easing the community-wide strain on municipal infrastructure can have a much more substantial and long-term benefit. Within Pickering City Centre, rainwater harvesting could be considered as part of redevelopment to supply rainwater for the irrigation of landscaped areas, and/or to supply water within a building as part of a greywater reuse strategy. Permeable Pavement: Permeable pavements are a type of otherwise impervious surface treatment equipped with spaces or gaps that allow for the collection of surface runoff, along with a suitably configured granular substrate, thus providing the potential for infiltration and groundwater recharge. Unit pavers are used for low traffic parking lots, streets, driveways, and walkways. For maximum benefit, permeable pavement requires suitable soils and a sufficient depth to water table to allow for infiltration. The area must also have a relatively flat topography and a low risk of spill or contamination in order to prevent contamination of the soils and groundwater. Rain Gardens: A rain garden is a planted depression area that captures stormwater runoff from either landscaped or impervious areas and allows for storage and infiltration. The rain garden can provide water quality, erosion, and water quantity control through the reduction in surface runoff and the increase in evapotranspiration and infiltration. For maximum benefit, a rain garden requires suitable soils and a sufficient depth to the water table to encourage infiltration. Vegetated Filter Strips: Filter strips are vegetated areas that are intended to treat sheet flow from adjacent impervious areas. Filter strips function by slowing runoff velocities and filtering out sediment and other pollutants, and providing some infiltration into underlying soils. Similar to rain gardens, the opportunity to incorporate vegetated filter strips relies on the green space available within the City Centre core Low Impact Development within ROW The feasibility of incorporating low impact development into right-of-ways and open spaces requires a detailed review of the other demands of these spaces with respect to utilities, services, transportation modes, and other urban design considerations. An evaluation of the anticipated benefits of incorporating low impact development practices into the public realm has been completed to provide future guidance on the feasibility of these approaches, to be reviewed in concert with detailed streetscape and open space planning. PAGE 24 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

27 FINAL APRIL 2015 A suitable low impact development approach within ROWs consists of infiltration trenches / linear bioretention trenches, equipped with porous filter media to provide runoff attenuation to address quality and erosion control requirements. Figure 4-2 illustrates a recent example, which was developed and installed for a section of Elm Drive West in Mississauga, and included concrete planter boxes as part of the design to integrate with the urban character of the ROW. Figure 4-2: Example LID Approach within the ROW This type of configuration was analyzed within the context of the vision for Pickering City Centre. A typical installation would include a granularfilled trench approximately 1 m wide x 1.2 m deep on one or both sides of the road. The trench could be open and landscaped, as illustrated in Figure 4-2, or buried under the pavement or boulevard. With an assumed porosity of 0.40, each trench could provide 0.48 m 3 of storage per metre of road length. For Elm Drive and other recent installations, the design targeted the capture of the runoff from up to a 25 mm rainfall for infiltration. Section 5.3 of the Downtown Pickering Vision for Intensification (Urban Strategies, June 2013) includes typical sections for a range of streets in Pickering City Centre. Suggested right of way widths range from 18 m for local streets to 28.5 m for Valley Farm Road. Hard surfaces (travelled lanes, bike lanes, on-street parking, sidewalks) typically cover 80 % to 90 % of the right-of-way width. For an 18 m wide right-of-way at 90% impervious, the runoff from a 25 mm rainfall is estimated to be 18 m x 0.90 x 25 mm = 0.4 m 3 per metre of roadway. This could be captured and stored within a 1 m wide trench on one side of the road. For a 28.5 m right-of-way at 90% impervious, the runoff from a 25 mm rainfall is estimated to be more than 0.6 m 3 per metre of roadway. It would be necessary to construct trenches on both sides of the road or install a wider and/or deeper trench to capture the resulting runoff for infiltration. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 25

28 FINAL APRIL Development of the City Centre SWM Strategy 5.1 Alternative Solutions Alternatives associated with stormwater management speak to the measures that need to be put in place to manage the quantity, quality, erosion, and water balance impacts of development, often in an effort to maintain existing conditions. However, within the redevelopment context needed to realize the vision for Pickering City Centre, the objective of the stormwater management strategy is to target enhancement rather than maintenance of existing conditions, feasibly and in a manner that will complement the future community. The alternatives defined in the following subsections have been developed with the intention of achieving this objective, yielding strategies that can be implemented as part of redevelopment. Broader watershed-scale stormwater management requirements and strategies have been evaluated as part of the Krosno Creek Flood Reduction Project Alternative 1: Current Formalized Criteria (On-Site Control with 5 mm Retention) The first alternative solution is a combination of the minimum stormwater management criteria described in Section 3. On-site control is assumed to be implemented in each development site or block, in order to provide post-development to pre-development peak flow control from the 2-year through 100-year storm events. Moreover, 5 mm of rainfall over the site area will be captured and utilized on-site through the implementation of low impact development measures, including but not limited to permeable pavements, green roofs, bioretention, and rainwater harvesting. The 5 mm threshold is documented as criteria within the TRCA Stormwater Management Criteria Document (August 2012), and has been implemented as part of the City of Toronto s Wet Weather Flow Management Master Plan (2006). This retention requirement is achievable and practical in relation to modern development practices. Quantity control can be provided through underground and/or surface storage on each re-development site or block Alternative 2: Enhanced Quantity Control (On-Site Control with 5 mm Retention and 50% Imperviousness) For the second alternative, on-site control is assumed to be implemented in each development block, in order to provide post-development to pre-development peak flow control from the 2-year through 100-year storm events. However, in this case, the pre-development peak flows must be calculated using a maximum runoff coefficient of 0.50, regardless of how much impervious surface covers the site prior to re-development. This is consistent with the City of Toronto s Wet Weather Flow PAGE 26 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

