STORMWATER MANAGEMENT REPORT. Dundas Square Gardens Inc. High Rise Residential/Commercial Development

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1 STORMWATER MANAGEMENT REPORT Dundas Square Gardens Inc. Revised: April 6, 2016 Revised: January 12, 2016 Revised: July 10, 2015 OUR FILE: 14-RE-352 June 16, 2014

2 TABLE OF CONTENTS PAGE 1.0 Scope of work Existing and proposed land use Rainfall Data Calculation of flows Allowable release rate Post development runoff and control Post development combined sanitary, storm and u/g pumped flow discharge Proposed sanitary runoff Flow calculations Post development underground flow discharge Total post development combined sanitary and u/g pumped flow discharge into George Street combined trunk sewer Post development storm flow discharge into George Street storm sewer Pre development flow discharge Existing sanitary runoff Storm pre development runoff Storm, sanitary and u/g pumped flows prior and after development Summary of sanitary and u/g pumped flows draining into combined sewers prior and after development Total post development storm flow discharge into George Street storm sewer Calculation of the storage Major Flow Overland Route Design of tank Outlet control for the underground tank Water quality Water Balance Management Abstraction base on land-use Storm Water re-use for the Cooling electrical/mechanical facilities Summary APPENDIX APPENDIX APPENDIX

3 1.0 Scope of work This report outlines the stormwater management plan for Dundas Square Gardens at 241 Jarvis Street, Toronto, Ontario. The property is in the northwest quadrant of the intersection of Jarvis and Dundas Streets. Legally, the property is described as Lot 1-11, Lot 15 and Part of Lot 16, Registered Plan 10A, Part 1, Plan 63R The purpose of this report is to present a feasible stormwater management plan to meet the City of Toronto stormwater management criteria defined in the City of Toronto Wet Weather Flow Management Guidelines (WWFMG). 2.0 Existing and proposes land use The proposed site is 3223 m 2. The property in its existing state has a hotel and ground level restaurant and other retail space with underground parking. The development is as such that the runoff from the site will be controlled on the site to the requirements of the City of Toronto. There is no external drainage through the proposed site. The runoff coefficients for the land uses within the site are taken as follows: Landscape/Green roof areas = 0.50 Paved = 0.90 Roofs = 0.90 Controlled by tank Roof m 2 C = 0.90 Green&Landscap e C= 0.50 Total controlled area m 2 Cave = 0.87 Uncontrolled Area Hard surface m 2 C = 0.90 Soft surface 0.00 m 2 C = 0.50 Total uncontrolled area m 2 Cave= 0.90 Total site area m 2 The coverage of landscape, paved and roof areas is shown on the Site Servicing and Grading Plan in the Appendix 1. For controlled and uncontrolled area for stormwater management see Figure 1 in Appendix 1. Based on the proposed development, the following post development areas and runoff coefficients are derived. 3

4 3.0 Rainfall Data The City of Toronto rainfall intensities are used in the calculations of runoff from the site. For the 2 year storm, the intensity is calculated with the following relationship: i2 = 21.8T 0.78 where:i2 = intensity corresponding to the 2 year level, mm/hr T = duration of storm in hours For the 100 year storm the relationship is i100 = 59.7T The rainfall data is for extracted from The Wet Weather Flow Management Guidelines, November 2006, page Calculation of flows The Rational method is typically used in the calculation of flows for sites typical of the proposed development. The rational method is as follows: where: Q = CiA Q = flow in m 3 /s; i = rainfall intensity, mm/hr; C = runoff coefficient; A = area in hectares. 5.0 Allowable release rate The City of Toronto, Water and Wastewater Division requires that stormwater management mitigation be provided to attenuate the 100 year post development runoff to the 2 year pre-development to satisfy City s stormwater management requirements. According to the Wet weather flow Management Guidelines Section General Guidelines, paragraph (3) flows from the properties located adjacent to a public R.O.W s, which are used to convey major flows, can be controlled from 5 year post development to 2 year storm event. The development is located in the vicinity of the intersection of Dundas and Jarvis Streets, not in the proximity of Lake Ontario. However, the 100 year post to 2 year criteria will be used in this Stormwater management plan. The pre-development flows for the site is determined to be m 3 /s with a 10 minutes time of concentration as detailed in the Wet weather flow Management Guidelines (page 32), and a runoff coefficient of The details of the calculations are shown as follows: 4

5 Release rate Qallowable m 3 /s Quncontrolled m 3 /s Qtotal release m 3 /s The details of the calculations are shown as follows: Qallowable = x 0.50 x x = m 3 /sec An area of m 2 at the front of the property as shown in Figure 1 is not controlled. The 100 year storm flow from this area is Quncontrolled = x 0.90 x x = m 3 /sec Summarizing the above to determine the release rate from the site into George Street storm sewer: Qrelease = Qallowable Quncontrolled = = m 3 /s 6.0 Post development storm runoff and control Runoff from the area of the site is controlled in the tank. The City WWFMG requires that the 100 year storm be controlled to the 2 year with a 50% runoff coefficient. An underground storage tank will be used to store the difference in runoff, and release at the allowable controlled rate to the municipal storm sewer system. All of the site, except the uncontrolled part will drain to the tank. The tank will be discharged with an orifice tube to discharge the tank at a maximum rate of 34.2 litres per second at maximum water level. Flows in excess of the 100 year event will over flow from the tank via an overflow pipe. 7.0 Post development combined sanitary, storm and u/g pumped flow discharge 7.1 Proposed sanitary runoff flow calculations Podium Building 1 bedroom condominium 1.4 persons / unit 2 bedroom condominium 2.1 persons / unit 3 bedroom condominium 3.1 persons / unit Retail commercial: 1.1 persons / 100 m 2 Office Commercial: 3.1 persons / 100 m 2 Based on current statistic total population for the podium: (133+62) x x x3.1 = 545 p 5

6 Average Residential flow: 450 litres/capita/day = litres/capita/sec Total Retail commercial population: 1113 m 2 x 1.1/100 = 12 persons Total Office commercial population: 1300 m 2 x 3.3/100 = 43 persons Total Residential Average flow: 545 x = 2.83 l/sec Residential Peaking factor: (population in 1000). Peaking Factor = Sanitary peak residential flow from the site: 2.83 x = l/sec Total Commercial Peak/average flow: 55 x = 0.16 l/sec Infiltration Flow: Ha x 0.26 l/sec/ha = 0.04 l/sec Total Sanitary Flow from the podium: Qsan = l/sec This sanitary flow is discharged into George Street 600x900mm combined trunk sewer. Tower Building 1 bedroom condominium 1.4 persons / unit 2 bedroom condominium 2.1 persons / unit 3 bedroom condominium 3.1 persons / unit Based on current statistic total population for the tower: ( ) x x x3.1 = 1197 p Average Residential flow: 450 litres/capita/day = litres/capita/sec Total Residential Average flow: 1197 x = 6.22 l/sec Residential Peaking factor: (population in 1000). Peaking Factor = Sanitary peak residential flow from the site: 6.22 x = l/sec Infiltration Flow: Ha x 0.26 l/sec/ha = 0.04 l/sec Total Sanitary Flow from the tower: Qsan = l/sec This sanitary flow is discharged into 900x1350mm Jarvis Street combined trunk sewer. This is to confirm that proposed building sanitary system will have a back-water valve to protect the system in the event of municipal sewer s surcharge conditions. See Smith & Andersen Consultants letter in the Appendix Post development underground flow discharge Application for permanent discharge of groundwater permit was submitted to Mr. Dhiren Barot of Toronto Water together with Geohydrology Study, Water Quality Investigation and all data required by Dhiren. McClymont & Rak geotechnical consultants conducted Water Quality Investigation to determine suitability of groundwater for discharge into the municipal storm sewer. 6

7 As per results of the quality test groundwater can be drained only into combined sewer without pre-treatment facility required in the development. See McClymont & Rak Water Quality Investigation Report in the Appendix 3. As per Toronto Water request McClymont & Rak geotechnical consultants provided Permanent Drainage report with computer modelling/simulation of the groundwater influx for permanent drainage system. (See Permanent Drainage report of October 29, 2015 in the Appendix 3). The discharge rate for the project is USG/min or: Qu/g =1.58 l/sec. Groundwater level varies from 0.6 to 4.09m below surface grade. Proposed building has four levels of underground parking and the slab of the P-4 level is 13.65m below the ground floor. As a result required weeping tile system is below groundwater level. See groundwater level in McClymont&Rak Boreholes Records in Appendix 2. Pumped ground water will be drained into U/G Water Control Manhole and from there into Sanitary Control Manhole as shown on Site Servicing and Grading Plan. 7.3 Total post development sanitary and u/g pumped flow discharge into George Street combined trunk sewer Total post development flow discharged into combined trunk sewer is: Qpostdev = Qsan + Qu/g = = l/sec 7.4 Post development storm flow discharge into George Street storm sewer Total post development flow discharged into George Street storm sewer: Qrelease = Qallowable Quncontrolled = = m 3 /s = l/sec 8.0 Pre development flow discharge 8.1 Existing sanitary runoff As per IBI Group Municipal Servicing Report the existing site is currently serviced by 2-300mm diameter service connections, one to the Jarvis Street 900x1350mm combined trunk sewer and the other to the George Street 600x900mm combined trunk sewer. Based on IBI preliminary field investigation both these connections are conveying sanitary sewage and storm water in the same pipe. (See page 6 of the IBI report in the Appendix 1). As per IBI Group Municipal Servicing Report total sanitary flow from existing development is 6.40 l/sec. Qsan.predev = 6.40 l/sec See page 7, Table 1 and Sanitary Sewer Design Sheet, Existing condition of the IBI report in the Appendix 1. 7