29 FINAL APRIL 2015 Management Master Plan (2006), and this criterion has been requested by City of Pickering staff on recent re-development applications. The potentially increased quantity control can be provided through underground and/or surface storage on each re-development site or block. Moreover, 5 mm of rainfall over the site area will be captured and utilized on-site through the implementation of low impact development measures, including but not limited to permeable pavements, green roofs, bioretention, and rainwater harvesting Alternative 3: Enhanced Quantity and Control (On-Site Control with 10 mm Retention and 50% Imperviousness) The third alternative maintains the quantity control criterion from Alternative 2, whereby post-development peak flows are controlled to pre-development rates, and pre-development conditions are represented by a maximum runoff coefficient of 0.5. Moreover, 10 mm of rainfall over the site area will be captured and utilized on-site through the implementation of low impact development measures, including but not limited to permeable pavements, green roofs, bioretention, and rainwater harvesting. Mandating enhanced site runoff volume control will increase the extent of volume control, will assist in reducing peak flows generated by each parcel, and will further supplement conventional water quality treatment practices. Retention requirements of 10 mm tend to be associated with progressive sustainability mandates, such as LEED certified projects, and will usually require an extensive form of rainwater reuse to achieve the target Alternative 4: Enhanced Quantity and Control (On-Site Control with 15 mm Retention and 50% Imperviousness) The final alternative also maintains the quantity control criterion from Alternative 2, whereby post-development peak flows are controlled to pre-development rates, and pre-development conditions are represented by a maximum runoff coefficient of 0.5. Moreover, 15 mm of rainfall over the site area will be captured and utilized on-site through the implementation of low impact development measures, including but not limited to permeable pavements, green roofs, bioretention, and rainwater harvesting. Mandating enhanced site runoff volume control will increase the extent of volume control, will assist in reducing peak flows generated by each parcel, and may eliminate the need for water quality treatment practices. Retention requirements of 15 mm tend to be associated with progressive sustainability mandates, such as LEED certified projects, and will usually require an extensive form of rainwater reuse to achieve the target. 5.2 Evaluation of Alternative Solutions The effectiveness of each alternative stormwater management strategy was simulated by modifying the Krosno Creek watershed SWMM5 model described in Section 2.3. The results of the analyses are summarized in the following subsections, with additional detail provided in Appendix A. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 27

30 FINAL APRIL Alternative 1: Current Formalized Criteria (On-Site Control with 5mm Retention) The SWMM5 model for the Krosno Creek watershed was modified to reflect Alternative 1, which represents future conditions in combination with current formalized stormwater management criteria as described in Section This alternative was represented in SWMM5 by first calculating the area within each model sub-catchment that is proposed for re-development in the Vision for Pickering City Centre (Urban Strategies et. al., June 2013), and re-calculating the imperviousness of each model sub-catchment assuming that the redevelopment will be 80 % impervious (consistent with the recommended value for high density residential development in the City s Stormwater Management Guidelines). Similarly, the required 5 mm on-site runoff retention was represented by increasing the impervious area initial abstraction depth to 5 mm for the re-developing fractions of the City Centre SWMM5 model sub-catchments. Calculations for the revised catchment % impervious values and initial abstraction depths are included in Appendix A. Note that in many sub-catchments, the revised imperviousness is lower than existing conditions. The revised SWMM5 model was used to calculate the peak flow rates and water levels in Krosno Creek and the total runoff volumes from the Pickering City Centre sub-catchments for the 2 year through 100 year return period storm events. Table 5-1 summarizes the percentage change in peak flow rates from the existing condition that could be anticipated under Alternative 1, while Table 5-2 summarizes the corresponding percentage change in runoff volume from the model sub-catchments covering the Pickering City Centre area. Detailed model output can be found in Appendix A, with node locations illustrated on Figure 2-2. Table 5-1: Change in Peak Flow Alternative 1 Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Storm Event 2 year 5 year 10 year 25 year 50 Year 100 Year -1.5% -1.0% -0.8% -0.1% -0.1% -0.1% -2.5% -1.9% -1.5% -1.5% -1.3% -1.2% -1.6% -1.4% -2.3% -1.8% -1.8% -2.0% Table 5-2: Change in Runoff Alternative 1 Storm Event (Rainfall depth in mm) Study Area Reduction 2 year (23.8 mm) 5 year (32.6 mm) 10 year (38.5 mm) Change in peak flow relative to existing conditions 25 year (45.9 mm) 50 Year (51.4 mm) 100 Year (56.8 mm) -4.9% -3.6% -3.1% -2.7% -2.4% -2.2% Change in runoff volume relative to existing conditions The SWMM5 model predicts that the redevelopment of Pickering City Centre, applying standard formalized criteria, will reduce peak flow rates by up to 2.5 % for the 2 year storm, and up to 2.0 % for the 100 year storm. The greatest reductions in peak flow rates occur south of Bayly Street, downstream of the outlet from the large sewershed located between Highway 401 and Bayly Street. PAGE 28 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

31 FINAL APRIL 2015 The PFR for the Krosno Creek Flood Reduction Project determined that up to 4 buildings are at risk of flooding from Krosno Creek during a 2 year storm. The number of potentially impacted homes rises to 56 for a 10 year storm, and 64 for a 100 year storm. Reductions in peak flow rates from the City Centre area should reduce flooding and flood damages in the downstream reaches of Krosno Creek. The model also predicts that the total runoff volume from the Pickering City Centre area would be reduced by almost 5% for the 2 year storm, and by more than 2 % for the 100 year storm. The reduction in flow volumes, especially for frequent storms, will benefit Krosno Creek and the Hydro Marsh through reduced pollutant loadings and reduced erosion potential Alternative 2: Enhanced Quantity Control (On-Site Control with 5mm Retention and 50% Imperviousness) The SWMM5 model for the Krosno Creek watershed was also modified to reflect Alternative 2, which represents future conditions in combination with current stormwater management criteria as described in Section 5.1.2, along with a maximum pre-development runoff coefficient of 0.50 to establish peak flow targets. This alternative was represented in SWMM5 using the same approach described in Section 5.2.1, but the re-developing portions of the City Centre sub-catchments were assumed to be 50% impervious in re-calculating the overall sub-catchment imperviousness. The impervious area initial abstraction depths were maintained from the SWMM5 model of Alternative 1 to represent the required 5 mm on-site retention. Calculations for the revised % impervious and initial abstraction depths are included in Appendix A. The resulting reductions in peak flow rates and runoff volumes from the Pickering City Centre area are summarized in Tables 5-3 and 5-4, respectively. Detailed model output can be found in Appendix A, with node locations illustrated on Figure 2-2. Table 5-3: Change in Peak Flow Alternative 2 Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Storm Event 2 year 5 year 10 year 25 year 50 Year 100 Year -5.3% -5.7% -5.4% -1.6% -0.9% -1.1% -7.8% -8.6% -7.7% -6.8% -6.8% -7.1% -5.2% -6.2% -14.4% -8.0% -8.0% 0.6% Table 5-4: Change in Runoff Alternative 2 Storm Event (Rainfall depth in mm) Study Area Reduction 2 year (23.8 mm) 5 year (32.6 mm) 10 year (38.5 mm) Change in peak flow relative to existing conditions 25 year (45.9 mm) 50 Year (51.4 mm) 100 Year (56.8 mm) -17.7% -16.6% -15.6% -14.5% -13.7% -12.9% Change in runoff volume relative to existing conditions TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 29