8 8.2 Storm pre development runoff As per IBI Group Municipal Servicing Report the existing site is currently serviced by 2-300mm diameter service connections, one to the Jarvis Street 900x1350mm combined trunk sewer and the other to the George Street 600x900mm combined trunk sewer. Based on preliminary field investigation, it appears both these connections are conveying sanitary sewage and uncontrolled 2 year pre-development storm flow together in the same pipe. Uncontrolled 2 year pre-development storm flow is: Q2predev = x 0.90 x x = m 3 /sec = l/sec Municipal storm sewers exist across the road frontages of the site on: mm x 1450mm storm culvert on Dundas Street; - 525Ø storm sewer on George Street draining into Dundas Street storm sewer. Total pre development flow was discharged into the city s Jarvis and George Streets combined trunk sewers. 9.0 Storm, Sanitary and u/g pumped Flows prior and after development 9.1 Summary of Sanitary and u/g pumped Flows draining into combined sewers prior and after development Total Existing Sanitary Flow prior to development (Section 8.1 page 7) Total Uncontrolled Storm Flow prior to development (Section 8.2 page 8) Total Sanitary and Storm Flow prior to development 6.40 l/sec l/sec l/sec Total Proposed Sanitary Flow after development (Section 7.1 pages 5.6) = l/sec Total Post development underground flow discharge (Section 7.2 page 6) 1.58 l/sec Total Sanitary and Storm Flow prior to development l/sec Net Decrease in Peak Flow to the City s combined sewers l/sec As it can be seen total post development sanitary and u/g pumped flow into city s combined sewer system is 47% less than pre development flow discharge. 9.2 Total post development storm flow discharge into George Street storm sewer Total post development flow discharged into George Street storm sewer: (Section 7.4 page 7) l/sec 8

9 10.0 Calculations of the storage The storage is calculated using the Modified Rational Method. The figure shows the storage calculations, graphically. The details of the calculations for the Modified Rational Method are given in Table 1 in the Appendix 1. Duration of storm = minutes Inflow volumes Q100 = m 3 /s Volume = ((5+23)*0.5*60*0.154) = m 3 Release volumes Qsite release = m 3 /s (adjusted for site) Volume = ( )*0.5*0.0342* 60 = m 3 /s Storage = Volume In - Volume out = m 3 /s 9

10 11.0 Major Flow Overland Route Flows in excess of the 100 year storm will be directed to the City streets Design of tank As per The Wet Weather Flow Management Guidelines (WWFMG, City of Toronto, 2006), 5mm of the runoff from the site shall be used for irrigation of the green areas of the site. Hence the tank will have two storage volumes: For stormwater management For irrigation and cooling use The tank will have a bottom area of 32.24m 2. The depth is fixed at 3.90m. (For tank detail see Site Servicing and Grading Plan in Appendix 1). The depths are used as follows: Below is the design summary of the tank: Volume Bottom area Storage Use Required of tank Depth provided (m 3 ) (m 2 ) (m) (m 3 ) SWM Irrigation Total Note that the storage provided exceeds the storage required for stormwater management and meets the requirements for irrigation and cooling use of storm water. Stormwater Management Tank is shown on Architectural plan prepared by Page & Steeleles Architects, architectural drawing title P1 PARKING LEVEL, Job No , Dwg. No. A

11 Figure 3: Details of the storage tank are shown below Outlet control for the underground tank The underground tank is located on thep1 level of underground parking. (See Site Servicing and Grading Plan in Appendix). Storm water from the tank will be discharged with a peak allowable rate of m 3 /sec via 80mmØ orifice plate. See Orifice plate detail on Site Servicing and Grading Plan. The orifice equation was used to size the orifice to control the flow to the municipal system. Q CA 2gh Where Q = discharge ( m 3 /s) g= gravity (9.81 m 2 /s) A= area of orifice (m 2 ) C= orifice coefficient (0.82) h= head (3.36m) The calculations are presented below: 11