32 FINAL APRIL 2015 The SWMM5 model predicts that the redevelopment of Pickering City Centre, applying the noted criteria, will reduce peak flow rates by up to approximately 7 % to 8 % for the 2 year through 100 year storms. The greatest reductions in peak flow rates occur south of Bayly Street, downstream of the outlet from the large sewershed located between Highway 401 and Bayly Street. The model also predicts that the total runoff volume from the Pickering City Centre area would be reduced by approximately 18% for the 2 year storm, and by approximately 13 % for the 100 year storm. The resulting peak flow rates and runoff volumes are also reduced considerably from Alternative 1. This would also translate into greater reductions in flooding and flood damages along Krosno Creek, and greater reductions in pollutant loadings and erosion potential relative to Alternative Scenario 3: Enhanced Quantity and Control (On-Site Control with 10mm Retention and 50% Imperviousness) The SWMM5 model for the Krosno Creek watershed was also modified to reflect Alternative 3, which represents future conditions in combination with the requirement to apply a maximum pre-development runoff coefficient of 0.50 to establish peak flow targets, and an increased on-site retention target of 10 mm (See Section 5.1.3). This alternative was represented in SWMM5 using the same approach described in Sections and The % impervious values for the City Centre subcatchments were unchanged from the model created for Alternative 2 to represent the maximum pre-development runoff coefficient of 0.5. The 10 mm on-site retention was represented by increasing the impervious area initial abstraction depth to 10 mm for the re-developing fractions of the City Centre SWMM5 model sub-catchments. Calculations for the catchment % impervious values and initial abstraction depths are included in Appendix A. The resulting reductions in peak flow rates and runoff volumes from the Pickering City Centre area are summarized in Tables 5-5 and 5-6, respectively. Detailed model output can be found in Appendix A, with node locations illustrated on Figure 2-2. Table 5-5: Change in Peak Flow Alternative 3 Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Storm Event 2 year 5 year 10 year 25 year 50 Year 100 Year -8.5% -8.3% -7.0% -2.2% -1.1% -1.3% -10.9% -11.0% -10.2% -7.7% -7.7% -7.7% -7.8% -8.4% -18.9% -9.6% -9.2% -0.7% Change in peak flow relative to existing conditions PAGE 30 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

33 FINAL APRIL 2015 Table 5-6: Change in Runoff Alternative 3 Storm Event (Rainfall depth in mm) Study Area Reduction 2 year (23.8 mm) 5 year (32.6 mm) 10 year (38.5 mm) 25 year (45.9 mm) 50 Year (51.4 mm) 100 Year (56.8 mm) -22.3% -19.8% -18.3% -16.7% -15.6% -14.6% Change in runoff volume relative to existing conditions The SWMM5 model predicts that the redevelopment of Pickering City Centre, applying the noted criteria, will reduce peak flow rates by up to approximately 11 % for the 2 year storm, and up to approximately 8 % for the 100 year storm. Note that this represents a noticeable improvement over Alternative 2 (5 mm on-site retention) for the 2 year storm, but only a small improvement for the 100 year storm. The model also predicts that the total runoff volume from the Pickering City Centre area would be reduced by more than 20 % for the 2 year storm, and by almost 15 % for the 100 year storm. As with peak flows, the reductions in runoff volumes relative to Alternative 2 are more pronounced for the smaller storms Scenario 4: Enhanced Quantity and Control (On-Site Control with 15mm Retention and 50% Imperviousness) The SWMM5 model for the Krosno Creek watershed was also modified to reflect Alternative 4, which represents future conditions in combination with the requirement to apply a maximum pre-development runoff coefficient of 0.50 to establish peak flow targets, and a further increased on-site retention target of 15 mm (See Section 5.1.4). This alternative was represented in SWMM5 using the same approach described in the previous sections. The % impervious values for the City Centre sub-catchments were unchanged from the models created for Alternatives 2 and 3 to represent the maximum pre-development runoff coefficient of 0.5. The 15 mm on-site retention was represented by increasing the impervious area initial abstraction depth to 15 mm for the re-developing fractions of the City Centre SWMM5 model sub-catchments. Calculations for the catchment % impervious values and initial abstraction depths are included in Appendix A. The resulting reductions in peak flow rates and runoff volumes from the Pickering City Centre area are summarized in Tables 5-7 and 5-8, respectively. Detailed model output can be found in Appendix A, with node locations illustrated on Figure 2-2. Table 5-7: Change in Peak Flow Alternative 4 Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Storm Event 2 year 5 year 10 year 25 year 50 Year 100 Year -11.3% -10.5% -8.8% -2.8% -1.4% -1.6% -15.0% -13.2% -12.1% -8.6% -8.4% -8.3% -10.7% -10.6% -21.0% -11.4% -10.4% -2.0% Change in peak flow relative to existing conditions TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 31

34 FINAL APRIL 2015 Table 5-8: Change in Runoff - Alternative 4 Storm Event (Rainfall depth in mm) Study Area Reduction 2 year (23.8 mm) 5 year (32.6 mm) 10 year (38.5 mm) 25 year (45.9 mm) 50 Year (51.4 mm) 100 Year (56.8 mm) -27.1% -23.1% -21.0% -18.9% -17.5% -16.3% Change in runoff volume relative to existing conditions The SWMM5 model predicts that the redevelopment of Pickering City Centre applying the noted criteria, will reduce peak flow rates by up to approximately 15 % for the 2 year storm, and up to approximately 8 % for the 100 year storm. This represents a moderate improvement over Alternative 3 (10 mm on-site retention) for the 2 year storm, but only a slight improvement for the 100 year storm. The model also predicts that the total runoff volume from the Pickering City Centre area would be reduced by approximately 27 % for the 2 year storm, and by more than 16 % for the 100 year storm. As with peak flows, the reductions in runoff volumes relative to Alternative 3 are more pronounced for the smaller storms Alternative Evaluation Summary Table 5-9 summarizes and compares the results of the scenario evaluations. Table 5-9: Alternative Evaluation Summary Alternative Change in Peak Flow Relative to Existing (At Bayly Street Node B) Change in Runoff from the City Centre Area Relative to Existing 2 Year 100 Year 2 Year 100 Year Alt 1 - Current Formalized Criteria -2.5% -1.2% -4.9% -2.2% Alt 2 Max predevelopment Rc of % -7.1% -17.7% -12.9% Alt 3 10 mm on-site retention -10.9% -7.7% -22.3% -14.6% Alt 4 15 mm on-site retention -15.0% -8.3% -27.1% -16.3% For quantity control, Alternative 1 represents the current formalized criteria of providing attenuation to reduce post-development peak flows to pre-development levels for the 2 through 100 year return period events. Alternatives 2 through 4 maintain this approach, but provide additional direction with respect to the predevelopment runoff coefficient, which should be assumed as 0.50 or lower. Adopting 0.50 as the maximum pre-development runoff coefficient results in a significant reductions in both peak flows and runoff volume, as compared to the basic formalized criteria. These translate into reductions in the frequency and severity of flooding in Krosno Creek. Furthermore, this approach eliminates subjectivity in the evaluation of PAGE 32 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

35 FINAL APRIL 2015 pre-development conditions, which can have significant bearing on the effectiveness of quantity control practices. For erosion and water balance, all of the scenarios provide for a minimum 5 mm runoff retention, or volume control. This approach is consistent with current minimum criteria, and will yield a reduction in runoff volume relative to existing conditions. The 5 mm target can also be typically achieved by a combination of the low impact development practices described in Section 4.2.1, irrespective of the proposed form of development or local soil and groundwater conditions. Exceeding the minimum by requiring 10 mm or 15 mm runoff retention will yield further and significant reductions in runoff volume generated over the Pickering City Centre area, with corresponding reductions in pollutant loadings to Krosno Creek and the Hydro Marsh, and improvements in the stability of the more natural downstream channel reaches. The increased on-site runoff retention depths of 10 mm and 15 mm also reduce peak flows in Krosno Creek relative to the formalized 5 mm criterion, particularly for more frequent storms. However, achieving 10 mm or 15 mm runoff retention can be challenging for some forms of development, particularly within the dense urban setting that is envisioned for Pickering City Centre, possibly yielding the need for an extensive form of rainwater harvesting, such as greywater reuse. All of the options satisfy or exceed current water balance and erosion requirements. For water quality, individual developments would be required to demonstrate conformity to the 80% TSS removal requirement, with credit given for the extent of volume control that will partially address the target. 5.3 City Street Strategies As described in Section 4.2.2, an opportunity exists to incorporate an LID solution into right-of-ways (ROWs) within Pickering City Centre, primarily to manage runoff generated from the ROW. However, the feasibility of implementation is dependent on numerous factors which can only be fully evaluated at a detailed design stage with specific local data regarding soils, water table depth, the presence of utilities and other services, as well as the desired form and function of the roadway and boulevard in that location. The analysis of a ROW LID solution presented in this report is intended to assist the City for future decision making purposes, in regards to the potential stormwater management benefits that could be realized with varying degrees of implementation. The example described in Section postulated an LID configuration within the ROW that could store the runoff generated over the ROW area from a 25 mm storm event. The existing conditions SWMM5 model of Krosno Creek was modified in a similar manner to the alternatives evaluated in Section 5.2 to assess the effectiveness of LIDs on City streets. The existing and planned road right-of-ways within each model sub-catchment covering the Pickering City Centre area were measured. These areas were assigned an initial abstraction depth of 25 mm and the overall catchment impervious area initial abstraction depth was recalculated. Calculations for the rightof-way areas and initial abstraction depths are included in Appendix A. To better understand the effectiveness of LIDs installed in City streets, the SWMM5 model TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 33

36 FINAL APRIL 2015 created for this alternative did not consider the future development (and associated SWM controls) envisioned within the City Centre area. The resulting reductions in peak flow rates and runoff volumes from the Pickering City Centre area are summarized in Table 5-10 and Table 5-11, respectively. Detailed model output can be found in Appendix A. Table 5-10: Change in Peak Flow LID on City Streets Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Storm Event 2 year 5 year 10 year 25 year 50 Year 100 Year -5.8% -4.4% -3.5% -0.7% -0.6% -0.5% -5.9% -4.1% -3.1% -2.1% -1.4% -1.1% -3.9% -3.3% -5.0% -2.5% -2.3% -2.2% Change in peak flow relative to existing conditions Table 5-11: Change in Runoff LID on City Streets Storm Event (Rainfall depth in mm) Study Area Reduction 2 year (23.8 mm) 5 year (32.6 mm) 10 year (38.5 mm) 25 year (45.9 mm) 50 Year (51.4 mm) 100 Year (56.8 mm) -8.5% -5.9% -4.9% -4.0% -3.5% -3.1% Change in runoff volume relative to existing conditions The analysis demonstrates that the application of LIDs to all ROWs within the Pickering City Centre area would yield a moderate reduction in downstream peak flow rates for the more frequent storms, but a negligible reduction in peak flow rates for the 100 year and Regional storms. The reduction in runoff volume would be beneficial with respect to quality, erosion, and water balance criteria. However, as the analysis is premised on full implementation throughout Pickering City Centre, any lesser degree of implementation would yield a proportionate reduction in the benefit to be realized. 5.4 Stormwater Management in Public Spaces The Downtown Pickering Vision and Redevelopment Framework (June 2013) states that: The City of Pickering remains a leader in sustainability and the downtown is an excellent area to advance sustainable city building objectives and demonstrate sustainability initiatives. In addition to the exploration of LID practices within the ROWs described in Section 5.3, the feasibility of incorporating stormwater management infrastructure into other public spaces can also be considered, as a means to advancing the sustainability vision for the City Centre area. In general the opportunities will become available as redevelopment proceeds, and the City must be cognizant of the potential for these opportunities to utilize PAGE 34 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

37 FINAL APRIL 2015 stormwater as a resource, and set in place the planning mechanisms by which feasibility can be evaluated and, ultimately, implemented. An example of integrating infrastructure into public spaces within an urban core is the development of Sherbourne Common. Sherbourne Common is an award-winning public park in the heart of the East Bayfront precinct of Toronto s waterfront. The park serves as an amenity to the new community of mixed residential, employment, and commercial space, and simultaneously contains elements of the stormwater management infrastructure servicing the broader community. The services within the park include a UV treatment facility incorporated into the park pavilion, and the utilization of treated runoff and lake water to supply a series of public art features. Figure 5-1: Sherbourne Common Water Features 5.5 Special Considerations for the Pickering Town Centre As noted in Section 2.4, the City worked with the owners of the Pickering Town Centre to incorporate approximately 12,350 m 3 of flood storage through the re-design of the south parking lot area during an expansion to the Pickering Town Centre in the early 1980 s. The approximate Figure 5-2: Pickering Town Centre Vision storage area is illustrated in Figure 2-3. The Downtown Pickering Vision and Redevelopment Framework (June 2013) envisions redevelopment in this area, and the figures in the report illustrating the vision show a number of new buildings in the existing flood storage area between Pickering Parkway and the existing Pickering Town Centre buildings (Figure 5-2). TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 35