12 Q = m 3 /s C = 0.82 h = 3.36 m Q= C A (2gh) 0.5 A= m 2 d= 80 mm 14.0 Water quality The City requires that water quality be implemented on site to treat runoff from the site to type 1 (80% removals). The subject site has no exterior surface vehicle parking areas or private driveways, where water quality contaminants are typically generated from the vehicles. The entire site is occupied by building structure and the roof areas flow considered clean and do not carry water quality contaminants. Hence, no water quality is required for the site and storm water quality treatment devices are not required Water Balance Management The primary objective of The Wet Weather Flow Management Guidelines (WWFMG, City of Toronto, 2006) is to encourage a water balance in managing (collecting and reuse) of annual rainfall on the development site through the control of runoff, infiltration and evapo-transpiration. WWFMG requires that the efficiencies of the provisions in place (infiltration, reuse, etc.) shall be measured in terms of runoff volume reduction (m 3 ) on an annual basis (WWFMG, page 4) Abstraction base on land-use The City of Toronto requires the following for water balance requirement. 12

13 The volume required to be retained on site Vrequired= x 8523 = 16.12m 3 For landscape & green roof area, as per the city criteria, 5mm abstraction (330.11) V = x = 1.24m 3 For paved and hard roof areas, as per the city criteria, 1mm abstraction ( ) V = x = 2.98m 3 Total landscape abstraction VA = = 4.22m Storm Water re-use for the Cooling electrical/mechanical facilities Proposed building will be designed with the pumping system to reuse storm water for cooling electrical/mechanical facilities in the building. As per Smith & Andersen the pump on the system will be using 4.50 US GPM/min which will provide mechanical cooling of the electrical room using 0.8 US GPM/min. It is equal to: 0.8 US GPM/min = 3.03 litres/min = 182 litres/hr = m 3 /hr. For 72 hours pump will use x 72 = m 3. Total volume abstraction and storm water reuse for cooling requirement is: VTOTAL = = m 3 See letter of Smith & Andersen mechanical consultant in Appendix 1. City s requirement to use m 3 of the storage in 72 hrs is met. 13

14 16.0 Summary In support of the development application and to address the City of Toronto concerns, this stormwater management plan has been prepared. The flows are controlled with an underground storage tank providing m 3 of storage for stormwater management. The tank also will provide storage of m 3 for irrigation and for cooling electrical/mechanical facilities in the building purposes, as required by the City of Toronto Wet Weather Flow Management policy. The flow release rate is 34.2 l/sec with 80mm orifice plate. The water balance criteria is met, as required by the City of Toronto Wet Weather Flow Management policy. Proposed site presently does not accepts any external drainage. Existing drainage patterns on adjacent properties shall not be altered and stormwater runoff from the subject development shall not be directed to drain onto adjacent properties.. Yuri Riaboy, P. Eng. 14

15 17. A P P E N D I X 1 1. Table 1, Calculations for the storage for 100 year storm 2. FIGURE 1. Controlled and Uncontrolled Areas 3. Smith + Andersen conformation letter to provide back-water valve to protect building sanitary system in sewer surcharge conditions 4. Smith + Andersen conformation letter to provide mechanical design to use storm tank water for cooling requirements 5. Jablonsky, Ast and Partners structural consultant letter dated October 22, IBI Group Municipal Servicing Report, page 7, Table 1 7. IBI Group Municipal Servicing Report Sanitary Sewer Design Sheet, Existing condition 8. Site Servicing and Grading Plan 15

16 Calculations of 100 year storage for site Rainfall data Release rate 100 year storm Qallowable m 3 /s A= 59.7 Quncontrolled m 3 /s T= 10 minutes Qtotal release m 3 /s B= -0.8 Area (ha) = C= Qrelease= m 3 /s Release Inflow Outflow Time Intensity rate Qrain Volume Volume Storage (min) (mm/hr) (m 3 /s) (m 3 /s) (m 3 ) (m 3 ) (m 3 ) Storage to control 100 yr post to 2 yr pre-development = m 3 16

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23 18. A P P E N D I X 2 McClymont&Rak Geotechnical Report Boreholes Records 23

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37 19. A P P E N D I X 3 1. McClymont&Rak Water Quality Investigation Report 2. McClymont & Rak Water Permanent Drainage Report 37

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