38 FINAL APRIL 2015 Without special considerations, new development in the existing south parking lot at the Pickering Town Centre could consume the current flood storage volume, potentially increasing peak flow rates in Krosno Creek south of the CNR and increasing flood levels upstream of Highway 401. Note that all of the stormwater management alternatives evaluated in Sections 5.2 and 5.3 assumed that the existing flood storage at the Pickering Town Centre would be preserved in some form, in addition to the on-site storage throughout the City Centre area needed to achieve the peak flow targets associated with the different alternatives. The SWMM5 model of the Krosno Creek watershed was used to assess the importance of the existing storage in managing flow rates and flooding in Krosno Creek. The existing conditions model was modified by removing the existing storage volume and the various storm events were simulated. To be conservative, no other redevelopment (which will reduce runoff volumes and peak flow rates) was considered in the SWMM5 model. The analysis determined that, with the storage removed, peak flow rates in the flood prone reaches of Krosno Creek south of Bayly Street would increase by up to 7 % during the 100 year storm. More significantly, the maximum water level on the upstream side of Highway 401 would increase from m to m during a 100 year storm. Although the loss of the existing flood storage at the Pickering Town Centre may increase peak flow rates and flood levels in Krosno Creek, redevelopment of the overall Pickering City Centre area, with appropriate stormwater management controls, is expected to decrease peak flow rates and runoff volumes in Krosno Creek. However, it is expected that full build-out of the Pickering City Centre vision (and full achievement of the predicted stormwater management controls) is expected to take several decades. Regardless, a final SWMM5 model was created to represent full implementation of the envisioned redevelopment and intensification in Pickering City Centre, with the existing flood storage at the Pickering Town Centre removed. The SWMM5 model created for Alternative 2 (peak flows controlled to pre-development levels with a maximum pre-development runoff coefficient of 0.5, 5 mm on-site volume retention) was used as the basis for this scenario. The SWMM5 model output is summarized in Table Table 5-12: Pickering Town Centre Storage Implications Location (Node) Highway 401 (A) Bayly Street (B) Alyssum Street (E) Peak Flow - Existing Conditions (m 3 /s) Peak Flow Alternative 2 (m 3 /s) Peak Flow Alternative 2 with PTC Storage Eliminated (m 3 /s) 2 Year 100 Year 2 Year 100 Year 2 Year 100 Year PAGE 36 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

39 FINAL APRIL 2015 With the existing flood storage preserved, the maximum water level upstream of the Highway 401 culvert for the 100 year storm drops from m under existing conditions to m with implementation of Alternative 2. When the flood storage at the Pickering Town Centre is removed from Alternative 2, the expected flood level upstream of Highway 401 increases to m, which remains a significant increase over existing levels. The SWMM5 model predicts that under full build-out of the City Centre vision with the suggested stormwater management plan, the elimination of the existing flood storage at the Pickering Town Centre would increase peak flows and flood levels upstream of Highway 401, but flows and flood levels would remain slightly below existing conditions in the most flood prone reaches downstream of Bayly Street. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 37

40 FINAL APRIL Recommended Stormwater Management Strategy As described in Section 1.1, the objective of this study is to define a stormwater management strategy for the Pickering City Centre area that will complement the vision for the City Centre. The intent is to establish an appropriate mix of stormwater management elements that, through implementation as part of redevelopment, will serve to better mitigate the impacts of urbanization and prioritize quality of life through the principles of sustainability. 6.1 Stormwater Management Criteria Section 5 of this document provides a series of scenarios that embody the latest approaches in stormwater management, with each simulated to quantify the extent of improvement that could be achieved in terms of quantity, quality, erosion, and water balance requirements. The analyses demonstrate the merits of the current quantity control criteria in combination with the stipulated maximum pre-development runoff coefficient of For volume control, the analyses also make clear that enhanced volume control targets greater than the current 5 mm minimum will yield further reductions in the runoff volumes and peak flow rates generated by the Pickering City Centre area. Enhanced volume control is also consistent with the principles of sustainability inherent in the vision for Pickering City Centre, and will contribute substantially to improved downstream water quality. Based on these findings, it is recommended that Alternative 2 be adopted as the basis for the stormwater management strategy for Pickering City Centre, and applied as criteria to all development and redevelopment within the Pickering City Centre area. Alternative 2 entails: Control of post-development peak flows to pre-development levels with an assumed maximum pre-development runoff coefficient of 0.50; control via low impact development to achieve a runoff retention target of 5 mm; and, Water quality treatment to achieve the TRCA/MOE requirement (80% TSS removal). 6.2 Site Specific Criteria for the Pickering Town Centre Lands As described in Section 2.4, the Pickering Town Centre currently provides storage within the southern parking lot, which is effective in reducing peak flow rates in the downstream reaches of Krosno Creek, and reducing flood levels upstream of the Highway 401 culvert. Up to 8,800 m 3 of floodwater is expected to be stored on the south parking lot during the 100 year return period storm. PAGE 38 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

41 FINAL APRIL 2015 The analyses documented in Section 5.5 found that if the existing flood storage was removed (in the absence of other improvements and redevelopment in Pickering City Centre), flood levels on the upstream side of Highway 401 would increase by up to 61 cm, and peak flow rates in the flood prone reach of Krosno Creek downstream of the Highway 401/CNR culverts could increase by as much as 7 % during a 100 year storm event. The earlier Stormwater Management Study (Simcoe Engineering, 1984) indicates that the flood storage on the south parking lot at the Pickering Town Centre (12,350 m 3 ) was created as a result of an agreement between the City of Pickering and the owners of the Pickering Town Centre during the expansion that occurred in the early 1980 s. There is therefore a reasonable expectation that the previously agreed upon flood storage at the Pickering Town Centre would be preserved in any re-development of the site. It is therefore recommended that any redevelopment in the flood storage area identified in Figure 2-3 preserve the existing flood storage volume on the site. It is further recommended that new development in the existing flood storage area be flood proofed to the predicted 100 year flood level (84.66 m) plus a reasonable freeboard depth. If significant re-development in the City Centre Area has occurred prior to redevelopment within the existing flood storage area at the Pickering Town Centre, the required flood storage volumes and minimum flood proofing elevations could potentially be relaxed. Ideally, the storage should be replaced at a similar elevation as existing (between 84 m and 85 m). At a minimum, the storage must be located above the invert of the Highway 401 culvert (81.5 m). If implemented on a site by-site basis, it is expected that the required flood storage (in addition to the storage required to achieve the quantity and quality criteria listed in Section 6.1) would be provided in a large underground vault, likely within each building footprint. It is estimated that the resulting underground storage system could cost between $4 Million and $6 Million for a typical 1 ha site located on the south parking lot at the Pickering Town Centre (See Appendix B). A comprehensive functional servicing and stormwater management plan is recommended for the entire Pickering Town Centre lands to determine how best to implement centralized stormwater management and replacement flood storage for all planned redevelopment. It is expected that centralized storage can be provided much more economically than preserving the flood plain storage and providing stormwater controls within each individual future building site.. In addition to the comprehensive functional servicing and stormwater management plan, short term strategies are also recommended to reduce the current risk of flooding at the Pickering Town Centre. Recall from Section 2.4 that the Pickering Town Centre was reportedly flooded during the severe storm of August 2005, and continues to be at risk of flooding for very large storm events. Backflow preventers and/or other measures are recommended to protect the Pickering Town Centre from surcharging conditions in the sewers currently servicing the building. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 39

42 FINAL APRIL Aspirational Targets As noted, enhanced volume control (10 mm or 15 mm) can further improve water quality, erosion and flooding conditions in Krosno Creek. Therefore, although the recommended criteria within Pickering City Centre includes a minimum 5 mm target for volume control, opportunities to incent enhanced volume control approaches as part of redevelopment should be explored. Incentives are particularly relevant with the recognition that achieving 10 mm or 15 mm of runoff retention can be challenging for some forms of development, and can require an extensive form of runoff reuse, such as greywater reuse, that can substantially impact the cost and potentially feasibility of a development project. To some degree, and as noted in Section 3.2, volume control can satisfy water quality treatment requirements which would otherwise need to be addressed via an oil-grit separator or similar hard infrastructure practice. The effectiveness of volume control with respect to water quality should be demonstrated for each individual development, to the satisfaction of the City, in order to offset or even eliminate other water quality infrastructure requirements. There are other incentives to encourage the adoption of aspirational targets. According to the U.S. Environmental Protection Agency, there are five main types of incentive programs (Water Environment Federation, January 2013): 1. Development incentives can include streamlined permitting processes, decreased fees, zoning upgrades, and reductions in other regulatory requirements. One established mechanism relates to Section 37 of the Planning Act, which provides the municipality with flexibility in the administration of zoning provisions to support community initiatives. 2. Grants can be made available to development proponents and community groups to achieve aspirational targets. Funding can be provided directly to proponents, or indirectly via sustainable design competitions or outreach initiatives. 3. Rebates and installation financing can include funding, tax credits, low interest financing, or reimbursements for those development proponents that endeavour to achieve aspirational targets. 4. Awards and recognition programs can be used to reward innovation and increase awareness of the merits of sustainable designs. 5. Stormwater utility fee discounts, which are applicable in jurisdictions that presently administer a stormwater fee program. As with many municipalities in the GTA, the introduction of a stormwater fee program within the City of Pickering could facilitate broader adoption of stormwater and conservation related sustainability approaches. These incentive approaches can also be applied to other aspects of sustainable development such as energy conservation or active transportation. PAGE 40 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

43 FINAL APRIL Public Realm Section 5.4 presents an approach to and the corresponding benefits that could be realized through the implementation of LIDs within existing and planned right-of-ways as the Pickering City Centre area redevelops. It is recommended that the renewal and revitalization of individual streets explore the feasibility, costs, and benefits of implementing LIDs within their construct to further improve the overall sustainability of the community. Similarly, Section 5.5 describes the opportunity to integrate stormwater management infrastructure into public spaces such as parks, squares, and related amenities. As the vision for the public spaces are further articulated, it is recommended that principles of infrastructure integration be maintained as a priority. Blocks of development could likewise explore integration of the infrastructure needed to address site specific requirements into adjacent public spaces, to achieve both the site targets in addition to the targets for the public space. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 41

44 FINAL APRIL Summary The Municipal Infrastructure Group was retained by the City of Pickering to establish a Stormwater Management Strategy to complement the re-development and intensification of the Pickering City Centre envisioned in the report Downtown Pickering A Vision for Intensification and Framework for Investment (Urban Strategies, June 2013). A number of alternative stormwater management strategies were analyzed and evaluated in the development of the strategy, ranging from business as usual (adopting current formalized criteria) to widespread and intensive application of emerging low-impact-development practices to significantly improve water quality, erosion and flooding conditions in Krosno Creek, to which the majority of the study area drains. The recommended Stormwater Management Strategy includes the following criteria and recommendations: Control of post-development peak flow rates to pre-development levels. A maximum runoff coefficient of 0.5 should be used to represent predevelopment conditions, regardless of how much impervious cover currently exists on a redevelopment site; Retention of the runoff from up to a 5 mm storm event on site for infiltration or re-use (i.e. no minor or major system flow from a site for up to a 5 mm storm); Enhanced water quality protection (80% TSS Removal), with consideration given to the water quality benefits associated with on-site runoff retention; Incentive programs to encourage development to achieve voluntary on-site runoff retention targets of 10 mm to 15 mm; Implementation of Low Impact Development practices within public right-ofways and integration of innovative stormwater management practices with public open space, where feasible and appropriate; and, Preparation and implementation of a comprehensive functional servicing and stormwater management plan for the Pickering Town Centre lands to preserve the existing flood storage and protect new development from flooding in the existing flood storage area at the south parking lot of the Pickering Town Centre. PAGE 42 TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

45 FINAL APRIL References MMM Group Limited, April Stormwater Management Master Plan, Frenchman s Bay Watersheds. Prepared for City of Pickering. Ontario Ministry of Natural Resources, Technical Guide River & Stream Systems: Flooding Hazard Limit. Ontario Ministry of the Environment, Stormwater Management Planning and Design Manual. Queen s Printer for Ontario. Simcoe Engineering Group Limited, Stormwater Management Study. Prepared for City of Pickering. The Municipal Infrastructure Group, Project File Report Krosno Creek Flood Reduction Project. Prepared for City of Pickering. Toronto and Region Conservation Authority, Krosno Creek Preliminary Stormwater Management Strategy. Prepared in association with City of Pickering and Ontario Power Generation. Toronto and Region Conservation Authority, Krosno Creek Floodplain Mapping Study. Prepared in association with City of Pickering. Urban Strategies, Downtown Pickering A Vision for Intensification and Framework for Investment. Prepared for City of Pickering. TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD PAGE 43

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47 Appendix A SWMM5 Model Input and Output TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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49 The built form vision for Downtown Pickering creates a foundation for urbanization of the Downtown to 2031 and beyond, laying out an enhanced street network, new public spaces, destinations, and a range of opportunities for intensification and new development. The vision forms the basis for downtown mobility, public realm, built form, land use, placemaking and sustainability systems as well as precinct-specific policies, each detailed in individual chapters within the framework. LIVERPOOL ROAD VALLEY FARM ROAD 7 The Built Form Vision The following are key features of the built form vision: 1 The Civic Precinct is the downtown s cultural and institutional hub with destinations and distinct public realm treatment. 2 An extraordinary public realm is formed through new public spaces that populate the downtown. A variety of small and large gathering places are within a five minute walk anywhere in the downtown GLENGROVE PUBLIC SCHOOL GLENGROVE PARK 3 A gateway at Kingston & Liverpool Road is characterized by distinct buildings and public plazas at each of the four corners. GLENANNA ROAD 2 4 The Transit Hub at the heart of an enhanced transit system is a waiting area, meeting place and entryway to the downtown. It is integrated with the rest of downtown through streets and pedestrian-ways, and surrounded by exceptional buildings. 3 KINGSTON ROAD PICKERING PICKERING THE ESPLANADE CIVIC COMPLEX PARK 1 PICKERING PUBLIC LIBRARY 8 TOWN CENTRE 5 Pickering Parkway is extended west of Liverpool Road. It is a key transit way, connecting Downtown from east to west. 5 6 Distinct tall buildings line Highway 401, signalling that Downtown is the core of Pickering to surrounding areas of the City HIGHWAY Enhanced connectivity is achieved by new bridges and street connections. PICKERING STATION GO TRANSIT 2 8 New Destinations are supported to enhance the range of activities, amenities and economic vitality of the downtown. The long-term built form vision for Downtown Pickering iv DOWNTOWN PICKERING A VISION FOR INTENSIFICATION AND FRAMEWORK FOR INVESTMENT

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51 Appendix A1 Existing Conditions TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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53 2 Year 1hr AES (23.8mm) Hazel Storm Runoff (ML=10^6 L) sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % sub_ % TOTAL Runoff (ML=10^6 L) Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Downtown Pickering Scenario: Existing Conditions 100 Year 1hr AES (56.8mm) 50 Year 1hr AES (51.4mm) 25 Year 1hr AES (45.9mm) PCSWMM output 10 Year 1hr AES (38.5mm) 5 Year 1hr AES (32.6mm) Name Area (ha) Width (m) Flow Length (m) Slope (%) Imperv (%) N Imper N Perv Dstore Imperv (mm) Dstore Perv (mm) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L)

54 City of Pickering Krosno Creek Diversion Project TMIG Project PCSWMM Model Output Existing Conditions Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East Tributa KC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

55 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Krosno Creek Diversion Project TMIG Project PCSWMM Model Output Existing Conditions Maximum Hydraulic Grade Line (m) flood damages incurred

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57 Appendix A2 Post to Pre Control 5 mm On-Site Retention TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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59 TOTAL EXISTING REDUCTION -2.2% -2.4% -2.7% -3.1% -3.6% -4.9% -0.6% Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Future Conditions in Downtown Pickering Scenario: 5 mm on-site retention, no quantity control PCSWMM output Sub- Catchmetn Area (ha) Area to be developed (ha) (targeted at 80% imp.) Original Imperv (%) Revised Imperv (%) Original Dstore Imperv (mm) Revised Dstore Imperv (mm) 100 Year 1hr AES (56.8mm) Runoff (ML=10^6 L) 50 Year 1hr AES (51.4mm) Runoff (ML=10^6 L) 25 Year 1hr AES (45.9mm) Runoff (ML=10^6 L) 10 Year 1hr AES (38.5mm) Runoff (ML=10^6 L) 5 Year 1hr AES (32.6mm) Runoff (ML=10^6 L) 2 Year 1hr AES (23.8mm) Hazel Storm Runoff (ML=10^6 L) Runoff (ML=10^6 L) sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_

60 City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 1 5 mm on-site retention, 100 Year Post to Pre, where Pre is based on current site cover Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East Tributa KC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

61 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 1 5 mm on-site retention, 100 Year Post to Pre, where Pre is based on current site cover Maximum Hydraulic Grade Line (m)

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63 Appendix A3 Post to Pre Pre Runoff < mm On-Site Retention TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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65 TOTAL EXISTING REDUCTION -12.9% -13.7% -14.5% -15.6% -16.6% -17.7% -7.6% Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Future Conditions in Downtown Pickering Scenario: 5 mm on-site retention, post-to-pre (based on pre at 50% impervious) PCSWMM output Sub- Catchmetn Area (ha) Area to be developed (ha) (targeted at 50% imp.) Original Imperv (%) Revised Imperv (%) Original Dstore Imperv (mm) Revised Dstore Imperv (mm) 100 Year 1hr AES (56.8mm) Runoff (ML=10^6 L) 50 Year 1hr AES (51.4mm) Runoff (ML=10^6 L) 25 Year 1hr AES (45.9mm) Runoff (ML=10^6 L) 10 Year 1hr AES (38.5mm) Runoff (ML=10^6 L) 5 Year 1hr AES (32.6mm) Runoff (ML=10^6 L) 2 Year 1hr AES (23.8mm) Hazel Storm Runoff (ML=10^6 L) Runoff (ML=10^6 L) sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_

66 City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 2 5 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East TributaKC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

67 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 2 5 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Hydraulic Grade Line (m) flood damages incurred

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69 Appendix A4 Post to Pre Pre Runoff < mm On-Site Retention TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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71 TOTAL EXISTING REDUCTION -14.6% -15.6% -16.7% -18.3% -19.8% -22.3% -7.9% Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Future Conditions in Downtown Pickering Scenario: 10 mm on-site retention, post-to-pre (based on pre at 50% impervious) PCSWMM output Sub- Catchmetn Area (ha) Area to be developed (ha) (targeted at 50% imp.) Original Imperv (%) Revised Imperv (%) Original Dstore Imperv (mm) Revised Dstore Imperv (mm) 100 Year 1hr AES (56.8mm) Runoff (ML=10^6 L) 50 Year 1hr AES (51.4mm) Runoff (ML=10^6 L) 25 Year 1hr AES (45.9mm) Runoff (ML=10^6 L) 10 Year 1hr AES (38.5mm) Runoff (ML=10^6 L) 5 Year 1hr AES (32.6mm) Runoff (ML=10^6 L) 2 Year 1hr AES (23.8mm) Hazel Storm Runoff (ML=10^6 L) Runoff (ML=10^6 L) sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_

72 City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 3 10 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East Tributa KC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

73 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 3 10 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Hydraulic Grade Line (m)

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75 Appendix A5 Post to Pre Pre Runoff < mm On-Site Retention TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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77 TOTAL EXISTING REDUCTION -16.3% -17.5% -18.9% -21.0% -23.1% -27.1% -8.2% Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Future Conditions in Downtown Pickering Scenario: 15 mm on-site retention, post-to-pre (based on pre at 50% impervious) PCSWMM output Sub- Catchmetn Area (ha) Area to be developed (ha) (targeted at 50% imp.) Original Imperv (%) Revised Imperv (%) Original Dstore Imperv (mm) Revised Dstore Imperv (mm) 100 Year 1hr AES (56.8mm) Runoff (ML=10^6 L) 50 Year 1hr AES (51.4mm) Runoff (ML=10^6 L) 25 Year 1hr AES (45.9mm) Runoff (ML=10^6 L) 10 Year 1hr AES (38.5mm) Runoff (ML=10^6 L) 5 Year 1hr AES (32.6mm) Runoff (ML=10^6 L) 2 Year 1hr AES (23.8mm) Hazel Storm Runoff (ML=10^6 L) Runoff (ML=10^6 L) sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_

78 City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 4 15 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East Tributa KC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

79 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output Alterantive 4 15 mm on-site retention, 100 Year Post to Pre, where Pre is max 50% impervious Maximum Hydraulic Grade Line (m)

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81 Appendix A6 LIDs in Road ROWs TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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83 2 Year 1hr AES (23.8mm) Runoff (ML=10^6 L) Hazel Storm Runoff (ML=10^6 L) sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ sub_ TOTAL EXISTING REDUCTION -3.1% -3.5% -4.0% -4.9% -5.9% -8.5% -0.6% Project: Pickering Downtown SWM Project No: Date: 07-Jun-13 Subcatchments Parameters for Future Conditions in Downtown Pickering Scenario: Application of LIDs to 100% of Road ROWs in Downtown Area 100 Year 1hr AES (56.8mm) 50 Year 1hr AES (51.4mm) 25 Year 1hr AES (45.9mm) PCSWMM output 10 Year 1hr AES (38.5mm) 5 Year 1hr AES (32.6mm) Sub- Catchmetn Area (ha) ROW Area (ha) (25 mm storage) Original Imperv (%) Revised Imperv (%) Original Dstore Imperv (mm) Revised Dstore Imperv (mm) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L) Runoff (ML=10^6 L)

84 City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output LIDs in City Streets 25 mm retention of runoff volume from road ROW Maximum Flow Rate Location Conduit Hazel Highway _ Bayly Street Weir Flow KC_CJ44_HC Culvert Flow KC_CJ Total Flow ADD Downstream Bayly Street KC_CJ Morden Lane Weir Flow KC_CJ37_HC Culvert Flow KC_CJ Total ADD Reytan Boulevard Weir Flow KC_CJ29_HC Culvert Flow KC_CJ Total ADD Alyssum Street Weir Flow KC_CJ25_HC Culvert Flow KC_CJ Total ADD Sandy Beach Road North Culvert Weir Flow KC_CJ20_HC Culvert Flow KC_CJ Total ADD Confluence with East Tributa KC_CA Sandy Beach Road South Culvert Weir Flow KC_CJ7_HC Culvert Flow KC_CJ Total ADD Outlet to Frenchman's Bay KC_CJ

85 Location Node Hazel Sandy Beach Road North Culvert - Downstream KC_J Sandy Beach Road North Culvert - Upstream KC_J Alyssum Street Culvert - Downstream KC_J Alyssum Street Culvert - Upstream KC_J Reytan Boulevard Culvert - Downstream KC_J Reytan Boulevard Culvert - Upstream KC_J Morden Lane Culvert - Downstream KC_J Morden Lane Culvert - Upstream KC_J Bayly Street Culvert - Downstream KC_J Bayly Street Culvert -Upstream KC_J Highway 401 / CNR Culverts - Downstream KC_J Highway 401 / CNR Culverts - Upstream City of Pickering Downtown Stormwater Management Strategy TMIG Project PCSWMM Model Output LIDs in City Streets 25 mm retention of runoff volume from road ROW Maximum Hydraulic Grade Line (m)

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87 Appendix B Pickering Town Centre Flood Storage Assessment TMIG THE MUNICIPAL INFRASTRUCTURE GROUP LTD

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89 Memo Date: PN: To: CC: From: Subject: April 21, Marilee Gadzovski, City of Pickering Tom Dole, City of Pickering Abe Khademi, TMIG Steve Hollingworth Downtown SWM and Diversion Study Constraints to Redevelopment at the Pickering Town Centre On April 1, 2014, TMIG met with senior staff at the City of Pickering to provide an update on the Downtown SWM and Diversion Study and discuss the implications of our findings and recommendations on the vision for redevelopment and intensification in the Pickering City Centre area. It was generally accepted by most at the meeting that the preferred solution should remain Culvert Improvements. While the Diversion to Pine Creek alternative could potentially facilitate redevelopment at the south parking lot of the Pickering Town Centre, the anticipated construction cost for the diversion alternative is more than $30 Million. The existing flood storage at the south parking lot of the Pickering Town Centre is significant in reducing flood levels in the downstream reaches of Krosno Creek. The existing flood storage volume should be preserved in some form through any redevelopment at the south parking lot of the Pickering Town Centre. The existing flood storage area is illustrated in Figure 1. At the meeting, TMIG agreed to investigate how the existing flood plain storage could be preserved during redevelopment of the area, and to estimate the additional cost required to replace the existing surface storage within a new development. Figure 1 Existing Flood Storage Area at the Pickering Town Centre